M1078 with 225hp and high speed gears: pro's and con's

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Plasa

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Hello!
I am thinking about putting on a M1078 with the 3116 engine and 225hp the high speed gears and 3.07 ratio. But I am not sure about the loss of the 20% torque, if it's noticeable and have on steep / sandy terrain a negative impact on handling/performance.

Does anyone have experience in such a config, I don't want to change the engine to 290hp, and I don't know if 225hp is enough to handle the truck with the high speed gears...

Christian
 

Suprman

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I went to the local truck pull after the regear. They had 17k of concrete on the sled it pulled it easy like before with the original gearing. They just ran out of time at the event and didnt get up to the heavier weights that they usually do.
 

Plasa

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But do they had 225 or 290hp? I think there is a lot of diffrence if you keep the original hp and the modified...

Christian

I went to the local truck pull after the regear. They had 17k of concrete on the sled it pulled it easy like before with the original gearing. They just ran out of time at the event and didnt get up to the heavier weights that they usually do.
 

tennmogger

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I concur with Suprman, the torque loss is not noticeable at all. The Allison transmission totally compensates for the ratio by selecting correct gear, plus the 3.07 really does seem to match the engine torque curve better at the achieved higher speeds.

I drive two M1078 trucks regularly. One has the 3.07 and the other not. All the roads I travel are speed limited to 45 or 50 mph, and to be honest, the work and cost to put in the new gearing was not worth it. I drive the "slower" truck more and like that I get to 7th gear much more often, with associated slow engine rpm at my low cruising speeds. Fuel mileage seems better but I have yet to actually check it. With the 3.07 gears, that truck has to be well over 45 before shifting into 7th.
 

fuzzytoaster

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I just put a gear set into a truck with 330 hp (C7 engine) and it absolutely flies through all gears uphill, against the wind, etc. What I've read is that 225 hp should be fine but in my opinion the extra 105 hp helps more on the top end. If you can modify your engine to make 290 hp (turbo, tuning, and something else I forget) then that may be the best of two worlds without swapping an entire engine out. Food for thought.
 

Reworked LMTV

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You could also turn up your 3116 per Sean's video.

Hello!
I am thinking about putting on a M1078 with the 3116 engine and 225hp the high speed gears and 3.07 ratio. But I am not sure about the loss of the 20% torque, if it's noticeable and have on steep / sandy terrain a negative impact on handling/performance.

Does anyone have experience in such a config, I don't want to change the engine to 290hp, and I don't know if 225hp is enough to handle the truck with the high speed gears...

Christian
 

coachgeo

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Slight thread hijack. I got a 290hp engine ready to rebuild for sell.. but one could just rebuild the turbo and swap it and governor onto their engine and be good to go... leaving you with spare engine parts to boot. Located in MO. PM me with questions
 

Awesomeness

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I had the 290HP engine in the truck before I regeared it, and I noticed the loss. The extra speed on the highway is nice, especially in Colorado where the speed limit is 75MPH. I wouldn't say it's really hurt because of the loss of torque, but it's definitely not as peppy accelerating any more. If there were another gear ratio in between 3.90:1 and 3.07:1 available, I would definitely chosen/recommended that instead.

On the highway, with the 3.07:1, I like to cruise at 65MPH, which is just after the shift into 7th at 60-62MPH for me. I get 7+ MPG that way, which is nice on long drives.
 
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fuzzytoaster

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On the topic of 3.07s, has anyone found a reasonable deal on a set? Going rate currently seems to be around $4k from a guy on fleabay.
Just picked up a set for $2500. You have check FB or network in the hobby. They're out there.



Update on performance: I took the truck out today with the M989A1 and a load of scrap. I grossed 39,080 lbs all in all. She handled well for the load and was rolling along around 45 mph (non-highway). There were two steep hills that I climbed from a dead stop and I could feel the change in power from a stock gear setup but she still accelerated up the hill to about 25 mph where it leveled off (note I've not reprogrammed my speedo so this is 30-32 mph-ish). The jake brake helped a lot when coming down the other side too. I'm running on old JP8 with old filter so performance can be marginally improved still. I think a 3116 would have trouble keeping up in this situation, even with 290 hp, but weight distribution and gross is equal to flat towing another LMTV. One would expect to feel a performance change in this situation.
 

