Hi Guys

Couple of questions

My volumes:

combustion chamber volume 59cc
volume above piston to deck 29 cc

Bore is stock no ridges

What is the compressed thickness of the steel shim gaskets? - what volume should I use ?

Rough calcs, with .040 as gasket thickness give me about 7.5:1 as to the advertised 8.4

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Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

Steel shim is 0.020"-0.022" compressed. Fel Pro is 0.034" compressed, give or take a few thousandths. Many others (for example, Oz gaskets) are 0.045" or more compressed.

Most stock 225s are more like 7.5-8.0:1 actual. Stock spec for deck ht was 0.141", but they're almost always 0.170"-0.220" with 0.185" typical.

Lou

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Home of Slant6-powered fun machines since 1988

thanks lou

figures is now 07.833

.1 of the head will take it to 9.22 - should I go Higher I have the ISKY 264 cam here 228@50....

Maybe go for 9.5?

_________________
Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

Can you deck block too? That can be more reliable since you know exactly how many cc's you remove by milling a certain depth. Head starts to get dicey as you mill deeply, since the chamber tapers.

I'd go 9.5:1 with that cam.

Lou

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Home of Slant6-powered fun machines since 1988

What sort of dynamic CR should i be aiming for?

_________________
Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

I don't usually think in those terms, but I would think 8.0:1 or 8.5:1 for pump gas.

Lou

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Home of Slant6-powered fun machines since 1988

Hi thanks for the pointers - the DCR with the existing cam and CR - 7.723 - is 6.123

Bumping her up to 9.5 with this cam gives 7.476 DCR and with the isky 6.908 DCR

BTW I will CC the head again after the over size valves and hardened seats are fitted - and the chamber volumes are equalized - final skim calc will be done then


We have 95 octane lead free available here

_________________
Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

Lou's right, most 'street' car in the US should not be above 8.5 at the worst unless you have very good octane available. Most of the 'milder' builds guys here have in the 9.2:1 SCR with a better than stock cam run in the 7.7-7.9 range so we can run 87 octane regular with some tuning. I've been mulling over the next block, and was going to go up in SCR quite a bit, but when my DCR weighed in at 8.77:1 and I can't get better than 91 octane that's "oxygenated", so I had to tweak the idea to come in closer to 8.2:1 DCR.

Like everything, I just use the DCR calculator as a tool to get the sense of how it might respond vs. my other builds, and there are other factors related including environment, altitude, timing curve, carburator, weather
that can still affect how the final product still works when it's in the car and doing it's job.

Good luck, sounds like you are really putting some thought into your mill.

-D.Idiot

Careful, remember U.S. octane numbers (as most often discussed on here) are not the same as rest-of-world octane numbers. Outside North America, only the fuel's Research Octane Number (RON) is stated. In North America, the average of the RON and the Motor Octane Number (MON) is stated. For any given level of antiknock performance, the RON is roughly 6 to 10 higher than the MON, so the RON is about 3 to 5 higher than the American number.

Typical (sea level) American octane grades are regular 87, mid-test 89, and high-test 92. This equates to RON grades of 91, 93, and 95 or so.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Midtest 89
And Hightest 92 - to equate to American measurements

Thx Dan

OOPs read the calculater intructions wrong

stock SCR 7.723 DCR 6.757 stock cam

mod SCR 9.5 DCR 8.278 stock cam

mod SCR 9.5 DCR 7.821 Isky Cam

_________________
Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars