New MN12 GTO Tranny Review (in Fbody)
10-29-2007, 11:19 AM
#1
New MN12 GTO Tranny Review (in Fbody) INTRO
I recently installed a brand new Six Speeds Inc MN12 GTO transmission into my 2002 Z28. I installed it a little over a week ago and just last night finished putting all 500 of the recommended city-type driving break-in miles on it (they said a lot of stop and go).
A little about my setup: Mild heads and cam with bolt-ons, Spec Stage 2 clutch, 3.5" aluminum driveshaft, Moser 12-bolt with 4.11 gears, stock SS wheels with Nitto drag radials. And now one MN12 transmission.
DAILY DRIVING
I don't actually daily drive the car, but I've been putting all of the break-in miles on it this past week and enjoy it a lot more than I did with the 4.11s and stock tranny. Something about the 4.11s and MN6 gearing felt very awkward to me and often kept me either very high in one gear or too low in another on the streets in my area. The new tranny has solved this problem.
I do have mixed reviews about the gearing. On one hand, I absolutely love first through fourth. First and second are VERY short; they get me going quickly and I get through them very quickly, especially with the 4.11s out back, but they lend themselves very well to street driving. Same with third, although it's not quite as big of a difference as first and second, and it makes the switch to the 1:1 fourth gear very smooth. When pulling away from a stop, I don't have to rev it as high as I used to to prevent from feeling like it's bogging on me.
As far as fifth and sixth go, sixth keeps me in a drivable RPM when just cruising around side streets, which makes me happy, but fifth is pretty much useless. The difference in RPM between fourth and fifth, and then fifth to sixth is so slight that I rarely use fifth gear anymore other than just a quick skip to sixth, if that. If I had to rebuild this tranny, I would consider swapping the MN6 fifth and sixth back into it if possible, but perhaps I will get used to them.
It was suggested to me that fifth and sixth were made shorter, even though you typically don't race in these gears, because the GTOs are much heavier and it helps them pickup speed and keep going with less effort. Makes sense to me.
On the highway, there is a pretty large difference in sixth, and this is why I originally would have considered going back to the MN6 sixth gear, although I'm getting used to it the more I drive it. I used to cruise at 70mph at just under 2000RPM, about 1975 or so. Now at 70, I am over 2200. The down sides are gas mileage and it's much louder on those long trips. The upside is that it makes passing much easier and quite a bit more fun, as the car pulls quite a bit harder at that RPM. No need to downshift if I want to make a quick pass.
NOT DAILY DRIVING
I have only gone WOT a few times since finishing the break-in miles, as I just finished last night, but when I did, I was impressed. The car went from first to fourth VERY quickly, but the shifts seemed smooth and it felt to me like the car was in a great power range the entire time. It pulled hard.
In fact, first gear has become useless. I don't know if it's the gearing, the colder weather, or both, but even with the Nittos, if I punch it from anywhere decent in first, the car goes sideways and I have to short shift to second or let off.
Downshifting is also completely different. When the car was totally stock (ie stock tranny and 3.42s), I would downshift to second for anything below 60mph and be in a good range. Last night, I dropped my speed to 55mph and downshifted to 3rd and was up in the HIGH 4000rpm range. I am going to have to completely reevaulate where my best speeds are from a roll and where I should downshift to if I have to make a quick decision.
I have not had it at the track yet, but I will be going to Atco, NJ on November 10th and will post a review after that day. I just installed linelock to help with the burnouts in case my first gear traction issue is still a problem. Hopefully the track will be prepped well (I hear good things about Atco but have never been there). I will be purchasing some Mickey Thompsons for next season, but don't have the money right now.
CONCLUSION
I plan on doing some more "testing" through the rest of the week and will post another thread when I have some more seat time without a leash now that it's broken in. So far overall, I am happy with the swap and, as it is not a daily driver, the 1-4 gears much more than make up for the useless fifth and crappy gas mileage sixth. More to come after further testing!
