More rocker geometry & valve lift curve stuff

[BradH]

I've either started, or contributed to, a number of threads over the past couple of months having to do w/ rocker arm geometry. Some of them got pretty long, and I didn't want to bring 'em back from the dead when there was already 10 pages of posts.

However, on the same general topic, I wanted to throw out some valve lift curves taken with two (2) different brands of rocker arms, and with some measurements taken from a low-pivot shaft orientation and others more consistent with the mid-lift approach.

A: Brand A "1.6" rocker w/ standard-location (low pivot) rocker shaft and .018" lash

A*: Brand A "1.6" rocker w/ relocated rocker shaft for mid-lift on valve side at .325", .018" lash

D: Brand B "1.6" rocker w/ relocated rocker shaft for mid-lift on valve & pushrod sides at .350", .018" lash

D*: Same as D, except .016" lash

Lift --- _A_ --- _A*_ -- _B_ --- _B*_
.010 --- 302 --- 300 --- 300 --- 302
.020 --- 293.5 - 292 --- 291 --- 293
.050 --- 273 --- 271 --- 271 --- 272
.100 --- 249 --- 248 --- 247 --- 247.5
.150 --- 230 --- 228 --- 227.5 - 228
.200 --- 214 --- 212 --- 212.5 - 213
.250 --- 198 --- 196 --- 196 --- 197
.300 --- 184 --- 181 --- 182 --- 182.5
.350 --- 169 --- 166.5 - 167.5 - 168
.400 --- 154 --- 151 --- 152.5 - 153
.450 --- 138.5 - 135 --- 137.5 - 138
.500 --- 121 --- 117 --- 120 --- 121
.550 --- 101 --- 96.5 -- 101 --- 102
.600 --- 77 ---- 69.5 -- 78 --- 78.5
.650 --- 40 ---- 17 ---- 42.5 -- 43.5

Lift -- .667" - .653" - .673" - .675"
Ratio-- 1.582 - 1.550 - 1.596 - <==

NOTES:
A. Sweep .085"and centered; pushrod/adjuster angle slightly under parallel at .325" lift
A*. Sweep .045" and offset slightly inboard; pushrod/adjuster angle slightly over parallel at .325" lift
D/D*. Sweep .055" and offset slightly inboard; pushrod/adjuster angle slightly under parallel at .350" lift

I think the main purpose of the above data is to emphasize that you really can't a$$ume anything as to what you'll see by changing rocker arm geometry, especially if you're also changing the type of rocker being used.

In my measurements A and A*, switching to a mid-lift orientation that many prefer resulted in a significant loss of high-lift duration. Changing the rocker brand to something with a more mid-lift friendly design (the location & angle of the lash adjustment screw being the biggest difference) reversed that trend, but also required tightening the lash to get comparable seat durations with the original measurements of the first rocker in the low-pivot location.

"Welcome to the Mystery of Geometry!" Subtitle: If you don't measure this stuff, you won't know what the results will be.

[ClassAct]

Am I reading this correctly?

It looks like A* cost some rocker ratio with the same rocker??? That seems wierd. Is that the ratio you calculated with the loss of lift?

This stuff does get complicated for sure.

[67satellite]

Brad, I installed the B3RE kit on my Edelbrock Perf. RPM, big mopar heads and had similar results to your "A" vs "A" test. Greatly reduced sweep with slightly less lift. Running Comp. pro magnum rockers.

[gruntguru]

Why do the values for A, B etc decrease with increasing lift?

EDIT. Sorry got it - values are duration in degrees. Not much in it except that A* loses a lot of high-lift duration.

[BradH]

Am I reading this correctly?

It looks like A* cost some rocker ratio with the same rocker??? That seems wierd. Is that the ratio you calculated with the loss of lift?

This stuff does get complicated for sure.

Yes, you read things correctly. And, yes, the overall ratio is calculated for each configuration as tested.

"A" is the rocker arm I posted about previously as having a regressive ratio.

[andyf]

So I guess the real question is if the contact pattern which one assume is better makes more or less power. I can understand why someone would want to do the work to make the geometry appear to be better but if a person is interested in making more power then that has to be tested. If the nicer looking pattern makes more power then I guess everyone will be happy. If it only looks nice but loses power then a person will need to decide whether they want nice neat wear patterns or if they want to make power.

[ClassAct]

So I guess the real question is if the contact pattern which one assume is better makes more or less power. I can understand why someone would want to do the work to make the geometry appear to be better but if a person is interested in making more power then that has to be tested. If the nicer looking pattern makes more power then I guess everyone will be happy. If it only looks nice but loses power then a person will need to decide whether they want nice neat wear patterns or if they want to make power.

Very true. But Brad is essentially doing a static test. What looks like it may be a power loser due to losing lift or whatever, may do better because it is more stable, especially as RPM goes up.

I've seen plenty of unhappy valve trains come through the shop. Most of the time the sweep was centered but very wide.

I wish I'd have done more testing but that testing is usually limited to the customer and his ability to pay, or willingness.

[digger]

three (3) of those are very close, such that on a running engine who knows where the numbers would lie

are these with a checking spring or with a spring that that would actually run?

[BradH]

Checking springs; I didn't (don't) have "real" pushrods that fit all the configurations. The "B" rockers were on loan for me to check out. The "A" rockers are what I built & dynoed the engine with.

It would have been interesting to see differences in deflection under actual spring loads.

And as far as whether there would be any detectable performance difference... ???

[ChargerST]

Brad, have you talked with Mike about the issue?

Which brand rocker arms did you use? Are the B rocker arms Mike's geometry optimized T&D rocker arms?

[Walter R. Malik]

So I guess the real question is if the contact pattern which one assume is better makes more or less power. I can understand why someone would want to do the work to make the geometry appear to be better but if a person is interested in making more power then that has to be tested. If the nicer looking pattern makes more power then I guess everyone will be happy. If it only looks nice but loses power then a person will need to decide whether they want nice neat wear patterns or if they want to make power.

I have sometimes made more power by intentionally making the valve geometry wrong and certainly not optimum.

This tells me that the camshaft lobe was not providing what that particular engine wanted to have; that bad geometry may have been good for power but, disastrous for longevity.
Using that information to get another cam ground would be a lot better.