dimented24x7

iTrader: (2)

At low throttle the primary mode of atomization is via the shearing from air entering the tbi past the throttle blades. Also, if the motor pullls decent vacuum at idle/PT the fuel flashes over to a vapor. You can feel this in the tbi. It literally goes down to around 35-40 deg F on an 80 degree day. As long as there is ample heat (like, no airgap manifold with CAI), the fuel wont be able to settle out. At wot with decent injectors, the fuel is sheared into a fine mist. The injector nozzles direct the fuel out in a spinning motion which causes it to atomize when it exits the tip of the injectors. As for the transient stuff, GM included routines to take that into account, namely accel enrich and decel enlean. Transients increase emmisions no matter what form of injection is used, its just worse with these older systems that third gens have

This also isnt limited to tbi. The batch fire system basically sprays the fuel in and it sits there untill teh intake valve opens. All that time is more then enough for some of the fuel to settle out. This is why SFI is in use today, to get that fuel in during the intake cycle rather then let it sit there.

As for emmissions, my camaro passed without me even knowing it would get smogged. I basically threw it together and went to get 'inspected', but was inspected instead. If that can pass, then surely a car with tuning can blow as good emmisions as it did stock, unless your using a super hot cam with a very tight LSA.

dimented24x7

iTrader: (2)

Uhh, both systems are old as HELL. All of these systems are sliding into the past as the new LS1s and other modern FI engines become ever more popular. Theres only a limited number of vets and TGs floating around so the market is limited at best.

Uhh, again there is a car that runs faster times with tbi... If I can stop blowing transmissions and rear ends I may take a stab at putting down decent times too. So far Ive only bought heads for my engine but Ive managed to spend neary $5000 to date on transmissions and rear ends. Cant get the things to last... Have a TKO and im eying an aftermarket rear when my latest 9 bolt pukes. If those dont last, Im buying another honduh.

Fast355

iTrader: (2)

QUOTE]Originally posted by GOY
I understand the effects that a vehicle can have on it's fuel economy - but bare none, MPFI has fewer inherent drawbacks than TBI in terms of preformance, economy, and emissions. If someone cares to debate that, they have a multi-trillion dollar automotive industry that has turned it's back on TBI to fight and try to convince. Typing it here for us to see is basically meaningless. The proof is on the dealership lots.

This thread has become purely hypothetical at this point. Kevin91Z posting the facts that people had been debating over and that TBI guys were standing on, MPFI came out on top. [/QUOTE]

The multi-point and SFI systems have more moving parts and more electrical to go bad. TBI is incredibly cheap and simple. TBI will probably end up costing less in the long run. TBI engines rarely build up deposits like MPFI ones will.

I looked into going to TPI but quickly decided against it when I saw what happened to low and high RPM torque. Tuned means just that. The runners resonate and make their torque at about 3,000 rpm or a little higher. What you get is increased mid-range torque with a loss of torque at lower speeds. Dyno tests have proven a loss of atleast 20-30 ft/lbs under about 2,200 or so. LT1 style intakes will actually make more torque down low than TPI will. Simple physics explain why. The TPI runners work off velocity. Change the diameter and length and the torque curve shifts. Just like headers.

When you run TBI injectors under alot of pressure, combine that with a heated intake floor, vacuum in the intake (under most normal driving conditions), intake velocity (under higher rpm and load),and have alot of swirl in the intake ports you won't have much in the way of un-atomized fuel.

Batch-fire TPI sprays the injector in a group. The fuel has plenty of time at low speeds to start to drop out of suspension. It wouldn't suprise me if the TBI actually supplied a better atomized mixture. You also notice how the factory TBI intake has the circles in the base to catch un-atomized fuel. One thing further on the ports that were prone to vaporization problems they added a little pocket to create turbulance to atomize the fuel better.

My TBI van properly tuned without cats ran cleaner than my moms factory tuned 1995 Acura Legend. Acura 3.2 engines use SFI. It runs great but is the factory tune. It was well within its limits.

GOY

That high PSI you are talking about - that wouldn't be the 11-14 lbs that the factory sets the fuel to dribble out of the injector at would it be?

The fuel is better atomized through smaller injectors under high psi - known. TBI uses two big injectors at low PSI - isn't that about as opposite as you can get? You want to make a big deal out of batch fire, but to you really think that TBI isn't batch fire? Are you possibly suggesting that the ECM fires the injector just before ignition?

The batch fire arguement is against TBI. Yes, in MPFI fuel sits at the valve if it's not opening. In TBI is sits "Someplace" in the intake (not even at the head!) if a valve doesn't happening to be opening just at the right time, and there is no just right time to be calculated with no crankshaft or camshaft position sensor. I'd rather have fuel sitting near a valve where I know it will be used, than sitting in a null or ledge in the manifold "Someplace."

Both have heated intakes, I'd by using Swirl Port heads.... hummm, thanks for convincing me further that MPFI is the way to go.

MrDude_1

well if you REALLY wanted to get into it.

yes, TBI is crap.

so's TPI..

they both have so many design flaws, its not even funny.

happy?

