Long story short, my 113 aluminum heads have been milled twice so the chambers are 53cc and with a stock shortblock ( flat top KB pistons, -4cc valve reliefs) and stock head gaskets, compression ratios are somewhere around 11.5:1. Ran OK on 93 octane but now that the motor is out I want to lower the CR.

I have two options, change the heads or the pistons. If I did the math right, a set of -12cc dished pistons will drop me down to about 10.5:1 which is where I want to be for a N/A street motor. I could swap the heads, but I don't want to have to find another set of 113's then have the machine work done (pressure testing, cut guides, new seals, valve job, yadda yadda) plus the cost of the heads.

I guess my question is are dished pistons an OK way to drop the compression?

 

Might look into taking CC's out from the combustion chamber, not sure how much can be removed from the 113's...you'd need to find someone who has experience doing this....along with a thicker head gasket, might get you in the mid 10's

Not sure you'd want to run a high CR, with dished pistons, I'm thinking (but could be wrong) the quench are may be too large.

I'd also think that the milled 113's would be a good upgrade for a 305-guy too, so you may have pretty good luck selling them since there's not a lot of heads to offer for those guys.

 

Thanx for the reply.

I'm running a .039" gasket now....pretty much the thickest. Anything else won't substantially drop the CR. Taking material out of the chambers seems like it would be expensive. Cheaper to just buy another set of heads which is what I'm trying to avoid. 400$ for some heads, 250 for machine work. The dished pistons are only 225. If I have to do heads I will, otherwise I'll slap the pistons in it.

 

Actually, you could take it out yourself (just get advice on where) easily with a dremel and some Al. bits...Al., cuts easy and fast, so the Dremel would be fine for this.

If the chambers on the 113's are like the CastIron 083's...I'd start with the sparkplug boss for a CC or two, then shape the chambers with a head gasket as a side...anyway..not knowing what they look like, I can't really offer experienced advice.

I did take out 6cc's on a set of 461's, the chambers on those look more like a 1/2 bowl..i/e no protrusions..maybe someone will jump in here...you may want to move this post to general engine forum for more/better replies.

 

I'm not big on the idea of chopping on chambers myself. I tend to get a bit carried away . Thanx for the advice though.

Anyone have any good articles about quench dynamics?

 

Is the block decked? Doing the math I figure your block is not decked.

When shooting for proper quench the desired clearance is .035-.045, .040 is really where you want to be.

Just do the new slugs and forget about it. If your not decked you might want to look at the -18s and run less gasket to get proper quench.