Rocker Arms
 

Who make a good SBC 1.5, 7/16 stud stamped rocker?

Re: Rocker Arms
 

SBC Chevy Nitro Rockers 7/16 Stud 1.50 ratio

http://nitrorockerarms.carshopinc.co...113129/R-1840N

The Car Shop started carrying these not too long ago when we were having trouble finding a good source. Good service and a great price.

Re: Rocker Arms
 

Joe, I have been taking an interest in following your car for sometime. As a Nova owner, a frequent visitor to StevesNovaSite and a member of SoCal Novas you understand my love of these ole ecomony cars.

Many years along, I had a 283 that I tortured for years but it was just in the wrong car but, it sure was fun to race and drive.

I would like to like to pick you brain from time to time about getting into racing in stock eliminator.

I noted in this thread that the stamped rocker arms were of the 1.5 flavor. Is 1.5 the only type you can use or is the 1.6 or even 1.7, if there is in the stamp steel, an option under current NHRA rules for a SBC.

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Not sure what the ruling is on rocker arm ratio,,,but some of the old timers might remember the story about Bill Jenkins using Ford 289 rocker arms on his A/S 66' Chevy II(327 4speed) back in the day against Jere Stahl's A/S 66 Hemi Plymouth. He was thinking outside the box, as usual. Danny Durham

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That may be a myth. The rules that year allowed those cars to use any aftermarket flat tappet camshaft and valve train. When I saw his car race at Tulsa that year, he had roller rocker arms.

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elgin rocker arms, then ship to jim bailey he will harden and polish them... shazaam nice pieces and very reasonable pricing

captain jack

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Any ruling on the ratio? I have an article written in Oct 1966 "What Makes Bill Jenkins' Chevy Run" He ran a Isky 550 flat tappet cam with a 108 centerline and Crane roller-tip rockers. Not real stock for a stock class but I guess those were the rules.

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You can run any ratio as all that is checked is lift as measured at the valve.

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Jeff, thank you for the information. I was reading an article about a gent with a 409 that found a Canadian source for stamped steel rockers that were 1.7. It was a simple question and all I need was a straight answer. I guess it's an Arizona thing about looking a man in the eye and getting a straight answer.

Re: Rocker Arms
 

Im not sure you understand what Jeff is telling you, the cam still has to check at legal lift specs so theres no advantage with the higher lift rockers. Maybe Im misunderstanding him too, who knows.

Re: Rocker Arms
 

It does not matter what the lobe lift is, tech will check the lift as measured at the valve spring retainer with zero lash in the checking lifter. The checking lifter will have the same plunger height in relationship to the lifter body as the one the racer is running.

If you have a "true" 1.5 rocker ratio, the lobe lift will be .333" if you have a cam spec of .500".
If you still have the same cam spec of .500" and want to use a 1.6 rocker ratio, the lobe lift will be .3125".

It's up to the racer to determine what rocker ratio he wants. That choice may be limited with a stamped steel ball stud arrangement. Maybe rocker to valve spring clearance comes into play as well.
But a higher (numerically) ratio will open the valve at a faster rate. The bottom line is, it can't open the valve more than .500" in this scenario.
You can juggle with Chevrolet ratio and Pontiac ratio if that's what you want to do.
I found on the AMC which is advertised as 1.6 (also stamped steel ball / stud system) most rockers checked at 1.55 or so and a SBC 1.5 ratio rocker was around 1.45. Since I was always using custom cams, I had the lobe lift adjusted to compensate for the true rocker ratio. Keep in mind what was said earlier, your net valve lift can be adjusted by pushrod length (or even plunger height).
The engines with shaft rockers like a mopar have it easy. The ratio is fixed. And with offset grinding of the shaft hole in the rocker, the ratio can be adjusted. I believe those racers are in the 1.85 range and I think they have been around the 2.0 range but I don't know as a solid fact. But it is allowable.
I know this, when I switched from Stock to Superstock and having a shaft style rocker system from T&D sure made it a lot easier. Where I once adjusted valves every 2-5 runs, the T&D is set and forget (as long as there are no problems of course). And we tried different ratio's on the dyno. There is a difference that can be seen in RR both intake and exhaust.
Hope all this helps...

