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Old 11-13-2013, 05:02 PM
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383 Chevy Turbo High Boost rebuild adivse

This be my first post here soooooo bear with me....

I have a 383 small block sitting in my k2500 right now. It is a tough little engine for what it is. Currently running stock TPI with around 400hp. However, as the title suggests, I've been looking into some boost... big boost. My goal is pretty substantial and broad, 600-800hp. And on a modest budget no less. I can get any part, its just a matter of time lol.

So here's the nitty gritty. As it sits the engine has a forged rotating assembly from Eagle. 4.03 over flat top pistons, 5.7" H beam rods, and the stroker crank. All of it forged. I know I'll need to get some dish pistons (probably) to get my compression down. Because right now, I think its around 11.8:1..... yeah. My heads are probably mostly to blame for that. They are some old twisted wedge heads from Trick Flow. Here comes a spec list for them...
combustion chamber: 64cc
intake volume: 180cc
CNC stainless 2.02i / 1.6e valves
1.25" single springs max RPM-6500
3/8top and 7/16 bottom studs
rough intake CFM at .5 lift is 229
rough exhaust CFM at .5 lift is 196
crane aluminum roller rockers
the valves are canted

Now those aren't the best heads around i'm sure, but I don't think they're trash either. Those specs are straight from Trick Flow tech support. I have a whole PDF on them. Anyway, I just don't know how these heads will breath with boost, keep them, trash them? Like upwards of 15-25lbs. So moving on to the other stuff, I have a high flow/pressure oil pump (it idles at around 40psi hot), the block is a 4 bolt 2 piece seal. So really, I'm all set on the short block I think. I plan to have it internally balanced with mallory metal. What I am curious about is cam selection, gasket types, blow through carb vs EFI throttle body.... that junk. My plan for the turbos is 2 60-65mm compressor wheels, fed by headers with at least 1 5/8 primary tubes. I think that will make my boost goals. ??? I know this is a big engine, not sure what the lag time will be like.

I know I'm going to need a high lift cam, but what about lobe separation and duration? I know that stuff can effect knock and timing. Especially in boosted engines. I just know nothing about it and how it effects it Summit has the cams sorted in little packs like 4x4, truck, street, dirt trakc, supercharged, exc..... Should I just pick a supercharged cam? i don't know :/ And as far as sealing this monster up, what are the best gaskets types for boost? I've just always used normal composite types and goo ARP fasteners. This will be my first boosted engine soooo.... yeah. My optimistic goal is like 800hp. But i realize that I may only get to like 600-700 (being a novice engine builder). I guess consider this a brain storm sorta thing. Not really sure how forums like this function. Any suggestions or criticisms are appreciated. What should I keep, what should I trash? lol

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Old 11-13-2013, 05:40 PM
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Will this be race only with race gas? Even at that, 11.8 c.r. with that much boost is a disaster waiting to happen. You're much better off dropping the c.r. down to 8:1 or even less, 7.5 wouldn't be out of the question, allowing more boost. I'm sure someone here will tell you no sweat, 11.8 or 12:1 c.r. and big boost is done all the time...take any help like that with a grain of salt, even with turbos, even using all the tweeks, intercooled, timing master, water inj.

Also, 800 hp out of an older GM block isn't a healthy recipe, not by a long shot.
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Old 11-13-2013, 05:48 PM
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Well first what type of boost? Roots blower, turbo, pro charger , screw blower what type of forced induction are u shooting for? Next what type of fuel will u run? and i wouldnt get caught up in boost numbers it takes more then boost to make good power.
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Old 11-13-2013, 06:04 PM
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Excuse my tunnle vision didnt see the turbo part lol. Twin or single turbo?
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Old 11-13-2013, 06:05 PM
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Quote:
Originally Posted by 78C10 sleeper View Post
Well first what type of boost? Roots blower, turbo, pro charger , screw blower what type of forced induction are u shooting for? Next what type of fuel will u run? and i wouldnt get caught up in boost numbers it takes more then boost to make good power.
He said twin 60/65 mm turbos.

Oops, I see you caught that.
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Old 11-13-2013, 07:04 PM
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Quote:
Originally Posted by 68NovaSS View Post
He said twin 60/65 mm turbos.

