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Old 02-21-2009, 09:47 PM
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GM Phase 6 Bowties on 327?

I ran across a set of GM Bowties, phase 6 aluminum heads. Will they work on my 1970 350 block? I run a 1968 327 crank and rods with trw flat top pistons, 4 valve reliefs. The heads are said to have 55cc chambers, 2.02/1.6 valves. Will this make my compression to high? With a 64 cc head, the specs from trw are 9.18:1

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Old 02-22-2009, 01:09 AM
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The compression ratio I get using a typical .041 thickness fel pro gasket and a guessed figure of a .025 deck clearence the compression ratio comes in at
9.8:1, slightly on the high side but liveable on 93 octane fuel, especially with a tight quench distance.
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Old 02-22-2009, 02:17 AM
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Assuming a 4.030" bore and a .025" piston deck clearance the cr is 10.18:1.

If the block is "0 decked" so the pistons are dead nuts flush at the top of the block @TDC, Use the thicker GM .051" L-98 "corvette aluminum head" gasket. The cr will be 10.5:1

Use 92+ octane fuel. Not a problem.
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Old 02-22-2009, 09:16 PM
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My engine is a .060 bore. Any idea what this will be on compression? What cam should I run? I have a manual 4 speed trans in a 64 nova about 2800 lbs. With 4.56 rear gear. It is a street car. But I want to run the biggest solid lifter flat tappit cam that I can. What about intake? What should I run? Are these heads going to work good??? Thanks
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Old 02-22-2009, 09:18 PM
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I forgot something. The carb is a new Holley 650 mechanical hp street.
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Old 02-22-2009, 10:10 PM
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I researched these heads a little. It seems that they were cast by Brodix for Chevrolet and were used on the NASCAR circuit until the raised runner heads arrived on the scene. The runners are 180/55. The specs call for 55cc's, but that was with flat-face valves and before machine work. I suspect the ones you have, if they have conventional dished valves, are closer to 60cc's. "Must be used with 14011051 guideplates and 10051155 3/4" head bolt washers". May need offset lifters.

Found some flow figures, but nothing less than 0.400" lift. I guess when you consider these heads were destined for 355 motors that revved to 9500 and used ??0.750"?? valve lift, there was no reason to list low-lift flow.??? At any rate, they flow worse than the L31 Vortecs on the intake side at 0.400". Exhaust flow is exceptional though. If I were bolting them on my motor, I'd want to know the flow at 0.100", 0.200" and 0.300" as well as the rest of it.

0.400" 222/169
0.500" 247/188
0.600" 262/199
0.700" 274/205
0.750" 280/204

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Old 02-23-2009, 06:33 AM
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Man, I looked on the net for info on these heads and never found that info. You sure know how to find that stuff out! Thanks. I sent you a PM as well Techinspector. I already have the recomended guide plates that come with the heads. Any idea about the rocker studs? Will any 7/16 stud work? Also, what is a offset lifter?
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Old 02-23-2009, 10:09 AM
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See the bottom right hand corner of page 244 here....
http://www.compcams.com/technical/Ca...07/242-247.pdf
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Old 02-23-2009, 04:12 PM
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Inspector, the flow #'s you've listed are for a fully ported head right?
We have run two sets over a flowbench in their out-of-the-box condition and they didn't come anywhere close to the numbers you put up. I remember they were only in the low 220's cfm peak on the intakes, they were worse than Vortecs. I was told that the port coring was the same as Iron Bowtie, and the low #'s made sense with that statement. Phase 6 aluminum's are cast thick everywhere to allow head porters to carve almost whatever port shape they want(within reason) and so are not very good in as-cast form. I know it took us a lot (A LOT) of time grinding to get the intake #'s up to 270, but the exhausts were easy to get 200. I wouldn't recommend these to anyone to use out-of-the-box unless class rules said no porting and factory part #'s only. Aftermarket heads are a much better place to start, with a lot less finishing time.
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Old 02-23-2009, 06:53 PM
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I have no clue Eric, I was just trying to make sense of them. What you're saying about being slugs out of the box and thick cast to allow porting makes perfect sense.
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