Expressions of interest - 338cc kits.

wombat200 · Post by **wombat200** » Wed Aug 05, 2009 5:38 am

Well, considering that over it's production life, the CB77's compression was DROPPED from 9.5:1 to 8.5:1, (the CB72 was dropped from 10:1 to 9.5:1) - IE, the early bikes had higher compression that the later bikes, I don't think I'd be interested in anything higher than 9.5:1. These pistons will also be used in the C&&, which was even lower in compression, so unless anyone has a compelling reason for 10:1, there is no point, otherwise they will only be suitable for those running higher-octane fuels, or other mods...... In order for a production run to be worthwhile, they need to have mass appeal...... And I don't think High-comp pistons do, for most people....... There old bikes are no longer about going really fast.........

LOUD MOUSE · Post by **LOUD MOUSE** » Wed Aug 05, 2009 8:04 am

The C77 pistons when used in a CB/CL77 engine actually raise the compression.
The lower compression was because of the head and valve differences.
Your last statement is very true to me cause last time I was at a red light with another like cc/make bike next to me was years back for sure. ........lm

wombat200 wrote:Well, considering that over it's production life, the CB77's compression was DROPPED from 9.5:1 to 8.5:1, (the CB72 was dropped from 10:1 to 9.5:1) - IE, the early bikes had higher compression that the later bikes, I don't think I'd be interested in anything higher than 9.5:1. These pistons will also be used in the C&&, which was even lower in compression, so unless anyone has a compelling reason for 10:1, there is no point, otherwise they will only be suitable for those running higher-octane fuels, or other mods...... In order for a production run to be worthwhile, they need to have mass appeal...... And I don't think High-comp pistons do, for most people....... There old bikes are no longer about going really fast.........

wombat200 · Post by **wombat200** » Wed Aug 05, 2009 6:19 pm

LOUD MOUSE wrote:The C77 pistons when used in a CB/CL77 engine actually raise the compression.
The lower compression was because of the head and valve differences.

[/quote]

Thanks, LM, I was vaguely aware of that, are you able to elaborate? The early CB77'S were 9.5:1, the late ones 8.5:1. How much would using C77 pistons alter this? I do know that later in the C77 production, they swapped to the CB/CL pistons (presumably for easy of production). Are you able to identify the head differences? I know the CB/CL used a bigger inlet valve... (or was it exhaust?)

sotxbill · Post by **sotxbill** » Wed Aug 05, 2009 7:05 pm

10.1 to 9.5 compression on the cb72e-110667 and lowered again to 8.5 on the cb77e-1007661.. if my info is correct.

so what will the compression ratio be??

LOUD MOUSE · Post by **LOUD MOUSE** » Wed Aug 05, 2009 7:09 pm

C77 head is deeper and intake valve is "deep dish" comparded to the CB/CL77.
I'm not aware that HINDA ever used the CB/CL77 pistons in a C77 engine. ..............lm

wombat200 wrote:
LOUD MOUSE wrote:The C77 pistons when used in a CB/CL77 engine actually raise the compression.
The lower compression was because of the head and valve differences.

Thanks, LM, I was vaguely aware of that, are you able to elaborate? The early CB77'S were 9.5:1, the late ones 8.5:1. How much would using C77 pistons alter this? I do know that later in the C77 production, they swapped to the CB/CL pistons (presumably for easy of production). Are you able to identify the head differences? I know the CB/CL used a bigger inlet valve... (or was it exhaust?)[/quote]

sotxbill · Post by **sotxbill** » Wed Aug 05, 2009 7:38 pm

got a set of 10.5s off ebay.. scratch me... thanks

wombat200 · Post by **wombat200** » Wed Sep 30, 2009 9:12 pm

After some emails between Bill Silver & Myself, I will continue to investigate getting these made, but with thinner skirts - Apparently the +3mm pistons simply had thicker skirts, thus were heavier....... Keeping the weight down would be worthwhile......

:)