12-1 If I shave the head?

Can I just shave the head and get 12-1?

Head on my dragbike was shaved and raised the compression to 14:1 with 12.5/1 pistons. So it can raise it that much but I don't know how much it was shaved. Looks like quite a bit though.

nads.com wrote:

Can I just shave the head and get 12-1?

What pistons are you using?
Watch your piston to head and piston to valve clearances.
Also cam chain adjustment is to be considered.

If your going drag racing then the place to get info is :

forums.dragbike.com/forum_topics.asp?FID=14

That is the Kawasaki specific question area...

I think you want to ask the question not in relation to piston compression ratio but cranking compression...

There are lots of guys running 300PSI in there 1400cc drag motors using modified on board starters.

Above 250PSI it gets pretty hard to kick start...

Oh come one...just change up the kick starter's gear ratio! Might end up with a bigger right leg if you start it often, though.... :silly:

I had 200lbs comp. once from carbon build up, but it didnt make any more power come about. I don't know if it was the head flow or not enough cam lift. I really horked out this head I'm sending to Larry and maybe that head will flow well and I'm millng it to get around 200lbs. I had no problem with cheap gas. It just needs to make power not just have more pressure. I really opend up around the valves and guides so I know it will flow MUCH more than stock. I couldn't guess how much the velocity dropped or not. I just know that if the head is what is choking off, this sucker is going to be able to flow it. I need to make power at higher rpm. I've got the cams part down pat, now I need to move some air. So at least I know it's not the head. I can tell the motor can produce a mean strong and clean power up top like from 8500 on up to 10000. But it isn't tuned right, it gets to about between 85 and 9 and pulls nice hard then hits the wall. It seems as though it gets ready gets set and goes then something limits the increase to quick. It hits the wall to fast. Like it's not able to let in or out the gases. Maybe it's way past efficient intake and combustion given the cams intake closing. I could back it down some more but I don't see where it would help power unless it SCREAMED up top. Whos knows but I'll find out what it is for sure through the cyl pressure, cam timing, head flow. And I'll take it to the limit one more time.

Are those 28mm carbs choking off air flow at 8500rpm? Is that the reason why my motor isn't as fast as a rocketship?

I've always wondered how you do the numbers to match CFM for carbs, head, exhaust.

CAVANAUGH RACING HEADS
Lots of wonderful info here...

DoubleDub wrote:

I've always wondered how you do the numbers to match CFM for carbs, head, exhaust.

You calculate piston demand and start right there.

As far as how much to take off a head to obtain a particular compression ratio, the best way is to cc what you have to start with.

Too many variables come into play to throw numbers out.

Sinking valves, installing larger valves, radius cutting chamber pockets.....add chamber volume.

As far as going by cranking pressure, that's not accurate at all. Different cams, different intake closing values will change cylinder pressure.

Your current piston to valve clearance at the closest point with your cams at your cam timing has to be taken into consideration.

It's not just a matter of saying oh yea...scratch .040" of the deck and you're good to go :silly:

There at lots of online calculators to help you out. Got to Wallace Racing, he's got lots of helpful online calculators.

I guess I should have said the most important factor is piston to head and piston to valve distances when shaving a head.

What I was trying to get at is that compression ratio numbers are only useful in pertaining to the octane rating of the fuel to be used and not as an actual performance indicator... you can have a 15:1 piston with low cylinder pressure.

I should have also noted that cranking compression numbers can be used as a performance indicator but can also be greatly effected by valve overlap... I alter my cam timing to achieve maximum cylinder pressures and maximum piston to valve in drag motors.

Formula For Milling Pistons

(For 4032 material only) Piston dome cc's to gram conversion:

1cc (volume) = 2.8 grams (weight)

This is a good way to remove excess dome without having to re-cc piston: Mill a small amount and re-weight piston until total reduction is reached.

Example: A piston has 12.5cc effective dome volume. The desired effective dome volume is 10.5cc.

To remove 2.0cc, cut 5.6 grams (2 X 2. from the piston dome.