[KyleG]

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.

[ap72]

You're probably closer to 9:1. What part number is on the pistons?

[KyleG]

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

[BOBCRMAN@aol.com]

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

[KyleG]

Goood! Soo regular gas is goood to run??

[ap72]

Maybe. Maybe not. The joys of messing with a "mystery engine"

[KyleG]

Originally Posted by ap72

Maybe. Maybe not. The joys of messing with a "mystery engine"

Very true!

[painted jester]

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

[KyleG]

Its just a real bad photo, it was a little carbon build up..

[BigMo]

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.....

[KyleG]

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

[cobalt327]

Originally Posted by KyleG

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.

[KyleG]

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

[lg1969]

I use this cal

[hcompton]

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.