New Heads
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Joined: Nov 2009
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From: Farmington Hills, MI
New Heads 
Just picked up some ported and milled 243s from blakss. Should give 11:1 with a stock head gasket, but I want to use a 0.040" gasket with a small bore to get to around 11.3:1. With a 21 month old and 2 month old, it will be a bit before I find the time for the swap, but I'll get them on this summer. This should put me well into the 11s on street tires. I still have to get the gaskets, head bolts, and shorter push rods. The stockers are the right length, but I don't want to reuse them.
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TECH Regular
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From: Farmington Hills, MI
950 shipped, which I thought was fair given 243 cores cost around 400 and a decent port and valve job costs at least 1000. I figure around 4% (16+) from the bump in compression and at least 20 from the port job, probably more given my power band.
They were milled 0.030", which was what I've read is about the limit before you have to mill the intake face as well. They were ported by PRC. TSP worked with blakss, and they came up with the 11:1 number. I'll have to sit down and crunch all of the numbers to see what SCR and DCR I come up with. There is a little machine work done on the chamber to unshroud the valves too. Given how much I've advanced and retarded the cam without clearance issues, I'm not too worried about PTV clearance. With a 0.040" head gasket, I'll move to an effective mill of 0.041". The smaller head gasket should also reduce quench and help prevent pre-ignition. I should get 0.3 points of compression from the head gasket change.
They were milled 0.030", which was what I've read is about the limit before you have to mill the intake face as well. They were ported by PRC. TSP worked with blakss, and they came up with the 11:1 number. I'll have to sit down and crunch all of the numbers to see what SCR and DCR I come up with. There is a little machine work done on the chamber to unshroud the valves too. Given how much I've advanced and retarded the cam without clearance issues, I'm not too worried about PTV clearance. With a 0.040" head gasket, I'll move to an effective mill of 0.041". The smaller head gasket should also reduce quench and help prevent pre-ignition. I should get 0.3 points of compression from the head gasket change.
Hmmm...I'm coming up with just a touch under 10.7:1 with the .040 gasket and your mill.
I'm curious as to how they got to 11:1.
Anyway, I would agree that you should be okay on PTV, assuming the duration on that cam isn't too crazy. I looked but couldn't find any specs on it!
I'm curious as to how they got to 11:1.
Anyway, I would agree that you should be okay on PTV, assuming the duration on that cam isn't too crazy. I looked but couldn't find any specs on it!
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TECH Regular
Joined: Nov 2009
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From: Farmington Hills, MI
OK, so I sat down last night and did some math and some reading. I already knew stock 243s have 64.45cc chambers. Using the 0.006" mill per cc rule of thumb, a 0.030" mill takes you to 59.45. I searched, and others report a 59cc chamber with a 0.030" mill, so I feel good there. That takes me from 10.0 to 10.65. The compressed volume of the stock head gasket is 10.17cc, and by my math that leaves the piston slightly protruding above the deck. A Cometic C5475-040 gasket has a compressed volume 7.87cc. The gasket and the mill lead to a compression ratio of 10.98:1. Since there is some guess work in there on the exact milled combustion chamber volume, at worst I'm at 10.9:1 and at best I'm a little over 11:1. I'm guessing TSP was factoring in a 0.040" gasket or basing their calcs on a 5.7L. Either way, I'm happy. I may have to do some port matching on the intake manifold. I was already thinking of doing a little polishing on the exhaust ports.
