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Discussion Starter · #1 ·
Have headwork on my '92 . . . there was a supposed 50 thou shave done.
Question: Any of you folks done this, and what was the finished-up compression ratio?
 

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The compression ratio isn't based off just how much was shaved off the heads. That is just 1 part of a much larger equation to determine the compression ratio. You need to know the bore, stroke, what pistons and the CC's, deck height, head gasket thickness, and CC the heads to start.
 

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Nah,
I think you can rip near 70 off virgin heads run stock pistons
What you want to do is get the squish tight.
With stock heads that big flat spot is a problem in the head design.
 

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Discussion Starter · #5 ·
Nah,
I think you can rip near 70 off virgin heads run stock pistons
What you want to do is get the squish tight.
With stock heads that big flat spot is a problem in the head design.
Stock bore/stroke/pistons.
Smitty heads, .032 squish.
EV27 cam, 1.83 jet.
Modified Keihin.
Sportster module.
Exhaust/pipes.
Dyno sheet: Arrow Custom Cycle, Duncan, BC
75.6 hp - 84.3 tq.
Sea level.

This was done many years/miles ago.
Has run flawlessly.
Just curious as to what the compression ratio would be.
Thanks.
 

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What do your heads CC out to?
The squish has little to do with what could be removed from heads , as it usually attained by cylinder base adjustment
 

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Discussion Starter · #7 ·
What do your heads CC out to?
The squish has little to do with what could be removed from heads , as it usually attained by cylinder base adjustment
Don't know what they CC'd at.
They were virgin '92 OEM heads to start.
The barrels were lapped to the cases.
Sorry for the scattered info.
Thanks for your help.
GG
 

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On Evo heads milling them .060 gives you 9.39:1 plus or minus a point with an oem gasket. .040 results in 9.07:1 plus or minus a point with the oem gasket.

Any work done on the chamber, short of welding it up, will lower the result. And a .000 deck is assumed. At .060 you can run an EV-27 with stock parts. But bigger valves or aftermarket pistons will require checking the clearances.
 

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Discussion Starter · #9 ·
On Evo heads milling them .060 gives you 9.39:1 plus or minus a point with an oem gasket. .040 results in 9.07:1 plus or minus a point with the oem gasket.
Thank you.
That's the info I was looking for.
Much appreciated.
 

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For FUK'S sake! PLEASE lose the (blue) colored type.
It's black on my phone. Must be the app I'm using.

Sent from my SM-G965U using Tapatalk
 

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Have headwork on my '92 . . . there was a supposed 50 thou shave done.
Question: Any of you folks done this, and what was the finished-up compression ratio?
Is this engine still assembled and able to be cranked over? If so, do a compression test and then go to the Big Boyz site and play around with the numbers on their calculator. The numbers will not be exact but will give you an idea of where the compressions at.
 

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Why have it as an option, then whine about it when it's used?
Asking for a friend . . . :sneaky:
Bold or colored type on a forum is the same as yelling in a conversation. And some will say its a reflection of other things, all worse than yelling.

But carry on, as you say, it is an option.
 

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Background Color and Text ... There are 2 settings and I believe "Light Mode" is the default and what I run so the blue text doesn't look bad. There is also a "Dark Mode" and the blue text is hard to read. To change Modes....

269268
 
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