out with the vette 2 days ago after replacing lower ball joints (Moog),slightly lowered ride height,new wheels' alignement...the car's handling was astonishing, and i safely went up to 120mph. the car wants do more than 120mph but with my 4.11 and m21 it's not possible.
i'm on budget and the only feasible solution is the replacement of the M21 gearset with the autogear M21Y .
i can't afford the replacement of the tranny with tko, t56, new diff...too much $$$.

before placing orders for m21y and related stuff...

look at this , the gear spread of m21y and tko 600 compared

M21Y : 2.20 , 1.50, 1 ,0.86 (32% , 33% ,15%)
tko600: 2.87, 1.89, 1.28, 1, 0.82 (34%, 32%, 22%,18% )

so , even if the M21y is actually a 3 speed +OD , the rpm drop between each gear ( which is the main concern with M21y in respect to the M21 ) is about the same as tko600.

the 0.86 OD , even if not that much , is enough for me ( 0.82 would have been better)

some questions:
-where to get the m21y gearset , aside of autogear and 5speed?
-i have a 1970 m21 with 10 spline input. should i check the output too before placing the gearset order?
-i will add the iron midplate. i have also a leak at the front seal ( need an overhaul kit? )
-what about the speedo gear? need a new one? i'm not expert...but 4th is not 1:1 anymore but 0.86

 

ah...found this right now at usd500, autogear made
http://www.riversidegear.com/categor...oduct-166.html

so i keep my main shaft and replace cluster gear and 2nd and 3d...
thoughts?

 

Switch to 3.55s and get the TKO later, or switch to the TKO and figure out whether or not you wanna go to 3.55s then.

Sounds like a band-aid. Get more gears!

You won't need a new speedo gear. It's based on tailshaft speed, which is the same regardless of the cluster.

 

I changed my 4.11 diff to 3.36 in my 68 SB 4 speed and the RPM drop by 600 at 70 mph
Avner

 

Just one observation; driving the M21Y would be like driving the TKO600, but while always shifting from second gear to fourth gear, bypassing third entirely.

Since your current gears are a 1.64 second and a 1.0 fourth, try driving around without using third gear and see if you're happy with it. If so, and the cost is reasonable, then the M21Y might be for you.

 

thanks
i can't go and don't want to go for 3.55 or so because my engine is an L88 with 11:1 CR and starts to make torque above 1800 rpm ( there's nothing under). so i need at least 3.73 or better 4.11 to stay away from pinging and to make the car easier to move from stand still or low speed.
even if i'll have a tko 600 , i couldn't cruise at less than 2000 rpm because of the cam.
my 4.11 has been overhauled by PO at great expense.simply a pity to remove it and pay usd 1000 for a new diff...
i have to work on the tranny...
bobbarry, i'll try the test you say but if i shift with my current M21 from 2nd to 4th i will actually have a 40% drop , when with the m21Y it's 33%. it could be misleading.
what i see is that both the famous tko600 and M21Y are same wide ratio, so with proper rear end gear ( 4.11 with m21y ) they should have about the same feel

 

If you're shifting @6000rpm, either the TKO600 or M21Y will drop you down to about 4000rpm, whereas your current close-ratio will drop you down to about 4500-4700rpm with each gear-change (2nd to 4th in your current M21 would drop you to about 3700rpm). The main differences is that that TKO600 gives you more rpms when shifting into 4th, more like your current shift into 4th gear.

There's lots of calculators out there to see what the different transmissions would do in each gear; here's a basic one:

http://wahiduddin.net/calc/calc_speed_rpm.htm

It really depends on how peaky or torquey your current motor is; if it's happy pulling from around 4000rpm, then you'd probably be happy with either of those transmissions. If it doesn't come alive until you're over 4500rpm, though, you might explore other close-ratio options, or consider a gear-vendors overdrive, but either of those will easily cost $2000+ more than OD'ing your M21, unless you find a deal on used pieces.

 

Autogear is a good choice if you are installing it and you know what your doing in there
If you have to pay someone to do the work then a 5spd OD would be the better all around choice to address your concerns of pinging and hard starts.

 

If that motor is truly an L-88, you should be able to do nearly 140mph with your current setup no problem. If you're drag-racing the car, then you're setup perfectly. If you're not, the car will be less fun to drive with the huge gear split.

I'd seriously consider going to the TKO and a 3.55 when funds permit - you'd have a lower first than the M21/4.11 and a taller 4th & 5th.

 

IIRC, doesn't that gearset utilize a repurposed 3rd as top gear? No transmission expert, but from what I've read that may not be the best of ideas.

