Do I have higher compression than I thought????
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Do I have higher compression than I thought????
I just checked some of my engine specs... When I purchased my new engine - the CR was advertised to be 9.8:1... Later I asked for exact part numbers of the pistons used. They are Speedpro H600P. The heads are 64cc Dart Iron Eagle 215cc heads... I just checked the part number for the pistons and they show up as 10.34 : 1 with 64cc heads... The block was also zero decked which would add some additional compression... Now I am starting to understand why my engine is dieseling... My compression is very likely closer to 10.5!!! :eek: :eek:
I will still check with the engine builder but when checking all the numbers they gave me - the engine has 10.5:1 and not 9.8:1 compression unless the heads are actually 72 cc heads but they were advertised as 64cc heads! I'm actually happy if the compression is actually higher!!! I will just start to add some octane boost...
:cheers:
Olivier
I will still check with the engine builder but when checking all the numbers they gave me - the engine has 10.5:1 and not 9.8:1 compression unless the heads are actually 72 cc heads but they were advertised as 64cc heads! I'm actually happy if the compression is actually higher!!! I will just start to add some octane boost...
:cheers:
Olivier
Le Mans Master
Joined: Apr 2000
Posts: 5,202
Likes: 10
From: cincinnati ohio
St. Jude Donor '09
Re: Do I have higher compression than I thought???? (GrandSportC3)
! I'm actually happy if the compression is actually higher!!! I will just start to add some octane boost...
:cheers:
Olivier
:cheers:
Olivier
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (yellow 72)
! I'm actually happy if the compression is actually higher!!! I will just start to add some octane boost...
:cheers:
Olivier
Or just switch to a shiney new set of aluminum heads of your choice and that 10 1/2 tp one will live happily ever after :cheers:
:cheers:
Olivier
Or just switch to a shiney new set of aluminum heads of your choice and that 10 1/2 tp one will live happily ever after :cheers:
When going to the strip next time - I'm going to put 100 octane in the tank.. This might help my performance even more!!!
:cheers:
Olivier
Le Mans Master
Joined: Apr 2001
Posts: 5,941
Likes: 281
From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Re: Do I have higher compression than I thought???? (GrandSportC3)
How high is the idle. My zz4 was diseling because it was idling at 1000 rpms. I had to hold the brake and let the clutch out a little in gear to drop the rpms then turn it off.
Mark B.
Mark B.
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Sigforty)
How high is the idle. My zz4 was diseling because it was idling at 1000 rpms. I had to hold the brake and let the clutch out a little in gear to drop the rpms then turn it off.
Mark B.
Mark B.
BTW - I use the same technique to shut off the car to prevent dieseling!!!
:cheers:
Olivier
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
For comparison purposes - I am running the 70 LT-1 on 91 octane pump gas without any dieseling issues. Timing is set to 750 RPM and timing is a 17 degress advanced. Gas mileage when running at 2500 RPMs with NO playing is about 12 mpg. Tried to drop the timing, but she would stall.
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Robert N)
For comparison purposes - I am running the 70 LT-1 on 91 octane pump gas without any dieseling issues. Timing is set to 750 RPM and timing is a 17 degress advanced. Gas mileage when running at 2500 RPMs with NO playing is about 12 mpg. Tried to drop the timing, but she would stall.
:cheers:
Olivier
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
What does the manufacturer list as the proper RPM for idle? If dropping the RPMs to shut iff without dieseling, I would probably try to drop the idle by small increments to find the spot that solves the issue. Then try to set the timing, etc to meet that idle. Why the idle jumps back up - that would be the next item to tackle. Found this to better explain why dropping the idle:
"99 percent of the time, dieseling is caused by an idle speed that's set too high. The engine is turning so fast that it simply has too much angular momentum, and can't stop right away. So when you turn off the key, the engine keeps turning. And because it's still turning, fuel gets sucked in from the carburetor. And since the engine is still hot, some of that fuel gets combusted. So the engine continues to run (albeit poorly) for a few seconds after you shut off the ignition."
[Modified by Robert N, 1:47 PM 8/12/2002]
"99 percent of the time, dieseling is caused by an idle speed that's set too high. The engine is turning so fast that it simply has too much angular momentum, and can't stop right away. So when you turn off the key, the engine keeps turning. And because it's still turning, fuel gets sucked in from the carburetor. And since the engine is still hot, some of that fuel gets combusted. So the engine continues to run (albeit poorly) for a few seconds after you shut off the ignition."
[Modified by Robert N, 1:47 PM 8/12/2002]
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: Apr 2002
Posts: 7,281
Likes: 5
From: Boston
Re: Do I have higher compression than I thought???? (GrandSportC3)
I'm going to put 100 octane in the tank.. This might help my performance even more!!!
