Rocker Arm Ratio
 

Are we allowed a 1.6 rocker where a 1.5 is listed to make our camshaft lift legal? Thanks for your help.

Re: Rocker Arm Ratio
 

Absolutely not in Stock Eliminator.

Re: Rocker Arm Ratio
 

Get the rulebook, it has what we can and cannot do to the eingines

Re: Rocker Arm Ratio
 

David,

I read the rule book where does it say what rocker ratio?

Re: Rocker Arm Ratio
 

Rocker ratio is in the blueprint specifications. You absolutely cannot have a rocker ratio higher than that specified in the guide for your engine.

Re: Rocker Arm Ratio
 

Thanks Alan, I had a conversation last evening and the fellow seemed to think the rule had changed.

Re: Rocker Arm Ratio
 

Thanks Alan, you beat me to it

Re: Rocker Arm Ratio
 

Get a cam made that meets the lift spec with the stock rockers

Re: Rocker Arm Ratio
 

PJ, I heard the rocker ratio was dropped too. I called Travis and he said it was still in full effect. He was the one who checked them at the Allstars this year. Lift at valve as well as ratio will be enforced.

Wade O

Re: Rocker Arm Ratio
 

If your rocker has no number (ratio) stamped on it, don't worry about it. I was thrown out because mine were stamped 1.65 and the rules said 1.60. The cam checked ok. Without the numbers nobody knows or cares I think.

Re: Rocker Arm Ratio
 

They can, and will, check lift at the valve, and then lift at the cam. From that they will check rocker arm ratio. If the ratio is greater than what is in the blueprint specs, they will throw you out.

Feel free to ask Travis Miller, or Dave Ley about this, they will explain it to you. There are also several threads on the subject that explain why and how about rocker ratio. I have seen people thrown out for rocker ratio.

Re: Rocker Arm Ratio
 

Rocker ratio is not constant in the swing of the arc. Check max lift at the valve and at the cam all you want and you will never catch it that way, unless you went crazy and tried to go from something like 1.6 to 1.8

Re: Rocker Arm Ratio
 

If they check lobe lift and x it by the correct ratio it better be the same or damn close to what it checks at the valve, you will always loose some from spring pressure but not the difference between 1.5 and 1.6, but when was the last time they checked lobe lift ? and is that something there doing now ?

Re: Rocker Arm Ratio
 

As per Danny and Bruce at Chicago nationals this year any ratio is allowed.
Dalles Glens corvette had 1.55 rockers from comp cams on his lt1 corvette and 1.5 is the spec .Danny told me all NHRA cares about is that the cam checks
And that is fact.

Re: Rocker Arm Ratio
 

Charley,

Wade O. said Travis checked all the rocker ratio's at Chicago so how could Dallas Glenn be legal with 1.55 rockers when 1.50 are in the blueprint spec.
Travis can you clear this up for the guys going to Indy.

Thanks

Re: Rocker Arm Ratio
 

Get it in writing from Glendora. Email them, and then follow up with a phone call.

Re: Rocker Arm Ratio
 

Alan,

You can use a letter from Glendora for toilet paper. I spent $1000 for a Pontiac carb for my Chevy and have a letter that it's legal but I can't run it. I have another letter from Glendora that says angle adapters for spark plugs are legal and wasted $500 and there not legal.

Re: Rocker Arm Ratio
 

It holds up a little better than their word, or second hand information.

I'm betting Travis will not post any clarification, as NHRA won't want him to. Not to mention they may over rule him on a whim. Which is one of the reasons Wesley Roberson has completely quit.

Re: Rocker Arm Ratio
 

Thanks Alan, I will roll the dice at Indy and if I get thrown out at tear down I will be just another cheater.

Re: Rocker Arm Ratio
 

And folks wonder why people just stop racing, the rules are still not the same across the board. Alan, you are right even tech directors are at a loss when Danny is around.

Re: Rocker Arm Ratio
 

I'm thinking roller cams will be legal next,lol. Good luck guy's.

Re: Rocker Arm Ratio
 

Why not. Just lift check it and go. Wouldn't that be a lot easier on tech not to mention the engine!
What do you think the power gains if any would be from rollers for the old solid lifter cars vs. the cars that already have roller lifters? I am limited by piston valve relief as it is.

Re: Rocker Arm Ratio
 

Now Wesley has quit too ?? That's not good. Period.

Re: Rocker Arm Ratio
 

To Quote a famous un named Tech Man, " its all just dial in anyway"

Problem is the racer pays in money and frustration at lack of consistency

Re: Rocker Arm Ratio
 

Yep!

Re: Rocker Arm Ratio
 

I remember talking with a very successful builder of 283's years ago who mentioned going through a bucket of about 100 stock rockers before he found 16 that were right. OEM stamped parts can be all over the place as to their actual ratios.It is very possible to assemble a stocker motor with a set of them and have one or more over as well. If they check lift at the retainer, then lobe lift and even though net lift at the valve is OK, it can be and often is that the OEM rocker arm is over enough to render the combination illegal. On a SBC, rocker arm ratio is 1.5 to 1. That is a finite spec. Check the lobe lift at the lifter, multiply by 1.5, there is your maximum allowable valve lift. If lobe lift checks, rocker arm ratio is good, but valve lift is a little shy, try different length pushrods to see if it brings things up where they belong.That can be your variable to make this whole thing work. Remember, check EVERYTHING, leave nothing to chance, because they will if you don't, and nobody wants to be sent home early over something as simple to avoid as this.We had a very fun involved discussion on push rod length determination here in the last off season if you care to locate and review it.

