Ambulance 2wd regear for lower noise and better fuel economy?
- Thread starter iggi
- Start date
iggi
Ian
Right, I've read this as well and apparently it's a reason the 6.0 doesn't self destruct quite as often in the vans as the pickups.
Bbasso
Expedition goofball
Something to read.
www.motorauthority.com
Here's why you should never lug your engine
To start, let's talk about what it means to lug your engine. This is the term used to describe when you're puttering along in a higher gear than you need to be in and the engine is turning low RPMs. When you're cruising along in 6th but you should've downshifted into 4th about a half mile back...
iggi
Ian
Thanks @Bbasso I understand lugging but... dropping from a 4.11 to 3.73 doesn't seem like it would "lug" the engine. Especially as 3.73 was a factory option, and even more so that's it's an automatic.
At my average cruising speed that puts the 6.0 just above it's peak torque.. (2000 rpm). The 3.55 would seem the best match to the engine specs as it's almost exactly 2000 rpm at 70mph but I also drive secondary highways a fair bit so the 3.73 would seem a good compromise.
Looking at the torque curve for the 6.0 it seems that cruising even down to 1500 rpm is well within the operating conditions.
It's been a long time since I obsessed over such things but that's what looking at the graph brings back in my memory.
Hopefully my other soundproofing efforts work well and this is just a mental exercise but I like knowing what my options are.
However,
At my average cruising speed that puts the 6.0 just above it's peak torque.. (2000 rpm). The 3.55 would seem the best match to the engine specs as it's almost exactly 2000 rpm at 70mph but I also drive secondary highways a fair bit so the 3.73 would seem a good compromise.
Looking at the torque curve for the 6.0 it seems that cruising even down to 1500 rpm is well within the operating conditions.
It's been a long time since I obsessed over such things but that's what looking at the graph brings back in my memory.
Hopefully my other soundproofing efforts work well and this is just a mental exercise but I like knowing what my options are.
However,
Something to read.
Here's why you should never lug your engine
To start, let's talk about what it means to lug your engine. This is the term used to describe when you're puttering along in a higher gear than you need to be in and the engine is turning low RPMs. When you're cruising along in 6th but you should've downshifted into 4th about a half mile back...
Len.Barron
Observer
The weight difference between an F350 and an ambulance is considerable and requires extra power across all driving conditions, the extra gearing accomplishes that. In general the higher the unladed weight the closer to centering your "normal driving" rpm to be in between peak torque and peak hp.
Mwilliamshs
Explorer
Once rolling, weight is of little effect given that mass is both a load and aids momentum. If frequent hill climbing is to be done, which I doubt given the OP's thoughts of regearing at all, I would discourage regearing but again, doesn't seem to be the case. The major consideration other than weight is aerodynamics, a loss for the ambo vs a pickup but to the point of making a gear change the defacto hard-pass it's been portrayed as? No. The rig still has a transmission. If bbassho thinks the engine will lug with 3.73s, I hope he knows it can and will downshift to avoid it. 3.73s will necessitate more shifts from OD to other gears but everything's a compromise.
If you want lower highway rpm and have the torque and transmission and cooling capacity to allow them, go for it. In the case of this ambo, I'd say you do.
Len.Barron
Observer
Well...if you live or travel the west coast "frequent hill climbing" is the only kind, if I go more than 80miles I have to climb a mount pass to get where I'm going...weight is everything out here, and the lower gears make a huge difference both on the climb and the engine braking descents. The more time you spend in gears that allow TC lock up the better your mpgs and the cooler/longer life your trans will live.
Mwilliamshs
Explorer
Torque converter lock-up is just a toggle switch away. Google "5R110 lockup mod"
You can probably swap a salvage yard axle in faster and cheaper than a re-gear, and if you get 6 months in and have buyers remorse, swap back.
Or put on taller tires, also likely to be cheaper and easier than a re-gear and you could probably borrow some to try or get them off craigslist.
My 6.0 truck has, IIRC, a 4.30 ratio, and the 2100 RPM cruise noise has never bothered me, but I also have the speed sensitive stereo. I’m notably not sitting beside or on top of the engine like a van body either.
When the engine fan clutch engages, that noise is noticeable, but not insane. Maybe just live with the noise if you’re driving that sort of rig? Or run a dB meter to see if there is a real difference?
I’ve never checked the mileage on a slower run over a meaningful distance.
Or put on taller tires, also likely to be cheaper and easier than a re-gear and you could probably borrow some to try or get them off craigslist.
My 6.0 truck has, IIRC, a 4.30 ratio, and the 2100 RPM cruise noise has never bothered me, but I also have the speed sensitive stereo. I’m notably not sitting beside or on top of the engine like a van body either.
When the engine fan clutch engages, that noise is noticeable, but not insane. Maybe just live with the noise if you’re driving that sort of rig? Or run a dB meter to see if there is a real difference?
I’ve never checked the mileage on a slower run over a meaningful distance.
Mwilliamshs
Explorer
Van c&c axles aren't terribly common and certainly not in 3.73
Changing tire height with an ambulance body isn't that simple
Yeah trucks are quieter than vans
That quiet 6.0 fan/clutch combo is quiet because it's weak. A few aftermarket companies adapt the bigger, more effective 7.3 parts to 6.0s for better cooling
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Len.Barron
Observer
and a good set of custom tunes with an SCT could be a better solution for the entire issue
Bikersmurf
Expedition Leader
I'd factor in that you're 9K+ empty every day. It also depends on your tire size. With 225/75R16s it would be quite different than with larger tires with 3.73.
That said, I'm running 225s with 4.11s and get better fuel economy than most others on the forums. I'm not sure 10% lower rpm would necessarily help economy
That said, I'm running 225s with 4.11s and get better fuel economy than most others on the forums. I'm not sure 10% lower rpm would necessarily help economy
iggi
Ian
Hey ya'll, thanks for bantering this around. Appreciate all the good feedback.
Just back from about a 1000k (600 mile) trip. A bunch of it was on smaller highways with lower speeds and cruising at 2000 rpm vs 2350 in the faster highways isn't that much different in the noise dept.
Seems that my best returns will come from continuing to work on the sound insulation.
I will look into the 5R110 lockup mod as I'm curious.
@Bikersmurf I didn't measure the economy specifically on the lower speed sections but I agree that dropping 10% rpm is not likely to be all the significant in it's effect on the economy and the time/money spent on an axle regear is likely better invested somewhere else.
@Len.Barron Can you point me at a good resource for custom tunes?
Thanks!
Just back from about a 1000k (600 mile) trip. A bunch of it was on smaller highways with lower speeds and cruising at 2000 rpm vs 2350 in the faster highways isn't that much different in the noise dept.
Seems that my best returns will come from continuing to work on the sound insulation.
I will look into the 5R110 lockup mod as I'm curious.
@Bikersmurf I didn't measure the economy specifically on the lower speed sections but I agree that dropping 10% rpm is not likely to be all the significant in it's effect on the economy and the time/money spent on an axle regear is likely better invested somewhere else.
@Len.Barron Can you point me at a good resource for custom tunes?
Thanks!
Len.Barron
Observer
I'm a duramax guy so I don't look at a lot of the ford tuner stuff but I've heard nothing but good about Innovative Diesel: http://www.innovativediesel.com/sct-x4-edge-insight-monitor/
You should troll the ford diesel forums for some specifics.
You should troll the ford diesel forums for some specifics.