I am trying to decide what to do to the engine for my 85 IROC. Currently it has a 350-.030" 2pc main 4 bolt block, flat top pistons 10:1 comp, Comp Cam XE274H flat tappet, GM Vortec heads w/upgraded springs, Edelbrock Performer RPM Air Gap intake, and a Edelbrock 600cfm carb. It had a 750cfm, but I found the 600 was better around town. On a engine dyno it made 386hp. The car is a 5spd conversion with 3.42 rear gears.

The car was originally a 305 TPI and I bought a parts car to swap it all back to fuel injection. I have a couple engine options I could do:

1) Use the current block, xe274h flat tappet cam, and Vortec heads and get a Edelbrock Vortec TPI base with a mild port job. I have AS&M siamesed runners that are extrude honed ported and use a ported stock upper plenum. I just absolutely love the look and originality of the TPI intake.

2) Use above longblock combo but with a Holley Stealthram intake.

3) Freshen up the roller 350, put on the Vortec heads, get a better roller cam, Comp 266HR-14 with the above AS&M runners, Vortec TPI base and upper plenum ported.

This is for a purely street driven car and I don't need to go fast. Just looking to work with what I have.

Is freshening up the roller block to use it with a roller cam worth it? Would the Vortec heads need to be machined for screw in studs to use a roller cam with higher spring pressures? If I went roller cam, would it be easier/just as good to use the fresh flat tappet block with link bar roller lifters?

 

idk man. Unless you're tyring to go racing or something, I would leave your bottom end alone until you absolutely have to change it. And from the sounds of it you aren't.
The cam package you have now seems like it's making some really good power for such a basic setup. I would leave it alone and work on the top end.
I think if you explained what your goals are, as far as what you hope to change..ie hp/tq, rpm pwrband, or just for the lulz?..that would help people give you better advice.

 

That's the hard part, I never know what I want to do. I want good street manners, mileage, and torque, but I also want the high end power. I know I can't have both! I just want something that works well together. I don't quest for specific hp/tq numbers.

Would the current engine combo with the xe274 cam be a mismatch for a TPI setup? Power peaked near 6000rpm, though I don't have the specific RPM. My friend built the engine years ago and neither of us can remember. A TPI setup would boost low torque which would be fun around town, but might bottleneck the top end, I do have ported siamesed runners/plenum that could move the RPM range up a few 100.

I would have to buy a Vortec TPI base which is about the price of a HSR, so it would be pretty much the same cost to go either direction. It mostly comes down to what intake setup would work best with the engine combo I have now to make a all around decent street setup.

 

I hear you saying that you like the look of TPI. You also mention considering the Stealth Ram. If original appearance is what you're after then TPI is the way to go. However, to get your power level from TPI means using at least large tube runners. You mentioned siamesed runners but you need to know, they will not look OE. If you just want EFI for improved drivability and power, the Stealth Ram is the better choice. It will easily support your current cam and heads and has the flow potential to go well beyond 400HP.

I run high flow, long tube TPI and spent alot of money on the base and runners. You could buy two HSRs for what I spent just on those two parts of my TPI. This doesn't include the many hours I spent porting the base and plenum. I choose not to siamese my TPI because I feel that once this is done, it isn't really TPI anymore and I'd rather just go with a higher flowing design like the miniram or stealth ram than cut up my TPI trying to squeeze more power out of it.

Short of siamesing, I've taken my TPI about as far as I've ever seen it taken. The ported twisted wedge heads, the ZZX cam(240/240 @ .050 .560/.560 112lsa), low tension rings and vacuum evacuation are all intended to push the TPI as far as it can go. I have been pleased with the results but I know that to go any further, I need to move away from the long runner intake.

 

In a dyno test with my basic same setup, but with ported stock heads, the ZZX cam made 408HP at 5,950 rpm and pulled hard to 6,200rpm. I shift at 6,300-6,400 and my engine hits the 6,900 soft rev real quick if I get stupid and forget to shift on time. The vacuum evacuation, odd as it may sound, actually made a significant difference above 6,000. But the motor, even with the first cam I put it before the ZZX(an SLP grind for extensively modified TPI (223/230 @ .050 .513/.520 112lsa) pulled hard to 6,000. The ZZX gave it a flatter, longer torque curve and took it past 6,000 with much more authority. The Moroso vacuum pump gave it an easier rev so that it flies past 6,000. I feel no drop off at all right to the 6,300 shift point. The long tube runners produce enough torque that street driving is still very pleasant. Even my wife has no trouble driving it around town.

 

To me siamesed aftermarket runners are close enough to stock looking, I would still consider it TPI. I would be able to get the runners and loads of other camaro parts from a friend who abandoned the hobby years ago, so the cost wouldn't be much, pretty much what a Vortec TPI base would cost. He hasn't touched the runners in 10+ years, so hopefully he will give them to me for free. Assuming free or next to free runners, going either TPI or Stealthram would be about the same cost.

ASE doc - as you stated above, improved drive-ability and power are my main goals.

Would putting a HSR on my current engine combo leave lots of low end torque on the table compared to a TPI setup? With street driving and a 5spd manual trans, the engine will spend most of its time between 1500-5000rpm

 

The stealth ram will cost you a little low to mid range torque but siamesed runners will do the same. Your cam and heads should support power to about 6,000, though the heads would be better with porting. The stealth ram will allow you to make much better use of that power band above 4,500 than the stock TPI. With you current set up, I don't know how much difference you would see between the siamesed TPI, assuming everything is well ported and properly matched, and the stealth ram. The stealth ram would give you alot more room for growth.

 

Yeah I would leave the bottom end alone for sure after hearing more about what you want out of your car.
And since you're really into adjusting the intake system, I would for sure send off the heads to get them ported and which ever intake you go with, make sure you get it port matched. So send them both to the machine shop at the same time.

That's not just a "track performance" benefit. It will help you're motor breath better all together, which could help you ease off the throttle a little more often.

Also maybe some new retainers&keepers wouldn't hurt.