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Old 03-06-2013, 06:57 PM
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Effective volume on piston



I am trying to come up with an around about cr. These are the flat tops in my 355. I think the deck clearance is around .030. The guy at the machine shop said it is very possibly, he did not measure though. He also said with the 64cc Double hump heads, it is probably around 10.1 to 11.1. The motor is all the way together, running. So to late to measure now..lol What IS effective volume? And What do these look to you? Of course, you guys wont be able to give me exact numbers, just wanting around abouts.

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Old 03-06-2013, 07:42 PM
How fast is fast enough?
 
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You're probably closer to 9:1. What part number is on the pistons?
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Old 03-06-2013, 07:45 PM
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No idea man. Its already thrown together.. /: And I was thinking it was that low.. Hoping it was haha Cheaper gas. Been running 93, because I thought it was higher than 10:5
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Old 03-06-2013, 07:50 PM
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Nowhere near 10-1. Those pistons look like rebuilders pistons, note the large double valve reliefs and front large notch. All bleed off compression. Plus most rebuilders pistons are .020" short
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Old 03-06-2013, 07:54 PM
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Goood! Soo regular gas is goood to run??
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Old 03-06-2013, 07:57 PM
How fast is fast enough?
 
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Maybe. Maybe not. The joys of messing with a "mystery engine"
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Old 03-06-2013, 08:08 PM
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Maybe. Maybe not. The joys of messing with a "mystery engine"
Very true!
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Old 03-07-2013, 08:45 PM
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that #3 piston (2nd one back) looks like its got a bad spot above the ring land at 2 o clock is it damaged or just a bad photo? These eyes are old!!!

Jester
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Old 03-07-2013, 08:53 PM
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Its just a real bad photo, it was a little carbon build up..
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Old 03-08-2013, 04:57 AM
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Yeah, youre like 9-1 or so....those 4-brow pistons have like 6 to 7.5 cc loss of volume....and with that large of a deck (.030) you are down quite a bit......unless the heads are shaved to the max and the chambers are like 62 or something w a really thin head gasket.....
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Old 03-08-2013, 07:09 PM
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I dont think the heads are shaved any, and stock spec head gasket. Filled up on regular and can't tell a difference. So probably around 9:1 thankfully lol
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Old 03-09-2013, 10:44 PM
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Quote:
Originally Posted by KyleG View Post
I dont think the heads are shaved any, and stock spec head gasket. Filled up on regular and can't tell a difference. So probably around 9:1 thankfully lol
You have a 1 point range of between about 9.2 and 10.2:1 depending on the block deck, gasket thickness and whether the pistons are 1.56" or 1.54" compression height.

The problem at the low end of the CR shown is the quench distance will be VERY wide (as much as 0.086" w/a 0.045 piston deck caused by a rebuilder piston combined w/an unmilled deck along w/a 0.041" gasket thickness).

As long as it'd not detonating, at least it shouldn't beat the bearings out of it or pinch a ring.
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Old 03-13-2013, 05:43 PM
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Hard to say. Its running fine though. I'm just gonna drive it lol Drives smooth, pulls smooth. Sometimes may have a little bog. But thats part of it I guess
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Old 03-14-2013, 10:07 AM
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I use this cal
Attached Files
File Type: doc compression ratio.doc (174.5 KB, 79 views)
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Old 03-14-2013, 01:14 PM
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Most four vavle reliefs without the dish are 6 to 12 cc's But the deck hieght is the most important here. Zero deck or .045 in the hole makes a big difference.
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