GMC JE 9500's with a 637 Gas
 

As some may remember, the '71 GMC 9500 I used to drive had a 637 Gas with a 10-Speed Road Ranger. To this day, I have never seen another. Here is one that is pretty close though. It's a '70 9500 with a 637 and a 5 X 3. Under the picture is a short story on the truck. There are also some pictures before this one and should be able to be seen by clicking on the arrows.

It looks like Madison County, NY bought 16 of these trucks all with 637's between the years of '67 and '72. Interesting, the '69 and older trucks has 5 X 2's (Trans and Aux) and the '70 and newer ones 5 X 3's.

Still no 10-Speed RR's though, but closer than anything else I've seen in the last 44 years. They are even the same color as my old truck, lol.

https://www.flickr.com/photos/919717...n/photostream/

Re: GMC JE 9500's with a 637 Gas
 

Lovin' it. I've said it before, I have a thing for any GM tandem dump. What year did Road Rangers come along?

Re: GMC JE 9500's with a 637 Gas
 

I believe they were first out in the 1950's. Probably available in the H and J 9500's since the beginning. Also note the 9500's with the 637, the Dog House was smaller, enabling the shifter to be in the more typical location rather than a lot further back with 6-71 and 8V-71 Detroits.

Re: GMC JE 9500's with a 637 Gas
 

A 637 video is pretty hard to find, but here is one I found that was posted recently. It sounds pretty different without any exhaust system on it and typically, not as good.

Re: GMC JE 9500's with a 637 Gas
 

I have seen HE-9500's, but not any JE-9500's. Seems quite a few HE's ended up as fire apparatus. Anyway, yes the 637 has a different sound than any of the big V-6's! I believe it probably has to do with the 637's oddball combustion chamber/head design, which is completely different than that of a 478. The 637 is not actually a 478 with 2 more cylinders, it really is a gasoline fuel conversion of the DH637 Toroflow V-8. Like the Toroflows, the 637 heads were flat on the bottom with no combustion chamber pocket. The combustion chamber was in the piston crown. The 637 heads didn't have both intake and exhaust manifolds on the outboard side like the Toroflows, so in that respect they were different, along with having spark plugs rather than injectors.

The 478 V-6 compared well with the other large displacement V-8's like the Ford 534, IH 549, and the REO/White (whatever displacement that thing was). The 637 was quite a bit more powerful than any of those. GMC never sold many, but they were around from 1966 to 1972. Most probably went in to H/J models, but the T/W Steel Tilt and the aluminum cab 'Crackerbox' offered then as well. Someone on the ATHS website years ago found a tandem axle Crackerbox with a 637 in it.

Re: GMC JE 9500's with a 637 Gas
 

Bob,

Appreciate the explanation on some of the internal differences. My first indication of that was how it sounded and how it performed in comparison to the 478, which we also had in our small fleet. The 478 had tons of torque and drove a lot like a 237 Mack where the 637 was a "Rev-er" more like a Detroit.

Re: GMC JE 9500's with a 637 Gas
 

I have heard the same comment from others who have driven 637's, you had to spin them up to get the power out of them. Not sure if that characteristic had anything to do with the head design, it could also have been due to the cam profile.

Re: GMC JE 9500's with a 637 Gas
 

That engine sounds sweet! I like the GMC deflector on the hood of that orange truck.

Re: GMC JE 9500's with a 637 Gas
 

A buddy of mine said them 637s is just two 318 4cyls stuck together. Hey wait, 4cyl 318? WOW!!! :lol:

Re: GMC JE 9500's with a 637 Gas
 

The 637 sounds different because it is an uneven firing V-8.

The V-6 block has a 60 degree angle which gives the engine an even firing interval. A V-8 normally will have a 90 degree angle to make it even firing.When there were two more cylinders added to the 60 degree V-6 block it became uneven firing.