84 Z-28 350

the problem with TBI in genral (NOT JUST OUR CARS- THIS STATMENT COVERS ALL TBI) is that it's halfway between and a carm and true FI system like TPI, MPFI, EFI, or DFI. you have 1-4 injectors located in a central location constantly flowing, that are either modulated (quickly switched on and off by the computer) or have a fuel pressure regulator that varies the pressure to compansate for demand, also the central location with no venturi effect gives poor fuel atomazation, (the only mixing that happens is in the spray the pintle creates, and fine droplets of fuel tend to join to form larger droplets when they have to travel a distance thru the intake, thats why all others have the injectors as close to the valve as possable or in the case of DFI, in the combustion chamber after the valve, also you have allot of fuel puddeling in the intake manifold with TBI, again due to poor atomazation and the distance travled to the valve. Just my $0.02, and no flames for spelling, I took chemistry, meatelurgy(I know that's not spelled right), and physics in collage, not english (beyond minimum requiered classes)

dimented24x7

iTrader: (2)

There is truth to that. At p/t it doesnt matter much since the fuel will be atomized by the turbulence around the throttle blades, not to mention that the heat and vacuum help the fuel to evaporate and mix in with the air as a vapor. Helps to cool the mixture as well. My tbi will get very cold, even on a hot day, jsut from the fuel flashing over to a vapor once it passes the throttle blades and the passages and goes into the low pressure of the manifold. At WOT, though, having good injectors that atomize the fuel is critical. I had a set of autozone ones that didnt do a very good job. The fuel came out in blobs and pretty much just hit the floor of the intake at WOT. The fuel is supposed to come out in a cyclonic motion and be sheared into a fine mist but that didnt really happen with those. The smaller fwd'er ones I have now do a very nice job of atomizing the fuel and it makes for a much smoother running motor.

The main reason it no longer exists is because tbi is old technology that cant keep up with todays more stringent standards. The fuel is jsut dumped in on top and left to its own devices to get into the cylinders. There isnt as much control as there would be with a sfi system, which can meter the fuel with more precision and inject it just when the cylinder is taking in air. The tbi is affected by weather jsut like a carb as well. Cold weather interferes with the fuels ability to evaporate and as such, the gas just pools on the bottom of the intake when its cold. I really cursed my car when I first got it. Once it got cold out, the car would always flood out and run like crap. Experimentation with the fuel and other things on startup helped to give turn the key and drive away starts even in below zero temperatures but it will never be quite as good as a late model sfi system. Although, even in cold weather they can have trouble. Had a late model car that would surge a bit when cold and stall when it was very cold if I hit the gas just right. No trouble with the car, jsut a few things that they didnt manage to polish out.

84 Z-28 350

I'm going to say one word that will get this subject really going....crossfire

Poncho Villa

Hi, I'd just like to say that I love my 91 Firebird with the LO3 TBI. It has over 150,000 miles on it, doesn't burn a drop of oil, and actually runs much better after the 10,000 troublefree miles I've put on it (bought it last fall, and I drive a lot for work). My auto trans was rebuilt by previous owner, and the motor seems as though it was rebuilt too, but I think it's original.

Even so, my TBI car always starts up and runs reliably, no flooding or anything else. I run high octane gas, and throw in a bottle of Berryman's fuel injector cleaner once in a while. My open air element gives a nice whistling induction sound, and my Flowmaster cat rumbles nicely.

No, it's not a 12 second car, but fast enough to put a smile on my face, winding up smooth with power to redline.

Sure, you always want more power, so down the road I plan to drop in a 310hp 350 crate motor, which is compatible with my ECM, TBI and all accessories. I will need bigger injectors, a new fuel pump and a chip.

There are several engine builders that make performance replacement motors specifically for third gen TBI F-bodies. So, while the bulk of guys with fast cars might be running TPI, there are definitely performance options for TBI as well. A TBI crate motor, with headers, ignition upgrades, and other tweaks would be plenty fast. And you should still be able to pass smog.

To sum up, my car came with TBI, (and a GTA body kit), so I'd rather stick with that system instead of changing everything for a TPI motor with the same performance. Already, my TBI car is lots of fun as is, no complaints.

"One of the things we KNOWS is, it's not how you stand by your car, it's how you RACE your car, you better learn that."
-sage words from "Fast And The Furious"

Son Of Toretto

P.S. This setup would be nice...can you use TBI's with one of these suckers? Still use the ECM? Ultimately, I'd like to have a huge blower poking out my hood, pumping 800+ ponies. You gotta dream big...

