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Discussion Starter · #1 ·
I am in the process of assembling my motor this evening

high comp JE forged pistons 3.875 bore
andrews 60 cam
head is ported 1.90 ex 1.652 in valves 90 cc volume and cut .080 thosandths
compression 11.2 with .040 head gasket


My question is::
What will my compression drop by if i run a .050 head gasket. does anyone have the formula for this or a qwk answer?::beer4u:

thanks in advance
 

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90cc's? 11.2 compression? sorry I can't help but that just sounds wrong? heads shaved .080? I don't get it.....
 

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Discussion Starter · #4 ·
adlerx said:
90cc's? 11.2 compression? sorry I can't help but that just sounds wrong? heads shaved .080? I don't get it.....

You Dont Get It... Your probably to DAMN OLD..:laugh:

I like to go fast..Real fast
 

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heliopilot said:
I am in the process of assembling my motor this evening

high comp JE forged pistons 3.875 bore
andrews 60 cam
head is ported 1.90 ex 1.652 in valves 90 cc volume and cut .080 thosandths
compression 11.2 with .040 head gasket


My question is::
What will my compression drop by if i run a .050 head gasket. does anyone have the formula for this or a qwk answer?::beer4u:

thanks in advance
You stated ported heads so I will assume they were stock. You don't state what type of motor but your profile say 05 so again I will assume it is a twin cam. You claim 90cc combustion chamber volume. The stock heads start out at around 85-87cc. Then you say you shaved .080 off the heads. This would reduce the combustion chamber size approximately 10cc. Yielding 75-77cc. Were the combustion chambers opened up for some reason?

I will also assume you just transposed the intake and exhaust valve sizes.

.010 change is head gasket thickness will only yield about .1:1 CR difference. Meaning you would end up with approximately 11.1:1 CR, if any of your other information is correct.
 

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My question is::
What will my compression drop by if i run a .050 head gasket.



11.2? Not enough to stop your engine from detonating into junk.
RB
 

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Discussion Starter · #7 ·
thanks Springer
i was getting late here in new england
i did transpose my valve numbers on the intake/exhaust
yes, my head volume is 90 cc's After the milling of the heads.
and with long duration cams this doesn't pose that great a risk
detonation wont be a problem with an unlimited supply of 100LL avgas
 

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Road Bag said:
My question is::
What will my compression drop by if i run a .050 head gasket.



11.2? Not enough to stop your engine from detonating into junk.
RB
You can get away with high static compression numbers if you run a big cam with lots of overlap...so 11.2 isn't so bad.

That said, I've read elsewhere that you shouldn't try using thicker gaskets to reduce compression as it reduces the squish factor and impedes optimal combustion flame travel. Optimal is supposed to be the .03" gasket on the twin cam. Pick the right cam, and forget about the thicker gaskets.
 

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heliopilot said:
thanks Springer
i was getting late here in new england
i did transpose my valve numbers on the intake/exhaust
yes, my head volume is 90 cc's After the milling of the heads.
and with long duration cams this doesn't pose that great a risk
detonation wont be a problem with an unlimited supply of 100LL avgas
How do you arrive at 90cc heads. If they started out stock and you milled them, they got smaller, not larger. If they are 90cc, HOW did you get them to 90, by ruining the combustion chamber? The point you missed is that you made a lot of mistakes in your first post and then you don't supply enough information to accurately answer your question. I think you are mistaken on the heads also. You are the one that put up the requirement of "No guessing allowed", well I am guessing and it sounds like you are too.

But what do I know, I ride a Shovel !!!
 

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Discussion Starter · #10 ·
Not to be rude but jasilva gave me the info I needed , and seahag was right on the money with his answer too he appears to have done it already.

Springer was so cynical? yes it was late when i was assembling this motor and i did make a typo on the intake/exhaust valves.forgive me.........
FWIW the heads are "stage 4" by probably one of the 5 best engine builders in the country.. D shaped port floors and vortex fin in the intake.
 

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heliopilot said:
Not to be rude but jasilva gave me the info I needed , and seahag was right on the money with his answer too he appears to have done it already.

Springer was so cynical? yes it was late when i was assembling this motor and i did make a typo on the intake/exhaust valves.forgive me.........
FWIW the heads are "stage 4" by probably one of the 5 best engine builders in the country.. D shaped port floors and vortex fin in the intake.
Springer isn't being cynical (he was correct, by the way). It's simply impossible to mill stock heads and make the chambers larger without removing material from them to increase the chamber volume. You can't expect a "fast" AND accurate answer if you don't give a reasonable amount of information about your engine. If you had mentioned in the first place that the heads were not stock, then you wouldn't have received the supposedly "cynical" answer. Would you go to the dentist and tell him that your tooth hurts, but not tell him which one, then expect him to fix it? Some people..... ^rolleyez^
 

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Seahag said:
You can get away with high static compression numbers if you run a big cam with lots of overlap...so 11.2 isn't so bad.


That said, I've read elsewhere that you shouldn't try using thicker gaskets to reduce compression as it reduces the squish factor and impedes optimal combustion flame travel. Optimal is supposed to be the .03" gasket on the twin cam. Pick the right cam, and forget about the thicker gaskets.
Your right, a big cam will bleed off cylinder presure down low. In many cases it just moves the detonation problem up in the power band where the big cam starts to make power, and cylinder presure. I assumed it was a typical pump gas torque build. I quess not. Like he said, he wants to go "real fast". If he does'nt learn some math, his engine won't be doing it for "real long". Springer's a good dude for trying to help, but to no avail.
RB
 

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heliopilot said:
Not to be rude

Springer was so cynical?

FWIW the heads are "stage 4" by probably one of the 5 best engine builders in the country.. D shaped port floors and vortex fin in the intake.

FWIW-Then why didnt you just ask the 5th best engine builder in the land????????????????? or did you manage to pizz him off too??


Ozzie
 

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:thumbsup: :thumbsup: :thumbsup:
 

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I believe heliopilot knows just enough to be dangerous to himself, and his bike. Fourth post in seven months and you're insulting another member? :whatever: :corn:

darrell
 

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SEDELUXE05 said:
pete i think you should shoot this in the ass now while its still young
Not my call.
 

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Don't shoot it yet, I just settled in with a cold one to watch the action. :cheers:
 
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