Highest safe rpm driving

[mattpresley]

I drove to San Diego for thanksgiving and plan to go again for New year. The speed limit on I-8 in Rural Arizona is 75 mph. Last time I drove 75-80 but was scared to go over 80 because my rpm was 4,500. My truck being an auto(I guess thats why) dont have a redline on the tach. Whats the highest safe rpms for sustained periods of time? Of course when the mountains come up it will be 55 MAX is my 4 banger struggles on them

 

[LittleHorse]

WOW! You sure your speedometer is right and you're not going 100 and just thinking you're doing 80?

I used to have a Miata that ran 4k @ 80mph, I just don't see a truck geared that way.

That said, I've never driven a 99 Ranger w/ auto trans so hopefully somebody will be along soon to confirm or deny.

 

[dirtracer81_2]

Hey I run a 2300 in my race car. I turn mine 7900 going in the turns on a good night and it has a bone stock bottom end right now. Now a stock head your gonna come into valve floatage issues after around 6500. Nice thing about a ranger block is it has metric rings and they are stroked a bit different.

Heres a video of my car idling and a little rev to about 5 grand
http://www.youtube.com/watch?v=HHLef2tnryI

 

[scotts90ranger]

stock they have a rev limiter set at 6000 or 6200, as long as it's oil is in good shape and the coolant is under control you can run at 6000rpm all day long and not hurt anything

 

[mattpresley]

WOW! You sure your speedometer is right and you're not going 100 and just thinking you're doing 80?

I used to have a Miata that ran 4k @ 80mph, I just don't see a truck geared that way.

That said, I've never driven a 99 Ranger w/ auto trans so hopefully somebody will be along soon to confirm or deny.

Yes my speedo works great. this little 2.5 W/ auto is a joke my friend. If your ever in the phoenix area call me I'll let you test drive for yourself 480-266-7540

 

[mattpresley]

Umm can someone figure out my top speed based on the 4500 rpm at 80? Im curious but dont wanna face a felony charge getting caught trying

 

[exbass94]

1. Divide Engine RPM by transmission gear ratio
2. divide that by axle gear ratio
3. multiply by circumference of your tires (diameter times pi)
4. divide by 12
5. multiply by 60
6. divide by 5,280

and you get the speed of your truck in mph.

 

[mattpresley]

stock they have a rev limiter set at 6000 or 6200, as long as it's oil is in good shape and the coolant is under control you can run at 6000rpm all day long and not hurt anything

 

[4b316]

we race a basically stock 98 2.5 ranger and we run it about 5900 with 4.10,s and in 4th gear.we put in a new motor last year but before that we had one in with 175,000 on it and turned it the same.You can go to www.adirondackspeedway.com and look at the truck,it is the 22 truck.

 

[Gotta_gofast]

Its possible that you're pushing on the throttle hard enough (at 80mph) that the transmission won't shift into OD. I could see 4500rpm in DRIVE at 80mph. As for your top speed, its roughly 95mph.

 

[LittleHorse]

Its possible that you're pushing on the throttle hard enough (at 80mph) that the transmission won't shift into OD. I could see 4500rpm in DRIVE at 80mph. As for your top speed, its roughly 95mph.

that was my second thought, that maybe it's not going into OD.

Have you started from a stop and counted how many gears you've shifted through?

The way I like to calculate speed vs RPM (because tires of the same nominal size can vary so much in actual size) is to look up the "revolutions per mile" of the tire on tirerack.com. It's on the specs page of the tire.

(rev/mile) x speed x (1 hour/60minutes) x axle ratio x transmission ratio = Engine RPM

So if you're running 215/75R15's and your rev's per mile are 748, you have a 3.73 axle and an auto with a top gear of .75:1 (pretty typical OD ratio)

748 x 80 x 1/60 x 3.73 x .75 = 2790 RPM

So you can plug in your own numbers and figure out what's going on.

You can work backward the other way...

 

[Hopman]

One reason whil I like stick shifts. I can go into OD when I need to.

I've safely run my Ranger a 3,000 RPM all day on the highway, doing 70-75. I try to keep my truck below 4,000 revs under normal circumstances so that I have 2,000 rev cusion before I redline it.

 

[mattpresley]

that was my second thought, that maybe it's not going into OD.

Have you started from a stop and counted how many gears you've shifted through?

The way I like to calculate speed vs RPM (because tires of the same nominal size can vary so much in actual size) is to look up the "revolutions per mile" of the tire on tirerack.com. It's on the specs page of the tire.

(rev/mile) x speed x (1 hour/60minutes) x axle ratio x transmission ratio = Engine RPM

So if you're running 215/75R15's and your rev's per mile are 748, you have a 3.73 axle and an auto with a top gear of .75:1 (pretty typical OD ratio)

748 x 80 x 1/60 x 3.73 x .75 = 2790 RPM

So you can plug in your own numbers and figure out what's going on.

You can work backward the other way...

I always drive with OD off or my truck will stall after stops(whole other issue). Plan on buying a new ranger in October when registration expires

 

[Ranger Sport Honduras]

ive reached the 95 mph on mine, so thats your top speed
and when going at 80 it stays around the 4000, 4500 rpms and mines 5 spd, and ive driven it at those speeds in 4th and 5th gear.

 

[LittleHorse]

I always drive with OD off or my truck will stall after stops(whole other issue). Plan on buying a new ranger in October when registration expires

oh, well ok that explains it.

4500RPM isn't going to cause any problems on a trip...but might not be a good practice over the lifetime of the truck. Might take it from a 300,000 mile motor to a 250,000 mile motor.