Compression question regarding ported 5.3l heads.
Thread Starter
Safety Car
Joined: Jan 2000
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From: Midlothian, VA
Compression question regarding ported 5.3l heads.
When adding ported heads or milling them you effectively are just taking the air/fuel charge and compressing it into a smaller package. this results in a faster burn and a greater pressure delta - so you make more power. However, if you go too high with the compression you get detonation, KR.
My question is, is this correct so far?
If so, wouldn't the 5.3L heads, ported with an appropriate cam be the most economical H/C setup one could go with?
What is the max compression, on pump 92-93 gas that a stock 346 CID motor, such as ours, be allowed to manage? Thanks.
[Modified by C5Noir, 9:24 PM 2/4/2002]
My question is, is this correct so far?
If so, wouldn't the 5.3L heads, ported with an appropriate cam be the most economical H/C setup one could go with?
What is the max compression, on pump 92-93 gas that a stock 346 CID motor, such as ours, be allowed to manage? Thanks.
[Modified by C5Noir, 9:24 PM 2/4/2002]
Le Mans Master
Joined: Jan 2001
Posts: 6,429
Likes: 1
From: God's Replica
Re: Compression question regarding ported 5.3l heads. (C5Noir)
you are correct in regard to milling the heads, all else being the same. The more comprression you can get away with the more power. I think with the 5.3 heads you would not have to mill them though, as I think the cc is smaller than either the ls1 or 6. But if not then you could mill them and get away with a 10.7 or maybe, just maybe 11. I know of one guy running 11.1 and doing fine on 93 octane. Gotta watch the cam duration though. However, when it gets hotter he runs some xylene in it and a lower stat. With a reverse cooled electric water :D you could run that 11:1 and be OK. Add Ls1 edit to fool with and you could adjust the timing when needed and in the rpm ranges... oh the power... :cheers:
Thread Starter
Safety Car
Joined: Jan 2000
Posts: 4,965
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From: Midlothian, VA
Re: Compression question regarding ported 5.3l heads. (intel55)
intel55, thanks for the reply, sorry about putting milled heads. I was thinking of regular 5.7L LS1 heads on that one :D. I have gathered that 10.7:1 is about as high as you should take it.
I'm just trying to gauge the most compression as this is my daily driver and I don't want to have "random misfire codes", having to let the car warm up for 10 minutes before it will run properly, replace springs every year and a half, etc.
I want around 400+ RWHP with H/C/I/Und Pulley.
Just researching so I come to an educated decision. Thanks again.
[Modified by C5Noir, 9:55 PM 2/4/2002]
I'm just trying to gauge the most compression as this is my daily driver and I don't want to have "random misfire codes", having to let the car warm up for 10 minutes before it will run properly, replace springs every year and a half, etc.
I want around 400+ RWHP with H/C/I/Und Pulley.
Just researching so I come to an educated decision. Thanks again.
[Modified by C5Noir, 9:55 PM 2/4/2002]
Safety Car
Joined: May 2000
Posts: 4,819
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From: Albuquerque NM
Re: Compression question regarding ported 5.3l heads. (C5Noir)
Some tuners are getting away with more static compression than that with no problems. I am running MMS stage IIX heads, starting with the 5.3 cores, lots of port work, bigger valves, etc. Also milled, now the compression ratio is 11.3-11.4. They work great, the additional compression nets you greater efficiency, and low end torque. The computer MAY have to pull some timing at high rpm's, but its worth it, overall. FWIW, at sea level, on 92 octane gas, on a hot day, mine produced the numbers in my sig, with 25 degrees of timing. The next day, I drove it 800 miles at 85 MPH av, and got 34 MPG for the trip. A balanced combo; well prepped, high compression heads and a good sized but not radical cam will surprise you. :cheers:
Race Director
Joined: Sep 2000
Posts: 11,309
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From: Valley Ranch, Texas
Re: Compression question regarding ported 5.3l heads. (C5Noir)
An option in the G-5 package from LG Motorsport's or Corvette's of Houston is LS6 heads, which are milled a bit to have 11:1 or so compression. BTW, this option is not cheap, but IMO gives the "curve" a broader/smoother range. Info with dyno charts are in my sig. My package consists of Heads/Cam/LG Headers/LS6 Intake/Rammer intake w/ BPP air bridge/PRT's w/ x-pipe/No CATS. I DO NOT have a pulley, ported TB or MAF or any bottom end work. :cheers:
Melting Slicks
Joined: Mar 2001
Posts: 3,255
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From: League City TX
Re: Compression question regarding ported 5.3l heads. (JWSchmidt3)
I have been researching this to death...
