EDIT: My math is slightly off for using a gasket bore of 4.166 not 4.125 in the calculator, and a cyl head volume of 54 and not 53 to compensate for the .006 milling off the heads...but you can still compare...


Oh, wow...that's a tad higher than the stock 10.4:1 LOL. Even though you guys don't have detonation issues, is it possible that the knock module is pulling timing instead? Not saying it isn't possible, just trying to look at all angles. What type of piston did you run with? Going to check out your site now...

Yeah I do want to keep it down to be able to run off pump gas. Reason I'm talking about the #'s with the 5cc pistons is because that's what the builder ordered on the rotating assembly. Doing the math last night / today, it's pretty clear they aren't going to give me what I want. I think I'd be FAR better off with the 16cc dished...read on:

The problem with a flat-top is this (Keep in mind that .22 compression must be added for each .010 milled off the heads, which I will probably have to mill .010 to clean them up since they were beaded?):

With the 5cc flat tops:

Bore: 4.030
Stroke: 3.75
Conn Rod: 6
Cyl Head Vol: 54
Deck Height: -.005 (.005 out of hole)
Head Gasket Bore: 4.166
Head Gasket Thickness: .039
Piston-Wall Clearance: .003
Top Ring Land Height: .25
Piston Dish Vol: 5
Compression Ratio: 12.748:1 + .022 = 12.968:1

Now, if I DON'T deck it, and leave the piston .025 in the hole, + .039 gasket:
Bore: 4.030
Stroke: 3.75
Conn Rod: 6
Cyl Head Vol: 54
Deck Height: .025 (in hole .025)
Head Gasket Bore: 4.166
Head Gasket Thickness: .039
Piston-Wall Clearance: .003
Top Ring Land Height: .25
Piston Dish Vol: 5
Compression Ratio: 11.739:1 + .022 = 11.959:1


Going with the 16cc dish piston we have as follows:

Bore: 4.030
Stroke: 3.75
Conn Rod: 6
Cyl Head Vol: 54
Deck Height: -.005 (.005 out of hole)
Head Gasket Bore: 4.166
Head Gasket Thickness: .039
Piston-Wall Clearance: .003
Top Ring Land Height: .25
Piston Dish Vol: 16
Compression Ratio: 11.086 : 1 + .022 = 11.306:1

Now, if I DON'T deck it, and leave the piston .025 in the hole, + .039 gasket:
Bore: 4.030
Stroke: 3.75
Conn Rod: 6
Cyl Head Vol: 54
Deck Height: .025 (in hole .025)
Head Gasket Bore: 4.166
Head Gasket Thickness: .039
Piston-Wall Clearance: .003
Top Ring Land Height: .25
Piston Dish Vol: 16
Compression Ratio: 10.333:1 + .022 = 10.553:1

This is assuming a compressed gasket thickness of .039", and a gasket bore of 4.166. Results will vary slightly if either is different, but as you can see, I can take the quench to .034" to take advantage of that, and still run an 11.3:1 Compression ratio...

Thoughts on that?

 

not a BIG deal, but cleaning up the chambers and unshrouding valves and all that good stuff removes a few cc's of metal.

Again, check out the thermal coatings to reduce detonation

 

No offense Trey, but someone saying "not a BIG deal" when I'm abo0t to drop $4000 on a rebuild/parts just ain't gonna cut it for me Not that I DON'T appreciate your help...hope ya understand. Kinda looking for some definites here. Then again, nothing is definite in the 'hot-rod' world except that one can expect to blow tons of money that they will never get back

I'll check out Advanced for those coatings...thanks!

 

i should have said significant... although i'd say .4 points of compression is significant

 

Have you figured it with the stock compression head gasket?

 

What's the stock Compression HG? .059"?

.025 in the hole on a 5cc=11.119:1 + .22 = 11.339:1
.005 out of the hole on a 5cc = 12.011:1 + .22 = 12.231:1

Both VERY ****ty...

 

What's the stock Compression HG? .059"?

.025 in the hole on a 5cc=11.119:1 + .22 = 11.339:1
.005 out of the hole on a 5cc = 12.011:1 + .22 = 12.231:1

Both VERY ****ty


11.339:1 is still too much for you?
How are you going to be driving ?

Compression = H.P.

 

So how much compression can you run while using pump gas?
I'm getting ready to have the same problem.
I was planning on 11.1 max

 

11.339:1 isn't really the problem...it's the .054" gap there between the head and the piston that I don't like...

...not when I can get the ~same compression with a .020" tighter clearance...Plus, If the right way to go is with the dished piston, and he got the wrong one, it would make sense to tell him to get the right one so I can run the quench I want with the right compression...

Just to let you know I'm going to be buying ANOTHER set of pistons to do it...just have him return these and get me the right ones...

For some reason I feel that you guys think I should stick with the flat-tops, ****ty quench, and high compression? LOL

 

depends on FAR more than static compression

octane? whats in your fuel? Cam? heads? rev cooling? Coated?

 

I went with SRP pistons from Nu-Tekmotorsports.com and a Felpro head gasket.

Previously a machine shop had shaved off too much off my heads so my overall CR would have been around 12:1 but the engine builder re-shaped the chambers on the heads and lowered it to 11.3:1.

 

Gripenfelter, what happened to your homepage?

 

Yeah, your homepage doesn't work

How much had they shaved off the heads if you remember?

Are you satisfied with the 11.3:1 CR? How's it run?

 

I stopped by the machine shop at lunchtime, and he is in agreement that we shouldn't use these pistons. He's going to order up the reverse dome pistons for me with the -16cc dish, and he said he should be able to sell of these other ones no problem.

DAMN! These SRP pistons are light!!!

 

if you use 16cc dishes, you are gonna need ot get your chambers down to 51-52cc