Someone please explain, "bearing speed".

My initial thought is the reduction in rotational mass for the crank.

I've heard that turning a crank down and using plus size bearings can help
acceleration.

Another thought is that the oil wedge will be stronger between the crank and
bearing since the diameter is smaller (hydrodynamic wedge?).

Beyond that, "bearing speed" is a mystery to me.

 

Suppose the crank journal O.D. is 2.45" (standard SBC). If you mark a point on the crank journal, it has to slide over 7.7" of bearing surface per revolution. With 2.30" mains, a point on the crank journal only has to slide over 7.2" of bearing surface. So at 8500 rpm, it's like the 2.45" main crank is sliding on the bearing at 90.9 feet per second, while the 2.30" main crank is only going 85.2 fps.

 

The rules keep them from running super small(super light cranks)rod and mains now. But they are doing some wild things with camshaft and valve trains right now. Testing rocker ratios and valve lifts unheard of a few years back. And to keep it alive right at and above 10000 rpm is pretty damn good not to mention 850-875 HP.

 

As TheNovaMan suggested, larger bearings equate to higher velocities between the stationary bearing shell and the moving journal. Higher velocities mean more heat generated and more shear of the oil wedge/film. You approach a velocity where the oil wedge is compromised.

Higher bearing velocities also mean more bearing friction hp losses, maybe 10 hp @ 9500 on a Cup engine, but I suspect the heating of the oil might be some of a problem for an endurance engine.

To calculated the bearing velocity: V= rpm x dia x .262/60, where bearing diameter is in inches and Velocity is in ft/sec. So 9500 on a 2.30 in main = 95.4 ft/sec. and a 2.45 dia. bearing would have an equivalent rpm for the same bearing velocity of 9500 x 2.30/2.45 = 8900 (approx). You can do this because bearing speed is directly proportional to bearing circumference which is directly proportional to bearing diameter.

FWIW, 88 ft/sec is 60 mph.

 

INTMD8,

Yeap it's a way to control oil flow, reduce windage and bathe the camshaft in lots of oil for lubrication.

The Toyota block does have a cast in cam tunnel like the DRCE3 Pro Stock Block. I'm not sure about the Mopar in that area though....

As for the sheetmetal and epoxy, it's actually ok to do that, it's amazing how well this stuff holds up and how paranoid well all are about things like this.

Bret

 

Awesome pics!

I have a friend that works at DEI...I usually get to see some cool stuff on his street car motors!

 

ws6t3rror, sent me this link as well....
http://cgi.ebay.com/ebaymotors/ws/eB...982037291&rd=1

Bret

 

Cam tunnel would work very well on a street driven solid roller car...

 

Much nicer pics! Bigger lifter bores too.

 

Yeah especially if you drain the oil out of it high enough so you can bathe the cam about halfway up.

Bret

 

Thanks for the explanation guys. Just when you think you've heard it all!

Is this feature used at all on drag motors? I would think not as the crank
strength would be compromised.

Safe to say, you'd see small journal diameters in Indy/F1 engines as well?

 

Yep.... actually they don't need the crank to live as long so they have even less journal overlap than a endurance motor does.

Bret

 

Larger mains, larger lifter bores (without bronze sleeves), different lifter valley draining scheme, and no cam bath/tunnel. Definitely some different ideas than seen in the DEI motor.

Another thing I noticed is that all the sharp edges have been broken. Is that just a creature comfort for the engine builder, or is there an engineering reason for it?

 

Both. Less cuts on your hands for sure and also relieves stress points. And to a very small extent it reduces weight.

 

Yeah, first thing I do too... get the sharp edges off, my hands get beat up enough.