1. The 5.3L heads do have smaller chambers, and will considerably bump compression over a stock LS1. They are about $300/pair on the open market. They have smaller valves, and a slightly different shaped chamber for more swirl (no surprise on a truck swirl = torque). The valves are smaller, so when installing the common larger valves, many people are opening up the chamber to unshroud the valves. When one starts performing these mods, the price for these "budget heads" will start to climb quickly.
2. LS6 heads are great, but a little expensive.
3. 6.0L truck, 01 and up are awesome, but have big chambers 71-72 cc, thereby lowering compression to 9.6:1. If you mill them down .030 and use 7.35" pushrods, your geometry will be close, but compression will be 10.1-10:2:1 (stock). People will start welding the chambers to reduce the volume, but again the cost starts to go up.
4. Many, many, many LS1 tuners have LS1 heads available. With proper proting and valves, one will get of over 300 cfm flow and an easy 10.8:1 compression. Your LS1 heads probably will give you the best bang for the buck in the end.
1. The 5.3L heads do have smaller chambers, and will considerably bump compression over a stock LS1. They are about $300/pair on the open market. They have smaller valves, and a slightly different shaped chamber for more swirl (no surprise on a truck swirl = torque). The valves are smaller, so when installing the common larger valves, many people are opening up the chamber to unshroud the valves. When one starts performing these mods, the price for these "budget heads" will start to climb quickly.
2. LS6 heads are great, but a little expensive.
3. 6.0L truck, 01 and up are awesome, but have big chambers 71-72 cc, thereby lowering compression to 9.6:1. If you mill them down .030 and use 7.35" pushrods, your geometry will be close, but compression will be 10.1-10:2:1 (stock). People will start welding the chambers to reduce the volume, but again the cost starts to go up.
4. Many, many, many LS1 tuners have LS1 heads available. With proper proting and valves, one will get of over 300 cfm flow and an easy 10.8:1 compression. Your LS1 heads probably will give you the best bang for the buck in the end.
Safety Car
Joined: Nov 1999
Posts: 3,891
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From: Houston, TX
Re: Compression question regarding ported 5.3l heads. (C5Noir)
We are doing another set of 5.3's right now. They do work great!
Your statements are generally correct, or on the right track, but there is a lot more to it than that. If you run a larger camshaft with more overlap, you can get away with more static compression. The tumble and swirl of the heads also effects the compression that you can get away with. Compbustion chamber design will also effect detonation tendencies, and so on.
The setup that we are using is 5.3 heads on a stock cube engine with our custom ground 226/226 .591/.591 camshaft. We will be putting this one on a 112* LSA and are expecting some pretty good numbers out of it with great drivability. We will know in another few weeks. :)
The last one we did dynoed 426 RWHP, but has not been to the track yet.
Your statements are generally correct, or on the right track, but there is a lot more to it than that. If you run a larger camshaft with more overlap, you can get away with more static compression. The tumble and swirl of the heads also effects the compression that you can get away with. Compbustion chamber design will also effect detonation tendencies, and so on.
The setup that we are using is 5.3 heads on a stock cube engine with our custom ground 226/226 .591/.591 camshaft. We will be putting this one on a 112* LSA and are expecting some pretty good numbers out of it with great drivability. We will know in another few weeks. :)
The last one we did dynoed 426 RWHP, but has not been to the track yet.
Racer
Joined: Jun 2001
Posts: 424
Likes: 0
From: OKC OK
Re: Compression question regarding ported 5.3l heads. (Closer_2001)
power house in OKC has two sets of Ls1 heads sitting on the floor for sale.
These are brand new castings no clue price have to call them
405-737-8264 ask for brien
These are brand new castings no clue price have to call them
405-737-8264 ask for brien
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From: VENTURA Ca
Re: Compression question regarding ported 5.3l heads. (Iboomalot)
West Coast Cylinder Heads out here in Ca does some great CNC 5.3 heads at a reasonable price. Richard is at 818 705 5454. He really knows his stuff.
