Need help with squish on SD 800

[ncdoo]

96 XP Installing AM Miller head. http://<span style="font-family:Aria...tions? </span>

[Bill O'Neal2]

Re: Need help with squish on SD 800

Is there a question about installing a Miller head that you would like to ask?

[ncdoo]

Re: Need help with squish on SD 800

I dont know what hahttp://ppened to that last post? <br... /> Joe<br />

[Bill O'Neal2]

Re: Need help with squish on SD 800

That link goes nowhere. If you have a question please ask it.

[Technical Support]

Re: Need help with squish on SD 800

Stop trying to use formatting - just type.

[ncdoo]

Re: Need help with squish on SD 800

I wasn't using formatting....
Anyway I'll try again. 96 XP I'm installing 43 cc Miller pent domes. I checked the squish with a .020 (5 hole) base gasket. .044 mag, .040 PTO. I was told I need .055 to .060 for 93 pump gas. If I use an .030 8 hole base gasket, that will only give me .050 and .054 squish. Can I stack the gaskets or will this squish be sufficient? I rather be on the cautious side with the squish.
Thanks
Joe

[Bill O'Neal2]

Re: Need help with squish on SD 800

Who told you you need .055-.060 clearance? That is a very safe number on a 787.

A true #8 is .032 thick.

I really doubt there is a .004 difference in the piston clearance between clyinders if you loosen the head bolts and re-adjust the head forward or backward on the clyinders and get it perfectly centered. Lets assume your squish with the #5 is .042. Adding another .012, you get .054, which should be enough with 93 octane on a 787 engine if the max rpms is under about 7200.

No, stacking gaskets is a sure way to get a case air leak. If you need a thicker gasket than the standard #8, you must order it from Cometic or another gasket company. Another alternative is to use a lathe to cut a few thousandths off of the squish bands in the chambers, but then you will have unique-to-your-motor-only domes.

[ncdoo]

Re: Need help with squish on SD 800

Bill, I got the 055 to 060 from reading some of the past posts on this forum, and others. I also read where you said that the pent domes weren't as forgiving as the parabolic domes. Thats why I wanted to stay on the safe side with the squish. I've seen what detonation can do do a head and piston. I'll try readjusting the domes as you stated and I would assume I would want the larger squish and the mag cylinder knowing that the pto is more prone to deto. So what do you think is the minimum squish I should be able to safely run with this setup on 93 octane?
Thanks
Joe

[Bill O'Neal2]

Re: Need help with squish on SD 800

Sorry, I missed the part about 43 pent domes.

Miller never made any 43 cc pentinum inserts for his heads. Only 37 and 35's were offered in pentinum configuration.

If you have 43cc domes, you need at least minimum .050 squish clearnces to use 93 octane fuels.

[ncdoo]

Re: Need help with squish on SD 800

I think these were special made for someone that races. They are brand new, got them from a guy named Jeff that races. He's in Riverside, CA. They are definitely Miller domes and 43 cc, I checked them with a burrette. As for as them being pent domes, I can only tell you that the dome shape is drastically different than the standard domes. The dome angle is a lot steeper and the dome height is much taller. Why are pent domes be more difficult to run? Do you or SBT sell the 8 hole gasket. I was told OEM no longer makes them. If they are pent domes, is .050 still a good number?
Thanks
Joe

[Bill O'Neal2]

Re: Need help with squish on SD 800

You are not describing a pentinum insert. You have parabolic inserts. I talked to Mel Miller this morning and he said he never made pentinum domes in a 43cc size. A pent dome is much flatter, not steeper.

I do not sell base gaskets. Maybe SBT has them? or any aftermarket dealer who sells Hot Products, Cometic Gaskets ( they are owned by Wiseco ).

[ncdoo]

Re: Need help with squish on SD 800

So the pent domes have a flatter dome more like the shape of the stock head? For the gaskets, I'll call SBT, I tried to order them from another unmentioned website, they wanted me to pay to have the gaskets shipped from Hot Products to them and then again to have them shipped to me. I dont think so. I'd be paying more in shipping than for the gaskets.
Thanks for the help.

[ncdoo]

Re: Need help with squish on SD 800

Bill, since you're talking to Mel Miller, this might help clear up things, the numbers on the domes are S78133-43.0 cc
thanks

[Bill O'Neal2]

Re: Need help with squish on SD 800

That number represents a 781 parabolic insert with 13.3 compression ratio and 43cc's of chamber volume.
S= Sea Doo
781= engine size
133 = 13.3 CR
43cc = 43cc's chamber volume.

Pent inserts do not look like stock chambers. They have a much wider squish surface and a smaller cup shaped combustion chamber.

A Miller pent insert for a 781 engine would be marked S78P352 or S78P368

[Bill O'Neal2]

Re: Need help with squish on SD 800

As for your base gasket, if you cannot find one locally, try calling Cometic Gaskets and have them ship you one. You will have to pay the shipping though.

Unfortunetly, for any shop to sell you that base gasket when they do not have it in stock, they would need to spend time on the phone with you, then the gasket supplier, then write up the order,then pay the frieght to get it, then package it and write the shipping documents. On a sale of under $10.00, and a gross profit of about a buck and a half, less credit card fees, they would go out of business if all transactions were so small, and even faster if they didn't charge you shipping costs. Then, you would be left without a local shop to get anything for you...... Can you think of anything else you need? If you combine orders so that it makes some sort of sense to do the transaction for the local shop, they may be much more cooperative with you.