Joined: May 16, 2011 Posts: 385 Location: arkansas
Posted: Mon Jan 23, 2012 5:38 pm Post subject: more horsepower
i read this from another mlitary forum, and kinda wanted to get all of you guy's opinion on this subject. thxs
One thing I've found that makes a noticeable difference in performance is timing. The factory spec for timing is usually fairly late for most military vehicles so that they can run on low octane gas (68 is the minimum spec listed on the M38A1 data plate, if I remember correctly). Since the lowest available these days from the pump is 87, the timing can be advanced from the factory setting. I usually do it by feel, advancing it in small increments until I get a little spark knock when under load at a low RPM, say, going up a hill. Then back off on the timing a little until you don't have any spark knock. This is your optimum timing setting.
After you have made sure all of the above listed items are correctly set, there are a few more things that you can look into. As Zout pointed out, friction from engine and drive train oil creates significant drag, especially when cold. The previous owner of my M35A2 (IornHorseTheGeneral) put all synthetic oils in the engine and drive train. I acquired the truck in the summer and didn't think that much about it to start with, but when winter came around, there was a big difference! The engine cranks over quicker and starts easier due to the viscosity of the oil. The transmission shifts easier, and there is much less rolling resistance when cold. If I were using one of my old jeeps or trucks as a daily driver, it would get synthetic oil in the engine and drive train.
Joined: Jan 03, 2012 Posts: 48 Location: Kansas City, MO
Posted: Tue Jan 24, 2012 12:03 pm Post subject:
I've heard of and used your methodology for setting timing before with success. However, the "optimum" timing settings is achieved with a vacuum gauge, is it not?
I'm guessing both methods would get you in the same ballpark, but I always like to have an actual metric to use, whenever possible. _________________ 1953 M38A1 #55997
Optimum timing point depends on where in the RPM range you want the optimum timing and which timing setting we are discussing. We have an initial static setting and we have total mechanical governor advance which is another 11 degrees.
For initial static RPM setting we:
In the low RPM range which is also where we start the engine then the optimum timing provides a quick startup. This is 5 to 7 degrees BTDC.
In the mid RPM range where we do most off road maneuvering then 7 to 10 is the optimum.
In the high RPM range where we cruise the highway at 50 to 60 MPH then 10 to 15 is the optimum setting. (This setting will severely hamper starting.)
Since we don't have the option of using an on board computer to adjust the optimum timing to the actual, at that moment, conditions we must select a compromised optimum setting.
The manufacturer did that for us using the 68 Octane fuel setting. All we really need to do is add a couple of degrees initial static timing to make up for the higher octane we are using.
Keep in mind the mechanical governor (centrifugal) advance gives another 11 degrees of advance after we hit 2000 to 2500 RPM. A high performance racing engine putting out 7 or 8 thousand RPM and 400 plus HP only uses 28 to 32 degrees of total advance so why would you need anymore than 20 to 22 total advance for an 87 Octane, 50 MPH, 3500 RPM low performance engine?
The single most performance improving act you can undertake on any piston engine is cleaning and gapping spark plugs correctly. Tired or dirty plugs will degrade your engine's performance a lot more than 2 degrees of timing.
Using a vacuum pump for a system troubleshooting tool is a very good idea. Using it for routine setting of timing is not a good idea. As the writer mentioned above once you find that highest vacuum reading then the guessing starts. You tweak it back until you don't get any spark knock. Well guess what you have to do to see where the spark knock threshold really is? You have to load the engine up at cruise power to find that threshhold. Guess what else? That threshold changes with outside air temp and pressure altitude. Then you have to tweak it back a little to make starting easier. Guess what? You are guessing again. So why not just use the manufacturer's recommended settings and work your way carefully up from there? _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Not worth the money they ask for the synthetics today. You would really have to put some serious miles on an old MV to realize any great gain in mileage and see the value of the synthetics actually pay for themselves.
In our jeeps and M37's a simple switch to 30 weight motor oil in the tranny and transfer will do the job. For the diffs any good quality multigrade gear oil is good enough.
The thing that drags a jeep down in the winter is the #2 chassis grease in the front steering knuckles. With #2 grease in my knuckles at 10 or 20 below zero you can feel it and the hear the engine strain to move her and you don't need any brakes to stop. Just let off the gas. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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