capps10e

Hey guys I'm new to the sight and have a 90 Iroc. I just wanted some suggestions on performance upgrades without changing the stock appearance of the engine and exhaust. I know there are limited options but I thought some of you guys might have some good thoughts. I don't need 400hp, but a little more grunt would be nice.

PhoenixFirebird

iTrader: (2)

There are actually quite a few options for keeping the stock appearance. But, you will be limited in the sound department with cam selection. Headers are the very first thing I, and probably everyone else on here, would do. Through a full exhaust, they won't change the sound much. If you have 2.5" pipe after the cat, that'll choke it a bit. 3" is good. You can do nearly anything to the motor and it will have the stock appearance. The only thing that would look different would be the runners. If you're looking for just cheap HP upgrades and don't want to really dive into the motor, the biggest gains you'll see are from headers, a 3.42 rear gear, and a custom tune. Don't bother with mail order tunes. Buy the Moates hardware, and burn your own chips. It's a VERY good skill to know for your car. Once the equipment is bought, you can burn chips until you're blue in the face. Mail order tunes you have to pay for them to be reflashed/burnt.

Honestly, it depends on your goals. I realise you're not trying to make huge power, but do you have a goal in mind, like a certain ET? Just the mods I listed will (should) get you into the mid 13s from a stock L98.

I'm building a sleeper at the moment. It's a 385 CID TPI motor, and the only things that will show it's not stock are the runners, the tires, and the cam. Aiming for 11s, with a stock look.

yaj15

iTrader: (3)

Another hidden upgrade would be to get some aftermarket high flow airfilters and gut the factory airbox where they sit. All the baffling that's below them can get removed and with the factory box all closed up nobody will know that the car isn't stock.

You can get hawks thirdgen ram air boxes or some hvac ducting routed behind the fog lights and seal them up to the bottom of the gutted ram air boxes for a custom cold air intake. With a modified car this is worth a lot more than a stock car but there are some noticeable gains with this mod.

You can also upgrade your transmission as well. Higher stall converter, stronger internals, etc. will also make a huge difference in the way the car performs as well.

You can also upgrade some of your suspension components to aftermarket boxed style such as the control arms, panhard bar, etc. Even if you keep everything all stock think about upgrading to poly bushings all the way around and getting some new shocks.

Also while we are on the suspension side make sure that you have some good Z-rated or higher tires on your car if high performance street driving is your goal. The factory performance thirdgens (IROC's, Z28's, Trans-Am's, etc.) are very good handling cars to begin with and the suspensions were designed with high performance tires in mind. This is your cars only physical connection to the road so it's very important that you have good tires in good shape to get the best out of your car.


I know the suspension stuff isn't technically an engine mod but, making power means nothing if you can't hook up and get it to the ground.

chazman

iTrader: (4)

First make sure your car is running right and maintained. Then do all the tried and true free/cheap mods on your TPI. Gut the air boxes, add a throttle body airfoil, bump up the timing a few degrees, add a cooler t-stat, (perhaps with a chip change so your fans come on sooner), maybe port the plenum wall away if you want.

Individually, these won't do too much. Together, they really add up.

yaj15

iTrader: (3)

It's about balance. One mod alone won't be much of a difference but dealing with an entire system (such as the exhaust from the headers back to the muffler) will really make a big difference compaired to stock with respect to performance.

Just a side note since you have a 1990 IROC with the L98 you should have the N10 dual cat set up. Your exhaust is the highest flowing system that you could get from the factory.

89 350

iTrader: (1)

I would also reccomend a set of 1.6 RR

capps10e

Thanks guys for the suggestions. I have upgraded the suspension with poly bushings and new shock and struts and yes I do have the dual cats. That's one of the reasons that I don't want to remove the manifolds and cats. Thanks for the airbox idea, I'll try that. If it were a different model year than a 90, I wouldn't mind changing things more, but the productions numbers were so low in that year, I want to keep it as factory as possible. This is my 3rd camaro. I have previously owned a 92 RS and a 85 Iroc Z. After I sold the 85, I realized what a huge mistake I made and looked for two years until I found this prestine 90 model, which I love and isn't going anywhere anytime soon.

VincentZ28

iTrader: (2)

I have a 90 IROC L98 too. All you have to do is install Dyno Don's Headers with the dual cat y-pipe set up, A good 3in catback and gut the air box under the air filters then a good tune up and chip tune. Your car will run in the low 13's@104-105mph.

If you just do a good tune up and gut the air box, your car will run 14.0-13.8@98-99MPH.

capps10e

Thanks. if I put the headers on, do I have to remove all the smog control from the car?

ninetyone

iTrader: (2)

-

VincentZ28

iTrader: (2)

No!

jjcuff1

Maybe not right post, but I am in same boat with 88 Iroc Auto LB9.
Can I change to dyno dons without pulling engine out? Cam?

