ir3333
Well-Known Member
i have heard different values for the ratio of these rocker arms.
Anybody ever measure them or stock factory stamped rocker arms?
Anybody ever measure them or stock factory stamped rocker arms?
273 adjustable rocker arms
- Thread starter ir3333
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nm9stheham
Well-Known Member
I take those reports with a grain of salt.....Some of those reports appear to just take the lifter lift and the actual valve lift and divide the first into the second. That will not give actual rocker ratio, as there are several factors that reduce valve lift from the ideal 1.5:1 SBM number besides the rocker ratio, like:
It's cold and raining, so I might just check mine out! No promises...it's cold in the garage too LOL
- Lifter to pushrod angle
- Normal loss of valve lift that occurs with the rotation of any rocker arm through an angle of rotation
- Overall setup, which can change where the rocker's valve end contacts the valve tip, and where the adjuster is set.
It's cold and raining, so I might just check mine out! No promises...it's cold in the garage too LOL
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And at what lift do you measure it, and maybe calculate the average ratio.
In any case, I keep hearing that they are more accurate than the stamped pieces.......... which are often called 1.42s ........ with no relevant spec included.
And they are stronger; You will never see a 273 rocker arm impaled on a pushrod, or a pushrod cup MIA.
In any case, I keep hearing that they are more accurate than the stamped pieces.......... which are often called 1.42s ........ with no relevant spec included.
And they are stronger; You will never see a 273 rocker arm impaled on a pushrod, or a pushrod cup MIA.
Agree. They are strong and they are what they are. If you have enough intestinal fortitude, bump up to the next cam lift if the "less than 1.5" is an issue. The aftermarket rockers are more accurate from what I have heard. The comparison sounds like a good project for the Hot Rod Magazine crew. 
ir3333
Well-Known Member
tx guys...it's not a real big deal, but it would be nice to know the real measurement.
I don't think anyone here has ever measured it for certain. I remember seeing some estimates in a thread somewhere.
Search may help you: Search Results for Query: 273 rocker ratio | For A Bodies Only Mopar Forum
Dave hughes did a lot of study on the 273 and after market rocker ratios several years ago.
Because the 273 rockers flex less, they are good for an extra 500 rpm . That is what I read somewhere. I will be happy if someone can explain this to me. Wrong or right. Maybe it has something to do with being adjustable but I swear it had something to do with flex or maybe handling spring pressure which I think I may have just answered my own question.
Link? Inquiring minds want to know!
You would probably have to call Hughes. But then if you do that remember you have to buy something from him over the phone. Otherwise he's just a butthead.
Here's a link that had same questions on it too.
Stock sb rocker arm ratio ?
383Scampman
Well-Known Member
The big issue with 273 adjustable IS , unless they are NOS or aftermarket they are probably worn to the point of them not being effective . Ditto with stamped ones . The advantage is their strength . As far as measuring them goes , to do it right you need a fixture and a dial indicator to determine the ratio . O course , if your using a solid lifter cam you must use adjustable rockers . Hope this helps .
nm9stheham
Well-Known Member
Well, the OP threw down the gauntlet and I foolishly picked it up.... at least for the 273 adjustable rockers. Set this all up and got better results than I expected, even up to .505" valve lift.
Here are data points using .010" valve lift as a baseline; first number is valve lift & 2nd number is ratio, computed as pushrod lift delta from baseline divided into valve lift delta from baseline. The ratio's listed in this tabulation do NOT include the loss of ratio caused by the pushrod to lifter angle. (More on that below)
0.028/1.64
0.061/1.50
0.100/1.55
0.141/1.56
0.174/1.56
0.204/1.55
0.230/1.53
0.256/1.53
0.283/1.53
0.309/1.54
0.340/1.53
0.383/1.53
0.447/1.56
0.505/1.55
I'd ignore out the 1st 2 numbers (as they are computed from very small deltas and so prone to error); the average of the rest of the numbers is 1.54 (excluding lifter-to-pushrod angle). This includes pushrod-to-rocker angles changes and rocker-to-valve tip changes.
