What makes the 305 TBI suck so bad?

Ive always wondered why the 305tbi has sucked so bad. How come the torque is decent 240ish but the hp is crap 170? Is it all because of the Throttle body injection?

BTW: I am looking to buy a nice 3rd gen i the future. What is the fastest year and make? Im guessing a z28, but of what year? I looked at an Iroc once but it had a few things that were pretty wrong.

I think its the 1le firehawk that is the fastest but hard 2 find.

I think its the 1le firehawk that is the fastest but hard 2 find.
There is really nothing wrong with the TBI motors, they were pretty good in that era, plus it is not that hard to swap a TPI setup if you so desired. I believe as stated above that the 1LE firehawk was the fastest, but hard to come by. Anything with a 305 or 350 TPI will put out some decent power and with some mods. can be made into a quick, fun daily driver. The hard part is finding one in good condtion.

The 305 TBI sucks for a lot of reasons. First of all, there are all sorts of things sitting directly in the path of intake air such as the warm air diverter and the fuel injectors themselves. Second, the single snorkel intake is pretty restrictive and doesn't work all that great as a CAI. Third, the intake manifold design is not as good as the TPI intake (Port injection is a LOT more flexible). Fourth, its only a 305. Finally, the heads and cam are pretty weak as well. The 305 TBI has a reasonable amount of potential, but it's far more complicated (and expensive) than using a carb with only improved fuel economy and emissions as an upside.

As to your second question, just go for an IROC/Z-28 or Formula/Trans-Am and make sure it has a 350. If you can find a 1LE then great but any 350 has good potential.

The 305 TBI sucks for a lot of reasons. First of all, there are all sorts of things sitting directly in the path of intake air such as the warm air diverter and the fuel injectors themselves. Second, the single snorkel intake is pretty restrictive and doesn't work all that great as a CAI. Third, the intake manifold design is not as good as the TPI intake (Port injection is a LOT more flexible). Fourth, its only a 305. Finally, the heads and cam are pretty weak as well. The 305 TBI has a reasonable amount of potential, but it's far more complicated (and expensive) than using a carb with only improved fuel economy and emissions as an upside.

As to your second question, just go for an IROC/Z-28 or Formula/Trans-Am and make sure it has a 350. If you can find a 1LE then great but any 350 has good potential.


Like he said but my carbed motor gets better mileage then neighbors TBI.

Ok, first off the TBI is bad because the heads, intake, and cam on it are HORRIBLY restrictive. Second off, there is NOTHING wrong with modding a 305, ESPECIALLY when you whoop your first LS1's a$$. Third off, the FASTEST third-gens are the Turbo Trans Ams. Besides that, I am guessing the 350TPI IROC but like everybody else is saying, it may be the 1LE Firehawk.

First the 305 TBI was not designed or sold as a performace engine. It was a V-8 that was a option on some models and standard on others. Thats all it was a fuel efficient & low emission v-8 engine.

First the 305 TBI was not designed or sold as a performace engine. It was a V-8 that was a option on some models and standard on others. Thats all it was a fuel efficient & low emission v-8 engine.

Huh it was the base engine for the z-cars after the carb disappeared what on earth do you think they marketed the thing for getting groceries?
Also at the marketing time the stick was not an option in a 350 hmmmmm.....
Sounds designed for performance (but a flop) to me.

They can be made to run pretty well.

A buddy of mine had an 89 RS auto, we put a set of TPI shorties 3 inch cat and cat back. Replaced the 2.73's with 3.73's and a posi, installed a 2200 converter and shift kit. Put in a K&N in the stock air cleaner setup and a chip.

He paied 1500 for the car with 50k miles, painted it for 800, and the above mods for about 1200 ;) (used parts and slave labor) and had a nice car.


It wouldn't come out of the 17's stock and had a best of 14.65 with above mods. Not too bad for 3500 bucks. Heck he got 4500 for it when he sold it 2 years later.

So they can go with the right stuff, his might have been a freak.

They can be made to run pretty well.

Just ask the character above you on that one ;)

I wouldn't suggest a Firehawk or even a TTA as they are both considered collector's items and not something you'd buy and mod and drive around on the street as they would be worth far more being left as stock. there isn't even 100 Firehawks out there.

TBI falls short in the crappy cam, small port intake and heads...they do not flow worth a crap from the factory.

