Ok, i know this subject has been done to death. But even with searching, I'm not finding what I really need. 87 IROC 350TPI. Rebuilt 350 stock. rebuilt 700-r4. Have done the SFC, suspension, rear end, brakes, cooling system. We put on 30lb injectors when we did the engine. New Bosch fuel pump. So its basically a stock engine making around 225HP and 320 tq. This is GENERALLY a sunday driver, but when my DD goes down for work, it becomes my DD. What I want is to make some more HP and TQ WITHOUT destroying the driveability of the engine. I am guessing heads, cam and exhaust, but I'm trying to make a GOOD combination, without running premium gas, or having a loud exhaust. I would like to hear from people who have made mild mods, and have a good working combination, and what they got out of it. Porting the TPI could be an option, but I would like to hear from people who have done this, and if they had any issues. I want to make the mods MATCH, so I can throw it together, and have it run without a lot of tinkering. Also whether the stock computer can handle mild mods, or if I need to modify it as well. Thanks in advance!

 

Go to the faq page (I believe) and there's a page on this exactly. As far as what the computer will handle, as far as cams go you couldd swap in an lt1 cam and the computer will adjust for this, but just about any bigger and you'll need a tune. You can push around 300hp with very little on l98s so the goal your searching for is easy and fairly cheap to achieve. I'm going to try to push 350 out of my mild build. But the faq page and the other informative page are an excellent starting point.

 

And IMHO, 30# injectors are a bit much for a stock, or even mildly built, 350. When I'm done with my build I will either have 22s still or 24s, but on a mild 350 30# is a bit overkill imo. You can get an AFPR and tune in 22 or 24# injectors just fine and they will probably be better for performance. Just slapping bigger injs doesn't mean more power. This is probably something to look into.

 

when the engine was rebuilt, we slapped in the 30# just so we wouldn't have to change them later. They were also WAY cheaper than the 'factory' 24# injectors. Since TPI fuel system is setup to return fuel it doesn't need, there have been no issues. So now I can feed whatever I want. I want to keep the TPI, and my budget isn't huge. I did do searches, but I'll try the FAQ page again, thanks.

 

30lb injectors are too big,even 24lb are too big for a stock motor,you need a custom chip now. Lt1 cam is not much bigger than what you have now. I wouldn't bother with that. You can start with a catback exhaust,headers custom chip and adjustable fuel pressure regulator. You will want that anyway if you plan on upgrading the heads,intake system.

 

your car will pick up more power with stock 22lb /hr injectors or a custom chip that has the injector constant corrected

 

https://www.thirdgen.org/forums/tpi/669911-upgrading-87-350-tpi.html

Like others have said the LT1 cam isn't going to boost power that much. This is a link to some camshaft specs: https://www.thirdgen.org/mods3

The biggest factory L98 cam (between 1988-1989) was rated at:
Part # 10066049
207/213 at .050" Duration
0.415’’intake / 0.430’’ exhaust with the stock 1.5 rocker arm ratios.
0.443’’ intake / 0.459’’ exhaust with 1.6 ratio rocker arms. Added 0.030’’ of lift.
Lobe Separation Angle: 117degrees

The 1987 factory L98 cams were rated at:
Part #14093643
202/207 at .050" Duration
0.404’’intake / 0.415’’ exhaust with the stock 1.5 rocker arm ratio.
0.431’’intake / 0.443’’ exhaust with 1.6 ratio rocker arms. Added 0.030’’ of lift.
Lobe Separation Angle: 114.5 degrees

The stock LT1 cams were rated at:

http://www.grandsportregistry.com/lt1vslt4.htm

0.447’’intake /0.459’’ exhaust with the stock 1.5 rocker arm ratio.
Lobe Separation Angle 117 degrees

So if you change the 1.5 ratio rocker arms on a stock L98 camshaft with 1.6 ratio rocker arms, you essentially have an LT1 cam.

The 305 TPI motors came with 19 lb/hr injectors and the 350's came with 22 lb/hr injectors from the factory. If you were running a really modified 383 or larger cubic inch engine then I would possibly see the need for 30 lb/hr injectors. With a bolt-on internally stock L98 the stock 350 injector flow rate is just fine.

