I need some advice on what material to use to make a spacer to lower the compression on my old Pro Stock Hemi to get it down around 11.25:1 so I can run pump gas.

From all the calculations it looks like I need a total of .155" thickness including head gaskets so my questions are -

1. What material & grade do I make the spacer from?
2. What type/material head gaskets do I use with cast iron block, ? spacer & alloy heads.
3. What thickness head gaskets should I use, the thinnest possible to keep the spacer as thick as possible or what?

I know changing the pistons would probably be a better idea but the block & pistons were owned by Don Carlton & I want to keep them together for personal reasons, Thanks

Maybe search for an old set of DC spacer plates. It seems to me they were .1 there's liable to be someone on here that still has a set. Head gasket goes on each side of them.

Sheldon

Thanks Sheldon, I'll try tracking some of those plates down.

I was slightly off with the figures above but here are all the measurements as recorded from my block, piston & head combo -

My head volume is 165cc

my dome is 109cc

bore 4.310"

stroke 4.150"

With a head gasket of .040" I get 16:1 compression

A head gasket of .157" would give me 11.5:1 which I think would be pushing things with our gas

My 1.000" down fill volume was 130cc taken off 239cc (the volume of 1.000" x 4.310" dia) = 109cc dome

I'm not sure how much the block has been decked or how much has been machined off the heads but the pistons do come up .958" above the deck.

Call them...They will make them:

Make sure the numbers you have are varified...Volumes on Hemi heads can get ineresting...Just for the record, I run 11.6:1 on pump gas in my Hemi...No issues.

https://www.flatoutgroup.com/shimsspacers.aspx

A friend of mine offered me a set of the DC spacers last year for $100. If you want, I will see if he still has them. Not sure, but I think they were about .100" thick

I think i have a set of those ...if you are interested i will try to find them.

I would be happy to get a hold of a set of these plates so if you have a set please massage me, thanks.

I'm still keen to know what the best head gaskets are between the cast iron block & MP spacers as well as spacers to alloy heads, I know there are some gaskets you shouldn't use with alloy heads, Thanks.

We have a few sets of various thickness spacers.We usually use steel shim head gaskets between the block the spacers and aluminium or iron heads.The steel shim head gaskets seal great on the smooth surface of the spacers and don't dig into the aluminium head surface like a gasket with a fire ring.It works similar to a Cometic MLG.We used these on old race blocks from the era that were decked close to .250 to make them usable for low compression street use.