I think this article came in car craft mag or something like that, not sure.
Paul
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Robert N)
What does the manufacturer list as the proper RPM for idle? If dropping the RPMs to shut iff without dieseling, I would probably try to drop the idle by small increments to find the spot that solves the issue. Then try to set the timing, etc to meet that idle. Why the idle jumps back up - that would be the next item to tackle. Found this to better explain why dropping the idle:
"99 percent of the time, dieseling is caused by an idle speed that's set too high. The engine is turning so fast that it simply has too much angular momentum, and can't stop right away. So when you turn off the key, the engine keeps turning. And because it's still turning, fuel gets sucked in from the carburetor. And since the engine is still hot, some of that fuel gets combusted. So the engine continues to run (albeit poorly) for a few seconds after you shut off the ignition."
"99 percent of the time, dieseling is caused by an idle speed that's set too high. The engine is turning so fast that it simply has too much angular momentum, and can't stop right away. So when you turn off the key, the engine keeps turning. And because it's still turning, fuel gets sucked in from the carburetor. And since the engine is still hot, some of that fuel gets combusted. So the engine continues to run (albeit poorly) for a few seconds after you shut off the ignition."
:cheers:
Olivier
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (inferno-vette)
I'm going to put 100 octane in the tank.. This might help my performance even more!!!
Not really, I read an article a while back that said that just because there is more octanes the engine is not going to produce more power, the best gas for an engine is teh one that runs it without any knoking, pinging, detonation... because high octane fuel has a slower burn in order to prevent det, knok, ping... but if you put more than is required the engine actually looses power. The less octanes gas has the faster it burns thus producing more power, but in high compression engines it can't be had becasue of that. It doesn't mean that high CR isn't worth, of course but it would have more hp with 87 than 100.
I think this article came in car craft mag or something like that, not sure.
Paul
Not really, I read an article a while back that said that just because there is more octanes the engine is not going to produce more power, the best gas for an engine is teh one that runs it without any knoking, pinging, detonation... because high octane fuel has a slower burn in order to prevent det, knok, ping... but if you put more than is required the engine actually looses power. The less octanes gas has the faster it burns thus producing more power, but in high compression engines it can't be had becasue of that. It doesn't mean that high CR isn't worth, of course but it would have more hp with 87 than 100.
I think this article came in car craft mag or something like that, not sure.
Paul
:cheers:
Olivier
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
The cam in the 1970 LT-1 is also prettry radical. At 750 RPM, there is a VERY noticeable lope - camshaft had .458” intake and .484” exhaust lift, and duration figures of 317° intake and 346° exhaust. Not sure how this relates to yours - but the ZZ4 is showing (best as I can tell) 650 RPM at idle and 10 degrees BTDC. You should be able to drop the idle.
As for octane, too much will cause an issue, but unless you know exactly the rating needed, your thoughts mirror mine. I personally saw no difference in performance with an octane booster.
As for octane, too much will cause an issue, but unless you know exactly the rating needed, your thoughts mirror mine. I personally saw no difference in performance with an octane booster.
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Robert N)
The cam in the 1970 LT-1 is also prettry radical. At 750 RPM, there is a VERY noticeable lope - camshaft had .458” intake and .484” exhaust lift, and duration figures of 317° intake and 346° exhaust. Not sure how this relates to yours - but the ZZ4 is showing (best as I can tell) 650 RPM at idle and 10 degrees BTDC. You should be able to drop the idle.
As for octane, too much will cause an issue, but unless you know exactly the rating needed, your thoughts mirror mine. I personally saw no difference in performance with an octane booster.
As for octane, too much will cause an issue, but unless you know exactly the rating needed, your thoughts mirror mine. I personally saw no difference in performance with an octane booster.
Another thing is that my idle timing is 23 degrees BTDC!!!
:cheers:
Olivier
[Modified by GrandSportC3, 4:35 PM 8/12/2002]
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
I agree that the numbers seem off, but the part number for the 1970 LT-1
Z28 Camaro (same part if not mistaken) is 3972182 or 3972178 symbol: (1) square Solid lifter - 0.458(I)/0.484(E) lift, 317I/346E duration. This could be wrong specs, but my local GM dealer quoted a 300 intake and 312 exhuast duration.
Z28 Camaro (same part if not mistaken) is 3972182 or 3972178 symbol: (1) square Solid lifter - 0.458(I)/0.484(E) lift, 317I/346E duration. This could be wrong specs, but my local GM dealer quoted a 300 intake and 312 exhuast duration.