Also the 90 1LE Irocs with 5 speed and 305 were pretty fast, they were lighter than a regular IROC and had a HP rating of 230 so they were close behind the 350 but didn't have much potential because you are starting with a 305...not a 350. The fastest regular thirdgen(no super limited production/something you could buy and mod for reasonable amounts) would probably be the 92 Z28 with the 350, from the factory they were rated at 245HP and 345lbft torque. The 1LE handled better though, these cars' strong point...they will outhandle many performance cars on the road to this day.

i'm putting together a 305 ci TBI on a 5spd box. Maybe the power on the engine isn't great but the torque is ok. I'm modding it a little.. flowtech headers, MSD ignition, LT1 camshaft :D, open air filter and aftermarket cooling (thermostat & fan switch). A/C and Emissions deleted.
next in line is probably a new intake :cool:
http://memimage.cardomain.net/member_images/12/web/396000-396999/396728_467_full.jpg

i'm putting together a 305 ci TBI on a 5spd box. Maybe the power on the engine isn't great but the torque is ok. I'm modding it a little.. flowtech headers, MSD ignition, LT1 camshaft :D, open air filter and aftermarket cooling (thermostat & fan switch). A/C and Emissions deleted.
next in line is probably a new intake :cool:
http://memimage.cardomain.net/member_images/12/web/396000-396999/396728_467_full.jpg




Clean and gotta love the air horns :D

But as for an open air filter, I would try to do something else. maybe see if you can find a L69 duel snorkel and do the right mods to it.

Eric

[QUOTE=Jazsun]How come the torque is decent 240ish but the hp is crap 170? QUOTE]


kinda funny.....my 1997 GMC Jimmy 4.3L is rated at 190HP and 250 FTLBS

Ya.. that is kinda funny :think: I wonder why a known-dog of a motor that is 10-20 years old, is at the same power levels as a newer Jimmy that's designed to tow/haul stuff hence the coined term "SUV" :confused:

As it's already been mentioned before; it's the cam/heads/valve shrouding that kill the TBI engine. Pls there isn't much of an aftermarket for it (before someon gets their panties in a bunch; compare the aftermarket of simple carb and all the real FI systems out there).

A 92 is probably going to handle just as well as any of the earlier iroc cars out there (althought the irocs will have the wonderbar to help with front end/steering box strength). Either way the later the model, the more power it will have and the if you get a G92/5speed/305 car it'll be just as fast (stock) as the 350 cars. And handling will improve lightyears with a simple new shock/strut/spring combo.

Ive always wondered why the 305tbi has sucked so bad. How come the torque is decent 240ish but the hp is crap 170? Is it all because of the Throttle body injection?
I never understood how GM could make a engine as poor as the 305 in general (TPI and TBI).. The best HP they ever made was 170 crank HP which is just absolotly terrible out of a engine that size and that get the MPG that these do. My civic produces 170 HP stock out of a engine that is only 96 CU and weighing in at around 2500lbs it eats these 305 camaros/firebirds and even the rustang 5.slows and still manages to get 28MPG in the city..

Do you know how much horsepower Civic Si's were making back in 92 when the last 305 TBI motor was placed into an F-Body? 125. If you're proud of beating a 15 year old car, more power to you I guess.

No, the TBI 305 was never a performance motor. I don't care that they were placed in bottom level Z28s and Formulas. TPI 305s are a completely different story and were more than competitive in thier day.

I'll never understand why people act like "OMG I can't beleive GM made these horrible 305s!!!?!?!?!1"

THE LAST 305 WENT INTO AN F-BODY OVER 13 YEARS AGO. A total technology and horsepower war has ensued since then. Be thankful for it, but don't discount these older cars, F-Bodies were always competitive for thier day.

The TBI was never designed as a performance motor, except for the one that went into the corvette with the dual-TBI intake(crossfire). They knew it was induction-limited, that's why they tried the dual throttle bodies on the corvette and some 82-83 z28's and trans ams.

It was designed as a truck-bottom end motor for good mileage and longevity. It is a good motor for what it was designed for, which is bottom end. It runs out of breath around 3500 rpms because it wasn't designed to run over that. Stop trying to take the motor out of it's original design limitation. People have been doing that for years with TPI also.

If you want to go fast with a TBI motor, change to a carb, change heads and intake, and it will be just like any other sbc. For a daily driver, it fits the bill. Mine has 195,000 on it with no signs of stopping any time soon.

I never understood how GM could make a engine as poor as the 305 in general (TPI and TBI).. The best HP they ever made was 170 crank HP which is just absolotly terrible out of a engine that size and that get the MPG that these do. My civic produces 170 HP stock out of a engine that is only 96 CU and weighing in at around 2500lbs it eats these 305 camaros/firebirds and even the rustang 5.slows and still manages to get 28MPG in the city..

