Engine Builders: Stumped looking for some input

[GPW]

Be very careful with the cp pistons you order as we had a 12.5 to 1 stock spec'd motor with only a piston upgrade,cc out 14.5 to 1 as they made a 3mm bigger piston but with no dish and called it 12.5 to 1 pstons.we confronted them and was basically told oh well.

I would talk with John at Woessner and see what they might can do for you.

thank you I will

 

[GPW]

I can see how making the valve relief smaller would effect the C.R.But what I dont see is how using all of the valve relief will affect power.I know a larger cam or cam timing or less valve relief cc will change something,but just using all of the space available should not change anything.

If your target is 13.5:1 and you can't get there due to deep recess sections for the intake valves it will rob all the power you should be able to make.

You will still be able to make power but not every nuk and cranny. I am working on the identical set-up on another bike. It has a different set of pistons. After light fly-cutting on the exhaust side piston to head is .040, intake valve to piston is .060 and exhaust valve to piston is .075. I am certain this bike will make more power. Same head and same cams. The CR info was very valuable to me answered my initial questions.

 

[GPW]

Greg,
To get back that lost 1.4 cc in the valve pockets, you would need to remove .25mm (.010") of head gasket or piston to head clearance. No can do. Sorry. Put bigger cams in instead perhaps?

Draco,

would like to compare your CR numbers. Just buttoned up another motor with same bore and stroke, different pistons to start, much better clearance numbers after milling and fly cutting my final clearances.

Intake piston to valve .050
Piston to head .039
Exhaust valve to piston .083

 

[Draco1340]

Greg,
you haven't provided much information on the CCs of the head, pistons, etc. Also, I don't know if the change is valve clearance is due to change in cam timing, or a different piston. But lets assume you have 83 mm bore and 65 mm stroke. Thats 351.7 CC. Lets assume the first motor you built in this thread was about 12.5:1 CR. That means that first motor had about 31 CC of compressed volume. (352+30.6)/30.6 = 12.5
That first motor had a piston-head clearance of .042, intake clearance of .084, and exhaust clearance of .074. This second motor has a piston-head clearance of .039, intake clearance of .050, and a exhaust clearance of .083.
Tightening up the piston to head by .003" decreases volume by .4 CC.
Tightening up IV clearance .034" decreases volume by 1.64 CC. HUGE!
Loosenging up EV clearance .009" increases volume by .3 CC.

So your compressed volume went from 30.6 CC to 28.86 CC
Your compression jumped from 12.5 to 13.2:1, or by about 7 tenths.

This calculation is only a differential calculation, meaning that I assumed what you had before, and took a look at the change that the intake valve clearance had on it. If you have actuall CC volumes for all componenets, I can help you much better.

 

[GPW]

Greg,
you haven't provided much information on the CCs of the head, pistons, etc. Also, I don't know if the change is valve clearance is due to change in cam timing, or a different piston. But lets assume you have 83 mm bore and 65 mm stroke. Thats 351.7 CC. Lets assume the first motor you built in this thread was about 12.5:1 CR. That means that first motor had about 31 CC of compressed volume. (352+30.6)/30.6 = 12.5
That first motor had a piston-head clearance of .042, intake clearance of .084, and exhaust clearance of .074. This second motor has a piston-head clearance of .039, intake clearance of .050, and a exhaust clearance of .083.
Tightening up the piston to head by .003" decreases volume by .4 CC.
Tightening up IV clearance .034" decreases volume by 1.64 CC. HUGE!
Loosenging up EV clearance .009" increases volume by .3 CC.

So your compressed volume went from 30.6 CC to 28.86 CC
Your compression jumped from 12.5 to 13.2:1, or by about 7 tenths.

This calculation is only a differential calculation, meaning that I assumed what you had before, and took a look at the change that the intake valve clearance had on it. If you have actuall CC volumes for all componenets, I can help you much better.

I will get with my head guy and get some harder numbers. Due to intake valve clearance issues as stated the first motor had 13.5:1 pistons and the CR is on the low side.

Cam timing is the same. The second motor has 13.25:1 pistons but much better recess numbers and the CR is almost dead on. Thanks a ton and I expected the numbers to be better. I know you are a master at spread sheets. I would be willing to buy one from you assuming I use the same head on all my builds, lets see if I can get the numbers today. Thanks again!!!!!!!!!!!!!

 

[GPW]

Draco, thanks again for all your help. 9HP difference between the two set-ups based on squish and piston to valve clearances.