dynamic c/r: will i have a problem?
Thread Starter
Team Owner
Joined: Sep 2002
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From: OBAMA IS HITLER
dynamic c/r: will i have a problem?
I've selected a decent mid-grade forged piston (Speed Pro) that will give me a final static c/r of 10.188:1.
however, the calculator comes up with a dynamic c/r of 8.849:1
this seems really high. my LPE 219 cam closes at 37.3 degrees ABDC @ .050" on the intake.
am i still going to have detonation? OR, does proper A/F tuning correct this?
however, the calculator comes up with a dynamic c/r of 8.849:1
this seems really high. my LPE 219 cam closes at 37.3 degrees ABDC @ .050" on the intake.
am i still going to have detonation? OR, does proper A/F tuning correct this?
Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Hi, Brad.
Seems like something's wrong with the math. 10.1 with a 219 shouldn't be that high.
On my engine the intake closing at .050 is 42 degrees and with:
10.56 with a 224 @ 050 gives me 8.15
11.03 with a 224 @ .050 gives me 8.5
What program are you using?
Jake
Seems like something's wrong with the math. 10.1 with a 219 shouldn't be that high.
On my engine the intake closing at .050 is 42 degrees and with:
10.56 with a 224 @ 050 gives me 8.15
11.03 with a 224 @ .050 gives me 8.5
What program are you using?
Jake
Last edited by JAKE; Mar 23, 2005 at 02:39 AM.
Thread Starter
Team Owner
Joined: Sep 2002
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From: OBAMA IS HITLER
i used the calc at the united engine & machine co site:
http://www.kb-silvolite.com/calc.php?action=comp
here's my data:
cyl. head vol. = 56cc
piston head vol. = 10.9cc (dish)
gasket thickness = .041
gasket bore = 4.166
cyl. bore dia = 4.030
deck clearance = .015
stroke = 3.48
rod = 5.7
int. closing point + 15 deg. = 37.3 + 15 = 52.3
now the deck clearance i'm not 100% sure here. the pistons have a compression height of 1.550". my deck height was measured at .005". i believe this means they will be in the hole .010 + .005 = .015? if so, then total deck height is correct.
which means i'm no thrilled about the quench, its on the high side with that gasket.
anyway, maybe thats a bad calculator.
i don't have measurements @ .004" lift, but i do @ .006"......the intake closing point with my 219 cam measured out to 67.5 degrees ABDC.
http://www.kb-silvolite.com/calc.php?action=comp
here's my data:
cyl. head vol. = 56cc
piston head vol. = 10.9cc (dish)
gasket thickness = .041
gasket bore = 4.166
cyl. bore dia = 4.030
deck clearance = .015
stroke = 3.48
rod = 5.7
int. closing point + 15 deg. = 37.3 + 15 = 52.3
now the deck clearance i'm not 100% sure here. the pistons have a compression height of 1.550". my deck height was measured at .005". i believe this means they will be in the hole .010 + .005 = .015? if so, then total deck height is correct.
which means i'm no thrilled about the quench, its on the high side with that gasket.
anyway, maybe thats a bad calculator.
i don't have measurements @ .004" lift, but i do @ .006"......the intake closing point with my 219 cam measured out to 67.5 degrees ABDC.
Le Mans Master
Joined: Feb 1999
Posts: 6,172
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From: somers, ny
I dont care what your DCR calcs tell ya....a 10:1 CR with a 219 in a FI application will not have detonation problems especially with aluminum heads. I ran mine around 10.8:1 and i know some that were around 11:1. In fact LPE used to sell 219 crate engines with 11:1. Been done 1000s of time. Going over 11:1 could be a problem.
Thread Starter
Team Owner
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From: OBAMA IS HITLER
sounds fair enough, ralph. i appreciate your input.
its kinda tough for a newbiw like me when you see a calculation, and yet hear about how terribly important it is to control it, i always hear you don't want to go over about 8.4:1 DCR. so i never know for sure if i'm a risk candidate or not.
its kinda tough for a newbiw like me when you see a calculation, and yet hear about how terribly important it is to control it, i always hear you don't want to go over about 8.4:1 DCR. so i never know for sure if i'm a risk candidate or not.
Le Mans Master
Joined: Mar 2002
Posts: 5,889
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From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Originally Posted by bradvette
sounds fair enough, ralph. i appreciate your input.
its kinda tough for a newbiw like me when you see a calculation, and yet hear about how terribly important it is to control it, i always hear you don't want to go over about 8.4:1 DCR. so i never know for sure if i'm a risk candidate or not.
its kinda tough for a newbiw like me when you see a calculation, and yet hear about how terribly important it is to control it, i always hear you don't want to go over about 8.4:1 DCR. so i never know for sure if i'm a risk candidate or not.
Again, I'm at 10.66 with true LPE events and seem just fine with 91 octane and aluminum heads. My IVO is 28* with an EVO of 72.......how are you getting your valve events?
Thread Starter
Team Owner
Joined: Sep 2002
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From: OBAMA IS HITLER
Tim, yup, its called major gun-shy, and I'm always paranoid anyway 
I got the intake closing event from the cam doctor report.......the Accel cam card says 37.5 (I had to obtain this separately, since none cam in the box with the cam), mine measured out to be 37.3.
You're mentioning intake open event.
