Do I have higher compression than I thought????
Safety Car
Joined: Feb 1999
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From: Fountain Hills 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.
I have browsed through many racing catalogs but never saw any small block cams that radical - especially not with that little lift (considering the duration).....
:cheers:
Olivier
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.
I have browsed through many racing catalogs but never saw any small block cams that radical - especially not with that little lift (considering the duration).....
:cheers:
Olivier
Instructor
Joined: Oct 1999
Posts: 139
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From: So. Miami
Re: Do I have higher compression than I thought???? (GrandSportC3)
The engine runs fine on pump gas - exept the dieseling when shutting off.. (no knocking or pinging)
When going to the strip next time - I'm going to put 100 octane in the tank.. This might help my performance even more!!!
I'm NO expert, but wouldn't it knock and ping with 10.5 to 1 on 93 pump gas and iron heads??? :confused: :confused:
When going to the strip next time - I'm going to put 100 octane in the tank.. This might help my performance even more!!!
I'm NO expert, but wouldn't it knock and ping with 10.5 to 1 on 93 pump gas and iron heads??? :confused: :confused:
Thread Starter
Team Owner
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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???? (Vetterodder)
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.
I have browsed through many racing catalogs but never saw any small block cams that radical - especially not with that little lift (considering the duration).....
:cheers:
Olivier
A cam's total duration is commonly advertised at a point after it has actually started to open the valves, typically at .008" lift, but GM used to advertise the duration of the entire circumference of the cam minus the base of the circle. Cam's that were actually less than 200º @ .050" might have advertised durations of over 300º (that same grind might be advertised at about 250º by after market grinders). Also keep in mind that a solid lifter cam doesn't begin to actually lift the valve until it's lash has been taken up, further skewing the numbers. In any case, though hardly comparable to "normal" ratings, GM did actually advertise those huge numbers.
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.
I have browsed through many racing catalogs but never saw any small block cams that radical - especially not with that little lift (considering the duration).....
:cheers:
Olivier
A cam's total duration is commonly advertised at a point after it has actually started to open the valves, typically at .008" lift, but GM used to advertise the duration of the entire circumference of the cam minus the base of the circle. Cam's that were actually less than 200º @ .050" might have advertised durations of over 300º (that same grind might be advertised at about 250º by after market grinders). Also keep in mind that a solid lifter cam doesn't begin to actually lift the valve until it's lash has been taken up, further skewing the numbers. In any case, though hardly comparable to "normal" ratings, GM did actually advertise those huge numbers.
:cheers:
Olivier
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From: Lakeland, FL
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St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (7tea1)
I'm NO expert, but wouldn't it knock and ping with 10.5 to 1 on 93 pump gas and iron heads??? :confused: :confused:
:cheers:
Olivier
Thread Starter
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From: Lakeland, FL
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St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (GrandSportC3)
I just checked all the numbers on my heads to determine if they are 64cc or 72 cc chamber. Here are the numbers that I found:
215 OF22 45 R2
I know that the 215 stands for 215 cc but I cannot decipher the rest...
:cheers:
Olivier
215 OF22 45 R2
I know that the 215 stands for 215 cc but I cannot decipher the rest...
