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dome compression question
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Posted by: danbobsR

Allright I have about given up on finding a 23cc dome for a stock cylinder cool head I have found a 21cc how would compression compare with a 23cc with a single split gasket and with a 21cc and a full trx head gasket.

Posted by: DezSled

Just a thought, you could go to a auto parts store and get gasket material thats thicker than an OEM base gasket. Making a thicker base gasket does two things, it would lower your compression ratio, and raising the exhaust ports increases performance to a certain degree. just another option

Posted by: Rich250RRacer

I run a 20cc dome, one thin piece of a stock gasket, about 190lbs compression, on pump gas. No problems.

Posted by: danbobsR

the reason I have to use a 23 is when the cylinder was resleeved the top of the cylinder was milled down some

Posted by: 86 Quad R

what psi is your engine with the 21cc dome using the thin one peice gasket?

Posted by: danbobsR

I havent bought a dome yet so I dont know what it would be with the 21. I had originally asked him could a 19 be used he said that would put me at like 18:1 compression I dont know what that equals in lbs. this is the only thing I havent bought to make this thing run and Im getting a little flustered he said I could use a 21 with a stock gasket but it would run better with the 23 and the thin gasket I dont know why it would make it run any different but that is what Im told.

Posted by: 86 Quad R

if a 23 cc cant be had then you could get the 21cc and install it, check the psi's and see what it is. if it is too high then you could have the dome re-shaped to a 23 or what ever.

Posted by: wilkin250r

It depends on how much you're willing to spend, and how much work you're willing to do for it.

LOTS of race shops get blank cool-head domes. I'm sure you can get one custom-cut for you.

However, there is more to your cylinder head than simply dome volume. There is the dome shape, squish band width, squish angle, and calculations for squish velocity that all contribute to how and where your engine makes power and dissipates heat. However, those factors are measured and determined by your piston shape, cylinder, and your personal preference and riding style.

So, you have a few options. Either you can send your complete motor to a race shop for THEM to measure those aspects and cut your dome, or you can try to spend a couple hours yourself bouncing between your motor and the phone for YOU to measure them, but they will need to tell you what and how to measure.

In either situation, expect it to cost significantly more than a standard off-the-shelf dome. But it's certainly possible.

Posted by: danbobsR

thats not what I wanted to hear lol. Im still hoping someone will chime in and say I got one you can get for 50 bucks and I say Sure But I guess Im dreamin. This is starting to suck I got over a grand in this motor already and I cant find a 40 dollar dome. and Im really not looking to send the thing to someone else and wait 2-3 months for someone to make a dome. I guess I will order that 21cc and see what I got with that.

Posted by: GPracer2500

Would a 22cc dome help? Nac's Racing lists a 22cc dome: part #PD313H

Not sure if they have them on hand or if that would even help your situation but I thought I'd mention it...

Posted by: danbobsR

That is close I forgot to try them. THANKS

Posted by: x.system

Hey I was moving some parts around today and ran across this dome and remembered your post. Get ahold of Robert and ask him if this one will work for that cylinder.

It reads 22.75cc 13 degree 68.50

http://i2.tinypic.com/23k97wy.jpg
http://i6.tinypic.com/23k98o5.jpg

Posted by: danbobsR

He just Pmed me saying that he has one on the way for me how much do you want for that one? he said a 22.5- 23cc would be the best.

Posted by: x.system

quote:
Originally posted by danbobsR
He just Pmed me saying that he has one on the way for me how much do you want for that one? he said a 22.5- 23cc would be the best.

If he's sending you one I would stick with that, this one may not even work with that setup. No need to mess up that nice cylinder with the wrong dome. Once you get it running I want a full report on what you think about it. When your ready to sell that cylinder look me up

I showed this dome to Robert when he did my motor so maybe he will remember it and let you know if it will work. Its not going anywhere so if you do need it just let me know. I would rather you know if it will work first though.