383 Rebuild - New Piston Suggestions

[1 Wild R/T]

Not to sure this is true without qualifying which heads.

Okay.. With stock heads... Be it 915's /906's /516's /452's /346's.... Yes a 72cc aftermarket head will get you there.. A 516 might get you close... But forget any 68 & newer head & the 67 915 would need to be milled quite a bit...

 

[BSB67]

Maybe I’m confused on where the conversation has gone. The IC687 is an off the shelf piston. 9.5:1 with 90cc heads, 11:1 with 75cc heads. Zero deck the piston, which will require about a 0.020” cut on the deck

 

[RemCharger]

I'll be working with my old 383 soon here, I milled 516s .060 with a steel shim, iirc about 60 70 in the hole. This was 25 yrs ago. But I will have to cc the heads and see what was really going on.
I'd calculated 10:1 but we'll see. Good thread

 

[1 Wild R/T]

The IC687 is kinda the new kid on the block & a good choice if running any of the open chamber heads, but it it a domed piston, which honestly on a 383 that's what you need.. But domed pistons can have negative impact on combustion flame travel...

 

[RemCharger]

The IC687 is kinda the new kid on the block & a good choice if running any of the open chamber heads, but it it a domed piston, which honestly on a 383 that's what you need.. But domed pistons can have negative impact on combustion flame travel...

For sure they do. And the 383 dome is higher than a 440. 41-42 degree on a race compression 383 and up to 45 on the eighth mile.

 

[BSB67]

Before the 2293/2295 pistons, TRW/SppedPro had pistons for both the 383 and 440 with +0.4” dome. Perfect, no, but guys with wheels up cars ran the all the time. I ran a 0.180” dome in my 383. What a beautiful thing.

If there is any measurable disadvantage to the iC687’s 0.146” dome, it’s meaningless compared to the compression advantage.

 

[33 IMP]

Holy smokes, that was a lot of information to process. Thank you to everyone who has replied so far!
To answer a couple of the questions so far:
Yes, the block will be decked, but I don't know the final number they'll need to shave off just yet.
The heads I'm looking at, assuming they'll ever be available, appears to have an 84cc combustion chamber. So I'm assuming that translates to a 8.8 CR based on the pistons I shared?
@HawkRod thanks for the explaining the materials. I had seen a lot of terms thrown around and hadn't brushed up on them yet.
@65CopCar (or anyone else) what is considered a "useable" compression? Factory CR was 9.2 for the 2bbl 383, right?

Imo, it depends on what quality fuel is available, and what grade you want to run.
Some parts of the country have non-alcohol available, some have 93 octane pump gas available.
In my part of california (short of $12/gal race gas) the best available anywhere is 91, with at least 10% alcohol (an actual 5 points of octane less than was available when Mopar was building 9-10.5 cr engines)
For me, if I'm making an engine to run on 87, mid eights cr is the target. For a 91 garbage-gas engine, I'd shoot for 9.5. For sure, nothing above that for a mild streetcar rebuild.

 

[gtxrt]

is there a reason why no one wants to order custom pistons ? for 850.00 you can get exactly what you need. seems like everyone is happy getting inferior trw, kb or icn pistons and then decking, milling and trying to find a head gasket that might work.

 

[33 IMP]

is there a reason why no one wants to order custom pistons ? for 850.00 you can get exactly what you need. seems like everyone is happy getting inferior trw, kb or icn pistons and then decking, milling and trying to find a head gasket that might work.

For a 413, or a 426 wedge, I would assume custom pistons would be necessary. Imo, a 383 shouldn't need custom pistons...... but if that's the direction the op wants to go.......


If I was doing a 383, it would end up at 489-496.

 

[BSB67]

For me, if I'm making an engine to run on 87, mid eights cr is the target. For a 91 garbage-gas engine, I'd shoot for 9.5. For sure, nothing above that for a mild streetcar rebuild.

For an iron head? Or aluminum?

 

[Kern Dog]

And for an iron head 383, the 915 head and Speed Pro 2315 piston is a great match, with a reasonable street cam.

