How much of a diff. in compression ratio?
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
How much of a diff. in compression ratio?
How much of a difference in compression ratio would I see if I went from a 58cc head to a 64cc or a 74cc head?
Is there a linear relationship between the cc's and the actual compression ratio?
Say I 'm at a 9.75:1 with a 58cc 113 head , but moved to a afr 195 with a cc of 64cc or 74cc.
If you can figure it out ,could you figure it out with both the 64cc and 74cc?
Is there a linear relationship between the cc's and the actual compression ratio?
Say I 'm at a 9.75:1 with a 58cc 113 head , but moved to a afr 195 with a cc of 64cc or 74cc.
If you can figure it out ,could you figure it out with both the 64cc and 74cc?
Burning Brakes
Joined: Nov 2003
Posts: 1,011
Likes: 1
From: Marietta Pa
St. Jude Donor '10-'11-'12-'13-'14
If I remember from my rebuild...the bore and stroke is 4.00 and 3.48.
I was looking at new heads....anyone correct me if i'm wrong, but I think 64cc would give you a 9.1-9.2 or there abouts and the 74cc would be right around 8.2-8.3 range. It also depends on the gasket thickness that you would go with.
I was looking at new heads....anyone correct me if i'm wrong, but I think 64cc would give you a 9.1-9.2 or there abouts and the 74cc would be right around 8.2-8.3 range. It also depends on the gasket thickness that you would go with.
Last edited by 1990dtgL98; Aug 11, 2006 at 02:26 AM.
Le Mans Master
Joined: Aug 2000
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From: Australia
Racer
Joined: Jun 2005
Posts: 416
Likes: 0
From: Gansevoort NY
Originally Posted by black_89_vette
How much of a difference in compression ratio would I see if I went from a 58cc head to a 64cc or a 74cc head?
Is there a linear relationship between the cc's and the actual compression ratio?
Say I 'm at a 9.75:1 with a 58cc 113 head , but moved to a afr 195 with a cc of 64cc or 74cc.
If you can figure it out ,could you figure it out with both the 64cc and 74cc?
Is there a linear relationship between the cc's and the actual compression ratio?
Say I 'm at a 9.75:1 with a 58cc 113 head , but moved to a afr 195 with a cc of 64cc or 74cc.
If you can figure it out ,could you figure it out with both the 64cc and 74cc?
Team Owner
Joined: Jan 2003
Posts: 20,333
Likes: 262
From: Summerland B.C. Canada
Originally Posted by rodj
Play with one of the many calculators out there.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by black_89_vette
If you can figure it out ,could you figure it out with both the 64cc and 74cc?
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Ugh.... I do not know the Head Gasket Bore Diameter , Compressed Head Gasket Thickness , Piston Deck Clearance and such as I did not build the engine.
So, 1990dtgL98 thank you for your input, it was at least an attempt.
I thought that with the knowledge on the forum, a general (fairly close) answer could be attained. Oh well...
So, say the 74 cc heads dropped me a full CR point, without getting into the engine, how much could I get the CR to increase via gaskets and/or other means?
So, 1990dtgL98 thank you for your input, it was at least an attempt.
I thought that with the knowledge on the forum, a general (fairly close) answer could be attained. Oh well...
So, say the 74 cc heads dropped me a full CR point, without getting into the engine, how much could I get the CR to increase via gaskets and/or other means?
Burning Brakes
Joined: May 2006
Posts: 1,097
Likes: 2
From: Richfield Utah
Originally Posted by black_89_vette
Ugh.... I do not know the Head Gasket Bore Diameter , Compressed Head Gasket Thickness , Piston Deck Clearance and such as I did not build the engine.
So, 1990dtgL98 thank you for your input, it was at least an attempt.
I thought that with the knowledge on the forum, a general (fairly close) answer could be attained. Oh well...
So, say the 74 cc heads dropped me a full CR point, without getting into the engine, how much could I get the CR to increase via gaskets and/or other means?
