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Old 03-28-2008, 07:57 AM
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206 Heads?

I'm building 454 street/strip motor for my 1967 chevelle. I've got a pair 0f 1966 206 closed chambered heads with stock valves. I was wondering how much these would limit my over-all torque and horsepower numbers? Also anything I can do to get them to flow better? I've heard you would run into water jackets trying to put bigger valves in; porting work? polishing? thanks Josh

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Old 03-28-2008, 10:28 AM
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I am not sure about the 206's but most BBC castings especially the early ones will accept at least 2.05 1.72 valves, and you can really hog the heck out of them when porting. I would say go for it, it is not like anybody will give you much money for them in stock form anyways.

Chevy didn't make any "Light Casting" BBC heads so there is not much chance of them cracking like small block heads.
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Old 03-28-2008, 04:49 PM
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I was curious about these heads, so did some research.
3856206
65-66 396, 325 hp
97.2 cc chamber
Oval port
Closed chamber
2.06"/1.72" valves
225 cc intake runners

In my opinion, your build will be limited by the intake runner volume more than the valve size. With 454 cubic inches suckin' on 'em, I suspect the runners will begin stalling around 5,000 r's, so I'd be building for idle to 5,000 with this build. Block deck height is 9.800" stock, so you want to get close to this with your stack of parts. With a 2.000" stroke radius, 6.135" rod and 1.645" piston compression height, you should be at 9.780", leaving the piston deck height at 0.020". Using a GM 14015351 head gasket (0.022" compressed) will set the squish at 0.042". I'd take a very, very light cut on the heads and block decks just to make sure they're flat and true.

Pistons would include Keith Black KB200 (hyper, 1/16" rings), KB202 (hyper, 5/64" rings), KB780 (forged, 1/16" rings) and KB9920 (forged, 5/64" rings), TRW 2377F (forged), SRP 139477 (forged).
The 2377F has a compression height of 1.640". All the others listed are 1.645". I'd use the thicker rings on a low-rpm build. They may seal a little better.

Using any of these pistons at 0.030" overbore will result in a 9.6:1 static compression ratio. This will allow you to choose a cam that will sign off about 5,000 rpm's to match up with the intake runners' capability and make good power from idle-up.

I'd use a bowl profiler tool to open up the chambers out to the cylinder walls to unshroud the valves, install hard exhaust seats, do a good 3 or 5 angle valve job, do a little blending under the valves and call it good.

For the cam, I'd use something like this hyd roller. THIS IS NOT A CAM RECOMMENDATION, IT IS ONLY TO GET YOU INTO THE BALLPARK. Always call your favorite cam grinder and give him all the specifics of your motor so he can recommend the exact cam for your application.
http://www.cranecams.com/?show=brows...tType=camshaft

Up top, I'd use a standard Performer and a 700/750 vacuum secondary carb of your choice. Equal length headers, 2 1/2" pipes and mufflers of your choice to the rear of the car with a X or H connector ahead of the mufflers.

I'd also use a 1,800 to 2,000 stall converter to get you up on the cam a little sooner.

Last edited by techinspector1; 03-28-2008 at 05:31 PM.
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