Darkshot

iTrader: (4)

First of all I want to say that I have zero experience with carbs. I am asking an honest question, not trying to make a point. I notice that many people prefer carbs to TBI for performance. Why is this? If fuel injection is more accurate and more efficient than mechanical carburation, what is the big difference? How could a carb possibly be better than TBI?

Fast355

iTrader: (2)

Most people do not want to spend money to buy a prom burner, dataloging cable, and laptop to tune their car. They want to buy something that cost $250.00, slap it on their engine, and for it to start and go. Not always the case with TBI.

Sonix

iTrader: (1)

Fast is right, a couple of screwdrivers is all you need to tweak your carb. I don't have a laptop, or that datalogging stuff, nor the programming skill to do it. Hence it'd be a huge jump. Most "hot rodders", (ready for a stereotype?) are farm guys, or fabricators, not computer geesk, so a carb is more user friendly.
That's also why TBI isn't very popular, which leads to choices in parts, max size etc. You can get a 1050CFM carb which will support a very high 3 digit HP level, and dual carbs is always an option too. You save weight without a computer too

drifter-x

yeah. theoreticly, tbi will outdo carbs. but our tbi setups are inefecient, and any good fuel injection setup out in the aftermarket is going to be mpfi, even the tb setups. just the way the world spins. one of those the way things SHOULD happen vs. the way things DO happen things

Fast355

iTrader: (2)

I would hardly call the TBI setup inefficient.

Blazin4x4

I know this is OT but I just notice all your mods fast355... What kind of power are you making with the blower? What are your et's and mph?

OK hijack over

TierAngst

He dumbed down his blower setup because he hadn't built up his trans but ended up shredding the trans after two weeks of mild driving. I'm sure fast355 is more excited than any of us to see what that van can really do when fully tuned up with a good trans behind it.

Fast355

iTrader: (2)

All I can say is the blown 350 TBI would rape my LT1 cammed Vortec. Its still pretty much stock with a PCM tune and LT1 cam. It will squeal them and GO!

I also need to say screw Kennedale and go to Ennis to make a pass.

TierAngst

There we go lets see some quarter mile times, well I guess first you have to unlazy yourself and get that trans together!

Blazin4x4

reason I ask is I was seriously considering a blower until I realized that with some afr's I can max out my tbi's potential at around 430 hp...

Do you have any dyno runs on the blown motor or estimated hp and tq? I'm curious to see if your over 430 hp on tbi... like to know how you did it if you are

Fast355

iTrader: (2)

I am at 423 FWHP from a 312 CID 305 TBI engine.

With a supercharged engine, you can run crazy fuel pressure under boost. Lets use my 350 as a prime example. I have 80# injectors. The VAFPR gives 15 psi at idle(18 in/hg), 22 open to the atmosphere, and 27 PSI at 6 psi boost. Here is the math for the HP my injector combination can support. Sqrt of 27/12 x 80 lb/hr x 2 injectors x .5lb/hr/hp BSFC x .85% DC = 408 FWHP. With the EBL you can run Asynch mode and go higher than 85% duty cycle. BBC injectors CAN idle at 20 psi, giving you 5 more PSI, NA. Raising boost higher than that will increase the pressure further. Some injectors have been tested to 70 PSI. I have used the stock regulator diaphram at 45 PSI without any signs of trouble. For higher pressures I would recomeend fabing a block off plate, eliminating the stock regulator, and fitting a FMU. The BBC TBI is limited to around 500 FWHP, even when bored to 2.2". Above that two TBIs could be used along with a dual carb blower, the B&M 420 comes to mind.

gheatly

iTrader: (2)

I would bet that TBI is not any more efficient that a well tuned Quadrajet carb once the engine has warmed up and in "normal" weather. It is when the engine is operating outside of those parameters that TBI really does its thing.