P.S.S. Just read my post, and realized I'm a TBI freak...

NjccBflo

my $.02:
in summary we stick with are delinquent, inefficient, and outdated TBI's because they are cheaper to play with, easier to wrench on, and require low level computer skills to get high level tweaks.
All that being said, i've had 2 TBI V8's and a TBI V6... you know what? All three of them have given some pretty surprising grins. Thats all I'm looking for.
I know I cant run in the 11's with this car and i know that I'm not about to drop upwards of $8k to try and do so (paying for house, land, and electricity are more of a priority), when i can spend $2k and have a rock solid 13-14 second car that will also haul 4 people to the beach, powerslide nicely, and in the end, all F-Bodies are sexy beasts on any given day. IMO

Mark A Shields

try 4500 rpms

owned

TPI gets aftermarket support? Not that I can tell, at least not significantly more than TBI... For ****s sake, you can't even get an aftermarket MAF...

There are lots of options for a better flowing TBI unit, and you can use 1 out of the 18 billion intake mnifolds out there. That pretty much all there is to TBI specific parts.

TPI is limited to some crap aftermarket parts that make little difference (runners, bases, plenums, etc) or 2 high dollar replacement manifolds. (superram, miniram).

I know I am not including the stealthram, but thats because I do NOT view that as a product designed to support TPI. They do not sell it intending it to be used on TPI vehicles, and didn't even design it to fit under a stock hood. I view it as another example of guys using whats out there and modifying it to work.

Ditto for engine management. It says volumes that the best solution for changing the computer controls on a TBI/TPI came from home hobbyists.

Compare that to the 5.0 world, or the LS1 world, and you see that TPI does not get support worth a dick.

SweetS10v8

I think just putting 2 stock TBIs would feed that plenty. Iron heads, short valve covers, stock dampner and all.....

Looks like a stock 350 with a tunnell ram on it, lol

Kevin91Z

iTrader: (1)

Yes you can get an aftermarket MAF for TPI. Its from Granatelli and it costs $400. http://www.granatellimotorsports.com/

You do NOT get the same performance from TBI as you do with TPI. The limiting factor with TBI is the two fuel injectors. The largest ones you can get is 92lbs/hr, right? That's enough to support about 300 HP. If that's all you want, then great. But I hear countless people wanting to make their TBI's perform like TPI or LT1 or LS1 cars do. 300 HP will get you there, but it wont keep you there.

For example, take my dad's car. Its a 1992 Camaro RS that came with a 305 TBI and a 5-speed. After putting on a stock 2.75" IROC cat, exhaust and muffler, along with a K&N air filter, it made 158 HP and 220 TQ to the wheels, with a stock computer and chip. After switching to a stock TPI setup with a stock speed density computer and chip, it made 175 HP and 290 TQ to the wheels.

I do custom chips as a side business. Let me tell you, speed density TPI is one of the easiest, followed by MAF TPI. TBI chips are similar to SD TPI, but with only 4k of data compared to 32k of data, TBI is very limited in what you can modify. There isnt even an injector constant. You have to do some math to compute the injector constant vs the engine size vs some other numbers.

Poncho Villa

Ok, so now you've got me thinking about an LT-1 swap again. I found a 350 TBI crate motor (marketed specifically as a replacement for TBI Firebirds and Camaro's), that makes 310 hp, and 365 ft/lbs of torque, and is supposed to work with stock ECM, harness, and pretty much everything else. I guess you would need bigger injectors and a chip. I was considering this mainly for PASSING SMOG IN CA. That would be a sweet setup. However, a crate motor with TPI, or a nice rebuilt LT-1 would be even better, by the sounds of it.

Research I've done also says that, any replacement motor from the same type of car, that model year or newer, with all smog hardware, is classified as an ENGINE CHANGE, and that will also pass smog. However, with an LT-1, LS1 swap, you've gotta change out a lot of stuff. Harness, fuel system, ECM, dashboard interface, etc. I'm not a mechanic, so that's pretty intimidating. There are places that do turnkey swaps, that might be the way to go. My motor runs great now though, so for now I think I'll stick to exhaust, ignition and TBI tweaks, and worry about major changes about 50,000 miles from now.

Any thoughts on hotrodding TBI vs. engine swaps are appreciated.

P.S. Just for the hell of it, I've looked around for TPI cars, haven't found any in my area in near as good shape as my TBI Firebird. So mine's a keeper, just want to make her a bit faster. Quite a bit.

