422 cube Compression Suggestions

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metallidart

metallidart

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I'll make it short and sweet. 70' 340 block, .060 over, plate honed/sonic checked/decked to blueprint/line bored/main studs-girdle/oiling mods/bushed lifter bores. Forged 4" crank (forget the brand...its been a while.) Eagle h-beams, JE flat-tops with 2 valve reliefs, internally balanced, Fluidamper. All assembled, was a friends and he built a bigger small block.

My top end consists of Indy cnc-ported rectangle port heads, a Crane solid roller that, with 1.6 rockers, will have .670ish lift (again, I forget at the moment) with 260/266 @ .050. I have yet to buy my rockers, going to go with T&D if that day ever comes. The intake will be an Indy intake ported by Ryan J and possibly cut down to fit under the hood of my latest creation, a 1973 Dart Sport 340.

Now the question. With these heads, etc, my compression will be approx 11.7:1. The guy I got the shortblock from ran these same heads, slightly larger cam, and claims he ran mainly pump gas. I'm thinking I don't want to risk it. So. I am broke, and at the rate this engine is going, it will be a very long time until I finish it.

My options: Going to call JE tomorrow and ask how feasible it is to have a machine shop cut a slight dish into the pistons to bring it down to the 1.5 range, rebalance the bottom end, double check everything, and also have a peice of mind knowing the exact condition of the bottom end.

Do the same as above, but down to 10:1, finish porting my set of x-heads I have here, sell my Indy heads/crane cam, buy a smaller Voodoo Mech roller, intake, etc, and have a very torquey, much more streetable engine, plus pay some bills off.

Or, give Indy or a superb guy like Ryan J a call, and see if it is also feasible to open up the chambers of those Indy heads to 70 cc or so to drop the compression down a little.

What do you guys think?
 
I'd call Ryan or Brian on the compression, my thoughts, with that cam & aluminum head i think 11.1 would be fine on pump premium.
 
I think I'd be looking at opening up the chambers a little rather than redoing the bottom end. That said, with premium gas I don't think you're far away from safety.
 
just add a thicker head gasket ...or head gasket shims i believe there called .. i watch my machinist do it to a small block chevy ..the heads where studded though .. i dont no if that made a difference or not .. worth the time to ck out though
 
When I bought my 340, it was a bare block, had to .060 over it to clean the walls up and bought my bottom end as well as top end before I got my block back from the machinist only to find when assembling that my deck height was .015 lower than factory, I'm assuming to bump compression, I was in the same predicament you are. I just bought a couple of custom MLS head gaskets from cometic on their website. They'll probably have just the right thickness to dial in your CR
 
I'd open the chambers to get the compression to 11.1 or so and keep good quench. My new build is 11.2-1 with Indy 360-1s with a 70cc chamber, it has .044" quench. Planning on running pump 93.
 
You could probably run pump, depending on what your dynamic CR is. Get it to around 8.5:1 with aluminum heads and you'd probably be set. I'm just under that with iron heads and run 91 with timing pulled out of it.
 
Yes very good info!! I just happened to decide to check up in some of my threads. If I still had the shortblock I would probably go with the MLS idea, at least to help it out.
 
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