GOY

The question really is, what is the best peice of crap? I'm still going old MPFI over old TBI.

dimented24x7

iTrader: (2)

Have you actually observed a properly running system in action? They dont dribble. At least mine dont. Delphi also claims max operating pressures of 100 psi for some of them. That would drown my motor in an estimated 380 pph of fuel. Dont need quite that much. 20 psi seems to provide a good mix of fueling. TBI works more like a carb then batch fire. Each injector alternates firings to coinside with ignition firings. This keeps a relatively constant supply of fuel in the manifold.

I too agree with Mr. Dude. These are antiquated systems that have long become obsolite. Doesnt mean we still cant use them

dimented24x7

iTrader: (2)

Goy, if you think about it 15 mph is pretty darn good fuel economy for a truck. My old 4.3L CPI blazer had a hard time getting that, even with a new $400 dollar spider inj. assembly. Its really a simple matter of thermodyamics and physics. large vehicles get rotten fuel economy. Bout the best thing you could do is get a tiny little cam, tight TC, and the highest numerical ratio gears you can find if you do alot of city driving.

Fast355

iTrader: (2)

I agree, with a heavy vehicle on the highway you need to keep the cam small and the gears tall too. Keep your foot out of it and slow down. I try to stay under 75 at all times. i usually cruise about 65-70.

I also agree with dimented in that if your stock TBI injectors are dribbling something is wrong. On the other hand my pressure is much higher. My 305 is using 4.3 injectors with a VAFPR and the spring out of a latter TBI 454. That makes 32 PSI under load and about 22 psi at idle. The fuel is sprayed in a very fine mist. You don't realize it but at that pressure it will support 300 HP.

87TPI350KID

Heres my idea. I believe TPI would get better gas mileage than the TBI. TPI makes a decent bit more Torque than the tbi, thus under less throttle it will go on just as well because the torque will get you up to speed well. Less throttle, less gas being used.

Fast355

iTrader: (2)

Makes about 10% more torque in the MID-range ONLY. TBI will broaden the torque curve. TBI makes more torque at low-rpm and at higher RPM.

I don't know about you but my 305 TBI almost never reaches 2,500 RPM in daily driving. Pulling 5,000 lbs up to highway speeds in reasonable time usually results in shift points around 2,200 rpm.

Kevin91Z

iTrader: (1)

Well yah, I sure hope your modded 355 is making more power than my dad's stock 200k mile 305 TBI shortblock with a stock TPI on it. Way to go, buddy!

Claiming you would have 400 HP is bench racing and not admissable in this court. Without dyno runs or 1/4 mile trap speed at a racetrack, you have no proof and no leg to stand on. What size injectors are you going to run to get 400 HP, anyway? I'm not aware of any larger than 90 lbs.

Kevin91Z

iTrader: (1)

220 to 290 TQ is a lot more than 10%, my friend. I'll do the math, its 31%, almost 1/3 more TQ in the midrange. Your last sentence is so funny I'm laughing too hard to come up with a response.

Fast355

iTrader: (2)

You didn't notice that my tbi 350 was running a 15.6 @ 87 and it wasn't in a F-body. It was in a 5,300 lbs with me in it FULLSIZE CHEVY CONVERSION VAN with a 3.08 gear. It is safe to assume that it was making over 330 FWHP. It dynod 279 RWHP on a Mustang dyno. Too bad the crank gave out or it would have been a TBI vortec with a LT4 hot cam. That is a proven 400 hp and 430 ft/lbs of torque when tuned right.

90 lb/hr injectors flow a hell of alot of fuel when you drive the pressure up. With the VAFPR and late model 454 spring it would still see around 22 psi at idle and about 32 @ WOT. That with 90 lbs/hr injectors is good for 525 HP @ .80 duty cycle. Fuel is not a problem. I also do my own chip work.


The current 305 is 245 RWHP on the Mustang dyno and runs a 15.9. If TPI was so great why am I making 345 ft/lbs @ the rear wheels on a stock cam and ported head 305.

You can't compare untuned fuel injection setups. The TBI was setup from the factory for fuel mileage and emissions. There was over 50 ft/lbs of torque at 2,500 rpm at the wheels hidden in my factory calibration. TPI came with a much better spark table that TBI did. Hell at WOT my factory TBI engine was only getting 26* advance per the calibration. It is a well known fact that SBC like 34-38 for best power. It is also a known fact that OEMs use spark retard to kill torque for traction control systems. In the early 80s a 3.8 buick was put on the dyno and only the timing curves varied. With just 3* too little timing torque was already 25 ft/lbs down. Don't believe me! Why do you think L03s and L05s respond to advancing the timing so well. They were undertimed from the factory for lower emissions. Not to mention the advance rate sucks bad too. Go pull 10* of timing out of your dads TBI converted TPI, put it back on the dyno, you will see most of that torque gain dissapear. Take a L03, change the spark tables and you will see lots of added torque.

dimented24x7

iTrader: (2)

You can run them at higher pressures like Ive said above. VA454 SS has run up to 50 psi (more then Id run with the stock rubber nylon re-enforced diaphram) and that was more then his 454 could handle fuel wise. Considering its a low 13 sec. pickup Id say its safe to assume thats more then enough for 400 hp. The only limits on fueling are balancing the needs at idle with the needs at WOT. Typically high pressures and high flowrates require that a VacAFPR or some other form of variable pressure fueling is needed.

