NEEDforSPEED

Whats this board your talking about,
some of us use altavista and i posted it for the unaware, your post was just as amusing by the way

Fast355

iTrader: (2)

I hardly call one engine proof. Perhaps the TBI had some fault in it. His numbers are low for a TBI engine, less than I get with a 5,000+lbs G20 van with TBI. His MPG sucked with TBI, leading me to believe that his had a problem somewhere. His torque increase also leads me toward this as well. In proper operating condition they are about the same with a slight advantage to the TPI in the mid-range. Look at the L69 and the 1985 LB9. They are the same engine only one has the old E4ME Q-jet on it and the other the TPI. The LB9 arguably has a little better exhaust with larger outlets on the manifolds and a larger Y-pipe. It also lacks the emissions handicaps of the carb that cut power. Give the L69 about 6-8* more timing and they really respond.

L69=190 HP @ 4,800 and 240 ft/lbs @ 3,200
LB9=215 HP @ 4,400 and 275 ft/lbs @ 3,200.

Yeah it made more torque but it made it in the resonance period. With the proper 36* @ 2,800 timing the L69 would be about equal in power to the LB9.

The difference is not near the 30+ percent claimed earlier. It is a much smaller 14.58% in torque and 13.15% in HP. I have taken the older carbed LE9 305 and picked up 20 RWHP and 25 ft/lbs on the Mustang by retuning and tweaking the carb. Properly tuned they would be about even, MPG, HP and TQ. The advantage would go to the TPI with cleaner emissions and better driveability.

Put a TBI on top of the L69 intake by using an adapter, do a little tuning on the fuel (use stock LB9 timing curves)and you are making what the LB9 makes. I've done it before. That was the first transition of my LE9 from stock. It was TBI on an adapter plate.

YenkoST

iTrader: (5)

I will put in my .02, I had a 383 TBI in my truck making 275hp and it was getting 14-15mpg in the city and best mpg on the highway was 20.4mpg. However, I put a HSR system, AFR heads, and big cam on the 383 making 425hp and I was transporting a bed in my bed along with some other stuff and got 19mpg, in the city I get 12.5 consistently.

John 89 Formula

I've had both an LO3 and an L98 in the same car, the L98 got better mileage than the LO3. It wasn't a huge difference, but I got maybe 10 or 15 miles more per tank with the 350.

TPIgirl

My husband and I think this is a really good discussion topic about induction & control systems. He used to do a lot of fuel mileage testing so of course he had some input.

First he mentioned two 305 TPI cars he tested at 55 MPH that got 29.5 mpg and 31 mpg. One was an 86 with headers, the second was an 88 with just a hollowed CAT. Both were automatic cars with 2.73:1 gearing (2.77:1 for the 88) & factory 16" wheel/tire. Both tested on the same loop with weather conditions recorded. He said the 88 had a slight advantage due to stock exhaust manifolds (no scavenging) and it ran much warmer than the 86. The 86 had a functioning cowl & lower temp tstat.

He says that's very good for the TPI, but that there are many more cases of TBI cars on the road that exceed these numbers in steady-state highway tests. He says that "as is" running closed loop that the TBI has the advantage on the highway.
He says there are a few reasons for this & I'll list some:
1 says TBI mixture has quicker burn-rate in chamber due to fuel vapor
2 more people run 87 octane in TBI then they do in TPI, and 87 burns quicker or more efficient at low-load
3 TBI cars come with smaller tires & better front alignment for highway cruising
4 more TBI cars run factory exhaust manifolds & fewer exhaust modifications
5 most TBI cars had less brake drag and are lighter in weight

he also says that since the O2 reading is an average, that TPI has a disadvantage when running closed loop unless the injector flows are matched.

He did say that the TPI was overall a much better system and that it could exceed the fuel efficiency of the TBI if you are allowed to change the conditions of the test.
Well that's some of what he says to me, so even though there are more TBI cars getting higher mpg, I'm still going to vote for the TPI.

Red Devil

Oh for chuckles ask him:

1. What's hotter, the bottom of the plenum area of the TBI intake, or the back of the intake valve in a TPI engine?
2. Pointless, assume both are running properly on 87 with optimal timing.
3. Same for same we're talking. I'd rather take coated headers over manifolds anyway. Higher overall VE typically means better gas milage.
4. See #2 and #3 and edit to apply.

