stroker rod comparison

Tennessee Bullitt December 5th 2011, 9:05 pm

What would be the difference on a 6.605 rod vs a 6.8 rod on a 4.3 crank? Got a little curious why ford racing did that on their crate engines. Does one have a better ratio than the other? How about the piston?

dfree383 December 5th 2011, 9:34 pm

Piston "could" be a little lighter on the 6.8 combo. But Honestly IMO the additional .195 is of no real noticable benifit on 98% of the applications for a BBF for angularity

Couple advantages going with the 6.8 are Bearing and piston pin selection and their are alot of different shelf rods avaliable.

c.evans December 5th 2011, 9:38 pm

I've got one of those Ford 4.300" stroke crankshafts here right now. They are a really nice piece imo. The rod journal is a true ford size of 2.500". The counterweights are all rounded and smoothed and the main oil holes are chamfered.

The compression height of the pistons that go with the FRPP 4.300" + 6.605" rod combo is 1.540". I have Diamond pistons for this engine and they are a catalog item.

I wouldn't worry about the rod/stroke ratio and the 6.800" verses 6.605" rods. It's just internet theory and might be made out to be a big issue, when it isn't in an actually running engine. Food for thought; there's a couple million 454 Chevys out there and with a 6.135" rod and a 4.000" stroke, they had a r/s ratio of 1.533. With the Ford stroker you have a 6.605" rod and a 4.300" stroke and the r/s ratio is 1.536. So,,,,,,no problem.

Charlie

Tennessee Bullitt December 6th 2011, 12:20 am

good info there, thanks guys.

rmcomprandy December 6th 2011, 12:38 am

c.evans wrote:I've got one of those Ford 4.300" stroke crankshafts here right now. They are a really nice piece imo. The rod journal is a true ford size of 2.500". The counterweights are all rounded and smoothed and the main oil holes are chamfered.

The compression height of the pistons that go with the FRPP 4.300" + 6.605" rod combo is 1.540". I have Diamond pistons for this engine and they are a catalog item.

I wouldn't worry about the rod/stroke ratio and the 6.800" verses 6.605" rods. It's just internet theory and might be made out to be a big issue, when it isn't in an actually running engine. Food for thought; there's a couple million 454 Chevys out there and with a 6.135" rod and a 4.000" stroke, they had a r/s ratio of 1.533. With the Ford stroker you have a 6.605" rod and a 4.300" stroke and the r/s ratio is 1.536. So,,,,,,no problem.

Charlie

Yea Charlie ... there's a fewer number but, at least a couple million OEM production 400 small block Chevrolets at just under a 1.49/1 rod to stroke ratio; ( 5.585" length rod and a 3.750" stroke).

Tennessee Bullitt December 6th 2011, 12:29 pm

One other thing what is the difference between the 2 as far as keeping the piston at TDC? I seen where the talk is the longer rod keeps it closer to TDC and there for it is better suited for T/R and long runner manifolds. There was also the theroy that the longer rod is better suited for high rpm applications. If I can find the link I will post it later.

Mark O'Neal December 6th 2011, 1:44 pm

Interesting thread.

Ford did it because it was cheaper. They used a pinto rod in their original 347 ...because it was cheaper. It was stupid, but they'd sold the 5.315 to John Fenton so that's what they had laying around.

It doesn't make any different to the user at all, unless they're spinning the motor high enough for bearing speed to matter. So.....it doesn't maker any difference at all. Not bearing speed, not dwell at TDC, not torque curve, not nothing.

Tennessee Bullitt December 6th 2011, 3:00 pm

here is the link, don't know how true this is but seems to make a good read......

http://www.rustpuppy.org/rodstudy.htm

Curt December 6th 2011, 4:46 pm

What was the big difference with a 360 rod vs a 390 rod. I remember as a kid that 360 rods seemed to be problems.. Never owned one, so it is just recollection of others experiences.

Diggindeeper December 12th 2011, 12:42 am

Curt wrote:What was the big difference with a 360 rod vs a 390 rod. I remember as a kid that 360 rods seemed to be problems.. Never owned one, so it is just recollection of others experiences.

Difference is .050" in length and a hell of a lot of beam width. At least comparing the 352/360 to the 390gt stuff

138 December 13th 2011, 11:44 pm

so are these ford 4.3 cranks forged?...and are they readily availabe?...

466cj December 14th 2011, 12:13 am

Only advantage I could see to the longer rod other than bearing selection is not pulling the piston as far down at BDC. The FRPP 4.3" crank is cast steel, but is a quality piece and the larger rod journals means more journal overlap that makes it stronger.

Steve

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