Seeking advice on a 383 SBC build

[Yinzcity]

Hey folks,

Hoping for some input on a 383 build I'm putting together before I start ordering parts and getting the machining done. This will be going in an 84 corvette, manual trans, 3.45 rear, probably about 3200 lbs when its finished. Its a nice weather car, almost exclusively street driving. Im not out to win any events with it, if I ever do take it to autoX/Drag, it would be for fun, not to be competitive. I don't plan on spinning it above 6000. Running Terminator X Stealth EFI.

I'm starting with a O.E. roller block from a ZZ4 crate engine, 1 piece rear main seal, bored 30 over. Deck height is currently about 9.028" but I do plan on taking some off that.
AFR 195 Street heads, 65cc chamber
3.75 forged Scat crank
6" Scat pro series I beam rods

Playing with numbers in Desktop Dyno and reading the info on the forum tells me I should be looking at a cam with a 224/230 or 230/236 duration to end up with peak power around 5500 RPM and have a nice flat torque curve. I'm looking at the XR276HR or XR282HR cams as possible examples.

Where I run in to issues is with piston choice. With a 0 deck and 0.040" gasket for good quench (or piston slightly in the hole and a thinner gasket), I either get 11:1 compression with a flat top piston or 9.7:1 with the smallest reverse dome I can find (16cc). Looking at dynamic compression ratios, 11:1 static needs a bigger duration cam than I want to keep the DCR in the safe range for pump 93 gas. Bigger duration, like an XR288HR, looks like it would hurt the performance in the RPM range where this engine will probably spend most of its time.
Since this is a street build, my gut tells me that 9.7:1 is the safer choice here. I'd love to find a 12cc reverse dome piston, but seems like Probe was the only off the shelf option and they are out of business.

So, is my thinking correct here? sacrifice a bit of compression to be able to run a shorter duration and more street friendly cam?
And a related question, I'm looking at forged components for future proofing the engine if nothing else, but is that complete overkill for what I am trying to accomplish? Would it be better to go with hypereutectic pistons and a Scat 9000 crank?

Thanks!

[prairiehotrodder]

I've used a few sets of the mahle powerpack pistons and they have worked well for me at a reasonable price. I think a scat 9000 crank would work great for what you are trying to do.

[nwticerider]

wiseco has some d cup pistons to get the compression down,
there may be a few other that use the d cup to keep a good quench and lower compression.

[F-BIRD'88]

Kb hyper piston KB197 12 cc d cup.
Just right with 65 cc heads and 92 octane.
10.17:1 on a O decked block. .030 over 383

[F-BIRD'88]

Another solution is to use a -7 cc flat top piston and only cut the block decks so the piston sits .010" below deck
(this will allow you another few cleanup cuts on future rebuilds.. Then with this and a .038" gasket and AFR 65 cc chamber heads your CR will be 10.49:1.

I like to keep these builds 10.50:1 for premimun pump gas street strip stuff.. I recommend you do too.
It will run like a champ., reliabily.
Before you rush out to buy that Comp cam
consult with Mike Jones (CamKing) here.
See what Hyd Roller he has for your 383 Vette build.

Note: I have over 10 years on the KB hypers and GM 400 cast crank in my 406 SBC. I may even supercharge this one one day.

[Bill Chase]

Speedpro h859cp30 has a 12 cc dish with valve reliefs. Zero decked with a 5.7 rod and 64cc head and felpro 1003 (.041) comes out just shy of 10.5:1. 5/64 rings but pretty cheap. For a low rpm engine like you are describing they would work. Less than $200 a set with rings and pins. Blueprint uses them in their base 420 hp 385 engines. Far from the best, but the fact they warranty these engines for three years or 30,000 miles says they'll take some abuse. Very similar crown to the 97-2001 l31 stock pistons. If tuned right they should take some abuse.

[Yinzcity]

Thanks for the recommendations guys, the KB hypers at 12cc look promising. One followup question, I'm guessing for my application, 5.7" vs 6" rods really won't make much of a difference?

[dfarr67]

I regret not going with the competition option on the heads. AFR oversold me on the springs- just get what you need and don't over spring it. Look into the ST line of oil pumps.

