Doug Nash overdrive - The 1947 - Present Chevrolet & GMC Truck Message Board Network

19Suburban69 · 07-19-2019, 10:56 PM

Bought DN2 unit attached to rebuilt 400 for $700. Wanted to go with 4L80, but cost was an issue. Had to shorten front shaft and add yoke to connect to unit. The 3 wires were just cut off and I don’t have any idea how to wire it up thru a switch. Anyone out there know anything about these units for wiring?
Drove it today for first time and noticed it’s in overdrive. A little sluggish around town, but not too bad. On freeway it did exactly what I was hoping for, dropped rpm by 500. First big block I’ve owned and didn’t think cruising down freeway at 3000 rpm was the best for engine.

**kwmech** · 07-20-2019, 01:34 AM

My dad has one in his 83. May have the truck in Colfax next week to check the AC system.

geezer#99 · 07-20-2019, 08:59 AM

Why is everybody so afraid of rpm on a motor?
A big or small block will run 3000 rpm all day, every day!
That’s right in the rpm range where they’re most effficient.
However, here’s some info on DN2.
https://www.bangshift.com/forum/foru...-range-revival

AcampoDave · 07-20-2019, 09:21 AM

Quote:

Originally Posted by geezer#99

Why is everybody so afraid of rpm on a motor?
A big or small block will run 3000 rpm all day, every day!
That’s right in the rpm range where they’re most effficient.
However, here’s some info on DN2.
https://www.bangshift.com/forum/foru...-range-revival

I think part of it is that they seem loud as hell at higher rpms especially if you have performance exhaust.

19Suburban69 · 07-20-2019, 10:09 AM

Geezer#69, I found that write up and registered in the site, but photos and tech write up are blurred. Looks like it’s exactly what I need. I sent message to OP, but it was an old write up and he hasn’t responded yet.

**kwmech** · 07-20-2019, 11:04 PM

Quote:

Originally Posted by geezer#99

Why is everybody so afraid of rpm on a motor?
A big or small block will run 3000 rpm all day, every day!
That’s right in the rpm range where they’re most effficient.
However, here’s some info on DN2.
https://www.bangshift.com/forum/foru...-range-revival

That's not always true, cam selection, gear ratio, tire size and weight of vehicle all come into play. An older suburban I had got its best mpg at 55mph with 3.73s and an overdrive. About 1800rpm. I'm currently running a big block,--getting over 2500 rpm and you can almost watch the fuel gauge move

'63GENIII · 07-21-2019, 10:49 AM

Quote:

Originally Posted by kwmech

That's not always true, cam selection, gear ratio, tire size and weight of vehicle all come into play. An older suburban I had got its best mpg at 55mph with 3.73s and an overdrive. About 1800rpm. I'm currently running a big block,--getting over 2500 rpm and you can almost watch the fuel gauge move

Aint that the truth. With the old 396 / 400 combo I had the tach needle would go right and the fuel needle left almost in unison!

The 7.4 / 4500 set up seems to get better mileage (or I have to fill up less often anyways). Need to get a speedometer reverser on the NP205 since the speedometer drive rotates opposite of the T221. Mileage does seem much better. It just costs less to drive overall now.

Tom · 07-22-2019, 03:58 PM

Quote:

Originally Posted by geezer#99

Why is everybody so afraid of rpm on a motor?

Because we like gas mileage and not being buzzed like a vibrator everywhere we go. Nobody is afraid of it, we just don't want it constantly.

rpmerf · 07-23-2019, 08:09 AM

Quote:

Originally Posted by kwmech

I'm currently running a big block,--getting over 2500 rpm and you can almost watch the fuel gauge move

I had an 87 Suburban once with a 350, 3 speed, 4.10 rear, 21 gallon tank. You can see the fuel gauge move on the highway if you look close enough. My 70 is almost as bad, the only things saving me are the 31.7" tires and a vibration that keeps me under 60 mph.

19Suburban69 · 07-23-2019, 09:20 AM

I bought the truck from member here, Ranger Danger. He had installed 40 gallon tank so it helps on long trips, but is a killer when paying to fill it up. The cost of installing overdrive is never going to pay for itself unless trans was free, but just wanted to drop rpm. Still looking for wiring diagram to finish the job.

DieselSJ · 07-26-2019, 03:24 PM

Quote:

Originally Posted by geezer#99

Why is everybody so afraid of rpm on a motor?
A big or small block will run 3000 rpm all day, every day!
That’s right in the rpm range where they’re most effficient.
However, here’s some info on DN2.
https://www.bangshift.com/forum/foru...-range-revival

Because 9mpg on a 454 without an overdrive, and 12mpg with an overdrive is a huge difference.

07-19-2019, 10:56 PM	#1
19Suburban69 Registered User Join Date: Nov 2018 Location: Applegate, Ca 95703 Posts: 53	Doug Nash overdrive Bought DN2 unit attached to rebuilt 400 for $700. Wanted to go with 4L80, but cost was an issue. Had to shorten front shaft and add yoke to connect to unit. The 3 wires were just cut off and I don’t have any idea how to wire it up thru a switch. Anyone out there know anything about these units for wiring? Drove it today for first time and noticed it’s in overdrive. A little sluggish around town, but not too bad. On freeway it did exactly what I was hoping for, dropped rpm by 500. First big block I’ve owned and didn’t think cruising down freeway at 3000 rpm was the best for engine. __________________ 1955 Chevy, 2 dr post, my first car 1969 Chevy C20 Suburban, 6.0 LS w/4L80 2001 Silverado Z71, 5.3 extended cab

07-20-2019, 01:34 AM	#2
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,420	Re: Doug Nash overdrive My dad has one in his 83. May have the truck in Colfax next week to check the AC system.

07-20-2019, 08:59 AM	#3
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,528	Re: Doug Nash overdrive Why is everybody so afraid of rpm on a motor? A big or small block will run 3000 rpm all day, every day! That’s right in the rpm range where they’re most effficient. However, here’s some info on DN2. https://www.bangshift.com/forum/foru...-range-revival

07-20-2019, 10:09 AM	#5
19Suburban69 Registered User Join Date: Nov 2018 Location: Applegate, Ca 95703 Posts: 53	Re: Doug Nash overdrive Geezer#69, I found that write up and registered in the site, but photos and tech write up are blurred. Looks like it’s exactly what I need. I sent message to OP, but it was an old write up and he hasn’t responded yet. __________________ 1955 Chevy, 2 dr post, my first car 1969 Chevy C20 Suburban, 6.0 LS w/4L80 2001 Silverado Z71, 5.3 extended cab

07-23-2019, 09:20 AM	#10
19Suburban69 Registered User Join Date: Nov 2018 Location: Applegate, Ca 95703 Posts: 53	Re: Doug Nash overdrive I bought the truck from member here, Ranger Danger. He had installed 40 gallon tank so it helps on long trips, but is a killer when paying to fill it up. The cost of installing overdrive is never going to pay for itself unless trans was free, but just wanted to drop rpm. Still looking for wiring diagram to finish the job. __________________ 1955 Chevy, 2 dr post, my first car 1969 Chevy C20 Suburban, 6.0 LS w/4L80 2001 Silverado Z71, 5.3 extended cab



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