Approx CR needed
Melting Slicks
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From: New Cumberland PA
Just with some rough numbers I would guess closer to 8.9 :1.
I figured with a .030 bore, .043 head gasket, piston to deck height of .025, 67cc heads, and 10cc for the pistons.
To get closer to 9.5 to 1 you would have to reduce the quench area by about .025". Or you could drop the cc of the heads to 64 and get pistons with 2 reliefs.
I figured with a .030 bore, .043 head gasket, piston to deck height of .025, 67cc heads, and 10cc for the pistons.
To get closer to 9.5 to 1 you would have to reduce the quench area by about .025". Or you could drop the cc of the heads to 64 and get pistons with 2 reliefs.
Race Director
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From: central FL, near the beach.
Originally Posted by gtr1999
355 with 4 relief flat tops and 67cc heads, I'm guessing about 9.5:1??
Anyone know for sure?
Thank you,
Gary
Anyone know for sure?
Thank you,
Gary
But my guess is it's not decked, and has a thick HG, 9.1:1 + or- 1/4
Last edited by Matt Gruber; Feb 8, 2005 at 12:21 PM.
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Gtr, more info is needed to get it exact. Here are a couple of calculators I have used to figure, first the piston deck clearance, and then with that info you can figure the static CR.
http://www.kb-silvolite.com/calc.php?action=deck (deck clearance)
http://www.csgnetwork.com/compcalc.html (compression ratio)
http://www.kb-silvolite.com/calc.php?action=deck (deck clearance)
http://www.csgnetwork.com/compcalc.html (compression ratio)
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From: Denmark
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Originally Posted by StingrayDK
You know the old saying..."First one to the trough...". But I did leave you a "floaty"!
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From: Connecticut, USA
Thanks guys. This is an original non machined block. I will be using the thick FEL-PRO's, flat tops, and have no idea of the depth-didn't check it before pulling apart the engine. I was going to use the stock cast pistons but have decided to bore it so I'll go with the cast FT's and moly rings. I want to keep it within 9-9.5 max I was planning on the 260H cam with the stock 8.5 CR and didn't know how much the higher CR might affect the cam choice?
Gary
Gary
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Assuming all of the following:
Bore: 4.030
Stroke: 3.480
Gasket Bore Diam.: 4.166 (Fel-Pro Steel)
Gasket Thickness: .041 (compressed)
Chamber Volume: 67cc (big assumption)
Piston Dome Volume: -6cc
Piston Deck Clearance: .026 in the hole (another big assumption)
It calculates out to 9.30:1. By milling the heads to achieve a 65cc chamber, you would be at exactly 9.50:1.
Bore: 4.030
Stroke: 3.480
Gasket Bore Diam.: 4.166 (Fel-Pro Steel)
Gasket Thickness: .041 (compressed)
Chamber Volume: 67cc (big assumption)
Piston Dome Volume: -6cc
Piston Deck Clearance: .026 in the hole (another big assumption)
It calculates out to 9.30:1. By milling the heads to achieve a 65cc chamber, you would be at exactly 9.50:1.
Thread Starter
Tech Contributor
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From: Connecticut, USA
Originally Posted by kcmk
Assuming all of the following:
Bore: 4.030
Stroke: 3.480
Gasket Bore Diam.: 4.166 (Fel-Pro Steel)
Gasket Thickness: .041 (compressed)
Chamber Volume: 67cc (big assumption)
Piston Dome Volume: -6cc
Piston Deck Clearance: .026 in the hole (another big assumption)
It calculates out to 9.30:1. By milling the heads to achieve a 65cc chamber, you would be at exactly 9.50:1.
Bore: 4.030
Stroke: 3.480
Gasket Bore Diam.: 4.166 (Fel-Pro Steel)
Gasket Thickness: .041 (compressed)
Chamber Volume: 67cc (big assumption)
Piston Dome Volume: -6cc
Piston Deck Clearance: .026 in the hole (another big assumption)
It calculates out to 9.30:1. By milling the heads to achieve a 65cc chamber, you would be at exactly 9.50:1.
The heads are WP S/R Torquers and that was their published size. I didn't measure to see how acurate they are as it's not that important to me. Sounds like I'll be in the 9-9.5 range I wanted so that's good.
Gary
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From: Connecticut, USA
Hi Matt,
I thought about the 268 but this isn't a road rocket car. I doubt I'll be pushing past 5500 much if at all- th400 w 308 gears. The 260 seems to be the right fit. I just wasn't sure if the increased CR would play into it, but looking at the comp catalog last night I see those cams are for 8 -10:1 CR. I think the 260 will produce a little more lower end where this will run.
Next I'm looking at torque convertors. Was thinking of the 2000 stall B&M but Comp has their own line and has one in the 1800 range.
Gary
I thought about the 268 but this isn't a road rocket car. I doubt I'll be pushing past 5500 much if at all- th400 w 308 gears. The 260 seems to be the right fit. I just wasn't sure if the increased CR would play into it, but looking at the comp catalog last night I see those cams are for 8 -10:1 CR. I think the 260 will produce a little more lower end where this will run.
Next I'm looking at torque convertors. Was thinking of the 2000 stall B&M but Comp has their own line and has one in the 1800 range.
Gary
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Originally Posted by gtr1999
Thank you for taking the time to figure this out for me
The heads are WP S/R Torquers and that was their published size. I didn't measure to see how acurate they are as it's not that important to me. Sounds like I'll be in the 9-9.5 range I wanted so that's good.
Gary
The heads are WP S/R Torquers and that was their published size. I didn't measure to see how acurate they are as it's not that important to me. Sounds like I'll be in the 9-9.5 range I wanted so that's good.
Gary
Glad to do it. Good luck.
Race Director
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From: central FL, near the beach.
Gary
did u know stock 72 stall is 2100?
260H good w/308(move the kickdown switch to 1/2 throttle and it will LEAP!
SEE MY HOMEPAGE FOR MORE TIPS),
but i'm not sure if u can get away with 87 octane as i do.
did u know stock 72 stall is 2100?
260H good w/308(move the kickdown switch to 1/2 throttle and it will LEAP!
SEE MY HOMEPAGE FOR MORE TIPS),
but i'm not sure if u can get away with 87 octane as i do.
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Tech Contributor
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From: Connecticut, USA
Matt no I was never able to find the 72 vette stall rating anywhere. From what others have said here I thought it was around 1500-1600??
Where did you find the information at?
Thank you,
Gary
Where did you find the information at?
Thank you,
Gary
Race Director
Joined: Oct 2000
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From: central FL, near the beach.
Originally Posted by gtr1999
Matt no I was never able to find the 72 vette stall rating anywhere. From what others have said here I thought it was around 1500-1600??
Where did you find the information at?
Thank you,
Gary
Where did you find the information at?
Thank you,
Gary
a 2500 stall would do the trick imo.
Melting Slicks
Joined: Jan 2004
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From: New Cumberland PA
I have never seen published stall rating for the C3 or GM. When a cam manufactures says to use a stall speed 500rpm over stock it's just a guess as to what stock is. I believe since the stall speed varies with the torque of the engine, it's just a shot in the dark anyway. From my understanding the 1500-1600 seems about right.
Race Director
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From: central FL, near the beach.
Originally Posted by Matt Gruber
was in the free GM spec's(call chevy toll free)
a 2500 stall would do the trick imo.
a 2500 stall would do the trick imo.
page 15 of the power train section
stall
2110
anyone who does not have this free spec&resto kit is not playing with a full deck