I was gonna do full tune up, (plugs wire fuel MSD) gears out back, I have a posi 9 bolt already, then CAI with headers and NO CATS just 2.5" all back from y pipe.

then test and dyno with moats as baseline then port polish heads/intakes and throw cam and retune with bumped fuel PSI

I hope to be in low 14s

PhoenixFirebird

iTrader: (2)

You can do headers with lifting the motor off the mounts at most. Most headers fit in without lifting the motor if you're creative enough. My AC was in the way, so I had to raise the passenger side off the motor mount by like 2".

Open headers and a tune put my 3500lb race weight Formula to a 9.30 1/8th mile, which converts to roughly 14.5x. No other major mods or bolt ons. Throw a set of 3.45s in that 9 bolt, and you'll see low 14s.

jjcuff1

Thanks wow that's is awesome low 14s for street cruiser. would be awesome. Enough to pull on most stock or I/H/E ricers 4 & 6cyl. My main goal is to have good looking repainted car that has that torque seat of pants pull and sounds good cruising with top down. I like to be able to break loose in 1st and 2nd for fun.

If I could do that with out major engine work and just I/H/E tune gears polish and even be in 13s or good 0-60 I be happy and wait till teh 5.0 dies then build a 383 or LSX swap

jjcuff1

One more thing. My old 92RS 305TBI with work done pulled low 14s NA and 9.2 1/8 and with 100shot did 13.5-13.6 and 8.8 in the 1/8. Been a while and hence my new project car.

But with the TPI torque advantage and being a v8. Do you guys find that 1-2gears on the street is where the lb9-l98 own the newer cars? All that torque and a set of gears are these things stump pullers compared to v6 350z or 4cyl turbo gen coupes and they reall own from a dig most non-v8 sports cars like 0-60 that are sub 6sec? Of course after that they die out and get walked on by newer hi revving, DOHC, cars.

blackbmagic

Get some head work done, or grab a set of better stock heads and re-work them.

Valve-train...Performance cam, rockers, springs....

Carb..something more performance oriented and tunable, with a better booster, and better venturi design. Holley 4150, Demon, Proform, AED, Quickfuel...650cfm should be just right.

Rearend gears above all else wake the car up. If you have something like 2:73, or 3:23, or even 3:42, you will see a huge difference in your 0-60 and 60' times by swapping to a 3:73 or 4:10 or 4:11. If you do little highway driving 4:10 or 4:11 will be your best option.

jjcuff1

I agree with what you said but we both have Autos so for DD street car the 4.10 I think would be too hi?

Also I am TPI I do not want to go carb. I like the TPI for PC, Looks and nostalgia. If anything I would keep it, or go LS swap or RAM system on a 355 or 383

ninetyone

iTrader: (2)

Even a 373 is a little too high for TPI. When i had 342's on my 350 tpi bolt on car, i barely had a first gear. Stick with 342 and numerically lower gears.

jjcuff1

Thx

matt smash

Hey guys hope you don't mind me jumping in.

I have an 88 iroc 5spd that just had the 305 TPI rebuilt stock maybe 1000 miles ago. (I bought it like this).

What can I do performance wise (the engine was just rebuilt so I'm probably limited)

The cat sounds pretty hollow and has a magnaflow muffler

3.73 rear and new socks.

was thinking of a custom pcm chip

Any advice?

VincentZ28

iTrader: (2)

I agree. It may feel faster at the seat of the pants but you will not be going any faster. I did it all before 20 years ago and the track times and MPH were the same with 3.23, 3.45 and 3.73 with a 1.80 60ft. 3.23 or 3.45 or 3.42 are your best bet with a stock Or bolt on TPI.

VincentZ28

iTrader: (2)

Custom chip and headers.
I've seen back in 1992 an 89 305 5 speed IROC run 13.95@101 with just a full exhaust system and stock 3.45 gears.

matt smash

Ok thanks, what headers would you suggest?

PhoenixFirebird

iTrader: (2)

Hooker 2055s or Dyno Don's.

matt smash

I appreciate it, think I'll go with the hookers since I've heard alot about them on this site. Thanks

PhoenixFirebird

iTrader: (2)

IMO, Dyno Don's are better, but will cost more.

matt smash

Ok, I'd better start saving then

jjcuff1

How easy it to swap a cam without pulling the motor. Like a ZZ4 with springs or a LT1 both with RR

blackbmagic

TPI, TBI, CARB.. has nothing to do with what rear end gear you should or should not have. Period.

Jus Sayin.

A 3:23 equipped rear will have a higher top speed than the 4:11 rear but it will take a lot longer to get there. Period. Its simple physics.

Johnny Blaze

iTrader: (15)

Rear gears, like everything else, is part of the Combo. All parts shoulc match.

If rear gears did not matter, they would not make so many different ratios.

blackbmagic

What matters is the power band, weight, tire size, and what driving you are doing ie. 1/4 mile, 1/8 mile, road race, circle track...Sunday cruiser...

