Compression Ratio Question with Vortec heads
Thread Starter
Heel & Toe
Joined: Jun 2004
Posts: 22
Likes: 0
From: Tucker GA
Compression Ratio Question with Vortec heads
I'm trying to finalize parts specifications for a very mild 350 rebuild. Our criteria is for a street engine, AT with stock torque converter, 3.08 rear. We'd like a usable rpm range of 1000 - 4500.
Block is a '69 vintage, bored .40 and decked .015. I'd like to stay with a static compression range of 8.5 - 9 and am concerned that if I go with the Vortec heads (64cc) that the CR will be way too high. Everything I plug into the CR calculators seems to end up around 11 using a flat top piston. Am I just plugging in the wrong values? What experience can other forum users share?
BTW - I spoke with a rep at Crane cams this morning and he recommended their H-260-2 (pn 113902) cam.
TIA - Dennis
Block is a '69 vintage, bored .40 and decked .015. I'd like to stay with a static compression range of 8.5 - 9 and am concerned that if I go with the Vortec heads (64cc) that the CR will be way too high. Everything I plug into the CR calculators seems to end up around 11 using a flat top piston. Am I just plugging in the wrong values? What experience can other forum users share?
BTW - I spoke with a rep at Crane cams this morning and he recommended their H-260-2 (pn 113902) cam.
TIA - Dennis
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
It seems you are plugging in the right numbers. My 60 over block was zero decked and with flat top pistons (appox -5cc) and .041 head gasket, I was coming up with 11-1. It's more compression than what I wanted but I didn't know the block was zero decked until I put the pistons in. If you're going to lower the compression, you'll have to go with dished pistons or a head with a larger combustion chamber.
Misread that you were building a 350. Compression Ratio using flat top will be closer to 10:1 .
Cylinder Head Volume 65(cc)
Piston Head Volume 5(cc)
Gasket Thickness 0.041(in.)
Gasket Bore 4.100(in.)
Cylinder Bore Diameter 4.040(in.)
Deck Clearance 0.10(in.)
Stroke 3.48(in.)
STATIC COMPRESSION RATIO 10.145
Changing to 16cc dish pistons
STATIC COMPRESSION RATIO 09.039
Here is the calculator I used, http://kb-silvolite.com/calc.php?action=comp.
Misread that you were building a 350. Compression Ratio using flat top will be closer to 10:1 .
Cylinder Head Volume 65(cc)
Piston Head Volume 5(cc)
Gasket Thickness 0.041(in.)
Gasket Bore 4.100(in.)
Cylinder Bore Diameter 4.040(in.)
Deck Clearance 0.10(in.)
Stroke 3.48(in.)
STATIC COMPRESSION RATIO 10.145
Changing to 16cc dish pistons
STATIC COMPRESSION RATIO 09.039
Here is the calculator I used, http://kb-silvolite.com/calc.php?action=comp.
Last edited by mandm1200; Feb 7, 2006 at 03:53 PM.
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
With the vortec heads and the typical head gaskets (.039-.041)...your comp. ratio will be too high, IMO, for 93 octane; partially because you will be outside the recommended quench limits of .040. Might be better to find some 70-76 cc. chambered heads. 
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Typical 350 flattop has about -5cc dome volume, typical 350 dish about -11.5cc.
Typical 350 flattop has CD about 1.560" ... down in hole 0.025" on uncut 9.025" block ... (down in hole 0.010" after your 0.015" cut).
Typical 350 dish has CD about 1.540" ... down in hole 0.045" on uncut 9.025" block ... (down in hole 0.030" after your 0.015" cut).
W/ 64cc heads, your 357" sbc motor would be close to 9.1:1 w/ typical dish; close to 10.2:1 w/ typical flattop.
If you want to figure it more closely, you must know exactly which piston & gasket will be used.
-edit-
SpeedPro Piston: reverse-dome, skirt-coated, hypereutectic piston P/N H126CL-40 has -16cc dome volume & 1.560" CD ... CR will be right at 9.1:1 w/ 64cc heads in your 357" sbc w/ 0.015" cut from OE decks & 0.041" gasket.
SpeedPro Cam: .443"/.465" 214*/224*@0.050 hydraulic flat tappet camshaft P/N CS1013R will work good with H126 pistons & vortecs & your gears & trans ... yours will make an honest 310HP at crank, if not more ... on pump gas. You can get SpeedPro stuff through a local parts house or machine shop that sells Sealed Power/TRW/Federal Mogul/SpeedPro.
