|
440 Dynamic Compression and Pump Gas
#1179422
02/16/12 04:49 PM
02/16/12 04:49 PM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
I know there's a similar post already on here, but I would like to have someone double check me. I used an online calculator and came up with 8.53:1 DCR. Cam Card  Static CR 9.35:1 bore 4.35 stroke 3.75 Here's the actual info after degreeing the cam: Int open - 1* BTDC Int close - 41* ABDC Exh open - 54* BBDC Exh close - 2* BTDC Lobe centerline - Int 109* ATDC Lobe centerline - Exh 120* BTDC How will this be on pump gas? I read that 8.1:1 DCR or so is good. Is mine too high? What's optimum? Thanks 
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: Dodgem]
#1179426
02/16/12 07:21 PM
02/16/12 07:21 PM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
That will be right on the edge with iron heads so sneak up on the total timing and don't run it lean!
Just My
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179427
02/16/12 07:45 PM
02/16/12 07:45 PM
|
Joined: Jan 2003
Posts: 75,015
U.S.S.A.
JohnRR
I Win
|
I Win
Joined: Jan 2003
Posts: 75,015
U.S.S.A.
|
Quote:
Quote:
That will be right on the edge with iron heads so sneak up on the total timing and don't run it lean!
Just My
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
Static 9.35 with alum heads , it would probably run on diesel ... 
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: JohnRR]
#1179428
02/16/12 08:10 PM
02/16/12 08:10 PM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
Quote:
Quote:
That will be right on the edge with iron heads so sneak up on the total timing and don't run it lean!
Just My
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
Static 9.35 with alum heads , it would probably run on diesel ...
I think kerosene is cheaper, maybe I can use that 
Quote:
This seems to be a pretty good calculator: http://www.kb-silvolite.com/calc.php?action=comp
I think to be accurate you'll need more info than your post has.
Darren
thanks. I used that one and got the same result. I had read that 8.5:1 is high. I realize that 9.3:1 static is low, but from what I understand, the dynamic number is what really determines if you will have detonation issues or not. I'm still on a learning curve so I'm just trying to gather as much knowledge as possible.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179429
02/16/12 09:41 PM
02/16/12 09:41 PM
|
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
master
|
master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
|
Quote:
Quote:
Quote:
Quote:
That will be right on the edge with iron heads so sneak up on the total timing and don't run it lean!
Just My
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
Static 9.35 with alum heads , it would probably run on diesel ...
I think kerosene is cheaper, maybe I can use that
Quote:
This seems to be a pretty good calculator: http://www.kb-silvolite.com/calc.php?action=comp
I think to be accurate you'll need more info than your post has.
Darren
thanks. I used that one and got the same result. I had read that 8.5:1 is high. I realize that 9.3:1 static is low, but from what I understand, the dynamic number is what really determines if you will have detonation issues or not. I'm still on a learning curve so I'm just trying to gather as much knowledge as possible.
Generally, 8.5 w/al. heads is as high as I would go.
Right or wrong, I shoot for a static CR that gets me around 180 psi cranking and then dial in DCR with duration.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: 64Post]
#1179430
02/16/12 10:04 PM
02/16/12 10:04 PM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
Quote:
Quote:
Quote:
Quote:
That will be right on the edge with iron heads so sneak up on the total timing and don't run it lean!
Just My
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
Static 9.35 with alum heads , it would probably run on diesel ...
I think kerosene is cheaper, maybe I can use that
Quote:
This seems to be a pretty good calculator: http://www.kb-silvolite.com/calc.php?action=comp
I think to be accurate you'll need more info than your post has.
Darren
thanks. I used that one and got the same result. I had read that 8.5:1 is high. I realize that 9.3:1 static is low, but from what I understand, the dynamic number is what really determines if you will have detonation issues or not. I'm still on a learning curve so I'm just trying to gather as much knowledge as possible.
Generally, 8.5 w/al. heads is as high as I would go.
Right or wrong, I shoot for a static CR that gets me around 180 psi cranking then dial in DCR with duration.
Ok. Where do you think the timing should be in order to avoid detonation?