As for the "I hate to stereotype" comment above, none of the "hot rodders" I know are farmers. We are accountants, lawyers, engineers and any other profession you can think of. Hell, everyone on this board is a "hot rodder". How many farmers here?

firebirdjosh

iTrader: (1)

I'm willing to bet the crowd is evenly divided:
1/3 kids getting on as a first car thinking its a race car
1/3 guys using 3rd gens as a cheap/affordable base for a high performance car
1/3 older guys remembering back when they first came out and finally got around to owning one (or have owned one since new)

TierAngst

You forgot a good percentage... guys with huge vehicles ie; trucks, vans, station wagons that need a good reliable vehicle that can get out of its own way while hauling stuff.

Sonix

iTrader: (1)

hmm, yea, I think Josh there is onto something...
I'm in the 1st part there


But no seriously, this forum doesn't really represent the hot rodding community all that accurately. The real racers are off turning wrenches, or bail wiring their exhaust, not posting threads. This forum is probably more the white collar hobbiest, rather than the blue collar "make 'er go" crowd.

That being said, i'm an engineer. But if a poll was made to ask "blue collar vs white collar", I think it'd be a pretty even split. Then again, that goes back to the people who aren't here to answer the poll, and those aren't the office works sitting at their desks, it's the mechanics/farmers/welders who're dragging their welder across the bay, without internet access...

anyway, that's wayyyy off topic. I think it's been said here how TBI and carb differ. To each his own, bla bla...
If I wanted to step up to the "complexity" of FI (from the simplicity of my carb), i'd go all the way and use some sophisticated port injection. TBI is just a "smart" carb afterall... (gasp! I'm in trouble now eh? )

68C15

in simple terms a factory TBI setup doesnt have the ability to atomize fuel the same way a properly tuned carb can. I realize this is due in part to the low fuel pressure of a TBI system. but truth be told a venturi has much higher affect on turning a liquid into a vapor. this is due to the fuel molecules being pulled away from each other as opposed to being forced apart.
case in point; I had an '80 K20 with a Crower cam'ed 355 with 11:1 static compression pushing out close to 450 HP and over 500 ft/lbs at the flywheel while having the ability to get 17MPG on the highway @ 75MPH. (I dont remeber the RPM at this time, it was a 3.73 gear with 31" tires and a manula trans) from a custom Holley carb. I started with a 600DP main body, a 750 base plate, stepped annular boosters (this was the key ingredient) and #76 jets with a 3.5 power valve. on the main circuit there was literally a FOG emitting from the primaries!!!! not to mention the way the thing just pulled like a frieght train. 1/4" throttle to go 60 MPH, if you slightly touch the pedal you could feel the thing wanting to run away. ( this IMO is the true definition of a throttle)
DO THAT WITH FUEL INJECTION!!!!!!!!

Blazin4x4

LOL man fog from the tbi or carb is completly normal on a bone stock motor. And its the other way around... most carb setups run off about 8-10 psi... a hot tbi system will hit 25-27 psi.

Take your carbed motor in the mountains and see how she pulls compared to tbi. And as far as the hp and mpg one of them HAS to be off. My bro's MPFI bone stock s-10 blazer get about 17 mpg.

68C15

no sir, the dyno and gas station pump proved it. my boss and the guys at the speed shop were amazed.
Volumetric Efficiency is the key factor.
you do have a good point about barometric pressure though.

Fast355

iTrader: (2)

I have, my old 305 was 301 RWHP and got nearly 20 MPG @ 75 mph, pulling a 5,300 lbs G-series Van.

61lb/hr injectors at 36+ PSI to make 301 RWHP. Keep in mind this was a 9.8:1 compression 312 CID engine.

It would pull pretty well down low, probably 1/3 pedal to run 65 to 80 mph @ 2,000-2,300 rpm.

I was running in closed loop at the time to keep the catalysts in good shape. Lean cruise offers a huge benifit in MPG and I have found that catalyst life seems to be OK using it, as long as the engine is not missing.

