The Stovebolt Site Forums The Parking Lot Big Bolts GMC 4000 top speed

1962 gmc 4000 fire engine with a 351 V6, NP540 5spd trans and a 7.20 axel ratio. The tires are 9.00X20 39" tall. anybody know the top speed? It only has 18,000 miles and everything is in great shape.

Unless fifth gear is an overdrive, I'd bet that ole engine would be screaming at 45mph. Also that v-6 is not made for high rpm use, it is a torque monster by design. let us know how it goes!

And how about this one?
A 261, and 4 speed, 2 speed rear... what can be the guessed top speed?
The same ? 45 mph ?

http://i185.photobucket.com/albums/.../BpHpPuQmkKGrHqQH-CwEuYw1oB-IBLqBeob.jpg

I dunno about it screaming at 45, seems a bit slow for a 7.2:1 final drive to me. However it wouldn;t be the 1st time I've been acused of being a [censored]. :P
Just saying, my old dump, in stock configuration, with a 10/8.5:1 2-speed rear, & same size tires, will do 50-55 all day long.

By my calculator, taking the tire diameter and R&P ratio given, if your 5th gear is 1:1 you should be running around 48 MPH at 3000 RPM, and if you have the 0.82:1 ratio you should be running 59 MPH at the same RPM. There are around 9 sets of gearing for the NP540, but from what I have found 5th gear is one of those 2 ratios.
With that information, the question then becomes what's the RPM limit on your engine, or, at what RPM does the torque drop off. Given that number & I can tell you approximately what your top speed will be in each gear.

Two speed rears in our old trucks only give you lower gears to work with, they do nothing to help top speed. They are just there to help the small engines pull larger loads. The top speed will still be the same regardless of 2-speed or not. Like Freq2002 said, mid 50's is about as fast as they go in stock configuration.

Mike B

Just click the link and plug in your variables, it spits out the answer.
There is no guessing or speculating, it's simple math, and simpler with the above link, just plug and play.

Grigg

When I put in the numbers, I got 48 mph at 3,000rpm also. From everything I've read, the V6's are torque monsters that turn into bombs at high rpm's. I'm going to put a tach on it because I think it sounds faster then its really going. thanks guys.

Not sure what gears it had, but my '62 6500 with a 478 V-6 would go 62 MPH. I believe it was governed, but at that speed it didn't seem to be over-revving and still had plenty of power.

That was just for short distances tho. I don't think I would want to drive it all day like that.

Bill

I looked at the data plate again and got more info for the trans- np540 type GL speed 5DD. does the GL or 5DD help to find the 5th gear ratio? thanks

5DD to me means 5th gear is Direct Drive (1:1)...can't help with the "GL".

Mike B

Your New Process 540 is direct drive in 5th. Good transmissions, rather unusual shift pattern, at least for me. James

thanks guys.

Couldn't find anything on an NP540 with a GL suffix. However I found a couple references that say the '57-'69 NP541GL transmission should have the following ratios:
1st 7.24
2nd 3.88
3rd 2.19
4th 1.37
5th 1.00
7.22:1 R&P

Oh, and if anyone wants it, and ya have Microsoft Excel, I can email ya my engine/transmission calulator.
Allows you to figure exact displacement (numbers are plugged in as mm’s but gives results in Metric and SAE), compression ratios, & camshaft data. On the 2nd tab, it gives speeds according to tire diameter, R&P ratio, gear ratios up to 5 gears. You just plug in your shift RPM/redline for each gear and it will give you your top speed for each as well as the approximate RPM at bottom of next higher gear. I made it for building engines & figuring gears for drag racing to keep the engine in the top of the torque curve. Still pretty handy for fun questions like these.

James, what actually was the shift pattern? Was Granny 1st to the right down and Reverse to the right and up?

First was toward the driver and toward the dash. Second was right next to it. Reverse was away from the driver and toward the dash. Shifting between first and second was rather awkward.

That does seem awkward. The trans I was talking about was:

2 4 R
3 5 1

It was a long way from 1st to 2nd. It also had a 2-Speed Rear and the sequence was

1L
1H
2L
2H
3L
3H
4L
5L
4H
5H

Bill

Bill, the New Process shift pattern was just like crenwelge mentioned and it was awkward...

1 - 2 - 4 - R
- - 3 - 5
For us in the dump truck business it was hard to 'rock' a mired down truck, going from reverse to 1st or 2nd quickly sometimes meant clashing gears and missed opportunities to move forward, at the same time we dug a deeper hole.

The Clark transmissions that we used were somewhat better, there shift pattern was...

2 4 R
3 5 1
My favorite were the Spicers...

R 2 4
1 3 5
A driver could quickly go from reverse to 1st or 2nd without a lot of effort. Reverse and 1st were spring loaded on the shift lever. These were the shift patterns that I'm familiar with these trans, but I imagine Spicers may have used other patterns. We favored the Spicers on our Chevys from the late 50's thru the early 70's, when we wore out a Clark or NP it was replaced with a Spicer.

Just my 2 cents worth, James

Top RPM's on the V6 is 3600 we max ours out at 3200.

OK, so if you take the RPMs ABento said and the gear ratios I listed for the NP541GL, shifting at 3500 for 1st thru 3rd, 3200 for 4th, & cruising at 3200 in 5th, your approximate speeds should be as follows:
1st: 7.8MPH @ 3500RPM
2nd: 14.5MPH @ 3500RPM
3rd: 23.5MPH @ 3500RPM
4th: 37.6MPH @ 3200RPM
5th: 51.4MPH @ 3200RPM

And just for giggles, at redline, 3600RPM, in 5th, you should be pushing 57.9MPH

And looking at this, I really need to get my RPM guage hooked up and working,... If I have a 8.5:1 high range and a 1:1 trans, AND I can run at 60?... My lil 270 must be spinnin at about 4500RPM. Yeesh!