 

thanks guys,
of course it's a quick easy fix to enjoy the car this summer-autumn.
i'm talking about spending just usd 650 for m21y gearset,iron midplate and seals versus usd 4500 for tko 600+3.55 diff or , even better ,usd 3500 for T-56 and keep my 4.11 (close ratio)
going back to some maths about tko600 and m21y , i've seen that in 1st , 2nd and 3rd the m21y with 4.11 is like using a tko600 with something between 3,08 and 3.36 :
2.20x4.11= 9,042
2.87x3.08=8.839
2.87x3.36=9.64
--------------------------------------
M21Y : 2.20 , 1.50, 1 ,0.86........(32% , 33% ,15%)
tko600: 2.87, 1.89, 1.28, 1, 0.82 (34%, 32%, 22%,18% )

bobbarry
yes the rpm drop due to wide ratio could be somewhat an issue, but would be the same if i go for a tko 600.it would be better to stay with a close ratio of course (T-56 would be better). btw my motor ( an L88 build with ZL1 cam , CR reduced to 11:1 to run on pump gas , and dual plane intake to help at low speed) has a quite flat torque curve starting from 3000 rpm. i suppose it would be fine with a wide ratio. i think people are running tko600 with 3.08 or 3.36 and less powerful motor than mine and are happy anyway.

TSW,
not an expert too of trannies and we are figuring out with my mech how the m21Y works.
the gearset includes the replacement of cluster gear , 2nd and 3rd only

 

That M21Y is not well thought out. I don't even understand what they are trying to accomplish other than if you have a big block with 4:11 rear end you might be able to buzz on the highway at less than 6000RPM at 70mph

I don't know the cost but for another grand or two you can get a TKO 600 and then you have something to work with. I have the .64 OD with a 3.08 rear end and get good mileage on the highway. The first 4 gears are for power and OD is for cruising on the highway at 80mph @ 1800RPM

 

motorhead ,
yes the m21y is intended by autogear for BB and 4.11 owners...
the m21Y conversion will cost me just usd 650 parts and 120 work

some more brainstorming about the need of so tight gear ratios like in the m21-m22. i think not ... no modern car seems to use anymore so tight gears. i report below the gear ratio of the corvette Z06 compared to M21 , M21Y and tko600 .

i'm going to test drive a Z06 on monday at the racetrack (having my very first racetrack lesson). i'll see if i find myself fine with that gear spacing

Z06 2.97 /1.94/ 1.35 /1 / 0.84/... (35%-30%-26%-16%)
M21Y : 2.20 , 1.50, 1 ,0.86........(32% , 33% ,15%)
tko600: 2.87, 1.89, 1.28, 1, 0.82 (34%, 32%, 22%,18% )
m21-22: 2.20, 1.64, 1.28, 1 (25%, 22%, 22%)

ah...i forgot another thing...i'm so reluctant to go for 5 speed also because i'm trying to keep the car stock so it will match the FIA or similar rules (no mods to suspensions,steering...and tranny ).that's why a went for a flat tappet L88 instead than a roller cam BB. it's always in my mind to have the car racing in hillclimb events or vintage racing

 

You do realize to run in FIA, you're gonna have to chop your car up quite a lot, right? If the car in your av is the car we're talking about, don't know that I'd want to do that.

Also, it's hard to compare a Z06's LS6(I'm assuming LS6 because you listed the gear ratios the LS6 car has. The LS7 has the "base" T56 gearing) to an L-88, much different power curve.

 

shark
to race the car is always on my mind...i know i have to do a lot if ever, but at least i'm trying to don't go too far from that project doing mods with aftermarket parts.

can you list the ls7 z06 gear ratio you know? i found those i listed on a forum,but you say are those of the c6

 

I agree with you about the intended target for sales of the M21Y. It seems thought the market is getting smaller and smaller each year, is this a new product ?

Also Muncie has had a 5 speed version of their tranny in the works for some time now. It is supposed to look the same only have 5 gears. I don't know anything about it other than rumors. Have you looked into it ?

Good luck on whatever you do and that M21Y would be better for a big block with a 4:11 rear end

 

Yes.

The C5 Z06 used the ratios listed above (plus a 0.56 overdrive gear)

The C6 Z06 uses the following:
2.66, 1.78, 1.3, 1, 0.74, 0.5

 

What is the stock rear gear for that ?

 

3.42s for all manual transmission vettes, 97+.

The autos typically have a tall ratio standard, and a slightly lower ratio option (G92). They changed the gearing schemes for autos in 2006 when they brought out the 6-speed auto.

 

thanks for the info

so here it is :

33%-27%-23%-26%-...

all this brainstorming about close ratios just because i always felt that the m21-m22 gears are spaced too tight but in previous threads about the m21-m22 (and transmissions in general) strenght seemed mandatory to have such tight gears or failure would occur with power shift. but i see that no transmission , except m20-21-22, uses such tight gears

corrected

Z06 2.66 /1.78/ 1.3 /1 / 0.74/... (33%-27%-23%-26%-...)
M21Y : 2.20 , 1.50, 1 ,0.86........(32% , 33% ,15%)
tko600: 2.87, 1.89, 1.28, 1, 0.82 (34%, 32%, 22%,18% )
m21-22: 2.20, 1.64, 1.28, 1 (25%, 22%, 22%)