5.3 final compression question
Thread Starter
Teching In
Joined: May 2002
Posts: 19
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From: Palm Harbor, FL
5.3 final compression question milling these heads out .15 would give me what compression, and .30 would give me what compression, sorry for the random question, last day of the deal and scrambling to purchase the heads, such a last minute person. been researching this the past 2 weeks and pretty much decided on 5.3 milled to .15 unless someone can throw out some reason otherwise.
Re: 5.3 final compression question Unmilled 5.3 heads should net you a CR near 10.75. Milling .015 would give an estimated CR of near 11:1. If you decide you want a higher CR at a later time, use the FelPro gasket. It has a compressed volume of .041 compared to stock .054 and will up your CR .35 more than the stock gasket.
Re: 5.3 final compression question A stone stock 5.3 head has 59cc chambers, thats around 11.1 and if you mill it .015" then it would be around 57cc or 11.3. Our CNC ported chamber is 63cc or around 10.8 and milled .015 would put it at 11.0. I would not install a 5.3 head without chamber work to open it to 3.900" bore size. Hope this helps.
Re: 5.3 final compression question Brian, I'm not trying to argue with you since I have never actually cc'd a set of these heads. I guess if I could do it accurately with common household items, I'd give it a shot on the 862s I have in my garage. Compression ratios for the stock LM7 motor @ 9.5:1 with 6 cc dished pistons work out to be a 62cc chamber. I've seen others post that number as well. A 59cc chamber would call for a 9cc dish, which would then be larger than the dish in the LQ4.
Wouldn't your final cc number of 63 after porting be somewhat skewed smaller if you install a larger intake valve?
Wouldn't your final cc number of 63 after porting be somewhat skewed smaller if you install a larger intake valve?
Re: 5.3 final compression question No problem, I just see alot of misinformation and try to correct. I have not tried to reverse calcualte the chamber size, we just measure them, a good flat 3/4" piece of lexan, a burette and some isopropyl alcohol is what you need. The 4.8/5.3 is in the 59-60cc range. Maybe the piston is in the hole to get at that compression.
