I am new to the f-body scene and i got a 89 Trans Am with 305 TBI. I always see people changing from tbi to carb or tpi and i don't understand why its always badmouthed. I didn't want to post this on the tbi forum bc then i'll get answers from all the tbi freaks. Thanks.

 

Freaks?

None of them around here...

Oh, you asked "why".

Because the factory never intended it as a performance system. Therefore, trying to make it perform (other than the way the factory intended) is difficult and limited.

 

Precisely....

It was intended as the gas-mileage successor to the LG4. Just yerbasic motor, nothing special. They deliberately designed features into it that purposely defeated "performance" as we know it.

Then, by the time you the hobbyist finally get all that "designed in" anti-performance stuff (swirl-port heads, crappy exhaust, tiny intake, pitiful cam, and so forth) "designed out", you've replaced basically every single piece of your engine, and spent far more than you would by either converting it to carb, or putting some other FI system on it that was designed from the get-go as a performance system.

Plus, the cars it came in were always the low-end ones, as far as performance. Terrible gears, limp suspensions, and all of that. So not only do you have to replace the whole engine a piece at a time, then you have to go to work on the entire rest of the car too.

Notice how there's NOBODY running fast with one. You see lots of "planning" and "building" and "I'm gonna" and stuff like that, but ...... no time slips. If it was affordable and practical, there'd be at least a couple of people stumble backwards into making a fast one; hell, anybody can slap a set of Vortec heads and a 750 carb on a 350 and break into 12 seconds. But you can't seem to do that with TBI, on any size motor. Not even a big block.

Basically, if you want a fast car, it's just not sensible to use one of those as your starting platform, unless you are already intending and prepared to completely redo the car; and virtually everyone that does that, upgrades the fuel delivery system. It doesn't make sense not to.

/rant mode off

 

Most people diss it because they don't understand it. RB and five7 hit it on the head with why it was desinged and how these cars have a lot of weak links. However, the parts you replace on them can be used on any other motor or 3rd gen car. So modding the LO3 is no different than modding an L98 when it comes to heads and cam and exhaust selection. One just starts out with much better stuff. The tides are starting to turn as the eprom burning craze increases. We are seeing faster and faster times out there. There is currently one memebr going 14.5 with the stock heads and cam and a few others that are in the 13's. Jprevost hit high 12's with his GM HO 350 TBI awhile back. Many people get disscouraged when they add heads and cam and thier car runs like poo. The key is chip burning with these cars. keep an eye on the CHP vortec buildup on their 305 project. They are really turning some heads because they are addressing every part of the car.

 

you could get the tbi in the trans am or formula, not exacty low end models
seriously.. what the f*ck, everytime someone mentions trying to get some more performance out of there car, they automatically must be headed for the dragstrip... so as far as anyone here is concerened, throw in a 350, posi with 3.73s and a shift kit and off you go..
meanwhile cars with less then 2 liters are spanking thirdgen's.. f*ck if your gonna go big.. go big, the 350 is not the only other engine out there.. and if 45 cubes is that important, why not get yourself another 100...
gas-mileage successor??? awesome! anyone happen to notice gas prices soaring...
youd spend more time swapping heads, and intake manifold etc, then you would swapping it to a TPI???? is that what your saying??? cos im lost
and an engine swap is a cheap day long jobbie? alright, let me recover, that last post has me going in circles.. *2nd to last post by the time i got done writing this*
the lesson here is, never mention TBI.. ever.. unless your maybe in the TBI forum, its not in the performance section of the edelbrock catalog so that means you cant get anything out of it

seriously.. go look at the ratings for the 305 tpi and 350 tpi.. then after your done having yourself a good laugh, take all the "trash the 305, throw a 350 in there" posts for what they are worth
tbi is not the limiting factor, your heads, cam, intake are all different and werent intended to make the most hp
long story short: very little aftermarket support, difficult to tune.

/end rant/

 

EXACTLY

However, I don't agree with this statement. A SBC is a SBC. The aftermarket is only different in what's available for the induction systems, but it's only getting bigger. . . I cite Holley as my example. And 2, tuning a TBI is just as easy as tuning anything else, it just takes time to learn it.