I recently installed a brand new Six Speeds Inc MN12 GTO transmission into my 2002 Z28. I installed it a little over a week ago and just last night finished putting all 500 of the recommended city-type driving break-in miles on it (they said a lot of stop and go).
A little about my setup: Mild heads and cam with bolt-ons, Spec Stage 2 clutch, 3.5" aluminum driveshaft, Moser 12-bolt with 4.11 gears, stock SS wheels with Nitto drag radials. And now one MN12 transmission.
DAILY DRIVING
I don't actually daily drive the car, but I've been putting all of the break-in miles on it this past week and enjoy it a lot more than I did with the 4.11s and stock tranny. Something about the 4.11s and MN6 gearing felt very awkward to me and often kept me either very high in one gear or too low in another on the streets in my area. The new tranny has solved this problem.
I do have mixed reviews about the gearing. On one hand, I absolutely love first through fourth. First and second are VERY short; they get me going quickly and I get through them very quickly, especially with the 4.11s out back, but they lend themselves very well to street driving. Same with third, although it's not quite as big of a difference as first and second, and it makes the switch to the 1:1 fourth gear very smooth. When pulling away from a stop, I don't have to rev it as high as I used to to prevent from feeling like it's bogging on me.
As far as fifth and sixth go, sixth keeps me in a drivable RPM when just cruising around side streets, which makes me happy, but fifth is pretty much useless. The difference in RPM between fourth and fifth, and then fifth to sixth is so slight that I rarely use fifth gear anymore other than just a quick skip to sixth, if that. If I had to rebuild this tranny, I would consider swapping the MN6 fifth and sixth back into it if possible, but perhaps I will get used to them.
It was suggested to me that fifth and sixth were made shorter, even though you typically don't race in these gears, because the GTOs are much heavier and it helps them pickup speed and keep going with less effort. Makes sense to me.
On the highway, there is a pretty large difference in sixth, and this is why I originally would have considered going back to the MN6 sixth gear, although I'm getting used to it the more I drive it. I used to cruise at 70mph at just under 2000RPM, about 1975 or so. Now at 70, I am over 2200. The down sides are gas mileage and it's much louder on those long trips. The upside is that it makes passing much easier and quite a bit more fun, as the car pulls quite a bit harder at that RPM. No need to downshift if I want to make a quick pass.
NOT DAILY DRIVING
I have only gone WOT a few times since finishing the break-in miles, as I just finished last night, but when I did, I was impressed. The car went from first to fourth VERY quickly, but the shifts seemed smooth and it felt to me like the car was in a great power range the entire time. It pulled hard.
In fact, first gear has become useless. I don't know if it's the gearing, the colder weather, or both, but even with the Nittos, if I punch it from anywhere decent in first, the car goes sideways and I have to short shift to second or let off.
Downshifting is also completely different. When the car was totally stock (ie stock tranny and 3.42s), I would downshift to second for anything below 60mph and be in a good range. Last night, I dropped my speed to 55mph and downshifted to 3rd and was up in the HIGH 4000rpm range. I am going to have to completely reevaulate where my best speeds are from a roll and where I should downshift to if I have to make a quick decision.
I have not had it at the track yet, but I will be going to Atco, NJ on November 10th and will post a review after that day. I just installed linelock to help with the burnouts in case my first gear traction issue is still a problem. Hopefully the track will be prepped well (I hear good things about Atco but have never been there). I will be purchasing some Mickey Thompsons for next season, but don't have the money right now.
CONCLUSION
I plan on doing some more "testing" through the rest of the week and will post another thread when I have some more seat time without a leash now that it's broken in. So far overall, I am happy with the swap and, as it is not a daily driver, the 1-4 gears much more than make up for the useless fifth and crappy gas mileage sixth. More to come after further testing!
Last edited by PewterScreaminMach; 10-29-2007 at 11:31 AM.
