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Discussion Starter · #1 ·
Y’all know what a sh!t year I had. Thought I’d post a fresh thread since I don’t want to dwell on past failures. So here we go....please feel free to chime in.

I have a freshened stock block. Early in the year it was +.030 and got new hyper pistons. Most recently at a different shop it was jet cleaned, align honed, re ringed, rebearinged, and got a better stock crank +10/10. My old crank was the cause of previous thrust bearing failures.
In the meantime I ordered a custom cam and AFR165’s from Ed.
I’m waiting on that stuff, so to kill some time I figured I’d learn how to use a degree wheel, and find absolute TDC with a piston stop. Also going to confirm the specs on the existing cam (XE264) just for fun and practice. Made a solid lifter too.
Wondering where I might be in terms of compression ratio with these pistons and heads. They are a 58cc combustion chamber.

Also, are there any things on the shortblock I should be double checking or confirming while I’m at this stage? Endplay came to .006...so right in spec. Cam endplay is a little tight at .002 but I’ll check and address that when I get my Ed cam. I‘d just as soon not go to the point of taking off caps and checking bearing clearances....I trust the shop that did that.
Cheers.
 

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What compression height pistons you have? I'm surprised that you didn't have the block decked, if for nothing less than a true surface for the headgasket to seal.
 

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Discussion Starter · #3 · (Edited)
Block was decked when bored. Still good.
Should add that rotating assembly was balanced as well at the new shop.
Pistons are Speed Pro H273CP 30. I know they’re not the greatest...it’s what the original shop installed.
 

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Discussion Starter · #5 · (Edited)
No, just a bad pic. It’s right about even with the deck all around.
I punched the numbers into the Summit calculator. The only thing I don’t know is Deck Clearance. I thought it must mesn the amount it was decked, which I believe was .012. But when I put in higher numbers to test that, the CR goes down. Higher numbers should raise the CR. Unless I’m supposed to put -.012. That would give me a solid 9.7:1 based on a .04 thick gasket.
 

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Deck Clearance is from the deck to top of the piston at TDC. If I remember correctly, on the Summit calculator if the piston is below the deck, it is positive.
 

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Those pistons have a 1.605" compression height. Add that to the rod length and 1/2 of the stroke then subtract from 8.206" and that is your deck height. 8.206 is factory block height
 

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Discussion Starter · #8 ·
Ok, I wasn’t aware of that calculation. If so, my math says my block height is 8.194 (8.206 minus .012 decking).
1.605 compression height plus 5.09 rod length plus 1.5 (half of 3” stroke, equals 8.195.
According to the calculator I get 9.24:1 with a .047 gasket (P333).
Meh, I’ll be able to run regular gas.
 

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Deck Clearance is from the deck to top of the piston at TDC. If I remember correctly, on the Summit calculator if the piston is below the deck, it is positive.
Yeah......I tried to explain t to them. But some people just have to march to the beat of their own drummer. Or something.
 

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Discussion Starter · #12 ·
58cc
 

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Discussion Starter · #14 ·
no idea yet.
 

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K. Thanks. Would you post it when you find out? I read over your first post to fast as you said that the block had been decked 0.012" and your combustion chamber size is 58cc. I need to pay attention more.
 

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Discussion Starter · #16 ·
You'd be good with a .043 gasket. Octane will depend on the cam.
Hi Mark. Is that dependant on the open duration of the intake valve? Just curious as I thought octane was based solely on CR. Thanks.
 

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Discussion Starter · #18 ·
Ya, been on that merry go round. Just sticking with the tried and true from now on.
Heard ok things about the Promaxx heads but no first hand. After my personal experience with Flotek, I wouldn’t go out of my way to recommend them. They were ok. I’ll leave it there.
 

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65 fastback pump gas .060 289 (297) solid roller, T5 all motor. 11.12 122 mph
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The valve reliefs and those pistons are going to add up to a lot of cc’s. Almost like a dished piston. I would try to find the actual cc’s the valve reliefs account for and not trust what the company advertises. Then calculate compression.
Back in the day advertised valve relief cc was not an exact science when it came to advertised numbers. Have an old set of Mark O’s old SRS Probe pistons in a 289. Great piston for the money but advertised didn’t add up to measured with the regular and TFS TW valve reliefs.
 

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The valve reliefs and those pistons are going to add up to a lot of cc’s. Almost like a dished piston. I would try to find the actual cc’s the valve reliefs account for and not trust what the company advertises. Then calculate compression.
Back in the day advertised valve relief cc was not an exact science when it came to advertised numbers. Have an old set of Mark O’s old SRS Probe pistons in a 289. Great piston for the money but advertised didn’t add up to measured with the regular and TFS TW valve reliefs.
It was only about double, 8ccs instead of 4. One of the first things I did in 2008 was ditch that. My partner also had a BBC dome that was listed at 50cc that I measured at 39.
 
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