alnukem

Hi, I have a somewhat unusual 81 vette with a stock L81 engine & a Magnuson MC220 Supercharger hooked to a Doug Nash 5 speed. It feels as if I still have the stock 2.72 gears in it. If I use the old "10" rule of "1st rear ratio x rear axle ratio" it would indicate that I should use the 3.08 ratio. Also, the original literature from Magnuson states that the 3.08 ratio is excellent. The difference in gear ratio is a little over 13%. Any input on this? I know it's a very unusual situation. Thanks in advance!

63mako

3.36-3.55

alnukem

Thanks 63Mako. I guess I should have posted the Transmission Ratios. Note how low 1st is. "3.27/2.13/1.57/1.24/1". I also wondered how the Positive Displacement blower affects diff ratio choice.

63mako

I figured it was a 3.27. Just like any power adder, likes low gears, tighter ratios and RPM. Others will know better, Im not a blower guy. That said a 13% ratio change is not real noticable and would barely be worth the effort. A 25% difference will be noticable SOP and a 3.36 to 1 in fifth is not bad to cruise with.

7t9l82

with experience on my 2 favorite play toys , when it comes to gears or breast implants always go one size bigger than you planned. don't pay to do something twice because you didn't go big enough. right suzy,?

AGVI

Yeah, we need pics of your car!!!

alnukem

Actually, they're in my album. Just click my name & the photo on the right with the 81 in it. Thanks guys!

gkull

A blower adds TQ across the rpm range. since a DN 5 speed is non-OD tranny a 2.72 is perfect. I ran a 4.11 with a .70 OD for many years and .7 X 4.11 is something like an overall ratio of 2.84 or so.

superchargers are made to run in lower rpm motors. where N/A motors need rpm to make power

qwank

I think I remember that car on Ebay not too long ago. Did you just buy it?

your gear pattern plate on the console says Richmond 5 speed on it i think. Do you have any idea where to get one of those? I've seen a few in cars and can only find the 6 speed version

Matt Gruber

1st gear is the same as my 61.(4.11x2.20 1st)
something else is wrong if it is not quick off the line. Put a boost gauge on it and make sure it is making boost.

vetteman1976

and the implant too .... couldnt resist!!!!

alnukem

Yes, I did just buy it in November. I would call Richmond to see if they would know where to source the plaque. truthfully, I haven't driven it much, I bought it in November & haven't put plates on it yet, so I drove it 25 miles in a snow storm to it's new home & a few blasts up & down my rural road. I'm just getting "yancy"! Spring is almost here!

ajrothm

Interesting blower setup on that car! I've never seen anything like that before.... Pretty cool stuff..

Yeah I'd leave the 3.08 in it since you have a Nash with the low first gear... Then you'll still have decent highway RPMs.. You "could" go to a 3.36 and still have OK highway cruise rpms but I doubt you notice much increase acceleration...Not enough to spending the money to change gears/diffs anyway..

tracdogg2

If you still have the Dana 44 in it your choice of ratios are 3.07 and 3.31.
Mike