positive / negative effects changing rocker ratios...

[yullose]

I need to order another set of roller rockers tomorrow... and was wondering what benefits I might gain, or problems might occur if I went from 1.55's to a set of 1.65's on my hyd roller ???

I'm really not sure what the limitations are on hydraulic roller cams. Everything I've run in the past has been a solid roller, some North of .800" lift.
This is my first hydraulic roller... and I just wondered what the limitations were.

My cam is already .548 lift with 1.55's. (.354 lobes)
1.60's would = .566 lift
1.65's would = .584 lift

Here's the cam card:

 

[TURBOTWIN2]

Taller valve covers, clearance the rocker pedestals for roller rocker fitment, clearance the push rod holes, watch the rocker arm geometry. Not sure what else, so I'm subscribed to this thread, as I will be doing the same in the future.

 

[Jerryl]

(Thinking out loud) . . . . . .
-The valve will accelerate harder to max lift, and therefore give better overall flow. - Increased area under the curve
-At max lift, you will negate some of the shrouding in the chamber, depending on the chamber design and system set-up.
-With more lift/higher spring pressure, you will get increased wear of the guides, and better than std pushrods are needed.
-I do not belief increased flow is direct result of increased lift, but from time spend at higher lift, and acceleration of the valve.

I think the clarifying statement on increased rocker ratio should be; This is for a track car.
That being the case, there are no real downsides to increased ratio.
As far as lifters; If the lifter bores are good, there should not be any issues, pending max RPM stays the same.
Any weight reduction at the valve will make a tremendous difference in the shock forces applied through the pushrod on the lifter.

Having thought about this "out loud" I must also add; I have been wrong before . . . . . VERY wrong.

 

[yullose]

I'm waiting on a set of heads from TA... so they should be "good to go" right out of the box.

My main concern was the add'l load on the hydraulic lifters from the increased rocker ratio... and whether the hyd valvesprings will handle it.

It's only another .040" of lift, so I don't see how it could be a major problem. I'll probably just go with the 1.65's anyway.

 

[bison]

Check for clearnace issues. More ratio moves the pushrod cup closer to the fulcrum. Id prime the engine with and rotate to check for any possible interference issues. Ive had to mill the pushrod holes in heads before. Hopefully you will be gtg without milling. For the vavlesprings you already know your lift so check on the specs of the springs to see how close you are.

 

[yullose]

Check for clearnace issues. More ratio moves the pushrod cup closer to the fulcrum. Id prime the engine with and rotate to check for any possible interference issues. Ive had to mill the pushrod holes in heads before. Hopefully you will be gtg without milling. For the vavlesprings you already know your lift so check on the specs of the springs to see how close you are.

Spoke to Tim at TA a little while ago...

He said the heads should have plenty of pushrod clearence out of the box...

I ordered the 1.65 T&D's from him, along with a pair of valve covers, grommets and breathers.
He said he'd also send along an adjustable pushrod to check for correct lengths so we could order the right ones the first time.