[RevTheory]

Can anyone comment on the HP potential of an 880 block along with the shorter cylinder walls with regards to a 3.75 inch crank and either 5.7 or 6 inch rods?

Anything to be cautious of?

[Clemson327]

I’m running a Howards cam that’s right between those two Comp cams at 227/233 @.050 with .560 lift (.600 w/1.6 rockers) and the same duration at .200 as the 282hr at 151/157. It would be another good option if you don’t want to go the custom cam route and is part number 180525 for an OE roller block. If you want a custom cam to know you’re getting something that matches your expectations, I’ll second the Mike Jones recommendation.

I’m running it with 10.5:1 compression with a set of AFR 195s milled to 70cc, and I agree with the others that 10.5 is a good target for a cam in that range with your setup.

[MELWAY]

If you can find someone with a piston vice or jig for lathe
Get a flat top and machine a shallow dish
Or contact Racetec pistons and they will be able to adjust an Autotec shelf piston to the exact cc dish you want
I would stay away from hyper pistons

[Orr89rocz]

Since this is a street build, my gut tells me that 9.7:1 is the safer choice here. I'd love to find a 12cc reverse dome piston, but seems like Probe was the only off the shelf option and they are out of business.

Do that with a mild shave on the heads to get 10:1. I dont think it be a big difference between 9.7 and 10.5 with the intake and cam range you are considering

Keep it simple. With a stick i’d stay with the milder 224 deg cams. Easier to tune and more drivable

[BadSS]

Icon makes a reasonably priced 4032 alloy for 6" rod with 10cc flat-top using 1/16-1/16-3/16 rings in their FHR series (IC9961-030).
https://www.cnc-motorsports.com/icon...ore-4-030.html

64cc heads, Felpro 1003 (4.166/.041) head gasket, zero deck yields 10.43:1

[BadSS]

Thanks for the recommendations guys, the KB hypers at 12cc look promising. One followup question, I'm guessing for my application, 5.7" vs 6" rods really won't make much of a difference?

Typically the 6" piston/rod combo will be lighter when using the same brand/series 5.7" pistons/rods. I remember studying an article that Big Joe wrote in the late 80's or early 90's (IIRC) comparing 5.7 and 6" rods in a 406. I've since built a number of both piston/rod combos, more 406s than 383s, and it seems to me that the 5.7" rod combo makes FRACTIONALLY better lower end and the 6" rod combo makes FRACTIONALLY better top end - just as that article showed. I prefer the longer rod combo as I've found it seems I can drop a couple degrees duration with the 6" rod combo and make similar power curves while pulling a little more vacuum, which may or may not be that important to you.

[rebelyell]

>FYI: GM's OE 383 series all use 880 block AND those have a 3.800" stroke ... piston pulled 0.025" into farther into liner than 3.750" stroke.
>880's shorter liners: suggest run the 6" rod: that'll keep more of the skirt in the liner. AND 6" rod motor typically balances w/ less Mallory/Tungsten.
>Suggest steer clear of KB hypers: those typically have top ring much closer to piston crown ... less forgiving (catastrophe) if/when there's any detonation.
>For street performance, Suggest piston w/ forged alloy 4032; MANY good manufacturers offer 4032.
>Chose a specific piston (thus KNOWING compression height) BEFORE speculating about deck height.
>Quench/Squish IS important. A Target Nominal total quench/squish 0.040" will help mitigate detonation/ping/spark knock.
>Take only as much off the deck as will level & square it WHILE achieving nominal quench; calculate with the THINNEST gasket that will achieve nominal quench. In future (if deck becomes damaged and requires subsequent decking) you'll have the meat left to deck again, AND at that time you'll also have the option of a thicker gasket.
>Gage Repeatability & Reproducibility (GR&R): Unless you have both really good gaging and gage skills; trust critical measurement to your local auto machine shop. FWIW, there's usually a bit of error in each measurement; sometimes more than others. When you compound the shop's error w/ your error; that can lead to a larger error. Once machined, that larger error may or may not be so easily corrected. Pay the man.