91 Firebird 305 TBI, rebuilt auto trans, open air element, Flowmaster catback, 160* stat, GTA body kit, Weld type aluminum mags, cobalt blue paint, chrome exhaust extensions (add 3hp), Alpine CD :lala:

dimented24x7

iTrader: (2)

With the injectors, you can get a good deal more flow by not running the stock fuel pressure. Ive heard of people runnign them at 30+ psi. Might even be able to go higher if the stock FP regulator was blocked off to prevent a blowout.

As for the prom, keep in mind that there is an additional 8K of firmware on roms that isnt normally accessable, although with some minor mods (as per suggestion of other users here at TGO) I was able to get access to that and add an additional 4K of free space for whatever. This enabled me to and expand the tables to go for the full range of the engines rpms. The stock tables are smaller to conserve space given that only a small prom is available to store the calibration. Basically it was a trade off to alow for the necessary ammount of code to be present to control everything. Dont let the smaller prom fool you, the algorithm is still pretty complicated. There is a constant, but its a tad different. Not that the additional math really matters since the injector constant should be set to match the injectors and just be left alone. All further fueling can then be handled via the VE tables.

dimented24x7

iTrader: (2)

Not to discurage you but its a lie that the aftermarket motors will work with no mods to the FI. Your putting in a motor that has nearly double the horsepower of the origional so there isnt much chance that it will run correctly. Youll need to tune it yourself. All the aftermarket chip tuners are a joke IMO. You cant tune a motor unless you have access to it. If you dont want to tune it, get a newer setup. My other pick besides tbi is an LS1 or LS6. One of the things that always bothered me was the fact that gm just sort of sent the tbi cars out the door without much work in the performance or tuning department. The stock tune of my car was ****. Never liked teh way it ran. The exaust was pretty bad as well. People have shown that with some tuning and bolt ons like a properly sized exaust, the L03s can turn track times at or faster then that of the L98's. Wouldnt look too good if GMs base line F-cars outran their top of the line V8 models, would it. So, they just sent them on their way with the minimum to get by. Yet another reason for the bad rap that tbi got.

Poncho Villa

So you don't recomment the LT1 so much? It's a whole lot cheaper than the LS1 and LS6, however, I guess if you are going to swap motors, you might as well go for the gusto.

I agree with what many have said, that the LO3 is a diamond in the rough. Even just with an open air element and 160* stat, my motor runs way better, seems to make a lot more power than before (comparable to my old 350 '73 Camaro), and it's still a blast to drive. I'm sure if I had better rearend gears, that would help too. I have an auto, and there's a big flat spot, where the car feels like it's in the wrong gear, mainly between 50-60mph. There are some sweet spots too, like flooring it at 40mph or 70mph gives a kickdown and a big rush of acceleration.

The biggest hp boost for the TBI motor, based these boards, would seem to be heads and cam, with people approaching 300hp!

As for "tuning," not sure what all is entailed in that. Timing? With my cooler thermostat, the motor already runs way better, and timing seems to have changed, in that firing seems farther apart. Exhaust pulses are more defined now, as opposed to a steady drone.

For now, my L03 doesn't burn or leak a drop of oil, gives smooth power and gets up and goes. No problem stomping a manual trans Mustang off the line either, believe it or not. She's got 154,000 miles and no sign of slowing down. So any TUNING ADVICE is appreciated. In another 50,000 miles, I should have the dough saved for the LS1 or crate motor.

On the LO3, want to do headers, Y-pipe, cat, already have Flowmaster catback, TBI spacers, intake manifold, ignition upgrades, ram air setup, chip, and anything else I can think of.

Poncho Villa

Also, Dimented24x7, noticed you are running a 350 TBI. How do you like it? Did you swap it yourself? For your slipping tranny, I would recommend a LITTLE BIT of Lucas auto trans additive, you might have to pump some ATF out first, and lifting off the throttle a bit between shifts. Mine was slipping a bit from 3rd to 4th at WOT, especially after I put the open air element on, because now my motor revs like a sumbiyatch. So I put in a bit of Lucas, and now I lift off a bit between gears if winding out in 3rd, no more slippage. Lower gears are fine, and my trans was rebuilt a couple of years ago, so I'm going to try and get another year or two out of it.