10-29-2007, 03:46 PM
#3
Hahaha, that's too bad you don't want to race, because it's looking like Wednesday afternoon/night we might be having a little "get together", if you know what I mean. There will be "testing" going on... 
PS - I think my post is too long for anyone to get all the way through, hence the lack of responses.
PS - I think my post is too long for anyone to get all the way through, hence the lack of responses.
10-29-2007, 09:44 PM
#5
Why do you say that? Personal experience? I don't expect it, but, of course, I do hope for it. The car definitely stays in the power band better through the first few gears and it feels like it pulls very hard, most likely because of that. I'll let you know how it goes after I take it to the track on the 10th!
10-30-2007, 06:40 AM
#6
provided the car can stick it should do an easy 1.6 60 foot.
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10-30-2007, 07:42 PM
#8
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yeah i love mine.
i kno what you mean about the 5th and 6th gearing
your rite about where i am w/ rpm and speed. youll get used to it.
i went faster after putting the MN12 in my car.
only down side to the gearing is the 3-4 drop in rpm, but ive gotten over it, i shift into 4th a lil before the 1/8 and it pulls me through the traps.
youll def need MT DRs to hook, the nittos will prolly just spin
-brandon
i kno what you mean about the 5th and 6th gearing
your rite about where i am w/ rpm and speed. youll get used to it.
i went faster after putting the MN12 in my car.
only down side to the gearing is the 3-4 drop in rpm, but ive gotten over it, i shift into 4th a lil before the 1/8 and it pulls me through the traps.
youll def need MT DRs to hook, the nittos will prolly just spin
-brandon
10-30-2007, 08:10 PM
#9
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More gear is needed when less power is on tap . It makes up for the lack of torque . If you have the torque/power on tap , there is no need for the lower gear . The lower gear transmission is also weaker by nature due to the gear ratio itself . Why do you think power glides are used in racing ? They have a soft 1st gear and can be built to hold a hell of a lot of power .
10-30-2007, 08:22 PM
#10
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Also the close ratio is better to keep the engine in its power band . Take a look at the older 4 spds and the different ratios available for the different engine sizes . The big blocks had a different gear ratio than the small block units used .
10-30-2007, 08:57 PM
#11
More gear is needed when less power is on tap . It makes up for the lack of torque . If you have the torque/power on tap , there is no need for the lower gear . The lower gear transmission is also weaker by nature due to the gear ratio itself . Why do you think power glides are used in racing ? They have a soft 1st gear and can be built to hold a hell of a lot of power .
There is NO issues of strength on a stock MN12 trans, NOR on his SixSpeedsInc MN12 gears
PG are used when you have cars that make too much power and need to be toned down in bracket racing. Often when the class doesnt allow electronics such as a 2 or 3 step, or a trans brake.
In a race more gears are better, a auto is quicker and more consistant, but often doesnt have more then 4 gears (only 3 are useable). If these cars had 7 speed transmissions with the last gear 1:1 or even a 0.90 to 1, it would keep the car in the power band quicker and longer and ultimately be faster.
Look at a 1st gear ratio of a th400 vs a t-56 and compare it to a given rear, the overall ratio is fucked up
10-30-2007, 09:52 PM
#12
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Part what you are saying is true and part of it is incorrect .
I believe the MN12 gears are not as strong as the T56 ratio gears due to the lower gearing of the MN12 . Look at T5 gearing for example .......... the 3.97 ratio 4 cylinder box is weaker than the 2.95 T5Z . Why is that ? Both units are the same size and use the same type and size of bearings yet one is rated a lot higher than the other one . Look at the TKO500 and TKO600 , both are identicle yet one is rated at 100 hp higher and uses a softer 1st gear too .
Why do rear end gears get weaker the higher numerically they get ? It has to do with the size of the gear in relation to the other gear its turning . Same thing is true with a transmission .
