compression and squish

Wolf · **Joined:** Wed Jul 04, 2012 6:50 pm **Posts:** 101

Dear community,

i'm preparing a 750cc motor for my TT2. currently i deal with the compression ratio which is way over the 10.3:1 which is my goal. I'm using pistal pistons, heads with the bathtup-geometry. Since the crankshaft is already balanced (the other way around might have been favorable) I don't want to remove too much material from the pistons...anyway, is there a rule of thumb how thin the piston dome might become?

an easy way to get rid of the compression, is to use a thicker gasket - how large may the squish become?

Any comments are welcome!

Cheers

Wolf

Carlo · **Posted:** Sun Nov 06, 2016 4:42 pm

Hello, you make one squishy 1.2 mm, and the compression ratio is just so, for my humble opinion

sports · **Joined:** Wed Mar 21, 2012 9:56 am **Posts:** 112

As Carlo says, 1.2mm is OK for squishy. I find 1mm is still OK but 1.2 is a good starting point.

If the pistons are up to 10 grams out either way on a 50% balance factor it isn't worth the effort of getting closer and risk loosing the desired compression - In my own humble opinion.

Eldert · **Posted:** Mon Nov 07, 2016 5:17 am

Hi Wolf

another option would be tulliping the valves .

Eldert

Wolf · **Joined:** Wed Jul 04, 2012 6:50 pm **Posts:** 101

Thank you so far!

Eldert, this is an interesting idea with the tulliping of the valves

is there any experience how thin the piston dome may be?

I think this is my bottle neck....

Wolf

Eldert · **Posted:** Mon Nov 07, 2016 10:32 am

Lacey Ducati has some fitting notes for pistons on his website . see if the link works

http://www.laceyducati.co.uk/news/?page_id=75

Eldert

Wolf · **Joined:** Wed Jul 04, 2012 6:50 pm **Posts:** 101

Eldert,

this is helpfull, thanks a lot!

Wolf

Carlo · **Posted:** Mon Nov 07, 2016 6:07 pm

Hello friends, the problem does not present 'ever, if the motor shaft is more' heavy of a possible balance. If the crankshaft is heavy, it never vibrates instead if the crankshaft is more 'light of the rod weight calculation + half of the connecting rod, more' calculating the remaining oil inside the crank pin, then the motor will vibrate.

If you leave the original drive shaft and mounted lightweight pistons, the engine does not vibrate. The problems come if the crankshaft is lightened too.

brad black · **Joined:** Mon Jan 21, 2013 4:36 pm **Posts:** 205

when i fitted the high comp ferracci pistons to my otherwise factory 750 engine, they were 50 grams lighter (same as an 800 piston btw) than the originals and there was no change in engine vibration that i could feel.

i wouldn't open the squish. that can lower the comp, but also make it more likely to detonate.

Wolf · **Joined:** Wed Jul 04, 2012 6:50 pm **Posts:** 101

Brad,

this is good news for me - I estimate that each piston have a lesser weight of 18g - this should not matter than

Wolf

compression and squish

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