I've got an '89 Iroc with a 305 TBI, everything is stock and i am wondering how I can get the most power without any huge changes such as boring out,nitrous, or forced induction. Just wanna gain more power than stock!

Some good inexpensive choices are freer flowing air elements, a bigger throttle body, a high flow catalytic converter, or performance muffler.

Or you could take the even cheaper way, and get way more usable horsepower for free, by now you're probably saying "what?". But yeah, a lighter car, basically is the same as giving you more usable power. You can do what I did, take out all of that heavy sound proofing under the carpet, yet maintain a stock look. I'll post pictures.



As you can see through the hatch in the next picture, I just folded the carpet back down to get back to the stock look, but that night I took probably 50+ pounds out of the car.



Other options for using the power that you actually have now would be a carbon fiber or lightweight aluminum driveshaft, and if top end isn't really a concern with you, you could always stuff some 3.73's in the rear. It really all depends on how deep your wallet is. I read somewhere that a good rule of thumb is to expect to pay 10 dollars for each horsepower, that'll basically sum up your goal.

How much are you looking for anyway? A good reliable 250-300 horsepower? Or more?

Dude don't get me started on weight! I'm a weight ****. My car as it sits now is 2860lbs with a half tank a gas,without me in it (185lbs). My car is GUTTED. I can't wait to get the ZZ4's and the Tubular frontend/coilovers on. I should have the car down to 2900 WITH ME in the car soon enough.

To answer your question though you can do anything to a TBI motor that you can do to any smallblock chevy but the biggest power adder you can find is in the TUNE. Alot of people like to rag on TBI because they don't understand it. Honestly it's the easiest form of FI you can play with. HEre's a thread I wrote awhile back that covers alot of question you newbies have. Also check out Fast355's thread "Budget TBI Build" if you want to swap over to a Tree-Fiddy,lol Alot of the stuff there can be transfered to your current engine if you don't feel like swaping.

https://www.thirdgen.org/forums/tbi/...-synopsis.html

I have a TBI truck, but just did an injector spacer ($12.98 shipped from ebay) and an adjustable fuel pressure regulator ($50 shipped on ebay, but you can just modify the stock one if you like, just tap for a screw and put in a washer so the screw changes the tension on the spring, use stock spring and tighten all the way for 15psi). I noticed a significant gain, although the power band (idle-3500) is still the same due to the stock cam and restrictive heads. I plan on 1.6:1 roller tip rockers next, or just a new, mild edelbrock cam (204/214 - 420/442) in my non-roller block. Stock lift on my cam is .385/.401, so some more lift would be nice, and that won't really affect the tune too much.

I have cold air intake, and recommend that or an open element air filter (as cheap as $20).

Remove the choke collar and just put the filter right on the TBI unit, put a breather in the hole on the valve cover that used to go to choke collar.

Grind down the ridge around the tops of the throttle bore on your TBI unit and sand it smooth on the ridge and the top inside of the throttle bores, smooth down the backs of the throttle blades where the screws stick out.

Remove some of the plastic that holds down the wires that go to injectors so that more air can flow through.

New exhaust from the heads back and some underdrive pulleys gave me 2 mpg increase + more power too (but I needed a muffler), so figure that into your monthly gas bills and see if that helps you rationalize exhaust and pulleys, but mine caused cooling problems even though it said they wouldn't. I put on some LS1 fans and a 180* tstat, it never gets above 140* now, but I need a fan controller, they just run wide open on a 30amp fuse from the cab's fuse panel on an ignition-hot only circuit right now. LS1 fans would fit your car too probably (modify the stock fan shroud and use a piece of aluminum from lowes that is in an L shape), or just get some TPI car fans. Efans can turn faster than water pump pulley after underdrive.

Waiting on Rbob to email me back about an EBL for my truck and then I'm done for a while, will just tune and tune ... and tune and tune. Got some vortec heads and an LT1 cam already, and thinking about a single plane Edelbrock Victor intake for my vortecs once i get them port matched and cleaned up. I've been collecting the expensive parts for a while now. I was going to go TPI, but decided that I'd search for an older F-body to convert later on when I have more money and more time (if that happens).

You'll probably want to look up each of the things I recommended, there are better explanations on here than what I included, I just gave you a synopsis of what I did and each thing I did made a noticeable gain, but I did somethings together and don't know what did how much, and never have done a dyno, so just using SOTP dyno, which isn't reliable. I do however keep up with mileage on each tank. I noticed, as stated, a large increase (2mpg) in mileage with headers and underdrives. Swapped my Super44 for a 70 series big block flowmaster and picked up about a 1/2mpg. I'll report back on what the AFPR does to my mpgs and the EBL, when i get that.

I must agree this particular mods you listed are almost free, but they do not really make a LO3 any faster.


Thirdgens with the LO3 have electric fan.