 

How so? You can use the same parts on your built L98 as you can your TBI car. The only difference is the induction. They are not that hard to tune. We actually have more in terms of aftermarket when you take into consideration we can use any carb intake out there with an adapter plate. Most people just want to throw parts at the car and expect it to run right. This is the never ending debate that will go on forever. Everyone has their opinions. People dont mod thier TBI cars to hit 11's. Instead they plan on a reliabale daily driver with decent power and good gas mileage. Poeple mod TBI cars because it is cheap and all of the parts can be used on another motor down the road. There is no point in arguing. I geuss you just have to ride in a TBI car that pulls to 6200 making power the whole way there. Sure we may get passed by our high end competitor but that is not keeping us from having fun.

 

I love TBI, Yes it is not the best performance set up and that is why f-body people don't care for them but as far as relyability they are better than carb/tpi. I have had 5 tbi trucks and loved them all went over 200k. oh ya the wifes blazer 4.3 tbi is at 185,000 and has never let us down [I do maintain my fleet myself]. It's hard to make cheap upgrades that build horse power on tbi.

 

My 305 TBI was not very reliable at all. Mainly because the car wasn't maintained that well by the previous owner.

I switched to carb with my new motor because I did not want/know how to burn chips.

Overall I am happy that I switched to carb...I would much rather have fuel injection but not TBI...no offense to anyone. I would much rather have a MPFI setup.

 

People don't like it because they are misinformed. What they really mean is they don't like the L03, not tbi. TBI has virtually nothing to do with the low performance of the L03. I believe it has to do with people thinking, hey the 305 tbi (L03) has 170 hp and the 305 tpi (LB9) has 205 so tbi must be the cause of the difference, which in fact is is because engines with tbi on top just so happened to be blessed with wonderful swirl port heads that do not flow more than a straw can handle and the intake assembly is also far more restrictive than the stock tpi stuff. So in the end, it boils down to the crappy top end of the motor, not the induction system.

 

People don't like it because they are misinformed. What they really mean is they don't like the L03, not tbi. TBI has virtually nothing to do with the low performance of the L03. I believe it has to do with people thinking, hey the 305 tbi (L03) has 170 hp and the 305 tpi (LB9) has 205 so tbi must be the cause of the difference, which in fact it is because engines with tbi on top just so happened to be blessed with wonderful swirl port heads that do not flow more than a straw can handle and the intake assembly is also far more restrictive than the stock tpi stuff. So in the end, it boils down to the crappy top end of the motor, not the induction system.

 

I think the reason TBI gets a bad reputation is because its what comes with the base model L03 engine. Like others have said, its no the TBI that causes the sub exciting power output of the L03, but instead the heads, cam, and stock exhaust. People automatically associate the TBI with low power output. I wouldn't consider TBI a performance intake either, but you know what, I also dont consider TPI a performance intake. Of the three, I would say the Carb is the most performance oriented (not the best, the most performance oriented). Holley has a pretty interesting aftermarket TBI system. I wouldnt be supprised to see some good numbers out of this intake on the right engine.

 

I could not have said it better. :hail: A heads, intake, and cammed TBI motor will pull and make power up to 6500 rpm. TBI motors really got a kick in the crotch when it came to the generals part design selection. However, a little bit of money takes these cars really far and they end up being cheaper to mod than TPI set-ups.

 

I've seen some aftermarket TBI TBs and Manifolds and I guarentee that one of those setups, on a healthy longblock, could support some serious power! Like a few others have said...it is chip tuning that makes or breaks it.

I had my 355TPI motor with 9.5:1, a compucam (214/224, .480 .480, i think), sportsman II heads, edelbrock base, siamesed runners, freemods and so on BUT didn't have a custom chip. Guess what...IT SUCKED! I swear that it ran slower than the stock setup did. I dropped a carb on it...nothing else...and it livened right up (just no more super-duper seat of pants low-end ). With that carb i eliminated the whole chip process and it let me tune the motor to where it needed to be!

I think that one of those 4bbl throttle-body setups with MPFI would be the bomb-diggity-sheeit...hook it up to a laptop and its a digital carb!

 

