Pokky

Looking to get 400 crank hp out of my 1990 corvette. What do I all need to do? I know the intake is restrictive and the exhaust is very restrictive. How are the stock heads? My thought would be to intake,heads, cam, headers and 3 inch exhaust. all with a good tune. Will this get me 400? or don't I need to go that far? I would think what it should be very documented, if it is, please point me to it.

MatthewMiller

Yes, heads, cam, intake, and exhaust can easily get you to 400 crank hp. Something like AFR 195 (or maybe even the 180) plus a Miniram intake and Comp Cams XFI268 should get you where you want to be. Depending on what transmission and rear axle gears you have now, you might end up wanting a steeper rear gear ratio and/or looser torque converter to match your new powerband. For exhaust, honestly you could do a good 2.5" setup and not lose any power at all for the power levels we're talking about. The tune will be the hardest part, because you'll have to get chips burned and test/retest. I'm not sure who is available to do that work these days.

cv67

pcm for less and Tom Wong whos a memberhere still do them.
Both are good and reasonable.
You dont need a 3" exhaust all its going to do is drone like hell.
2.5 will give you more velocity thats what you want. No need for a special crossover either thats up to you

Phobos84

In today's day in age the cheapest (and probably best) way is to LS swap it. Any iron block 5.3L with 243 factory heads and an LS6 intake from ebay and a Sloppy Stage 2 cam will put 400 hp to the wheels all day. And you will have the motor for under $1k. The only expensive part is if you want to use a Holley EFI or if you want to keep the factory transmission and then you need a custom converter. But the easy way to do it is to swap in a 4L60e with the LS and then go Holley to run the show. Total build cost with a Holley and a good used 4L60e could be done for under $2k.

Take a look at my build thread. I'm shooting for over 600 hp to the wheels. My total build cost for the motor (without intake) is way under $2k https://www.corvetteforum.com/forums...d-v-2-0-a.html

vader86

400 crank HP is easy, so long as you're fine with swapping the TPI intake off it for something else.

You must have longtube headers, either remove the cat or put in a high flow modern unit, and change out the stock catback. 2.5" all the way is fine.

The rest is intake side. Your '113 heads top out at about 350ish, so you can port them, or go with aftermarket AFR 195s. There are certainly other heads that you can try but 185-195 is the port size I'd go with.

You then must decide if you want to keep it torquey, in which case you can try to find a used Accel SuperRam (no longer made), or you want it to rev, in which case you're forced to go the TPiS MiniRam route. Either choice entails a different cam choice, but something around 220-230ish on int/exh @050". Either choice also entails the recommendations for the transmission and rear gearing. Automatics need a different TC to take advantage of either.

Then after that is done, you must have a custom chip done or it just won't run right. Let the chip tuner have input on the injector size, but you can probably do it anywhere around 30lb/hr injectors.

MatthewMiller

I agree with the sizing requirements, but not the reason. After the collector section there is no tuning taking place: velocity doesn't matter at all. The only thing that matters is backpressure: the less the better, period. It's just that a 2.5" exhaust with good mufflers and (if desired) cats is plenty big enough to not cost any power at all with a 400chp goal, it's cheaper, and it's easier to package.

Pokky

Thanks to all, this is what I needed to know. I didn't mention that is a 1990 6 speed car, I drive back roads and vary little freeway. So I'm also working on how much hp I need. I love the LS engines, but I don't think I need it. I thinking a mini ram will work. the tuning is the next big issue for me. Is it just easier to simply go to a aftermarket ECU? I did burning back in the day doing testing at briggs and statton. that was on a dyno, and it was a pain, and what fun when the changes didn't take.

cv67

not sure about that Matt my car runs 10x better with a well thought out full exhaust vs just open headers
that velocity in the exhaust matters imo

vader86

I would not say easier, just different. Sometimes you lose the functionality of the dash, and I wouldn't bother with it if you did lose that.

if you intend do to it yourself, it can be learned, it would be steep at the beginning and you'll get discouraged. Better to send the combination specs off to a tuner and pay the $500ish you'll get charged, and then buy the tuning software yourself and perfect it at home. Ideally they'd tune it on a dyno to get the WOT, but the car must be driven around and calibrated for back road driving.

MatthewMiller

Then something is broken in the tuning or sensors in your car. Every car I've ever seen dyno or make a drag strip run with and without full exhaust has been faster without it. Some would benefit from short collector extensions (tuning collector volume does make a difference), but nothing else. Literally no race series has entrants running any more exhaust system than is mandated. This includes all circle-track cars I know of, all IRL cars (the last Indy cars that were n/a AFAIK), all n/a F1 cars, and all motorcycle racing classes. Top Fuel dragsters with 11,000hp and invidiual exhaust primaries don't even have collectors!

