I have been wondering about this common upgrade. If you use one of the 307 or 327 flat top pistons will there be any valve clearence problems or do the v8 valve notches line up for a 6 cyl also? I guesse I should have mentioned I was talking about these being used in a 250.
I have 307 flat tops in my 250 and there are no modifications required. I also have a Crane cam running .502 lift, and still no problems.
Back in 86 when i first built my 250 The skirts on the 307s(mine were popups) had to be trimed to clear I'm guessing the crank (maybe There is a differents in the flat tops or later yr. makeings of the 307 psiton). As for the 327 pistons Thats a 4in bore.hope this helps }[oooooo]
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NovaMan/Twisted6/Larry
So the 307 pistons touched the crank, how much clearencing had to be done to the skirt? Could you do it with like a dremal tool with a sanding roll or is there a more presise way to go about it? As far as the 327 pistons, since they share basicly the same crankshaft in the small block, the probably need the clearencing to. Now about the 4 inch bore. I did a search and have read that another user had them and was having good luck. But, would there be any real benefits going to a 4 inch bore? I know added cubes, and compression help, but what are the trade offs? Overheating, weak cylinder walls? I already have a freshened up 250 ready to go, but since I have another complete motor just sitting I thought I would play a bit and try and make some horsepower.
I don't recall how much had to be removed this was 17 yrs ago when I built the motor. Now I am rebuilding a new one/fresh one. after running it for 17yrs and Never been in side it in all that time From a daily driver to full race do to the rear gear changes. I don't know what all would have to be done Other then the .125 over bore. Yes the walls become thin. And in some cases I'm sure wayto thin maybe even Holes???? Before doing that Kinda Bore I would have the Block sonic checked. To check For core shift and to make sure the block could take that kinda bore. Some blocks may not be able to handle that With all Maybe having a sleeve put in it.
I would say Email these guys who have done this and that are running them. To me this just seems TO THIN for a Daily Driver.As a Race motor maybe fine???? But again To me To Thin as a daily driver. my2cents But Your call. Hope this helps.}[oooooo]
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NovaMan/Twisted6/Larry