Too much static compression???
Thread Starter
Melting Slicks
Joined: Feb 2003
Posts: 2,529
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From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
Too much static compression???
Well my new 383 with 900 miles, that smoked like a Studebaker, is back at the engine builder. While going over some facts, like the cranking compression tests, he was concerned that my comprssion is too high for pump gas!!!
I had a range of 202 lbs to 212 lbs @ 450 miles, the cam is a Comp retro roller, with 224/230 duration @.050 with .503/510 lift with a 112 LSA and 109 LCA, Trick Flow aluminum heads have a 64 cc. Calculated compression ratio is 9.7. Just as Speed pro published
Why are the numbers so high..?
Should I change cams while the engine is out and go with more duration to bleed off the pressure or go to a 110 LSA instead of the 112?
Car is an automatic, TH400, witha 2500 Hughes stall convertor, and a 3:08 rear. Mark
I had a range of 202 lbs to 212 lbs @ 450 miles, the cam is a Comp retro roller, with 224/230 duration @.050 with .503/510 lift with a 112 LSA and 109 LCA, Trick Flow aluminum heads have a 64 cc. Calculated compression ratio is 9.7. Just as Speed pro published
Why are the numbers so high..?
Should I change cams while the engine is out and go with more duration to bleed off the pressure or go to a 110 LSA instead of the 112?
Car is an automatic, TH400, witha 2500 Hughes stall convertor, and a 3:08 rear. Mark
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You're on the edge....doable.....but tune needs to be correct. You can add some duration and/or WIDEN the LSA. Tightening it will increase cranking compression. You want intake to close later..not earlier.
If you can get it to run as is with no detonation..it will be a heck of a fun street motor.
So why was it smoking? Does he think it detonated and killed rings/pistons?
JIM
If you can get it to run as is with no detonation..it will be a heck of a fun street motor.
So why was it smoking? Does he think it detonated and killed rings/pistons?
JIM
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
A slightly longer duration cam may be in order, or you may end up having to retard the cam, thus delaying the intake valve closing event and reducing dynamic compression, should detonation occur. Since you're on the theoretical edge here, keep an eye on your plugs for those tiny little shinny spheres or any signs of damage.
Last edited by TheSkunkWorks; May 1, 2007 at 02:31 AM.
Thread Starter
Melting Slicks
Joined: Feb 2003
Posts: 2,529
Likes: 27
From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
Motorhead thanks, thats encouraging!! I was trying to put together a good solid, fun to drive, reliable, long living, motor and have a little rumble from the cam that would run on 87 or 89 octane...looks like I missed on that one!! Mark
Thread Starter
Melting Slicks
Joined: Feb 2003
Posts: 2,529
Likes: 27
From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
A slightly longer duration cam may be in order, or you may end up having to retard the cam, thus delaying the intake valve closing event and reducing dynamic compression, should detonation occur. Since you're on the theoretical edge here, keep an eye on your plugs for those tiny little shinny spheres or any signs of damage.
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Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Hmmm? ... Sensing same scenario.
BTW: an upside-down second ring WILL pump oil while showing same cranking compression & same static cylinder pressure.
That 202-212 is OK. Frankly, if oil is getting past ring ... & you then reduce pressure via cam ... it might smoke worse.
I think all rings (& entire motor) need a close inspection by someone who both knows what they're looking at ... and would not be liable if it revealed an assembly error.
Thread Starter
Melting Slicks
Joined: Feb 2003
Posts: 2,529
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From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
Hmmm? ... Sensing same scenario.
BTW: an upside-down second ring WILL pump oil while showing same cranking compression & same static cylinder pressure. Thats been my theory all along...but I eliminated any chance for error!!!
That 202-212 is OK. Frankly, if oil is getting past ring ... & you then reduce pressure via cam ... it might smoke worse.
I think all rings (& entire motor) need a close inspection by someone who both knows what they're looking at ... and would not be liable if it revealed an assembly error.
Drifting
Joined: Apr 2002
Posts: 1,716
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From: New Baden Illinois
I cannot comment on the compression numbers, but 9.7 CR with that cam and aluminum heads certainly does not sound like too much compression.
I am also anxiously awaiting the tear down results.
I am also anxiously awaiting the tear down results.
Le Mans Master
Joined: Oct 2005
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From: Macon, GA
I'm running Comp's retro roller XR282HR-10 (230/236 duration and .510/.520 lift on a 110 LSA) in my 327. With my 64cc heads and pop up pistons, I'm at approx 10.3:1. So far I haven't had any problems. I think your combo will be fine and a helluva lot of fun.
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Curious if builder himself has ever raised possibility of ring-install assembly error?
If he hasn't ... but consistently leans toward a defective part ... I'd be suspicious.
This can & does happen even with very good builders ... to exclude or deny that possibility is mark of ill-informed or the sort that won't ever accept responsibility for his mistakes.
