Can someone help me out calculating my dynamic compression ratio. Not sure if im getting the right numbers.

bore: 4.005
stroke: 4.00
heads cc: 65
gaskets: .051"
deck clearance: I believe .0005?
Gasket bore: 4.100
dish pistons: -3cc wesico

when i type my cam specs on MGI cam calculator its giving me a IVC of 50*

@ 660ft elevation

= 11:43:1 Static compression
= 9.95.1 Dynamic compression???

seems a little high to me. Ca. Anyone with knowledge in this stuff help me out.

 

Deck clearance is likely .006ish. To calculate DCR you need the .060” valve events of your camshaft, not the .050” events. It will knock it down significantly.

 

If deck clearance is 0.0005 and intake closing timing degrees ADBC @ .006 is 50, then...

Estimated Modified Combustion Chamber Volume in cc 65.000
Swept volume cc 825.766
Gasket cc 11.034
Deck Clearance Volume cc 0.103
Total Chamber volume cc 79.14
Compression ratio (static) 11.43
Quench 0.052
Displacement (ci) 403
Intake closing timing degrees ADBC @ .006 50.00
Total static volume (inches) 904.90
Rod horizontal displacement (inches) 1.53
Rod distance below crank centerline (inches) 1.29
Piston Rise from RR on crank centerline (inches) 5.93
Piston rise from crank centerline (inches) 4.64
Dynamic stroke (inches) 3.48
Total dynamic volume cc 797.61
Estimated dynamic compression ratio 10.08

If deck clearance is 0.005 and intake closing timing degrees ADBC @ .006 is 50, then...

Estimated Modified Combustion Chamber Volume in cc 65.000
Swept volume cc 825.766
Gasket cc 11.034
Deck Clearance Volume cc 1.032
Total Chamber volume cc 80.066
Compression ratio (static) 11.31
Quench 0.056
Displacement (ci) 403
Intake closing timing degrees ADBC @ .006 50.00
Total static volume (inches) 905.83
Rod horizontal displacement (inches) 1.53
Rod distance below crank centerline (inches) 1.29
Piston Rise from RR on crank centerline (inches) 5.93
Piston rise from crank centerline (inches) 4.64
Dynamic stroke (inches) 3.48
Total dynamic volume cc 798.54
Estimated dynamic compression ratio 9.97

 

What are your cam specs @0.005 lift (advertised)? I have my own calculator I can run. I just need intake and exhaust duration, and LSA with any advance or retard on the ICL.

FWIW I get 11.31:1 static with your combo

 

You mean valve events at .006", not .060". Lots of typos in this thread. It's ok. It happens.

I think you also need rod length for most calculators. The calculator I use needs the rod length too.

 

the difference in a 6.125" rod or a 6" rod will be minor, but yes it is usually included in dynamic compression.

 

Lolzzz. I’ve had a few typos lately. You guys know what I mean, not what I say??? I’ve got 3 engine builds going, 2 complete vehicles to totally restore, and I operate 2 businesses. I’m going to Ecuador here in 2 weeks for a much needed vacation. I hate excuses, but that’s all I got…..😜

 

Piston Pin Offset will have an effest.
I always install the piston Backwards.

 

Use the old wallace racing calculator it matches up to what my old spreadsheet always did. Now many people say it doesn't matter, but my old cam combos did really well back in the day.

wallaceracing.com/dynamic-cr.php

 

I use the Wallace calculators for DCR, compression, cubes. Pretty much everything I need to figure in that regard.

 

The numbers I posted assume 6.125 rods.

 

so I dont have the advertised durations. Just the @.050 which is what i posted. But I did use the Wallace cam timing calculation. Got 50* for my ivc @.050. Had to do some digging but found someone on the forum that said Cammotion adds 27.5 to the .050 ivc to equal the .006. So that would give me 77.5*

my rods are 6.125"

so I think im getting 11:3:1 Static and 8.08.1 Dynamic ?

 

CamMotion uses the 27.5. That number will vary slightly from one lobe family to the next…very slightly. The 8.08 you got is likely very close.

 

With the 6.125" rod you are correct. I made up some cam specs to get a 77.5° intake closing event and I get 8.1:1 on my calc as well. You should be good with plenty of margin for 91 or 93 octane.