As for autos being quicker , they are quicker because there are no miss shifts and they do not shock the drivetrain as badly as a stick car does . If you could shift a stick as quickly and error free as a auto car , it should go faster because they typically use less horsepower than a auto with a big convertor . But thats not going to happen so who cares .
Power glides do infact tame higher powered cars to allow them to put more power to the ground and still harness it better than a lower geared transmission would . This is the reason that the after market has taken a liking to them and developed all kinds of after market goodies for them . A power glide sucks in a low powered car because of the softer 1st gear but is much stronger than a TH350 or TH400 .
I believe the MN12 gears are not as strong as the T56 ratio gears due to the lower gearing of the MN12 . Look at T5 gearing for example .......... the 3.97 ratio 4 cylinder box is weaker than the 2.95 T5Z . Why is that ? Both units are the same size and use the same type and size of bearings yet one is rated a lot higher than the other one . Look at the TKO500 and TKO600 , both are identicle yet one is rated at 100 hp higher and uses a softer 1st gear too .
Why do rear end gears get weaker the higher numerically they get ? It has to do with the size of the gear in relation to the other gear its turning . Same thing is true with a transmission .
As for autos being quicker , they are quicker because there are no miss shifts and they do not shock the drivetrain as badly as a stick car does . If you could shift a stick as quickly and error free as a auto car , it should go faster because they typically use less horsepower than a auto with a big convertor . But thats not going to happen so who cares .
Power glides do infact tame higher powered cars to allow them to put more power to the ground and still harness it better than a lower geared transmission would . This is the reason that the after market has taken a liking to them and developed all kinds of after market goodies for them . A power glide sucks in a low powered car because of the softer 1st gear but is much stronger than a TH350 or TH400 .
10-31-2007, 10:07 AM
#13
Well regardless, I'm not making anywhere near the 700rwhp/700rwtq rating of this transmission, and I don't believe it's the gears themselves that tend to be the first to go on a broken transmission anyways, correct me if I'm wrong, so I hopefully don't have anything to worry about in that department yet.
As far as the powerband goes, this car absolutely puts me in a better powerband, especially during a roll race. I raced my friend last night who has always pulled on me; he makes about 20 more rwhp and 10 more rwtq. We went from a few slow to fast rolls and minus a few shifting issues I had, it was a pretty dead even race, with me even just slightly pulling once we got into 5th for a brief time. Of course, the end result will most likely always come down to driving, which I'm working on, but it has evened up the score as far as the cars are concerned.
Now, I will let you know how it goes at the track next weekend (November 10th). It is a better track than where I usually race, so I am hoping for a slightly better time anyways, but we should be able to tell how the transmission either did or did not help. I'll post results.
As far as the powerband goes, this car absolutely puts me in a better powerband, especially during a roll race. I raced my friend last night who has always pulled on me; he makes about 20 more rwhp and 10 more rwtq. We went from a few slow to fast rolls and minus a few shifting issues I had, it was a pretty dead even race, with me even just slightly pulling once we got into 5th for a brief time. Of course, the end result will most likely always come down to driving, which I'm working on, but it has evened up the score as far as the cars are concerned.
Now, I will let you know how it goes at the track next weekend (November 10th). It is a better track than where I usually race, so I am hoping for a slightly better time anyways, but we should be able to tell how the transmission either did or did not help. I'll post results.
10-31-2007, 06:31 PM
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thats the same ratios as in the 93 LT1 trans that came w/ the 3:23 rear gears.
i'm looking for a way to ge the .84 5th in my 94-97 LT1 T-56 w/out f'ing w/ the 1st-3rd ratios. w/ the 93 T-56 and the GTO T-56, thereis a big jump when going from 3rd to 4th. not a big deal on a street car. it is on a road race car.
i'm looking for a way to ge the .84 5th in my 94-97 LT1 T-56 w/out f'ing w/ the 1st-3rd ratios. w/ the 93 T-56 and the GTO T-56, thereis a big jump when going from 3rd to 4th. not a big deal on a street car. it is on a road race car.