FWIW, I have found that 4.3 injectors at 22 psi give better MPG, better throttle response, and more HP than 350 injectors give at 12 psi, on the stock programming.

cheppibear

I have the opposite problem and can not seem to find the culprit. My TBI setup works horribly when cold and then is fine once the engine warms up. You hit the gas to go after starting it and the thing often falls flat on its face, idle seems rough too sometimes. Other times the engine runs ok, but everytime once the engine is warmed up, it rides fine.

Anyone have these problems?

brodyscamaro

Ehhh, I'd be willing to bet a theres at least 60% teens with hardly any real-world experience...

camaronewbie

Efficiencies? Inefficiencies? I don't know.

I know this.... As was mentioned, the carb is easy. I did alot of mods to my 1990 305 TBI, and spent hundreds of dollars and months of time trying to get a chip made (I don't have the knowledge/patience/time to do it myself), and in the end, all I got was a running car - no better than it was before. TBI seems to be more difficult to tweak chips for than TPI in general.

With my 1992, I yanked the ECM, went carbed 350, and I now have a very streetable, nicely performing, reliable, and adjustable (to dumb me) motor that I personally understand.

One thing I do think of when it comes to "efficiency" ....

Late 60's VW Beetle - 45mpg carb
2006 VW Beetle - 32 mpg FI

Hondas? None of them get any better mileage with the "efficient" FI than they ever did carbed.

Now I'm not saying that across the board FI hasn't given what it promised - but for the complications associated with diagnostics and repair of computer-controlled systems (at least for us old school farts), there are plenty of examples where it hasn't totally proven itself to me yet.

DM91RS

You ain't there yet..........

Dewey316

1200cc Carb vs 2.5L (2500cc) FI.

40hp Carb vs. 150hp FI

I don't know, I think the late model VW's win that one. They win in MPG/HP, and in HP/L.

Not to mention, they meet all new federal smog regulations.

Would you like me to look up the Honda specs to?

DENN_SHAH

iTrader: (1)

also, about the comparison of a late 60s beetle to a 2006, take a look at the weight difference, interior room, & the performance difference, late 60s, around 70~80 MPH max on a good day. 2006 beetle, 100+ MPH cruise all day with no problem,... thats with the A/C turned on. its the same with hondas too.
i can't believe i just paid a compliment to volkswagen & honda,... i need a bath & some beer now,....

fuel injection is about more than just performance & fuel economy, its also about federal emissions regulations.

Blazin4x4

And for a 4x4 guys like me FI is almost mandatory... carbs can't run at the angles tbi can and tbi will kick a carbs *** in the mountains... Oh yeah I live in cali so I'm pretty much stuck with tbi or a 2000 dollar mpfi system(probably more) but with the holley stuff and prominator and ebl tbi will work great.

dimented24x7

iTrader: (2)

I know Im sounding a bit like a broken record on this, but one of the biggest problems with TBI is that it uses speed density and isnt flow referenced. With SD, its critical to know the intake charge temp, and with TBI, you really dont know what the temp of the charge is because the fuel dynamics will cause the intake charge to get very cold under vacuum as the fuel flashes over to a vapor. This isnt a problem with a carb as its essentially flow referenced. If you put a MAF in front of the TBI, this problem goes away and it behaves like a carb. With SD, alot of the tune is going to be strictly empirical. If you know how to tune and understand some of the limitations of the stock system, it wont be a problem. I never had much luck with it, though, and wont be using SD any time soon unless Im using MPFI.

adashwood

allright so im new here...and a little embarassed to say, i know **** about my car.

im curious about tbi.

what kinds of things i need to be aware of as far as maint. or what to check for to see if its running how it should.

ive had people tell me to get a carb for it and ditch the tbi.

also which is more cost effective?

TierAngst

I'd start out by reading the stickies at the top of the TBI section. That should give you a fair understanding of everything, whatever questions you have afterwards feel free to make your own thread for.

As for cost effectiveness goes, usually sticking with what you already have is cheapest unless everything is broke and needs replacing anyways which I doubt is the case for you.