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Suprman

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I have had a lot of lmtvs. Most first gen trucks. Some trucks are a lot peppier than others. If you can find my truck pull vid from a few years ago and you can watch and hear my turbo spool right up. If yours dosnt spool right up then I believe your engine needs to be tuned up by cat. Or you have fuel/air restrictions.
 

Awesomeness

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Probably the biggest advantage is not running the engine at full RPM just to maintain normal highway speed... This is good for a few MPG...
I like the idea of running the engine at a lower RPM, too. I can go 72+ MPH on flat ground (even at altitude here in Denver), but 65MPH just after the shift into 7th feels a lot easier on the truck.

Just for the record, I wouldn't say "a few MPG". It's basically 1MPG (10%) increase, and only on long drives where you burn most of the tank in one shot on the highway. On more normal "around town" driving, it's less (maybe 5%). Given the cost of the gears, the math does not work out in many people's favor for this being any kind of "cost savings measure". To oversimplify the math a little bit, if the gears give you a 10% increase, for every $1.00 of fuel you would have bought, you now pay $0.90... you saved one dime by paying nine. Whatever the cost of the gears, you'll need to buy roughly 9x that much fuel before you break even... so at $2500 for the gears you're looking at $22500 in fuel, 7500 gallons @ $3/gal, or about 45000 miles @ 6MPG average. For $4500 gears, $40500 in fuel, 13500 gallons @ $3/gal, 81000 miles @ 6MPG average. While there are exceptions, I assume most owners only put hundreds of miles on their truck a year, and it's going to take tens of thousands to break even. Plus, I spent way more than just the cost of the gears to do the install (e.g. tools, gear oil, seals, beer, etc.).

I keep good records of my mileage, and I have a post around here where I documented the first ~2500 miles I put on the truck after the gear change. I think the people who are claiming/predicting better mileage just aren't doing a good job keeping track. For example:
- they're eyeballing the numbers... "27.23 gallons is about 25, and 231 miles is about 250, so 250mi/25gal = 10MPG!" instead of the 8.48MPG it should be
- they fill the tank a little short and get a higher MPG calculation without realizing that it balances out the next time when they have to add that missing fuel back in and then get an extra low MPG number for that next tank, and they tout that "best tank" number

There will also be some MPG variation between trucks, drivers, geography, load, etc. But those should fluctuate more in the +/- 10% range, not the 10+ MPG claims I've seen around.

Note: Yes, for the mathletes out there, I understand it's not actually 9x, it's 9.09091x = 1/1.1, but I was trying to keep it simple.
 
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BKubu

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I have had a lot of lmtvs. Most first gen trucks. Some trucks are a lot peppier than others. If you can find my truck pull vid from a few years ago and you can watch and hear my turbo spool right up. If yours dosnt spool right up then I believe your engine needs to be tuned up by cat. Or you have fuel/air restrictions.
Will, can you post a link to your YOUTUBE page? I could not find it under your screen name. Is it under your eBay account name?
 

Ronmar

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Last I recall, Sean "turned up" his 3116 by replacing the governor, turbo and taking it to Cat to tune it to the 290HP spec... Yes, you can make some adjustment to the aneroid valve setting on the governor to make it a little peppier, but in the end the 290HP engine uses a different governor and turbo for a reason...
 

Reworked LMTV

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Did he replace it ? I thought he opened the triangle and gave it a turn or 2.

Last I recall, Sean "turned up" his 3116 by replacing the governor, turbo and taking it to Cat to tune it to the 290HP spec... Yes, you can make some adjustment to the aneroid valve setting on the governor to make it a little peppier, but in the end the 290HP engine uses a different governor and turbo for a reason...
 
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