So we all know the 86 TPI engines crap out at high RPM's due to the long intake runners. Are there ways of adjusting this other than changing the intake runners? Thanks for any suggestions.

So we all know the 86 TPI engines crap out at high RPM's due to the long intake runners. Are there ways of adjusting this other than changing the intake runners? Thanks for any suggestions.

You can try porting the base. But the result is limited. The exhaust is also restrictive, those pre cats are horrible. Consider a "Y" pipe with no pre cats too.

So we all know the 86 TPI engines crap out at high RPM's due to the long intake runners. Are there ways of adjusting this other than changing the intake runners? Thanks for any suggestions.

To what extent do you want it to 'breath', and what is you budget? You can't improve the RPM range of the motor much w/o changing the LENGTH of the runners....which means an intkae swap. Then there are issues w/the rest of the package, as Injectors plus mentioned above.

So we all know the 86 TPI engines crap out at high RPM's due to the long intake runners. Are there ways of adjusting this other than changing the intake runners? Thanks for any suggestions.


If you want to twist your engine up higher, you really need to change the camshaft, cylinder heads, and the intake. All three of these stock components are the reasons your engine falls flat on it's face at about 4500 rpm.

You can try porting the base. But the result is limited. The exhaust is also restrictive, those pre cats are horrible. Consider a "Y" pipe with no pre cats too.

The benefit to porting it doesn't justify the time or expense to do it, imo. I've ported both the base and plenum. I've noticed some difference, but nothing to write home about. Definitely ditch the pre-cats. I think Summit has an exhaust kit that eliminates both pre-cats, is an H-pipe where the cat would be. All you need is the rear exhaust, the part where it comes out the rear of the cat. If you go with muffler eliminators, the whole setup is like $450.

you really need to change the camshaft, cylinder heads, and the intake. All three of these stock components are the reasons your engine falls flat on it's face at about 4500 rpm.

The main issue here is the intake itself. The cam can be improved upon for sure. The 113 aluminum heads aren't bad; their also a favorite of the late Lingenfelter in his street performance cars.

There's a dramatic difference just bolting on an Accel Super Ram, or the TPIS Miniram on an otherwise stock TPI engine over the stock manifold. I'd go with the Mini Ram, Super Rams are getting too hard to find since they've been out of production for a long time.

The benefit to porting it doesn't justify the time or expense to do it, imo. I've ported both the base and plenum. I've noticed some difference, but nothing to write home about. Definitely ditch the pre-cats. I think Summit has an exhaust kit that eliminates both pre-cats, is an H-pipe where the cat would be. All you need is the rear exhaust, the part where it comes out the rear of the cat. If you go with muffler eliminators, the whole setup is like $450.

Yeah, I don't disagree. I assumed the basis was keeping the stock parts and modifying them.

Didn't know Summit made a whole setup, that's a good idea.



The main issue here is the intake itself. The cam can be improved upon for sure. The 113 aluminum heads aren't bad; their also a favorite of the late Lingenfelter in his street performance cars.

The stock heads are good to 350-375HP in their stock form.

There's a dramatic difference just bolting on an Accel Super Ram, or the TPIS Miniram on an otherwise stock TPI engine over the stock manifold. I'd go with the Mini Ram, Super Rams are getting too hard to find since they've been out of production for a long time.

I've had both. I think the Super Ram was the better upgrade for a stock motor. When I went to the 427 I went mini ram. Car ran GREAT with the super ram.

Thanks for the input fellas. I agree with Robs1988, porting the base doesn't seem worth it. I've already got a Magnaflow exhaust on it with ceramic headers. Heads were mentioned a few times which brings up another question. I know a gentleman who used to work on the Nascar circuit, he has a set of heads off a 350 that were for a Nascar engine he said he would sell to me. I apologize I don't have an specifics on them but shooting from the hip do you think they would be a wise investment as far as my C4 is concerned?

As for the intake, I kind of knew there would be no easy solution other than the most obvious and expensive, swapping it. The TPIS mini ram is great and so is the HSR, according to an article I read that somebody posted on this forum they both put up impressive numbers.

I would have the heads checked by the machine shop of your choice first. Buying a used anything that is high perf parts is always a risky proposition.

That is an extremely good and overlooked point. :thumbsup3:

Didn't know Summit made a whole setup, that's a good idea.

I was wrong, its not Summit, its Corvette Central. Here is the link to it. Obviously if you have to pass emission test then this is a no go.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=250610392315&ssPageName=STRK:MEWAX:IT

If they are real Nascar heads they won't work w/ your tpi. They have a 18 degree valve angle & siamesed intake ports. Just do some research before you shell out money.

I deffinetly would, thats why I'm here. Thats good to know though thanks bud.

If they are real Nascar heads they won't work w/ your tpi. They have a 18 degree valve angle & siamesed intake ports. Just do some research before you shell out money.

Also with altered valve angles they may not work with your pistons. Just can't slap them on.

Why not Take advantage by of the TPI (hight torque low rpm) go after the torque not RPM buy a cam that gives higher torque at low rpms stick with flat tappet lifters they are cheaper and all thats required ,get TRW lifters( the cam must provide enough intake vacum so, not to much duration more lift). run the stock exhaust manifolds. You will Take em out of the hole and they will see your tail lights the only way they will get past you is if they have more usable HP. keep stock gearing car retains its daily driving abilites this way.