Okay guys just picked up a MN12 out of a 02 Z06 with 16k on it been sitting 2 yrs for 200.00 bucks. My MN6 is getting old 80k and is popping out of gear and having hard time getting into gear at times. I drive my car spirited and some times at the strip. My motor is putting 435 RWHP & 415 RWTQ

1st ?

Which one is Better 6 or 12 What is the differance between the two of them

2nd ?

What would you do to the MN12 before you put into the car or would you fix MN6


3rd ?

Last is this something I could do myself or should I send it out to someone ?

Any help would be great I live in California so shipping it somewhere needs to be close SoCal. or Sac.

 

An MN12 for $200 with 16K is awesome. Put it in and enjoy. The shift points are closer so the SOTP feel will be like you added HP

 

Not to nitpick but MN6 is an RPO for the assembly line to prep the car for a manual transmission car ( i.e. clutch pedal, clutch master cylinder, manual tranny programing for PCM, ect. The two manual transmission RPOes are MM6 and M12. The M12 came in only the Z06.

So the Z06 will have RPO on the build sheet MN6 and M12. Coupes and convertibles with manual transmissions will have MN6 and MM6. Automatic transmissions will have MXO to prep the car for a M30 automatic.

Just so we all speak the same language.

 

Good info. Didn't know that. MM6 MN6. As for the OP question. Depending on how often you go to the strip and how you launch, you might want to have it gone through. Read here many times that the M12 is like the MM6 with 3.90 gears. So a more SOTP kick for you. Nice deal as well on the trans.

 

The gear ratios of the mn12 are shorter and closer in gears 1-3, than on the mn6.. This will keep your engine in the sweet spot or power zone when racing at the drag strip or on a road course.. You will definately notice a nice gain in performance.. Nice find and a killer price!!

 

it went the other way for me..

i got better time at the strip: went from mn12 to mn6.

but why? that´s maby my TQ i think the first gear helped me it´s longer, went 55mph in-stead of 45mph in 1st gear, and there for i hit a higher rpms (better powerband) when i shifted to the others gears 2-3 and 3-4.

MN6:
1-2@55mph
2-3@80mph
3-4@115mph (hits good/higher powerband)
MN12:
1-2@45mph
2-3@70mph
3-4@100mph (i´m shifting right after 1/8 and finishing the track in 4th)

i think MN6 whith 3.90 is the setup i would like...
then you take the good things from the mn12 but still hold the a bit longer 1st gear.
MN12 whith 3.90 then the 1st gear is to low i think.

but i liked the mn6 better too on the streets. can use the 2nd gear a lot more....

baezi

 

I know that an MN6 is an RPO designating that a particular C5 is to have a manual transmission. But what is a MN12?

 

The MM12 is junk. I'll give you $100 for it.

 

Thanks dieseldave for the info

That is some of the info I was looking for I am real close to your numbers with M6 Tranny


Its a deal I only need 650.00 for shipping LOL

Now I need to figure out what I should do to the M12 Before I put it into my car should I put in Carbon blocking rings and new synchro's (sp) I work in a Machine shop and feel I can do a micropolish on the gears and synchro's is it worth all the work I dont know

Dale

 

the gear ratios are different m12 is a 2.93 and m6 is 2.66 . the m6 is strongher due to it being a nurmaricaly lower ratio. meaning more meat on the gears

 

Here are the gearing differences between all transmissions in the C5

A4... MM6 MM12
3.06 2.66 2.97 -- 1st gear (MM12 16.5% shorter)
1.63 1.78 2.07 -- 2nd gear (MM12 16.3% shorter)
1.00 1.30 1.43 -- 3rd gear (MM12 10% shorter)
0.70 1.00 1.00 -- 4th gear (same)
----- 0.74 0.84 -- 5th gear (MM12 13.5% shorter)
----- 0.50 0.56 -- 6th gear (MM12 12% shorter)
2.29 2.90 3.28 -- reverse

Taller gears (numerically lower) give you better mileage, and taller gears work better for top speed. Cars with tall gears and low torque (not the C5 situation) end up using the shifter like a row boat. Taller gears "work the engine harder" as it takes longer to spin up the engine through the RPM band, but the trade off is a higher top end speed (thus are "taller").