Personally, I feel that arguing whether tbi or tpi is better is like arguing over whether a camaro with an iron duke is better then a 4 cylinder mustang. Some will say the mustang is better because its lighter while others will say the camaro is better because it handles. In reality, though, theyre both pieces of crap. The reason I like the actual tbi is because it easily bolts to anything just like a carb and it works well. Ive scrapped the rest of the system in favor of a later pcm.

Fast355

iTrader: (2)

This is for the reading challenged that need a visual. With TBI it has run a 15.6 @ 87 with a LT1 cammed 350 tbi. It has also run a 15.9 with a stock cammed 305 TBI. TBI is making plenty of torque. It is also getting 22-24 MPG on the highway and about 17-19 in town. I seriously doubt TPI could do any better.


This is all this engine has.

Bored .040"
Balanced Rotating assembly
Ported 081s
Stock Replacement 1983 305 Van Camshaft
Stock TBI intake
Stock TBI assembly
4.3 Injectors w/ VAFPR and Late 454 TBI spring
Headers
Dual Exhaust
Custom Chip Tuning

The 245 number was with a 454 throttle body, 9C1 injectors at 17 PSI, and an edelbrock TBI intake. Past experience with this setup showed about a 10 Hp and 5 ft/lbs gain at the wheels on my old 355.

Red Devil

So WTF is the debate about? This seems pretty damn clear cut to me. Hell, it even fits all the 'all else being equal' arguments. Maybe it's b/c Kev lives in Cali... those liberal crazies aren't to be trusted right?



And whoever said TBI will broaden the torque curve over TPI had better put up something to back up that BS statement or start eating some serious crow pie. That's got to be the ignorance statement of the year so far. Unless that thread with rod length affecting stroke was this year...maybe it was a 'typi'?

TPI is THE swap in the trucks looking to maximize low end torque output (And get the WOW factor too not counting of course the serious guys swapping out to carbs). Also, TQ output is generally discussed in the lower RPM range not the higher RPM, most refer to that area in terms of HP. I think we've established over the years that TPI owns TBI in that regard already. You'll note that in most cases the intake system coming out is... TBI. Between the three of carb, TBI and TPI I'm pretty sure I know what most people would have at the bottom of their list for power and top of their list for milage. Seems like TPI is pretty damn good overall, esp. for ~25 year old technology.

dimented24x7

iTrader: (2)

Thing is RD, theres actual real world results that show that the TPI and TBI performance are about equal (I dont consider HSR, MR or MPFI manifold based systems to be Tuned Port Injecton). Same with the fuel economy.

As for the power band, the tbi will be like a carb where the tpi will be spikey around 3600 rpm. This seems to be common knowlege.

So, it then comes down to what you prefer to se on top of your motor...

87tpi

iTrader: (5)

Thank you,I did ask about the swap on the same car,nothing else changed except for the intakes.Thanks for answering the question.

Red Devil

I don't rcall seeing those real world results. :shrug: I've seen great results on TPI and seen some in the low 13's high 12's on a stock intake, and some with stock manifolds. Can't say the same for TBI. Heck, wasn't Tim's down in the low 12's before he swapped to the miniram? How many TBI's do we have down in the 12's n/a?

dimented24x7

iTrader: (2)

ben73 has teh current fastest tbi. N/A ET of 12.6 with the crust fire injection. Stock CFI manifold, ported, with 2" CFI throttle bodies + 8625 (?) pcm.

dimented24x7

iTrader: (2)

Actually doing 12.4@111 now. https://www.thirdgen.org/techbb2/sho...hreadid=312592

I think probably one of the biggest improvements on the tbi side was the PCM. The stock ecm for the tbi cars/trucks sucks ***. Thats one of the main reasons for cars being slow.

dimented24x7

iTrader: (2)

Va454SS is doing well, to. But with a full sized pickup hes in the low 13s. Theres also JP and a few others who where running low 13s and there was also a guy with a 4 bbl tbi running low 12's as well.

Fast355

iTrader: (2)

V8AstroCaptain is currently swaping intakes on his 305 in his astro. It was a TBI L03. Now it is going to be a TPI 305. His L03 had a custom tune by him. His TPI is surely going to be treated to the same. I guess we will see how his MPG goes.

Fast355

iTrader: (2)

It is simple physics. A tuned intake provides its main benefit in a very narrow rpm band. The TPI will NOT own the TBI in low-speed torque on the same engine. It will around 3,500 rpm or so but not at low engine speeds. That is the definition of tuned. The runners are the same length and will alter the power curve at the same point. The stock runners are also seperate from each other up to the plenum. TBI uses ports that vary in size and length which WILL BROADEN the powerband. Also the TBI has 4 intake runners/ports that join into a common plenum under the TBI. This causes the system to resonate at lower-rpms and helps build more torque. Dual plane vs. Single Plain vs. Tunnel Ram. Think of the TPI as a longer version of a tunnel ram. TBI will make more average power when put on the same engine. TPI makes more peak torque in a narrower band. That is a FACT. Sure a TPI might be good in an earlier truck with no OD that cruises at like 3,000+ RPM at 70, but when in OD at 2,000 rpm the TPI motors just can't pull like the TBI engines can.