So, 1990dtgL98 thank you for your input, it was at least an attempt.
I thought that with the knowledge on the forum, a general (fairly close) answer could be attained. Oh well...
So, say the 74 cc heads dropped me a full CR point, without getting into the engine, how much could I get the CR to increase via gaskets and/or other means?
I'd like to figure what CR I would get with a .027 head gasket vs the stock .054? 
Call me whatever, but I am not sure of the math CFI-EFI is getting at...
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Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Oh, I can call myself stupid LOL many many times here on the forum, hence the posting questions.
Too many variables that I do not know, but just a general answer (with all other things being equal like gaskets) would suffice.
I hope you get your answer too.
Too many variables that I do not know, but just a general answer (with all other things being equal like gaskets) would suffice.
I hope you get your answer too.
Racer
Joined: Jun 2005
Posts: 416
Likes: 0
From: Gansevoort NY
Originally Posted by black_89_vette
Ugh.... I do not know the Head Gasket Bore Diameter , Compressed Head Gasket Thickness , Piston Deck Clearance and such as I did not build the engine.
So, 1990dtgL98 thank you for your input, it was at least an attempt.
I thought that with the knowledge on the forum, a general (fairly close) answer could be attained. Oh well...
So, say the 74 cc heads dropped me a full CR point, without getting into the engine, how much could I get the CR to increase via gaskets and/or other means?
So, 1990dtgL98 thank you for your input, it was at least an attempt.
I thought that with the knowledge on the forum, a general (fairly close) answer could be attained. Oh well...
So, say the 74 cc heads dropped me a full CR point, without getting into the engine, how much could I get the CR to increase via gaskets and/or other means?
you'll have that info when you build the topend backup. If it is the original engine. Standard deck height is roughly .025 and you probably have a .038 gasket. But that is just speculation. You're CR will always be lower than it is now because you are increase the volume of your heads. Even With a thinner gasket and a lower deck height I dont think you could offset the larger volume heads.UNLESS you change your pistons. I dont know if you want to get that involved in the rebuild.
Use one of the calcs as recommended to give you theoretical CR's with numbers above and just change the head volume . Watch how much the CR changes. There are several thin head gasket available out there just remember that when you start to reduce the deck and gasket height that piston to head clearance gets closer at TDC. So you also have to watch your piston to valve clearance if you are running larger than stock rockers.
Burning Brakes
Joined: May 2006
Posts: 1,097
Likes: 2
From: Richfield Utah
Originally Posted by black_89_vette
Oh, I can call myself stupid LOL many many times here on the forum, hence the posting questions.
Too many variables that I do not know, but just a general answer (with all other things being equal like gaskets) would suffice.
I hope you get your answer too.
Too many variables that I do not know, but just a general answer (with all other things being equal like gaskets) would suffice.
I hope you get your answer too.
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Hey Steel Breeze, I used one of those calculators and started inputting what I actually did know, then adjusted the other numbers til I hit a 9.5:1 CR.
I then changed the head gasket from 0.54 to 0.27 and CR seemed to jump half a point.
By the way, just adjusting the cc of the heads from the stock 58 to 64, I lost half a point, and continuing to 74 cc from 58 I lost a total of 1.25, down to like an 8.25.
Again, not sure if I'm right or wrong, but 1990dtgL98 guessed around an 8.2 - 8.3 so it might be right.
I then changed the head gasket from 0.54 to 0.27 and CR seemed to jump half a point.
By the way, just adjusting the cc of the heads from the stock 58 to 64, I lost half a point, and continuing to 74 cc from 58 I lost a total of 1.25, down to like an 8.25.
Again, not sure if I'm right or wrong, but 1990dtgL98 guessed around an 8.2 - 8.3 so it might be right.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
In the articles I've read, one of which did actual back to back dyno testing to show the difference in power attributal to CR, one point in CR translates to between 3 and 4 percent difference in power.