When I do put in a new motor, I want to install the T56 as well.

dimented24x7

iTrader: (2)

The 350 isnt bad. It impoved alot with a slightly better cam. Wish I had degreed it, though. Think the cam may be off. Only pulls good vacuum at around 1000 rpm and it lopes at low speeds. Also only doesnt start to hustle until about 3000 rpm. Other tehnt he fact taht I have to wind it out to get going in a hurry its not bad. Certainly better then the origional L03 even though its jsut a factory replacement.

As a motor the LT1 isnt bad, just that I dont like the optispark system. Kinda prone to failure.

dimented24x7

iTrader: (2)

As for the trans, it started slipping after the swap. Really have to get something else. Between shifts teh motor will flare up to 6k if I hold the gas down.

Kevin91Z

iTrader: (1)

The LT1 is just a glorified TPI engine with a better intake in stock configuration. The distributor (optispark) fails quite often, and the extra cost of an LT1 engine is hardly worth the minimal performance boost compared to using an aftermarket TPI.

dimented24x7

iTrader: (2)

The LT1 was also SFI (hence teh dist. driven off of the cam), but some feel that batch fire works just as well.

Poncho Villa

By "aftermarket TPI," do you mean a crate motor with a used TPI system grafted on? I'm looking for most "bang for the buck."

Since a new LS1 is around 4500 bucks, I was thinking more along the lines of a 350 TBI setup (I already have TBI), an LT1 swap (found one used, with T56 for 1500 on Ebay), or just modding the hell out of my 305. Want to stay smog legal is the thing, and I live in California, so a more powerful stock replacement motor would seem to be the answer. But which motor?

Also, what was the name of the motor used in the 91-92 Trans Am GTA? The LT1 came out in '93, right? So there must be used 5.7L TPI engines kicking around. Did those have optispark?

P.S. I've read over and over on the LT-1 swap boards about "optispark" problems.

Poncho Villa

Ok, I answered my own question, looked up engine specs for the 91-92 cars.


91 RS
Firebird M5,A4 LO3 V8 9.3:1 5.0 (305) 170@4000 255@2400 TBI 3.08 ---- 2.73 ----
91 Z28
Formula
Trans Am< M5,A4 LB9 V8 9.3:1 5.0 (305) 205@4200 285@3200 TPI 3.08 ---- 2.73 ----
91 Z28
Formula
Trans Am M5 LB9 V8 9.3:1 5.0 (305) 230@4200 300@3200 TPI ---- 3.42 ---- ----
91 Z28
Formula
Trans Am A4 L98 V8 9.3:1 5.7 (350) 245@4400 345@3200 TPI ---- ---- ---- 3.23
_

1992 was the same, except a GTA model was offered with the L98. So, does anyone ever swap in the L98? Can the L98 make as much power as the LT1, if modded? The LT1 makes about 30 more horsepower, I think.

If I have to change a bunch of stuff to do a 350 TBI anyway, why not just go to a 350 TPI motor? Planning to change the rearend, too, to a GTA unit with disc brakes and posi, and I'd like to use the T56 as well, for better burnouts.

Kevin91Z

iTrader: (1)

Take a look at my signature and tell me if an L98 can make as much power as an LT1 or LS1, for a lot less money. You're lucky to live in SoCal. My dad is one of the masters at converting TBI to TPI. We're up in Orange County if you feel like making the drive.

25THRSS

You can decide for yourself

http://bitchincamaro.no-ip.com/dyno.html

dimented24x7

iTrader: (2)

Never liked the stock rear ends, even the 9-bolt I had. Big problems I had where the crush sleeve. Both my 10-bolt and 9-bolt had the problem of it crushing down some more after awhile and allowing the backlash to open up. Really trashed the 10-bolt and the 9-bolt I have now used to be really tight and wisper quiet but it got really clunky and started whining. No solid replacement available for it, either. I dont care what I run next but its definatly going to have a stronger aftermarket rear in it.

Poncho Villa

Holy cr^p that is a boatload of power. That is damn fast. I wouldn't be doing the swap for a while, but I am definitely interested. Was looking for an L98 on Ebay, only found LT1's and LS1's today. However, I'm sure one wouldn't be too hard to find. I'm in San Diego. Definitely wouldn't mind visiting you guys. That Camaro is badass.

To sum up, since this thread was started by somebody asking what's wrong with TBI, well nothing in my book. My TBI motor runs like a dream at over 150,000 miles, no oil burning or leaking, smooth idle and smooth power to redline. Even sounds pretty mean. The TBI longevity board confirms I'm not alone, these things run forever. My car is even pretty fast as is, and more than adequate for a sports car. I'm just looking for more speed, and apparently there are lots of options.
Thanks to everyone for all the info.