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Robert N)
I agree that the numbers seem off, but the part number for the 1970 LT-1
Z28 Camaro (same part if not mistaken) is 3972182 or 3972178 symbol: (1) square Solid lifter - 0.458(I)/0.484(E) lift, 317I/346E duration. This could be wrong specs, but my local GM dealer quoted a 300 intake and 312 exhuast duration.
Z28 Camaro (same part if not mistaken) is 3972182 or 3972178 symbol: (1) square Solid lifter - 0.458(I)/0.484(E) lift, 317I/346E duration. This could be wrong specs, but my local GM dealer quoted a 300 intake and 312 exhuast duration.
:cheers:
Olivier
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
Threw me for a loop too. That's why I called them. The response I was given - the car was built for pure speed in a straight line run (6000 RPM to hit peak HP) and not emissions. The car was built as a streetable race car.
Also, the LT-1 is running 2.02 intake and 1.60 exhaust valves. I am not an expert (please correct my theory here) but, you should be able to run a larger valve with a smaller lift and long duration to generate the same flow as smaller valves with taller lifts and less duration. shorter lift means less part movement (as does longer duration - fewer times opening and closing), generating less friction and less HP loss.
[Modified by Robert N, 5:16 PM 8/12/2002]
Also, the LT-1 is running 2.02 intake and 1.60 exhaust valves. I am not an expert (please correct my theory here) but, you should be able to run a larger valve with a smaller lift and long duration to generate the same flow as smaller valves with taller lifts and less duration. shorter lift means less part movement (as does longer duration - fewer times opening and closing), generating less friction and less HP loss.
[Modified by Robert N, 5:16 PM 8/12/2002]
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Robert N)
Threw me for a loop too. That's why I called them. The response I was given - the car was built for pure speed in a straight line run (6000 RPM to hit peak HP) and not emissions. The car was built as a streetable race car.
Also, the LT-1 is running 2.02 intake and 1.60 exhaust valves. I am not an expert (please correct my theory here) but, you should be able to run a larger valve with a smaller lift and long duration to generate the same flow as smaller valves with taller lifts and less duration. shorter lift means less part movement (as does longer duration - fewer times opening and closing), generating less friction and less HP loss.
Also, the LT-1 is running 2.02 intake and 1.60 exhaust valves. I am not an expert (please correct my theory here) but, you should be able to run a larger valve with a smaller lift and long duration to generate the same flow as smaller valves with taller lifts and less duration. shorter lift means less part movement (as does longer duration - fewer times opening and closing), generating less friction and less HP loss.
:cheers:
Olivier
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
OK, just spoke to a local race mechanic. The correlation between the lift and duration on my cam (32 years old) and yours is like comparing apples to oranges. The today's technology in the design of the cam, heads, valve train etc make mine obsolete. That explains why the numbers do not make sense. It also confirms that you have one heck of an engine :D . The LT-1 was awesome in its day, and compares to today's ZZ4. However, LS1s and LS4s blow it away.
Now that that is out of the way, it is still a wild cam for the set up, so getting the idle RPM on yours down should be possible - not sure how as that is out of my league. It does stand to reason that the idle speed is the source of the dieseling. I will be curious as to the results.
Now that that is out of the way, it is still a wild cam for the set up, so getting the idle RPM on yours down should be possible - not sure how as that is out of my league. It does stand to reason that the idle speed is the source of the dieseling. I will be curious as to the results.
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Robert N)
OK, just spoke to a local race mechanic. The correlation between the lift and duration on my cam (32 years old) and yours is like comparing apples to oranges. The today's technology in the design of the cam, heads, valve train etc make mine obsolete. That explains why the numbers do not make sense. It also confirms that you have one heck of an engine :D . The LT-1 was awesome in its day, and compares to today's ZZ4. However, LS1s and LS4s blow it away.
Now that that is out of the way, it is still a wild cam for the set up, so getting the idle RPM on yours down should be possible - not sure how as that is out of my league. It does stand to reason that the idle speed is the source of the dieseling. I will be curious as to the results.
Now that that is out of the way, it is still a wild cam for the set up, so getting the idle RPM on yours down should be possible - not sure how as that is out of my league. It does stand to reason that the idle speed is the source of the dieseling. I will be curious as to the results.
:cheers:
Olivier
Melting Slicks
Joined: Apr 2002
Posts: 2,103
Likes: 0
From: Tucson AZ
Re: Do I have higher compression than I thought???? (GrandSportC3)
You and me both. I understand how engines work, but making them work right is out of my league. In theory, dropping the fuel flow should allow for the idle to drop. Higher volume of fuel requires the engine to turn faster to to burn it avoiding flooding.