TPIgirl

The intake valve temp is probably the same in the TBI as the TPI, but the TBI has many times more hot surface area that the fuel passes over. I understand this part.

He only says as-is more TBI cars run on 87 octane, and that TPI cars would improve mpg if they run 87 also.

Again as-is more TBI cars run without headers, and headers hurt fuel economy. He says in general a lot of performance modifications will hurt the fuel economy at cruise...mentioned camshafts and headers as being the worst.

Where did you get the fact of higher VE means better gas mileage? Was that applying to WOT or high power output situations?
It was my understanding that VE applies to the volume of air being moved per measured displacement, and that higher mpg depends more on burn efficiency than volumetric efficiency.

83 Crossfire TA

iTrader: (2)

efficiency, yes… but the same, no. what does your average f-body cruise at? 1500rpm? In most cases you’ll never see that rpm in a ¼ mile, 1/8 mile or 60’ run (well, at least after the car is moving). You’re also not at WOT at that 1500rpm cruise.

Oh man you’re opening a can of worms… the TPI intake had probably the worst port entry characteristics of any production intake design because of trying to fit those bigass runners under the hood… I’d suggest that you don’t even go there unless you’ve got some evidence that a crappy port entry and disrupted flow over the port floor somehow increases efficiency over a more conventional design like what was used with a TBI.

I’d suggest that you’re barking up the same tree with the what’s warmer port floor/intake valve deal… no production small block actually managed to have the injector actually aimed at the back of the intake valve before the insanely tall, peaked ports of the LS1’s, and notice how somehow it’s starting to look like it didn’t work as intended (at least GM didn’t see the benefit, check out the ports on the LS2 and LS7). If you’re going to be bouncing fuel around, it’s much more likely to be suspended or vaporized by the time it hits the chamber if it is sheared by the throttle plate, has the long drop of the plenum and runners… vs being bounced off the port floor of a TPI setup in a stagnant area of the port because of the TPI’s crappy port entry.

Sure, the back of the valve is hot. It’s hot in both engines.

Huh, I guess I’m a TBI guy somehow, even though I drive my LT1 more then either of the others, probably followed by my TPI car, my crossfire car doesn’t even exist anymore but I do have an L05 truck that sees some road time if I need a workhorse.

A flawed test <> hard proof.

where does he get that manifolds are superior to headers WRT to gas mileage? If anything it’s the other way around unless the headers are greatly oversized. I’d put a set of 1-1/2” or 1-5/8” primary headers, especially long tubes against a set of factory manifolds any day, assuming that you have a properly mounted (possibly heated) O2 sensor.

I’d agree that it has a quicker burn rate, but not because of the vapor, but because the heads used create a higher swirl rate in the chamber.

That would depend on the rules of the test… there’s a ton of ways that you can fix it in favor of one side or the other, but if you went for the ultimate, do anything approach… huh… I’m not sure… I’d give TPI one way to win, and that would be if you could build a manifold with a tuned runner length optimized for the RPM that the test will be run at… otherwise, I’d go TBI…

TPIgirl

He said an engine with headers will pass more unburned fuel and air out the exhaust than an engine with log style manifolds. VE increases, but total fuel consumption goes up.
He says VE is not directly related to fuel efficiency at part throttle. I understand but can't explain it.

So far from what I understand is that the TPI or MPFI system has an efficiency advantage when AE is used, and that MPFI has the ability to run leaner than a wetflow system if the MPFI uses a flow matched injector set.

The TBI would have an advantage during steady state highway cruising, but requires more AE and cannot run to the same lean limit that a MPFI system can because of fuel distribution error.

Has anyone played with the TBI system to measure mpg increases with modifications? There may be potential in reshaping the throttle blades or changing the IAC function?

My husband says the biggest increase he has tested with a TBI system is +12% mpg by feeding the TBI 160*F air off the exhaust manifold. The improvement during highway driving only, and then showed a loss in mpg during stop-n-go testing along with greatly reduced power. He got similar results with carburetors, but has not yet tested a TPI or MPFI with the hot air intake.