:cheers:
Olivier
Race Director
Joined: Dec 1999
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From: Forked River NJ
Re: Do I have higher compression than I thought???? (GrandSportC3)
I just read your post o nthis subject. My cam has a 248 dur @ .050 and a .525 lift. I can idle it down to about 700 but it does not run well. I set it at about 900 and it runs fine. I estimate my compression at about 10 to 1. I wish I had a little more. My timing is set at 12 to 14 initial and 36 total. I very seldom have a run on but I attribute it to poor gas. (Not octane) just poor gas. 10.5 might be a little high with iron heads but it should not contribute to run on. I do have alum. heads and have never heard any rattling with this cam. Sounds like your initial timing is a little to advanced possibly
[Modified by Gordonm, 8:59 PM 8/12/2002]
[Modified by Gordonm, 8:59 PM 8/12/2002]
Thread Starter
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From: Lakeland, FL
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St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (Gordonm)
I just read your post o nthis subject. My cam has a 248 dur @ .050 and a .525 lift. I can idle it down to about 700 but it does not run well. I set it at about 900 and it runs fine. I estimate my compression at about 10 to 1. I wish I had a little more. My timing is set at 12 to 14 initial and 36 total. I very seldom have a run on but I attribute it to poor gas. (Not octane) just poor gas. 10.5 might be a little high with iron heads but it should not contribute to run on. I do have alum. heads and have never heard any rattling with this cam. Sounds like your initial timing is a little to advanced possibly
:cheers:
Olivier
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Melting Slicks
Joined: Apr 2002
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From: Tucson AZ
Re: Do I have higher compression than I thought???? (Gordonm)
It does seem high to me too. The 17 degrees on mine seemed high. If you can drop the idle speed, you should also be able to retard the timing. The octane rating, quality of gas, amount of fuel flow, idle speed, and timing are intertwined. The builder may have recommended the timing based on the engine as a whole. I am not an expert, but you will need to picka starting point and line everything up with that. It might take some trial and error. Again, see what you can do to drop the idle speed to solve the deiseling, then retard timing, etc.
Safety Car
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From: No longer a member
Re: Do I have higher compression than I thought???? (GrandSportC3)
I've had parts of this conversation with local speed shop guys and an engine tuner, here's some things that were explained to me. I can't say this is all true as I just don't know, but it seems to make sense and I hope I explain it right.
My timing is set for 16 degrees initial and 36 degrees total. Since my motor is known to be 10.5 to 1 compression with iron heads and XE284 CC I was asking about fuels. I was told to put about a 30% mix (or so) of a good hi-octane fuel in with a tank of premium so it would run a little better as the pump gas just wasn't cutting it. After putting in about 5 gallons of 108 it smoothed out nicely. The reason as it was explained is; the higher octane fuel burns more evenly whereas the lower octane is more of an explosion, so bringing the octane up letting each cylinder fire smoother is better.
I was advised to avoid the octane boost products (continually) as over time there will be a residual build up from it, where the gas would not. Like I said, I'm just relaying what I was told so nobody yell at me...I'm sensative :jester :lol:
My timing is set for 16 degrees initial and 36 degrees total. Since my motor is known to be 10.5 to 1 compression with iron heads and XE284 CC I was asking about fuels. I was told to put about a 30% mix (or so) of a good hi-octane fuel in with a tank of premium so it would run a little better as the pump gas just wasn't cutting it. After putting in about 5 gallons of 108 it smoothed out nicely. The reason as it was explained is; the higher octane fuel burns more evenly whereas the lower octane is more of an explosion, so bringing the octane up letting each cylinder fire smoother is better.
I was advised to avoid the octane boost products (continually) as over time there will be a residual build up from it, where the gas would not. Like I said, I'm just relaying what I was told so nobody yell at me...I'm sensative :jester :lol:
Instructor
Joined: Jul 2001
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From: kennett square,pa,us
Re: Do I have higher compression than I thought???? (GrandSportC3)
GrandsportC3,
What is your intake vacuum?
I was wondering if they have your idle speed and timing set high to get better intake vacuum with that much cam duration.
What is your intake vacuum?
I was wondering if they have your idle speed and timing set high to get better intake vacuum with that much cam duration.
Thread Starter
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From: Lakeland, FL
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St. Jude Donor '03, '06, '17
Re: Do I have higher compression than I thought???? (bud snyder)
GrandsportC3,
What is your intake vacuum?
I was wondering if they have your idle speed and timing set high to get better intake vacuum with that much cam duration.
What is your intake vacuum?
I was wondering if they have your idle speed and timing set high to get better intake vacuum with that much cam duration.
:cheers:
Olivier
Safety Car
Joined: Dec 1999
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From: Roxbury NJ
Re: Do I have higher compression than I thought???? (GrandSportC3)
Olivier, if you want to make an accurate guess at your compression ratio (without cc'ing the heads it's tough), you'll need to know which head gasket your builder used. Ask them what the compressed thickness is. I would also verify that your block was really 0 decked, since that will change things considerably.
