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Best way to Increase Freeway Speeds - Transmission or Rear End?


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croat77
New User

Mar 5, 2017, 1:08 PM

Post #1 of 5 (250 views)
Best way to Increase Freeway Speeds - Transmission or Rear End? Sign In

Hello Everyone, new to the forum and hoping to find some knowledge.
I have a 1994 Chevy 3500 crew cab, 6.5 turbo diesel, 2wd with a 4.10 rear end.
It is a manual "5" speed NV4500 with - L, 1st, 2nd, 3rd and OD.
On the Freeway in OD at 65MPH the RPM's are 2,500 and I don't want to take it higher with it being a diesel.
I'm seeking advice on the best way to get it to 75MPH+ at 2,500 RPM (or less).

1 - does GM make a newer transmission with a true 5 speed that would get me there and if so, would it take much modification. (input shaft, etc.)
2 - would putting in 3.55 gears in the rear end get me there?
Which one would get me there without sacrificing power?
(this thing is already not going to win any races)

Any help is greatly appreciated. Thanks!


kev2
Veteran
kev2 profile image

Mar 5, 2017, 2:36 PM

Post #2 of 5 (238 views)
Re: Best way to Increase Freeway Speeds - Transmission or Rear End? Sign In

75mph sounds like the you are already pushing the limit.
There is a trade off between power band vs speed - 4:10 being power and 3:55 being speed.
This being a 2WD changing to 3:55 and reprograming* would be easier, BUT why?


*the PCM likely has a 3:55 option with tech II.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Mar 5, 2017, 4:53 PM

Post #3 of 5 (236 views)
Re: Best way to Increase Freeway Speeds - Transmission or Rear End? Sign In

The 3:55 will accomplish the speed but the loss of power an acceleration you give up may not be worth it. It will be harder on the clutch also.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



croat77
New User

Mar 6, 2017, 11:18 PM

Post #4 of 5 (204 views)
Re: Best way to Increase Freeway Speeds - Transmission or Rear End? Sign In

Thanks gents.

I didn't know lowering the ratio couldput stress on the clutch. Can you please elaborate a little more on that?
Also, would it then be beneficial to meet in the middle with 3.73's?

There are a lot of freeways in CA with 70 mph speed limits and it's 75 between CA and Phoenix.

Thanks!


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Mar 7, 2017, 6:46 AM

Post #5 of 5 (195 views)
Re: Best way to Increase Freeway Speeds - Transmission or Rear End? Sign In

Look at it like taking off in second gear instead of first. The clutch has to slip more to get the vehicle moving and if the vehicle is loaded with weight, the issue is that much worse.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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