If you want to factor in ratio loss for the the pushrod-to-lifter angle (for a 14 degree angle), that is .970. Multiply that by the average above and you get an overall lifter to valve ratio of 1.49-1.50 for lifts up through .500" or thereabouts.
What is really interesting IMHO is that the ratio stays steady up to high lifts. One would expect that ratio to drop as the rocker angles down more and more. But, the rocker contact point on the valve tip 'walks' further and further out as the lift increases; this outward movement in the rocker-to-valve contact point increases the ratio enough to compensate for the loss of ratio due to the increasing angle of the rocker. Pretty neato! Juuust maybe those Chrysler engineers back-in-the-day could do a lot more on paper than we might give them credit for LOL
You can see the rocker-to-contact point movement in the last 2 pix; the first is at .100" valve lift and the next is at .505" valve lift.
Below is a pix of the setup, which was worked on to make it repeatable and stable. The rockers' adjuster was put where there were about equal threads exposed above and below the rocker body, which seemed like a reasonable place to which to adjust it. The head is a 675 head with the stock. You can see the shims (feeler gages) used to change change the pushrod height; they would be set and measured separately for accuracy.
Here are data points using .010" valve lift as a baseline; first number is valve lift & 2nd number is ratio, computed as pushrod lift delta from baseline divided into valve lift delta from baseline. The ratio's listed in this tabulation do NOT include the loss of ratio caused by the pushrod to lifter angle. (More on that below)
0.028/1.64
0.061/1.50
0.100/1.55
0.141/1.56
0.174/1.56
0.204/1.55
0.230/1.53
0.256/1.53
0.283/1.53
0.309/1.54
0.340/1.53
0.383/1.53
0.447/1.56
0.505/1.55
I'd ignore out the 1st 2 numbers (as they are computed from very small deltas and so prone to error); the average of the rest of the numbers is 1.54 (excluding lifter-to-pushrod angle). This includes pushrod-to-rocker angles changes and rocker-to-valve tip changes.
If you want to factor in ratio loss for the the pushrod-to-lifter angle (for a 14 degree angle), that is .970. Multiply that by the average above and you get an overall lifter to valve ratio of 1.49-1.50 for lifts up through .500" or thereabouts.
What is really interesting IMHO is that the ratio stays steady up to high lifts. One would expect that ratio to drop as the rocker angles down more and more. But, the rocker contact point on the valve tip 'walks' further and further out as the lift increases; this outward movement in the rocker-to-valve contact point increases the ratio enough to compensate for the loss of ratio due to the increasing angle of the rocker. Pretty neato! Juuust maybe those Chrysler engineers back-in-the-day could do a lot more on paper than we might give them credit for LOL
You can see the rocker-to-contact point movement in the last 2 pix; the first is at .100" valve lift and the next is at .505" valve lift.
Below is a pix of the setup, which was worked on to make it repeatable and stable. The rockers' adjuster was put where there were about equal threads exposed above and below the rocker body, which seemed like a reasonable place to which to adjust it. The head is a 675 head with the stock. You can see the shims (feeler gages) used to change change the pushrod height; they would be set and measured separately for accuracy.
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ir3333
Well-Known Member
Thanks, 1.5:1 actual ratio and if they are all that close that's blueprint territory!Valuable info that should be saved.
Your hard work will be appreciated by many and you may have increased the value of the small block mopar adjustable rocker arms.I'll add that if the original interference adjusters are worn i think slant six adjusters can be used with good results.
Your hard work will be appreciated by many and you may have increased the value of the small block mopar adjustable rocker arms.I'll add that if the original interference adjusters are worn i think slant six adjusters can be used with good results.
pishta
I know I'm right....
hey, your rocker shaft has a hole in it......I about gave up on weighing the rods until I saw that hanging jig on jenkins site. Ill try that. All my big and little measurements were not repeatable. All the Engineers had to do was to plot the 1.50 ratio dots on paper and then make the rocker tip follow that arc. Something the stamped ones cant do with their pockets, and the HD stamped rockers with their thicker cross sectional area at the pocket has been busted as a myth. I think Isky still has these rockers in their catalog. IIRC the 273 rockers were cast iron and the 340 mechanical rockers were forged. Any 2nds on that?