Here is a quote from How Stuff Works.

"The intake system on a four-stroke car engine has one main goal, to get as much air-fuel mixture into the cylinder as possible. One way to help the intake is by tuning the lengths of the pipes.

When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder. When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner.

If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively acting like a turbocharger.

The problem with this technique is that it only provides a benefit in a fairly narrow speed range. The pressure wave travels at the speed of sound (which depends on the density of the air) down the intake runner. The speed will vary a little bit depending on the temperature of the air and the speed it is moving, but a good guess for the speed of sound would be 1,300 feet per second (fps). Let's try to get an idea how long the intake runner would have to be to take advantage of this effect".

http://auto.howstuffworks.com/question517.htm

Black Bomber

Isn't that akin to swapping in a different intake on the TPI? I know people that are in the low 12' or high 11's on aftermarket LTR setups. A lot less money into those probably than that guy has into his TBI. I'm sure if you swapped out to DFI you could push those numbers down a bit too. Besides, if TBI were as good as you guys make it out to be, why didn't GM use that on it's performance platforms? I don't recall a vette without tpi after 1984.

Fast355

iTrader: (2)

More links

http://www.allpar.com/history/memories/bob-scott.html

http://www.hotrod.com/projectbuild/113_9907_efi/

http://www.nhra.com/dragster/1999/is...echnology.html

http://www.me.psu.edu/me415/SPRING02/intake/intake.html

http://circletrack.com/techarticles/73459/

http://www.mazda6tech.com/index.php?...d=14&Itemid=33

http://headerdesign.com/extras/engine.asp

http://groups.msn.com/ChevroletNova/...34180841268995

http://www.tfxengine.com/software7.html

GOY

I love this.

TBI guys can use CFI and 4 barrel throttle bodies talk themselves up, but damn those MPFI guys if they think of talking about anything other than a LTR setup. I think when desperation goes that far - it's clearly evident what's the ideal setup.

Hey TBI guys - if they aren't using the Rochester 220 unit don't even think about bring them up... I mean, after all, mpfi guys can't bring up their aftermarket upgrades, right?

Fast355

iTrader: (2)

My 5,000+ lbs G20 ran a 15.6 @ 87 which is roughly equivalent to low 13s or high 12s in a F-body. Stock intake and stock throttle body. Different injectors. Tiny stock F-body LT1 cam and worked over 193s. More cam and better heads and you see where I would be.

Pickups, Vans, and SUVs kept TBI until 1995. Geo Metro 3 cylinders were still runing TBI in 2000+ and it gets like 45 MPG.

Fast355

iTrader: (2)

Read above! Mine was an ultimate TBI moded rochestor 220. Stock bore and throttle shafts. Only thing done was the ridge removed. That was before the CFM-tech too.

GOY

Ahh yes, Fast355. I've come to the conclusion that you basically feel that as long as GM paid you to tune their proms, they would have never had a reason to go to MPFI. Forgive me, for now, but it's just the impression that you've put me under after reading maybe 100 or so of yoru posts in various threads.

That and I noticed you claims of MPG are FAR - FAR from consistant depending on which post you are responding to. After yesterday, I fugred I'd do some reading about TBI/7747 tuning - and I noticed that you've claimed to get anyplace from 32 MPG to 23 MPG. Well, which is it? Day in and day out I get an average of 15MPG. Sometimes it's 14.5, sometimes it's 15.5 - but on average it's 15. How can you vary so far?

Even more interesting is that your numbers changed compared to the numbers posted by others in the thread... if someone got 24 or 26 MPG - you had low 30's. If they had teen's - you have low/mid 20's. What gives? Just explain your position and how you come up with the varied numbers?

Chrome

He took an injector out and just ran with ONE!

dimented24x7

iTrader: (2)

I tossed the 4 barrel in there for yucks. CFI came stock on the car (duh). Its basically TWO tbi bores that have been divorced. Same injectors, blades, FPR assemblies, etc. It was what GM was using before TBI.

dimented24x7

iTrader: (2)

No. Its akin to porting... a stock tpi intake. And Im sure if you put a quality MPFI intake on a tpi car it could come down a bit too in the same situation.

As for why GM didnt swap it onto all their non-existant performance platforms of early through late 80's, Im not sure...


This is getting rather silly. People have shown that with some work a TPI car and a TBI car can lay down good times. People have also shown that incorrectly approaching each system can produce miserable results (like 350s that barely dribble out 200 HP on the dyno). Theyre both stock systems, they where both never intended for performance. They where intended to fuel older, low output V8s for GM cars so they could cheaply sell lots of units. GM really didnt really come about with a performance platform untill the newer LT1, and finally LS1 engines came out. They both have thier plusses and minuses. There really isnt a clearly better system IMO.