I'd wanna be there & looking right at it & checking each ring as each piston comes out.
If he hasn't ... but consistently leans toward a defective part ... I'd be suspicious.
This can & does happen even with very good builders ... to exclude or deny that possibility is mark of ill-informed or the sort that won't ever accept responsibility for his mistakes.
I'd wanna be there & looking right at it & checking each ring as each piston comes out.
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
Perhaps someone whose done this on an engine similar to yours can chime in here and give you a more accurate info than these generalizations. In any event, keep in mind that cranking compression is only an indicator of dynamic compression, and that it may still be possible at very high RPM's for cylinder pressures to exceed the limits of your fuel.
That said, if you're fortunate enough that you aren't experiencing detonation "as is", you'll only be taking away perfromance by making this change.
Last edited by TheSkunkWorks; May 1, 2007 at 03:46 PM.
Le Mans Master
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From: Graceland in a Not Correctly Restored Stingray
Fine cam. It's basically the next step up in duration from the stick in question, but with narrower LSA. I'm assuming the Intake LCA is at 106. How's idle and vacuum?
Le Mans Master
Joined: Oct 2005
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From: Macon, GA
It hits pretty hard. I have no vacuum accessories so that really wasn't a concern. But now you mention it, I may put my vucuum gauge on it tonight to find out.
Drifting
Joined: Apr 2002
Posts: 1,716
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From: New Baden Illinois
Shy of actual measurements, or taking the time to run a detailed sim of your exact setup on Engine Analyzer Pro, I can only speculate that you'll likely see anywhere from only 2-3psi to as much as 5-10psi reduction from retarding the cam 2*, as there are a multitude of variables at work here. If that first 2* doesn't do it, I'd strongly consider another grind before shifting the intake lobe centerline much further from it's optimum point, since that 2* will put it at 111* and place more overlap area after TDC.
Perhaps someone whose done this on an engine similar to yours can chime in here and give you a more accurate info than these generalizations. In any event, keep in mind that cranking compression is only an indicator of dynamic compression, and that it may still be possible at very high RPM's for cylinder pressures to exceed the limits of your fuel.
That said, if you're fortunate enough that you aren't experiencing detonation "as is", you'll only be taking away perfromance by making this change.
Perhaps someone whose done this on an engine similar to yours can chime in here and give you a more accurate info than these generalizations. In any event, keep in mind that cranking compression is only an indicator of dynamic compression, and that it may still be possible at very high RPM's for cylinder pressures to exceed the limits of your fuel.
That said, if you're fortunate enough that you aren't experiencing detonation "as is", you'll only be taking away perfromance by making this change.
All this is for naught anyway because his CR would not have caused his oil issues unless he has some serious damage to the pistons.
Melting Slicks
Joined: Aug 2004
Posts: 2,165
Likes: 950
From: Keizer Oregon
Don't fall for the bigger is better cam scenario!! Your cam is more than reasonable for you intended purpose. 9.7CR is not too high for an aluminum headed engine. I have run 10.5:1 and will soon be running 11:1...(with maybe a squirt of race gas per tank). Nail those M.F.ers for the smoking motor and don't pay them another $.....
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
As someone who believes it's far to easy to overcam and compromise low and mid range torque and power, I'm certainly not trying to sell one here...
I sincerely hope he can leave well enough alone after he gets the smoking issue resolved.
I sincerely hope he can leave well enough alone after he gets the smoking issue resolved.
Last edited by TheSkunkWorks; May 18, 2007 at 03:47 AM.
Le Mans Master
Joined: May 2006
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From: League City Tx
Mbeeman, I think you have a great engine combo for a street cruiser but your builder is an idiot. I would take it to someone else, cut your losses and keep the same combo. As long as your static is a true 9.7-1 you should have no problems with it, as long as its tuned right.
Even if your compression was too high, that has nothing to do with it smoking unless you have already melted or cracked a piston/ring land/rings etc.
Now I did cook an old 406" pontiac motor once from detonation. It was right around 10-1 compression but that was with OLD(ie. steel and crappy chambers) 68' 72cc heads and a 231/239 duration hyd flat cam. It took about 10k miles and a ton of beating on it at the strip but eventually it lost power. The teardown revealed severe detonation damage. Could have been anything back in those days though, too much timing, jetting a little off....anything. That was back in the day when I used to read plugs for tuning. It still never burned oil though.
Even if your compression was too high, that has nothing to do with it smoking unless you have already melted or cracked a piston/ring land/rings etc.
Now I did cook an old 406" pontiac motor once from detonation. It was right around 10-1 compression but that was with OLD(ie. steel and crappy chambers) 68' 72cc heads and a 231/239 duration hyd flat cam. It took about 10k miles and a ton of beating on it at the strip but eventually it lost power. The teardown revealed severe detonation damage. Could have been anything back in those days though, too much timing, jetting a little off....anything. That was back in the day when I used to read plugs for tuning. It still never burned oil though.
