rpm reducing
 

hi- mmonce has touched on a worthy idea-though not exactly as coasting........i have a 1995 ford ranger 4x4 with the 3.0v6 auto. o/d. this engine turns at a whopping 2500 RPM when at 60 MPH...it would seem 90% certain that there would be large savings on long trips if i had a device that i could set at whatever rpm i chose following the final hwy speed shift point....say 1200rpm?

Not quite sure I follow.
Your finally rpm at cruise is a product of 1. gearing and 2. load.
we have discussed on here about increasing the diameter of the tire (not the wheel) to lower the rpm at cruise. I did this on my Infiniti Q45 and saw some nice results. I increased the tire diameter about 6%. The trick is you need to spend a lot of time at cruise to offset the little bit of mpg loss while driving around town.
2. load - the energy needed to keep your vehicle moving down the road at the same speed. Aero plays into this. Rolling resistance also (air up the tires to above 40psi.)

Point is, you cant arbitrarily set the rpm to what ever you want with your current set up.
I just remembered you have a 4x4. I would imagine the rear gears are high and not really designed for a lot of freeway driving.

If you are considering gearing your truck for 1200rpm at 60 mph, you are making a mistake. I think 1800 is about as low as you will want to go. Even then you will have to downshift to accelerate in a reasonable amount of time.

thanks- lost my sense of gearing for a bit there.

The aero on your Ranger is likely a nightmare. Before dropping $1000's on changing your gearing - which would almost certainly have a good result, no denying - you can get pretty good results with a few aero mods. If you don't go offroad much - and few people really do - you could do a lot with a simple air dam. If you're worried about it getting torn off by deep snow, make it one that's easy to remove and reinstall.

My truck has 3.73 gears and I am certain it would be happier on the highway with 3.55, maybe even 3.35. It just sounds buzzy. But I'm too cheap to do it.

Elhigh, can we calculate what your cruising RPM would be with 3.55 and 3.35 gears and mileage improvements?

I cannot imagine the ROI would be reasonable, I am just curious.

Standard tire size = 195/75 R14
790 revs. per mile

Truck's rear = 3.73:1
W56 5th = 0.85:1


Overall top gear ratio = 3.17:1
engine revs = 2507

With 3.55:1 rear = 3.02

= 5% rpm reduction
engine revs = 2385

With 3.35 rear = 2.85

= 10% reduction
engine revs = 2251

The 22R isn't really powerful but makes good torque for its power, and makes it pretty low in the rev range. It's a super flexible, meaty engine down low if you don't ask too much of it. Puttering along at 50 in top feels great, 60 feels thrashy. Having 3.35 gears would move my cruising speed down into less buzzy territory.

As to what that would do to my MPG, I can only speculate. It's carbureted. I can only record tank-to-tank, there's no instant display that really helps. Even the vacuum gauge isn't much use, it keeps wandering up to where it shows 10" when the engine is off. But I know that this is a pretty light truck, I never drive very fast and rarely have a large load (firewood once in a while, the wood splitter once in a while, Lowe's once in a while). I've had it since it was new.

ROI = never. There is no such thing on a truck this old, there's just wrenching because it's more interesting than watching TV.

In my 2013 Honda Fit with manual 5-speed, cruising at 100 km/h (62mph) - which is the legal speed limit here - makes the little 1.5 L engine spin at 3,000 RPM. If I drive consistently at this speed, slow down a bit as climbing hills, and coast downhill, I can easily hit 40-45 mpg over an 1 hour drive.

My point is that RPM's aren't everything. If you have an instant fuel consumption display, it becomes very clear that fuel consumption depends on the load more than RPM's. I could be wrong, but I think engine load is affected by many factors such as grade/slope of road, air temperature, wind speed and direction, weight of car and all the stuff in your trunk, type of transmission, 4x4 drive, tires (type and pressure of tire), drag forces / aero of your car, type of engine oil, etc...and of course how many cheeseburgers you had that day.
:turtle:

Yes and no. Assuming a fixed power need to travel at a fixed speed, increasing RPM means you'll have lower percent load at the same speed (because the engine can make more power at higher RPM), and low load causes parasitic losses (mostly vacuum/pumping). Higher RPM also has exponentially increased friction = more parasitic losses. Sometimes this is partially offset by an engine being more efficient at higher RPM, but ideally you want to be geared so that you're at high load at the lowest RPM possible when cruising, to maximize efficiency.

EDIT: My previous car had a very, very short transmission. The 1.8L DOHC engine spun at ~4500RPM at 72mph, and at this speed, I usually got about 30mpg. If geared differently, let's say closer to 2500RPM, it's likely I'd have been closer to 45mpg, because of the tremendous decrease in pumping and frictional losses.

Decode the axle code on your sticker near the drivers door striker. Something like a 308 to a 335 would be good.

regards
mech

Don't recall the name exactly, "gear reducer" but you can install an extra gear box between the tranny and rear diff to reduce hwy rpm, I think they are $2,000 plus the driveshaft rework. It will never pay for itself with one truck, but if you keep it long enough through several trucks maybe.

I'd focus on low hanging fruit, drivers mod & tires.

this!:thumbup:

Gearvenders overdrive/underdrive? And $3k I think.

Bear in mind it's a 4x4, if you intend to use 4WD you'll need to regear the front axle as well. My personal gear rates are $250 in labor plus parts per diff, but you can easily sink $300-600 into each diff depending on how many bearings need replaced, the gear set, if you're going to install a new limited slip or locker (it's a 4x4)...

And in the end, you now have a 3.0L Ranger that is perhaps the most doggy truck on the planet that you'll HATE driving because it can't get out of it's own way, and you might get 1-2mpg highway out of it, potentially losing city economy because of how much harder the engine must now work to accelerate.

I'd personally stick with improving your eco skills (try the Torque Pro program with a Bluetooth device/adapter, it's cheap and fun!) and doing some efficiency upgrades to the motor. If you want to spend a lot of money, consider some lower rolling resistance all season M&S street tires (mudders not the best for economy, lol), then some aero mods like splitter and belly pans.

Good luck!

The engine working harder to accelerate generally improves economy, rather than the other way around.

"Pickup gearing" LOL, remember George Wiseman? http://ecomodder.com/forum/showthrea...ere-28068.html

On a serious note, it is possible to gear too tall, not just from a driveability standpoint but from a fuel efficiency standpoint as well by dropping too low off the BSFC peak. Searches will reveal many discussions of that here.

Any time forum threads are focused on gearing, I feel compelled to post this gear calculator link.

Hi Ecky, I'm curious about this statement. Are you saying that an engine working harder is more efficient, or are you saying that a vehicle reaching cruising speed in a shorter duration run-up is more efficient, probably due to the engine working harder for a shorter span of time to reach the same cruising speed?

In this case going taller on the gears could in fact cause the engine to work harder for a longer duration because it lacks the power to weight ratio to effectively get the vehicle to speed quickly, ergo working harder longer decreasing economy?

Lonesome Trail, to some degree I mean both, but mostly the former. Here's a BSFC chart for my car:

http://ecomodder.com/wiki/images/e/e...nsight_5mt.jpg


I'm not sure how familiar you are with these sorts of charts, but it's an RPM vs torque chart, with the amount of fuel needed to produce a given amount of power printed on contour lines over the load and rev range. Lower fuel consumed to make the same amount of power is better.

I'm going to draw some lines on this chart, and then explain them:

http://i.imgur.com/ydKRLBR.jpg


One important thing to note about this chart is that it is not a power (kwh or HP) chart - as you move from left to right, horizontally, you have a roughly linear increase in horsepower, because power = torque * RPM.

Another important thing to note is that the contours are elongated horizontally. Increasing or reducing load has more impact on efficiency than RPM does, meaning it's nearly always better to upshift.

Hypothetically, let's say you shift up at about 2500rpm, as I do, and the next gear brings you down to about 1750rpm. You accelerate at around 75% load, which you can determine with instrumentation, such as a vacuum gauge or scangauge. By doing this, you'll be moving back and forth alone the green line, staying in the engine's peak efficiency range. How long it takes you to accelerate is irrelevant, but ideally, you want to spend the greatest amount of time in the highest efficiency range.

The red line I've drawn represents (very roughly) a fixed amount of horsepower. If you need 20HP to cruise on the highway, you could do it at 6000RPM with 10% load, resulting in an incredibly poor BSFC of over 800, or you could do it at ~2000RPM with 80% load whit a BSFC closer to 200, which is 4x more efficient.

The only time taller gearing is not better is when you can't use it because you simply can't produce enough power in that gear.

Downsizing an engine is another matter. I used to be under the impression that downsizing an engine was always better. However, if I needed to produce 50HP, a 2.0L engine (all else being equal) would almost certainly do so more efficiently than my 1.0L engine, as long as it is geared correctly.