Benefit of a longer connecting rod

[Six_Silver]

Will a 6.3" rod benefit over a stock 5.9" (I think) rod? I know the pistons stay at the top and bottom of the bore longer, but is it enough to really make a difference in HP? I have an oppurtunity to use a set of 6.3" rods and have new pistons made, but I dont know if it is worth the money to go this route over using my stock rods and my current JE's. Thanks for any feedback.

 

[Turbonics]

Originally posted by Six_Silver
Will a 6.3" rod benefit over a stock 5.9" (I think) rod? I know the pistons stay at the top and bottom of the bore longer, but is it enough to really make a difference in HP? I have an oppurtunity to use a set of 6.3" rods and have new pistons made, but I dont know if it is worth the money to go this route over using my stock rods and my current JE's. Thanks for any feedback.

If the choice was available to use a longer rod such as the ones you have, I certainly would.

There was a good thread on using longer rods on the board recently, & the majority of the posts were positive. One fellow even gave a link to an excellent article that detailed some of the significant advantages from using a long rod, quoting Kenny Duttweiler.

Smokey Yunick constantly championed the benefits of longer rods from all his R & D work on the the Buick Indy engine.

 

[chevyII]

wont make any difference till after 6500-7000rpm.

 

[TurboJim]

Long rod and long stroke are different. Long rods are used to minimize side loading of the piston. Additionally, the angle between the crank throw to center of the piston is less, therefore more power is made during the piston UP/Down instead of into the cyl wall and tryiong to cock the piston in the bore. Longer rods will require special or possibly custom pistons.

 

[Six_Silver]

Thanks for the replies so far. I see there are a few different oppinions. I would like to know if there is a noticable difference in HP by going to a longer rod. It will set me back $850 for custom made JE pistons, rings, and wrist pins, plus the cost of the rods. I am trying to decided if the money would be better spent elsewhere...

Originally posted by TurboJim
Longer rods will require special or possibly custom pistons.

Yes, the piston wrist pin gets moved higher in the piston so I cant reuse my old JE pistons that were on the stock rods.

 

[snodgrass]

I my opinion... unless you are spending a ton of money on this motor, like going with stage II stuff, you're money would be far better spent elseware. The stock rod angle on a Buick v6 with a 5.9 inch rod, and a 3.4 inch stroke is better than a majority of race engines. Long rods are better in most cases, but you will likely notice no difference in this application.

 

[Six_Silver]

Thats what I had figured. This is just going to be a 10 second stock block car.

 

[cool 84]

Out of curiosity, would less side loading help reliability at all, say if you had thin cylinder walls? I have a 4.1L .035 and I'm worried about cracking a cylinder wall. I know it's cylinder pressure that cracks them but I wonder if it would make any difference with less sideloading also.

 

[fuzzyGN]

If you are not planning on using the longer rods would you be interested in selling them? These rods are from a 3.0L correct?

 

[Mike Licht]

Long rods USUALLY give more peak power, Short rods USUALLY give more average power across the RPM band. Short rods can help eliminate some detonation by accelerating the piston away from the chamber faster from TDC (less dwell time). In some applications (na) this extra dwell time is better for detonation. One part will not make your combo. The sum of all the parts can give sucess. I would use a stock lenght rod for your application and intended RPM range.
Mike Licht