Knife Edging a 7m crank....

[Whasian]

Is it worth doing? I am geting very mixed opinions with this. I am wanting to be able to rev at about 7500 (since the redline on my ecu is about that). What will it do to the integrity of the crank itself. Will it cause any sort of downside?

Whasian

*I have also heard of a crank scrapper... Are they any help at all.

 

[uenolove]

no help at all wankster..... dis is justin.... just kidding man i dont even know what your talking about lol

 

[AJ'S 88NA]

Knife edging is worth it IMO. It takes usually 5 lbs off the crank which means less rotating mass and quicker revs. Down side...I can't think of any, maybe somebody else can come up with some.

Crank scraper is a thin piece of metal to "scrape the oil off the crank. Again less rotating mass, putting the oil back down in the pan, less windage. Down side, you have to put spacers where the scraper stops so to speak.

There's a vendor on here that makes them. IMO worth it if you are going to be in the 7500 range alot.

 

[jdub]

I had my 7M crank knife edged, straightened, indexed and zero balanced w/ rods, pistons, flex plate, and damper weight included. Just over 5 lbs was removed...it's good to 10k RPM. The journals were also sized to stock diameter and the crank was nitrated, the the oil channel flushed.

Is it worth it...yes, if you plan on pushing the motor to high RPM and HP. You will have reduced oil windage on/around the crank. The downside is the cost and it has to be done by a machinist that knows what they are doing. If you go to this expense, use a fully counter weighted 7M crank. It will rev smoother.

A scraper kinda does the same thing oil windage wise...I'm actually debating running one or not.

 

[kmfdmk]

I opted for both. I've had my machine shop remove about 3 or so lbs off of my crank (and then had the whole rotating assembly balanced) and am also using a 6M crank scraper (7M block with 6M crank).

The upside to a knife edged crank is it's lighter, and has less rotational mass, therefore a bit more of your power (HP) can be transferred to the remainder of the driveline, and the fact that due to less rotational mass the engine will rev quicker and higher (assuming you had the whole rotating assembly balanced).

The downside to a knife edged crank is it's lighter, and has less rotational mass, therefore you lose a bit of your torque. Just like switching to a lightweight flywheel can take some getting used to (from keeping it from stalling on take-off).

The scraper as mentioned removes excess oil from the crank, but mainly reduces the oil present in the vortex created inside the crankcase/between the lower end of the block & the oil pan. Just as a boat propellor can spin much faster out of water, a crank can spin a bit faster w/ less mass/liquid/vapor in its way with a crank scraper. Personally I haven't heard of any "spacers" required to make them fit. I would say a crank scraper that required spacers wasn't properly designed.

Rich @ SIP Racing Mail Order sells these for about $90 bucks shipped.