NOT...what kind of intake you have.

The physics of you power plant, and they type of driving you do WILL determine the rear gears.

4:11 WILL have a faster 60' and likely 0-60 than the same vehicle with a 3:23 rear ratio.

Johnny Blaze

iTrader: (15)

Exactly.

jjcuff1

Blackbmagic.

I agree, was not flaming . My point was (maybe misread your quote) You said Carb... I understood that to mean switch to a carb. Since I stated I have a TPI.

Yes your intake method has nothing to do with rear ratio. It is just where your car makes it power and how you like to use it will determine the best match.

I am thinking street cruise, good sound (cam, headers), make some burnouts and chirps in 1-2 and some redlight mashing for seat of pants torque feel. track wise I like to be street hang or beat modern cars from the launch without making car unbearable and burning rpm on highway since I drive on hiway a lot. Maybe a shot at the 1/8 for fun

VincentZ28

iTrader: (2)

Well in that case leave the stock 3.23 alone since you travel on the HWY a lot. If anything, put a new posi unit in because the old posi is probably worn out. You are probably spinning one tire from a dig. Just install a set of Dyno Don's headers with dual cats and a good 3in catback and you will be good to go. Don't forget to gut the airbox and give it a good tune up. I have done it and was able to beat the heavier 350hp Dodge cars and a few LS1 F-bodies up to 115mph.

ninetyone

iTrader: (2)

No, the TPI intake determines the powerband in our cars mainly.

ninetyone

iTrader: (2)

Also, the 700r4 transmission already has a 3.06 first gear. It's like having a 3.73 rear already in most cases. When I had my 3.42 gears I barely had a first gear!

VincentZ28

iTrader: (2)

I agree! 3.73 are good for 6000+rpm engines. You will run out of steam before the 1000' and lose the race in a stock TPI. It's ok for the 1/8mi. This a low rpm engine fellas!

yaj15

iTrader: (3)

By design TPI was made for the 305 to boost low & mid-range torque and horsepower. GM was considering stopping production of the 350 motors in the 1980's because of the increasing fuel economy and emissions standards. They figured they had a better shot at this by developing the 305 motor but, GM knew it was down on torque compared to earlier 350 small blocks so that was part of TPI's goal.

We all know that GM kept producing 350's now but they stuck the same 305 TPI set-up on the 350 motors only changing the fuel injectors from 19lb/hr to 22lb/hr. This is why TPI is restrictive on 350 motors because the intake set up was designed for a motor that was 45 cubic inches smaller with respect to displacement.

Now you can improve on them a great deal with aftermarket runners, ported plenums, etc. and that's what I have done on my car.

3.42's are the deepest rear gear set I would go with for a long-tube factory style TPI system - stock or modified. You don't need a lot of rear gear to get good performance out of that set up because of the massive torque down low and mid range power band-off idle until 4,500-5,000rpm. With mods you can string that out to 5,500rpm maybe up until 6,000rpm but, that's not where a long-tube runner TPI intake shines.

If you have a car with a mini-ram/LT1 with shorter intake runners you will spend a lot more time making power in the 5,000rpm-6,500rpm range with respect to your power band. You'll need more torque multiplication to easily get the motor in that higher rev-range so now is where the 3.73 - and steeper gears come in to play.

jjcuff1

So for cost to tune and upgrade the tpi maintain it with tuning injectors fuel system is just a lb9 or l98 with polishe heads cam exhaust slap a carb on it provide more hp? Like lot more n lot healthier rpm range for street n track?

VincentZ28

iTrader: (2)

You will loose gas milage if you go carb.

conlinj

iTrader: (3)

Really can't beat that...

jjcuff1

Thats awesome!

I had my purge lines hooked up to my wiper nozzle pointed towards passenger side. Love striking fear to the guy next to me at red light

Johnny Blaze

iTrader: (15)

There is a lot that can be done and still look stock. As stated above it depends on your goals.

Cam, head swap, would still look stock.

Heck, you could build a 383 or a 400 sbc and most would not be able to tell.

The free mods, like gutting air box, collent bypass, etc.... will help.

The stock manifolds will hold you back the most. I would get some of Dyno Dons headers with the Air pipes to keep it looking factory and emissions legal. High flow replacement cats and a catback of your choice.

Porting the upper and lower pelnum will help.

A good tune.

Shift kit in trans will make it feel faster, and more fun.

Start with the basics. Don't overlook minor things like good plugs and wires.

Johnny Blaze

iTrader: (15)

Would not want to be in that car if the clutch/flywheel/flexplate/converter came apart.

chazman

iTrader: (4)

Good point.

PhoenixFirebird

iTrader: (2)

I'd much rather have them coming out the front right under the coolant and temp sensor holes lol. It just seems safer up front...

But regardless, a very neat setup.