Maybe I'm screwed up because its the wrong calculator. I used the only one I could find, at the website in my post above.
I got the intake closing event from the cam doctor report.......the Accel cam card says 37.5 (I had to obtain this separately, since none cam in the box with the cam), mine measured out to be 37.3.You're mentioning intake open event.
Maybe I'm screwed up because its the wrong calculator. I used the only one I could find, at the website in my post above.
Last edited by Red Tornado; Mar 23, 2005 at 10:17 AM.
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Le Mans Master
Joined: Mar 2002
Posts: 5,889
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From: Castro Valley Calif.
St. Jude Donor '03 thru '26
I thought I sent you one in an IM. If not, here's one I like quite a bit...it's fairy close and easy to use. The dowload part is toward the bottom of the page:
http://members.uia.net/pkelley2/DynamicCR.html
http://members.uia.net/pkelley2/DynamicCR.html
Instructor
Joined: Oct 2000
Posts: 152
Likes: 0
From: des plaines, il
Check the 'engine' board for a thread on DCR.
You were asking about your 'tune' in yesterdays flurry of activity. You should have someone look at your chip and make sure the GM knock retard routine is not altered. It's in there to reduce timing during a detonation situation. You might want to be sure its working next time, at least until you are confident in your new engine parts.
You were asking about your 'tune' in yesterdays flurry of activity. You should have someone look at your chip and make sure the GM knock retard routine is not altered. It's in there to reduce timing during a detonation situation. You might want to be sure its working next time, at least until you are confident in your new engine parts.
Le Mans Master
Joined: Feb 1999
Posts: 6,172
Likes: 11
From: somers, ny
Brad FWIW, my engine analyzer SW puts the DCR at 7.8 for my 350/219 10.8:1 combo. Theorectical cranking compression was 190 and it tested out at about 185 psi.
EDIT:
Interesting, i loaded the engine specs into the pro version of the SW and it calc'd the DCR as 8.3 and the cranking compression at 213psi????? I know the cranking compression was 190 in the best cyl. I haven't got much experience with the pro version of the SW, but the std version has typically been pretty darn close.
Nonetheless......you shouldn't have a problem. LPE wouldn't sell an engine that was on the edge of detonation and you're planing a full point less compression. Shouldn't have a problem, assuming the fuel/air mixture is ok.
EDIT:
Interesting, i loaded the engine specs into the pro version of the SW and it calc'd the DCR as 8.3 and the cranking compression at 213psi????? I know the cranking compression was 190 in the best cyl. I haven't got much experience with the pro version of the SW, but the std version has typically been pretty darn close.
Nonetheless......you shouldn't have a problem. LPE wouldn't sell an engine that was on the edge of detonation and you're planing a full point less compression. Shouldn't have a problem, assuming the fuel/air mixture is ok.
Last edited by ralph; Mar 23, 2005 at 11:56 AM.
Le Mans Master
Joined: Feb 1999
Posts: 6,172
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From: somers, ny
Originally Posted by bradvette
ralph, would you mind running the DCR and cranking compression numbers for mine? if you need any more info, just let me know. Thanks, Brad
Dropping the CR to 10:1 the DCR came to 7.3 DCR on the std version with 175 psi cranking compression...and...on the proversion it came to 7.7 DCR with 190 psi cranking compression. General rule of thumb: once it's built....cranking compression under 190-200 psi shouldn't be a problem with pump gas.
Good luck
Last edited by ralph; Mar 23, 2005 at 12:11 PM.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
Originally Posted by bradvette
ralph - and everyone else, thanks for all your help. looks like the home team'll be in good shape.
The .050 intake closing was 37.5. with the cam installed 4 degrees advanced.
Just shows how different programs can calculate things a little differently.
Jake
Le Mans Master
Joined: Feb 1999
Posts: 6,172
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From: somers, ny
Jake.....my calcs were assuming striaght up and 10:1. At 4 deg adv and 10.1 i come up with exactly the same DCR and CCR as you do. However, I doubt it will have over 200CCR and the EA pro gives my old 350 combo way too much HP. For a simple 350/219/SR it's showing almost 450 hp.....and a torque peak at 5300. The std version of the EA SW, gave me 390 hp and a torque peak at 4200, which i think is much closer than the pro version. I've got a couple of engine dynos from LPE and their 383s were making around 450 and the 350s around 400. The std version also gave me my exact cranking psi for both my 350 and 406. It will even be right on for different lash settings. The pro version seems too optimistic and off on some of the conclusions. Strange...same company's SW with supposedly more intelligence and it seems less accurate to me.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by ralph
Jake.....my calcs were assuming striaght up and 10:1. At 4 deg adv and 10.1 i come up with exactly the same DCR and CCR as you do. However, I doubt it will have over 200CCR and the EA pro gives my old 350 combo way too much HP. For a simple 350/219/SR it's showing almost 450 hp.....and a torque peak at 5300. The std version of the EA SW, gave me 390 hp and a torque peak at 4200, which i think is much closer than the pro version. I've got a couple of engine dynos from LPE and their 383s were making around 450 and the 350s around 400. The std version also gave me my exact cranking psi for both my 350 and 406. It will even be right on for different lash settings. The pro version seems too optimistic and off on some of the conclusions. Strange...same company's SW with supposedly more intelligence and it seems less accurate to me.
Sometimes too much is just that.
Jake
