Hello all! Long time reader, first time posting. I apologize in advance for beating a dead horse so to speak. I’ve recently been collecting opinions and parts to rebuild/upgrade my 89 iroc with 350TPI. I’ve settled on what I think will be a pretty good combination of parts for its intended use, which is weekend driver and auto cross racing. I doubt I’d be lucky enough to find out someone built this exact engine but I’d love some HP/TQ estimates if anyone has that info available. So here goes…

355, 10:1 or so for 91 pump gas
AFR 180 heads #0919
Comp Cams XR269HR
1.6 rockers
AS&M runners
extrude honed oem intake and plenum
24lb injectors
larger throttle body if needed
1-5/8” headers, no cats
custom tune when assembly is complete.

I’d love to hear anyones results if they have desktop dyno or built something similar.
I’d also like to thank you all for the wealth of knowledge I’ve already collected from here!!!

 

Basically did that build on a stock bottom end 350 L98. Lt4 hotcam clone, dyno don shorties. Ran ok, honestly expected abit more out of it. But it did seem to have a lot of blowby/crankcase pressure so idk. Made 272 whp 350’s wtq. Good solid street build. Fairly easy to tune, idle good, was quiet with magnaflow exhaust

ran that cam or something very close on a rebuilt stock L98, with longtubes and dual 2.25 exhaust. Made 227 whp, cant remember the torque, in the 300’s. Not bad i guess for stock head stock tpi

 

If I hadn't saved $$$ on the TPI parts that I have, then I'd suggest to use that money to go to another intake style/setup. Stealthram would be my choice if I wanted to change the least.

 

Thanks for the replies!
It doesn’t take much research to find out the short runner systems do offer some benefits and everyone seems to prefer them over the long runner setups. I like the appearance of the TPI and the auto cross courses I have locally are small enough that the low RPM, broad torque the TPI offers has been beneficial. I won’t be drag racing and the closest high speed road race track is 4 hours away so high RPM runs will be few and far between.
I did however choose the larger, better flowing AFR heads over the TFS-175 just in case I do change to a stealth or mini ram in the future.

 

Doing it all over again i may have gone with the 195’s for that build. If you have the budget, the First TPI systems and those heads imo would be superior and give even better gains down the road with a short runner intake if you ever decide to change out

 

I looked into the 195’s while doing some research. There’s no doubt they flow better and would leave room for future upgrades. That can be a good and a bad thing! Lol. I don’t need to leave the door open to spending more money on it in the future. I’m just trying get the best match of components and hope for good results.
The AS&M runners flow 260cfm and the AFR-180’s flow 260cfm @ .500 lift. The gentleman I spoke to about extrude honing my base and plenum seemed confident they could get my intake to flow 260cfm as well.
I was advised by someone I trust to switch to the smaller Comp Cam XR264HR with 1.6 rockers which would be…
.520/.528
212/218
lca-214
On paper it it appears to be a good combination. However, good planning doesn’t always mean good results… 🤞

 

The intake despite the flow numbers usually always drags down the head flow. Sometimes not a lot sometimes a fair amount. Def want less restriction in the intake, and thats why i feel the 195’s are a better investment overall. I dont think they are much different in price and certainly arent too big a head for a 350.

id leave the cam alone, i wouldnt go any smaller. In fact contrary to what most would think, i feel tpi needs more cam than you’d think to make up for long runners. Need more duration time to fill cyl since air has to move thru such a long runner tract

 

With a lot of personal experience with the long tube TPI, and various versions for ported and aftermarket components, my feeling is that you definitely need to pick a priority. Looks or performance. I love the long tubes, but I was never happy with the amount of time and effort vs. performance that I was able to see. If you like the looks of the FIRST system, it's a no brainer. Personally I DO NOT. I think it looks too big, and almost silly. But that's just an appearance opinion. It's proven to be a performer, and if you like the looks, then that's the way I'd go if I were you.

 

I know that the long tubes are not going to provide the BEST possible performance. I’m okay with sacrificing some of the performance to keep the car looking “date correct”. The FIRST injection sounds like a great system and has some impressive numbers. It’s just not the system I wanted for the car.

I’m sure tons of people will be shaking their heads in disgust with me but I based all my parts selection off of the maximum flow I could get from my AS&M runners and extrude honed oem intake and plenum.
That number came to 260cfm and that, at least on paper, seems like enough to make for a decent performing car when mated with well matched heads, cam, etc… It is after all just a weekend driver and auto cross car, not a drag car.

 

I am confused by how much variation there is in performance results with a TPI engine. I have had numerous individuals say that they perform best with small cam and small heads to maximize airflow “velocity”.
Some report very disappointing results after extensive mods and others are claiming amazing results with what appears to be a more “mild” build. Are all these various results a product of poorly matched components maybe? I even had one individual say that it’s a total waste to change from factory heads on a TPI car because the original heads flowed more than the TPI could provide. Some may hate the TPI for one reason or another. I like it and still think that when modified properly and paired with the right components it will perform very well.
Now I just have to find those components!!!!!
Thanks again to all for the input!

 

I would expect that those that built their engines, and were disappointed, were either expecting to much for what they used, had mis-matched parts, or a combination of the two. I only did minor mods to my Firebird, and I LOVED driving that car. My health just got the point that I couldn't get out of it any more.

 

I’ve enjoyed driving my Z for over 26 years now and hoping for 26 more! 🤞
I love the way the TPI feels. I’ve had faster cars but still enjoy my TPI. My dream would be 400hp and around 475lb of tq. and a 6 speed conversion if/when my 700r4 breaks.
I am a realist and would be really happy if I made it to 350hp and 425lb of tq. and with my luck the trans will outlive me…
Appreciate any suggestions as long as it involves keeping my long tube setup with my AS&M runners.
Thanks again for all the replies, I’ve enjoyed the input!