RPM Query

jpjeep26uk

jpjeep26uk

YJ Enthusiast
Joined
Nov 12, 2022
Messages
324
Location
UK
Hi all
I have a 1989 2.5l 4 cyl.
Can anyone tell me what revs they are happy going to in 2nd, 3rd, 4th and 5th gears please?
Silly question I guess - had it three years - but I do tend to play it very safe to preserve the engine.

Recently I did a speed test with a 'sat nav true mph' app to see if 60mph was truly 60mph as i always seem to be overtaken by trucks and we have a 56mph limit for trucjs in the UK on motorways/interstates.

Turns out my speedo is only accurate up to 40mph. When it shows 60mph, its actually only doing 53mph. I presume its to do with the big KO2 wheels being retrofitted.
So to actually get a true 60mph and not annoy trucks, I have to actually do 69mph on my speedometer.
I have NEVER driven at this speed for very long for fear of blowing the old girl up haha.

So - do I need to man up and crank her up to true 60mph as she'll handle it just fine?
And what rpm do you folks shift at?
I tend to get her into 4th or 5th asap, but apparently she'll take a lot more than I give her and will happily handle being taken up to 40mph in 3rd and say 55mph in 4th?
Be good to see what you come back with.

Got a 200 mile trip on Friday (Lutterworth to Newcastle on Fri and back again on Sunday night for those of you tuning in from ole blighty - I know - crazy idea but it's for charity ) and just preparing for that as the cold weather is playing havoc with my Carb settings and just wanted to know how hard I can really push her.
She's got 159,000 miles on the clock.

Thanks!
 
Any rpm below redline is fine if the engine management keeps up. I regularly take my 4.0 up to 4000-4500 rpm, no reason the 2.5 can’t do the same.

Your speedo is actually calculating the opposite of how you’re thinking. If it shows 69 but you’re only really going 60, then that mean it’s programmed for larger tires than what you have. Did it come with larger tires when you bought it and then you downsized to the 215s you have now?

Either that or somebody changed the gearing from 4.11 to something deeper like 4.88 maybe.

Big tires slow down the speed reading, not speed it up.
 
Macho that's a good point,
machoheadgames said:
Any rpm below redline is fine if the engine management keeps up. I regularly take my 4.0 up to 4000-4500 rpm, no reason the 2.5 can’t do the same.

Your speedo is actually calculating the opposite of how you’re thinking. If it shows 69 but you’re only really going 60, then that mean it’s programmed for larger tires than what you have. Did it come with larger tires when you bought it and then you downsized to the 215s you have now?

Either that or somebody changed the gearing from 4.11 to something deeper like 4.88 maybe.

Big tires slow down the speed reading, not speed it up.
Click to expand...

Macho that's a good point. Yes speedo shows higher rpm than reality so yes it must have had bigger wheels or tyres at some point in its life. I guess it won't affect the rpm limits as red line is red line no matter what the wheel sizes are?

I guess it's the sound of the engine in higher revs compared to a modern car. Mine sounds like it's labouring but it's probably not at all.
I should perhaps trust it a bit more in the higher rev ranges as I don't get even close to red, nowhere near. Most itts been is upper 3000s haha.
 
I ran my 2.5's all day long at 3200 +- when on the highway. No 5th use 95% of the time either as its just wouldn't pull it. You could hold the speed in 5th with it floored, but when shifted down to 4th you quickly gain speed. To me that's bogging so why bother even if the rpm dropped to 2800 or whatever it was.
 
Gilaguy23 said:
I ran my 2.5's all day long at 3200 +- when on the highway. No 5th use 95% of the time either as its just wouldn't pull it. You could hold the speed in 5th with it floored, but when shifted down to 4th you quickly gain speed. To me that's bogging so why bother even if the rpm dropped to 2800 or whatever it was.
Click to expand...

Interesting. Someone else said they hardly ever use 5th as it's gutless on even a simple freeway incline and you drop to 4th just to keep up.

That's what I have.

It's great in 4th but I feel I'm stressing it out as the engine roars at that speed. Well, I say roar, more like a 'holy cow you want me to do what speed?' So I stick it in 5th as soon as possible.
OK. I'll play around on my 200 miler up country this Friday.

I think a lot of it is that these are rare vehicles in the UK, in decent condition,and hard to get parts and I fear for damaging it.
 
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