Typical 350 flattop has CD about 1.560" ... down in hole 0.025" on uncut 9.025" block ... (down in hole 0.010" after your 0.015" cut).
Typical 350 dish has CD about 1.540" ... down in hole 0.045" on uncut 9.025" block ... (down in hole 0.030" after your 0.015" cut).
W/ 64cc heads, your 357" sbc motor would be close to 9.1:1 w/ typical dish; close to 10.2:1 w/ typical flattop.
If you want to figure it more closely, you must know exactly which piston & gasket will be used.
-edit-
SpeedPro Piston: reverse-dome, skirt-coated, hypereutectic piston P/N H126CL-40 has -16cc dome volume & 1.560" CD ... CR will be right at 9.1:1 w/ 64cc heads in your 357" sbc w/ 0.015" cut from OE decks & 0.041" gasket.
SpeedPro Cam: .443"/.465" 214*/224*@0.050 hydraulic flat tappet camshaft P/N CS1013R will work good with H126 pistons & vortecs & your gears & trans ... yours will make an honest 310HP at crank, if not more ... on pump gas. You can get SpeedPro stuff through a local parts house or machine shop that sells Sealed Power/TRW/Federal Mogul/SpeedPro.
Last edited by jackson; Feb 7, 2006 at 01:10 PM.
Melting Slicks
Joined: Jan 2003
Posts: 2,804
Likes: 1
From: OKC Oklahoma
Go with a dished piston-or have you already purchased flat tops? I agree with everything these guys said, but I believe that your hp numbers will be quite a bit higher with the vortec heads-more into the 340-350hp range if you use a good intake, carb, headers and ignition.
Taken from Ryan dyno pages:
Displacement: 350 cu. in.
Carburetor: Holley 750
Heads: GM L31 Vortecs
Intake: Edelbrock Performer RPM Vortec
Camshaft: Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.503/0.529 in.)
Rockers: roller, 1.6:1
Headers: Hooker 1 5/8 in.
Pistons: Speed Pro forged
Rods: Federal Mogul
Crank: Federal Mogul
Distributor: HEI
Comp. Ratio: 10.6:1
MAX HP: 375 @ 5400
MAX Torque: 413 @ 4300
I actually just looked up the cam you listed-it's tiny.Even with a cam that small, I would guess you to be at least even with the crate vortec 350 which rates at 330hp.
Taken from Ryan dyno pages:
Displacement: 350 cu. in.
Carburetor: Holley 750
Heads: GM L31 Vortecs
Intake: Edelbrock Performer RPM Vortec
Camshaft: Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.503/0.529 in.)
Rockers: roller, 1.6:1
Headers: Hooker 1 5/8 in.
Pistons: Speed Pro forged
Rods: Federal Mogul
Crank: Federal Mogul
Distributor: HEI
Comp. Ratio: 10.6:1
MAX HP: 375 @ 5400
MAX Torque: 413 @ 4300
I actually just looked up the cam you listed-it's tiny.Even with a cam that small, I would guess you to be at least even with the crate vortec 350 which rates at 330hp.
Last edited by 79VetteMike; Feb 7, 2006 at 06:35 PM.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
From metro/Dennis post ... seems he wants CR about 9:1 w/ vortecs ... not the 10.6:1 from ryan's dyno page ... thus the reverse dome -16cc pistons and the smaller 1013R cam to match the 9:1 CR.
Moreover, Speedpro (FM) does not make such a cam Camshaft: Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift.
However ... if you run the 1013R cam I suggest ... and run it with 1.6 rockers ... you will get 0.472/0.496 in. of lift ... plus you'll get about 2-3 more degrees of duration. But that's probably a bit too much for a 9:1 motor ... I suggest the 1013R w/ stock 1.5 rocker ratio w/ -16cc pistons & vortecs.
Moreover, Speedpro (FM) does not make such a cam Camshaft: Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift.
However ... if you run the 1013R cam I suggest ... and run it with 1.6 rockers ... you will get 0.472/0.496 in. of lift ... plus you'll get about 2-3 more degrees of duration. But that's probably a bit too much for a 9:1 motor ... I suggest the 1013R w/ stock 1.5 rocker ratio w/ -16cc pistons & vortecs.
