Thread: 336 cam??
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Old 07-03-2011, 10:10 PM   #13
because I can
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 9,116
I just want to reiterate that the stock pushrods work fine. I ran mine with the stock aluminum pushrods for many miles and more than a couple of missed shifts at 8000rpm plus with no problems. (I do run titanium retainers!) It's just that I recently did some experimenting with a spare engine in order to find out what it is exactly that rubs on almost all aluminum pushrods 308 or 336. I always assumed that it was the head gasket. It isn't. The pushrods are flexing all the way over and rubbing on the pushrod tube right where the tubes stop and start in the cylinders and heads. I thought that maybe the radius of the rocker arm was swinging the pushrod real close to the pushrod tube so I assembled an engine leaving the pushrod tube seals out and stuck a small light there and watched how centered the rods stayed going through their motions. I was surprised at just how centered they stay and just how far those pushrods must be flexing in order to be getting into the sides of the pushrod tubes like they almost always do. All that flexing has got to effect valve timing! It seems like Nascar and drag racers have been figuring out the exact same thing in just the last twenty years and have gone to way stiffer pushrods for quite a bit more power. Guess what? I am going to do the same thing although I am sure it will be for just a tad more power but, like I always say, it all adds up!

I was debating running BMW steel pushrods. They are 40% lighter than my custom rods and I have a set of them. All four of them show no sign of getting into the pushrod tubes. Then I was at a friend's house and he had some laying around and they had rub marks in the same place as most all aluminum tubes. Not nearly as prominent but they were there. I told my friend that seeing that made up my mind. I am running my .058 wall 4130 pushrods so my valves will open faster and further like that good cam intended! 40% heavier than BMW steel rods and right at twice as heavy as aluminum flexers? It turns out that the car guys are running rods up to three times as heavy for more power. Twice as heavy as they were just twenty years ago ALL the time.

I just thought that maybe those rods are just flexing during missed shifts? I kind of doubt it because I see them marked up heavily all the time on engines that could barely get to red line in neutral if you held the throttle open for ten seconds plus the owners liked to pretend that they were driving a VW Microbus while they were riding their BMW motorcycle. I can't think of a way to be any slower and easier on an engine?

Hp cost big bucks? Not if you do it right!

supershaft screwed with this post 07-03-2011 at 11:00 PM
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