GOY

I know - but the thread began with TBI - and to toss CFI and 4bl in is fine, but to say that other MPFI intakes are not acceptable to be compared to is holding a double standard. You are altering what you want to compare your side without providing the same lateral movement to the MPFI group.

Nonetheless, what's good for power can be good for economy, because both require the best efficiency in operation possible - the engine just has to be suited to it. MPFI has proven over time to be the superior form of fuel delivery, in it's multiple forms - over TBI's multiple forms of fuel delivery - in specific applications power and hence forth - in specific applications, economy. That being the case, it appears that because MPFI lacks the fuel condensation, pudding, and turbulence problems associated with trying to fit runners between the small space of the cylinder banks that it can be the superior form of induction for economy.

While the TBI *MAY* make more torque below 2200 RPM, that doesn't mean it's more economical in doing so. You still have low air speeds with the above mentioned flaws. On top of that, I say *MAY* because that CLAIM as been made with NO DYNO SHEETS BEHIND IT as of yet. TPI very well may make more torque below 2200 RPM than it's "Comparable" TBI counterpart - nobody has proven one way or the other yet.

Fast355

iTrader: (2)

I have never ever purposely claimed 32 MPG. Maybe in a typo trying to type 23???? I have claimed nearly 24 but in reality it is close to 23. 23.17 to be exact. Point me to the innacuracies(claimed 32 mpg??) and I will change them back to the correct numbers not to confuse anyone. I am never more than a couple of MPG different.

The MPG are for different engines, in different states of tune, at different times, etc. Go back and re-read the posts. As you notice my fuel system, tune, etc are always changing. I can't leave things alone and have to mess with things. My latest change was the 4.3 injectors, VAFPR and 32 psi fuel pressure under load and 22 at idle. Earlier it was 9C1 injectors at like 17 PSI. I have also taken the 454 throttle body off and the edelbrock intake as well. Stock 350 pieces are now in place.

My old stock carbed 305 got between 13 city and 20 highway and averaged 17. My overcammed carbed 305 got 12-14 city and 18-20 highway. My 601 305 headed 355 TBI got 18-21 on the highway and around 15 in town (never drove it much in town). The 193 swirl port headed LT1 cammed 350 got 17-19 on the highway and 14-16 in town. (never drove it much in the city). My current stock cam, ported head 305 is getting about 21-23 on the highway. It almost hit a little over 23 on a long non-stop run at near legal speeds. Around town it gets between 17-19. My average over the last 20,000 miles has been a strong approximately 18 MPG through the various engines, tunes, etc.

On another side note, I am tired of people treating TBI like paperweights. You can do as much with TBI as you can with most other combinations.

Fast355

iTrader: (2)

Read the last post here. Funny how over 2 weeks ago I was getting the same MPG I quote here.

https://www.thirdgen.org/techbb2/sho...an+gas+mileage

GOY

You mean the non existant Fbody and Corvette - the Fbody which had the TUNED PORT UNIT as it's PERFORMANCE OPTION, and the vette dropped CFI as soon as TPI became avaliable?

TBI was meant as a low cost system to fuel low output V8's, not TPI! When TPI came around, it was a high cost Bosch design, put on high output V8's at the time. You know what, forget the "At the time" part of that - those "Low output, low cost, high production" tuned port l98's still made more torque than then LT1 which you consider the "performance platform." Torque, being a direct measure of power... not that performance should be consdered with power output I suppose? Yes, the LT1 made more HP, but isn't that more of a side effect of the msitake of removing intake tuning? I noticed the LS1 makes even more HP than the LT1 with it's tune intake runners. Obviously there's some performacne to be gained by tuning runners - so obviously the TPI setup has something to offer the performance community.

The fact is the LT1 was a mistake, and was corrected with the LS1. A tuned intake is required.... and thank you Mr. Fast355 for posting the very link I'm about to use to prove that point. http://www.hotrod.com/projectbuild/113_9907_efi/ With tiny 9 runners - similar to the nearly non-existant runners of the LT1, the engine produced far less power than it did with the tuned 17 inch runners. The intake has to be tuned unless you are turning 8 or 9000 rpm, in which case any tuning becomes an airflow obstacle.

.... now back to economy....

GOY

Wow, I'm amazed you managed to say the same thing twice. Now what about the other times?

GOY

sigh

dimented24x7

iTrader: (2)

It may have been high cost, but that was about it. The bosch stuff was garbage like most everything else theyve produced through the years. Stock was only set up to read up to around 240 g/s of airflow, the A/D converter and the code had poor resolution, the injectors werent that great. I had a TPI car at one point and both the MAF and the injectors where major sticky points with that car. Both eventually needed replacing, and the car wasnt even that old at the time.

Another thing your forgetting is that the TPI was set up to resonate at 3600 RPM, turning what is a 300 HP longblock into a 240 HP motor that has an immovable torque peak right where the system resonates. Not to say you cant make power, but you have to be mindful that the intake will want to resonate there no matter what.