bah... The only limitation to tbi is the fueling. Thats it... There are way overbored units that will flow close to 900 cfm and the holley OEM replacements flow as good as a 650 some odd cfm carb. Carb is not cost effective. With a tbi car everything has to go whether your putting carb, tpi, mpfi, etc. With a carb, not only is there the need to replace the entire driveline, but you also have to buy the carb and a dist. With the tbi, all youll need to tune it is a chip programmer. Someone with their eyes peeled can get one for pocket change. All it takes is about a week and your tuning. If your adventagious, or jsut curious like me, you can switch to a newer 749 ecm or get into the actual software that runs on the ecm and go in there and cart all of that smog **** out. It can be replaced with such things as, say, expanded higher resolution tables that can give pin-point tuning precision (well, at least around 1 bit precision) control over fueling and spark to 6000+ rpm and control alg. that can operate external hardware. All those unused outputs from the smog equipment can be used for things like, say, cooling fans with customizable control and high speed serial communications. Cant get that with a carb, can I? No. . TBI has to be one of the most misunderstood efi systems around. People, ignorant of how it functions, cant get their motors to run right and instantly blame it on the tbi system while in reality it would have been fine for what they wanted but they just didnt know enough to get the sytem to cooperate. Its like everyone saying that holleys are complete **** because you have to tune them. TBI is the same way, it just wants to be tuned in a different way. Not with fuel pressure or different wieghts for the dist., but with changes to the ecms calibration so it actually has an idea of what the hell the engine really needs. Agian, its only real set in stone limitation is fueling sicne the injectors are only so big. To me thats the reason why the high water marks for tbi/cfi remains in the upper 12's and low 13's. People have found out that there jsut isnt enough fuel. Its not that the system is garbage. If you can solve fueling problems, then you can go farther with it.

To me, tbi is the carb system of the 21st century. All the ease and simplicity of carb with the precision and power of a computer. Its a really good meld of both if you know what to do. I dont know about you but being able to precisely tune my engine from the comfort of my home while not having to turn screws, jet the carb, or touch the distributer. The only things I need to change my engines tuning are good cup of joe and a limber index finger. Pushing around these electrons sure is hard. Feel the burnnnn!

 

Man... No matter where you post this youll be opening up a can of worms...

 

I used to own a L03. I tossed unported 305 torquers, Comp cams 206/210* & .450/.480 cam, shorty headers, stock intake, stock catback (no cat). I didn't get around to tuning it, but I ran it as is with Gtech and managed to get a 14.4@98mph. It felt to me like a 97-98mph car. It's really too bad I didnt burn a chip, get an aftermarket cat back and intake before I sold the car because it definitely had potential. I didnt give up on TBI, I just didnt want to own a vert anymore.

There's talk in the tuning world that, there is a 325hp wall with TBI because it's an inheriently flawed form of fuel injection. It's definitely a theory and open to debate.

Even though I dont own a TBI anymore, I stop in the TBI forum every once and awhile and TBI has come a long way since I joined. At the time I did my TBI work, I was the only member who had actually swapped heads, cam and exhaust on a L03; everyone else was just planning. Now if you stop in the TBI forum, quite a few people have gone many steps further than I did. Once these people finally finishing the steps on their buildups, we could see some respectable times I would think.

Stock the L03 is equipped with a 2bbl which flows in the neighborhood of 450cfm. How many performance carbed cars from the 60s do you remember with 2bbl carbs that flowed 450cfm? If more members swapped their stock 2bbl units in favour of 4bbl units, then some serious power levels could be achieved.

Another thing I have noted, is that the people who seem to shake TBI off as nothing, are the ones who have never even owned a vehicle with TBI before. Just something I have observed.

 

thats what i meant, your choices specifically meant to make power with a TBI is limited, and time is money.. i think most people who have been in the scene plenty long dont want to bother learning something different when what they know works fine, and another large portion is afraid to mess with it
personally i like learning things, so ill mess with it.. even if it doesnt turn out the way i wanted, ill have learned something in the process

 

Jsut remember. Burning proms is easy. What to put in them in terms of spark advance, fuel, accel enrich, etc is hard. I found that timing is by far the hardest thing to do, especially if you dont have access to a dyno. Too much and the motor runs harsh, overheats, and runs slow. Too little and the car bogs down.

 

What are you talking about here guy? What "driveline" needs replaced when you switch to a carb? And how is it not as cost effective, like gas mileage wise??

Putting a carb on is the cheapest AND easiest thing in the world! I sold my TPI for 1200 and got a holley 4bbl and dual plane manifold, summit HEI and fuel regulator and BAMMO...carbureted! Also I only spent about 600 in the process.

Now my car runs better than ever AND my engine bay looks pimp without all that junk in it.

Im not bashin EFI...just giving tha carb the props it deserves. It is MUCH simpler like the simpler times that it came from...cheaper too!

 

I can't see how it's practical to significantly upgrade TBI (or any other stock FI system for that matter, including TPI) without burning your own PROMS. Even the best of the over-the-phone ones, like from Howell or whoever, are pretty much hit or miss. They're only as good as the info they get from the owner, and even then, it's just an educated guess. But with TBI especially, if you modify the motor to have any kind of flow at all, you are making such a drastic change in its fuel and timing needs, there's no way any stock chip has a prayer of being close.