I am enjoying this discussion as I'm learning a lot!
I'd like to hear some more test results from some of you guys.


edit: 83 Crossfire, Where do you stay around DC?
My husband was working at the Pentagon for 3 months this year and I went up to visit for a few days. His place was in Falls Church, and we took the train around DC to see the Smithsonian and monuments. It's very expensive up there.

jumpinjoe

I've owned 6 350 TPI cars and 1 305TPI/5 Speed car. I averaged about 22-27 in my 350's and darn near 30 in my 5 speed car. I also had a 91 305 TBI(not by choice but got it cheap, 300.00) formula that got crappy mileage. I personally dont buy anything other than TPI cars, unless they're gifts (wink,wink). Also I think mileage isn't as big a concern for us in Minnesota. I just fill the tank and go.

Fast355

iTrader: (2)

I have to say something against the unburned fuel theory. It would have shown up in my HC emissions on the G20 when I switched to headers due to the fact I do not have cats. My HCs were almost identical before and after. Had the headers over-scavenged the engine it would have shown up.

My headers greatly added in the low and mid-range torque. That keeps my foot out of the pedal as much. That keeps the converter locked longer and me out of PE aor 3rd gear. My headers actually helped my fuel mileage, but then again look at what I am hauling around.

I run a functioning heat stove setup on the G20 which works well in winter. It does however like to run with cooler air most of the time. My air cleaner setup ran about 125* on the IAT when I had the 8746 runnin it.

Changing up the TBI didn't really help or hurt that I could tell.

IAC makes a huge difference on TBI (It works just like a vacuum leak). I try to shoot for no more than 20 counts on the IAC with the engine fully warmed up and the A/C off, transmission in Park/Neutral. I adjst the minimum air rate to get the desired idle speed, then let the IAC fine tweak. This helps in the fuel being sheared off the throttle blades.

83 Crossfire TA

iTrader: (2)

Same here… I’ve never seen a car not gain gas mileage when adding a reasonably sized set of headers. My crossfire car got downright incredible gas mileage (I wish it was still around now) with a set of headman 1-5/8” headers (the sorta ¾ length ones), and I actually had problems with emissions tests in that it read too clean (I would fail because the numbers were a bit on the low side and it would assume that I was cheating somehow, stupid computerized setup, I would actually pass by jacking the fuel pressure as high as it would go and goosing the throttle a couple times during the test to get it to dump some extra fuel, one of the emissions stations monkeys showed me that trick for the old tailpipe idle test).

83 Crossfire TA

iTrader: (2)

VE is VE, as long as we’re talking about under the same conditions. In general, if you increase VE at the part throttle condition that you cruise at the engine will be more efficient, but as I’ve already mentioned in this thread, BSFC is a much bigger issue.

yes/no/maybe? I tinkered with it quite a bit, but the mileage was secondary. Pretty much everything I did improved performance and MPG as long as I had it tuned right, but I didn’t have specific numbers about what was doing what. When I went to 54mm bores it got much better, I suspect that it was because the throttle plates were closed more at part throttle cruise atomizing the fuel mixture better…

I built a house on the Montgomery/PG county line in MD… about 9 miles north of the beltway, right between DC and Baltimore. Yea, life is a bit pricy around here, but out as far as the pentagon it shouldn’t be as bad as closer in. In general, besides right in by the city NoVA isn’t as bad as the MD suburbs.

JPrevost

It takes a lot of ***** to say that 1 biased test is proof for us all (reply to Kevin's dad's gains). He did have gains, but he didn't optimize the tuning in either and for some reason his TBI was getting less milage than most everybody else with the same combination. With tuning done to both I bet their highway would have been similar, the same, or better with TBI and city would have been better with TPI.
What about taking a TPI long block and swapping on TBI and the TBI ecm? Has anybody done that? Unlikely, so doing one test doesn't prove the point, it only answers a different question.
I'm going to re-word the original question;
Is there a taste difference between apples and oranges?
What if the apple is rotten, or orange? What if I'm an apple farm owner?
The question is too general. Be more specific with the question and you'll get better answers with less a-holes replying.