Really? They never made a 305 with 230fwhp and 340lbs of torque :confused: And 28mpg's is bad? Because that's what these 305's get boy. You better learn your facts before you start spouting off your uninformed mouth :rolleyes: And I guran-d@mn-tee you a 5.0 Camaro, Mustange, what-have-you.. will EAT up a civic. Let alone the 350's. Oh ya, the f-body's weigh more too, so you figure that one out.

Do you know how much horsepower Civic Si's were making back in 92 when the last 305 TBI motor was placed into an F-Body? 125. If you're proud of beating a 15 year old car, more power to you I guess.

No, the TBI 305 was never a performance motor. I don't care that they were placed in bottom level Z28s and Formulas. TPI 305s are a completely different story and were more than competitive in thier day.

End of story.

Oh, no not yet; I still have to rip into the other guy for being an idiot.

Ok, so a '92 civic had 125 CRANK hp. A '92 305TPI had 220-230 crank hp. Torque was in the 340-ish range. Smack that into a 3200lb car matted with a 5spd standard, posi 3:23 rear end and that equals a civic EXTERMINTOR. Oh ya, I forgot. This "pos 305 with no power" will also obtain 28mpg :rolleyes:

The 305TBI is not as bad as people try to make it. Sure it's slower than the TPI cars, but like said before, it wasn't bad in its time. Reliability stands for something, and so does just plain *fun to drive*. My RS with this engine is at 157,000 miles, and runs as good as it did 6 years ago when I bought it. It has been extremely reliable, all I have done is an alternator in all those years! The 305TBI is also fun to drive. I have 2 Camaros, this 90 RS, and a 96 Z28. I know some of you will think I'm crazy for this, but I *enjoy* driving the RS better than the Z. If I'm gonna race someone yeah, the LT1 is much better, but I feel the third-gen is more comfortable, steers much easier and handles just as well. I like the fact that you can see the hood while driving in the 3rd. gen cars. The guy with the Civic: You are crazy! Own up to it buddy, your Civic won't take a 5.0 Camaro or Mustang. Sorry.

Ditch the Flowtech headers. They're absolute crap. You won't gain that much with the MSD stuff for the money. I would look into getting the chip tuned. Some guys can pick up to 20hp on a stock motor by simply retuning the chip.

The headers are already installed, as well as all the other stuff i listed. I bet the headers are better than the stock manifold anyway , thats a plus :)
chip tuning...hmm in Poland it's hard to find anyone who knows anything about f-body ECM's, mostly they do rice machines.
I'm switching from a 2.8 auto to a 5.0 TBI 5spd so it should make me happy for a few months :D after that i think i'll go with a 4bbl carb and a new intake manifold... maybe do some work on the heads and get better pistons.

Really? They never made a 305 with 230fwhp and 340lbs of torque :confused: And 28mpg's is bad? Because that's what these 305's get boy. You better learn your facts before you start spouting off your uninformed mouth :rolleyes: And I guran-d@mn-tee you a 5.0 Camaro, Mustange, what-have-you.. will EAT up a civic. Let alone the 350's. Oh ya, the f-body's weigh more too, so you figure that one out.
What year was there ever a 230hp 305 TBI, the 350 was up there, never heard of of a 305 making that power. And 28 MPG in the city out of one of these cars is just bullsh1t, my LT1 stock which is much more advanced than throttle body injection never got more than 15 MPG, That car wouldn't make 28 mile per gallon in the city unless you plan to push it the other 15 miles.

To brains96Z, bring it with that 1990 305, hell if it is modded and therefore I don't win with the civic, I'll put money down on it that my Z will eat that thing up.

No crap an LT1 will take the 305TBI. You are sounding dumber all the time. I didn't say my RS was the fastest thing on the road, I was meaning that they would take a Civic of that era. You need to read posts a little better.

The 305TBI is not as bad as people try to make it. Sure it's slower than the TPI cars, but like said before, it wasn't bad in its time. Reliability stands for something, and so does just plain *fun to drive*. My RS with this engine is at 157,000 miles, and runs as good as it did 6 years ago when I bought it. It has been extremely reliable, all I have done is an alternator in all those years! The 305TBI is also fun to drive. I have 2 Camaros, this 90 RS, and a 96 Z28. I know some of you will think I'm crazy for this, but I *enjoy* driving the RS better than the Z. If I'm gonna race someone yeah, the LT1 is much better, but I feel the third-gen is more comfortable, steers much easier and handles just as well. I like the fact that you can see the hood while driving in the 3rd. gen cars. The guy with the Civic: You are crazy! Own up to it buddy, your Civic won't take a 5.0 Camaro or Mustang. Sorry.
Well put..I work with a guy that has a 305TBI in a 91(not positive of the year). He can care a less about going fast or how much horsepower it has. Hell, he doesn't even know how much power his car makes, he only knows that he has a V8. He just drives the car for the "coolness" factor. After all, it is a all black car with chrome exhaust tips and polished aluminum wheels. Everybody has different expectations and goals for their cars.