Re: Rocker Arms
 

Not so, Jeff. The rocker arm ratio for Stock Eliminator engines are still listed in the Engine Blueprint Specifications on NHRA.com.

While it is true that the Tech Dept checks valve lift at the retainer, we can still check rocker arm ratio if we so desire. That could happen anytime we run across a set of rocker arms that do not appear to be correct. A racer was DQ'd a few years ago at Gainesville for using 1.6 rockers on a SBC even though the lift at the valve met the spec.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)

Re: Rocker Arms
 

Looks like they need to start checking rocker ratio at teardown, just in case they thought it was "OK".

Shawn 6383

Re: Rocker Arms
 

I suspect that would be a tough one to handle since you (I assume unless you correct me) do not have a tolerance. Since a 1.6 RR may check out to 1.53-1.55, is that within the tolerance allowable for an advertised 1.5 RR?
And if the tolerance is "dead nuts", you would be able to throw just about everybody out. Right?
My guess is somebody in Gainsville a few years ago must have really PO'd a tech guy off to get bounced for that...:rolleyes:

Re: Rocker Arms
 

I agree with you Jeff, if they did the lobe lift to the valve lift to check R Arm ratio.. everybodys out... good luck with that NHRA Tech...

Re: Rocker Arms
 

Typical NHRA tech.....a few can interpet the rules completely different than a few hundered racers. I can't wait to see what they'll use to check with!

Re: Rocker Arms
 

Bruce, rocker arm ratio is very simple to check. One only needs to know two numbers. Cam lift read at the lifter and valve lift read at the retainer. Simple math gives the ratio.

Jeff, the racer that got DQ'd did not PO the techman. I was quite calm about the situation. When the cam came up way short, I asked him where the rest of his rocker arms were. Seems he had two on the engine and sixteen in the trunk. Two from the trunk made the cam read correct at the retainer but when I checked the cam at the lifter and did the math, it came up more than the listed 1.5 ratio. His engine builder told him over the phone that any rocker ratio was allowed as long as the cam checked at the retainer. His engine builder was wrong.

For the racers following this discussion, rocker arm ratio is a spec listed in the Engine Blueprint Specifications on NHRA.com. Up until now it was something we only checked if the rockers did not appear to be correct. Now it seems that some have shown their hand and we may have to look more closely.

It's amazing what an open forum will bring to light.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions. And I was only letting everyone know what the rules were. I did not realize what would be exposed.)

Re: Rocker Arms
 

[QUOTE=Travis Miller;186147]Bruce, rocker arm ratio is very simple to check. One only needs to know two numbers. Cam lift read at the lifter and valve lift read at the retainer. Simple math gives the ratio.

That will not give you the true rocker ratio. That will only give the ratio as ran. As you know cam base circle, lifter seat height, pushrod length, and valve stem height figures into the sum. I suppose you have all the "stock" dimensions for that too. You'll need to have an "off the car tool" to check the rockers the right way...not the NHRA way.

Re: Rocker Arms
 

Travis,
In the interest of trying to be legal, and trying to get along with the Tech officials, exactly what is the tolerance here.

Lets be brutally honest about this stuff.

First off, stamped steel ball and stud rocker ratios vary, in no small amount, when checking real factory stock pieces. A stock GM 7/16" stud 1.7:1 big block Chevy rocker may check anywhere between 1.65:1 and 1.74:1 or so, and that's out of maybe 30 pieces. That's JUST the rockers themselves, with NO other changes. You might not find a set of 16 that are exactly 1.7:1 out of 100 rockers. I know, I've sorted them that way. And that was genuine GM stuff, not aftermarket stuff.

Second, we all know that rocker arms are NOT a truly constant ratio device. Change ANY of the three points of the fulcrum, and the ratio changes. This means that as the rocker travels from valve closed to maximum valve lift and back, the actual ratio of the rocker changes. This also means that changing pushrod length changes rocker ratio.

