Afr Cylinder Heads Ques..

5.0stang_gt · May 10, 2005

Hey guys I am looking at a pair of 165cc AFR heads and there is an option of either a stud mount or pedestal mount.I dont know if that is a dumb question or not but what is the difference and what should I get?

custom90GT · May 10, 2005

Pedestal mount heads use a pedestal that the rocker mounts down on and then a bolt goes through to hold the rocker down.

Stud mount heads have a stud on wich the rocker attaches to. Stud mounts are much stronger and adjustable whereas ped are weaker and non adjustable.

I would say get the studmount heads, but then you have to buy new rockers (not a bad idea if you still have stockers).

tjm73 · May 10, 2005

Not to muddy the waters, but their is a pedestal mount system that's adjustable and as strong or stronger than the stud mount.

Steeda sells a pedestal mount shaft roller rocker system (here) that is pretty slick. Reasonably priced too at $350 bucks. The really good pedestal roller rocker kits cost just as much. The Cobra 1.7:1 kit is not that great IMO so I won't go there.

custom90GT · May 10, 2005

tjm73 said:
Not to muddy the waters, but their is a pedestal mount system that's adjustable and as strong or stronger than the stud mount.

are you sure about that?
here's a quote from http://www.mustang50magazine.com/techarticles/18679/

For most street applications, pedestal-mount rocker arms are perfectly adequate. However, when high horsepower and proportionately high valvespring pressures are used, pedestal-mount rockers have their shortcomings--the most important of which is strength (or lack of it). Though the basic rocker layout is the same used in higher-horsepower racing applications, pedestal-mount rockers employ a 5/16-inch cap screw, which has a tendency to deflect and even break in a high-horsepower application. We’re reluctant to state specific numbers here because we know of many racers who have used pedestal-mount rockers well into the 500hp range with a variety of cam/valvespring combos.

The other shortcoming of the pedestal-mount rocker is its lack of adjustability. Factory rockers and some aftermarket replacement roller rockers use shims for adjustment, while other models use pushrod cup adjusters. These, however, are mainly for the purpose of obtaining correct lifter preload during installation.

Suffice it to say that if you have heads designed for pedestal-mount rockers, use them. If you get the chance to run heads that use stud-mounted rockers, do it.

Stang8URMPRT · May 10, 2005

He was talking about shaft mounted peds... Those are way stronger then your run of the mill peds or studs.

tjm73 · May 10, 2005

Stock pedestal to a stud mount, the stud mount is stronger hands down.

But take a look at the Steeda rocker set. You have 2 studs tied together via a short shaft. For one to deflect or break the other would have to do the same. It's the same basic concept as axle splines.

The splines on a 28 spline axle are bigger so youwould think they are stronger. But a 31 spline axle has smaller splines and it's stronger. It's stronger becasue the work load is more evenly distributed to a larger contact area.

With this setup, two smaller bolts are better than one bigger bolt. Shaft mount rockers are the best setup you can get. This setup is a hybrid shaft type set up.

I can't point to any hard data, but I know from research that shaft systems are the strongest, most stable systems you can run. So even if the shaft only contains 2 rockers, it's stronger and more stable than a single rocker on a single stud.

custom90GT · May 10, 2005

I see what you are saying, I misread your post and thought you said that studmounts were non adjustable and weaker than the normal ped mount. And like Stang8URMPRT said, i belive those are called shaft mount rockers, not ped...

tjm73 · May 10, 2005

custom90GT said:
.......... i belive those are called shaft mount rockers, not ped...

The Steeda kit bolts down on stock style pedestal heads. I guess I should have kept my mouth shut.

custom90GT · May 10, 2005

tjm73 said:
The Steeda kit bolts down on stock style pedestal heads. I guess I should have kept my mouth shut.

lol, of course not. Im glad you said something since i learned something.

Modular2v · May 10, 2005

tjm73 said:
Stock pedestal to a stud mount, the stud mount is stronger hands down.

But take a look at the Steeda rocker set. You have 2 studs tied together via a short shaft. For one to deflect or break the other would have to do the same. It's the same basic concept as axle splines.

The splines on a 28 spline axle are bigger so youwould think they are stronger. But a 31 spline axle has smaller splines and it's stronger. It's stronger becasue the work load is more evenly distributed to a larger contact area.

With this setup, two smaller bolts are better than one bigger bolt. Shaft mount rockers are the best setup you can get. This setup is a hybrid shaft type set up.

I can't point to any hard data, but I know from research that shaft systems are the strongest, most stable systems you can run. So even if the shaft only contains 2 rockers, it's stronger and more stable than a single rocker on a single stud.

the thickness of a 31 spline is alot more than a 28 spline....the 31 is more beefy

tjm73 · May 10, 2005

Modular2v said:
the thickness of a 31 spline is alot more than a 28 spline....the 31 is more beefy

each spline cut adds more surface area to an axle for engagement to a center section. More surface area = more holding power, to a point at least.

Take 2 identical axles and cut one with 28 spline, the other with 31. Test for strength. The 31 spline will win.

Or take a flat blade screw and screw driver. How many screws have you messed up over the years when getting heavy resisitence to turning the screw? NOw think about the last Torx screw you fought with. You used A LOT more force getting that undone than a flat blade screw would accept.

Modular2v · May 10, 2005

tjm73 said:
each spline cut adds more surface area to an axle for engagement to a center section. More surface area = more holding power, to a point at least.

Take 2 identical axles and cut one with 28 spline, the other with 31. Test for strength. The 31 spline will win.

Or take a flat blade screw and screw driver. How many screws have you messed up over the years when getting heavy resisitence to turning the screw? NOw think about the last Torx screw you fought with. You used A LOT more force getting that undone than a flat blade screw would accept.

wow that is a really good analogy!

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