Hey y'all

I got the summit k6400 cam and lifter set, with stock rocker arms. Some of my old pushrods are bent so i need new ones but i am unsure of the length to chose. Theres a bunch of sizes available. My stock ones were 9.275 inches i believe. But not sure if different cam and lifters mean different pushrods. Thanks in advance

stock 440 is 9.31.

You can't determine pushrod length with any sort of accuracy until you've got the cam installed, heads bolted on, lifters in the bores and rockers snugged down. Then you really need an adjustable checker pushrod to determine what you need.

HOWEVER, if you have an old lifter and a vernier caliper you could compare the height of the pushrod seat with a new lifter. Remember - its not the depth from the top edge that counts, its the height from the lifter face. All else being somewhat equal add or subtract the pushrod seat height difference between old and new lifters to determine your new pushrod length. You have "wiggle room" with a hydraulic cam BUT I would tend to err on the longer side. A tad to long will just mean a little more preload. A tad too short can mean no preload, noisy lifters, unnecessary valvetrain wear and possibly disaster.

Hey, you're half an hour down the road from me !!

Thanks! So if im getting this right, i should put an old and a new lifter beside each other, put a pushrod on top of each one pointing up, and then measure the difference? To then add the difference to my old stock pushrods obviously. And eh, thats crazy. Small world haha. Where are you from more specifically? Im just outta Norwich

To be accurate you need to mock the engine up with the components you intend to use. Then with an adjustable push rod you use it to determine the correct length. Anyone's guess is just a guess.Measure once and order what you need.

Millions of factory built engines would disagree with you.

Factory tolerances are measured with a yardstick !

Brantford. Go through Norwich every couple weeks or so …. My car’s in a body shop just west of Brownsville.

What year is your 440 motor?
The early, mid 1967 and earlier RB motor had different size and length pushrods and different lifters than the ones made after that The early ones had two different size ends on them, 1/4 ball on the lifter ends and 5/16 ball on the rocker arm ends the latter ones all had 5/16 ball on both ends
How many and which type do you need to get you going?

Millions of factory built engines used the exact same cam grind and exact same design of lifter rolling down the assembly line, so this is a bit like saying there is no need to degree the camshaft when the factory just slapped them together dot-to-dot.

Assuming OP is not using NOS factory replacements, then the base circle of the aftermarket cam grind may be different, the manufacturers recommended preload on the lifters may be different, thickness of head gaskets used may be different. Pushrods are probably the most overlooked part of an engine, and probably one of the biggest reason builds have disappointing performance or noisy valvetrains.

Cab is correct When I had to get some for the 65 dated 440 block I had they had longer rods than 67s did.The 66 are thin on the lifter end.As for a pretty much stock cam unless your racing a stock length should work.Ran stocks in my 440 when it was mild for years.

the 9.31" length i mentioned is the "theoretical" length. almost all ball and ball push rods have a small flat or oiling hole on each end. this means the full 5/32" radius isn't included in the measurement. this could shorten actual measurement .030" or more. the 6400 cam is nearly identical to a stock magnum cam with the exception of the 6400 ground on a 112lsa vs a stock magnum at 115lsa. the 6400 cam could easily use stock magnum springs/rockers/pushrods. the only fly in the ointment here is if the heads and block have been milled. this will increase pre-load in what i feel is an unacceptable range.

This isn't the race forum and he's using a broomstick for a cam. Factory tolerances are more than adequate here.

Advertised Duration 288/298, Lift .444/.466

Watch "Engine tech: valvetrain geometry" by Straub on Utube

Not very relevant in the OP's case where rocker height is fixed. The only time this would apply to Mopars is if you 're concerned enough to get B3R's rocker spacers.

i just measured a stock 440 push rod. it was 9.299" and had small flats on each end.

Actually it is about getting the correct length pushrods, at half lift you want the rocker CL to be at a 90 deg right angle to the valve stem for the most area under the curve.

i've looked at and discussed the straub method with chevy guys. basically what straub is doing is using push rod length to set rocker geometry; two processes at one time, which makes sense for ball stud valve train. with a shaft system setting rocker geometry first and then finding proper push rod length makes more sense to me. the ball stud is an adjustable fulcrum point; shafts don't have that. the straub method could work on the small block magnum engines.

Pushrod length has nothing to do with the rocket centerline on a BB Mopar and while he doesn't mention Mopars he does point out that pushrod lengths are only determined once the rocker/valve relationship is established.

On Chebbies that 90 degree relationship is achieved with the adjustable ball/stud but on Mopars that fulcrum is fixed by the rocker shaft pedestals so you're pretty much screwed with regards to the 90 degree thing. I suspect the pedestal height will give you very close to that 90 degree relationship with a stock cam but as soon as you put more lift in that lift midpoint changes and therefore that angle increases. There's no solution to be found with pushrods. To illustrate the point, if all you did was swap in a higher lift cam with the same base circle you could use the same pushrods.

The stock stamp steel rocker arms slide backwards and forwards as well as sidesways some on the shafts and do not make the valves lift the same on every opening