Here is a pic of a crank I just knife edged and lightened. I removed 3.5 lbs from the entire assembly.

 

heres another

 

What is the crank out of??I have done the same with a few of mine..but have taken more like 11 lbs off from it.

 

This particular crank is for a Mitsubishi Lancer EVO 8 I am building for a car. Sorry its no Porsche, but the same principal none the less. There really is no downside to this type of modification, it lightens the rotating mass and frees up hp, as well as improve throttle transients and response. The motor is also getting lighter rods and forged pistons, ported and polished heads with modified combustion chambers, larger valves, springs and titanium retainers. Hand fabbed intake and exhaust manifold and running a larger Garret turbocharger with a stand alone engine management. The block was honed .030 over and I blueprinted and machined the entire block and its components to dead on dimensions. ARP hardware for the top end bottom ends and a modified twin disc clutch setup is being used.

 

The total wieght of this crank when it started was 29 lbs. 3.5 lbs from this unit was a drastic reduction. What crank did you take 11 lbs. from out of curiosity. I had a guy tell me he took 23 lbs from a 944 crank once. I must be doing something wrong.

 

I posted a reply to this thread here:
https://rennlist.com/forums/showthre...hreadid=111803

 

and i repsonded to your reply right after it

 

I need some understanding of this process! I am aware of this and why it is done but I have a couple of questions to enhance my knowledge.

What is being done to assure the grind is not out of balance? I can see where one(lobe?) could be machined more than another throwing the rotational weight out of balance?

The other is dry sump and the need to do this. Isn't a dry sump system designed to limit the amount of oil in the pan and if so how does this crank justify this process if the crank is barely submerged in oil? TIA! Dal

 

Wow! Hard to see where mist is that much of issue! Same principle as heavy air I guess. I appreciate the info! Dal

 

With a flat 6 or straight 4 you don't need any counterweights for the engine assembly to be balanced. The manufacturer put them there to reduce crank flex and bearing loads. I don't think that that removing the internal counterweight is a good idea. Might be OK if you are going to titanium rods.

 

Flat six or a straight four, don't you need a balanced crank to reduce rotational imbalance. The flat motor should balance out firing forces, but don't you still have static balance issues that will increase with rotation?

 

Grinding the journals on a crank does not change the balance. Also, remember that the counterweights are there to offset the 1st through third (usually) vibrations. On a flat or even number inline motor, the counterweights are not "balancing" the crank. Becuase of the throws, the opposite rod/piston set is providing the true balance. The counterweights are to reduce the bending and load on the main bearings.

Matt

 

Nope, you actually do grind a crank and put in new fillets. Most cranks can get up to 3 grinds before being junk.

Matt

 

A crank gets reground when the journals become damaged. You mount the crank in a purpose built grinder and proceded to frind off the correct amount of material. You then grind in new fillets and polish it. This is not an uncommon practice.

This is completely different than taking weight off a counterweight. That is for lightening. Grinding is for maintence.

Matt

 

Nice work Christian.

David Katz