My 540 should be around 10.4:1 using the advertised numbers provided by all the manufacturers. When I actually measured everything, I was at 9.75:1. My block had to be decked beyond 0 deck to bring the compression back and get the quench height right. The Dart heads that spec at 118cc were really 121-122cc, etc.
-Joe
My 540 should be around 10.4:1 using the advertised numbers provided by all the manufacturers. When I actually measured everything, I was at 9.75:1. My block had to be decked beyond 0 deck to bring the compression back and get the quench height right. The Dart heads that spec at 118cc were really 121-122cc, etc.
-Joe
Drifting
Joined: Sep 1999
Posts: 1,411
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From: Wylie TX
Re: Do I have higher compression than I thought???? (Flareside)
Olliver, as you know, I have a simialar spec'ed solid roller cam with 236/242 @.050. The car will idle at 600 RPM and have run with it for a while set at 700 RPM, but I like 800 RPM.
My timing at idle is set at 18*. I've played around with it a bit and this is where it seems to like it, but I got scared and didn't try any more advance.
I get 14" of vacuum at 800 RPM. I know you don't care much about the vacuum for accesory reasons, but you can tune your idle based on vacuum.
I'm running 69cc heads, flat-top pistons with 7cc valve reliefs, .028" head gasket, and .010" deck height. This gives me a 10.4:1 comp ratio. I never like it when the piston mfg only gives a comp ratio with their specs. Some will give you the actual "cc" either +/- which can be used to get an accurate comp ratio. Also, I found on their web page that their comp ratios are a "guidline" using standard deck height (.025") and head gasket thickness (.041"). If I would guess, I'd agree that you are around 10.5:1 or slightly higher with 64cc heads.
My timing at idle is set at 18*. I've played around with it a bit and this is where it seems to like it, but I got scared and didn't try any more advance.
I get 14" of vacuum at 800 RPM. I know you don't care much about the vacuum for accesory reasons, but you can tune your idle based on vacuum.
I'm running 69cc heads, flat-top pistons with 7cc valve reliefs, .028" head gasket, and .010" deck height. This gives me a 10.4:1 comp ratio. I never like it when the piston mfg only gives a comp ratio with their specs. Some will give you the actual "cc" either +/- which can be used to get an accurate comp ratio. Also, I found on their web page that their comp ratios are a "guidline" using standard deck height (.025") and head gasket thickness (.041"). If I would guess, I'd agree that you are around 10.5:1 or slightly higher with 64cc heads.
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
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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???? (Flareside)
Olivier, if you want to make an accurate guess at your compression ratio (without cc'ing the heads it's tough), you'll need to know which head gasket your builder used. Ask them what the compressed thickness is. I would also verify that your block was really 0 decked, since that will change things considerably.
My 540 should be around 10.4:1 using the advertised numbers provided by all the manufacturers. When I actually measured everything, I was at 9.75:1. My block had to be decked beyond 0 deck to bring the compression back and get the quench height right. The Dart heads that spec at 118cc were really 121-122cc, etc.
-Joe
My 540 should be around 10.4:1 using the advertised numbers provided by all the manufacturers. When I actually measured everything, I was at 9.75:1. My block had to be decked beyond 0 deck to bring the compression back and get the quench height right. The Dart heads that spec at 118cc were really 121-122cc, etc.
-Joe
:cheers:
Olivier
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Joined: Jul 2001
Posts: 182,997
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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???? (Chris A)
Olliver, as you know, I have a simialar spec'ed solid roller cam with 236/242 @.050. The car will idle at 600 RPM and have run with it for a while set at 700 RPM, but I like 800 RPM.
My timing at idle is set at 18*. I've played around with it a bit and this is where it seems to like it, but I got scared and didn't try any more advance.
I get 14" of vacuum at 800 RPM. I know you don't care much about the vacuum for accesory reasons, but you can tune your idle based on vacuum.
I'm running 69cc heads, flat-top pistons with 7cc valve reliefs, .028" head gasket, and .010" deck height. This gives me a 10.4:1 comp ratio. I never like it when the piston mfg only gives a comp ratio with their specs. Some will give you the actual "cc" either +/- which can be used to get an accurate comp ratio. Also, I found on their web page that their comp ratios are a "guidline" using standard deck height (.025") and head gasket thickness (.041"). If I would guess, I'd agree that you are around 10.5:1 or slightly higher with 64cc heads.
