427TTA4

iTrader: (1)

Okay here's the story my mm6 was starting to going in 3rd so I was going to rebuild it but changed my mind so bought a mm12.After installation took it for a drive obviously felt shorter geared like how 5th feels but meet up with the buddies and that's where it hit me.My car is a 99 w/z51 pckg. and 3.15 RE,LG intake and a c5 z modified exhaust and would pull 2 care on my buds I/E cts v, walk on base c5 and would hang with my cousins lq9 cam. bolt ons z28. So we are hanging out and leave to hooters and you know what happends when gear heads drive some where so I do rolls with the v and c5 and they pull me by 2 cars?? Wtf?? Now I've done like 100 rolls with the v and I know that the mm12 slowed me down can anyone explain why??

skeeters65

iTrader: (1)

I would guess your car makes power in a part of the RPM range that was more suitable for the mm6 than the mm12 gearing..

SCM_Crash

iTrader: (2)

This sounds right.


The LS6 made power higher in the RPM range than the LS1. In addition, to make up for the shorter gearing, the LS6 pulls 500 RPM more than the LS1. Seems now you should change over to the LS6 heads, intake and get either an LS6 cam or a 224R cam. Set your rev limiter to 6500 and you should have a 99 Z51 w/ an LS6 drivetrain. Personally, I would have stayed with the MN6 with a stock motor. But you're better off at least getting an LS6 cam at this point.

BTW, if you car has 3.15 gearing, you had an auto originally. So your gearing is going to be completely different. The 4L60E ratios worked well with the 3.15s. But at this point, you're going backwards. You'd be best off upgrading to 3.42s.

427TTA4

iTrader: (1)

I think I have it figured out now the mn6 made my 3rd go to like 115 mph now it goes to 95 mph but in the gear ratios the 4th gear is the same gear from c5 and c5 z.So by adding more rpm to the gears will put me at higher mph from 3 to 4..so I guess its off to buy a cam

OneBadZ0Sick

Like crash said get a LS6 cam and some 243 heads, I see them all the time on CF for good prices. And btw your car is so sick Speedway White is my favorite color by far and with them CCW's its just nasty.

skeeters65

iTrader: (1)

Too bad its not Speedway White. 99's were Artic White.
But you are right Speedway White is the best. I love my SW Z06!!

SCM_Crash

iTrader: (2)

I agree... A used set of LS6 heads/cam usually go for $600-700. Pretty cheap horsepower, actually.

I think Speedway White started in 01. (I could be wrong about that, though)

I'd LOVE to have either an FRC or another Z06 in white.

OneBadZ0Sick

You are correct Speedway White was only for the 01 Z06's. Just sucks they got robbed of a few HP, but like I said they go pretty cheap for the amount of power you pick up from factory parts.

And I second that I am actually on the prowl for another vette and I have my eyes set on a 01 SW Z06.

His sig picture had me confused, his looks exactly like one. But had to read the fine print and your right his is a 99 but it still looks sexy Thought he had two cars there for a second.

jbs02somws6

iTrader: (1)

SCM_Crash hit the nail on the head before I could reply, regarding the ls6 powerband. You're blowing right through your powerband when you shift especially the 1st to 2nd and 2nd to 3rd gear changes. The M12 gears were exactly designed for the higher rpm capabilities of the z06 engine. OP, nice ride by the way.

ysb02

The mn6 is better for roll racing. The mn12 uses ratios that are good on the road course.

99C5JA

I've heard the contrary from people who road race. Those I talked with preferred the M6.

99C5JA

I disagree completely. No way I would go through the hassle of a head/cam swap (and the requisite tune) for the small gains a stock LS6 cam/heads give. You can make more power with just a decent cam and headers on an LS1.

If you are going to do that sort of swap, put in a moderate cam and an affordable stage one head from a vendor. You'll make a lot more power and be a lot happier.

ysb02

https://docs.google.com/spreadsheet/...US&pli=1#gid=0

Quick spreadsheet I threw together to compare the two. It should be close but not 100% on the money.

Probably the best setup would be 1-4 (well 4 doesn't matter) from the MN6 + 5/6 from the MN12.

427LS7HCI

Thats what I think as well

SCM_Crash

iTrader: (2)

Nobody's saying you can't make good power with a decent cam and headers. But to over-come the LS1 heads (which robs at least 25HP with headers), you need to go with a bigger cam which may not be what the OP wants. Especially because you're affecting driveablility. But the truth is that if you get an LS6 heads/cam set for $600, you're looking at 50HP minimum. (600/50 = 12) $12/hp. If you pick up headers and a cam you're going to spend ($700+$350) $1050 (before shipping) for about 60HP. (1050/60 = 17.5) $17.50/hp. My point was that you can pick up pretty good power with a used LS6 heads/cam. It'd be reliable, perfect driveability, smogable (if needed), and it would still sound stock. And you don't need a tune. You just have someone flash a stock Z06 tune and you're done. That doesn't cost more than $50 because anyone with HP tuners can just download (if they don't already have it) a Z06 tune and flash it to your ECM.

Also, keep in mind that with any cam-only setup, you're still going to have to pull the valve covers and replace the springs anyway. So add in the cost of springs. If you go with a LOT of lift, you'll have to fly-cut... So exactly how much power do you want to make without changing the heads?

What's easier and cheaper? LS6 kit. What's going to make more power? A big cam and headers. What's going to achieve his goals? Both. So why is this an argument?

Ragtop 99

iTrader: (7)

3-4 gear change is a big drop on the mn12. It is the opposite of what you want for roll racing unless your race ends at the top of 3rd.

Spacing of the mn12's 1-2 and 2-3 are similar to the mn6, but since 4th gear is 1:1 on both trannys, the mn12 has the big 3-4 spacing to make up for the numerically larger 1st ,2nd and 3rd gears.

jbs02somws6

iTrader: (1)

If you have a cam that pulls good up top (5000-6500 rpm) I'd say the M12 would be better for a street car. The 2nd to 3rd shift on the M12 is much better than the m6, and on the street this is where most races take place (2nd and 3rd). I don't think I'd run much past 100 anyway. Too much traffic where I live and I'm too old to get crazy on public roads.

Ragtop 99

iTrader: (7)

Both the 2-3 and 3-4 favor the base MN6 transmission and as the ratios are closer; i.e. rpms will drop less on the base tranny car.

WKMCD

iTrader: (2)

Sorry to interject some reality here but both the M6 and the M12 ratios are built around 4th gear which as has been pointed out it 1:1. On the M12 the ratios are closer together by having 1st gear taller and 6th gear lower. The ratios on the M12 tranny are closer together than the M6. If you are slower with the M12 - chalk it up to the time spent shifting more often or having a taller 1st gear.

Ragtop 99

iTrader: (7)

True, by a small margin, but for the purpose of acceleration on the street, 6th gear isn't a factor; at least for those of us w/o a monster build.

In the relevant range they are not closer as the OP is talking about races that go no higher than 5th gear. The MN12 has a bigger drop on the 2-3, 3-4, and 4-5. Here are the numbers: