Ideal cruising revs??

[kpwemu]

I'm still trying to decide on what diff ratio to use in my soon to be 1UZ and stock Crown auto Zephyr ute. Maybe I should look at it backwards. Has anyone settled on what is the best crusing revs (100 kph) for the 1UZ. My car will mainly be doing highway klms, but at the same time I don't want it to be a slug around town. I read an article that said at cruising speed, having your motor revving too low is not good for the drive train. Based on the calculations so far, my ute with 9 inch and 3.0 :1 ratio will be doing about 1800 revs at 100 kph. Wouldn't the motor be labouring at these revs? Acceleration would be poor as well, and hopeless around town. I read on another thread that low revs doesn't mean good economy either. Each motor has its ideal rev range for power and economy. Any suggestions? Kevin

 

[Peewee]

I sit on 3000rpm @ 100 at the moment.
I'm hoping to drop that to 2450ish with a 3.73:1 diff and 0.681:1 5th gear.
Currently have 4.10:1 diff and 0.763:1 5th gear.

 

[Zuffen]

You will achieve maximum economy at peak torque.

I'd work toward 2,5-2,700 rpm @ 100kmh.

This would give a theoretical top speed of 250kmh. More than enough.

My car runs around 2,500 and it has plenty of go at 100kmh.

 

[1UZFE Matt]

I'm running a 3.15 diff with 225/45/16 tyres in my 1300kg BMW.
With a w58 Supra box in 5th, I am doing 2700 RPM @ 110Kmh and getting about 10.5 Litres/ 100Km. Still pulls hard at that speed in 5th.
Regards Matt.

 

[Peewee]

Something of yours is out Matt
With those numbers you should be doing under 2400rpm @ 110kph

 

[1UZFE Matt]

Must be an error in the tacho. I have never run the numbers, which I now intend to do. Thanks for that Peewee.
Regards Matt.

 

[Peewee]

What does it do in 4th @ 100kph?
(just in case its not a W58 and is infact a W57 or W55)

 

[1UZFE Matt]

Good point Peewee I am not 100% that it is a w58, I think it does about 3000 rpm @ 100 in 4th. What are the overdrive ratios of the w55, w57and w58?
Cheers Matt

 

[Peewee]

W55 is 0.850
W57 is 0.861
W58 is 0.783

You should be 2750ish rpm @ 100 in 4th.
Sounds like your tacho is out 10% ish.

 

[1UZFE Matt]

I did some measurements and calculations and I must have a W57.
My rolling distance is 1872mm or 0.001872km. Done by
marking a wheel and rolling one rev then used a tape measure.
I divided 110kmh by 0.001872 to get wheel revs per hour @110kmh = 58760.7
Multiplied this by the diff ratio 3.15 to get tailshaft revs per hour
and got 185096
Then divided this by 60 to get 3085 rpm in 4th
Then multiplied this by 0.861 (W57) to get 2656 rpm in 5th.
So not too far off the 2700rpm my tacho was showing. What do you think Peewee, does it all sound reasonable? Anyway it is going to change again as I am putting a 3.45 LSD in it.
Regards Matt

 

[Peewee]

I've got a rolling distance of 1913mm (225*45/100)*2+16*25.41 = 1913.5

This gives 2750rpm in 4th @ 100, and 2350rpm in 5th (W57) or 2150rpm for W58

 

[madmont]

looking at the fuel consumption chart it would suggest the most economical cruising speed for the 1uzfe would be 2600rpm

 

[sideshow]

hey mat is that 10.5 normal

i have a crown 1uz in my hilux with a 4.3 diff and i get 350 kms from 47 litres

i now have a 3.7 diff but i still get like 350 kms from 47 litres

which its ok but i would have expected better

on the highway i can get just over 400 kms from a tank which is about 47 to 50 litres

 

[kpwemu]

Amazing, check this out.

Thanks Madmont, I can't read Japanese so I'll take your word for it that the ideal cruising revs for a 1UZ is 2600 rpm. Some of the feedback so far seems confusing, and some seem to contradict the other so I set out to search the web for a gear / rev calculator and found the amazing site linked below. It calculates anything you can imagine. I was looking for what diff ratio would be best for 2500 rpm at 100 kph.
Based on the following:
A341E overdrive ratio = 0.705 : 1
My tyre height 14" x 60 profile = 25 inches (This is an American site)
Nominated speed (100 klms) = 62 mph
Enter any diff ratio and it calculates what revs you are doing.
Answer =
Even with 4.11 : 1 ratio, I would still be doing only 2442 rpm according to this, and that's with a fairly small tyre diameter. See how it doesn't seem to match what some of you have said so far. Are these calculators correct?
Anyway, check it out for yourself as well as the rest of the site.
http://www.csgnetwork.com/multirpmcalc.html
Good luck, Kevin

 

[sideshow]

well i know my tacho is accurate

and i know i just fitted a 3.73 diff

i have 16 in tyres i think

i have a gps navigater and it is accurate with its speed so ill take it tonight and check what revs im doin in overdrive at 100 kph

 

[kpwemu]

Gear / rev calculator

Hi Sideshow, I got my tyre measure by simply measuring the tyre from road to top of tyre across the middle which gave me 25 inches (63.5 cm). I entered this into the calculator on this site. Next I put 62 mph which is the same as 100 kph. I entered final gear ratio of 0.705 which other threads tells me is the ratio of the overdrive of the A314E auto and then entered a variety of common 9 inch diff ratios. Pressed calculate and there is the answer.
The critical and variable piece of info for the calculation will be the tyre height. The rest of the data is the same for all of us using the A314E auto. These are the results I got for the common 9 inch diff ratios at 100kph with a 25 inch tyre height in overdrive, assuming it has a final drive ratio of 0.705 : 1
3.0 : 1 at 100kph = 1782 rpm
3.25 : 1 = 1931 rpm
3.5 : 1 = 2079 rpm
3.7 : 1 = 2198 rpm
3.9 :1 = 2317 rpm
4.11 : 1 = 2442 rpm.
Based on what Madmont said being that the 1UZ is most efficient at 2600 rpm, it looks like 4.11 : 1 is the way to go. I don't usually over 100kph so even if it is assumed that it will rob me of top end, it wont bother me. Even at 160kph I would be doing around 4000 rpm which these motors handle easily. 4.11s should give me good acceleration and supposedly reasonable economy.
For anything automotive, make sure you check out other links on this site. It has the lot. Kevin

 

[thefastj]

You will achieve maximum economy at peak torque.

sorry to be a noob.
but this is what this whole topic is based on... and i just don't get it.

how does the engine use less fuel @ 2600rpm than what it does @ 2000rpm??

if that was the case wouldnt they make the engine idle at this speed to reduce fuel consumption??

to add to this... you may be saving a minute amount of fuel (if this is true) but you are still making the engine work 1.3 times as much. (2600,2000 example) thus, wearing all engine components 1.3 times more.

i just don't get it. :-S

 

[sideshow]

what i think can happen is with a taller diff and lower revs the load on the engine is greater therefore the airflow meter might give it more fuel

cause i was hopin for better fuel economy with taller diff but so far its worse

 

[TOBES]

If you look at the graph posted by madmont the bottom curve is the 'Brake specific fuel consumption'. It shows fuel usage efficiency. In this case grams of fuel used per ps per hour. The lowest point is around 2500 -2600 rpm.

In other words it is the amount of fuel required per hour to produce 1 hp. The lowest point is the most fuel efficient rev range of the engine.

In theory the car requires a certain amount of hp to maintain a set speed, say 100 kph, and if the engine is operating at its most efficient point in its rev range then it will use the least amount of fuel.

Marine engines are set up to operate at this point at cruising speed to provide the best fuel economy...

 

[madmont]

I bought a Majesta half cut for my conversion and before i dismantled it I checked the engine revs against the speed .At 3000 rpm the speedo was reading 130kph so at 2600 it would have been doing 112kph. The diff ratio according to the book is 3.91. Tyre size was 215/65r15. Weight of vehicle was about 1700kg.