custom length pushrods are needed for a hybrid

[ForcedFirebird]

Everyone that does a hybrid needs to check there preload since it will vary engine from engine and can effect performance extremely.

That's the ultimate answer

It's easy to do, and worth it. Just thread the rocker bolts until the pushrod stands on it's own, count the turns. Every turn = .059"

[ForcedFirebird]

Just verified this on my engine. I went out to the garage and pulled the valve covers and manis. I measured the plunger movement when it was first assembled and IIRC it was .056". I just used the method of no slop in the pushrod then turned the rocker bolt in almost a full turn.

[923.4v6]

What length do you have?

[ForcedFirebird]

Stock Cavi 3.1 pushrods, but I have a custom cam with a good amount of lift/dur. Since a cam can only be so big and fit through the brearings, the base circle gets smaller as the lift increases. I forgot about this important fact. Even Ben's re-ground roller cams on the store need custom length pushrods due to the pedistal rocker arms.

Every engine built for performance should have the valvetrain geometry checked/measured, specially when using custom items and/or parts from another year/model.

Really makes me wish I would have measured the base circle on it before the short block was assembled, that would be invaluable information to the rest of the guys doing the swap.

EDIT: The only other factor left would be the lifter length. re-ground lifters will also change numbers. You might actually be able to have them ground to compinsate, but don't know if thats easier/cheaper than buying new pushrods.

[Superdave]

I'd just put it all together, measure it the right way and be done with it.


When i did mine, i went by the base circle difference. I had .040-.050 preload with .096 longer exhaust and .073 longer intake. I have some valvetrain noise but that's to be expected with a radical cam. The only time i get knock counts is if i hit the 7K rev limiter.

[Guest]

The "preload method" of measuring pushord length only applies when engines are using the stock length valves and stock rockers. Change one or both of those items and the only way to determine proper pushrod length is by checking the valve train geomtry. Making sure that the rocker is using the proper area of the rocker tip on the top of the valve (or lash pad if the engine uses one). Preload will be also be a factor.

IMO the geometry should be checked anyway, even when using the stock length valves and rockers, who's to say the OEM manufacterer got it right the first time?

[923.4v6]

I'm going to order some more pushrods for the engine, along with a few other things.