A programmable ECM of some sort is a great way to get that done; but it doesn't make alot of sense to spend that kind of $$$ on that, and not upgrade the fuel delivery too. I've seen it done, had a hand in tuning it over a period of a year or so, and saw the pitfalls and limitations of the whole TBI concept first hand, even with infinite tuning ability on the fly; and that owner finally got sick of TBI (he went through the Holley 4-barrel thing along the way) and put a port system on it.

 

Thats if you own a tbi car. Some people make it sound as if you jsut put a carb in place of your tbi, your problems will magically dissapear. Just about every part in a tbi vehicle has to go. I replaced the stock stuff with a crap goodwrench 350 and junkyard parts (700 + 9-bolt) after i trashed the origional rear and trans I stuck in. 350 trashed those parts as well. Im amazed that the motor still stays in one piece given the way I treat it. Probably going to trash the car soon as well since its all rusty and its been in a bunch of accidents. I dont have anything against carbs, but tbi is a capable system. For me it was more economical jsut to modify the present induction system. Ive been slumming it the whole way and so far Ive gotten more then I expected out of it. It has its frustrating moments, but its also rewarding when you ovecome some of the limitations imposed by smog and other rquirements.

 

Just out of curiosity, what problems did you encounter? Like I said the major problems that Ive had where with how to get enough fuel at WOT and still satisfy the requirements at idle. One major problem I see is that if you where using the holley stuff you where very limited with the fueling. The newer injectors they use where for 4 banger fwd systems and they hardly flowed anything at all. That was one of the reasons I origonally got into source coding is because I wanted to run a 4 bbl unit and then I find out that the injectors they use are only equivelent to a set of standard big block tbi injectors. hmmmm... I have a set of them in my present holley tbi unit and they arnt even close at around their stock rated pressure of 12 psi or so. I have them open all the time at full duty cycle at WOT and its still no enough. Another problem can arise at idle when the duty cycles of the injectors shorten up. Since there are 2 firings per revolution it means that, for me at least, ill see async fueling.

Those, to me, are the two real limitations. Properly fueling at WOT usually means that the duty cycles will be really short at idle and will cause real drivability issues if the ecm used doesnt have good provisions in place to handle this. Conversly, properly fueling at idle will leave the engine real short of fuel at WOT. The stock stuff is usually somewhere inbetween.

 

The motor was a 400 with Edelbrock RPM heads, some real mild cam with 218ish duration, and I forget what intake he had the thing stuck onto. I think it was a single-plane 4-barrel one, with an adapter; but I don't remember any more.

He started out with the stock TBI unit (this was a L05 truck). Obviously that didn't work, I don't have to go into details as to why not. So then he got some 454 injectors. He was using Howell for his chips BTW, he certainly spared no expense there and went straight to the top. That got his duty cycle below 100% some of the time, but it still would lean out bad above 4500 or 5000 RPM. So he though maybe it was not enough fuel pump, so he got some Porsche pump for it, 700 some odd liters per hour IIRC. Didn't help in the slightest. So then he got the Holley unit. That was when his problems really started. The one he had was about 900 CFM I think, equipped with some sort of Chrysler injectors IIRC, around 65 lbs/hr or so. They were EXTREMELY prone to sticking open due to even the most minute dirt or whatever; so he would think it was too rich, pay for yet another chip, then notice that one injector was dripping, fix (replace) it, discover that it was now surging and backfiring lean, so he'd have to get another chip, a couple of days later it would hardly even cruise down the highway and he'd notice that one wasn't spraying at all, etc. etc. etc. I think we changed an injector at least 5 times, more than one a couple more, and all 4 injectors at least 3 times. I can distinctly recall at least 8 chips in a carrier and there might have been more. It NEVER EVER ran right, not one single time that I can recall, not even accidentally, although once when we changed all 4, it ran almost OK for a couple of days, then one of those died (quit spraying). Finally he gave up on Howell and bought a Haltech. We monkeyed around with that for a few months, replaced all the injectors again, got it to almost semi sort of somewhat behave some of the time partly, then it suddenly went MASSIVE rich again. Black smoke plug fouling burn your eyes rich. On close inspection we discovered his Holley had developed a crack or casting porosity or something on the back, where the FPR mounts, such that fuel was leaking into one of the back barrels. About that same time the motor started smoking from a ring problem (he had put over 100k miles on it by then over the course of about 4 or 5 years, cursing it every foot of the way). So he gave up and bought an Accel Pro Ram to go on his new motor. Problem solved. We put the Holley unit on the floor of a massive construction dumpster I had in my yard at the moment for a roofing job, climbed in with a 15 lb mattock, and took turns relieving our frustration on that TBI unit. We didn't stop until the pieces were so small that we couldn't hit them any more. I was still finding little bits of chinesium casting in my yard that had exploded out of the dumpster several weeks later.