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179431
02/17/12 12:02 AM
02/17/12 12:02 AM
|
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
master
|
master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
|
Quote:
Quote:
Quote:
Quote:
Quote:
Quote:
That will be right on the edge with iron heads so sneak up on the total timing and don't run it lean!
Just My
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
Static 9.35 with alum heads , it would probably run on diesel ...
I think kerosene is cheaper, maybe I can use that
Quote:
This seems to be a pretty good calculator: http://www.kb-silvolite.com/calc.php?action=comp
I think to be accurate you'll need more info than your post has.
Darren
thanks. I used that one and got the same result. I had read that 8.5:1 is high. I realize that 9.3:1 static is low, but from what I understand, the dynamic number is what really determines if you will have detonation issues or not. I'm still on a learning curve so I'm just trying to gather as much knowledge as possible.
Generally, 8.5 w/al. heads is as high as I would go.
Right or wrong, I shoot for a static CR that gets me around 180 psi cranking then dial in DCR with duration.
Ok. Where do you think the timing should be in order to avoid detonation?
That's going to take trial and error testing on your part once you get it one the road. It might look something like this: 16 degrees initial, 34 degrees total, advance all in by 2800 rpm.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179434
02/17/12 09:34 AM
02/17/12 09:34 AM
|
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
master
|
master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
|
I'm running aluminum Stealth heads if that makes a difference. Sorry, should have mentioned that.
makes a big difference you will be fine!
When I put aluminum heads (that and the intake was the only change) on mine was 11.5 to 1 and gave a dynamic compression of 9.68 and i went from 102/103 octane (had to mix 60% 110 with 40% 93) right down to 93 and it was perfect. Bigger cams allow more static compression but you will be fine!
Last year I ran 11.9 to 1 with a bigger cam came to 9.8 to 1 dynamic and still ran 93
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179437
02/18/12 03:07 PM
02/18/12 03:07 PM
|
Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar
master
|
master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
|
Using the Kb Calculator:
Entered these specs:
Cylinder Head 79cc
Piston Head 20cc
Gasket thickness 0.040"
Gasket bore 4.5"
Bore 4.35"
Deck 0"
stroke 3.75"
--Calculated compression ratio = 9.349:1
Rod length 6.768" (440 length)
Intake Closing point @ 0.050 = 41 + 15 per calculator instruction = 56 degrees after BDC.
Dynamic = 7.911.
That should be a cranking pressure of about 156 psi?
The advertised duration numbers look large for that cam? I'm guessing they were measured at 0.002" lobe lift? I think the true intake closing point may be more than the 56 degrees so the DCR and cranking pressure may be lower than the calculated value?
Last edited by 451Mopar; 02/18/12 03:14 PM.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: 451Mopar]
#1179438
02/18/12 07:24 PM
02/18/12 07:24 PM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
Using the Kb Calculator:
Entered these specs:
Cylinder Head 79cc
Piston Head 20cc
Gasket thickness 0.040"
Gasket bore 4.5"
Bore 4.35"
Deck 0"
stroke 3.75"
--Calculated compression ratio = 9.349:1
Rod length 6.768" (440 length)
Intake Closing point @ 0.050 = 41 + 15 per calculator instruction = 56 degrees after BDC.
Dynamic = 7.911.
That should be a cranking pressure of about 156 psi?
The advertised duration numbers look large for that cam? I'm guessing they were measured at 0.002" lobe lift? I think the true intake closing point may be more than the 56 degrees so the DCR and cranking pressure may be lower than the calculated value?
The actual specs of the engine are:
Heads 82cc
bore 4.35
deck .085
piston (flat top) 0cc
stroke 3.75
gasket .027
gasket bore 4.38
I never saw the "add 15*" notation on the calculators I used. But, I found this page however that has a lot of good info and I entered the actual cam numbers into the calculator downloaded from there to figure the exact intake closing.
http://www.chevytalk.org/fusionbb/showtopic.php?tid/92966/
Based on that it turns out to be 71*, which yields a 6.99:1 DCR
That should be pump gas friendly...it should run good on 87 octane...though it may be a slug...
