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1G AWD trans in FWD?

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4gfun

Supporting VIP
2,009
55
Dec 10, 2007
Ask Me, Virginia
It looks rather likely that I'll have to replace the transmission in my 94 FWD Turbo Laser or have it rebuilt.

I have a working 1g AWD transmission laying around that I'd like to possibly use for it.

I know that I'd have to use a viscous coupling eliminator etc. I don't want to talk about that now, I'd like to stay focused on the below specific question please.

I also know that I can use taller tires to change my effective gear ratio. I know this already, I'd like to stay focused on the below specific question please.

Question:

1) This FWD Turbo Laser is intended to be a fuel economy build . The AWD transmission looks to have numerically lower 2nd - 5th gears than the FWD transmission, which would assist in the goal of lower RPMs and better fuel economy.

Please see this URL for a comparison:

http://www.roadraceengineering.com/eclipsetech/transgearratios.html

However, I notice that the final drive is numerically much higher on the AWD.

Does this mean that even though the gears are numerically lower in most of the gears on the AWD than on the FWD, the numerically higher final drive would actually cause a higher RPM (in 5th gear for example) and accordingly worse fuel economy when put into my 1g FWD Turbo Laser?

Feel free to explain all you want, and it is appreciated....but due to the sheer amount of questions, goals, and problems with this gorgeous lemon of a DSM, I need to come to conclusions ASAP so that I can fix my next problem.

Thank you!!
 
Last edited:
Hi Jose,
It can be a little confusing to sort through the different gear ratios when also looking at the final drive ratio as well. I like to use an online gear calculator at f-body.org/gears. If you punch in the various ratios and compare a fwd trans to AWD trans you'd see that the AWD trans has a worse ratio. In the stock trans, FWD @ 65mph=2700 rpm. AWD @ 65mph= 2900rpm. The biggest benefit for fuel economy is to swap 5th gear out of the awd trans and install into the FWD trans. This will lower your cruise rpm in 5th gear. Gears 1 through4 don't matter much for better gas mileage since you should try to shift up to the next gear as early as possible. If you swap the AWD 5th gear into the FWD trans 65mph = 2433 rpm.
 
Thanks very much as always Dave!! I won't waste my time with this to meet my objective of mirroring your old Laser.
 
So, I played around with the calculator at F-body.org and couldn't get it to give me the right information. Must be some input I didn't get right. :)

I found the below site and had better luck using that calculator:

http://www.csgnetwork.com/multirpmcalc.html

I made my assumptions based upon a 24.9 inch stock tire height and got the same calculations as Dave did.

I am getting a used FWD transmission that I hope works.

I have a spare working AWD transmission here that I can pull the .666 5th out of.

My target speed is no more than 79 MPH, which would leave me at 2949 RPM at that speed.

Do you think this is sufficient for Fuel Economy purposes or would you go with the EVO3 .617 (I think Dave did this) or even the TRE .500 if I can ever find a set?

At what point might I experience diminishing returns e.g. lower oil pressure, too hard to pull in 5th off of boost etc?

Would you just pull the 5th from the AWD transmission or go with another 5th gearset?

I know that we can be extreme here, but we are also pretty good at identifying diminishing returns. :)

Thanks!
 
The evo 3 5th gearset as well as the TRE 5th gearset have been long gone for years, only way you will find a set is a used one.

Just use the DSM AWD 5th gearset.
 
The evo 3 5th gearset as well as the TRE 5th gearset have been long gone for years, only way you will find a set is a used one.

Just use the DSM AWD 5th gearset.

Lol, I just typed this and you responded immediately. Thanks!
 
Nobody mentioned that the 93 94 fwd axle splines are different. Awd Trans won't work in those without modification or an axle change. Same for 92 or earlier fwd.turbo only.
 
Only ones that would work straight into the AWD are the 90 through early 91 25-spline axles. You would otherwise have to do a 92-94 AWD axle and halfshaft swap as they are 25-spline. Later FWD are all 27-spline.
 
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