Last edited by jackson; Feb 7, 2006 at 07:23 PM.
Thread Starter
Heel & Toe
Joined: Jun 2004
Posts: 22
Likes: 0
From: Tucker GA
All,
Thanks for the replies. I really don't want to make this harder than necessary, fact is we're building a very mild engine. However, the more I try to learn and determine what's best, the more questions I have.
I see so many articles that seem to imply you can just toss a set of Vortec heads on a stock 350 short block, add a Vortec specific intake and your off and running. Yet when I start looking at the CR it would imply that it's not that easy.
Jackson - I tried to find the specs on the Speed Pro H126CLs but they are only shown in a 30 over not a 40 over.
Regards,
Dennis
Thanks for the replies. I really don't want to make this harder than necessary, fact is we're building a very mild engine. However, the more I try to learn and determine what's best, the more questions I have.
I see so many articles that seem to imply you can just toss a set of Vortec heads on a stock 350 short block, add a Vortec specific intake and your off and running. Yet when I start looking at the CR it would imply that it's not that easy.
Jackson - I tried to find the specs on the Speed Pro H126CLs but they are only shown in a 30 over not a 40 over.
Regards,
Dennis
Melting Slicks
Joined: Sep 2002
Posts: 2,783
Likes: 2
From: Engineers do it better.
Originally Posted by metro
...However, the more I try to learn and determine what's best, the more questions I have...
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Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
In my opinion, 8.5 to 1 would be good if using old style smog heads and running on 87 octane or less. From what I read the Vortec heads will allow a half point higher in compression without pinging. Switching to 92 or 93 octane would allow the compression to be in the 10-1 range. I do not recall reading anywhere that someone had issues when switching to Vortec heads and running flat top pistons. Flat top piston in a 350ci will put you in the 10-1 range. Some pistons have 2 valve reliefs while others have 4. The ones with 4 may be a way of getting away with a little less compression.
Here a link to Speed Pro. Click on 'Application' then click on the 'pull downs' to find what you are looking for. They give the part numbers and compression ratios for different cc heads. One thing you'll want to look at is ring width. Street engines nomally use the 5/64 not the 1/16.
http://www.21cgt.com/FMWebCatalog/default.htm
Here a link to Speed Pro. Click on 'Application' then click on the 'pull downs' to find what you are looking for. They give the part numbers and compression ratios for different cc heads. One thing you'll want to look at is ring width. Street engines nomally use the 5/64 not the 1/16.
http://www.21cgt.com/FMWebCatalog/default.htm
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by metro
Jackson - I tried to find the specs on the Speed Pro H126CLs but they are only shown in a 30 over not a 40 over. Regards,
Dennis
Dennis
Or ... you can try this Speed-Pro factory tech phone number 1-800-325-8886 ... ask for "JIM" in tech support ... JIM has helped me before with pistons ... he has actually been able to pull up pistons' engineering drawings (aka blueprints) on his computer.
1/16 rings WERE not so common on production cars ... our C3's typically have 5/64, 5/64, 3/16 (.078", .078", .188") ringpacks. But even thinner ARE common in today's production ... thinner rings work just fine. In fact, since about MY1996, most corvette & vortec motors have 1.5mm, 1.5mm, 3mm (.059", .059", .118") ringpaks.
The above combo w/ 0.041" gasket about 9.1:1 CR ... quench a bit large at 0.051". If same pistons, heads & deck ... but with Victor Reinz P/N 5746 composition gasket (0.026") has about 9.4:1 CR and quench in optimal range at 0.036".
I'm not gonna recommend CR of 10 or more in a mild street motor with IRON heads ... but that's what you'd have in this motor with GM Vortecs & flattops.
Last edited by jackson; Feb 9, 2006 at 11:47 AM.
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Also take a look at these H423NCP40 or H670CP40. Complete specs including engineering drawings are here.
http://www.21cgt.com/FMWebCatalog/default.htm
http://www.21cgt.com/FMWebCatalog/default.htm
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by mandm1200
Also take a look at these H423NCP40 or H670CP40. Complete specs including engineering drawings are here.
http://www.21cgt.com/FMWebCatalog/default.htm
http://www.21cgt.com/FMWebCatalog/default.htm
