G744 said:
My thinking of theis is highway speeds and the resultant RPM (around 2700) is where the crank harmonics come into play causing the failures.
Perhaps the trick might be to regovern the high idle to no more than 2100, and reset the fuel timing and boost (higher pressure, re-mapped, & intercooled) to maximum torque somewhere around 1800. Essentially one would be making it conform more like a larger engine in road service.
This would require the addition of a taller overdrive, but the HP/torque figures would greatly improve and it might just go on forever.
Every catastrophic multifuel engine failure I've personally witnessed or had described to me has been at highway speeds.
dg
I've been reading through this thread, somethings in total agreement and sometimes shaking my head and I think G744 hit the nail on the head on at least a couple of major issuess.
I've been playing with and attempting to make M37s (G741s) "highway traffic" worthy for years and have finally come to the realization that the wisdom that my buddy John Bizal of Midwest Military gave me ten years ago was true. John's advise was that it's simply too expensive to make an M37 keep up with traffic --- that they were designed to keep up with the troops NOT highway traffic.
I made the move to a bobbed (4X4) M35 because it was closer to meeting the demands of highway driving. Yes, I know I'll immediately turn off quite a few that read this post when I say "bobbed" deuce because it a modification and therefore isn't true military.
Well .... technically, neither is turning up pumps and other serious gemoetry changes. My two cents worth --- as a conservative old man that once scattered a 220 Cummings from Little Rock to West Memphis because of a turned up pump is that expectations of longevity and hot rod mods don't make good bed fellows.
I agree with Dr Foster and Bjorn's postings but I also think they would agree that pushing the Multi (or any engine) too far out of it's intended (engineered) envelope of operation AND then expecting longivity is about as rational as removing the glass from the tach and twisting the needle while driving down the interstate in hopes of increasing top speed.
As an engineering company imagine being tasked with building a tactical engine designed to run under any and all conditions for 20 years while being driven by a bunch of young fire pissing GIs that are paid to hurt people and break things? (I say that as a compliment!). When I was in Vietnam they changed engines in M37s like sox compared to the deuces that were lucky to see fresh oil and the deuces kept going and going and going. Regardless of the professionalism of the motor pool, (my deuce was owned by the boys of the Tenth Mountain and the engine is so clean you can eat off of it), I can't help but believe that the first 20 years takes a hard toll.
Given my deuce is a bobbed, hobby (light service) truck that only weights 10.5K and totes tall (47") rubber it's easier for me to hit HWY speeds of 65 MPH @ 2,500 RPM without breaking the harmonic balance bank.
If I were running a conventional deuce and therefore 5,000 lbs heavierand limited to smaller rubber I would explore going with a higher speed overdrive (say .70:1) AND turning the up the pump a click or two (not much) before "ever" entertained going past 2,500 RPM --- 2,500 NOT 2,600 would be the max RPM.
If anyone has any insight into what gears would have to be fabricated to increase the OD speed I would enjoy hearing from you. Last year I bought two sets of special built 4.89s to replace the 5.38 ring gear and pinions in an M37. There might be sufficient interest in a special run on HI-Speed-OD gearing to justify a production run. I may buy a spare Spicer transmission and stick my finger in it to see what's involved.
From everything I've read, two-hole injectors perform best in the LD & LDT and installing single hole LDS injectors requires different timing and perhaps even pump calibrations with no guarantee of added performance
