Compression on new shortblock
Thread Starter
Joined: Sep 2004
Posts: 2,552
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From: Visalia, California
Compression on new shortblock I'll keep this short and to the point...
8.25:1 OR 8.9:1 on the new motor? What will I need to successfully run 12-15# boost? Want to keep stock crank, and H-beams. Am switching cams (currently Hot cam) to something more "turbo friendly". What head bolts/gaskets and main bolts? Opinions anyone?
8.25:1 OR 8.9:1 on the new motor? What will I need to successfully run 12-15# boost? Want to keep stock crank, and H-beams. Am switching cams (currently Hot cam) to something more "turbo friendly". What head bolts/gaskets and main bolts? Opinions anyone?
SSU'S Vice Mod
Joined: Jul 2004
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From: Hazard Co. Maryland
Originally Posted by 67Firebird455
I'll keep this short and to the point...
8.25:1 OR 8.9:1 on the new motor? What will I need to successfully run 12-15# boost? Want to keep stock crank, and H-beams. Am switching cams (currently Hot cam) to something more "turbo friendly". What head bolts/gaskets and main bolts? Opinions anyone?
8.25:1 OR 8.9:1 on the new motor? What will I need to successfully run 12-15# boost? Want to keep stock crank, and H-beams. Am switching cams (currently Hot cam) to something more "turbo friendly". What head bolts/gaskets and main bolts? Opinions anyone?
Thread Starter
Joined: Sep 2004
Posts: 2,552
Likes: 12
From: Visalia, California
I had thought of ARP mains and head bolts as they can be reused. I have #317 heads like everyone else I guess, and going H-beams. Keeping stock rockers, and going hi-tech pushrods. I don't need this thing to be a high-revving mouse, but it's going to be 346ci with the T70 T4 turbo. I would imagine I will be switching to 60# injectors from the 42's. @ approx 9:1 will I be able to manage 15# of boost without KR? I don't want to pull the timing ALL the way back to 12-14 like I did before. I also agree with the driveability factor since it's not a race-only vehicle, and gas mileage is a huge factor with gas prices the way they are now adays. Thanks for the advice, I will very likely use ARP main/head bolts. Any other things I should take into consideration? Had a post already on the Internal motor section and got nothing as far as a cam recommendation. Will the MTI stealth II work well, or is there something else I should use? I need a "close to stock" sounding cam that is reverse split (or something that will help build boost) since the T70 is *** mounted on a stock-cube. Thanks again guys, let me know what you think...
I have a 346 w/Diamond -8.66cc inverted dome pistons and 317 heads. I honestly can't remember what the compression is I think it is something between 8.5 and 9:1 with the block decked 0.010 inches with a stock gasket. As far as a cam goes, I am using a 1998-99 Fbody cam. It has a lot of overlap and should give me a nice torque curve around cruise for my heavy-a$$ car.
Thread Starter
Joined: Sep 2004
Posts: 2,552
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From: Visalia, California
Originally Posted by FastKat
I have a 346 w/Diamond -8.66cc inverted dome pistons and 317 heads. I honestly can't remember what the compression is I think it is something between 8.5 and 9:1 with the block decked 0.010 inches with a stock gasket. As far as a cam goes, I am using a 1998-99 Fbody cam. It has a lot of overlap and should give me a nice torque curve around cruise for my heavy-a$$ car.
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Hey thanks... putting SBC's in Jags is nothing new, but very few LS1 cars and even fewer turbo cars. It's very much a project and I enjoy working on it... hopefully it will all be worth it when it's done. Right now there's still so much to do and so much money to spend that it's tough to see the end in sight, but yes I am happy with it!
What brand our those -16cc pistons? I remember being able to go with a Probe unit that's something like that, but I haven't heard a whole lot of good stuff about Probe pistons. I also know that I wasn't able to use some of the other good brand names because they were made for a 383 and not a 346... just be careful! I was shooting for somewhere between 8.5:1 and 9:1 with a stock gasket and a truck head.. and I think I got it.