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: 451Mopar]
#1179440
02/19/12 02:55 AM
02/19/12 02:55 AM
|
Joined: May 2009
Posts: 62
montreal, quebec,canada
7e5dartsport
member
|
member
Joined: May 2009
Posts: 62
montreal, quebec,canada
|
from the cam card, i see you calculated dynamic compression ratio (dcr) from .050 duration numbers . you cannot do that. you need to use advertised numbers. from the advertised duration and max lift degrees (both on the intake) , i calculate the intake closing point is 70* abdc ( 109 + 282/2 - 180) . using this (70*) and the other engine specs you stated, gives me the following results : static cr is 9.35:1, dcr is 7.13:1 , and cranking pressure is 137 psi, which, in my book , will be fine with 91 octane. in my opinion, you will need as much as 37-38* timing 
fully legal sounds the same as full illegal...
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: 7e5dartsport]
#1179441
02/19/12 03:39 AM
02/19/12 03:39 AM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
from the cam card, i see you calculated dynamic compression ratio (dcr) from .050 duration numbers . you cannot do that. you need to use advertised numbers. from the advertised duration and max lift degrees (both on the intake) , i calculate the intake closing point is 70* abdc ( 109 + 282/2 - 180) . using this (70*) and the other engine specs you stated, gives me the following results : static cr is 9.35:1, dcr is 7.13:1 , and cranking pressure is 137 psi, which, in my book , will be fine with 91 octane. in my opinion, you will need as much as 37-38* timing
Thanks for the info. I'm still learning.
I was just curious, how you came up with the 7.13:1 dcr. Originally, I input 110 ICL by mistake, that's how I got the 71*. Using the calculator I have with this 70* info, I come up with 7.054:1?
Not that it really matters that much, just struggling to understand.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179442
02/19/12 06:00 PM
02/19/12 06:00 PM
|
Joined: May 2009
Posts: 62
montreal, quebec,canada
7e5dartsport
member
|
member
Joined: May 2009
Posts: 62
montreal, quebec,canada
|
i use wallace racing`s calculator. i have my own formula to calculate dcr and both give me 7.12 or 7.13 dcr. input numbers to plug into the wallace racing calculator are bore=4.35, stroke=3.75, rod length=6.768, static cr=9.35, altitude=0, boost=0, 8cylinders and intake closing point=70*. it should give you the same results as mine. you can use their calculators they are accurate and very powerful.
fully legal sounds the same as full illegal...
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: 7e5dartsport]
#1179443
02/19/12 07:30 PM
02/19/12 07:30 PM
|
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
master
|
master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
|
Pretty sure wallace uses .050 numbers it's the same as this http://www.rbracing-rsr.com/comprAdvHD.htmStatic compression ratio of 9.35:1. Effective stroke is 3.39 inches. Your dynamic compression ratio is 8.57:1 . Your dynamic cranking pressure is 173.77 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.57 :1. V/P (Volume to Pressure Index) is 210 I have a detailed dyno program and it gives the same cranking compression! 
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: Dodgem]
#1179444
02/19/12 07:48 PM
02/19/12 07:48 PM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
Pretty sure wallace uses .050 numbers it's the same as this
http://www.rbracing-rsr.com/comprAdvHD.htm
Static compression ratio of 9.35:1.
Effective stroke is 3.39 inches.
Your dynamic compression ratio is 8.57:1 .
Your dynamic cranking pressure is 173.77 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.57 :1.
V/P (Volume to Pressure Index) is 210
I have a detailed dyno program and it gives the same cranking compression!
Hmmm, Using that calculator, I got the same result as you, except as I understand it, you are supposed to add about 30* (which would make it 70* seated) to the Intake Closing to correct for the @.050 number because the chamber doesn't start building pressure until the valve is fully seated. Maybe that calculator automatically adjusts for that?