Third, we also know that valvespring pressure changes the amount of lift generated. I can increase my seat and open pressure by 50 pounds or so and my lift may change 0.020".

Also, we had an engine at one point that actually had a cam with extra lobe lift ground in because they could not get to the factory valve lift.

So exactly what tolerance exists? If I put a short pushrod in so that I'm 0.010" under the valve lift spec and have enough piston to valve clearance, and that reduces my rocker ratio slightly, have I made the engine illegal? If an engine has a geometry problem, and I need an extra 0.005" lobe lift to get within 0.010" or so of the correct valve lift, is that illegal?

Re: Rocker Arms
 

Just a novice here asking a stupid question and trying to learn something. What differance does it make if the spec is correct at the retainer? The valve will not open any more or less. Am I wrong on this? Thanks for your help.

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Rate of lift is affected. Could be good, could be bad.

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To Bruce, Alan, and anyone else concerned with this rocker arm discussion,

I got in this discussion when the statement was incorrectly made that any rocker arm ratio could be used. That led people to believe that it was legal to use 1.6 or 1.7 rockers when the specs call for 1.5 rockers. Then it expanded to therotical measurement using off the car tools. We could not care less what the rocker arm ratio is when it is laying on the workbench. We are concerned with the "as run on the engine ratio". That ratio is figured by taking the lift at the retainer and the lift at the lifter then doing the math. As long as that ratio does not exceed the spec in the Engine Blueprint Specification for an OEM or accepted replacement rocker arm, it will pass.

We know that the ratio of stamped steel rocker arms can vary, usually to the short side. That is why the spec given is the max allowed. However an OEM rocker arm that the factory says is 1.5 is not going to figure out to be 1.6 or 1.7. That ratio comes from using the wrong rocker arm. If the spec says that the ratio is 1.5, then that is the max the ratio can be. If anyone wants to play with having a cam ground to make up for factory shortcomings, fine. Just be sure you meet the lift specs at the valve retainer and you do not exceed the rocker arm ratio specs. If you do happen to run across a rocker that exceeds the spec for the ratio, then its simple...do not use it.

Now you know how we check ratio....lift at the valve retainer and lift at the lifter, then do the math.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)

Re: Rocker Arms
 

All correct and good points.
I would ad that since NHRA allows for an adjustable pushrod (no spec given), or adjustable rocker (but not both), and doesn't check lobe lift (as the spec is not given), and clearly indicates that lift is measured at the retainer, that it doesn't really matter what the RR is.
I wont pretend that I've checked even a small percentage of the millions of stamped rockers out there, but the ones I have checked, buckets full, have NEVER checked exactly as advertised. I don't recall ever checking a 1.5 SBC or 1.6 SBC or 1.6 SBF or 1.6 SBF that ever showed a higher than advertised RR. But I'm sure some are out there.
So from there, I must conclude there has to be a tolerance. And I would bet the SBC racer in Gainesville had an advertised rocker that in reality was 1.5something. Do we round up or do we round down?
Tech can bust any racer out there at anytime for any reason. I just can't believe with no tolerance given in such a sloppy atmosphere of undefined specs (the valve train) that this is an area of concern.
Yes, It's amazing what an open forum will bring to light.

Re: Rocker Arms
 

Looks like I was typing at the same time Travis was typing.

Now wouldn't this be a lot easier if NHRA allowed accurate $279 Gold roller rockers in stock? :)
Oh yea, that will ruin the sport...:rolleyes:

Re: Rocker Arms
 

So, if we have a cam that is suppose to have .400 lift, but the closest rocker we can find figures out to 1. 46 ratio. it would be ok to have a cam ground with a.273 lobe to make up for the rocker ratio, but if we have a rocker that actually has a ratio of 1.56 you can not have a cam ground that has a .256 lobe lift to get the lift to check legal?

Just curious.....

Re: Rocker Arms
 

You are correct Pat as tech has explained to us..... on our Mopars we bush and have ratio corrected and equalized before anything else.

Re: Rocker Arms
 

If you are talking about an engine that has a spec of 1.5 rocker arm ratio, the first senerio would be okay. The second one would mean you have used a rocker arm that is sold as a 1.6 ratio and that would be illegal. While the total lift at the valve retainer would check correct, the ratio would be incorrect if it were to be checked.

