cutlassefi

A longer rod is easier on the walls and pistons. Not sure yours is a good explanation, sorry.

fleming442

What explanation? I was just saying that in the mid-60's, they may not have been able to cast a production piston that short. Were you there? I sure wasn't.

madmax442

I think it was beer thirty on a Friday when the choice probably needed to be made and they said screw it!.

bobus8

It's always been my understanding that the longer rods (probably because of the piston dwell time at TDC) improved top end horse power. Since Olds engines (big blocks) have weak main bearing webs, (unless you put in the expensive girdles) you probably shouldn't be revving them to 6000 or 6500 rpm so the question is moot.

Warhead

I'm sure they were more concerned with making huge torque/power from idle to 3000 rpm with existing cylinder heads. Haul a 5000 lb barge cross country at lower engine revs.
JMO

rad

i know engineers at the time didnt like the wrist pins up into the oil ring area of the piston (sbc 400) so they shortened the rods, latter on in life we figured that its not that big of a deal, personally i like the longer rods for angularity reasons, in the past ive built 496 chevys with 6.800 inch rods using a tall deck 427 block and depending on the brand of pistons (wiseco) ive ended up being 0.005 to 0.010 out of the hole,but as long ss you have a quench (piston to head clrearance) of 0.035 - 0.040 its not an issue, as far as today goes i wouldnt build a 350 - 383 chevy with anything shorter then a 6 inch rod, but the parts are on the shelf, are there any piston combos available for say a 425 olds from another application ( pontiac mopar etc.) or a piston for the 455 that would work with a 7.00 inch rod 455 olds?

joe_padavano

I've been watching this thread with amusement.

Look, Olds was NOT in the business of building ultimate output engines. It was in the business of maximizing profits over hundreds of thousands of cars a year. Rod length selection for the new-for-68 455 (and long stroke 400) was not made randomly by idiots. It was a carefully considered selection based on minimizing production cost and maximizing engine longevity and driveabiltiy for the NORMAL Olds purchaser. All but a handful of buyers of 455s knew or cared about rod length. The buyers cared that they purchased a smooth-running car that would last over 100,000 miles. Olds engineers cared that the new 455 could be machined and assembled on the existing 425 assembly lines with minimal cost for changes. The 0.27" longer stroke on the new crank required shorter rods to retain a traditional piston compression height. Keep in mind that the compression height needed to allow for appropriate long-term piston strength while accommodating the soup-bowl-sized dish that Olds engineers knew was coming for the 1971 model year (the pending EPA requirements were known well in advance).

This is all about production engineering and minimizing cost for the largest number of users. The engineers (and beancounters) frankly didn't give a rip about the couple of hundred drag racers using these engines.

captjim

Well stated^^^^ I basically said the same thing earlier in this thread, though not as succinctly.

android 211

Olds 455: Olds 425/early 400 7" rods with Pontiac 455 pistons. The later 15cc dished versions to bring the compression down for the street or flat tops for drag. Deck height comes out close enough to be adjusted.