If you think about it, you can understand why this absolutely has to be. Individual primary tuning occurs in two ways. The length affects the RPM at which the resonance creates a vacuum at the exhaust valve to pull out exhaust, and the diameter affects the speed/inertia and therefore the magnitude of this effect. At our usual RPMs, there is no resonant tuning happening with primary lengths, either, because the required lengths would be longer than the car! The longer header usually just helps prevent one primary affect its neighbor that's only 90-degrees apart in the firing order (in a flat-plane engine they are all 180-deg apart, but in our crossplane engines they are either 90 or 270 apart). But any primary tuning happens in a single-cylinder system. Once all four primaries converge into a collector (on a typical V8), one cylinder's pulse barely has any effect on the other three cylinders. You can get some positive effects sometimes with collector volume tuning, but on our crossplane V8s even that is more about minimizing backpressure than creating any increase in power. Once you're past the collector, the pulses in the exhaust system are no longer "tied" or tuned to any one cylinder anymore at all and you cannot possibly improve power with any tuning - you can only hurt it. If you happened to find a specific exhaust tubing size/shape/length/whatever that improved one cylinder's performance at a certain RPM, then it would also have an equal and opposite effect on at least one other cylinder. This even goes for two-stroke engines: tuned pipes only work when they are attached to individual cylinders, not a collected exhaust for multiple cylinders.

Tim H

That is absolutely wrong, You might as well just take the whole exhaust system off and run straight off the head exhaust ports if less is better.

MatthewMiller

Did you miss the part where I said the primary length and diameter does affect tuning? You definitely are better off with headers than without (if they're sized right), plus it's supposedly bad for exhaust valves to be exposed to cool ambient temps in sequence with hot exhaust gases (I have no idea if that's really true or not). And then there's the minor issue of needing to actually route the exhaust gases out of the engine bay and out from under the car for safety and legality. So yeah, you don't want to run without headers.

But anyway, I've laid out the case for why I'm right both in terms of how exhaust tuning actually does and doesn't work and also with the evidence that all race cars use the most minimal exhaust system past the collector(s) that they can get away with. If a full exhaust system actually improved power, don't you think that at least the GT, stock car, and touring car classes would run them?! Besides, it's not like I've developed all this research myself: you can pick up any number of books or videos that will tell you the same thing. . Notice that everything he talks about is referenced to open headers (with an extension tube to get the collector length correct), and nothing is discussed that improves the power levels of that - the only discussion is focused on not hurting the power levels of open headers. It's literally called "Zero loss...muffler systems," not "power-boosting muffler systems," because no such thing exists.

Pokky

Engine Masters TV show did a show on engine dyno runs with and without exhaust. a tune exhaust made more power than just a header. And we ran gross power runs at Briggs and Stratton, no exhaust at all. Never hurt the head or valves. Nasty sound, vibrate the dyno walls

MatthewMiller

"With and without exhaust" is not the same thing as "with and without a muffler system bolted onto the end of a properly tuned header and collector." I'm talking about the latter. Again, there is no question that a header with properly tuned collector can improve power levels over no exhaust at all. It's what comes after that (after the "termination box" in Vizard's discussion) that can only hurt power and cannot possibly increase it. In short, there is no power or "tuning" to be found in a post-collector exhaust system, and the only thing that matters is reducing backpressure to a level that doesn't hurt power.

Good to know. I always wondered if that was a myth or reality. I'm sure it sounded horrific.

Pokky

So I need to asked about the tuning, is it possible to use a newer ECU? maybe one from a 1996? I never thought about using a aftermarket ECU and losing some of the dash function. or maybe cruse control. I plan on talking with the guys in Waukesha that tuned my truck and see what they are willing to work with. I like to tweek a tune, but doing the hard part is just so much quicker to use someone that just knows what a engine wants.

auburn2

Getting the AC to work with an LS is a PITA.

MatthewMiller

The 94-95 PCMs are sort of a "pre-OBD2" and way different than yours. The 96 is similar but it's a full-on OBD2 and not particularly more desirable. But I don't think you could easily use any of these in place of your ECM. I think you'd lose communication with your CCM for starters, and I'm not even sure you'd have the correct sensors on your engine to make the PCMs happy. If you're going to try something like that, you might as well go aftermarket. However, I don't think you need to be that drastic: there's no reason your stock ECM can't have chips burned to cope with 400rwhp, but finding the person to do it will be the challenge.

Pokky

Sounds good, I think I'll go for mini ram, headers/duel exhaust and tune and see where that gets me. I think that will get me a fun back roads car. I will also be doing a brake up grade so i can slow her down repeatably for about 55 mph.

MatthewMiller

Kind of off topic now, but honestly I don't think you need to upgrade the brakes, other than to flush the fluid and use something good like Motul RB600 and get decent pads. Powerstop z26 pads front and rear will probably be all you'll ever need unless you track the car. You could replace the brake lines with somethign stiffer. If you can get the larger J55 brakes from a later C4 (unless yours already has those), that's worth spending a few hundred dollars on. Otherwise, save your money and use it for a good tune, or maybe good shocks.

eutu1984

I did my own tune on my 90 383 TPI, a bit of a steep learning curve I have some video's on YT https://www.youtube.com/playlist?lis...dktX0orGjpxz6v , another option is to send your
ecm to be updated to http://www.dynamicefi.com/