Altogether not a happy TBI customer.

 

Ouch... No offence to him but thats teh text book example of how NOT to modify a tbi system. Dont take any offense to this. Its not your fault that it didnt work out properly, just that you got bad parts.

Coming after alot of other tbi modders really helps to know what works and what doesnt.

First thing that never works is the stock unit in any way, shape or form. I pulled well over 3 inHg at 3000 rpm with it and threw it in the trash. Bought the holley and problem was solved. Finally pulled past 3000 rpms. Goes out to around 5k fuel permitting. Could fix that too but I dont know if its worth while spending money on a nice fuel pump for a junkyard camaro.

Second thing is those damn mostly old parts and rust fuel injectors. Absolute trash. The only thing to run is genuine gm injectors. Theyre the toughest things around and will almost never malfunction

Third thing is to always do your own tuning. You dont need one of the aftermarket ecms, either. GM provides just about everything you need in a nice, cheap package thats readily available at a nearby salvage yard. Tuning is alot of touch, smell, feel... Cant send those things though the mail to some chip or ecm company. It takes literally hundreds of 'chips' to get it right. Now, I didnt spend all my time burning chips. Most of it was: drive the car like I normally would, but with a computer hooked up datalogging. At the end, Id write down a few notes and quickly burn another calibration to my eeprom. Next day, drive the car about as usual and do the same thing. On my test bench I burned so many chips experimenting with the source code that it literally wore out the eeprom I was using. Alot of it is experimentation with intuition and educated guessing untill you figure out what works. Could I tune a 10 second car? Probably not right away, but at least Id know where to start.

Fourth thing. Holley tbi stuff sucks. Thank *** I didnt pay good money for mine because its ****. Doesnt even bolt up like a stock one should. There are hairline fractures all over the casting and the throttle shaft rides on only two ridges so it immediatly cuts into the aluminum. My gas pedal is hard as a rock and the throttle always hangs

I think jsut about everyone has horror stories. Me and my brother had an 86 camaro with a rebuilt 70's 350 in it + carb. Must have had every problem in the book. We didnt really know what we were doing so it was jsut a total disaster. In the end, it broke down in Camden and by the next day there was nothing but a shell left after looters got to it. IIRC, the only feeling he really had was a sense of relief that it was gone.

 

I completely disagree with this statement, my TPI is extremely reliable. I too had a 90 K1500 (TBI 350) and it was awesome, and it ran great, but my GTA runs way better. That may be apples and oranges, but I just don't like TBI in sports cars. I do agree that the TPI isn't the best induction system out there and that TBI cars can seriously haul ***, just read up in CHP on that 91 RS they are messing with, like 300lb/feet & almost as much hp out of a TBI 305!?! TBI can kick ***, but I think that it LOOKS better between truck fenders, that's all. I personally like fuel injection better than carbs (and TBI engines look carbed), and I was lucky enough to get a GTA with the 350.

 

Yeah you got that right.

What he did wrong, was to try to keep it TBI.

He had already been through TPI, and knew he wanted nothing to do with that (in fact he traded in a 85 Vette that he had bought new for this truck, also new when he got it); past a certain point, its difficulties are just as insurmountable, but even more expensive to try to deal with, without a wholesale yank and replace of some sort.

The problem wasn't "mostly old parts and rust". Everything was brand new. He even replaced the fuel tank at the time he put in the higher capacity pump.

The fundamental problem is that the stock TBI sucks as you noted, and the aftermarket TBI sucks. Now last time I looked, there's only 2 kinds of car parts in existence: stock, and aftermarket. So, when both of those are inadequate, where do you go next? I guess it's possible that a third type of parts may have popped up since this morning, but I haven't noticed it yet. Please clue me in if it has.

