3.625 (?)

[aquickv6]

Would there be any reason not to use the maximum stroke if buying a new crank? Will it still turn the same RPM or is it a limiting factor. Thanks

 

[S2V6RACER]

Still can turn the RPM's most of us dare to spin. Clearancing is the biggest concern with that crank.

Overbore concerns with the 109 blocks may deter using that big stroke because you may end up over 250 CI and who would want to break that rule.

 

[aquickv6]

Thanks Ted, this is for a Stage 4.1 BMS block, std bore. What would be the preferred crank for this block?

 

[S2V6RACER]

The preferred crank seems to be 3.625" for CID reasons. The 3.59" is the second IMHO.

 

[gnsrule]

3.625 x 6.5 rod x 4.0 bore= 273.319 cid
vrs
3.59 x 6.5 rod x 4.0 bore = 270.680 cid

Not much of a differance there. Maybe a tad stronger. I'm recomended to go a 3.59 and screw the 2.639 cid loss.

Just some o2's i've heard.

 

[S2V6RACER]

Originally posted by gnsrule
3.625 x 6.5 rod x 4.0 bore= 273.319 cid
vrs
3.59 x 6.5 rod x 4.0 bore = 270.680 cid

Not much of a differance there. Maybe a tad stronger. I'm recomended to go a 3.59 and screw the 2.639 cid loss.

Just some o2's i've heard.

I would say nobody would dare to post some hard data to support strength between the two. Heck, we couldn't get hard facts on a 2.100 rod journal crank strength other than speculation. The 3.59" stroke will be more suitable for 6.5" rods for piston design issues. I do not know what the 6.5" rod in the above equation means, the piston still travels the same distance either way given different rod lengths with the same stroke, the pin on the piston would be in a diffent location. Dwell time comes into play, but Ruggles stated no dyno differences have been noted on his engines. I would go with the bigger stroke if I could choose either crank for the same $$ unless I would compromise piston strength because I had long rods already.

 

[Nojug]

3 inches does not sound like a lot but you could be losing 10-12 free horses.