Now, its really not TPI when you get another completly different intake, is it? Its now a TPI ecm with an aftermarket MPFI manifold. Most of those strive to take some of the tuned out of the tuned port so the motor doesnt have to be such a close match to the intake. Id liken this to switching over to an edel MPFI kit for tbi and saying its still tbi.

Im getting tired of beating this old horse skeleton of a thread to death again and again like so many others. Peace...

Fast355

iTrader: (2)

Or these places

https://www.thirdgen.org/techbb2/sho...an+gas+mileage

https://www.thirdgen.org/techbb2/sho...hlight=tbi+mpg

https://www.thirdgen.org/techbb2/sho...hlight=tbi+mpg (Prior to Highway Mode)

https://www.thirdgen.org/techbb2/sho...hlight=tbi+mpg

https://www.thirdgen.org/techbb2/sho...ht=van+350+mpg

https://www.thirdgen.org/techbb2/sho...ht=van+355+mpg

https://www.thirdgen.org/techbb2/sho...an+gas+mileage

https://www.thirdgen.org/techbb2/sho...hlight=van+mpg

https://www.thirdgen.org/techbb2/sho...hlight=van+mpg

https://www.thirdgen.org/techbb2/sho...hlight=van+mpg

http://www.chevytalk.org/threads/sho...0&fpart=8&vc=1

http://www.fullsizechevy.com/forums/...50#post1736050

http://www.chevytalk.org/threads/sho...ue#Post1300952

http://www.chevytalk.org/threads/sho...ue#Post1291806

http://www.chevytalk.org/threads/sho...ue#Post1256845

http://www.chevytalk.org/threads/sho...ue#Post1235272

8Mike9

Original question:

Is there a gas mileage difference between tpi and tbi?I heard that tpi offers about 30% more mpg's but am curious to know for sure.

Only known real reply:

Yes we do have swap results from swapping only the TBI to TPI on the same engine. My dad's old car (DynoDon) went from 158 RWHP and 220 TQ on a 305 TBI, and got 28 MPG going from SoCal to Phoenix, AZ and back. Then a year later, he swapped to a stock TPI intake, went to 176 RWHP and 290 TQ, and got 31 MPG going from SoCal to Reno, NV and back.

And we are still arguing about something?

I know you can tune a TBI for better power and MPGs and yadda, yadda, yada.

Is there anyone listening to this thread or posting here that is defending "the TBI", not think that you can do the same to a TPI tune?



Hell, been a few years, but Glenn had is 91? GTA L98 in the low 30's.

Black Bomber

Some smart *** made that point a while ago, then he decided to stir the **** up a tad. Typical crap outta him. :P

Fast... I only went to the first three of the slew of 'stuff' you posted, here's the simple of what I picked up:

1) "Someone, I think a brilliant engineer by the name of Bob Graham, deduced that if we tuned our intake runner to the point where the resonance was greatest, it would give the maximum push to the air and fuel when the intake valve opened at any given speed. "

Any given speed...

2) "Free horsepower. What a great idea. In the case of resonant manifold tuning, most commonly known as ram tuning, an engine can actually realize additional horsepower and torque simply by catching the wave."

Free... additional... I don't see where they mention at cost of, or somewhere else. Notice that?

3) Spacer tuning?!? Ok, new argument, intake velocity?!? I don't see what the point of that was.

2x4... yes it is, the runners are just 'tuned' higher. Most all manifolds are 'tuned' in some respect from my understanding. The term TPI was more of a sales thing. And that 'tuned' area can be changed pretty easily. Ask Mad Max.

I'm still waiting on some FAST setups on some real motors to see what happens there.

83 Crossfire TA

iTrader: (2)

Have you ever driven a crossfire setup? I had a crossfire TA, and currently own an L98 Formula and an LT1, ’97 WS6 TA and an LO5 powered K1500 blazer, I think I have a pretty good means of comparison.

FWIW, the crossfire TA had and auto and 3.23’s and 27.5” tall tires (about the equivalent of 3.0:1 gears with stock height tires), the L98 is also an auto with 3.27 gears, and the LT1 has a 6 speed and 3.73 gears (4.10’s most of it’s life).

At the dragstrip, the LT1 has about .5s on the L98, which has about .2s on the crossfire car (stock long blocks in all cases, some exhaust work… otherwise), but the crossfire car EASILY is the most fun from a stoplight, followed by the L98, followed by the LT1. Even with the 4.10 gears and 6 speed it’s much more work to send the tires up in smoke/do something stupid in that car then it was in the crossfire car, which by far has the most low end of all of them, even being short 45 cubes with much bigger tires, BY FAR.

FWIW, the LO5 truck… well it’s a big freaking heavy brick with 3.43 gears and pretty much stock it’s a burnout machine with 33” tall AT tires… you do the math

Plain and simple, port fuel injection replaced TBI for one real reason… Emissions standards, and with that respect, TPI was just a stepping stone to the LT1, which by ’96-97 had pretty much everything that the LS engines now have (which were developed as truck engines, not as performance engines). I guess that you can give a second reason, it’s easier to tinker with tuned manifold lengths with reasonable packaging with port fuel injection, but that can be worked around without much difficulty.