My timing at idle is set at 18*. I've played around with it a bit and this is where it seems to like it, but I got scared and didn't try any more advance.
I get 14" of vacuum at 800 RPM. I know you don't care much about the vacuum for accesory reasons, but you can tune your idle based on vacuum.
I'm running 69cc heads, flat-top pistons with 7cc valve reliefs, .028" head gasket, and .010" deck height. This gives me a 10.4:1 comp ratio. I never like it when the piston mfg only gives a comp ratio with their specs. Some will give you the actual "cc" either +/- which can be used to get an accurate comp ratio. Also, I found on their web page that their comp ratios are a "guidline" using standard deck height (.025") and head gasket thickness (.041"). If I would guess, I'd agree that you are around 10.5:1 or slightly higher with 64cc heads.
:cheers:
Olivier
Drifting
Joined: Jul 2001
Posts: 1,418
Likes: 1
Re: Do I have higher compression than I thought???? (GrandSportC3)
As Chris A pointed out the SpeedPro Hyperuetectics are estimated ar .025 down in the cylinder on the small chevy pistons. If it is Zero decked it will of course raise the ratio.
This calculator might be of some use for you
http://www.kb-silvolite.com/
When using a higher octane gas,I have found stepping down of the carb jets is needed. Just a suggestion,find a pump gas that works for you and stick with it.
That cam is not that radical,,crack open the rear throttle plate with the screw provided for this,the carb must be removed to see this screw. This will give you more idle air and allow for the idle mixture screws to show a difference when adjusting and will enable you to get the curb idle down . To further a bit,I would also tune the primary powervalve,to do this a vacumm guage will be needed
http://www.holley.com has some tips for this
This calculator might be of some use for you
http://www.kb-silvolite.com/
When using a higher octane gas,I have found stepping down of the carb jets is needed. Just a suggestion,find a pump gas that works for you and stick with it.
That cam is not that radical,,crack open the rear throttle plate with the screw provided for this,the carb must be removed to see this screw. This will give you more idle air and allow for the idle mixture screws to show a difference when adjusting and will enable you to get the curb idle down . To further a bit,I would also tune the primary powervalve,to do this a vacumm guage will be needed
http://www.holley.com has some tips for this
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???? (mountainmotor)
As Chris A pointed out the SpeedPro Hyperuetectics are estimated ar .025 down in the cylinder on the small chevy pistons. If it is Zero decked it will of course raise the ratio.
This calculator might be of some use for you
http://www.kb-silvolite.com/
When using a higher octane gas,I have found stepping down of the carb jets is needed. Just a suggestion,find a pump gas that works for you and stick with it.
That cam is not that radical,,crack open the rear throttle plate with the screw provided for this,the carb must be removed to see this screw. This will give you more idle air and allow for the idle mixture screws to show a difference when adjusting and will enable you to get the curb idle down . To further a bit,I would also tune the primary powervalve,to do this a vacumm guage will be needed
http://www.holley.com has some tips for this
This calculator might be of some use for you
http://www.kb-silvolite.com/
When using a higher octane gas,I have found stepping down of the carb jets is needed. Just a suggestion,find a pump gas that works for you and stick with it.
That cam is not that radical,,crack open the rear throttle plate with the screw provided for this,the carb must be removed to see this screw. This will give you more idle air and allow for the idle mixture screws to show a difference when adjusting and will enable you to get the curb idle down . To further a bit,I would also tune the primary powervalve,to do this a vacumm guage will be needed
http://www.holley.com has some tips for this
I just got an e-mail back from DARTHEADS describing how to identify them heads... The numbers are on the drivers side head and I was checking the passenger side head... I will check tonight to be sure about my CR.
Thanks again
Olivier
[Modified by GrandSportC3, 2:42 PM 8/13/2002]
Thread Starter
Team Owner
Joined: Jul 2001
Posts: 182,997
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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???? (Fevre)
Is your block bored at all? That will also drop comp.
:cheers:
Olivier