Crank choices...?

[DaltonD]

Hey guys, I have a 6m crank in my 7mGTE right now, and it has a little bit of damage on where the rod sits.
Should I spend the money for someone to fix it, or just use the money to buy a 7m crank? From what I understand, the 7m crank is better for boost.

 

[jdub]

The 7M crank is fully counter weighted...it's a smoother running crank, but you can't rev it as high stock. The 6M is lighter and you can rev it higher. I wouldn't call the 7M crank "better for boost".

 

[Rennat]

he probably read somewhere in the BC Crank intrest thread where someone said that because its heavier it loads the engine better to give you more boost.

7m>6m

there was a reason for the change.

 

[jdub]

Alrighty
Not too sure if I buy that one...especially since I just spent a nice chunk of cash knife edging and lightening a 7M crank about 6 lbs.

 

[HommerSimpson]

id like to see some pics of lightend 7m cranks...please..

 

[jdub]

Don't have a pic of mine yet Greg...here's one of IJ's though

 

[Rennat]

looks like all he did was taper the ends... which im sure with 12 of them it adds up.


i like the OEM crank... nice and heavy keeps it smooooth. haha.
hopefully my supra idels like my moms van... hella quite.

 

[jdub]

LOL..."knife edge" is a misnomer. What you are doing is removing weight and reducing oil windage. This has to be done by a machinist and then the crank has to be spin balanced...considering the weight of each rod/piston, flex plate or fly wheel, and dampner is the best way. Don't try this at home

 

[Rennat]

you mean i cant just take my 4'' angle grider to my crank huh? :sarcasm:

 

[IJ.]

looks like all he did was taper the ends... which im sure with 12 of them it adds up.


i like the OEM crank... nice and heavy keeps it smooooth. haha.
hopefully my supra idels like my moms van... hella quite.

You really have NFI sometimes....... :nono:

 

[Rennat]

wasnt trying to be super serious...

but doesnt a heavier crank keep the roational mass going a little easier so its a smoother engine? i know the flywheel and crank damperner help with this, other wise we would have 5lb flywheels on everything...

 

[jdub]

Maybe so, but there's a point where just kidding around comes across as BS.

A fully counter weighted crank helps to dampen harmonics...otherwise, it's balance not weight that has the biggest impact. Also, it's the rubber in the crank dampner (not weight) that makes it effective...case in point, the ATI dampner is a good 5 lbs lighter than the stock dampner.

 

[DaltonD]

I think I'll just buy a 7m Crank and pay someone to have everything balanced after I have all the parts I need.

 

[IJ.]

I've ran both cranks in the same motor within weeks of each other, 6M is far more responsive due to the lighter weight but has a harshness to it from idle to 8300.

7M is slower to spin up but is turbine smooth, my "solution" was to have 6lbs removed from a 7M crank for the best of both worlds

 

[suprarich]

Here is a pic of a 6m next to a 7m. The 7m crank in the pics has been put on a diet.

Here is more pics of the counter weights with material removed.

 

[jdub]

^^^ Hmmm...take off 5.75 lbs and balanced within 1/10 of 1 percent (good to 10,000 RPM) including the weight of the rods, pistons, flex plate (bolts too) and dampner. Add on the nitride job and she's better than new (at least as near perfect as you can get)

Like IJ said...the best of both worlds!

 

[suprarich]

^^^ Hmmm...take off 5.75 lbs and balanced within 1/10 of 1 percent (good to 10,000 RPM) including the weight of the rods, pistons, flex plate (bolts too) and dampner. Add on the nitride job and she's better than new (at least as near perfect as you can get)

Like IJ said...the best of both worlds!

Don't give out all the secrets just yet John.:icon_bigg

 

[HommerSimpson]

whats harder to find ? 7m or 6m cranks

 

[jdub]

7M...no doubt. Took me several weeks to find a good one. You can also look for a late model Cressida...the good think about one of these is it's likely led a fairly benign life

 

[suprarich]

Here is a pic of a finished 7m crank, from a cressida I think.