Too much compression???

[Lachie04]

Hello fine peeps 

I'm building up a 1052 with dot head and after painstakingly measuring everything along the way including cc'ing the chambers and piston dome displacement (by my calculations) the final build works out  @13.4:1 CR.

chamber volume 21cc (slightly deshrouded), dome volume 5cc, zero deck and  0.8mm compressed gasket 3.6cc  263/19.6 = 13.41

Which is too much for my basically stock motor build .... well for me anyway.

I could live with @ 12.5 which is basically what you would get with a B12/Dot head setup (I think).

So options I'm thinking of is either a thicker head gasket 0.04+ compressed thickness (currently 0.03 or 0.8mm) or skimming 0.6mm off the piston dome both of which would give me an extra CC and then @12.5:1.

Trouble is I can't find any 0.04 gaskets for the 1052 .

Any thoughts 

Or random idea a second base gasket ?

Cheers

Edited July 30, 2020 by Lachie04

[fatblokeonbandit]

How thick is a base gasket?? use 2?? or get a compression lowering base spacer like the Turbo  blokes use.

 

 

[Lachie04]

yeah might be the idea   I believe a base gasket is @ 0.01" or 0.25mm so a 0.03" spacer plate would give me .5mm below deck and @ 12:1  0.04" = 11.6:1

[clivegto]

As FB says use 2 base gaskets. 

[Lachie04]

[dupersunc]

Machining the piston dome is the best way.  Thicker gaskets increase your squish clearance , which isn't ideal.  0.8mm squish is Ideal.  

These engines are under valved as stock so you can get away with quite high CRs,  as long as you run a fair bit of overlap in the cam timing, as this bleeds  off piston pressure at lower rpms, and the valve sizes restrict flow at high rpm, both keep the dynamic CR down.

But I think you are correct that 13.4 is a bit ambitious for a street motor.

[Lachie04]

16 minutes ago, dupersunc said:

Machining the piston dome is the best way.  Thicker gaskets increase your squish clearance , which isn't ideal.  0.8mm squish is Ideal.  

These engines are under valved as stock so you can get away with quite high CRs,  as long as you run a fair bit of overlap in the cam timing, as this bleeds  off piston pressure at lower rpms, and the valve sizes restrict flow at high rpm, both keep the dynamic CR down.

But I think you are correct that 13.4 is a bit ambitious for a street motor.

That sounds like a plan I was someway thinking skimming the dome but didn't know if it was a good way to go. I can get that done pretty easily. It is actually for a track bike but still looking for some longevity without overstressing the beast. I think mid 12's would be high enough for me.

Edited July 30, 2020 by Lachie04