VinMichael

I have a stock high compression 455 that I want to re-ring. Is it advisable to turn the pistons around to use the built-in pin offset to make more power?

cutlassefi

Are you sure they’re offset, can you see it?

VinMichael

I am not sure yet. The block is still together.

I thought thats how they all came from the factory...

Schurkey

How much do you want to listen to the knocking that is reduced by offsetting the pin?

The whole reason to offset the pin is to cut down the piston slap. You turn it backwards, the knocking is even worse. Especially on a worn cylinder bore. But what do I know? Maybe you have a really loud radio.

There there's the issue of having to press the pistons off the rods. Be lucky if you don't score a piston pin, or break a piston in the process. OR you could take the piston and rod and move it to another hole so the piston offset ends up bass-ackwards, but you have to make sure the bearing offset stays correct.

Far as I'm concerned, it's nothing but heartache.

VinMichael

have you ever done it?

My rods that are in my 455 now are “backwards.” The pistons are not

Schurkey

Hell, no.

How are the crank fillets not riding on the bearing edges? I'm gonna have to dig out the 425 rods from the barn and take a look at them. My 455 photos are inconclusive.

cutlassefi

Olds cranks are undercut, no radius. They most likely could be flipped.

VinMichael

Okay I was just wondering where you got your opinion from

Based on what I've read reversing the pistons when there is an offset makes the rod act longer and makes more power and throttle response.

66-3X2 442

We use to do that in Chevy small block stockers to change the rod angle. The idea is to flatten the rod angle which helps.

Schurkey

That makes things easier. Still have the piston slap to deal with, though.

BillK

If you really want to do it all you would have to do is swap the piston and rod assemblies from one side of the engine to the other. You dont need to press them off and back on. Personally I dont think you will gain anything on a stock engine.

edzolz

If your rods have "spit holes" this would not be a good odea.

BillK

Why not ? When you flip them to the other side the spit holes still go towards the camshaft but the pistons will be backwards. You put the #1 piston in the #2 hole etc.

cutlassefi

All of this is a moot point anyway. IF it amounted to any gain it would be minimal anyway. And the increased piston slap would make it even more of a waste of time.
Vin if you want better performance then replace the pistons with a set of Wisecos in std. They make em.

Run to Rund

I quizzed Mahle some years ago on pin offsets, and they assured me that racers have standardized on zero offset, and do not go for a reverse offset.

cutlassefi

x2

307's dont suck

This is an old thread, but I was wondering about a mild street stroker build for a 307 Olds. If you use the 3.51" offset crankshaft, 6.250" LS Rods and LS pistons that are 3.799" plus .030" we have an engine that displaces 323ci and if we add up the numbers we have 9.33" that is very close to the deck height.


Your thoughts?

307's dont suck

I should add that that compression height of the pistons is 1.325"

Here is the calculation

3.510"/2 = 1.75"

1.75 (stroke) + 6.250" rod length + 1.325 compression height = 9.33"

Is the deck height on the 307 the same as a 350?

If so what would the compression be on a motor with 5A heads?

Schurkey

Are there valve reliefs on those "LS" pistons, and are they in the right place for the Olds valve positions?

Deck height of all Olds small blocks is the same within typical production variations.

Without more info on the pistons, and head gasket thickness, there's no way to calculate compression. Might be worth actually measuring the chambers on the heads, too,

cutlassefi

Worrying about valve reliefs on an Olds with less than .650 or so lift is a waste of time. It’s irrelevant.
3.510/2 is 1.755. Just do 3.500 with the 6.250 rod and 1.325 comp distance piston. That’ll give you approx 9.325 in total distance. That should give you right about a zero deck.