Checking Rocker Ratios

[Ron Earp]

With my SCCA 3.8L V6 Mustang I have to use the stock rocker arms. These are stamped steel jobbies that obviously have a lot of compromises. But, I do not have an alternative rocker arm that I can legally run.

The rocker ratio for these is 1.73 and they are the typical Ford pedestal mount type. I've got loads of them from pulling motors apart and want to hand pick units that have the most favorable rocker ratio.

Questions:

*Those with experience, do you see much of a difference in rocker ratio with stamped steel rockers?

*Is there a jig available for checking this out? I thought about welding up a "go/no go" spring loaded fixture that would report if one was less than the set point of the rig.

Ron

 

[Jac Mac]

These rockers swap with those fitted to the Boss 302, Aussie 302c, 351c, 400m & 429 base engines, there have been several different shape stampings over the years along with a few changes in the pedastal materials & design. Some early 429 models used a cast rocker arm that mounted on a ball stud [ala early SBF windsors & SB chev 283>400].

Of the stampings the ones to avoid are the version that are quite deeply scalloped each side of the pedastal area as this allows the arm to flex/distort slightly in use, part of the blueprint info for Boss 302/351c as to smooth the 'edge' around the top of the stamping to prevent stress risers.

Only 'failures' I have experienced is having pushrods punch thru the pushrod cup of the rocker & in all cases that was due to drivers exceeding the valve spring limitations.

How would I go about creating an advantage on the stock items....
As the valve guide centerline & the centerline of the pedastal bolt are divergent I would shorten the overall length of the valve to move its tip away from the bolt C/L, I would then cut down the pedastal fulcrum to position it closer to the cyl head & rework the valve contact pad of the rocker arm [ this would increase the rocker ratio slightly & by moving the pedstal closer to the head it should not flex quite as much ].
You will then have to correct the pushrod length to match all this.

Probably a bit more than a saturday afternoon though

 

[Ron Earp]

Probably a bit more than a saturday afternoon though

Oh, we're not afraid of longer than Saturday afternoon projects. We've got plenty of long term projects including a couple of engines on the go we're doing from scratch. Our abilities have progressed dramatically over the last few years. Nothing like people you pay to do stuff that don't do it right to breed necessity of skill development.

I can't have more valve lift than what is called for in the rules, but I certainly want to be sure get all that we're due! I will check for any tolerances in the shop manual that we could take advantage of though. I'll take a few pictures of these and see what you think but I don't think these are the heavily scalloped rockers.

 

[Randy V]

Jac's info is spot on as usual..

Since you did not start the thread to ask about preparation tips, I'll leave that out, but if you're interested - let me know.. I'm sure Jac has info on that as well..

 

[Jac Mac]

Jac's info is spot on as usual..

Since you did not start the thread to ask about preparation tips, I'll leave that out, but if you're interested - let me know.. I'm sure Jac has info on that as well..

Best we dont Randy, or Ron might find the SCCA tech guys logging in here to find out what to check next!!

 

[Ron Earp]

Best we dont Randy, or Ron might find the SCCA tech guys logging in here to find out what to check next!!

An SCCA white suit logging into a web site? Sheeeeiiit. Jac Mac, there is a higher probability of me landing on the moon next week in the Earp LEM V1.0 than an SCCA tech official logging into a website. Present company excluded Randy.

Randy and I exchanged PMs and I learned some things, and he might have too. It isn't just the wise older hands that have the cards - new guys have some ideas too....and not all of us put ideas into the "too hard" bucket.

 

[Gord Zonailo]

Ron, if you have the engine out of the car it is easy to use one cylinder for checking a bunch of the rocker arms to check the actual lift at the valve. You could use a lighter checking spring to simplify the process and exchange and record the lift at the valve to determine any differences. Also check with the actual spring pack that you are using.

From what you indicated in the first post the spec that you will be checked on is lift at the valve So you will want to make sure that this is achieved.

Do they also check duration of the cam and if so, at what valve lift? If it is at full duration off the base circle there is possibly quite a lot of latitude in the actual cam profile to build more effective duration in with faster ramp angles on the cam. It is maximum area under the curve between the checking points that you will want to achieve. Even if the cams are checked at .050" lift there is still probably some latitude to steepen the lift ramps and gain more area under the curve. This is done by all the stock class NHRA drag racers and companies like Competition Cams or other manufacturers. Keith Craft Racing and Kuntz and Company are two of the engine shops that also do a lot of NHRA stock class racing preparation and the cam selections for these classes. But it can be done by yourself also working with a cam company.

If they check the total valve lift curve then you are hooped!

Gord Zonailo