whats the difference

[Holy Roller]

I have 383 that was apart when i bought it. It has 516 high compression heads, a four barrel intake and regular exhaust manifolds, I'm not sure about the cam. what difference does the high compression heads make? The date on the engine is 65/66 I know it's not a HP but just wanted to see what the differences are. Thank you.

 

[Jim Lusk]

No such thing as "high compression heads" in the Mopar world, although those would give higher compression on a LATER short block. In any given year, Chrysler set compression by the use of different pistons. If that is an original four-barrel motor, it will have higher compression pistons than that year two-barrel motor.

There's no great value in that motor (but it's worth more than scrap), but it's still a great starting point for a build.

 

[AJ/FormS]

Stroke it.

 

[Holy Roller]

Thank you for the info, right now the block is bored 30 over. I know that would raise the compression but I was told that I would have to have at least 92cc's. Or I would fry the pistons at around 5500 RPM's. The only thing I would have to to stroke it is change the rods to 440 rods..right, the 383 crank should work or do I have to change both?

 

[d55dave]

To stroke it you need to increase the stroke of the crankshaft, which changes how far the piston travels therefore increasing displacement. So yes, you need a different crankshaft.

The early (67 and prior?) Big block heads are closed chamber and yield higher compression ratios over the later open chamber heads.

 

[AJ/FormS]

"I was told that I would have to have at least 92cc's. Or I would fry the pistons at around 5500 RPM's."
I think somebody is feeding you misinformation.

 

[zac_F71]

440 source makes a couple bolt in stroker kits - 438cu in, and 496cu in. - if on a budget you could use a forged 440 crank and rods, then custom and I mean custom pistons -


My next low deck build will be a 438 - stock forged 440 crank, Eagle H beams w/ Chevy pin, 440 source dished pistons (uses a chevy pin) built for 15psi or so..

 

[Holy Roller]

THANK YOU for all the information, what about changing the size of the exhaust valves on my 516 heads, would that help me any?

 

[496 polara]

Yes.Installing the later 1.74 exhaust valves and opening the bowls up to them will help some.If you plan on keeping the heads and using them it is a worthwhile performance upgrade.On a stock 383 with factory intake/exhaust manifolds and factory cam....a lot of money for little gain.

 

[Holy Roller]

Ok, if I use the 1.74 valves on the 516 heads, and use a thumper cam with the springs abd rockers and a aftermarket intake, headers ect. Would the valve swap still work? Thank you everybody for the advise and good information.