[gtofreek]

For the little difference in overall length, there is really no HP gain with the longer rod. Pontiacs rod was so long to begin with. Going longer mainly just reduces piston weight, and the Chevy rod is lighter than the Pontiac, even though it's longer.

[hurryinhoosier62]

Originally Posted by HWYSTR455

Yeah, wasn't sure actually, if the rod angle would free some up or not. My 1st thoughts were based on a higher RPM potential.

Was hoping to dig up my H-O bible, refresh my memory, but can't seem to locate it at the moment.

.

A stock length Pontiac rod (6.625) gives a 1.7667:1 rod ratio. A 6.800 BBC rod would give a 1.8133:1 rod ratio. I'm with Tom and Paul. While it would give a slightly lighter reciprocating mass and a lower rod bearing speed, it would do little to increase hp.

[taff2]

Longer rods (IMO),do have benefits besides the ability to use a lighter piston. They lessen thrust loads on the bores, (maybe important when using a stock block), a lower tension ring pack can then be used, (meaning less frictional losses),they cause the piston to dwell longer at TDC -increasing combustion chamber pressure,(maybe important in a lower compression engine),they give a longer,slower 'pull' on the intake charge,(maybe important with limited flow iron heads to stop the intake ports going into sonic choke), the lighter reciprocating mass does give you the opportunity to lighten the crank a bit too if desired,(again,easier on the block, engine revs more quickly).
If, as a lot of engine builders say- "It will make no difference,the rod just connects the piston to the crank"- then there really is no downside to using longer rods but you may reap some of the benefits.
ps,cost is not an issue any more as BBC long rods are reasonably priced nowadays.

[gtofreek]

taff2, I fully agree with your comments. What we are getting at is going from 6.625" to 6.8" isn't enough to see any real performance improvements[other than the lightening of the assembly]. With a BB Chevy, on the other hand, going from 6.135" to 6.8" is a whole different story.

[steve25]

Using these 6.8" rods was originally done more for dropping the cylinder wall thrust loads when you where building 500 CID out of a factory block with paper thin walls!

[tom s]

The BBC rods were originally used in our pontiacs to get cheaper forged rods!The less side load was just what came with them.Tom

[slowbird]

Originally Posted by tom s

The BBC rods were originally used in our pontiacs to get cheaper forged rods!The less side load was just what came with them.Tom

X2!

[Skip Fix]

Originally Posted by tom s

The BBC rods were originally used in our pontiacs to get cheaper forged rods!The less side load was just what came with them.Tom

Yep! Why when I built my RAIV motor in '88 I had $1200 Crower billets as an insurance package. Thought the cast rods in the previous shortblock were a risk and nt impressed with the forged early rods after heat treating.They also took up some of the piston CH going to the offset ground 4.25 2.20 rods on the factory cranks.

[chiphead]

I just used them because of the wide selection of BBC bearing inserts.

KRE uses comp lobes for this shelf roller. I compared the adv duration of the KRE 224/230 cam to the infamous 224/230 XE276HR and it appears to be different. The LSA is 112 vs 110 and the lift is different too. So it doesn't appear to be the same grind.

There is kinda a "dead zone" in this area of HR cams. I find several cams in the 219/227 range and many in the 231/239 range. There are only a few in the middle at 225/230. There is a Comp, a Crane and this KRE grind. I'm wondering if there is a reason for that?

Engine is not built yet, so no ring gaps. Haven't even bought any parts, waiting until I get the block/heads back from the shop. I'll use TS's recommendations for gap. I could use their gapless AP top ring, but I'm a little shy since I've never used one.

[blueghoast]

Put a 2 inch spacer on the RPM intake and you'll gane 20 HP.
I did that on a 400 build for my 64-Tempest.
This was dyno proven, I did lose a little tork witch only helped as
this is A 4-speed car. And the nitros plate under the carb works perfect.
I had that combo on another car.

GT.

[Steve C.]

"They lessen thrust loads on the bores".

Agreed, but the big effect on a larger stroke Pontiac with 6.8 rods. Jim Butler has seen tear down differences between the two.

.