I used the standard 7.4 with my old set-up. Now with my new set-up I'm not sure if I will need the same length. I know I need to use the pushrod length checker but my engine is not assembled yet and I'm trying to get all the parts together. The PRC kit I'm getting comes with pushrods so I want to get as close as I can and then change out the pushrods if I have to.

Heres the set-up:

LSX, standard deck
lq4 iron 373 heads, non milled
MLS layered metal gaskets
Stock rockers
Futral cam 246/250 .632/.635 on a 112+4
Cadillac race lifters

Is there anything in there that would alter the pushrod length? As far as I can tell it should be the same as my original stock block set-up. Would a 7.4 pushrod be a good starting point or is there anything that stands out that will throw the length off?
TIA

 

I would hazard to guess that the large lift will alter your rocker wipe pattern in a bad way, correctling this by shimming wil change pushrod requirements. Pushrods should be the last part ordered.

 

i think its a combination of how the deck is, cam profile and the rest of the valvetrain

 

You can put the cam in the block and two lifters and put a head on with a couple of head bolts, and get you a push rod checker to find out what size push rods you need , That's the only way you can tell what you need.

 

Block is at the machine shop so I guess I'll have to just wait on the pushrods. Thanks guys.

 

Are you talking about having to shim the rockers? Is it normal to have to shim them with a cam this size? I didn't think anything would have to change with this cam except possibly the pushrod length. I'm going with the PRC spring kit that's good to .660 so I still have some room to spare there. I just don't understand this rocker wipe pattern you speak of. I didn't think anything like that became an issue until you start changing rockers and milling heads. Shouldn't the geometry stay the same even though the lift is a little higher?

 

No, as the rocker pushes the valve down, it also moves across the top of the valve stem. Since you are now moving the valve a lot farther, the rocker will go further towards the exhaust manifold side of the valve stem. Depending on how the wipe pattern comes out, the only way to correct it with a non-adjustable rocker is to alter the height of the rocker pivot point. To move it up you need to shim and to move it down with stock rockers you likely need lash caps. Not many guys check this, but it is a vital part of setting up the valve train geometry.

Here is a link to how I set up my Yella Terra's, same methods apply to the stock rockers.

Link

 

I see, it's just a little shim under the rocker to help center the contact patch on the valve. I don't think that has to be done with the stock rockers too often, it's more of a roller rocker thing. But I'll check none the less.

 

Actually, stock rockers have a very poor wipe pattern from the factory, but the spring pressures are low enough and they use harder guides in the heads. Bump up the spring forces and use aftermarket heads with bronze guides and guide wear will be greatly accelerated.

An adjustable pushrod is $20, pick one up and measure once its together and the rockers are set. That will ensure your pushrod length and resulting lifter preload are correct.