1071 compression ratio question

[swifty]

i have a slark race head with 15.8 cc . What would be the compression ratio be if used with flat top pistons .... Bore size is +40 . Thanks ken

[LarryLebel]

Allowing 4 cc for the other volumes in the head, I get 11.8:1.

[mk1]

I get a bit more than that.

The following calculation assumes 1071 crank, +40 thou overbore & 10 thou between piston & deck.

[Fanfaniracing]

could not explain it better than mark!

[251 ENG]

Think you may need some dished pistons or a different head

[swifty]

The block is +20 at the moment and needing a rebore , hence why I’m asking the comp ratio at + 40 . So to add to the original post , what cc pistons should I use bearing in mind I will be using the 15.8 slark head and a swiftune SW10 camshaft , twin H4 carbs .... thanks for reply’s .... ken

[mk1]

Is this for the road?

[mk1]

6.5cc dish would give about 11:1

If it was mine, I'd be aiming for 10.5:1.

I'd machine a bit off the top of the pistons to give 15 thou clearance between the top of the piston & the deck.

cr2.jpg

[swifty]

Yes it’s for the road mark. Not to worried about a slightly lumpy tick over . I know that you’ve had a few 1071 so what make of Piston would be the best to use . . Thanks

[mk1]

Personally I stick with die cast omegas in most applications nowadays, but a slightly less expensive alternative is the MS / Swiftune C-STN103's

[swifty]

That’s great thanks. Omega pistons it will be . ... ken

[OzOAP]

MED do a 10cc Omega...could be ideal