Knife-edging the crank, er..what?

[Zendalar]

So people keep talking about knife-edging the crank. I know that it has something to with engines inner aerodynamics, but could somebody give more details what to do and where?

I believe this affects the power positively, but how much it would increase HP in 2.4T and does it come less reliable or more prone to engine failure?

Thanks

[Formerly Steve Wilkinson]

I suppose it has something to do with "windage"--the amount of power lost to the crank thrashing its way through whatever oil is in the case. Obviously with a dry-sump engine this is less of a problem, but there still is a windage effect in dry-sump engines. It's not so much "aerodynamics"--the crank spinning smoothly through the air--as it is "oilodynamics." Hopefully, you'll get a more authoritative answer from those who are more knowledgeable than I am...

Stephan

[Zendalar]

My friend told me that usually race cars have these "splash plates". These are installed below the cranks and these inhibit unnecessary oil splashing and therefore making cranking more "oilodynamic" as you said. But is this the same method?

[Thomas Owen]

Stephan is on the right track. The leading edge of the crank is machined from a somewhat flat surface to have a beveled, or 'knife' edge. The idea is that it would decrease some of the losses due to the wider surface contacting oil in a sump. With the dry sump system I do not think it is such a factor, or advantage.
Regards,

[gaijinda]

The machine work would be very, very expensive and would not be worth the money. The additional hp realized in a "T" motor would be low.
There are more cost effective upgrades that can be made. Any suggestions out there??

[RarlyL8]

The cheapest way to bump up the power of a 2.4L is to install a 3.0L (just kidding, Leland made me do it).

Engines that do not use dry sump systems can utilize the effects of a knife edged crank and a windage tray. I had both done to the SBC in my street machine years ago. The effects aren't noticed unless higher RPMs are used.

[cds72911]

I think it actually does have to do with aerodynamics. If I read Bruce Andersen's book correctly there is all kinds of airflow inside the engine and this helps smooth parts movement through that air. Made sense to me when I read it...

Cheers.

[911pcars]

It's like having the leading edges of a propeller flat versus beveled to a sharp edge. Other aero mods include notching the bottom of the cylinder barrels and contouring the main bearing webs in the crankcase; all in the name of less aerodynamic drag. Is it worth it? Race car - yes. In a race engine where you're trying to squeeze any advantage you can, you add up all the little HP gains and end up with a significant number. You can also take weight off of the pistons, piston pins, con rods, valves, retainers, flywheel, etc. etc. etc.

For a street car? It depends on how much loose change you have after the initial rebuilding investment. Do you have the budget allocated for all these little mods?

Sherwood Lee
http://members.rennlist.org/911pcars

[Roland Kunz]

Hello

Some effects come togehter:

The aerodynamic effects
The mass effect
The engine wight benefit

The money loos effect


Knife edging is only interessting if you have gone all they way to the max and have only some things left over to push the power limit in your class.

The good thing on the 911 engine is that they are allready there where most other engines need investment to achive the same level in hardware. Look at a stock 911 engine and then compare it with what others sale as race engines.

Grüsse

[pwd72s]

Roland made a good point! Years ago, I got into a street "sprint", I guess I'll call it, with a guy who owned a '57 'Vette that was "improved" by the insertion of a 327 csb with some improvements. On an (almost) straight road, we were fender to fender...but he ran out of gears, and I still had 5th.
Afterwards, Wally, the guy with the 'Vette and I were Bsing. He asked "how can those Germans make a sewing machine motor produce so much power?" Then I started listing thing...like tuned mechanical fuel injection, tuned headers inside the heat exchangers, hemi heads, overhead cams with lots of overlap, etc. You know...I just explained it to a USA hotrodder in terms he'd understand. But his problem understanding came about when I explained that all these "tricks" were stock. Yeah, he'd just been smoked by 2.4 liters, but he had trouble understanding why any factory would do such things and make them stock equipment. It was a fun conversation....

[Efrain68912]

A friend of mine knife-edged the crank in his vintage racing 911R. He said it made a good difference in power but killed the idle.

Efrain
68 912 Coupe