6m Crank in a 7mgte

[hatchet9mm]

Hey guys back again with another question I can't seem to figure out.

I am acquiring a 7mgte complete rebuild, but the guy selling it to me has put a 6m crankshaft in it. He said that since the 6 and 7M had the same displacement and the 6m crank is lighter, with 6m crank it will move the 7mgte redline from 72k to 75k.

I was just wondering if any of you guys have heard of this, if there are any mechanical/ balance issues with this, and if it is safe (now and later after I have bumped the boost and fuel)?

I do have a resurfaced 7mgte crank that I can put in it, if the consensus is it isn't sound with the 6mcrank in it.

Thanks preemptively

 

[supraguy@aol]

redline from 72,000, to 75,000?
Don't think I wanna spin any motor that fast. Actually, the early 7m's ALL came with the 6M crank. The later motors came with the 7M. The consensus is that the 6M gives you a slightly higher redline as it is lighter, but the 7M crank is fully-counterbalanced, so it revs smoother. Regardless, there's nothing wrong with the 6M crank, so no worries.

 

[jdub]

All 7M engines had a 6M crank until the '90 model iirc. The 6M crank is lighter allowing the higher red line on the earlier cars. The 7M crank is fully counter weighted and is a smoother running crank.
I'm using the 7M and had about 5 lbs removed during a knife edge job...the best of both IMO.

You can use either crank.

 

[Poodles]

Also, the redline is determined by the ECU not the crank...

 

[hatchet9mm]

Thanks you guys, but what do you mean by smoother. Revs aren't going to be erratic or anything right?

 

[Poodles]

It's just a smoother feeling engine (less vibration), revs won't be erratic, no.

 

[hatchet9mm]

redline from 72,000, to 75,000?

lol Brain fart on my part, 7.2k to 7.5k sorry

 

[gtsfirefighter]

FWIW, my previous supra had a 6M crank in it. My current one has a 7M crank. I can't tell the difference. They both idle and rev so smooth.:icon_bigg

 

[MA70witBoost]

6m crank revs faster due to the lighter weight but due to the inbalance at higher revs it tends to wear out rod bearings faster. 7M crank ftw!

 

[Kb865supra]

Since when did a 7M ever have a 7200 or 7500 RPM redline? Rev cut maybe.

 

[tbcmorris]

^^^^^^^ standalone maybe

 

[7M-KDL]

Since when did a 7M ever have a 7200 or 7500 RPM redline? Rev cut maybe.

i think the japanese cars have a 7k redline...

 

[tbcmorris]

Find out for sure before you "think"


This is the tech section

 

[7M-KDL]

Find out for sure before you "think"


This is the texh section

well..the tach redline is at 7k on japanese cars..whether it is accurate to the motor or not im not sure (hence i said "think"):icon_bigg

 

[hvyman]

^sure its not a jz car? got any pics?

 

[Poodles]

ummmm no, not on the 7M

 

[tbcmorris]

Your looking at a tach for a jza70

 

[7M-KDL]

^^^i dont think so, jz has 7.5-8k iirc...although, it is possibly that i am misinformed

 

[Poodles]

1G revs that high...

 

[tbcmorris]

You are misinformed. The main point is no factory 7mgte revved that high,or had a 7k redline on the tach