what size domes

[krauss4]

i just got a 421 cub and the guy said he ran race gas and premium mix i want to run full race gas what size domes do i need, its a trinity head

[tundish2800]

17cc is what i ran with race gas

[Alex29573]

which race gas?

what timing advance?

[firebanshee]

i just got a 421 cub and the guy said he ran race gas and premium mix i want to run full race gas what size domes do i need, its a trinity head

I run a 21cc dome on a 68mil cub and pump 180psi at sea level. If you run a smaller dome with a 68mil bore at sea level then your compression will get way high, and you will lose alot of overrev on your motor. Alot of compression will give you alot of torque and bottom end and kill your top end. With a gas motor +4 timing would be a good starting point.

Edited March 3, 2010 by firebanshee

[krauss4]

its at 4 -5 degress advanced this will be a drag bike with shears pipes i want to run c12 112 octane gas

[firebanshee]

I don't claim to be a pro motor builder, but i think right around 180 on the compression is the sweet spot

[_Hex*]

alot of guys like using the cub on low compression around 165-170 seem to get more volume, from what ive tried

[Alex29573]

I run a 21cc dome on a 68mil cub and pump 180psi at sea level. If you run a smaller dome with a 68mil bore at sea level then your compression will get way high, and you will lose alot of overrev on your motor. Alot of compression will give you alot of torque and bottom end and kill your top end. With a gas motor +4 timing would be a good starting point.

 

 

Hey, is that a stock stroke cub? is it ported?

 

Whats overrev? I've heard of it but never understood what it means...

[firebanshee]

Hey, is that a stock stroke cub? is it ported?

 

Whats overrev? I've heard of it but never understood what it means...

It's a 4mil stroke, and the cylinder has been decked and ported. If you have to much compression then the motor has to fight against itself and does not allow the motor to rev up as far or as quickly.