Shorter gears (numerically higher) provide you with better acceleration, but you are higher in the rpm band at any given speed (all other things being equal), so you use more fuel. So shorter gears accelerate the car faster by climbing through the rpm range of the motor faster, but at the expense of top end speed (thus are "shorter")

Everything I just said is also impacted by the final drive gear. So, for example, a car equipped with an MM6 and 3.15 r&p is relatively the same as the same car with and MM12 and 3.05 r&p (at least in first gear)

As you can see, the MM12 is shorter in every gear but 4th, when compared to the MM6. What that translates too is a quicker revving engine, quicker acceleration and lower top end speed (unless you change your ring and pinion to compensate). The gearing is actually *not* closer together but the engine is revving quicker, making it seem so. The gearbox when viewed in total is actually "wider" than the MM6 with the 6th gear ratios being pretty close.

 

It has to have come from an 01 or newer, so it should already have carbon blockers. I'd say flush it with some good synthetic fluid, slam it in and enjoy. Keep your stocker to build up in case this one fails...for $200 who cares?

 

The Zs had a couple hundred more rpm than the standard C5 so speeds in the gears at the 6500 rpm red line were:

1st 50 mph
2nd 70 mph
3rd 100 mph

I imagine you would actually shift at a somewhat lower rpm to get max acceleration but if you can rev a little higher in third then you can come close to running the complete quarter in the first three gears. Power might be dropping off but it would probably be better than shifting to 4th with its large gap from third.

Bill

 

I like that info

Bill good info as I didn't take this factor into account my Redline is 7500 but have my shift light set at 6800 so I dont hit the limiter with the motor work I have done

Dale

 

Yeah, in "trannyspeak" the -6 tranny is actually a "close ratio", and the -12 is a "wide ratio". In the old days everybody wanted the "close ratio" M22 rockcrusher with the 2.20 1st gear, so they could install 4.54gears and not overpower the tires in 1st gear.
As stated above, the -12 has a much lower ratio in 1st, but the same ratio in 4th. So, the -12 will see more of a drop in RPM between each gear shift. Thus, the -12 is "generally" better for dragstrip work, giving a better 1st gear launch, which compensates for the greater RPM drop on the subsequent shifts. The -6 works better on road courses due to less RPM drop and smoother transition between gears.

Personally. for street driving, I prefer the -12, because it's so easy to launch, and feels so torquey on takeoff (Ford has known this for years). The increased RPM drop between gears is not really noticeable with the LS engine.

DG

 

The challenge is here most ppl prefer the MN6 gear ratio over the MN12 ratio for road racing.

the MN12 2nd and 3rd gears are too low. Where the MN6 is very good for a high torque motor

5th gear in the MN12 is great, but way too high in the MN6.

1st and 6th gears are immaterial on a road course. Most road races or track days on a road course, one only used 3rd and 4th gear once the race starts.

 

I have had:

MM6 with 3.42
MM6 with 4.10
M12 with 3.42

I hated the MM6 with 3.42 (stock motor) because I was in between 5th and 6th on the highway. I did the FFAT (Friday at the track)@ Summit Point and almost never left 3rd.

I loved the MM6 4.10 (heads/cam) because rowing through the gears FAST was really like driving a car! Hated @ Summit because I was shifting too much. 1/4 mile was excellent and the trap speed was good.

M12 with 3.42 (444/392 RWHP/TQ) was the right choice (current). With this much power, the 4.10 were useless. The FFAT was perfect (Z06 was intedned for the track) and really enjoyed the gearing. The 1/4 mile track didn't produce the trap speed I had hoped.

I know this isn't exactly apple to apple thing but take it for what it's worth. You can't have the both the road track and 1/4 mile track IMHO but I like my current combo since I think it's 2 out of 3 in my book (road track and street).

MM6 with 3.90 probably would be the best compromise. By the way, M12 with 3.42 is same as MM6 with 3.90 EXCEPT for 4th!

 

Summit Point is mostly a 3rd gear and a little bit of 4th gear( front straight) track, with a MN6 or MN12