This was a whole lot different from someone like you describe with the carb that doesn't know what they were doing. He and I are both electronic engineers by trade. Neither of us has any trouble with the concepts or execution of modding computerized vehicles. Although, the Haltech was definitely over the top: he should at least have tried burning his own chips, when he finally came to the conclusion that the over-the-phone deal wasn't going to work; the results may have been slower, but it would have cost him less. As it was, we didn't have to bother with "datalogging" if we didn't want to; we could just drive around and leave the laptop hooked up and tune the thing in real time during a blast up a freeway ramp or whatever if we wanted to.

Of course, this also wasn't somebody with a grocery cart trying to break the 15-second barrier, either. You always have to remember the unspoken assumption in something "not meeting expectations": namely, that the expectations are realistic. If they're not, then no matter how flawless the execution, expectations will not be met. And so it may have been in this case. I think alot of this has to do with the level that this motor was expected to perform at. This guy was used to big block Chevelles, and so of course the Vette had been pitifully inadequate by comparison, with (at the time) no upgrade path at all. He hated how gutless that car was from the minute he bought it. So, part of the problem was, he was attempting to duplicate serious power. His benchmark was getting beat by my near-stock 454 car (not a Camaro) which upset him no end. Still, I doubt we ever got that truck into the 13 second bracket with that TBI; it was always snail-slow. Although, with the Haltech, it showed promise; might eventually have been able to keep up with a carbed equivalent, if the Holley thing hadn't been such a POS. And, he eventually did manage to twist off an axle right at the end, so it was beginning to come around.

 

[QUOTE]Originally posted by RB83L69
The problem wasn't "mostly old parts and rust". Everything was brand new. He even replaced the fuel tank at the time he put in the higher capacity pump.
[Quote]

Just because their new doesnt mean their good. The mopar injectors where garbage from the get-go. Thats why holley compromised with the smaller delphi units. Becuase they are actually good injectors. They jsut dont flow alot like the larger bb units. There are actually decent parts available. The larger gm tbis are equivelent to an ~659 cfm carb. There are even larger overbored units that are rumored to have tested at close to 900 cfm. Good parts. Would you be able to run tens? Probably not. But 12's and 13's are realistic goals. People have showed that. Not directed toward you but alot of people build a motor and then stick the tbi on it hoping it will work. After they fail miserably because the ecm is set up for the crap 305 they give up, buy a carb, and instantly say how much they hate tbi. TBI is a good system and it works quite well. Ive seen complaints about alot of the parts holley makes for efi and that tbi wasnt any exception. The newer units finally come within spitting distance of being a good quality part. The flow is there, and so is reliable fuel delivery via properly designed gm injectors, up to around 350 pph worth of it at moderate pressures. I imagine even more, like 400+ pph, could be available if it where pressed. Although its a shame they messed up with the older units. The new ones are rare and expensive because they only sell a few thanks to the poor quality **** they handed out before. Granted that my car probably only runs in the 14s and goes 0-60 in around 6 secs., but im still very pleased with it and im going to have a second go at it with actual performance parts instead of cheap second (or third) hand trash that I made my car out of. It actually made it possible to get something dimly resembling performance out of a trash engine. Its sort of unfair to pass judgement off on a system because you have a bad experience with it.

 

I rest my case. You've got a 350, and you're just barely keeping up with a L69.... a carbed 305 ... after how much tuning? That's what's wrong with TBI, right there, in 20 words or less.

But, I applaud you for your honesty; it's better to tell the truth, even if it hurts. I get so tired of "My car runs 16.3 now but the next motor I put in it I'm going to be different and it'll run 11s on pump gas and I'll shift it at 7500 RPM". I hope that you can get yours to run up there with a stock carbed 305, if nothing else, as a reward for honesty in the face of the temptation to spank the monkey instead.

 

hmmm... thats a rather snide remark. This is a goodwrech pre-86 350 with 8.5:1 CR with a 2.25 in exaust + flowcrap muffler, wasted trans, 2.77 gears. What do you expect out of it? 400 hp? 500HP? 700HP? Do you really think a carb would be any faster? Would I be as happy with it? I bought all this stuff for a few bucks because I wanted something to tinker with. I havnt been tuning because I want to pretend my motor is fast. Ive been tuning to learn more about how efi systems work in general and because im interested in it. I knew it was going to be slow from the day I scraped together a garage full of junk + an old cheap rusty accedent victom, namely my 88 SC. I did it just for the sake of learning. When i started out, the car would bearly be able to go 0-60 in under 10 secs. I thought of carb but decided to stay with the efi instead. After several weeks I had it pretty much there and I stopped burning chips and started driving it. Then I got interested in source coding. Some may say its a waste for someone like me who doesnt have a fancy EE degree to learn about electronics and programming on a PC and in machine code to get into this stuff but for me I find it enjoyable to discover and learn new things. I could have jsut gotten X heads, Y carb, and Z cam like everyone else does but to me that wouldnt have been what I wanted to do. I wanted to try something different that not too many people have tried before, namely take a stock efi system and an oddball ecm that noone has done any work with and see what I could find out about it. I like to try different things, no matter what people may think of them. If I succeede, all the better... If not, at least I tried rather then jsut saying 'oh, that wont work.'

