Off-Center, Insufficent rod offset

[CTX-SLPR]

Howdy,

As I'm trying to cobble together the low power version of my 3.0L destroker with off the shelf materials the problem of finding a rod with a long enough C-C length for the 2.66in stroke crank and any off the shelf 3.800in bore piston is proving a challenge. I think I've settled on turning the crank journals down to 2.20in and using narrowed BBC rods with a stock 3.0L Buick flattop piston and save my pennys for a forged replacement piston in later times.
The other option is to use a BBB rod and a forged 0.020 over 2.3L Ford piston. Again I'd have to narrow the rod to fit on the crank but with the off center's motor 0.110-0.127in (seen both numbers refferenced as well as 3.0mm) offset on the rods, you can't get the proper offset using a even a narrow bearing on the BBB rods. Your basically looking at half the offset. While I am planning on starting at only 300hp, I certainly want to increase that as the budget allows.
What is the down side to running only a 0.065-0.070in offset on the rods and what is the minimum you can shave the divider between the rod journals down to too decrease the offset needed?

Thanks,

 

[Eticket]

Machine the top of the rod and shave the piston too.

 

[BlownV6]

Howdy,

As I'm trying to cobble together the low power version of my 3.0L destroker with off the shelf materials the problem of finding a rod with a long enough C-C length for the 2.66in stroke crank and any off the shelf 3.800in bore piston is proving a challenge. I think I've settled on turning the crank journals down to 2.20in and using narrowed BBC rods with a stock 3.0L Buick flattop piston and save my pennys for a forged replacement piston in later times.
The other option is to use a BBB rod and a forged 0.020 over 2.3L Ford piston. Again I'd have to narrow the rod to fit on the crank but with the off center's motor 0.110-0.127in (seen both numbers refferenced as well as 3.0mm) offset on the rods, you can't get the proper offset using a even a narrow bearing on the BBB rods. Your basically looking at half the offset. While I am planning on starting at only 300hp, I certainly want to increase that as the budget allows.
What is the down side to running only a 0.065-0.070in offset on the rods and what is the minimum you can shave the divider between the rod journals down to too decrease the offset needed?

Thanks,

I have narrowed a number of sets of rods including about 4 sets of BBC rods for off-center use , what seems to be the problem?? Mike

 

[CTX-SLPR]

Mike,

With BBC rods, nothing. The 0.992in width means there is enough meat to get them offset like the factory units. The BBB rods which share the same 2.250in rod journals are only ~0.925in wide and aren't wide enough to fully offset to the factory units. If it's just a matter of getting them to fit under the pistons than I'm sure I can also offset the small ends and/or the pistons to get them to fit but it doesn't seem like that's actually a very good solution.

 

[BlownV6]

Ok I guess thats my bad. I though you were talking about BBC rods. For the limited amount of HP that your going to make , if the beam CL is not centered up just perfect its really not going to cause much of a problem. Mike

 

[CTX-SLPR]

Mike and any others,

At what sort of power level do you think it would cause a problem? Early BBB rods were forged and even the later cast ones seem to live to 6500+ rpm with the massive coffee can sized pistons they use as well so I think it'd be enough rod for me till I'm over 450hp. Then again on a factory 2.66in crank turning it down could actually improve it's strength by doing a good job on the journal radius vs. the factory 90 though I guess widening the journals could accomplish the same thing.

 

[Mike E]

Those BBB rods typically have a +750 gram piston and pin hung on them. So, you'll be reducing the stress on them quite a bit with a 3.8 piston.

Have you looked at Big Block Pontiac rods? They also use a 2.250 journal. I think they are .99x wide. You could pick up a set of eagle pontiac rods pretty cheap, just have to bush down the .980 pin.

 

[CTX-SLPR]

Those BBB rods typically have a +750 gram piston and pin hung on them. So, you'll be reducing the stress on them quite a bit with a 3.8 piston.

Have you looked at Big Block Pontiac rods? They also use a 2.250 journal. I think they are .99x wide. You could pick up a set of eagle pontiac rods pretty cheap, just have to bush down the .980 pin.

Looks like the Pontiac rods would work with an offset bushing to drop the C-C length to 6.60in and the width is nearly the same as the BBC (heck they almost sound like BBC rods with a 2.25in rod journal). They are however almost twice the price of the BBC rods though only looking at eBay with a very course search.

I wrote the crankshaft grinder about widening the journals to put a better radius on them even at the cost of going undersized and see if it's possible to go to the "wide journal" 0.890in bearings on the OEM crank.