Again, remember, the LS engines were designed as TRUCK ENGINES. Trucks operate in a relatively narrow power band where harmonic tuning is an advantage.

Real world, remember that for every harmonic peak there is also a low spot. Most intakes are tuned for a second, third or 4th harmonic, and there is an equal/opposite power loss at the low spot between the peaks. That’s why the TPI is SO PEAKY on either side of it’s 3rd harmonic peak at around 3800rpm, but that it has to hit a low spot before the second harmonic at around 5200rpm and another low spot before it hits it’s 4th harmonic at around 3000rpm (which at that point is so weak that you don’t even feel it or really see it in the hp curves)

No, no way. At least not intrinsic to the TPI

if anything there might be about a 7% increase in VE in a vehicle that cruises at between 3600-4000rpm, which would translate to a few percent mpg.

Since none of us runs steep gears and no OD in a heavy enough vehicle that this makes sense and worries about gas mileage that part of the discussion is academic.

Slap them both on the same engine that is not assembled/tuned to work better with one or the other, I doubt that you’ll see a measurable difference.

Totally optimize what it’s sitting on and I’d put money down on the TBI setup. Lots of reasons but one that will have the biggest impact is that compression and timing advance is what lowers BSFC, and the wet flow intake allows you to use the fuel to cool the charge (and the flow to homogenize the charge also, it has advantages both ways) allowing you to run more compression and timing. My crossfire car had 9.8:1 compression, my K1500, a much more heavily loaded engine which should traditionally be much more detonation sensitive runs at 9.3:1 compression, both run well with no issues on 87 octane gas. The 9.3:1 L98 doesn’t like anything less then premium on a hot summer day, and from experimenting with burning chips for all of these it looks like the timing is about optimized on the TBI vehicles at this point, where the L98 still responds to more timing if I give it more octane.

The only place that port injection would beat TBI is possibly in a situation where you are constantly changing throttle position quickly, but from my experience I don’t know that I’ve seen an increase with TPI rather then just a decrease with all of them to the same ****ty level (try DC metro area, rush hour traffic out for size…)

But the thing is that I don’t know that it answers the question… yes, he got positive results, and I don’t doubt them, but I don’t know what I believe WRT to the state of tune of either combination. To be honest, the mpg number seems pretty sad for the TBI setup (my crossfire did better then that highway), and the TPI setup seems pretty high (I’ve never seen more then 22-24 on my L98, no matter what I tried, even with highway mode on)

Not at any given speed, only at the rpm where you hit a harmonic, helmholtz resonant peak.

Again, out side of that peak you will actually loose cylinder filling capacity and power, by the same percentage as the resonant peak

WOA there big guy… resonant and ram tuning is TOTALLY different. Resonant tuning is due to the reflection of the pulse created by the exhaust valve. Ram tuning is due to the shape of the port.

Not only are they different animals but they are largely incompatible. As you shape the port for stronger ram tuning you put a taper in the port that completely breaks up resonant tuning, and even if you settle for a very, very small ram tuning effect you wouldn’t be able to get the ports long enough to effectively resonant tune them.

that’s because you’ve never worked out helmholtz equations… there’s a cost to everything, and again, in this case it’s equal and opposite.

NOTHING is free.

possibly ram tuning actually, but in the case of TBI, the higher you get the injector off the manifold floor the cooler the engine could be running without ANY fuel puddling problems. Injector tower spacers accomplish the same thing PLUS making the space between the injector pod and throttle bore larger for better air flow.

Real world, between the warm manifold, the height of the injectors above the intake, the shearing created by the small gap in the throttle plate and most importantly the vacuum in the manifold it’s actually pretty difficult to create a situation that you will get puddling in a TBI intake manifold under normal running conditions.

ShiftyCapone

iTrader: (7)

As I mentioned before I got 30 to 32mpg average on every highway trip when my LO3 was stock. I have no doubt that if I were to swap to TPI I would have had the same results when cruising. I would have just had more peak power. There are many decently powered GM induction set-ups that have great highway manors. I don't know why we are arguing this to death.

All numbers are highway MPG's.
My old stock 4200lb '98 A4 4.3 vortec truck would get 24mpg
My old stock 3500lb '95 M6 Z28 would get 29mpg
When stock my LO3 would get 30 to 32
My M5 '05 cavy coupe gets 40
My buds '02 M6 SS gets 27

All of these motors consume fuel much differently when at WOT and in the city but for peak fual ecomnomy none of them is terrible given the vehicle/power they came in/with..

At part throttle cruise speeds these motors aren't making much power. So why is it hard to think that GM couldn't dail in resonable part throttle fuel consumption for its fuel injected motors. I think it would be helpfull if some of us picked up an IC engine book or two and did some reading. Engine design and fuel economy will make a lot more sense.

