Bottom End

[larrysupersport]

Ok, here's the deal.
I have a 68 Coronet 440 it has the low compression 383 with the 2 bbl carb. I have purchased the Eddlebrock RPM heads, and have the block sitting on a stand right now. My question is this. How do I bring the compression up to the high compression 383's IE Superbee/Roadrunner etc.
Do I just change the Pistons? (which would be the best choice)
Or do I have to change the rods as well?

I don't have a bottomless wallet but I don't want to have to mess with the bottom end again for a long time once it goes back in the car.

Thanks

 

[67 coronet]

the best way is to change the pistons and do a good rebuild.you dont need to change your rods and you can run a cast or hyperteknic(spelling?) piston as long as you are not trying to build big power,or run nitros.that should save a bunch of money,and still get you a stable botom end.

 

[70rr-brian]

Head gasket thickness is an additional consideration for increasing or decreasing compression. The thicker the gasket the lower the compression.

 

[Sublime440]

The "high compression" 383's you're referring to are in reality more like 9.2-9.5:1. The best pistons I've found, which the aftermarket sucks for 383's, are the Speed Pro 2315's. They have a taller compression height and are a flat top design with no valve reliefs. I had .010" cut off my block to get close to zero deck, I think it spec'd within .010". With the Stealth heads (closed 80cc chamber) and .039" head gaskets my 383 has ~9.7:1 CR. Going much more will either require the KB400's, which I think are a waste as they only bump compression ~ 1/3 point higher, or stroking it.

Another thing, the KB400's CH is ~1.908 and the Speed Pro 2315 is ~1.920. So you will gain .012" in height just by going with the flat top which, at .010" cut off the block and using a .039" head gasket, will give you good quench, that the KB400 will not.

 

[Meep-Meep]

I'm pretty sure the Eddy heads can be cut quite a bit. You might look into that option, and if you do, don't forget to cut the intake side so the manifold fits.

 

[YY1]

There's a 400 build thread on the a body side where they guy milled the block and the iron heads to gain comp. Over 420 HP. Good thread.

 

[Sublime440]

The 400 has a very large bore, 4.34" vs 4.25 for the 383, so they are a little easier to make compression and power with.