Thread: crankshaft bearing speed and other questions ( might be kinda long!!! )

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Just having some random thoughts going through my head, thought I'd pass them on and see if I can get some info. Thanks in advance.

1) A long time ago I saw a formula for calculating bearing speed for given engine RPM. Does any one here know that formula??

2) I was reading an article in GM High Tech Performance. Justin (?) Massingil from SAM was claiming that about 15% of an engines power is comsumed by ring friction. I know that measuring rotational torque of a piston,ring,crank assembly is a good way to measure this friction on the stand. I believe I was told that 20-30 ft/lb was norm for a street engine.

How loose can the ring package get and still provide adequate oil control on a street engine?? Is there a tension gauge or some chart I can buy or refer to?

3) Can I not run say a medium tension ring pack for oil control and have the crank mains and rods cut down for a little friction reduction??


Sorry if these are a little elementary, I've Googled and I can't seem to find what I want.

Again, thanks for reading and I appreciate the input....



Robert

Where does the car run, track or street??? We run low tension oil rings on a drag engine, replace them after one season, usually about 100 to 150 passes. The big crank radius' and narrowed bearings work good.... Guess it'd be up to you and the engines' intended usage as to whether or not it's worth the extra expense and effort... Don't think I would bother on a street engine, hard to hook up and use the available horsepower without even going to all the trick stuff...... Some of these power gains will only show up on a dyno, not much "seat of the pants" improvement....

Originally Posted by Dave Severson

Where does the car run, track or street???

Right now it runs nowhere. This is just all in my head. If I had to pick it would be street.

These are just things floating in my head. Smaller diameter coated main and rod bearings, slightly thinner metric ring packs. I ask these questions because there is much to be learned from you guys. Thanks....


Robert

Robert, first off, let me applaud you for thinking outside the box.

Dave has pretty much nailed it as far as street or street/strip motors that most of us on this forum would build.

I was just reading the other day about the rod journal sizes on NASCAR motors. The builders have been running 'em as small as 1.880" and using Honda rod bearings. I think in that article was a reference to an even smaller journal and bearing, but I didn't pay that much attention to it, so don't remember it. But just as Dave said, this kind of "out in left field" stuff has little appeal to us hot rodders. A Cup builder may be able to dominate the field by having a motor with 5 additional horsepower over his competitors, whereas you would never feel 5 horsepower in the seat of your pants on a street motor.

The flip side is the money. I have no idea about NASCAR cranks or Formula 1 cranks or any of that high-buck stuff, but I would be willing to say that I could build a couple of street motors for the cost of a crank that would use the smaller journals. I further suspect that I could make up the difference in power between a production motor and a real good runnin' street/strip motor with a good 5-angle valve job on the seats and a couple of back cuts on the valves without having to go to a Cola or Callies or whatever crank with 1.880" rod journals. Those high-buck guys have already done the valve and fine-tuned every other piece on the motor several times, so the smaller journals may be getting toward the end of finding additional power.

I did notice with interest that the Gen I small block's days may be numbered. The new NASCAR "spec" motor is based on a warmed-over LS2.

I'll just end this with saying that if you have run the cam in needle bearings, are using roller tappets and roller rockers and have tweaked every other part in the motor as far as you can, then you may be looking to decrease the crank journals. Otherwise, it's just so much fluff, blowin' in the wind.

However-----
Today there are some choices in crankshafts/blocks that can be made to vary from the everyday norm and go bigger or littler----Ford cranks are common place with Chevy rod sizes and also even the smaller sbc 2.100 and 2.000 rod journals---Chevy sb can use early 283 main size cranks with a spacer bearing or replacing the caps and using just an upper spacer.

Having said all that---one of the reasons for using the smaller rod sizes is to cut down on the amount of block/cam clearance problems and helps in balancing rotating mass

yep if you build the right engine first off you do not much have to worry about this much like a chevy .the ones that come to mind ford olds pontiac some guys go smaller on main and rods on the sbc on the bbc guys go to 2.100 rod for more room and use a 409 main bearings smaller then stock bbc.it is pro stock stuff . like jerry said most rods you can get smaller rods bores to use other bearings and off set grind the crank for more cid but getting the mains smaller can take abit more$$$ and work .but on very big cid they some times go up on mains size and pin size so there is more pin over lap make for a stronger crank as for thinner rings and smaller rod jounals this stuff is out there callies .howard and many others make rods for smaller bearings and crank jounals .and other sell pistons with the 043 or mm ring packs are very pricy