Thanks for taking the time to post/document!
nm9stheham
Well-Known Member
You're welcome.... you made a bunch of piston and rod measurements a while back that I was able to make use of, which I appreciated.
Ductile iron on these rockers.....
nm9stheham
Well-Known Member
I'll be curious if the stamped ones do something similar. I might do that later.
pishta
I know I'm right....
well, let me take that last statement back. The stamped may be able to do that too. Ill let you prove it....
Now, a roller may/will NOT be able to do that for all its hype.
Now, a roller may/will NOT be able to do that for all its hype.
nm9stheham
Well-Known Member
What ir3333 wants, ir3333 gets LOL.
Here is rocker ratio data for 1 stamped rocker. This one came off of a 340 or 360.... so the rocker and the shaft are just a random sampling. The results were surprising.... I have seen numbers reported at and below 1.45.
Same test set up used on a 675 head as shown above with the change of the rocker, shaft and pushrod.
Valve lift/ ratio (excluding lifter-to-pushrod angle)
0.049/1.41
0.101/1.58
0.148/1.54
0.199/1.53
0.253/1.53
0.312/1.54
0.375/1.54
0.442/1.56
0.496/1.55
Again, toss out the 2 lowest lift numbers and average the rest and you get 1.54. This is without the loss of lift due to the pushrod-to-lifter angle. If you factor in that approximate number, the result is an overall lifter-to-valve ratio of 1.49-1.50.
Not bad at all....
Here is rocker ratio data for 1 stamped rocker. This one came off of a 340 or 360.... so the rocker and the shaft are just a random sampling. The results were surprising.... I have seen numbers reported at and below 1.45.
Same test set up used on a 675 head as shown above with the change of the rocker, shaft and pushrod.
Valve lift/ ratio (excluding lifter-to-pushrod angle)
0.049/1.41
0.101/1.58
0.148/1.54
0.199/1.53
0.253/1.53
0.312/1.54
0.375/1.54
0.442/1.56
0.496/1.55
Again, toss out the 2 lowest lift numbers and average the rest and you get 1.54. This is without the loss of lift due to the pushrod-to-lifter angle. If you factor in that approximate number, the result is an overall lifter-to-valve ratio of 1.49-1.50.
Not bad at all....
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Well you de-bunked that myth!
I totally agree with nm9stheham !
I too did some R&D several years ago and found very similar ratio's. I got 1.53:1
Keep in mind, the geometry of the LA heads is not perfect, that's the reason the ratio changes slightly through the lift cycle.
Without spending a bunch of money, I have always used .050 taller stem height, and ran the adjuster as close to the rocker as possible. (longer/custom length pushrods)
FYI these rockers can also be re-ratio'd with larger adjusters to go well beyond 1.6:1 (did several set's in the past) (with no breakage !!!)
I too did some R&D several years ago and found very similar ratio's. I got 1.53:1
Keep in mind, the geometry of the LA heads is not perfect, that's the reason the ratio changes slightly through the lift cycle.
Without spending a bunch of money, I have always used .050 taller stem height, and ran the adjuster as close to the rocker as possible. (longer/custom length pushrods)
FYI these rockers can also be re-ratio'd with larger adjusters to go well beyond 1.6:1 (did several set's in the past) (with no breakage !!!)
nm9stheham
Well-Known Member
That is interesting on the higher ratio... I had thought about moving pockets on the stamped ones but not using the larger adjuster on the 273's. You only need to move the pushrod contact point about .050" in to move the ratio up to 1.6 IIRC. New project!
You're exactly right. I pushed the envelope a bit and was rewarded with 1.64:1
dibbons
Well-Known Member
When do the 273 rockers need to be ground for clearance? I just purchased some Comp 901 springs and was wondering if the factory adjustabel rockers need to be ground for spring clearance (stock 340 cam).
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