What is the acceptable "pump gas" limit on dynamic compression? With the cam and compression I should be in the 8.89 range.

you should be okay, but im no expert



[This message has been edited by Mwilson (edited October 18, 2005).]

<font face="Arial,Verdana" size="2">Originally posted by Mwilson:
You have a long ways to go Im thinking around 10:1?</font>

10:1 DCR??? You must be thinking about just the ratio of the cylinder volume compared to the combustion chamber volume and not Dynamic Compression Ratio.

I'm far from an expert, but 8 or so?

[This message has been edited by mgtshawnee (edited October 18, 2005).]

Im probrably wrong then!

There's enough info here to make your head spin:

http://members.uia.net/pkelley2/DynamicCR.html

Basically between 7.5 and 8.5 DCR will live on 91 octane pump gas.

These guys also make a DCR calculator that works off your cam and engine information:

http://www.virtualengine2000.com/DCRCalculator.htm

Try the "Boost Calculator" site and put .001 in for boost.

Here's a link to it.

http://www.rbracing-rsr.com/comprAdvHD.htm

AND read Pat's site over at LEAST three times until it makes since!!

Great site!!

pdq67

In general keep at or under 8. Your calculation is too high for pump gas.

[This message has been edited by Rick WI (edited October 18, 2005).]

does altitude make a difference? This is for vail co so it should be pretty ping resistant at that height it is just here (1320) when it will cause problems. Ok I will work for 8 to 1 or so.

DCR of 8.0:1 is a good # for a performance pump gas mill. 7.8:1 to 8.0:1 is what I shoot for on most of my builds

If your on the brave side and like to run at the limits, then you can go up to 8.25:1 DCR, but you better not go lean, run hot, or have too much timing dailed in.

that link is cool it said I have 8.76:1 and 179 psi

I don't think that one site is right.

Mwilson... after you posted the DCR and psi it showed yours at, it hit me.. Hmm that don't add up. A DCR that high with the cyl psi. that low. It don't make any sence. With a true DCR of 8.76:1 you couldnt run on anything but about 105 to 110 octane and your cyl psi would be around 230 psi or so

So I put in my info. I CC'ed everything so I know 110% what my true specs are.. My SCR is 10.18:1, DCR is 8.241:1, and cyl. psi is 210-218 psi (checked just a few weeks ago.)

That site shows me having... DCR of 9.37:1 and cyl psi of 194.84 PSI.

I'll stick to Pat Kelly's DCR program, and carfor program for est. cyl psi untill engine is built then check it with the gauge like I always do.

I cc'd everything as well so I know all my specs if you want to try it somewhere else
should be 11.33:1

63.2 chambers
.015 gasket 3.9cc
+1.5cc for .125 piston dome after deducting releifs
.22 in the hole
4.030x3.48
Cam
Intake 36 btdc 68 abdc
exhaust 73 bbdc 41 atdc



[This message has been edited by Mwilson (edited October 19, 2005).]