Check My Compression Ratio Calculations .

Check My Compression Ratio Calculations . - 01/04/09 12:49 AM

I'm ready to take my 440 block in to be decked, (already bored, honed and aligned honed). I am installing Diamond forged pistons and was using their C.R. calculator to figure my static comp ratio. Their number seems a bit high and I was hoping someone smarter than me (not hard to do

) could double check my figures. My numbers are as follows: Bore 4.350, Stroke 3.750, Rod Length 6.760, Gasket Bore 4.500, Gasket Thickness .039, Top Ring Down .240, Valve Relief -4cc, Chamber Volume 84cc, Proposed Piston to Deck Height .005. Diamonds calculator shows that combo adding up to a static CR of 10.89 to 1

. The heads are aluminum (440Source).

Thanks.

Posted By: mopowered

Re: Check My Compression Ratio Calculations . - 01/04/09 12:57 AM

I got 10.25 using your proposed deck height at the RBR site:

http://www.rbracing-rsr.com/compstaticcalc.html

Posted By: Classof70Chally

Re: Check My Compression Ratio Calculations . - 01/04/09 01:04 AM

Thanks! That's a little closer to what I was shooting for. The car (Sig) will be strictly street driven with a 4 spd and a 3.54 Dana.The best pump gas we have here is 92 octane. Anyone else?

Posted By: Pacnorthcuda

Re: Check My Compression Ratio Calculations . - 01/04/09 01:08 AM

Welcome back Steve! You've been gone awhile.
Glad to hear the engine is progressing.
One question 4speed????

Posted By: Classof70Chally

Re: Check My Compression Ratio Calculations . - 01/04/09 01:15 AM

Uh, OK you got me. It's really a 5 spd. I'll blame it on CRS (Can't remember *&^%).

Posted By: ProSport

Re: Check My Compression Ratio Calculations . - 01/04/09 01:16 AM

I got 10.25 on the Wallace calculator.

Posted By: StealthWedge67

Re: Check My Compression Ratio Calculations . - 01/04/09 01:30 AM

Just a question, but why run the ragged edge of detonation with 10.25:1 compression in a street only motor?

Posted By: Classof70Chally

Re: Check My Compression Ratio Calculations . - 01/04/09 01:37 AM

Well with aluminum heads, .044 quench distance and 224int/230ex @.050 duration on a hyd roller cam I don't think it will be on the "ragged edge", but I'm far from an expert on the subject. Anyone else think I'm pushing it on the CR for this set up ?

Posted By: Sport440

Re: Check My Compression Ratio Calculations . - 01/04/09 01:38 AM

And from www.kb-silvolite.com i got 10.194 comp. so I dont think your anywhere near that 10.89 with two other 10.25,s and a 10.194 from 3 different sources. mike

Posted By: Cab_Burge

Re: Check My Compression Ratio Calculations . - 01/04/09 01:49 AM

Quote:

Well with aluminum heads, .044 quench distance and 224int/230ex @.050 duration on a hyd roller cam I don't think it will be on the "ragged edge", but I'm far from an expert on the subject. Anyone else think I'm pushing it on the CR for this set up ?

My 518 has 10.29 to 1 on OR pump gas with Eddy RPM heads, the 464 C.I. 440 six pak motor in the car now has 10;6 to 1 comp ratio with another set of Eddy RPM heads and runs fine also on the local OR pump swill, the trick is to use a cold plug and a fine tune up

Posted By: Classof70Chally

Re: Check My Compression Ratio Calculations . - 01/04/09 04:46 AM

Thanks for the replys so far. I don't know if I didn't work the Diamond Pistons calculator right or if it's that far off. What I was trying for was somewhere between 9.75 and 10.25 to 1 so it looks like I'll be there. One of the reasons I'm building a new motor is the one that is in my car now has maybe 8.0 to 1 CR even with closed iron heads. The pistons are about .150 below deck and cruising around town it just doesn't run sharp or clean. My sons 500 stroker motor is running about 11.2 to 1 with Eddy heads and flat tops. Granted he is running a bigger cam than I will but it does fine on 92 pump gas on the street. When he races it he likes to add some racing fuel for a little extra kick.

Posted By: 572B1

Re: Check My Compression Ratio Calculations . - 01/04/09 05:09 AM

Quote:

I'm ready to take my 440 block in to be decked, (already bored, honed and aligned honed). I am installing Diamond forged pistons and was using their C.R. calculator to figure my static comp ratio. Their number seems a bit high and I was hoping someone smarter than me (not hard to do ) could double check my figures. My numbers are as follows: Bore 4.350, Stroke 3.750, Rod Length 6.760, Gasket Bore 4.500, Gasket Thickness .039, Top Ring Down .240, Valve Relief -4cc, Chamber Volume 84cc, Proposed Piston to Deck Height .005. Diamonds calculator shows that combo adding up to a static CR of 10.89 to 1 . The heads are aluminum (440Source). Thanks.

The diamond calculator rates your motor at 10.1 not 10.89.you put in the wrong info.-4 for dome + 4 for dish. valve reliefs would be a dish not a dome.Try +4 instead of -4 and you will see your compression ratio is around 10.1 to 1 cheers Rob.

Posted By: Classof70Chally

Re: Check My Compression Ratio Calculations . - 01/04/09 05:40 AM

DOH!

That could cause a problem. Next time I'll do my math Before I have that second glass of wine!

Posted By: 440Jim

Re: Check My Compression Ratio Calculations . - 01/04/09 02:45 PM

Quote:

The diamond calculator rates your motor at 10.1 not 10.89.you put in the wrong info.-4 for dome + 4 for dish. valve reliefs would be a dish not a dome.Try +4 instead of -4 and you will see your compression ratio is around 10.1 to 1 cheers Rob.

Bingo! Ding, ding, ding

With aluminum heads, flat tops, etc. even 11.+ would be fine, IMO. Sleep easy on this one.