Oops, I see you caught that.
lol Yeah, I tried to be specific about as much as I could. This engine is going to be primarily strip dedicated. I might drive it around on the street every once in a while, but that would be rare. As far as CR goes, I know my 11.8 is pretty atrocious for boost. I was thinking dish pistons, but I would need -28cc dish pistons to get my CR to just 8.5:1. :/ do they even MAKE dish pistons like that? I'm trying to avoid getting new heads, but everything about them seems to scream replace.
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Old 11-13-2013, 07:25 PM
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Quote:
Originally Posted by 68NovaSS View Post
Will this be race only with race gas? Even at that, 11.8 c.r. with that much boost is a disaster waiting to happen. You're much better off dropping the c.r. down to 8:1 or even less, 7.5 wouldn't be out of the question, allowing more boost. I'm sure someone here will tell you no sweat, 11.8 or 12:1 c.r. and big boost is done all the time...take any help like that with a grain of salt, even with turbos, even using all the tweeks, intercooled, timing master, water inj.

Also, 800 hp out of an older GM block isn't a healthy recipe, not by a long shot.
I never really did think about block integrity. Mine is a 4-bolt, but the caps aren't splayed. And I can't find a main bearing cradle for the life of me, not for a 350. Summit sells blocks ready to go if that would be better...? I know my HP numbers are ridiculous, but I'm kinda just going for maximum safe power at this point :/ My local engine shop says it would be safe.... but he's a bit slow.... I know my CR is to high. But to get mine low enough, the dish in the pistons needs to be too large. Which means new heads, that I'm looking at now. Starting to think already that I might as well scrap it all. -_-
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Old 11-13-2013, 07:25 PM
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Is keep the pistons and the entire short block as it, and replace the heads instead. 200cc+ runners and 76cc chambers will help a lot. Combine that with a single properly built turbo and bigger injectors and you're done. No need for dual turbos no need to open up the short block, likely won't need more than 10-12psi of boost to hit 600hp either if you use a properly built turbo. One good single beats two half assed turbos every time.

Btw I'd plan on using e85 if it's available. Even if you need to test it before fill ups it's still much cheaper than race gas. It also allows you to drive this on the street if you so choose.



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Old 11-13-2013, 07:28 PM
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Keep the rpm low and run a healthy stall and you should be okay around 700hp. High loads at low rpm and high rpm can both kill engines.



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Old 11-13-2013, 07:36 PM
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Actually 2-bolt blocks are stronger in the webbing than GM 4-bolts. I went for billet splayed mains on my 383 blower motor, it's also a 2 piece main block from the '70's.

Being on a modest budget, build it for what you want it to do, going big boost isn't a build to skimp on.

If you go E-85 be aware it takes more than 1.5 times the volume over gas, so mileage won't be anything to brag about.
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Old 11-13-2013, 07:51 PM
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1.3X the volume. That's important to get right when choosing injectors. You could try to hit it running pump premium but that requires lower compression and you better have the tune spot on.



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Old 11-13-2013, 08:40 PM
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So far I'm thinking new heads. Maybe AFR 1120NP heads. 227cc intake runners and 75cc chamber. I can get my hands on a 2 bolt block from my brother most likely. Then it's machine work after that for the splayed caps and bore. haha this opened my narrow view quite quickly. I need to start thinking differently.
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Old 11-13-2013, 08:43 PM
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Don't waste your time on putting splayed caps on a 2 bolt block. By the time you're done machining it all a SHP block is only a little more and gives you a much much better foundation. Use what you haveor buy some real equipment.

The 227 heads will require offset rockers, ideally a shaft system. Be sure to account for that. With boost 210cc heads could easily get you to your goal and use a standard valve train.



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Old 11-13-2013, 09:10 PM
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X2 on the SHP block.
Depending on whose caps are installed and the angle of the out board bolt, you can easily wind up into the water jacket. By the time you get done prepping a factory block, you can easily have a grand invested in a 40 year old block that may have came in your Grandmas station wagon.

It sounds like you have a pretty good piece right now.
Sell it and help finance your new build.

A new set of heads with a bigger runner and larger combustion chamber will be a good thing as well.

Any kind of boost on gasoline leaves a very narrow tuning window.
E85 for sure. If this is strip only you may want to look into straight methanol.
On straight alcohol you can run a much higher CR.

sounds like a fun project.
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Old 11-13-2013, 09:23 PM
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I have a set of Elemanators on my 388 and i used stud mount rockers and stud gurdles. Afr says they flow around 325 i belive. But they are pricey but i did use titanium retainers ect witch drove the price up.
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