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-   -   Offset grinding crank ? (https://classracer.com/classforum/showthread.php?t=73402)

Dan Fahey 07-08-2019 12:42 AM
Re: Offset grinding crank ?
 
Quote:
Originally Posted by GTX JOHN (Post 591853)
The .013 Offset only adds a very small amount of displacement!
The impact is a bit more compression from the added stroke.
Draws .013 more air and then compresses .013 a differential of .026
Plus slightly smaller diameter crank diameter, less parasitic drag.
Most engines it is about 1.5 cuin increase.

Larry Hill 07-08-2019 06:40 AM
Re: Offset grinding crank ?
 
...

Dwight Southerland 07-08-2019 06:59 AM
Re: Offset grinding crank ?
 
Quote:
Originally Posted by Dan Fahey (Post 591966)
The impact is a bit more compression from the added stroke.
Draws .013 more air and then compresses .013 a differential of .026
Plus slightly smaller diameter crank diameter, less parasitic drag.
Most engines it is about 1.5 cuin increase.
Excuse me!?! Stroke is measured from BDC to TDC so the "differential" is .013", not .026".

340Cuda 07-08-2019 11:11 AM
Re: Offset grinding crank ?
 
Quote:
Originally Posted by Dwight Southerland (Post 591976)
Excuse me!?! Stroke is measured from BDC to TDC so the "differential" is .013", not .026".
This may be a stupid question but just because you are allowed a little extra stroke does that mean the piston can come out of the that much more than the spec?

pmrphil 07-08-2019 12:42 PM
Re: Offset grinding crank ?
 
Quote:
Originally Posted by 340Cuda (Post 591999)
This may be a stupid question but just because you are allowed a little extra stroke does that mean the piston can come out of the that much more than the spec?
No, no more than spec. You just don't have to deck the block as much.

Dwight Southerland 07-08-2019 05:00 PM
Re: Offset grinding crank ?
 
Quote:
Originally Posted by 340Cuda (Post 591999)
This may be a stupid question but just because you are allowed a little extra stroke does that mean the piston can come out of the that much more than the spec?
Yes. And max compression is dictated by spec limits. Adding stroke does not increase compression except for the additional displacement added to the mix.

Mark Yacavone 07-08-2019 05:13 PM
Re: Offset grinding crank ?
 
Quote:
Originally Posted by Dwight Southerland (Post 592033)
Yes. And max compression is dictated by spec limits. Adding stroke does not increase compression except for the additional displacement added to the mix.
Yes. There are comp. calculators all over the 'net. One can run the numbers and see if you think it's worth the extra effort.
To me, the indexing and smaller pin size are at least equal in value.

BTW, thank you to to Dwight for what you do for racers....Appreciated by 98% of them ,and called names by those who are Left.

Larry Hill 07-09-2019 08:40 AM
Re: Offset grinding crank ?
 
Gasket thickness (A) and deck (B) can vary, but total of A+B has to same as or greater than NHRA spec. .000 deck and .040 gasket = -005 deck and .035 gasket or +005 deck and.045 gasket. Give yourself a few extra thousandth to the good side so you can be fearless in tear down.


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