This percentage isn't totally linear though. As I recall, going from 8:1 to 9:1 CR resulted in a higher PERCENTAGE increase than going from 10:1 to 11:1.
As a rule of thumb, 8 to 10 ccs translates in a 1 point CR change, So 4 to 5 ccs would translate into 1/2 pt. If memory serves, years ago when I did the calculations, the change wasn't linear either. Up to 400 CID or so, the cc change pretty much holds but beyond that CID the effect is different.
Sorry I can't recall the specifics but you can do it yourself and just run the numbers.
Jake
This percentage isn't totally linear though. As I recall, going from 8:1 to 9:1 CR resulted in a higher PERCENTAGE increase than going from 10:1 to 11:1.
As a rule of thumb, 8 to 10 ccs translates in a 1 point CR change, So 4 to 5 ccs would translate into 1/2 pt. If memory serves, years ago when I did the calculations, the change wasn't linear either. Up to 400 CID or so, the cc change pretty much holds but beyond that CID the effect is different.
Sorry I can't recall the specifics but you can do it yourself and just run the numbers.
Jake
Burning Brakes
Joined: May 2006
Posts: 1,097
Likes: 2
From: Richfield Utah
Originally Posted by black_89_vette
Hey Steel Breeze, I used one of those calculators and started inputting what I actually did know, then adjusted the other numbers til I hit a 9.5:1 CR.
I then changed the head gasket from 0.54 to 0.27 and CR seemed to jump half a point.
By the way, just adjusting the cc of the heads from the stock 58 to 64, I lost half a point, and continuing to 74 cc from 58 I lost a total of 1.25, down to like an 8.25.
Again, not sure if I'm right or wrong, but 1990dtgL98 guessed around an 8.2 - 8.3 so it might be right.
I then changed the head gasket from 0.54 to 0.27 and CR seemed to jump half a point.
By the way, just adjusting the cc of the heads from the stock 58 to 64, I lost half a point, and continuing to 74 cc from 58 I lost a total of 1.25, down to like an 8.25.
Again, not sure if I'm right or wrong, but 1990dtgL98 guessed around an 8.2 - 8.3 so it might be right.
Originally Posted by JAKE
In the articles I've read, one of which did actual back to back dyno testing to show the difference in power attributal to CR, one point in CR translates to between 3 and 4 percent difference in power.
This percentage isn't totally linear though. As I recall, going from 8:1 to 9:1 CR resulted in a higher PERCENTAGE increase than going from 10:1 to 11:1.
As a rule of thumb, 8 to 10 ccs translates in a 1 point CR change, So 4 to 5 ccs would translate into 1/2 pt. If memory serves, years ago when I did the calculations, the change wasn't linear either. Up to 400 CID or so, the cc change pretty much holds but beyond that CID the effect is different.
Sorry I can't recall the specifics but you can do it yourself and just run the numbers.
This percentage isn't totally linear though. As I recall, going from 8:1 to 9:1 CR resulted in a higher PERCENTAGE increase than going from 10:1 to 11:1.
As a rule of thumb, 8 to 10 ccs translates in a 1 point CR change, So 4 to 5 ccs would translate into 1/2 pt. If memory serves, years ago when I did the calculations, the change wasn't linear either. Up to 400 CID or so, the cc change pretty much holds but beyond that CID the effect is different.
Sorry I can't recall the specifics but you can do it yourself and just run the numbers.
Pro
Joined: Jul 2005
Posts: 741
Likes: 37
From: Athens, GA
Originally Posted by black_89_vette
I then changed the head gasket from 0.54 to 0.27 and CR seemed to jump half a point.
Steven
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by black_89_vette
Ugh.... I do not know the Head Gasket Bore Diameter , Compressed Head Gasket Thickness , Piston Deck Clearance and such as I did not build the engine.
Originally Posted by Steel Breeze
Call me whatever, but I am not sure of the math CFI-EFI is getting at...
RACE ON!!!
PS. Watch out for those 1/4" and 1/2" thick gaskets.