Fast355

iTrader: (2)

Good advice on the design aspect shifty. Each setup is balanced with the cam, compression, gearing, etc. to get where GM wanted. Give the engine what it wants to make the desired power at part-throttle and it will get the best MPG possible. Whether it is a carb, TBI, or PFI, the BSFC isn't all that different (when correctly dialed in). A fuel injected engine is easier to dial in (whether TBI or TPI). There are many different intake designs each with thier own purpose. Had GM thought that TPI would have been a better choice for the pickup at the time, they would have used it. In reality the TPI was to make a 305 have the same mid-range torque as a Cross-fire injected 350 when the future of the 350 was questionable and to decrease emissions only.

91blue_fire

i get about 200 miles to 13 gallons of gas....15 mpg??? i dont get it..open element, headers and 3 inch exhaust and i even have my scoop opened up. i just fixed my tv cable so maybe not itll be better. i had some high shift points and some bogging issues...

NEEDforSPEED

I own both TBI and TPI, this threads gay they both suck end of story!
let me brake this down, TBI was ment to be a low emissions system, same as TPI but performance was in mind at GM, today these systems are both out of date compared to the new age!
i enjoy both, but in stock form THEY SUCK! i dare you tbi, tpi, guys to dive into your engine bay and look around then come back and tell me how bad they both suck....

TPI GUY, Whats this TBI crap?


Answer: What is TBI or Throttle Body Fuel Injection?


THROTTLE BODY FUEL INJECTION-- The throttle body injection system is one of the first mass-produced fuel injection systems in the US auto industry, and is the most cost efficient system. If not for more stringent emission standards and second generation onboard diagnostics (OBDII), it more than likely would still be widely used. Some of the original designs were developed in the early 70's by GM's AC Delco division anticipating the upcoming emissions standards change. Some of the first applications were found with Cadillac in the late 70's. By 1982 GM was converting most of their powertrains to use this type of system, and was the mainstay of the GM fleet until 1995.

TBI's use either 1, 2, or 4 fuel injectors and inject metered fuel directly on top of throttle plates much the same as a carburetor. The TBI unit is centrally located on an intake manifold that distributes an air/fuel mixture to each cylinder. GM systems used a low fuel pressure of about 12 psi.

TBI uses a speed density control strategy along with a few electronic sensors to allow a constant monitoring and feedback to the ECM. These signals processed in the ECM control spark advance and fuel metering under all engine operating conditions. TBI equipped vehicles provide excellent drivability, improved fuel economy, and as stated previously are very cost effective.

TBI GUY, i make 500hp, TPI sucks but what is it?

Answer: What is MPFI, Tune Port, TPI, Multi Point Fuel Injection?

MULTI POINT or PORT FUEL INJECTION—MPFI (Multi Point Fuel Injection) uses an individual injector placed directly above the intake valve for each cylinder. This is the most commonly used type of system in today's vehicles. MPFI allows full compliance with OBDII requirements and produces less HC emissions on cold engine start ups. These systems also eliminate most fuel distribution problems since the fuel is injected directly on top of the the intake valve, and not mixed prior to that point.

One of the biggest advantages of MPFI is the flexibility of intake manifold designs. Most systems are designed with long intake runners, producing more low end engine torque, which is where most daily driving is done. This allows good camshaft grinds for idle stability while providing this drivability advantage. Some of the newer systems are designed with a long and short runner design. A communication valve is placed in the intake manifold that switches between long and short runner depending on the driving condition that you are currently in. The Long runner is for low-end torque and short runner is for higher rpm horsepower.

MPFI can be either speed/density or mass air. Most systems of today are mass air and very expensive to produce. This is because of the # of injectors needed, sophistication of the induction system, and the # of sensors required for proper monitoring and feedback. Another part of this cost equation is the amount of skill and time required to calibrate MPFI systems. There is alot of discussion in the industry as to what is better, mass air or speed/density.

TPI is a GM trade name for Tuned Port Injection. TPI is a multi point injection system with a long runner design that was very popular from the mid 80's to the mid 90's. These systems by themselves allowed for more torque and horsepower in the engines they were used on. The long runner design allowed for more low-end torque and even though it limited the amount of high-end horsepower, horsepower was increased with these systems.


So you see there's pros and cons, i assume you can figure that out

Red Devil

Need, go back to the POTB boards, every one of us in this conversation can use google and has a pretty damn good idea about the 'what' we are talking about.

I'm none too shocked that the TBI guys are taking the stand they are taking. It's rather amusing.

A set-up is unto itself, however, if you drop a dry flow TPI onto one of those engineered marvels of a TBI motor, you'll see an increase in performance and efficiency. There is no way around it. A dry flow system is more efficient. It may, and that's a loose 'may', loose something in very high velocity situations in which the actual medium has a heavier weight, but kinetics will be discussed somewhere else, not TGO.

Mark, they were slapped on the same engine, TPI made measurable gains with regard to gas mileage, the original question. Hard proof > theory. If you postulate a theory and the datum does not correspond, you alter the theory, not the datum.

Dimented, why do you think Bosch sucks? That's an asinine blanket statement and you know better. :P And as mentioned by some hack, the TPI can have it's torque band can be manipulated to increase that latter measured TQ.

Ok, I've ad enough fun for one evening. I'll stir the pot some other time. And yes, that's my shorthand.