Lightning the rotary mass?

[diegom6]

Hey folks,

does anybody while rebuilding their engines, besides balancing it, decided to take out few lbs of the flyhweel (if possible) and from the crank? If so, how many lbs did you take out of it? How did that change the actitud of the engine?

I'm not planing to modify my s14, but while I'm rebuilding it,I might be interested in make this to have the first gen 2.3L more happier along with 11.0:1 CR pistons.

Just wondering.

Thanks for any input.

PS: No, I won't buy the alu flywheel.

[ColinM]

Lightening the flywheel is definitely something I would do. The Evo3 (maybe it was implemented earlier) weighs about 12lbs and has no drawbacks. Most people don't mess with the crank unless they plan to run very high rpms.

[Jake]

Agreed! Don't mess with the crank.

Jake

[GGray]

I have on a few cars. Typically a good machine shop should be able to shave 5-6lbs off the stock flywheel. On my 87 325i they took 6.4lbs off. On my Miata they got right at 6lbs off.. Cost under 200 for each one. Including resurfacing.

I liked the results. Its kind of in the middle for wieght Stock vs LTW. No chatter and idles is not hurt.

[diegom6]

I guess I will shave some of the flyhweel only. I do not want to mess p the crank either. Just well balanced all the parts.

Thanks for the feedback.

[ADA///M]

Agreed! Don't mess with the crank.

Jake

How come no one wants to mess with the crank?

Isnt this a common mod when building an engine?

[Jake]

How come no one wants to mess with the crank?

Isnt this a common mod when building an engine?

Because the crank is counter balanced. I've not seen a lightened stock crank that doesn't maintain full counter weights. You can cut a lot of weight off by shaving them, but this is the wrong way to go about it. They will balance them after lightening them, but this is a static balance only, not dynamic.

There just isn't a lot of weight that can be removed while maintaining it's dynamic balance. It's not worth the trouble or the chances of screwing it up.

Jake

[Gregg]

I agree that for the cost one should look at the flywheel first. Clutches (smaller diameter, multi-plate) are also a consideration, although they take some getting used to when driving, imho. Not a lot of bang for the buck, either.

Knife-edging the crank is another option. Not saying it's for you and I've never done it on any engine I've ever owned, but it is out there. If not familiar with the process, take a look at a couple sites that deal with the forged crank from an RSX w/86mm stroke,

http://www.turbomagazine.com/tech/06...ice/index.html
http://forums.clubrsx.com/showthread.php?t=252476

Now when's the last time a Bimmer mag had anything that interesting? Makes me want to build a lean, mean 2.0L....

Hope this helps,

Gregg

[ADA///M]

Because the crank is counter balanced. I've not seen a lightened stock crank that doesn't maintain full counter weights. You can cut a lot of weight off by shaving them, but this is the wrong way to go about it. They will balance them after lightening them, but this is a static balance only, not dynamic.

There just isn't a lot of weight that can be removed while maintaining it's dynamic balance. It's not worth the trouble or the chances of screwing it up.

Jake

i hear you, but wouldnt knife-edging be lightening it also?

I'm pretty sure some people have done that before.

There has to be ways to lighten the crank safely.

What did the DTM cars run?

[Jake]

It does. But I don't think that mod amounts to anything worthwhile either. In my opinion, it's one of those things people do but doesn't offer any real advantages when the downside is a non-dynamically balanced bottom end. However, if you're designing a crank from scratch and profiling the counter weights is worked into the design, then I think it's a good idea. But not something for an already factory balanced crank.

I'd like to see one documented dyno run that shows the difference between a knife edged crank (or lightened) and a standard one. I just don't see it as giving you any real advantage. And considering this, and the potential for some speed shop to screw it up, it's not something I'd consider.

There was a sprint DTM crank that was not fully counter balanced. But that's a sprint engine. In fact, if that was your goal, an all out sprint engine, then sure. They're not meant to last long at all. But for a street and/or track engine, there just isn't any worth while mods to do to the crank in my opinion.

Jake

[ADA///M]

It does. But I don't think that mod amounts to anything worthwhile either. In my opinion, it's one of those things people do but doesn't offer any real advantages when the downside is a non-dynamically balanced bottom end. However, if you're designing a crank from scratch and profiling the counter weights is worked into the design, then I think it's a good idea. But not something for an already factory balanced crank.

I'd like to see one documented dyno run that shows the difference between a knife edged crank (or lightened) and a standard one. I just don't see it as giving you any real advantage. And considering this, and the potential for some speed shop to screw it up, it's not something I'd consider.

There was a sprint DTM crank that was not fully counter balanced. But that's a sprint engine. In fact, if that was your goal, an all out sprint engine, then sure. They're not meant to last long at all. But for a street and/or track engine, there just isn't any worth while mods to do to the crank in my opinion.

Jake

i love you :HeadsSpinning:

[Jake]

Shhh.... :hee:

Jake

[90///M]

When machining the crank, wouldn't decreasing journal size(although not by much) lighten the crank? Then a competent machinist/engineer could lighten and balance the crank. I haven't had experience with this on these cranks, and I don't know the smallest reliable main and conn. rod journal size, but I've worked with lightening [including the counter weights(but with a different harmonic balancer)] and balancing on v8's and had good results (of course these are completely different engines). However like you've heard already, if you are not going for high rpm (10k+)and/or max hp(sprint/drag cars) the benefits from these mods are not worth the risk in reliability. I feel converting to a dry sump oiling system would give you more benefits than knife edging/ polishing the crank (also no oil starvation issues!).

[diegom6]

When machining the crank, wouldn't decreasing journal size(although not by much) lighten the crank? Then a competent machinist/engineer could lighten and balance the crank. I haven't had experience with this on these cranks, and I don't know the smallest reliable main and conn. rod journal size, but I've worked with lightening [including the counter weights(but with a different harmonic balancer)] and balancing on v8's and had good results (of course these are completely different engines). However like you've heard already, if you are not going for high rpm (10k+)and/or max hp(sprint/drag cars) the benefits from these mods are not worth the risk in reliability. I feel converting to a dry sump oiling system would give you more benefits than knife edging/ polishing the crank (also no oil starvation issues!).

I don't think by machining the journals to the next super will dropp some "worth" weight that you can "feel" or the engine could benefit. Although, I might be wrong. We have a person that has a dynamic balance machine for cranks, so I will talk with him and see what he has to offer me and if it worth the extra risk and cash. If not, he will light the flywheel and balance the whole thing with out reducing the weight of the crank. No knife edge for me.

[keith]

Be careful if having a machine shop removing weight from a stock flywheel . I have actually seen the fly wheel explode and virtualy destroy a bell housing and cut into the transmission tunnel. Im contemplating welding and repairing the bell housing but im not sure its worth the effort. It is perfectly safe if its done right and makes a noticable difference.