What year was there ever a 230hp 305 TBI, the 350 was up there, never heard of of a 305 making that power. And 28 MPG in the city out of one of these cars is just bullsh1t, my LT1 stock which is much more advanced than throttle body injection never got more than 15 MPG, That car wouldn't make 28 mile per gallon in the city unless you plan to push it the other 15 miles.

To brains96Z, bring it with that 1990 305, hell if it is modded and therefore I don't win with the civic, I'll put money down on it that my Z will eat that thing up.

As a matter of fact, my old formula with the 305TPI and a T-5 was rated at 230fwhp and saw a little over 20mpgs without a problem.

What year was there ever a 230hp 305 TBI, the 350 was up there, never heard of of a 305 making that power. And 28 MPG in the city out of one of these cars is just bullsh1t, my LT1 stock which is much more advanced than throttle body injection never got more than 15 MPG, That car wouldn't make 28 mile per gallon in the city unless you plan to push it the other 15 miles.

To brains96Z, bring it with that 1990 305, hell if it is modded and therefore I don't win with the civic, I'll put money down on it that my Z will eat that thing up.

Hey you said ALL 305'S ARE DOG'S. I showed you a 305TPI car that isn't
As a matter of fact, there are SEVERAL members on this forum getting 28+mpg out of their cc-Q-Jet 305's. Shall I make a poll and find out how many there are?

I didnt' read through all the posts in this thread but I think this is a decent example of what 305's are capable of.

http://chevyhiperformance.com/techarticles/148_0409_mission/

No crap an LT1 will take the 305TBI. You are sounding dumber all the time. I didn't say my RS was the fastest thing on the road, I was meaning that they would take a Civic of that era. You need to read posts a little better.
Umm.. no, as quoted you said "The guy with the Civic: You are crazy! Own up to it buddy, your Civic won't take a 5.0 Camaro or Mustang. Sorry." I'm trying to figure out how that suggests that you would take a civic of that era, being you said that MY civic won't take a 5.0 camaro or mustang, being that MY civic is a 99.

Anyway, my point here wasn't to start a pointless arguement (being that we can't settle this on the road because you live in another state)... Brian96z, you might want to try chitownracing.com that website is just full of sh1t talking.

My point here was the 305 is a horrible motor for anything performance related, like 2000GTP said, if you got you car for the coolness factor, then great, cuz i'll be the first to admit that 82-92 camaros with that factory lip kit are dope looking cars, which is why I bought one orginally (I had a 92 RS, 5 speed). Unfortunetly, after you get past all the torque, the car went literally no where. Took a Fast Times 355 short block, $2600 dart heads, comp street/strip cam, weiland intake, 750 demon carb, 150 shot, TH350 W/ reverse pattern manual valve body, 12 bolt rear w/ 4.10 gears, SSM weld-on subframe connectors...
(and the list goes on) before that car met my needs for performance. Not saying a 305 is hopeless, but it would take a lot to make that thing make some real HP. But then again everyone has different goals.

lol, none of the factory 305s made over 300ft pounds. If they made 340ft pounds the 350 must have made 400 because EVERYWHERE I've seen the best 305(the G92, dual cat cars) made 230HP and 300Ft/Lbs, that's the highest from the factory.

The highest 350 stats were 245HP and 345ft/lbs.

Problem with the 305 is the potential, unless you are running some crazy ported world heads for the 305 and a matched cam, carb and the right tuning you will MAYBE get 300 horse, they hit a wall because the 1.84 and 1.5 valves can only flow so much before they just give up and you can't get any bigger or they are shrouded by the cylinders. Forced induction is another story, it is possible to cram a lot of air in there to make them run, there's a guy named Preston something that has a 9 second 305 TPI with turbocharger. N/A...12s are unheard of.

