The Ford Barn

AnthonyG · 04-06-2021, 10:02 AM

Reassembly on 8BA after Refresh & installing Ross domed Pistons w aluminum connecting rods after issues with Pistons from previous rebuilder. I’ve left one head off for calculating Quench Height / piston-head clearance. I was concerned as piston dome is projecting into combustion chamber area .170 more than the flat top piston. But actually a lot more space than I thought it would be? These are the numbers:
A-Piston dome height above block head mate surface=.170
B-Head surface to combust space piston C/L =.255
C-Compressed gasket =.060
Quench height B+C-A=.145?
Is that about where it S/B? Being my only ever Flathead it seems like too much space. I didn’t check previous setup but it had to be even more with flat top Pistons by the elimination of the dome. I think the calculation is right but sounds like a lot? Comments please!

I only question it as on typical GM OHV engines I’ve rebuilt I think I recall it’s been between .055-.065 with aluminum connecting rods & even less with steel? Does the Flathead compression which for stock I think is about 7:1 increase that quench height that much more than a OHV engine with 9:1 or 10:1 compression?

04-06-2021, 10:02 AM	#1
AnthonyG Senior Member Join Date: May 2013 Location: Pa. Posts: 2,174	Calculate actual quench height Reassembly on 8BA after Refresh & installing Ross domed Pistons w aluminum connecting rods after issues with Pistons from previous rebuilder. I’ve left one head off for calculating Quench Height / piston-head clearance. I was concerned as piston dome is projecting into combustion chamber area .170 more than the flat top piston. But actually a lot more space than I thought it would be? These are the numbers: A-Piston dome height above block head mate surface=.170 B-Head surface to combust space piston C/L =.255 C-Compressed gasket =.060 Quench height B+C-A=.145? Is that about where it S/B? Being my only ever Flathead it seems like too much space. I didn’t check previous setup but it had to be even more with flat top Pistons by the elimination of the dome. I think the calculation is right but sounds like a lot? Comments please! I only question it as on typical GM OHV engines I’ve rebuilt I think I recall it’s been between .055-.065 with aluminum connecting rods & even less with steel? Does the Flathead compression which for stock I think is about 7:1 increase that quench height that much more than a OHV engine with 9:1 or 10:1 compression? __________________ Nomad Last edited by AnthonyG; 04-06-2021 at 10:08 AM.