I used the one listed DCR Calculator with VB6 Runtime files at the bottom of the page on this site.
http://cochise.uia.net/pkelley2/DynamicCR.html
It calculates dynamic stroke length, cam timing / overlap and static and dynamic compression, but it uses seat to seat (advertised) timing, not @.050 specs. Maybe try that one and see what you think? I keep coming up with 7.054:1. This is very confusing.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: Dodgem]
#1179447
02/20/12 12:04 AM
02/20/12 12:04 AM
|
Joined: May 2009
Posts: 62
montreal, quebec,canada
7e5dartsport
member
|
member
Joined: May 2009
Posts: 62
montreal, quebec,canada
|
bob, i used cochises dcr calculator only to find out the dcr is 7.127. results are rd=1.762, rr=.641, pr1=6.535, pr2=5.894, dst=2.749. calculating compression ratio with dst instead of stroke gives the afformentioned dcr results. those thinking you should use .050 measurements instead of advertised ones should read your link to cochise`s dcr calculation. compare these results with yours to find out where you made a mistake. thanks, serge.
fully legal sounds the same as full illegal...
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: 7e5dartsport]
#1179448
02/20/12 12:13 AM
02/20/12 12:13 AM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
i use wallace racing`s calculator. i have my own formula to calculate dcr and both give me 7.12 or 7.13 dcr. input numbers to plug into the wallace racing calculator are bore=4.35, stroke=3.75, rod length=6.768, static cr=9.35, altitude=0, boost=0, 8cylinders and intake closing point=70*. it should give you the same results as mine.
You're right. I was giving a 7.768 rod length by mistake.  Sorry.
Thanks for your help.
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: bobs66440]
#1179449
02/20/12 12:36 AM
02/20/12 12:36 AM
|
Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar
master
|
master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
|
Dynamic compression ratio is just a re-calculation of compression ratio using the piston position at the point the intake valve closes, and technically it would be the point where reversion out of the cylinder stops. Because DCR is used to estimate cranking cylinder pressure, and cranking speed is very slow, the 0.006" "Advertised" duration number is used to estimate the intake valve closing point.
If you had zero lash and 1.5:1 rocker arms (and no deflection of parts) the valve would only be open 0.009" with 0.006" lobe lift. This 0.009" is what the calculation is estimating to be the point where the valve "looks" closed and has captured the newly calculated cylinder volume of air/fuel at the atmospheric pressure. With a solid cam the valve lash would have to be factored in. The equation then takes the new Dynamic compression ratio DCR raised to the power 1.2 (the 1.2 is an estimate of the polytropic heat ratio of compressing the air/fuel mixture), and multiplies it by the atmospheric pressure to get absolute chamber pressure at TDC (DCR^1.2 * 14.7.) Gauge pressure is just the absolute pressure - the reference atmosphere pressure.
In theory (with no heat lost to the engine) the gas temperature would also be increased by the DCR. That is why having cool incomming air/fuel helps lower the chance of detonation, because that temp is multiplied by the DCR. But also the heat is dissipated into the surrounding engine parts, so if the engine temp is lowered it also helps reduce detonation. On the flip side, on combustion a cooler engine also absorbs more heat energy so it is thermally less efficient.
The 0.050" duration numbers are not used for DCR calculation because the valve would be too far open (0.075") to be the capture point (at cranking speed.)
|
|
|
Re: 440 Dynamic Compression and Pump Gas
[Re: Dodgem]
#1179451
02/20/12 10:40 AM
02/20/12 10:40 AM
|
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
bobs66440
OP
top fuel
|
OP
top fuel
Joined: Mar 2010
Posts: 1,880
Out in Left Field, NY
|
Quote:
Quote:
Quote:
Who said @.050 is @.050!
I don't understand the question...
When a calculator say input the @ .050 number that's all you do and go on. If you put your numbers in @ .050 my dyno program that also gives the cranking compression give the same number.
you "DON'T" decide to make up your own math and add it into the mix.
I have lots of experience and within a couple pounds the boost compression calculator is real close to real world numbers i get. And my dyno program which also gives octane requirements always agrees.
Don't over think this just go on with your life!
at 1000 feet not sure where you live but your looking at 160 to 170 lb cranking compression safe with an aluminum head probably right at 165 anyway once you check it post it!
Ok, that clears it up, thanks!
|
|
|
|
|