What brand our those -16cc pistons? I remember being able to go with a Probe unit that's something like that, but I haven't heard a whole lot of good stuff about Probe pistons. I also know that I wasn't able to use some of the other good brand names because they were made for a 383 and not a 346... just be careful! I was shooting for somewhere between 8.5:1 and 9:1 with a stock gasket and a truck head.. and I think I got it.
Originally Posted by 67Firebird455
Yeah, your setup is pretty cool man, I've been following it... The pistons I was lookin at are either 9cc or 16cc dish. They claim with a stock block/head they yield either 9.8:1 or 9:1 (with the 16cc). With a 72.25cc head, I would imagine somewhere around .6-.7:1 drop from a standard #241 head. I really would like a higher duration, reverse split camshaft with a high LSA (115-117) under .600" lift. I run a 262/262 @ .050 and .615/615 on a 110 in my drag car, seems to work well for NA in a 464ci Pontiac (4.210 Stroke). Turbocharging a small-displacement motor is COMPLETELY different. You pretty happy with your car?
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I am going with Mahle -16cc pistons in my 346. If my math is correct my motor will have a 8.86:1 compression ratio with Dart 225 62cc chamber heads and .054 gaskets. I was shooting for a ratio between 8.4:1 and 9:1, so this works for me.
Well if 8.25 and 8.9 are your only choices I have to wonder if thats with a stock thickness head gasket, because the 8.9 leaves room to grow with a thin gasket, where as if you want to raise the cr with a 8.25 your options are limited to shaving the heads or new pistons.
If you can land it right around 8.5:1 with stock thickness gaskets I think thats a great place to be for boost
BTW : My motor is right around 8.3:1 on stock gaskets and I can drop low as 8.0:1 with just a gasket change.
If you can land it right around 8.5:1 with stock thickness gaskets I think thats a great place to be for boost
BTW : My motor is right around 8.3:1 on stock gaskets and I can drop low as 8.0:1 with just a gasket change.
Originally Posted by wickedred
I am going with Mahle -16cc pistons in my 346. If my math is correct my motor will have a 8.86:1 compression ratio with Dart 225 62cc chamber heads and .054 gaskets. I was shooting for a ratio between 8.4:1 and 9:1, so this works for me.
those are the pistons i got with my setup. i figured with my stock heads and GM MLS gaskets im at 8:5.1
Thread Starter
Joined: Sep 2004
Posts: 2,552
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From: Visalia, California
I was also going mahle -16cc or -9cc also. What type of head gasket really is best for this amount of boost? Good point on being able to lower the compression with just a head gasket swap. Give me a heads up on what to buy guys! Thanks for the feedback!
Yeah with the stock 67cc heads my compression would be 8.5:1, with 6.0L heads it is like 8.2:1. I decided that I would rather have the extra flow of the 225cc Darts and thier 62cc chambers. They will net me the 8.86:1 with .054 gaskets. I can always have the Darts chambers opened up to 70cc to lower my compression.
Thread Starter
Joined: Sep 2004
Posts: 2,552
Likes: 12
From: Visalia, California
That sounds excellent to me... What head gasket with the #317 heads (stock CC) and the -9cc pistons? Still curious on the quality and if I should use or not use the rings that come with the mahle pistons.
I am using the rings that come with the pistons. I dont see why they would be a problem. If there is a problem with those rings hopefully someone will chime in. with the 317 heads being 71cc, and using -9cc pistons I would use .054 gaskets to get 8.69:1. you could use .040 gaskets and get 8.92:1.
I'm doing the same..Mahle pistons with -9cc dish, H-beam rods, Hand ported 6.0L heads, stock crank, stock GM MLS 6.0 head gaskets, ARP head studs, brand new LS6 block. Shooting for 750rwhp at 14psi. It should make that easy... 