how can i tell a low compression head

[DaveKent]

i'm after a us spec low compression spitfire mk4 head. how can i tell it's still as i should be, rather than skimmed to suit uk market?

[James]

Measure it with some liquid paraffin and a syringe :)

[Jason]

Try contacting the usual suppliers, this is the kind of thing that sits on the shelf for years and never sells, you might get lucky and find a decent NOS one! I'd call Fitchetts, Rimmers and Canleys if I were looking for one :-)
I know Canleys had several sets of US spec pistons if they are of any use to you.

[CharlieB]

I thought the low compression was achieved by using dished pistons & the heads were the same (except maybe valve seats for unleaded)

[James]

Charlie - it was done that way on the 1500 - maybe not the 1300 though...

[Clive]

or how about a 1500 head on a 1300, gives nice low compression. Could have it skimmed to whatever you like then.

[auto]

If you want to lower the compression, you can take your standard head and fit a shim. (like a thick gasket) This will lower the compression, and what is done when converting cars for turbo's.

You can as a quick fix use two head gaskets to acheive the same results, however, it is best to have a shim made, costs about £40 including skimming your current head and making a new shim. You have to skim yours first to ensure surfaces mate perfectly, the shim will make up the difference plus the escess to lower the compression. Pop and see and engineering firm, one that skims and rebuilds heads would be better.

Skimming reduces the distance between pistons and chamber, making the chamber smaller hence raising compression - To lower it you need to take the head away to make the chamber larger, and thus the compression less.

[rotoflex]

I remember seeing GT6 Mk3 engines in the US with those sandwich plates to lower compression.  They probably were for utilization of existing heads at the first of yet another compression drop for the US market.

[DaveKent]

so am i right in thinking i can rebuild an FD uk spec engine using us spec pistons to lower the compression ratio? i'm looking for about 8.5:1, will that be about right using those parts?

[Slimboyfat]

No.
An FD block is a 1300, the low compression pistons are for 1500's. 1500 pistons have different gudgeon pin heights to 1300 ones.

[Tim Bancroft]

Dave K,

You building a forced induction engine then, or do you still like driving slowly???????????

[DaveKent]

ah mr bancroft, you are a very perceptive young man!!!! just toying at the moment, but you know what roger is like.......!!!!!!!!!!!!!!

[DaveKent]

timbancroft61 wrote:

Dave K,

or do you still like driving slowly???????????

kept up with you six pot boys on the HCR didn't i !!!!!!!!!