229 head question

[Ol,fart]

I've purchased a new head and a tt250 (thin) head gasket. I going to see
if I can remember how to do some porting (it's been about 35 years).
Has anyone done the chamber volume math enough to know how much deck to cut to get to between 9.5 to 10 compression?
I have not measured the tt gasket but it appears to be about half the stock 0.040. gasket.
I don't remember the math and I don't have an accurate way to measure chamber volume. tia

[Megadan]

The thinner HG on it's own combined with the TT250 head will give you the same 9.6:1 compression that the TT250 comes with. The thinner gasket gives about half a point on it's own, and having compared a Hawk and TT250 piston, if there is a difference in volume, it's no more than a couple of CC's off as the dimensions are more or less the same.

If your goal is 10:1, then take another half a mm off the head or jug deck.

I don't have all of my data in front of me and I would have to dig out my notebook from the abyss, but those are the figures I remember off the top of my head.

[Ol,fart]

Originally Posted by Megadan

The thinner HG on it's own combined with the TT250 head will give you the same 9.6:1 compression that the TT250 comes with. The thinner gasket gives about half a point on it's own, and having compared a Hawk and TT250 piston, if there is a difference in volume, it's no more than a couple of CC's off as the dimensions are more or less the same.

If your goal is 10:1, then take another half a mm off the head or jug deck.

I don't have all of my data in front of me and I would have to dig out my notebook from the abyss, but those are the figures I remember off the top of my head.

This is a generic ebay head with a tt gasket. My wild guess was about .015 so were on the same page.
My goal is to run pump gas without mixing av gas. I also have a 4degree key waiting to see if I can get away with, but it's pretty easy to undo if I can't.
Thanks for the info.

[Megadan]

Originally Posted by Ol,fart

This is a generic ebay head with a tt gasket. My wild guess was about .015 so were on the same page.
My goal is to run pump gas without mixing av gas. I also have a 4degree key waiting to see if I can get away with, but it's pretty easy to undo if I can't.
Thanks for the info.

My bike is sitting at about 10.3:1 total static compression. I have a TT250 head gasket, 1mm shaved off my head (but I did also do some chamber work and added a few CC's back in the process) with a 4 degree key and an adjustable "performance" CDI. I run around on 91 octane all day long and have yet to even think I felt or heard any knock. Even if you figure my dynamic compression is lower due to the increased overlap from the cam I am using, my compression is still likely in the mid 9's. It's high enough that I am nervous about breaking my kick start gear inside the engine, and my electric start struggles lol.
You will be ok. These CDI boxes have super conservative timing.

[Ol,fart]

Originally Posted by Megadan

My bike is sitting at about 10.3:1 total static compression. I have a TT250 head gasket, 1mm shaved off my head (but I did also do some chamber work and added a few CC's back in the process) with a 4 degree key and an adjustable "performance" CDI. I run around on 91 octane all day long and have yet to even think I felt or heard any knock. Even if you figure my dynamic compression is lower due to the increased overlap from the cam I am using, my compression is still likely in the mid 9's. It's high enough that I am nervous about breaking my kick start gear inside the engine, and my electric start struggles lol.
You will be ok. These CDI boxes have super conservative timing.

mind if I ask which box your using? And are you happy with it?