Pistons

[Larry Hill]

If the pin is offset, would it cause the piston rock and break ring seal due pivot point placement?

[Jim Hanig]

Well I am not sure about that Larry some pretty well known engine guys say to run them

[FED 387]

Offset pistons-----small amount of power there--- because of less power need to overcome rod load and easier crank rotation--- it makes engine RPM quicker---FED 387

[Dwight Southerland]

Originally Posted by Larry Hill

If the pin is offset, would it cause the piston rock and break ring seal due pivot point placement?

Piston rock is actually worse with centered pins.

[SSDiv6]

Originally Posted by Dwight Southerland

Piston rock is actually worse with centered pins.

Dwight is correct.

Piston offset reduces friction and cylinder wall loading; it also improves geometry.



F1 and NASCAR has been doing it and also using guided pistons.
Would not be surprised if Pro Stock is doing the same, especially with the use of short deck blocks.

[ss3011]

Depends on which way the offset is. Factory offset is to quiet piston noise.

[Larry Hill]

Is the piston balanced in the center or on the center line of the off set pin placement? Just wondering about inertia.

[Dwight Southerland]

Depends on the piston. A lot of piston configurations so not lend themselves to equal balance around the centerline of the pin. For example, BBC 396 high compression piston is unbalanced no matter what you do that is reasonable. You can add a lot of weight to the flat side of the piston to balance it, but is the extra overall weight infringing on the advnatge of minimum reciprocating weight? You can offset the pin, but it will take .150" to .210" offset to acheive balance.


Note: The above numbers were calculated using minimum weight Stock Eliminator pistons. You numbers will vary according to your restrictions.


When I built the engine for the Corvette (SS) I worked to achieve a better balance relative to the pin centerline. Did it help? Who knows?!? A-B-A was not attempted, it just sounded good and trick to converse about in techno-savvy circles.


I have seen pistons out of a very fast 283 SS engine that had the pin offset by .090"

[Jim Hanig]

Originally Posted by Dwight Southerland

Depends on the piston. A lot of piston configurations so not lend themselves to equal balance around the centerline of the pin. For example, BBC 396 high compression piston is unbalanced no matter what you do that is reasonable. You can add a lot of weight to the flat side of the piston to balance it, but is the extra overall weight infringing on the advnatge of minimum reciprocating weight? You can offset the pin, but it will take .150" to .210" offset to acheive balance.


Note: The above numbers were calculated using minimum weight Stock Eliminator pistons. You numbers will vary according to your restrictions.


When I built the engine for the Corvette (SS) I worked to achieve a better balance relative to the pin centerline. Did it help? Who knows?!? A-B-A was not attempted, it just sounded good and trick to converse about in techno-savvy circles.


I have seen pistons out of a very fast 283 SS engine that had the pin offset by .090"

Dwight would the off set be to right or to the center?

[fordteacherguy]

Originally Posted by Dwight Southerland

Depends on the piston. A lot of piston configurations so not lend themselves to equal balance around the centerline of the pin. For example, BBC 396 high compression piston is unbalanced no matter what you do that is reasonable. You can add a lot of weight to the flat side of the piston to balance it, but is the extra overall weight infringing on the advnatge of minimum reciprocating weight? You can offset the pin, but it will take .150" to .210" offset to acheive balance.


Note: The above numbers were calculated using minimum weight Stock Eliminator pistons. You numbers will vary according to your restrictions.


When I built the engine for the Corvette (SS) I worked to achieve a better balance relative to the pin centerline. Did it help? Who knows?!? A-B-A was not attempted, it just sounded good and trick to converse about in techno-savvy circles.


I have seen pistons out of a very fast 283 SS engine that had the pin offset by .090"

Here is a link to JE's new line of asymmetrical pistons that are built offset with attaching article and video..

Most are import applications but you get the point.

http://www.jepistons.com/Articles/10...d-Pistons.aspx