| Slant Six Forum https://www.slantsix.org/forum/ |
|
| Compression calculation https://www.slantsix.org/forum/viewtopic.php?t=34297 |
Page 1 of 1 |
| Author: | 68barracuda [ Sat Mar 14, 2009 8:54 am ] |
| Post subject: | Compression calculation |
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 
|
|
| Author: | Dart270 [ Sat Mar 14, 2009 12:21 pm ] |
| Post subject: | |
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 |
|
| Author: | 68barracuda [ Sat Mar 14, 2009 12:54 pm ] |
| Post subject: | |
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? |
|
| Author: | Dart270 [ Sun Mar 15, 2009 6:11 am ] |
| Post subject: | |
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 |
|
| Author: | 68barracuda [ Sun Mar 15, 2009 9:18 am ] |
| Post subject: | |
What sort of dynamic CR should i be aiming for? |
|
| Author: | Dart270 [ Sun Mar 15, 2009 9:35 am ] |
| Post subject: | |
I don't usually think in those terms, but I would think 8.0:1 or 8.5:1 for pump gas. Lou |
|
| Author: | 68barracuda [ Sun Mar 15, 2009 9:48 am ] |
| Post subject: | |
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 
|
|
| Author: | DusterIdiot [ Sun Mar 15, 2009 9:49 am ] |
| Post subject: | Yep... |
Quote: I don't usually think in those terms, but I would think 8.0:1 or 8.5:1 for pump gas.
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 |
|
| Author: | SlantSixDan [ Sun Mar 15, 2009 10:23 am ] |
| Post subject: | |
Quote: We have 95 octane lead free available here
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. |
|
| Author: | 68barracuda [ Sun Mar 15, 2009 12:51 pm ] |
| Post subject: | |
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 |
|
| Page 1 of 1 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|