They are claiming over 450hp for a 383 using stock ported heads, a pretty mild cam, and a heavily worked-over TPI intake. More importantly, they are claiming a near 200lb/ft improvement in peak torque over a stock L98! I am a skeptic. Note that the stock L98 with just a mild hydraulic cam was making roughly 75hp more than stock about 60lb/ft more than the stock peak torque. Something isn't adding up there. They do casually mention that it was dynoed with no accessories or intake, and probably not much of exhaust, so that's already a big difference between their actual number vs what you'll get with a real installation. But even still, if you look at their graph of torque, you see the expected drop-off with a torque peak centered at 4000rpm. If you used a MR-style intake you'd carry a flat torque curve much higher than that, and unlock a lot more power for free.


I think with the heads and cams you are considering, you will have a real chance to equal those numbers, though. With that said, I still don't understand why anyone would pay good money to use an intake with such limitations. But it's not my money.

 

EDIT: scratch all of what I wrote here, and see my post below. Sorry for the confusion. I need to get more sleep!

 

Here is my 355 with a Miniram intake on its baseline. Where did I lose torque ??
You want a flat torque curve on a V8 powered sports car gentleman. Not one that peaks up at 4000PM and drops like a rock. That's for pulling stumps with pick up trucks.

 

I ran a 383 for years on the street and at the track with a Superram and 30 lb injectors. The car ran mid to low 11's and the injectors were matched well. I am now running a 406 with a miniram with 36 lb injectors which runs well. My thought is that 30 lb injectors will work well for your situation.

 

Awesome. Exactly what I'm looking for. What all did you have in it parts-wise (heads, exhaust, crank/rods/pistons, etc)?

Also, what was the rest of that setup. I know engine performance is only part of the story when it comes to E.T.'s...

 

I know, As far as the numbers go, I take everything with a grain of salt. Still, from my perspective it's promising...

 

For the 383, I ran ported Holley 20 degree heads, 10.5 compression, nitrided cast 400 crank, Keith Black Hypereutectic pistons, Crane hydraulic roller 220-230 .600 lift, 1 3/4" headers. 3.73 rear, trapped 122 mph (have to look that up) @ 6200 rpm. I ran this combination for years and the short block still lives today in a C3. My 406 is a World Products block with forged everything and the same heads.

 

https://www.corvetteforum.com/forums...-manifold.html

Some of my readings regarding the FIRST Fuel Injections TPI manifold...

 

I'm an idiot. Sorry for my misinformation about my injectors in post #22. My LT4 396 has 38lb Lucas injectors. The engine has heavily ported stock heads, the best flow numbers I've seen for such things: almost identical to the advertised flow rates for an AFR Street 210cc head. The cam is Comp Cams XFI 3014 intake (218@.050 and .570") and 3015 exhaust (224@.050 and .573"), so small duration but serious ramp rates, with 108* LSA. I'm using a ported LT4 intake. I want to say it has around 10.5:1 CR. 1-3/4" long tube headers.

Never drag raced it or dynoed it with this cam. It's a very mid-rangey engine, great for autocrossing and street driving, not at all peaky. I know it will pull a stock C6 Z06 from a roll, and it's about 100lbs heavier, so one would think it probably has at least as much power as a stock LS7. FWIW, the previous owner had a considerably bigger cam in it at one time, so the injectors were sized for that.

 

Sooo... I should be good on 30 lb injectors, but sounds like 36's would work OK for my power range as well. (Ballpark, more research yet to be done...)
Now, since e85 is plentiful and fairly cheap in my area, and it seems to be a fairly easy conversion if I'm using the FAST EZ-EFI, would that require 36's or maybe higher? I seem to remember reading somewhere that you have to push more fuel through your system, but can run higher compression if you're running e85...
Thoughts?

 

I have to agree, with what some others have said about using a different style intake.

With a 383 you won't be lacking in low end torque, so why not use a super ram or edelbrock pro-flow XFI intake, etc, etc to unlock the higher end power?

 

Well, at this point with so many people telling me not to, I have something to prove (and don't take offense folks, that's just my personality... )
Basically, the manifold I'm looking at has runners that are large enough diameter to overcome some of the shortcomings of the length. From their website: "This manifold has been able to support in excess of 650 hp on numerous applications. So along with he great torque numbers that this manifold can generate, it has the ability to move large volumes of air to generate high horse power numbers on specific applications."
So the RPM range is a bit lower (although it still pulls to 6k+...)? So select the appropriate stall speed and rear end...
And if I'm really honest, as much as it might sound cliche, it's as much about the journey as the result. If it was really all about speed, I'd just slap a bottle of NOS on it, or do an LS swap, or better yet I'd sell the 87 and buy a c5 and start from there with my build. But I now love my c4 too much to do that, and just want to make it as good as it can be while staying somewhat faithful to the original concept...

I REALLY do appreciate all the input, and will continue to ask questions as I go if y'all are OK with that.

 

I'm with you on the 383 man, think I'm gonna do it also. I'm looking for a parking lot creeper that turns heads, mine probably wont ever see the strip or break 90 mph for that matter, just want a dependable machine that will always crank, and sound like a 60s muscle car beast. may even retrofit a set of midyear sidepipes and throw some torq wheels on, just gotta figure out how to make the tpi run that beast, is the fast ecm the way to go?

 

Yeah, pretty much what I'm thinking, haha. Although I've run mine to 130mph stock, so I'll have to see what it'll do eventually...
I'm looking at the fast ECM because it's self-learning and allows digital timing control. From what I understand you punch in a few specs, and then just drive it and it fine-tunes as you go. You can use the stock system, but you have to find someone to burn chips with the right settings, and it sounds like that's a time consuming trial-and-error process. So I think that will be the first thing I do, is get the computer into the 21st century...
Biggest problem with the TPI is getting enough air through it to feed the beast, especially a 383. Hence looking at the FIRST Fuel Injections manifold. The runners start out at 1.75" inside diameter vs 1.5" for the stock TPI, And can be ported to over 1.9".

 

The problem with the TPI intake isn't the diameter of the runners - it's the resonant frequency of the long tubes. No matter how large a cross section you have, there is a resonant frequency where those runners effectively stop flowing. It's the price you pay for using the resonance to pack extra air into the cylinders at a lower rpm. When GM designed these engines, they had to use teeny cams, very restrictive ports, and other emissions-related restrictions. The intake-imposed rpm cap didn't matter because the engines were never going to be any good over 5000rpm with any intake. And they could use the resonance to build some power under the curve. But if you're going to spend the money to buy AFR heads and an aftermarket cam, it makes absolutely no sense to handicap it in the exact same rpm range where those nice parts are going to be working the most magic.

It's not a matter of someone saying you can't do it. I already stipulated that you can probably make at least your minimum number even with the TPI. It's about the fact that if you spend all the money to do it that way, you'll have left 50hp (no exaggeration) on the table because you spent your money on an intake that hobbled the heads and cam you bought. So you may just barely hit your goals, but what you can't do is make the same power with the TPI as with a short-runner intake. And the TPI can't make up for that with "torque." That's not how any of this works. And this is not an opinion for someone to prove wrong, it's a fact born out by physics and lots of empirical data.

I don't know where you are located, but if you're anywhere near the St. Louis area you are welcome to go for a ride and see what a 396 with a ported LT4 intake, a conservative cam (very similar in all but LSA to the XFI268 you mentioned), and good-flowing heads feels like in street driving or autocrossing. You'll find a very wide powerband (2000-6000rpm) with extreme flexibility and lots of power. It's ideal for the kind of use you're describing.

 

I'm up in Michigan, so thanks for the offer but that won't really work for me.

I don't know. I'm just at the point right now where I won't be happy with the build if I don't try the TPI setup. Considering the extended time frame I'm looking at, maybe I'll change my mind before I get to it. Or I might try it, and change my mind then. Or it might suit my tastes and I'll leave it at that. Ultimately, being satisfied with what you build is what it's all about in the end, is it not?

I appreciate the effort you've put in to convince me otherwise, but my mind is made up for now...

 

Take my thoughts with a grain of salt but....those parts sound nice but the $$$ adds up quick. I bet you could still hit that HP mark or close to it if you went with something like a pair of GM Fastburn heads. You can literally find a great set for half the cost of the AFR eliminators if you keep an eye out.

Took a quick look at the Melrose headers and they're around $600 give or take a few bucks. After you pay shipping it'll be $600+.....chances are they won't just drop in. Depends on how you feel about denting and scratching up a new $600 pair of headers. A pair of Hooker Headers or even a used set with a fresh coat of paint and keep $400+ in your pocket. Keep the exhaust 2-1/2'' all the way through, cheaper and 3'' just makes it louder, not faster, makes it heavier, but makes your wallet lighter. Do yourself a favor and go with headers that have flanges for bolts, avoid slip fit connections, you'll never stop them from leaking.

Go any TPI variant if you want big torque but expect to pay $$$ if you want the torque and the high rpm. Some guys run ported Super Rams that let them rev it out past 6K rpm. To get a Super Ram is $800-$1000, without a throttle body or injectors. Personally, I would not do the FIRST as people are going to want a fortune for them and you can pull more rpm band for less with other intakes.

A miniram is normally $1000+ with everything minus TB and injecors. For comparison, there's a Holley Stealth Ram on Ebay right now for $590 complete and ready to drop on WITH a throttle body on it. If you can stand making a bump on your stock hood to accommodate the uncut Stealth Ram, that's a great buy in but there are guys that cut and reweld them so they fit under a stock hood. Never hear a bad thing about them.

Just some thoughts, not saying cut corners but if you can hit the same mark just as reliably with "lesser" parts, and pocket thousands of dollars that can go towards other aspects of the project like towards....oh I don't know, a sweet Tremec Magnum 6 speed...you get the idea. But if you insist on going dollars out, do not spend AFR head money on a 383. Cough up the extra money for a forged crank that will let you do a 396 to put those AFRs on, your 500 horsepower concerns will be solved but depends on how patient you can be as the years go by. Good luck either way.

 

I have a complete Mini Ram with 30 pph injectors left over from my previous motor. PM if anyone interested