350 to 383.
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
What are the specs on the motor, bore dia., stroke, pistons cc's + or -, combustion chamber volume, compressed gasket thickness, head gasket bore diameter, and piston to deck clearance ?
I'll figure out your DCR, I don't like giving out the wrong info to others and if you say what you have is there and it works out to 8.3 DCR then I will have to edit my post.
I'll figure out your DCR, I don't like giving out the wrong info to others and if you say what you have is there and it works out to 8.3 DCR then I will have to edit my post.
My 406 with 76cc heads and flat top hypertec pistons comes out to about 9.8 to 1 compression wth a .040 head gasket. You must be running 305 camaro heads with 56cc chambers to get that high.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I think you can get that compression ratio fairly easy with a 383ci motor for some reason a flat top piston in a 406ci always ( or used to anyway ) gets you near 11:1cr or a few points under with 64cc heads. It is the availability of the piston for the CR that you want is the difference. I remember my 406ci had to be just under 11:1 with flat tops that was all that was available at the time.
What I am questioning is the validity of telling fellow members to shoot for a 7.5 to 8.5 dynamic compression ratio, with 7.5 starting to get on the lazy side and 8.5 and over you are going to have to run premium gas, might have to retard your timing to prevent pinging.
When I built my current 427ci I wanted to stay safe and I am a little under 8:1 and I can run 91 octane gas, so far so good and everything makes sense to me.
Now if someone says they are running 89 octane gas in a motor with 8.3 DCR and the timing is not retarded then I have to figure out why this is. Either there was a calculation error or I have to stop and figure out why and how this can be. Then I would stop telling people what I thought was the correct info.
Nothing personal here, just the facts have to be laid out and someone made a calculation error or I will have to stop telling people what I thought was correct
What I am questioning is the validity of telling fellow members to shoot for a 7.5 to 8.5 dynamic compression ratio, with 7.5 starting to get on the lazy side and 8.5 and over you are going to have to run premium gas, might have to retard your timing to prevent pinging.
When I built my current 427ci I wanted to stay safe and I am a little under 8:1 and I can run 91 octane gas, so far so good and everything makes sense to me.
Now if someone says they are running 89 octane gas in a motor with 8.3 DCR and the timing is not retarded then I have to figure out why this is. Either there was a calculation error or I have to stop and figure out why and how this can be. Then I would stop telling people what I thought was the correct info.
Nothing personal here, just the facts have to be laid out and someone made a calculation error or I will have to stop telling people what I thought was correct
Thread Starter
Pro
Joined: Jul 2001
Posts: 704
Likes: 10
From: Blairsville Ga
Thanks for the offer MotorHead. I'm going to a machine shop tomorrow to see what it's going to cost me. I'm on a tight budget but if I can get it done for under a grand I'm going to do it. I see kits online for around 700 bucks that are balanced, but they come with the rods. I'm going to see if my machine shop can just piece it together and use my rods and then balance it. Once I get down to the actual cost I'll send you all my info before I order a kit. I do not what to be running any high dollar gas.
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
FWIW I'm running 383 with the Scat 9000 and 4140 Rods, internally balance.. Flat tops with 76cc heads riding at ~9.8:1cr. Also have the XE268H cam and roller rockers. At the moment my 882 iron heads, though well worked, are the limiting factor. but even so this motor rocks and gets 15mpg even with a little spirited driving. Barely put $3k in the build including machine work. Gobs of torque all the way through the power band! The cam sounds wicked but gives plenty of vacuum. Spins up to 6k and quite dependable. I say Go for it! As suggested you could step the cam up a little with your heads. Mine will also get cam and head upgrade at some point!
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
After a 93 Cavalier handed me my butt when mine was stock, I did the first upgrade. The motor was rebuilt with with a Comp 270H cam and around 9:1 or so compression.
With the stock heads and nothing done to them the motor wasn't very powerful at all. I upgraded the heads to 200cc Sportsman II heads with a steel shim head that bumped the compression up to about 10:1 then I added the Holley 750dp and Air Gap manifold then it really came alive. Made 297RWHP and 330RWT
With the stock heads and nothing done to them the motor wasn't very powerful at all. I upgraded the heads to 200cc Sportsman II heads with a steel shim head that bumped the compression up to about 10:1 then I added the Holley 750dp and Air Gap manifold then it really came alive. Made 297RWHP and 330RWT
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
Holley 4175 which was tuned on this motor... Also currently have 2101 Eddy intake which was matched to the heads and had the plenum opened up under the carb. I have a 750/4160 Holley in rebuild process and may try it this summer. The 4175 works well though and probably the source of better MPG with the smaller primary's.
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
What are the specs on the motor, bore dia., stroke, pistons cc's + or -, combustion chamber volume, compressed gasket thickness, head gasket bore diameter, and piston to deck clearance ?
I'll figure out your DCR, I don't like giving out the wrong info to others and if you say what you have is there and it works out to 8.3 DCR then I will have to edit my post.
I'll figure out your DCR, I don't like giving out the wrong info to others and if you say what you have is there and it works out to 8.3 DCR then I will have to edit my post.
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Safety Car
Joined: Nov 2005
Posts: 3,961
Likes: 573
From: Lompoc, CA. Santa Barbara County
My Super Chevy showed up yesterday. They have an article that compares a 350 to a 383 with identical cams, AFR heads, intake, carb, everything. The 383 has dished pistons so that the CR would be identical. The 383 kicked butt. 40 more horsepower and 40 more lb/ft of torque. Then they explained that the 383 would make even more power with a bigger cam. It's amazing what 33 cubic inches will do. I want to build a 396.
Bee Jay
Bee Jay
