Alternative piston/rod combo for a 392 build?

M

MrWolf

New member
I'm in the process of acquiring a 392 ic to fit in my Scout terra. It has a 345 today with the 272, 31" tires and 3.07 diffs. The truck is mostly a road queen with little use off road and gas prices keep it from being used for long, heavy hauls. I would like to have some fun with the 392 engine to improve power and plan on doing this by improving flow in the heads, stronger valve springs, hotter cam, higher compression ratio, oversized, lighter pistons and lighter rods.

I know the subject of building 392's has been covered lots of times here, on bp and bb but I haven't found anyone who have just replaced both pistons and rods with after-market parts for some other engine to improve on weight and compression. I have read that the 0.060 oversized pistons for a 425 cadillac or stock 413 dodge pistons has been proposed, but the rods are different. Anyone know if this would be possible and might know of a piston/rod combo which could fit (stock or undersized big end bearings)? Of course the new pistons and rods should be lighter than stock and it wouldn't hurt if the new combo could improve compression ratio at the same time.
 
Fun to play with combos but the IH sv tall deck platform is hindered by a heavy truck design. A very long rod and a bore length that can't take full advantage of the tall deck. The block deck and rod length can take 4 1/2 inches of stroke but you will run out of bore at the bottom of the longer stroke. You need to do the math and look at the geometry. It will be quickly obvious. After you receive the 392 tear it down and take some measurements.
Beyond that the heads can't handle the displacement or flow needed to make serious power.
 
Yes, I have read that if you stroke it too hard you will run out of skirt in the block before you hit the heads. Also getting into conflict with the cam lobes. But I wasn't thinking about stroking it, just give it a little more cid with boring it and giving it a higher compression ratio with taller pistons and/or longer rods. But I think you are right regarding doing some measurements first. When I calculate the stock conditions with a 100cc recess in the head, 10cc in the piston dish, 4.125x3.66 bore x stroke and 8:1 compression I can't see there is much room for bringing the pistons up without smacking the heads?
 
You can go up to 3.875 stroke and still be ok at the cam/rod area but you'll need a profiled bbc style rod. I have the tall deck rod length somewhere and it was around 6.900 c to c. Calculate at .125 over bore for displacement.
 
Can I use some of the bbc rods straight out of the box, do they have to be machined or will I need a custom rod job to make it fit?
 
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Missed this sorry,
no a bbc rod will not work out of the box. The big end of the IH is wide by a bunch. The bbc rod can be widened easily enough by a quality shop to fit that end but also you'll need a custom piston... Plan on about $95- $105 per hole for piston and rings fitted for the bbc pin.
 
Thanks for the reply.
I have finally acquired the 392 for this project now:) at the moment working on dismantling and cleaning everything before I take it to the machinist to agree on what to do and the price to be paid. Seems like I will have to replace a few valve seats as they are rusted, other than that most of it seems good.
Plan is to just go for new pistons on the old rods. It'll just get too expensive, and too little gain to go that route with widening bbc rods and milling down the crank that much. If the crank looks good I might have it offset grinded to .03 bearings for a little more stroke and cr.

Will there be any significant weight difference between stock (flat top with d indent) pistons and, the same style silvolite pistons in .04 overbore?
 
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