New Pistons:Cast or Forged??

6

60biscayne

Active Member
Supporting Member 1
My son and I have a 65' 409 truck block, std. bore. We also have a set of 11-1 pistons. BUT, we've done some careful measuring, the bores are straight, very little ridge, but still worn a couple of thousandths, 2 of them were honed up a little larger because of pitting. the pistons are worn anywhere from .002-.004 undersize on the skirt. Bottom line is The piston to cylinder wall clearances range from .005 to .008, with the pistons in upside down, and measuring at the bottom of the piston skirt, where they are the largest. Looks like a bore job to me, I think. We're wondering if we really need to go to forged pistons($669), when cast pistons ($300), might do. Being we have a truck block, with 11-1's, we actually will have about 10-1, so I'm told, with the headers, cam, carb, and heads(817's), combination, I'm guessing we'll be making about 380 or so horses. WE don't plan to spin this motor much over 5500 rpm's, no heavy racing planned, just playing around on the street. The car will have 3:55 gears, 4- speed. Do you guys think cast pistons will hold up to this not too radical of a re-build? Or is it worth it to spend the extra $$$ for the forged ones?? :dunno Thanks a bunch to whomever can shed some light on this. Brian. :cheers
 
M

Mr Goodwrench

Well Known Member
Well I'll take a stab at this one, there has been a lot of discussion on forged vs cast pistons, it seems the cast pistons avaliable today are not of as good quality as used to be, but for a low RPM street cruiser I personally feel they would suffice.
However when you add up the total cost of rebuilding one of these engines $369.00 is small potatoes. I'm not sure what piston to cylinder wall clearance these new forged pistons run but I know the older ones was pretty loose, I think because a forged piston expands more as it heats up than a cast one. good friend of mine has a LS- 6 chevelle with only 26000 originall miles which came factory with something like .0065 piston to cylinder wall clearance, it has piston slap so bad after being fired the first min you would think it was a 100,000 mile engine. said it done it from day one, also used a qt of oil every 500 miles from day one. I,m sure someone will shed more light than I know on this matter.
 
raymar58409

raymar58409

Well Known Member
Supporting Member 2
Ah yes, GM engine knock. GM says thats normal. So I guess the engines I build that don't knock are abnormal. Think that guy that Q checked the engine in my suburban (that knocks and is now using oil) will rethink his priorities in the unemployment line? "DUH should I continue to read my book or check the clearances on that engine?":coffee:
Ray
 
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