Do Hemi rockers lose their ratio over time?

One of the strangest searches I've done, stock rocker ratio's of the 426 Hemi.

Is there some mystery I'm missing to all of this? I had thought it was 1.56 intake 1.53 exhaust (no clue where I got that over the years) but now that I started searching for it, I find practically nothing, other than more modern or A/M rocker ratios.

And also this piece of info from this forum;

"The valvetrain geometry on the 426 Hemi is the most ... ROCKER RATIO The stock Hemi rocker ratios are in the 1.5 to 1.56 area. "

"The ratio of these rockers is same as factory 1.57 / 1.53 . True actual ratio from factory and on these is actually lower. "

Links to info no longer available.

So what's the deal? Were the tolerances in manufacturing so bad that there is no consensus on what the stock ratios are?

Or do those long, thin spider leg rockers, slowly Change ratio over time and when running larger cams ect…………

Reason I'm asking is we just dialed in the Erson 278/370 solid roller cam and with 370 lobe lift plus 1.50 rocker ratio we should be about 555 lift and we are at 525 lift on the intake. (was originally hoping for the 1.56 # which would have been 577!)

Could the rocker ratio be below 1.5?

Yes, they vary a lot. Stock rockers will be all over the place as far as the actual ratio.
You can have them corrected, but you're better off buying new roller rockers from somewhere like Stage V.

I'm about to start looking at this and don't have the answer but I can tell you the pushrod angle alone steals it's share of lift, as any deviation from
a straight line coming off the lifter results in a loss.

The more I study these, the more I realize the guys who put in .750 (theoretical) rollers back in the day....unless their rockers
were reworked of course.... I'd be willing to bet some had around .650 net lift once the lash and loss from rocker ratio + pushrod angle was considered.

I don't think the iron rockers can bend enough to lose ratio as described, I believe they would break first.

Stock ratio is 1.57 intake and 1.52 exhaust.
That is advertised ratio.

Every production rocker arm made will vary - when you blueprint an engine for class racing you check them and go through a box of them until they all match the advertised ratio.

I agree with this.

did you measure the lobe to make sure it actually was .370?

Is that with zero lash ??? you said it was a solid. the lash is taken off the gross lift #.

No, and I Kick myself now for not doing that!!! Just shows, gotta cover All the bases!

I did check duration and it was right on the money with what it's supposed to be.

I’ve never checked any hemi rockers myself, but I’ve heard from a few people who have that they can actually be as bad as the 1.3x’s.
You’re not too far off from that....... .525 at the valve with a .370 lobe is an effective RR of 1.41.

Hemi rockers that are actually 1.57in/1.52ex as taken from a production engine as delivered from Ma Mopar are probably even rarer than 906 heads that came from the factory with anything even close to 79.5cc chambers.

I use to race a Street Hemi in NHRA stock, I decided to check the valve lift at the valve retainers so I wouldn't get thrown out for to much lift on a 1970 street hemi Cuda.
What I found was that the ratio where no where close to each other in 2 and half sets of stock rocker arms
The intakes varied from .430 to .510 net lift (.464 was legal, I think) at the retainers using checking springs and solid lifter set at zero lash and the exhaust rocker arms varied worst than the intake rockers did
I use a old Racer Brown cheater cam on the driver side of the motor and the same pushrods and rocker setting on all of them with the same dial indicator set up on the same angles and relation ship the valve stem angles on the same head
BTW, I saw 4.0 CC variance on the four combustion chambers on that head also

Yep, that's adding the .012 to the #. Which reminds me, need to call Erson and see what they recommend for lash. This is the way it was set from engine builder.

I was just about to do the same over the next cpl days, but scared of what I might find!

Go ahead and check yours now so you know exactly what each one will lift
I was shock and disappointed by mine but I did learn a good lesson on that, never trust and NOT verify
I ended up with two rockers that wouldn't be legal so I put them on end cylinders under the advice of a Mopar sponsored SS racer back then and ended up selling the car to a street racer before I was caught with them by NHRA

I know the tips on Brents all looked reworked and machinist wasn't too pleased with them.

Makes me wonder how many of these issues are from them being messed with or band aided build after build...…..

ther are sum repos that can lose ratio

Bringing this back from the dead.

Maybe not good ideas but what if you ran through and tested each rocker ratio and......

-Had the cam ground with each lobe matched to that particular rocker ratio. Not perfect but could get them closer.

-Have rocker adjusters made with an offset ball. Would take some trial/error to achieve the right offset and valve lash but maybe could have some offset closer/further away to equalize ratios.

To that point, has anyone tested adjuster concentricity?

I feel it would be a better idea to throw that garbage in the landfill and get some Stage V rockers.

Completely agree that would be better.

Would also be better to put the entire iron engine in the landfill and use better parts entirely, was just thinking about how to make this a bit better without spending thousands on a rocker system. (since I need to order a cam anyway)

They used to be able to rebuild rockers and equalize the ratios in the process, usually they'd be a bit under the spec ratio, but that;s probably that way stock too, assuming stock rockers that is. Might be an alternative.

Well, I checked what I could and identified what's what within this context, but in this few batches of exhaust rockers I had to work with
I never found anything worse than 1.49 or better than 1.56.

I haven't worked with a whole bunch of these for my whole life or anything, and have only done
whatever it is I have done, and found what I found.

In my humble opinion...as stated earlier, I really feel they would break before losing ratio over time.

I would have to guess that the folks who rework old rockers and change the ratio....most likely accomplish that by relocating the adjuster.

Seems to me that this would be a pretty expensive camshaft.