Anyone want to guess what my CR is?

C

clutchdust

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I built this engine a couple years ago and didn't really take the measurements I should have so I would be happy with a WAG, I just want to have an educated guess as to my CR.
So the heads are older Chevy iron open chamber 2.02 heads. Because of the open chamber and the CR I wanted, I picked a set of domed Speed Pro pistons that net a +3.25cc.
Now here's where the guessing really begins. I checked my piston to deck clearance and I don't recall but I believe it was between .001 and .002". I also (this is embarrassing) don't remember the head gasket I used. I believe it was the Fel Pro that advertises 4.150" bore and .38-.40" compressed thickness.
I won't hold anyone to anything so feel free to throw it out there. I was shooting for a 9.2-9.3:1CR, if I was anywhere between 9.0 to 9.5, I'd be really happy.
 
IIRC, the 350 I have with the 2.02 heads were 74cc and with flat pistons was advertised at 9.0:1. Maybe use that and add the dome and get close. And that was with the GM steel shim gasket. .026 thick maybe?
 
I assume a 4.030" bore and stock 3.48" stroke ??

Acc to this online compression calculator you're at almost 10:1 CR.

This is assuming a .040" compressed gasket and the pistons .010" in the hole (.050" total).

What cam did you install ??

ooops: On the screenshot below I used 3.5cc for the dome (typo, missed the "2") with a 3.25 cc dome the CR is a little less, maybe .05 less.... not much....

214c964f3f97bee.jpg
 
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Wow! I would be surprised if it's that much. Not that I doubt your calculations but because I'm not getting any detonation. I took steps to help reduce the likelihood, but 10:1 on iron heads and 91 octane gas, I must have done something right.
And yes, .030+ and stock stroke.
 
That's why I asked about the cam - you can "bleed off" a lot of compression with a "hot" cam.

this online compression calculator seems to be quiet accurate, I've used it when selecting pistons for my 383.

On a stock late 70's 350 the CR goes to roughly 9.5:1 when changing to aluminum heads with 64cc chamber and flat tops. When using pistons with a dome and decking the block to "0" you end up with high CR....
 
That's one "step" milder than the cam I installed (230-236 duration). It seems to be a good choice for a 350 with close to 10:1 CR.
 
Thanks, I didn't want to overdo the cam selection. I worked P/T for Comp when I was in high school and asked the tech guys what the biggest problem was when building an engine. They all told me the biggest problem they ran into was people "overcamming" an engine. It was really tempting to go with the 282 but I bit my lip and went with the smaller grind.
I'm pretty happy with it but I do plan on bumping the lift a little with 1.6 rollers when I install the AFR 190 heads I picked up a few months back. I think I could get away with the 282 at that point but not sure the difference would be worth dropping another $300 for a different cam.
 
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