The difference is you have used a rocker that has altered the rate of lift as the valve is opening and closing from the original rocker arm ratio spec but hid it by meeting the total valve lift spec once the cam reaches max lift.

Travis

(Disclaimer: Opinions expressed by me on this forum are exactly that, my opinions.)

Re: Rocker Arms
 

how would that be any different from a cam being ground different?

Re: Rocker Arms
 

With a given tappet diameter, especially a flat tappet, there is an absolute limit as to how fast you can accelerate that tappet. So, given the tappet diameter, and a factory rocker ratio, there is a design limit on how fast you can accelerate the valve. Increasing the rocker ratio allows you to accelerate the valve faster. So, if you reduced your maximum lobe lift in order to use a higher ratio rocker, you'd be disguising a method of exceeding the design limit of the original valvetrain with regards to valve acceleration.

When you have a limited amount of lift, the secret to power, within reason, is how fast you can get to that lift limit from the valve being on the seat, how long you can hold it there, and how quickly you can get it closed. It's called, in general terms, "area under the curve". Again, this is a generalization, not an exact rule. For a given combination, there is an ideal, that combination may or may not be able to achieve that ideal. And that ideal may not always be the maximum amount of "area under the curve".

It is really hard to explain this, especially using generalizations as opposed to actual examples and the math involved. That's about as clear as I can make it here.

Re: Rocker Arms
 

I am no "engine master" by any means, but is there any real power by doing that? and isn't it the same thing as the way stocker cams are ground anyway? the dwell cam verse the rpm cam?

Is there any dyno proof? just curious.....

Re: Rocker Arms
 

I reserve the right to be wrong, but I believe the Nascar teams have experimented with larger ratio rocker arms in order to reduce the amount of spring pressure on a given lift/duration. Less spring pressure should equate to less parasitic hp loss within the valve train.

Re: Rocker Arms
 

On another thread, I remarked about a 283 racer who went through about 100 stamped OEM rockers to get the 16 that he used. That was back in the day when OEM was all that was allowable, and the best arms were the ones with the little triangle on top of the tip above the valve stem tip.I don't know ,however, if he was attempting to achieve accurate lift, or whether he was striving for as accurate a ratio as possible.With all the latitude that various length pushrods can produce,there is an almost infinite degree of possibilities. Yes, it's interesting what an open forum can produce.Thanks to Travis for the expose' on how rocker arm ratios are calculated.

Re: Rocker Arms
 

The higher ratio rocker arm will increase any action ground into the camshaft profile by a mathematical amount. One of the limitations of how radical a camshaft profile can be ground is the lifter diameter. So, when the camshaft has been designed to maximum acceptible rate of lift change dictated by the lifter diameter, then there is no more that can be done to make the valve open any more at a given lobe lift. The higher rocker arm ratio allows a little bit more lift at a given lobe lift, hence "more area under the curve". Also, you can grind a faster ramp into a camshaft profile if the lobe lift is less, also providing for more area under the curve.

See what Alan said above. If I could draw pictures here, it would be easier to see.

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Ain't that the cryin' truth.

Re: Rocker Arms
 

Elgin part number for the 7/16 rocker arms is R-1840.The rocker arm ball isn't included and the part number for the rocker arm ball is RM-1000. Don't try and use a big block ball. It won't fit down in the arm. 7/16" screw in studs and poly locks are everyplace . I've had to do other things on other engines to make stuff right such as using different length push rods on some valves. Good luck on your project.I'm in the middle of this on a 327 I'm doing for my Chevelle. Short block's done, I'm assembling and sorting out the heads and the valve train,now its time to measure lobe lift and compare it to total lift. One more thing to do.

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Well at least the lowly AMC came with 1.6 rockers and .903" lifters...:p

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Some of the latest Spintron "best results" have been with reduced ratio rockers and cam lobes that are larger diameter and shaped quite a bit different than what was once thought good. Less deflection, less spring pressure, less failure, sometimes more power!