knife edging m20

[autowerks]

I'm wondering if anyone has information on knife edging the crank. engine manegment, clutch, driveablility, piston setup, differencial gearing, rods, balancing, cost, worth, ect. any info is usefull, thanks.

[Ball325]

i have a knife edge crank other than that its stock internals mild head work and ltw flywheel driveabilty is fine as long as you like blipping the throttle

[Super Eurobeat]

i wouldnt worry too much about knife edging, all its doing is directing the oil splatter in the crankcase for less windage.
Its not that big of a deal until you start revving in the 8500-11,000 RPM range.
Its basically making it more aerodynamic, unfortunately a lot of machinists are generally shaving it off without knowing where the oil will land, making it sometimes worse than stock.

If you are gonna do that, you might as well teardrop the crankshaft for maximum effect, otherwise its pointless.

[nando]

to echo the above post, GRM had an article on all that stuff - balancing/blueprinting, knife edging - basically they came to the conlusion that you were better off just building a smooth running engine than wasting money and effort on the above mentioned items.

[autowerks]

ball325 i would love more info how much money did it cost where did you have it done and were they able to balance out the crank with out changing youre pistons or rods?

[h0lmes]

So knife edging serves a similiar purpose to a crank scraper?

[Super Eurobeat]

all knife edging is doing is shaving away the corner of the counter weight to direct the oil splatter to reduce windage in the crankcase to allow for more aerodynamics.
it aint gonna do crap, if you could say it added horsepower as an example it would be like 1 horsepower. Not much.

All that stuff should be left for motors that rev high cause every bit counts when you get that high.
Otherwise if you are only gonan see 7 grand there is no reason, you might as well invest in hyperutectic pistons, or forged rods or something that will help a ton.

tear dropping the crank is reshaping the counter weights by machining the crap out of them into the most aerodynamic shape according to physics, the teardrop.
This if you could say as example, it would increase 3 horsepower, not really changing the numbers once again but it would feel like that much.

There is no point cause you could just do some simple head work and get a ton of flow improvement, all i can say is 35 should be the top cut and you can go from there, that will increase a ton of flow, along with machining part of a certain part of the combustion chamer, i dont want to give away the m20 secrets though :p

You can easily get 16 percent more flow rate out of a M20 325i head, you just have to know where to look for.

[autowerks]

although on the figures the horsepower dosent amount to much, the less the rotational weight the quicker the throtle responce. I do understand do to the strength of the rods and the valve springs that the m20 engine would not be able to see that much higher revolutions than stock and even with stiffer valve springs and stronger rods I think the length of the crank may be a factor. I would love to hear more from ball 325 or somebody who has also shaved weight off of their crank.

[Super Eurobeat]

since these car are a lot lighter than e28's you should just stick with the 2.5 crank since you dont need as much stroke to get the car moving like a bigger e28.
I dont know how high a 2.5 crank can rev but a shorter stroke can theoretically handle higher revving, there is less rotational weight obviously.
If the 2.5 crank was forged or if you could get a steel billet crank with the same specs, then you could get past 7300 RPM.
The stock valve springs are good up to like 7150 RPM, the titanium ones are good up to like 12,000, and the forged rockers are good up to about 13,000 RPM.
The thing is when you start revving that high, there is a LOT of stress on the valve springs and the head itself, these heads have been known to crack on the #5 intake side valve due to stress. To sure if even shot peening would help that.
Of course to rev that high you would need a lumpy big overlap cam to produce those horsepower results needed to get revving that high, since the cam controls where the power is put out. And the car would need to idle like at 2700-3000 RPM so it doesnt stall.
The less weight on the crank, the less it lasts, when you start revving up that much higher, the engine is producing a lot more vibration on rotating and reciprocating parts, no matter how dynamically balanced it is.

But blueprinting reduces those loads on the parts by evening out the clearances on every part.

[Ball325]

knife edging as many described it does just that except you forogt its lighter but a good bit, which has the same effect as ltw internals and ltw flywheel. So theres a big plus there. and in a high performance motor like that youd be running dry sump so it wouldnt really matter at that point except that you want a LTW crank

it was done at a local shop and it was balanced