[gtorich]

Bore size in inches:
4.185
Stroke in inches:
4.21
Combustion chamber volume in cc:
82
Head gasket volume in cc:
6.40
Deck clearance in inches:
0
Piston dome volume in cc (negative for dish):
-5

Cylinder volume in cc:
948.9952785356373
Compression ratio:
11.16

Just wondering if i got this right...........was going thru my records and it showed 10.6 for ratio

this is with kre heads and .035 srp pistons...........am i missing something here, maybe this is why im having so many issues with this motor.

Rich

[Formulas]

I didn't run the numbers but will ask did you check head volume or is 82 advertised ?

11.16-1 many would consider doable with a tight tune nothing to hot nothing to lean nothing to quick or advanced (timing) especially if you have 92-93 octane
Also a balancer that is off a bit can mess with you on results.

What issues do you face?

[steve25]

With the info you provided here I get 10.15 to 1.

Make the math easy on yourself.
Take that 5 CC dish / valve notch volume and add it to the 82 CC chamber for a total of 87 CCs, then add head gasket volume to that for a total of 93.4 CCs.

The big question is what’s your hot cranking compression because with a Aluminum head 11.1 should not be a issue, but not on less then 91 octane I would say and assuming a good state of tune.

[b-man]

11.16 is correct.

10.6 - nope.

[steve25]

I stand corrected.

For a compression of 9.5 you need a total CC volume of 111.6

For a ratio of 10.5 you need 99.88 CCs total.

One easy way yet accurate enough way to look at this is from having a 10 to 1 compression.

This would take a total CC volume of 105.4, then for each 1/4 of a point change up or down that you wanted to go then that would take a 3..3 CC change.

[gtorich]

Steve, found an old post of mine, on cranking compression.
1...200 2...185.....re-test will oil.....194

4...200

3...194 6...195

5...200 8...194

7...185......not sure this is accurate, couldn't get
the hose on there right.

Kind of hard to read, but you get the drift.

Formulas...............having this motor redo, will have the guy check for sure on the kre heads, they were done by Dave at SD back in 2010, so im assuming the 82 cc is correct.

Steve, was playing around with the wallace compression calulator.................seems i have to have dish of -11 /-12 to get a 10.55 ratio and the pistons i have now are -5

The reason for messing around with this stuff is from my rear main seal leak awhile back.................titled Yet, another rms leak...........you can see some of the damaged parts i have from that post.

Think now im gonna see if i can get some different pistons.

[ta man]

Im at 190 at 10.8 to 1 with KRE with zero issues on 87 and 91.What cam ?

[gtorich]

ta man, cam would be the old faithful..............im done messing with the calculator, im getting different numbers everytime i mess with it, think im getting goofed up on that head gasket volume, .040 comes up as 6.36

Gonna try Steve 25 method..............that wallace calulator is messing with me.

[steve25]

Rich it’s easy to figure out how many CCs you need to hit a target compression ratio , but without carved in stone CC numbers getting what you have currently for a compression ratio can be frustrating.

Here’s the formula for finding the total CCs you need.

In your motors case a cylinder has 948.9 CCs of volume.

They let’s say you wanted end up with a 10.5 compression ratio .

You then minus 1 from that 10.5 number leaving you 9.5 and then you divide that into your cylinder CCs.

So the result is 99.88 CCs.

Keep in mind that chamber CC volume can change .

If you had CC numbers derived with flat face valves and then swapped over to dish face valves or visa versa that could change you chamber volume by 1.5 to 2 CCs depending on the valves used.

There no substitute for accurately CC ing at least 2 chambers in each head before committing to new pistons.

If you want to have about a 1.2 to 1.5 CC cushion against having too high a compression then do not factor this ring land CC volume into your total CC volume.
This will give you the max compression you could possibly have assuming your other CC numbers are dead on.

[PAUL K]

Originally Posted by gtorich

ta man, cam would be the old faithful..............im done messing with the calculator, im getting different numbers everytime i mess with it, think im getting goofed up on that head gasket volume, .040 comes up as 6.36

Gonna try Steve 25 method..............that wallace calulator is messing with me.

I think .040 is closer to 9cc depending if it has valve notches or not. Butler has an easy to use calculator on their website. Sorry I have no idea how to send a link.

[Tandyman]

Butler compression calculator
https://butlerperformance.com/n-1287...alculator.html

[GOAT8U2]

This calculator above is very cool, I like pretending I'm dropping $25k on a 535ci block on it. LOL

[Tom Pugh]

what was your problem with the rear main seal and how did you fix it?

[johnta1]

that wallace calulator is messing with me.

Are you using this one?

CR Calc




Mine uses positive number dish or valve reliefs.
Negative for domes.

Your head gasket volume seems low?

[VCho455]

The Diamond Piston calculator is my go to for compression ratio calculations.

https://www.diamondracing.net/compression-calculator/

[PAUL K]

Originally Posted by GOAT8U2

This calculator above is very cool, I like pretending I'm dropping $25k on a 535ci block on it. LOL

Where did you find one so cheap..... Or is that the pretend part

[grivera]

That Butler calculator is nice!

Rich - if you’re entering the same parameters each time no reason it’ll be different…other than user error.

[gtorich]

Originally Posted by johnta1

Are you using this one?

CR Calc




Mine uses positive number dish or valve reliefs.
Negative for domes.

Your head gasket volume seems low?

Your head gasket volume seems low.........lol, hey john not sure where i picked up that 6.36 number from, i was doing so much messing around the other day.

On butlers site im getting 10:59 with 8cc flat top......then playing around with numbers i get 10.4 with a 10cc dish.

When is use my srp -5 cc i come up with 10.88..........think im just gonna let the guy putting this motor together figure it out.

[gtorich]

Originally Posted by grivera

That Butler calculator is nice!

Rich - if you’re entering the same parameters each time no reason it’ll be different…other than user error.

User error, you hit that on the head. lol............in my defense i was drinking a few miller lites.

[Dragncar]

Originally Posted by VCho455

The Diamond Piston calculator is my go to for compression ratio calculations.

https://www.diamondracing.net/compression-calculator/

So what is a good number for the top ring down part ? When I put .040 in my CR is 11.39-1. Not 11.5-1