That's life with a 383.. The combustion chambers of Mopar BB heads are suited for a RB engine, they are to large to achieve a decent C/R with a 383... So either you work with what you have or you accept what the market sells... There are no off the shelf pistons that will get you close to a true 9.5-10 to 1 C/R... A few builders have designed custom pistons with enough C/H & proper valve notches & tried to market them but not enough people buy them to justify the cost...

For years the Speed Pro 2315 piston was the only real option, but it has no valve notches so you have to with be careful with cam selection or machine notches... Machining notches will lower the C/R but nothing like the huge trench across the top of the KB pistons which you can see just above in post 35....

The other option is domed pistons but that can create it's own can of worms...

When I built the 383 for my Jigsaw Charger, I had the decks milled to reduce deck clearance. I asked for .010, I ended with .009. Using a .039 head gasket, I came in around 9.2 to 1. The heads ( #346) had been milled and cc'd at 86. I've ran it with 36 degrees of timing with 89 and 91 octane and it hasn't knocked. I have a MP 280/474 cam, nothing radical. It runs okay but is not a screamer.

 

[gtxrt]

A few builders have designed custom pistons with enough C/H & proper valve notches & tried to market them but not enough people buy them to justify the cost...

the cost is 850.00 for a custom made piston for a 383 that is a justified cost.

 

[33 IMP]

For an iron head? Or aluminum?

If I'm building an aluminum head engine for me, it's likely to be on the more strip side of street/strip. It'd have a too-big cam for a daily, and probably around 11-11 1/2, and run on pump gas with a little av-gas sweetener.
I don't think that's what the o.p. wants.
( been high nines, very low tens, with just such a n/a small block. [Granted, in a very light car!])

 

[BSB67]

If I'm building an aluminum head engine for me, it's likely to be on the more strip side of street/strip. It'd have a too-big cam for a daily, and probably around 11-11 1/2, and run on pump gas with a little av-gas sweetener.
I don't think that's what the o.p. wants.
( been high nines, very low tens, with just such a n/a small block. [Granted, in a very light car!])

Okay. I agree. I just wanted you to qualify your statement for the OP so there is no confusion.

He’s planning aluminum heads. I’m sure he’d be okay at 10:1 - 10.2:1 on 91 octane.

I’m at 10.8:1 at 1,000 ft elevation with a heavy car, tall gear, and fairly small cam with 93 octane.

 

[33 IMP]

Okay. I agree. I just wanted you to qualify your statement for the OP so there is no confusion.

He’s planning aluminum heads. I’m sure he’d be okay at 10:1 - 10.2:1 on 91 octane.

I’m at 10.8:1 at 1,000 ft elevation with a heavy car, tall gear, and fairly small cam with 93 octane.

I understand he's thinking of the closed chamber rpm head. (Or was it the open? I don't think I'd ever choose the open chamber heads, unless I already had reverse dome quench pistons.)
I haven't done the calcs.
What would cr be with zero deck flattops and the heads he wants to use?

 

[Kern Dog]

What would cr be with zero deck flattops and the heads he wants to use?

Boom.

 

[gtxrt]

9.2 compression with aluminum heads will like having about 8.4 compression with iron heads. need a 11 cc dome will give you 10.25 compression just right for the alum heads.

 

[33 IMP]

KernDogs calculations show 88cc for the heads. The open rpms are a few cc less than that (84), so cr should be a little bit higher.
The closed chamber rpms are 75cc, so probably a full ratio higher, (if not more).
I don't know comb ch size of stealth , trick flow, speedmaster, or pro-max heads, tho that info should be easy to find.

 

[1 Wild R/T]

KernDogs calculations show 88cc for the heads. The open rpms are a few cc less than that (84), so cr should be a little bit higher.
The closed chamber rpms are 75cc, so probably a full ratio higher, (if not more).
I don't know comb ch size of stealth , trick flow, speedmaster, or pro-max heads, tho that info should be easy to find.

Actually the 84cc heads are the original closed chamber heads, the 88cc heads are the open chamber heads & the 75cc heads are what Edelbrock released later as their EZ street heads...

 

[gtxrt]

75 cc heads would give you 10.43 compression that would work with alum heads