Topic: Chevy Rod journal sized connecting rods

[SavingTheBird76]

I'm guessing the Chevy rods come in more sizes,giving you more options when stroking the 400 CID motor.
Any other advantages?
If ordering rods for a 455,I'm guessing using the Pontiac journal size makes more sense.
I know I must match the crankshaft and connecting rods.

[79T/Aman]

when trying to mix and match parts you need to think in terms of measurments not the brand or size of the engine, those are irrelevant.
-For instance both Chevy and Pontiac made a 400 CID engine, which one are we referring to?
-The rod "size" referres rod length.
-455 Pont. and 400 Pont. engines use the same rods.
-The Crank has to match the block first, the rod journal has to match the crank rod journal, the pistons have to match the crankstroke with a given rod length and the piston in size has to match the rod small end size

[SavingTheBird76]

http://butlerperformance.com/products/crankshafts/new_jbp_crankshafts.html

Notice the crankshaft is available with different rod journals sizing.
Changes in journal size should require different length rods to get the correct block deck height.
I'm talking pontiac at the moment.
I want to order a new crank and rods for a .030 over Pontiac 455.
Any advantage to either Crankshaft?
Thanks for the reply.




Pontiac- 2.250
Chevy- 2.200

[72blackbird]

I'm assuming you're starting w/ a 455 block. The 2.2 rod journal has a little less bearing speed, so it puts a little stress on the rod bearings as opposed to a 2.25 Pontiac. But it's also less metal, and if you're going with a cast crank and it's a 455 I'd just run the Pontiac rods. It also makes piston selection alot simpler too.

Geno

[79T/Aman]

"Changes in journal size should require different length rods to get the correct block deck height"

No the rod journal size does not affect rod length, rod length is measured center to center of the rod bore to the pin bore so it does not matter how big the bore is or size of the journal for that matter.

[Mr. P-Body]

   79T is exactly correct. Journal size has no affect on rod "length".

   The BBC rod journal offers less bearing speed, as Geno states. This is probably the single biggest improvement.  The rod length is also "longer" in most of the stroker kits we use. This will reduce rod "angle" (the relationship to the crank pin at full "swing"), and moderately increase "dwell time" (where the piston "sits" at TDC and BDC), increasing cylinder pressure ion "power" and increasing "fill" on "intake".

   Stock-length Chevy rods are WAY too short for any application in the Pontiac. The 6.8" rod is the most commonly used BBC length. 6.7" is also used extensively (with longer strokes).  These "long" rods were developed intitially for using the BBC "tall deck" block for racing instead of heavy-duty.

   BBC rods also allow more "choices" for both rod bearings and piston pins, enabling one to "fine tune" the internals to a specific point.

   Lastly, grinding a factory Pontiac crank the .050" "under" for using the BBC rods will only "hurt" the crank if the proper radii aren't ground. Otherwise, it can actually strengthen it.  That little bit of material removed is not significant.  Unlike certain "other" cranks, Pontiacs are all cast, and not 'hardened" in the same manner as forgings, thus not having the undersize "limits" hardened cranks impose.

Jim

[SavingTheBird76]

I'm buying a new forged crank from Ohio crankshaft.
If I go with the blem 4.250 stroke crank,which length connecting rods would I need?
Is this even a reality?
Thanks

[Mr. P-Body]

   If the Ohio crank has the BBC journals (2.200", HIGHLY recommended), the most common size is the 6.8". We use Eagle rods here, exclusively, when building engines like this. They are the best rod on the planet FOR THE MONEY. One must spend at least another $400-500 to equal them in a "domestic" product. None of the other imports share Eagle's finish quality.

   United Engine Parts (Silvolite) sells the Kieth Black forgings (avoid the hyper-eutectic castings) with the correct pin placement, and a couple of choices for compression. Ken Keefer (Pontiac Dude, Brookesville, FL) sells BRC (Brooks Racing Comnponents) forgings for similar price. VERY good, light-weight race pistons, the only "drawback" is the 3-4 week "wait" for them.

   The compression distance (pin height) should be in the 1.295-1.3" area for the 6.8 rod. .990" pins are also required. The pistons are designed as a "drop-in" deal for the stroker.

Jim