 

And now everyone understands my above post.

 

What people? I like TBI.

RBob.

 

It's all pretty much opinion; I don't think either side of the argument is going to convince the other here.

Let's settle it at the track or the dyno someday.

 

Both TBI and TPI generally suck *** in a performance application. Both flow like ****, crap out at a low rpm, and are a bitch to get to perform at a meaningful level, ie not getting their asses kicked by todays crop of sport compacts.

Still, TPI motors got the jewels (for the time) in the GM parts bin, while TBI got the garbage.

Plus, when you garbage the stock induction setup to put on something that works, at least a lot of the TPI setup (high pressure pump, harness, ECM etc) carries over to a high performance setup.

 

My "opinion":

For a street car, it is usually most economical in the long run to work with what system the factory put in it. That's especially true when you've got emissions inspection to deal with.

For the street rod or weekend warrior, it might make some sense to change to a different induction system. More often than not, that'll be carb.

I have a fellow 3rd gen bud who changed his '90 RS from LO3 to ZZ3-based TPI. He's got more in his engine than I've got in my car, and more in his transmission than I've got in my entire drivetrain. His 500-lb-lighter, more aerodynamic car runs the same times as mine does.

On the other hand...
There's this guy with his '89 Vette and mini-rammed 406. PG, back-halved, carbon-carbon tilt front, etc., etc., etc. That car will run mid-11's here all afternoon until midnight. I've seen him round-robin later rounds without changing his dial-in since the 2nd round. Of course, the $'s he has in that car...

 

My thoughts exactly.....

Tune and burn chips all you want, I've yet to see a TBI 350 run in the 12's. I'm sure there are a few exceptions, but again, if it were so easy more people would be doing it, including me.

FWIW, it's not that I don't "like" TBI, but from a performance standpoint I'd rather run a carb, given a choice between the two.

There's nothing more discouraging than seeing my friend's FORD ESCORT GT with a donut front spare and "**** on Chevy" sticker keep up door to door with an L03 Camaro RS.

 

True about the sport compacts but YOUR ON CRACK DOOOD

Whats this about the TPI flowing like crap "out at a low rpm"? I thought that they made peak power at 5900 rpms ?

Naw...80s EFI blew *****...it happens.

 

So wut were sayin here is that tbi has just as much potential as carb or tpi up to a certain point. Once you hit that point tbi stops performing. But tbi is good for gas mileage and is easy to work on however in order to gain the most performance from it you MUST burn yor own chips. And being that im broke i should keep my tbi and try to rig a homemade cool air induction for free.

 

Cold air probably wont make that big of a difference, reason being is that the fuel itself helps cool the charge, especially when vacuum is present. Ive noticed some power loss with hot air off the headers and such, but its not noticable as long as I set the ecm up to compensate for it. Burning chips is a necessity. The stock engine is about as low as you can go and anything else that actually has good VEs above 2000 rpm is jsut going to be way rich at idle and the timing wont be all that close, either. Same problem with WOT if you stick in a set of large injectors. Due to the fact that, in efi terms, tbis have very large injectors the stock stuff is set up to compromise between idle and high load so at WOT the injectors have very high duty cycle up to around 3.5k or so, at which point the commanded PWs begin to track along the maximum time available for the injectors to be on. Long story short is if your modding and you change stuff the fueling will be off everywhere. I found that at idle I was rich, lean in the middle, and way rich again at high load. After I got the timing done it immediatly began to come back the other way to being lean at high load. It can work in your favor. Since its so disgustingly rich at WOT to protect the cat, it hurts power. People have run reasonable times, like mid to low 14s with just bolt ons, probably in some part due to the fact that it helps put all that extra fuel to work. If you want some cheap power, then chip burning is definatly a good option. You can add some timing in since the tables are pretty conservative, and you can also take out some of the fuel, provided that you arnt running a cat.

