Head swap???

[cycledog]

Is it true that a head off of a 60 Lark L6 will give a significant compression increase if installed on a 185??

[Skybolt]

Could be true. I purchased an NOS earlier Champion head a few years back and the combustion chambers were significantly deeper than my 59 170's. I wanted a lower compression head because I wanted to turbo it at a later date.

[irish]

NO...it is not true, while a 1960 170 C.I. does have higher compression than the 185 the pistons are different. You will only get about a 1/4 point increase by switching the heads. The best way to increase compression on that engine is to mill the head and/or bore the cylinders. Now with that said IMHO the 1960 head is a somewhat better head than the original on a 185. Hope this helps.

Joe

Is it true that a head off of a 60 Lark L6 will give a significant compression increase if installed on a 185??

[Ron Dame]

NO...it is not true, while a 1960 170 C.I. does have higher compression than the 185 the pistons are different. You will only get about a 1/4 point increase by switching the heads. The best way to increase compression on that engine is to mill the head and/or bore the cylinders. Now with that said IMHO the 1960 head is a somewhat better head than the original on a 185. Hope this helps.

Joe

Werll I'm the first to say I'm no expert, but you are increasing the displacement by 8.8%, so wouldn't the CR increase by 8.8% (or close to it) as well?

[irish]

Unfortunately Ron, like most things in life, it isn't that simple. But their are some simple math formulas to calculate the new compression ratios, to calculate how much to mill or bore to acheive a certain comp. ratio etc. You can find the formulas online.

Joe

[Ron Dame]

Unfortunately Ron, like most things in life, it isn't that simple. But their are some simple math formulas to calculate the new compression ratios, to calculate how much to mill or bore to acheive a certain comp. ratio etc. You can find the formulas online.

Joe

OK, not knowing the size of the combustion chamber, the exact deck height, gasket thickness, etc, is there a way to back into an approximate CR?

My reason for asking is the 185 OHV6 I built...Using my guesstimate, the CR would be about 9.25, but you suggest it would be less...how can I find out?

Ron

[irish]

Yes there is Ron, If you start with the original factory compression ratio of an OHV 6 (assuming here that the shop manual is correct) 8.3 to 1 you would first calculate for any increase in bore size then you would calcuate for the increase in stroke. Unfortunately it's hard to list the formulas here otherwise I would. I have a book with the formulas, you can email me with what you have and I could tell you the compression ratio.

Joe

[Ron Dame]

Yes there is Ron, If you start with the original factory compression ratio of an OHV 6 (assuming here that the shop manual is correct) 8.3 to 1 you would first calculate for any increase in bore size then you would calcuate for the increase in stroke. Unfortunately it's hard to list the formulas here otherwise I would. I have a book with the formulas, you can email me with what you have and I could tell you the compression ratio.

Joe

Thanks Joe, email sent

Ron

[irish]

Ron you have mail.

Joe

[Ron Dame]

Ron you have mail.

Joe

Kool! 9.15:1! Now I know!