Re: Rocker Arm Ratio
 

So less rocker than the blueprint specs call for is ok? correct?

Re: Rocker Arm Ratio
 

Bill, from info I have absorbed off of here that would be yes. With the added caveat that lift comes in under spec.

Re: Rocker Arm Ratio
 

If a racer had a good stocker cam that used "stock" rocker arms that checked legal, then went to "stock" ratio roller rocker arms, more often than not, the lift would be over limit. Some had to go to a lower ratio rather than throwing away a good cam. As long as the lift is within the rules, it should be OK. Dyno

Re: Rocker Arm Ratio
 

Yes, Wesley is no longer working for NHRA.
He runs the Tech side of the Engine Masters Challenge.
RJ.Sledge, Sidney J. Bonnecarrere & I work for him.
He also does Tech work for a Mud racers association and a couple of other well known racing series.
A couple of years ago he and I had this discussion about rocker ratio. The paygrade above us at EMC was wanting us to limit Rocker Ratio.
According to him there is no real way to measure rocker ratio correctly.
Too many variables.
Example: In a Small Block Chevy you are dealing with three distinct intersecting angles. Pushrod, Rocker Stud, Valve angles. Yes, if extended far enough those angles will intersect. Where you locate the rocker on any of the various planes between those angles influences the effective ratio of the rocker.
Say you have a cam lift of .275 and you are looking for a 1.5 ratio to give you a net lift of .410. You set your valve length and pushrod length to get that .410 net lift. OK Presto we have 1.5 Rocker ratio. Does that make the rocker a 1.5 ratio rocker? Probably not. Now you drop the pushrod length by .100 and reposition the rocker and woops the valve lift is now .418.
OOPS, have we changesd the ratio of the rocker, what ratio was it and what is it now. Humm, lets see we lower the length of the valve tip and, oops again the measured valve lift goes to .412. Then if you want to get serious you can mill the stud bosses at an angle and tilt the stud back and the measured lift will change again, all with the same rocker. Wesley told me that measuring Rocker ratio on an engine is not a place you want to go.
Danny must know rocker ratio is a slippery slope. Wesley does.

Re: Rocker Arm Ratio
 

Please forgive my ignorance on this. Where is lift checked in teardown ? The pushrod, lifter or valve ? But if it's @ the valve I don't get why all of this matters. Again, new to stock but not racing.

Re: Rocker Arm Ratio
 

Dave,
The specs you see in the NHRA Blueprint guide list it as "Valve Lift".
Valve lift is measured at the valve. I have never seen a lobe lift listing in the NHRA Blueprint specs that I usually deal with. That is not to say they(lobe lift specs) may be there for some XXX engine that is or could be under the watchful eye of Billy Nees. (wink,wink)
Since you are new to this I would suggest you visit with a NHRA Tech inspector and ask questions while watching what goes on. It might help you and keep you from a costly mistake or two. See it never hurts or is bad to ask questions.

Re: Rocker Arm Ratio
 

In your example, you used a SBC with .410 net lift & I assume thats what the spec sheet calls for @ the valve. If so, why is there a slippery slope with changing pushrod length to get .418 lift @ the valve. Its over spec. I understand whats being said about different angles affecting lift. Was this some older school stuff trying to get more from the stock rocker before the rollers were legal ? Just asking.

Re: Rocker Arm Ratio
 

Dave,
It is about the geometry. You can do exactly the same thing with the new Roller rockers as with the older stamped steel rockers when it comes to making more or less lift to meet the specs. How can a rule for ratio be enforced when you can move the relationship of the rocker to other parts and have the ratio numbers change?

Re: Rocker Arm Ratio
 

It sounds like this could get into a maddening cycle but ultimately since these can be manipulated it sounds like its the job of the engine builder to make sure all this checks to spec.

Re: Rocker Arm Ratio
 

Adger -
While I agree with you in theory that you cannot measure the "exact" ratio of a rocker arm, you can determine the difference between a rocker that was intended to be used in the "1.5" range as opposed to one that is designed to be in the "1.8" range or the "1.3" range, especially when there is already a sub-industry that is based on the history of production rocker arms. And that is the purpose of restricting the engine to be built within the same parameters as it was engineered. Nothing wrong with that. Now there will always be those bit-twiddling brainiacs who will figure out how to squeeze the mechanical motion of a fixed rotating lever into a ellipse for their advantage, but it would be to the benefit of all to not reduce the technical acceptance of camshaft checking to what is measured at the valve. It introduces another plateau of expense to an already prohibitively expensive endeavor.

There is a decided difference between somebody fiddling with the production tolerances of rocker arms to change characteristics by a .01 of a ratio or so to attain a bit more lift at the valve and somebody designing a camshaft lobe be used with a rocker arm that is .2-.4 of a ratio more or less than the engine's original design spec to gain horsepower.

Re: Rocker Arm Ratio
 

As long as it does not exceed what the spec says at the valve....I don't see a problem.

Of course one could manipulate the valvetrain.....larger cam diameter, offset lifters, change the phasing, relocate the attachment point of the rocker, change the ratio, longer/shorter valve stem, ect. all in a quest to build a better mousetrap.

But, at the end of the day ,if the lift at the valve SEAT does not exceed the spec called for...who cares?

Re: Rocker Arm Ratio
 

It is a problem. You explained the considerations well. I do care.

Re: Rocker Arm Ratio
 

2013 Indy Tear Down - They checked total lift at the valve

Re: Rocker Arm Ratio
 

Correct, Dwight. All sorts of manipulations are possible if you only check lift at the valve.