The Stovebolt Site Forums The Parking Lot Big Bolts Military -v- Civilian exhaust systems during WW2

Could someone, with military truck experience, describe the difference in military truck exhaust systems as compared to the civilian version. Every military truck, I have heard, sounds a bit more "throaty" as compared to the typical "whiny" civilian truck from '42 or '46. I have never, in the past give it a second thought on this subject.....but with these longer winter nights....our thoughts tend to wander!
Al

Al,

My 41 GI uses the same muffler part number as its civilian counterpart. The only differences in the exhaust pipe are a couple of minor bends to accommodate a different steering box and transfer case. I don't really see any significant differences.

Could the "throaty" sound be from the original cast iron pistons vs. later model cast aluminum pistons?

Paul

Hello Paul, hmmmmm, I am surprised at your information about Military exhaust systems. I have heard several military trucks in person and also listened to MANY clips of military trucks on You Tube. Everyone of those military trucks sounds more "throaty" or "muscular" than does my bone stock 1946 farm truck. I wonder if maybe someone alters the original muffler to get the muscular sound that I refer to?
Al

I don't know, perhaps rustout resultant from a long idled relic?

I have never really looked at a WWII engine. I wonder if they might use a different exhaust manifold than civilian does. A naturally aspirated Cummins sounds like a completely different engine with a backdrop manifold compared to a center drop manifold.

If you have a WWII era military truck, was it set up for driving in high water? If so, the exhaust/tail pipe would be higher and would seem louder?

If we are talking 1941-45 Chevy 235 GI trucks, the intake/exhaust manifolds are the same as civy excepting a hydrovac port and PVC system on 1943-45 models. Early trucks had no provisions or design for high water driving.

Personally I think the cast iron piston GI 235 sounds like a diesel when at idle, but I would imagine a similar year civy should sound the same. GI 235's share more common parts with civy trucks than not and the unique GI parts would not contribute to a difference in sound.

Paul

A lot of the "restored" WWII Chevrolet trucks have been converted to a GMC engine. Would that explain the difference?

I doubt that the GMC engine will sound much different than a stock Chev. engine. They do have a bit more displacement and full pressure oiling as the improvement over the Chev. version. Any other thoughts or suggestions from readers?
Al

Yeah, I think a GMC 270 and a Chevy 235 sound pretty much the same.

Are you thinking of bigger WW2 5 ton trucks...ones with the big Hercules six cylinder engines...they sound like they have a low growl sound?

Most of the GM military trucks on You Tube are of the smaller version that would all run the 235 Chev. or 248 GMC engines. At least I assume the GMC trucks would use that size or were they still using the 228? The 270 GMC didn't come out until in the early 50's if I recall correctly? I haven't paid much attention to the large military trucks that would have had different power plants. I do have the makings of a 1943 Case LAIM GM special, with a 4-71 Detroit diesel. Tractors are for a different forum. Paul did many of the military trucks get fitted with Detroit diesels during the war?
Al

Al,

It seems as though it was once popular to transplant a 1941-45 GMC G-508 (CCKW) engine and transmission into the 1941-45 Chevy G-506. I think the compelling reason for the swap was that the Chevy babbit 235 engines bit the dust and the GMC 270 was always a insert bearing engine. Additionally, the Clark 5 speed transmission from the GMC gave the Chevy a little more top speed as it was an overdrive.

GMC CCKW's were always outfitted with a 270 from 1941-45. Chevy's were always outfitted with a babbit 235 from 1941-45.

I am not sure about the usage of diesels in WW2 military trucks/vehicles.

Paul

Hello Paul,
I read a bit of your back story about your military truck project. It came from Utah.....hmmmm. What area? I live in west central Utah.
Al

Al,

It was recovered from a ranch near Zion NP.

Paul

It would be my GUESS that the 270 was used over the 235,(in the Chevy G-506's),as Paul stated earlier. There's a Studebaker US-6 Tank Wrecker,about 15 miles from where I live. The owner's son,tells me it was used in the Korean Conflict,even though it looks like WW-2 Vintage. Difference is,it's powered by a 4-53 General Motors Diesel,Not the Hercules,like most WW-2 Studebakers/Diamond-T's were equipped with. White built a 200 horsepower 6-cylinder gasser for the war effort,as well. They were mainly used in half-tracked vehicles.

Has anyone used a Flowmaster muffler on one of our Big Bolt trucks?

Using a Dynaflow- Dynamax X on the 2 ton with Fenton duals

Hello Jim, Do you have a You Tube clip of your truck running? I am curious as to what tone your current exhaust system gives your truck. Do you know if the Fenton duals fit or can be made to fit the GMC engines?
Al

Or you could do what I did and put a 1972 292 in my CCKW with headers and Flo masters, Blasphemy I know, but man do you get throaty !!!!

Hello 1936only, You have some nice trucks. Do you happen to have any video of your CCKW running? I would like to hear how your 292 responds to the Flow Master mufflers. Which model are your mufflers?
Al

As for the exhaust sound.... generally military exhaust systems are shorter, have larger diameter pipes and fewer bends. Having larger displacement motors (like a 270) would help. Plus civvy trucks are designed to be quiet.. they give up performance for quiet. Military trucks not so much.