I've got a lot of gains out of the mods that I've put on my car. I've got an A/C Delco rebuilt L98 stock heads and cam motor. The main thing is getting the most air in and out of the motor as smoothly and efficiently as you can. An engine is just an air pump. More air in and more air out in an efficient manner should get you more power.

On the exhaust side I've got 1 5/8'' ceramic coated Hooker headers, matching y-pipe, high flow cat, and 3'' Flowmaster cat back exhaust.

On the intake side I've got Hawks Thirdgen Ram-Air boxes. The boxes sit right behind the fog lights and funnel the air right in to the air boxes. I've also gutted my factory air box so the filters just sit in the housing. I removed all of the factory baffling so nothing is in the way to obstruct air flow. I screwed in my ram air boxes to the bottom of the factory air box. I've got a 52mm BBK throttle body, ported SLP intake runners, ported plenum and, ported Edlebrock intake base.

With these mods I’ve also going to order an aftermarket chip from http://scotthansen.net/. Some of my friends have had good luck with his chips. Technically since I’m still running a stock L98 heads and cam car I don’t need a chip. But since I’ve gone through all the intake and exhaust components I’ll need a chip to get the most out of my mods.

You’re lucky, if you still have the factory original Borg Warner 9bolt in your car - those 1st year L98 cars all got 3.27 gears. Some of us that have 1988-1989 L98 IROC's (like myself) got 2.77 gears instead of the steeper 3.27 gears. In 1988 GM made the 3.27 gear a G92 option gear and the 2.77 gears were standard. In 1987 the only rear gear available in the L98 IROC's was the G92 3.27 gear set.
Also you can upgrade your ignition system with parts from MSD or other aftermarket vendors as well.

You also should be in good shape with your transmission. The 700r4 was used in thirdgens from 1983-1992. In 1987 the 700r4 got a lot of factory upgrades. When you look at core 700r4's is a good idea to start with a 1987-up 700r4 so that you get the advantage of the improved factory hard parts.

With the 700r4 automatic cars (aside from getting a proper performance rebuild – I got my trans and converter from Bowtie Overdrives and have been very satisfied) a higher stall converter changes the equation in terms of performance. Your car will get in to the power band faster, and stay within the power band while you are accelerating. Also with the lock-up converter that these cars have there is virtually no penalty with respect to fuel economy. You have to make sure though that the converter you pick is matched to the way you drive, your cam, basic operating range of your motor and, your gears.

Make sure your suspension is in good working order too. Making power means nothing if you can't get it to the ground properly. Look in to sub-frame connectors, aftermarket boxed control arms, panhard bar, shocks, poly bushings, etc.

A car is only as strong as the weakest link. When you make mods you want them to be balanced so that you get the most bang for your buck with respect to what you are trying to do. This too will help reduce / eliminate as many weak links as possible.

 

ok - so, i plan on doing the exhaust, so it breathes out better. I want to keep the TPI system. The idea is to make it reliable, but make it faster. I keep hearing about vortec heads, those have to be matched to an intake, correct? So what intake, what heads, what cam? And what compression ratio would vortec heads have on a stock 350 engine?

 

sorry yaj15, we posted on top of each other. Its NOT the stock 9-bolt, mine didn't have posi, so we got a 9 bolt with the 1le package out of an 89. We went from 3.42 to 3.27 gears. Its all upgraded and happy. As is the suspension, brakes, etc. ALL the weak links I could find have been fixed. So its down to making more power without destroying the reliability. Its NOTHING for me to put 300-400 miles on this car on a weekend. And my road trips can be 2500 miles easy. I wind up in places like Black Hills, Yellowstone, Ouray, 4-corners. So, reliability comes 1st, and power comes 2nd. If i break down, in say, DuBoise WY, I want any general mechanic to be able to work on her! So screwing with computer big time is out, major TPI mods are out. Heads, cam, exhaust and maybe intake? But they all have to work together.....

 

That sounds alot like what my goals are for my car. I updated my post with the mods I made to my car in more detail. You want more power and performance but stock style reliabilty.

 

Get rid of those 30lbs injectors. Way overkill. Your chip is not set up for them.
Get a set of Dyno Dons Headers and a good 3in cat back system. You will drop 3/4 sec and pick up 5 to 7 mph in the quarter with a gutted air box. Thats is what I did in my 1990 G92 L98 except I have SLP Headers and the car when 13.20.s@104mph. Also with the stock 3.23 gears.