It made my L05 in a 3900lb GMC Sierra a bit faster, but only in the idle-3500 range. But, I could have already bought an EBL for the money I've spent, and that is probably the single best thing you could do. Before these mods, I couldn't spin the 20" rims unless I popped the clutch, now I have to feather the clutch to keep the tires from spinning on normal take offs. It just happens to be raining today, too. I've already accidentally spun the tires while feathering the clutch as much as possible. I actually got some tire spin shifting hard into 3rd, but yes, it's a truck with poor weight distribution associated to it. Can't wait to move the powerband out a little and make some higher RPM power in the 3500-5500 range. My truck already has the powerful feel of a newer truck on the 230k L05, but it will probably fail sooner than it would have had I left it alone .

Dont get me wrong, I'm commenting the mods I quoted, only.

Reading the treads on top of this forum will also give you a good idea on how thirdgens came out of the factory.

Incase some people have never checked out Nelson Racing Engines, they have several extreme horsepower engines, 2,000 horsepower and over, and they're currently working on project "Kong". The 3,000 horsepower 700+ cubic inch 69 Camaro.

What's great is, their engines are mainly TBI.

Do you have some links? I could not find any Nelson racing engines using TBI.

http://www.nelsonracingengines.com/p..._572bbc_tt.pdf

That's basically their top of the line engine, a 572 big block twin turbo engine, running a 1700 CFM throttle body. I think you'll need Adobe Reader to view it.

I believe every single one of Nelson Racing's high powered 1,000+ HP engines, except for the 705 naturally aspirated Race & Pump gas warrior series engines are running throttle bodies, that alone says something.

Throttle bodies are just the way to go, they're simple, programmable, easily upgradable, with a huge after market availability.

I really can't wait until my engine is pulled and rebuilt, and I have the cash to put on a throttle body EFI system, then things will get rollin'.

You do know that there is a difference between a "throttle body" and a throttle body injection induction right?

Every car has a throttle body, it's where the throttle plate is and where air is let into the engine.

Not every car has throttle body injection, when the fuel is injected just at the throttle body electronically.

Yes. I'm very aware.. I'm not a total moron..

But seriously? How often do you hear people referring to a carburetor intake as a throttle body? Never. It's referred to as a carb, just that.

Sorry for any confusion, but by saying "throttle body", I'm implying the actual throttle body fuel injection, as in EFI.

Next time I will make sure to say "throttle body fuel injection". But anyway.. That's what Nelson Racing uses, that was my main point, it's reliable, and simple.

No need to get technical with terms..

Np man, I don't intend to offend.

But I'm pretty sure it's multiport EFI, it says there are two injectors per cylinder which doesn't coincide with TBI because the injectors are in the throttle body housing.

I don know why they use that term, its called EFI.
True TBI is a EFI, though 2 injectors that can spray fuel for 1000hp do not exist jet, and using multiple TBI's is probably not worth it.


The stock TBI needs wery little to support up to 280hp, best would be a VAFPR to supply the required fuel, EBL flash to adjust the fueling algoritmes and timing (tune).
The stock fuel pump can only handle around 200hp. Can be replaced with a TPI fuel pump, wil be ok for around 300hp with stock injectors, after that you can alway use higher flowing injectors.

To make more HP with the LO3 engine, exhaust, cam and heads.

man these guys are pretty helpful! i had the same question too about my L03, its in a firebird, i love it, even though i might get a 350 later on down the road(1400 for a new one), i still want to mess with this engine and get some experience on tearing apart a motor and rebuilding it!

i saw a supercharger kit(kinda looks like a turbo, forgot the type its called) for it for about 1700, that plus some good internals should make some good hp

im just looking for about 250 hp and 350 torque and ill be fine! lol

The supercharger you saw was called a Centrifugal.

If you're looking for only 250 horsepower, I'd suggest checking out an STS (Squires Turbo Systems) Universal Kit. You can run 5-8 pounds of boost on stock internals and make more than that 250 horsepower you want, easily. $1,695.

Or he can just throw in a cam in the 200-210 duration range and hit his very modest targets with a good tune.

I'm going to try for 300+hp out of crappy LO3 heads. It should be a challenge, but I want to see if I can pull it off without modding the basic long block (other than maybe a HG change to boost compression and quench, and make the valve spring change easier.)

yea i have heard of those systems before, and i love the sound of a turbo, but i would be a lil iffy hooking one up with stock internals being this is my DD

what cam would i be looking at getting? i have never changed one before

Plus theres always room to upgrade that kit too with very little work needed. i'm planning on doing an sts system next year hopefully.

I can promise you, you would be a lot better off with a turbocharged car producing 350 horsepower, than an all engine setup running the same power. You know why? Boost controllers.

When you're cruising around the city, you can literally turn the boost down to 1 pound.

