Rocker Clarification is up!!!

[X-TECH MAN]

Originally Posted by novassdude

If the stock stamped rockers were less and all the cam makers know this. What are the odds that just switching to a aftermarket roller rocker will bump the lift at the retainer over the allowed limit?

Thats for the racer to check to make sure this dosent happen. Not the cam company or rocker makers.

[X-TECH MAN]

Originally Posted by 69Cobra

I don't know how NHRA does it but I would think the easiest and most accurate way would be cam lift divided by valve lift.

Thats backwards.......divide the lobe lift into the valve lift. The number you get is the R.R. Ifs its over then your DQ'ed. There is a couple of ways to get it.

[Greg Reimer 7376]

Seems that the last several posts have verified what I wrote in my post on page 2. We need to look at some absolutes- two sources of absolutes come to mind- those provided by the engine designers, and those mandated by the sanctioning body.
Absolute #1-- Valve lift must be OEM or as specified.
Absolute #2-Rocker arm ratio must not exceed OEM.
Cam lobe lift isn't too well specified. In order for #1 above to be achieved in a desireable fashion,#2 has to be followed as well. In the case of a small block Chevrolet,ideal results are when valve lift is half again lobe lift.In the event lobe lift is correct,and valve lift is lacking, then another means has to be employed to achieve it. That is where push rod length comes into play. Now, you don't really want exact specs here, you want to be safe by .005-.010". This is because the tech guy at teardown might not read mikes the same way I do. Also, expansion due to heat might cause results to vary. If my intake lift spec is.390". I would love to see an actual.379-.382".Now, if I achieve this spec with a very long pushrod, I'm getting the maximum extra duration and rate of lift out of that valve train.
Now, the other booby trap has to be recognized. If you checked lobe lift, it passed right on the number, used a very close to optimum, a long push rod, you could still result in a rocker ratio that is a bit over, however,that couldn't help but make the valve lift over as well.Optimally, a cam lobe with the correct lift, a valve with lift good by .008-.010, and a rocker arm ratio of 1.47-1.49 would be the best of all worlds. Now, good luck getting it!

[novassdude]

Originally Posted by X-TECH MAN

Thats for the racer to check to make sure this dosent happen. Not the cam company or rocker makers.

I am well aware that it is the racers job to check I was just curios what the odds are that it is going to come up with a little extra lift. With the old set up knowing the ratio was generally a little short I assume that the cam company's add a little lift to compensate at the request of the racer. Not blaming them for any thing,
I was just wanting to know what the odds are you are going to have to change cams when switching to roller rockers that have a true 1.5 ratio.

[X-TECH MAN]

Originally Posted by novassdude

I am well aware that it is the racers job to check I was just curios what the odds are that it is going to come up with a little extra lift. With the old set up knowing the ratio was generally a little short I assume that the cam company's add a little lift to compensate at the request of the racer. Not blaming them for any thing,
I was just wanting to know what the odds are you are going to have to change cams when switching to roller rockers that have a true 1.5 ratio.

Probably a 50/50 chance or better. Id be talking to the cam grinder and find out what was done.

[X-TECH MAN]

Originally Posted by Greg Reimer 7376

Seems that the last several posts have verified what I wrote in my post on page 2. We need to look at some absolutes- two sources of absolutes come to mind- those provided by the engine designers, and those mandated by the sanctioning body.
Absolute #1-- Valve lift must be OEM or as specified.
Absolute #2-Rocker arm ratio must not exceed OEM.
Cam lobe lift isn't too well specified. In order for #1 above to be achieved in a desireable fashion,#2 has to be followed as well. In the case of a small block Chevrolet,ideal results are when valve lift is half again lobe lift.In the event lobe lift is correct,and valve lift is lacking, then another means has to be employed to achieve it. That is where push rod length comes into play. Now, you don't really want exact specs here, you want to be safe by .005-.010". This is because the tech guy at teardown might not read mikes the same way I do. Also, expansion due to heat might cause results to vary. If my intake lift spec is.390". I would love to see an actual.379-.382".Now, if I achieve this spec with a very long pushrod, I'm getting the maximum extra duration and rate of lift out of that valve train.
Now, the other booby trap has to be recognized. If you checked lobe lift, it passed right on the number, used a very close to optimum, a long push rod, you could still result in a rocker ratio that is a bit over, however,that couldn't help but make the valve lift over as well.Optimally, a cam lobe with the correct lift, a valve with lift good by .008-.010, and a rocker arm ratio of 1.47-1.49 would be the best of all worlds. Now, good luck getting it!

Any good machinist reads the "Mikes" the same way. I dont know about other tech guys but I used a dial indicator when I checked lift (and duration/overlap) in the old days. The Govt. spec. on tolerance of either a mike or a dial indicator is plus or minus .001(one thou.) My personal tools were alway certified by myself. ....I worked almost 18 years in a Navy Calibration lab after working as a tool maker for the Navy. Its not rocket science.

[Grant Eldridge]

We've just been through this upgrade with rockers, pushrod length etc. What we saw was changes in lift at the valve due to the rocker change, but also as we varied the pushrod length and went from break in to full racing valve spring pressure. After sorting out the rest, we had to order a cam with .006" less lobe lift to get back under our allowed lift of .398" on the 325hp 396. You get rid of a lot of deflection going to the new rockers, so if you'd used a cam ground with extra lift originally to get close to the spec, it would be important to check it after installing the roller rockers. Just my 2 cents.......

[Greg Reimer 7376]

Originally Posted by X-TECH MAN

Any good machinist reads the "Mikes" the same way. I dont know about other tech guys but I used a dial indicator when I checked lift (and duration/overlap) in the old days. The Govt. spec. on tolerance of either a mike or a dial indicator is plus or minus .001(one thou.) My personal tools were alway certified by myself. ....I worked almost 18 years in a Navy Calibration lab after working as a tool maker for the Navy. Its not rocket science.

You obviously were trained well and made constant use of your level of skill. Some people weren't and didn't.I don't know about some of these people masquerading as machinists out therehowever. How many times did you get parts back out here that weren't done the way you wanted them done?

[X-TECH MAN]

Originally Posted by Greg Reimer 7376

You obviously were trained well and made constant use of your level of skill. Some people weren't and didn't.I don't know about some of these people masquerading as machinists out therehowever. How many times did you get parts back out here that weren't done the way you wanted them done?

LOL......More times than I can count. When I went to metal parts inspection a LOT of parts for air craft ejection seats and stuff that goes "BOOM" came in from vendors out of spec.

[X-TECH MAN]

Originally Posted by Grant Eldridge

We've just been through this upgrade with rockers, pushrod length etc. What we saw was changes in lift at the valve due to the rocker change, but also as we varied the pushrod length and went from break in to full racing valve spring pressure. After sorting out the rest, we had to order a cam with .006" less lobe lift to get back under our allowed lift of .398" on the 325hp 396. You get rid of a lot of deflection going to the new rockers, so if you'd used a cam ground with extra lift originally to get close to the spec, it would be important to check it after installing the roller rockers. Just my 2 cents.......

BINGO ! A smart racer right there. Less deflection but more so in more accurate Rocker Ratio. But check what you order. Not all rocker arms are made equal. Some out there are as bad as OEM or worse. Some of the best are the ones you stocker guys are not allowed to use.