finding correct pushrod length

[Rapid Robert]

there is a utube vid by Straub industries where at half cam lift you want the rocker arm to be at a right (90 deg) angle to the valve for the most area under the curve but today I saw another vid where they went for having the contact pattern on the valve tip to be centered/narrow. which one is right? thank you for your time. RR

 

[Bewy]

This will be a can of worms. There are two sides of the story, pardon the pun. The valve side [ of the rocker ] & the PR side. While playing with PR length might give you a nice centered pattern on the valve tip, that PR length might not give optimum valve lift/area under the curve. Compromises often have to be made.

 

[RustyRatRod]

I agree about the can of worms. All I'll say is, while figuring for correct pushrod length, you should also have in mine rocker shaft location. I would call Mike at B3 Racing Engines. He's a huge help.

 

[Rapid Robert]

I could see where the narrow/centered method would give minimal guide wear I would think & I will call Mike.

 

[RustyRatRod]

I could see where the narrow/centered method would give minimal guide wear I would think & I will call Mike.

I think that' a smart move. He helped me greatly when I built up this last slant 6 head. We got it DEAD right.

 

[Ted265]

Shaft mounted rockers or stud mounted?
For stud mounted rockers I select a pushrod length that gives the best contact pattern. Don't know if that's the "right" way but that's how I do it.
A shaft mounted system pushrod length will not really affect the contact pattern as the pivot point is not changed with the change in pushrod length.
You need to move the shafts to adjust the contact pattern. Here I would select a pushrod length that gives you best "net" valve lift but ideally you would have the contact pattern sorted before hand.

 

[Rat Bastid]

Yeah, the old pushrod length to correct geometry is always brought up. It only matters if it’s a stud mounted rocker.

It does matter to some extent on shaft systems, because the angle of the adjuster going through the rocker body. If you look close, it goes through at an angle relative to the shaft.

So, if the adjusters are too far out (pushrod too short) you lose ratio which changes the geometry or if the and if the adjuster is too far in (pushrod too long) you gain ratio which changes geometry. Obviously the amount of change is small, but it matters for geometry and oiling of oiling through the shafts.

You’ll have to ask Mike about mid lift and all the other lift points to correct geometry. The geometry changes the way the valve moves off the seat and such. Mike can explain it way better than I can.

Read what Bewy said about two sides of rocker geometry. There is the valve side and the pushrod side. You are limited by the architecture of what you are working with in regards to both and the philosophy of the guy who designed the rocker arm.

You can really get into the weeds on this stuff, but it’s good to learn all you can about all of it.

 

[Rapid Robert]

Shaft mounted rockers or stud mounted?

stud mounted magnum heads & the straub vid was stud mounted.

 

[IQ52]

And then to really get it correct I've had to change the stud location on stud mounted rocker arm systems. This old world is a mean place sometimes.

 

[Rapid Robert]

there's a $550 claim on the engine, hell the EQ heads were twice that. I will be refusing any claim but hopefully the chebby boys will not claim me if I beat em. RR

 

[Krooser]

And the contact patch depends on if you are using roller tip rockers or the factory shoe style rocker.

 

[Rapid Robert]

roller tips. does this sound logical? for a race eng use the straub 90 deg right angle method for maximum output & for a DD for longevity use the centered/narrow contact pattern on the valve stem?

 

[Rat Bastid]

roller tips. does this sound logical? for a race eng use the straub 90 deg right angle method for maximum output & for a DD for longevity use the centered/narrow contact pattern on the valve stem?

Did you go to b3racingengines.com and was his tech pages? That would be a good start.

 

[Rapid Robert]

I'll do it today