An all motor setup on paper seems a lot more promising, due to it's simplicity, but when you get into a choppy-radical cam, you essentially lose all driveability of the car, plus gas mileage. Turbocharged engines rely on stock, or close to stock equal duration cams for efficiency, which means good torque for low speed in traffic, and an overall wider powerband and RPM range.

Just trying to lead you in a good direction for what you want to do.

i definitely know a bit about turbos, i onced turbocharged a 2.0 sunbird tbi, ofcourse its no firebird lol, but i learned alot and it was really fun to drive, sounded great!

its just that this engine has 150,000 miles on it, which isn't bad, but isn't really up to being turbocharged i dont think...i was actually leaning towards a brand new 350 which i have seen priced for under 2,000...

maybe have it on a stand for awhile, and build it for twin turbos or something until this 305 dies..should be a fun project lol

Wow...that's not how turbo setups work exactly.

You can't turn the boost down to 1 pound, it'll only go as low as base boost which is 5-10 psi depending on the turbo.

There's another variable you haven't considered. torque. The turbo system will boost the torque output of the engine an equal amount. That sounds great, but torque breaks **** real quick. Since we're doubling the power (which you can't do with only 8 psi, you'd need more like 15) we're doubling the torque too. So that's 500+ lb-ft. That'll rip a 700R4 apart in no time, followed by your diff, if you ever manage to hook up that insane tire spinning grunt.

And 350 hp from a 350 is hardly an "all-motor" setup. Vortec heads with a pretty modest cam should get you there with no trouble.

Another easy upgrade for OP is to put a 4 barrel carb intake manifold and a adapter plate for the TBI to attach it to the carb manifold.

I haven't decided yet, but I'm still up in the air on a lot of things at this point. The LO3 heads are unique in that they have almost balanced intake and exhaust flow (160/140, this is due mostly to their terrible flow in the intake side). They also don't take to high lift, going more than .400" of lift doesn't get you much more flow. So I'm looking for symmetrical cams (same intake and exhaust duration) that have low lift. I've found a Comp Magnum 270 solid flat tappet cam that's 224/224 duration at .468" lift.

That's my plan, and that's going to be on the border of over cammed. You only want about 250 hp, which a Comp XR252HR roller should do nicely. It's got a tighter 110 LSA, but the duration is so small that it has no meaningful overlap and the lift is below .500" which is the limit for aftermarket valve springs on a stock head. Another good cam is the LT1 cam. Or you could have your stock cam reground with more lift and duration for not too much. Basically anything in the 200-210 duration at .050" of lift and around the ball park of .450" of lift (no more than .500") will get you where you want to go without too much trouble. That sort of cam should idle smoothly, get pretty good gas mileage, and have gobs of low and midrange torque. It will fall on it's face at passed 5000 rpms, but these old engines shouldn't be revved more than 5500 anyway so it all works out.

I agree with saabster, you can hardly compare a 350 pushing 300+ horsepower to a car not drivable on the street.

I'd rather have a motor set up pushing that than a turbo set up any day.

after i would do the cam, im sure i would need it tuned..well there is no place where i live that does that, and i sure dont have the equipment myself

to tune my sunbird i used an aldl(spelling) cable, a laptop, and a free program i got off the internet

just curious, what trans did the 350's come with?

Yes, you'd need to get the equipment to tune it. Frankly, after an exhaust there isn't much you can do to the car that won't require tuning somehow.

With whatever trans you find it with. All the automatics for the camaro were the 700R4.

How do these mods help add power ?? I'm just playin' with TBI's after years of ignorance - but I do have some wrenching experience. To me it sounds like these 2 mods are a sure way to allow more heat into the combustion chambers. Sitting the air cleaner directly on the TBI and allowing hotter air to enter thru the hacked wiring hole,..... that doesn't sound like a good idea. Seems like the top of the TB unit would be sitting almost 'flush' with the cleaner lid..... and that can't be good. ( I gotta' test fit and see what it looks like rather than workin' from a mental image ! )

Just about every engine application I've owned the colder the incoming air --> the better. What benefit is achieved & is it really enough to offset the increased heat they are allowing in ?? Wouldn't a higher flowing air cleamer be a better idea if increased flow is the goal ??

this is the cam i've decided on. second choice being an xr258hr in either the wider lobe center 112 or maybe the 110. but looking at dyno sims (comp cams has a free one to download), i'll trade the 12hp up top, for the 12lbs of torque down low. not to mention better mpg and vacuum.
i just got the world products s/r heads (formerly called torquer, but 305 size called simply s/r now), which i'll do a very mild cleanup and porting on to match it. was going to do a 383 or 350, but think i'll enjoy the mpg on the 305 so i drive it more. and keeping the 2.73 rears for a while, will match better with the xr252hr type cam, than like the takeout zz4 cam I have sitting around. zz4 cam and the sportsman IIs are suited to a nice 350 or 383 build but not the street 305 i've decided on.