First off, being a 305 has nothing to do with it- don't know much about them, but from what Ive heard the intake system on them was shi-sty. I have a 92 Z28 305TPI (was) 5-speed and that ran a 14.7 with nothing more than a short throw shifter and K&N air filters! 2000GTP is right though, finding one in good condition is a task in it's self! I lucked out on mine! :eek: Also be carefull and research what your buying- check the numbers on the block and so forth- these cars see so much abuse and "experimentation", you have to watch it! :alert:

First off, being a 305 has nothing to do with it- don't know much about them, but from what Ive heard the intake system on them was shi-sty. I have a 92 Z28 305TPI (was) 5-speed and that ran a 14.7 with nothing more than a short throw shifter and K&N air filters! 2000GTP is right though, finding one in good condition is a task in it's self! I lucked out on mine! :eek: Also be carefull and research what your buying- check the numbers on the block and so forth- these cars see so much abuse and "experimentation", you have to watch it! :alert:


Well said. These days nice Third Gens. are almost a thing of the past. Glad I latched on to mine back in 1999!

didn't have time to read all the posts so i'm just gonna give some general inputs.

the problems with TBI: trottle body injection is a type of fuel injection which means its computer controlled, it doesn't have nearly as many inputs as say the tpi so it tends to not respond very well to mods. that and the factory tune sucks. to get good power out of a tbi work on the tbi unit itself is needed (either 4-barrel tbi or a port job etc.) and a tune is definitely needed so it can recognize the mods done. while it may look like a carb in some aspects its not and a screw will not change the tune.

the problems with the 305: same stroke as the 350 but .3"s less on the bore, this means it won't flow as good as the 350 and you can't stick as big a valve inside the bore as you could on a 350. also since the 350 is just if not more common than the 305 and they share the same aftermarket parts many argue that the 350 will produce more power for the same money.

but i can understand wanting to not undergo an engine swap since it can be a owerwhelming task specially if you don't have any help from someone who's knowledged. heck i was planning on doing a few worthwhile mods to my 305tbi but then i got a sweet deal on a 400 block from my boss (.030" over, 2,000 miles on it, heads have 2.02 1.60 valves). don't know yet if i'm gonna stick it in the RS or find another 3rd gen with a blown motor and stick shift to put it in.

I sold my '91 RS 305/5 speed some time ago, but get this weird urge to get another one and see what I can do with it since I know quite a bit more about performance now than I did when I had it. With some bolt ons my car got a best of 26 mpg on the road.

I do have some thoughts in regards to the original topic of why the 305 isn't that great (sucks) in stock form-

It was never intended to be a high performance V8. The 305 TBI was an optional engine so that you could say that you had a V8 under the hood. It was stricken by poorly flowing heads, a tiny cam and a less than satisfactory intake tract from the snorkel to the manifold. It all makes sense, if GM is already using the 305/350 TPI for performance applications, why would they need the 305 TBI for another performance motor? The TBI motor simply filled a niche between the V6 powered cars and the TPI powered ones. Simply put, if you want the 305 TBI to make some respectable numbers, you have to do some "re-engineering" on it to get it up to par. I saw the Hot Rod magazine article where they got about 325 hp at the fly out of a carb'd 305. That would actually be quite a fun motor in a thirdgen, but with the intake they used I'm not sure it would fit very well under the hood. Even if you got a hood that would clear, nothing will make you look like a fool more reliably than running mid/low 13's with a huge ass cowl hood:lol:

Put a 400 crank in it my Monte SS was whole new creature after the crank swap.

how bout just putting an LS1/6speed in it and calling it a day?

how bout just putting an LS1/6speed in it and calling it a day?

:lol: Because if it was that easy, I bet you 85_305 would have a LS1 Third Gen ;)

Hey you said ALL 305'S ARE DOG'S. I showed you a 305TPI car that isn't
As a matter of fact, there are SEVERAL members on this forum getting 28+mpg out of their cc-Q-Jet 305's. Shall I make a poll and find out how many there are?


I'd vote in that poll. My last 85 Z28 with a CC quadra jet got exactly that. 28mpg highway. Near 20 city. This was with a COMPLETE tuneup, and a new Q Jet carb too. So it was basically back to like new factory specs. This even on an engine with 97k on it.

That great Jon; how about your new 305TPI Camaro though? Is that about the same?
Shee-it.. I have to get my best friend to check out this thread because he is hell-bent on saying my 305, along w/ every other third-gen 305 gets shatty mileage.

I honestly can't tell you right now, never cared much to figure it up yet. That and it needs the injectors rebuilt, or replaced. So I don't want to give any bad numbers. It's actually not bad though, I can say that. If I had to take a guess with bad injectors, it's right around 20 highway. Let me give you a exact number as soon as I get the new injectors in about a month. I'm probably gonna be shipping them up to Cruzin Performance.

Kool :cool:
Let me know when you do that and how it turns out :)