 

The point is not that we want to run 11's with our TBI cars it is just that we want to perform on a similar level as most stock performance cars of today. If we can be on par with stock LT1's, LS1's and poorly drive vettes than we have accomplished a lot. I certainly consider those cars fast even though they may be stock. When failure occurs or tuning efforts are no longer sout after we can merely switch to carb or any other induction set-up without wasting much money on parts that can't be used on our next motor. TBI cars are great for entery level performace. You can learn alot obout bulding a motor, tuning FI and having good street and strip performance without killing yourself or breaking the bank. I love my TBI car but never intended it to be a 500hp monster. I have another car for that.

 

Personally I liked the trottle response and torque of my old L03 Firebird. My carbed Camaro would have killed my Firebird but the throttle response was way better with the L03 and the fuel milage was huge, albeit there is a huge HP difference. Besides every carb I have ever had has tip in and top end issues when the engine gets really hot. TBI never did that. Just some food for thought. Show me mercy.

 

TBI was introduced in 1988 on the LO3 (1982 on the cross-fire). We tend to forget the impact the EPA and CAFE were having on the industry at that time.

Put it into perspective. I would be willing to bet that a new 1988 RS with 170 horse LO3, TH700, and 2.73 gears would be able to outrun a new 1957 Bel Air with 220 horse Super Turbofire 283 4bbl dual exhaust powerpack with Powerglide and 3.36 gears.

The cruise between gas stations would be a joke. The results on the enhanced dyno sniffer wouldn't be close, either.

Then in the cornering and braking tests...

 

Even earlier in the 4-6-8 Caddy system, which was the GM pioneer for TBI.

The 4-6-8 concept was a good idea, if premature and immature. The TBI technology engineered by GM marched on into the Corvette (1982), then the Fcars (1983), and later in just about all GM models. And the motivation was primarily emissions control.

See

Throttle Body Fuel Injection (TBI) , by Lauren L. Bowler, Engineering Staff, GM Emission Control System Project Center, SAE paper 800164, 2-1-1980.

 

Dimented24x7...So wut you're sayin is that the tbi fuel delivery system is inconsistent at different rpms. So if a cool air induction wouldn't really help do you know of any cheap mods? I'm not lookin for a hotrod...just want to add some pep to it. Also, my suspension is shot...if i drive over a sewer cap my car will jump. Wut do you think of the KYB GR-2 series struts and shocks? Wut kinda springs are decent? Thats enough right? And wut does VEs and PW mean?

 

Its not really inconsistent, jsut that its set up to run the small stock injectors for all their worth at WOT. Youll need larger injectors if you mod the engine itself but theyll end up drowning the motor in fuel if you dont have the ability to change the calibration. A motor thats up to its eyebrows in gas wont make much power. If you cant burn chips, dont touch the motor as of yet. Good mods are a full exaust + headers for, say, a tpi instead, dual snorkel or open element, a new intake, gears, a second hand manual transmission to replace the ****box auto, posi, etc. Those things will definatly help get the lead out and the engine will be close enough that it should still work ok.

Suspention, hmm... search the boards i guess. I just replaced mine with OEM stuff so I could get a decent ride again.

 

If someone can show me a TBI system that will feed this, you sold me.

 

That's easy, use two 4bbl TBI units from Holley. If that is too much then just use one 4bbl TBI unit or 2 2bbl TBI units from GM. . .

This months Car Craft has a 1st gen Camaro with an Offy cross-ram manifold and two 4bbl TBI unts. He used the Holley Commander 950 to run the setup.

RBob.

 

I had my troubles with TBI in my S10 blazer that got a GMPP "HO" 3.4L. The problems were quite similiar to RB's buddys truck. Although I bet the TBI would have made more power in that setup over the 2bbl carb option.

TBI, TPI are fine for what they are and make ok power with minor modifications and do allow a slight amount of breathing room for engine modifications in stock/slightly modified forms but expecting major power out of a system that was designed for fuel economy is just insane.

Thats like saying I'm going to build a SB 454 toss the best heads money can buy on there the best intake ect, but instead of buying a cam that would suite the engine I'm going to grab a peanut cam from the old 305 and run it. After all the cam just needs to open the valves up right? A TBI only needs to deliver fuel right?

I agree with 57 it is better to keep the induction system you have. If your plans out grow that system then people need to realize its time for an upgrade.

 

TBI would be fine if the aftermarket supported it like TPI.

 

the problem with TBI in genral (NOT JUST OUR CARS- THIS STATMENT COVERS ALL TBI) is that it's halfway between and a carb 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)