My buddies 350 makes a deisel type sound, we thought it might be rod knock or this or that. Well I went to a pretty wellk nown performance shop and the guy instantly said that the zero offset pistons make that sound. These pistons are old, like 70's or 80's...he said that old style pistons with the pin pressed DIRECTLY in the center make that sound, and that the new ones are offset slightly to quiet it (at the cost of some strength).

Does that make sense?

 

new one on me

 

I've never heard that.

 

I've never heard of anything like that at all.

 

I had another tell me that the old pistons were like that. The one guy is like 65 and runs a shop....the other guy is like 45 and has had a half dozen chargers, sup bees, challengers...etc.....maybe it's to long ago for you "young guys". I dunno....the guy who is helping me build my engine is like 32, and he never heard of it. But his older bro who is in his 40s said thats how they used to do it. Hmmmm...

 

Maybe he's right. But wouldn't that mean that all the old cars have this "diesel" sound?

 

Most factory engines have pistons with offset pins for noise reduction reasons. Makes it so piston rocks over less at the top of the stroke, so there is less piston slap. But it costs power. One very respected engine builder (Joe Sherman) even goes so far as to install pistons reversed to extract more power from engines using stock type pistons.

Aftermarket hiperf forged pistons come with no offset, cause racers don't care about noise from piston slap. Besides, forged pistons run much more bore clearance, so they are noisy anyway.

 

So it's not unreasonable to believe some of the noise is just the pistons then? I'm glad to hear that.

 

Angel71rs is exactly right, if you look at a cast piston close enough you can tell the pin boss is offset without even needing to measure it.

Martin

 

Forged pistons will also make more noise than cast or hypereutectic pistons due to the wider piston-to-bore clearances they require (especially when started cold).

Most (all?) factory stock SBC cast pistons have a slight wrist pin offset to reduce both noise and bore wear.