2.25 Max RPM?

[Tim Smith]

Okay, so I did a search on the forum but all it picks up on is "2.25" no "Max" or "RPM" so figured I'd ask.

What is the maximum RPM one can get out of a 2.25 for top end highway crusing? I'm useless with figuring out the gearing numbers and wanted to know what my typical 2.25 is clanging away at when I'm doing say 65.

Again thinking about the engine swap issues here and know my Merc 300D motor should be good for over 4000 rpm. So theoretically, I'm trying to figure out what this would equate to as my highway crusing speed if I left the gearing alone.

Cheers,
Tim

[BackInA88]

Well I have an overdrive and 16" tires (235/85 R16) and I'm running about 3100 RPM's at 70 MPH.
I have run 65 without the overdrive but I didn't have a tach at the time.
I usually shift in to overdrive at around 60 because I feel it is screaming pretty well by than.
Tomorrow I'll check it for you.

[Tim Smith]

Well I have an overdrive and 16" tires (235/85 R16) and I'm running about 3100 RPM's at 70 MPH.
I have run 65 without the overdrive but I didn't have a tach at the time.
I usually shift in to overdrive at around 60 because I feel it is screaming pretty well by than.
Tomorrow I'll check it for you.

Thanks!

Thats good news for me I guess. I've seen the max HP rated at 4000 rpm but don't really know if that is the max rpm in general.

Don't blow her up doing any testing but if you can, let us know when the engine is sounding happy (and speed/gear if possible) and when it starts to sound like the 12 horseman are approaching.

Cheers,
Tim

[GrFa]

I asked this same question on another board and I think the concensus was not to run it over 4500rpm or so. I will be running 235/85/16 and no overdrive to start, with an ashcroft hi ratio transfer case that I could throw in.

[yorker]

I thought this info was on TAW's page? For some reason 4,200RPM sticks in my mind.

[Tim Smith]

I thought this info was on TAW's page? For some reason 4,200RPM sticks in my mind.

It could be on TAW's page but for some reason every time I start reading her site, I have the uncontrollable urge to just get in my truck and drive, or wrench or kiss it. Guess I've not got what it takes to figure out the numbers...

Actually, I've seen my truck at some unbelievable highway speeds and am really wondering what engine speeds I should be looking for in reality. And if I convert over what it would directly relate to.

Honestly, have you ever seen your truck read 85+ (very close to 90) while it was wearing 33" tires and in Roverdrive high? I think my numbers and experiences are probably acts of god, rather than what the truck was designed to do.

And I don't drink that much beer to make this up!!! At least I don't think I do.

[Tim Smith]

And I don't drink that much beer to make this up!!! At least I don't think I do.

After reading that, I feel that I have to explicitly say that I do not drink and drive. Bad, bad, bad stuff!

Only afterwards... like right now...

Also, I used to think I was a smart guy, until I realized what was telling me that...

[Tim Smith]

I asked this same question on another board and I think the concensus was not to run it over 4500rpm or so. I will be running 235/85/16 and no overdrive to start, with an ashcroft hi ratio transfer case that I could throw in.

Yeah but how can you tell without an rpm gauge? I might have run my motor up to 4501 rpm once, but wouldn't know any better.

Now that I think of it, oh gawd! What could I have done? Perhaps I was the reason that last motor blew all it's seals and started knocking... Still it saved me from getting run over that day.

Cheers,
Tim

[TeriAnn]

What is the maximum RPM one can get out of a 2.25 for top end highway crusing?

I've too never seen an official red line RPM for the 2.25L petrol but I have seen power specs out to 4250 RPM.

I'm useless with figuring out the gearing numbers and wanted to know what my typical 2.25 is clanging away at when I'm doing say 65.

Well you can be thankful that I can't even seem be able to say good morning without supporting data. Series gearbox/ standard Series transfercase/4.7 R&P/32 inch dia tyres (stock 109 dia) 65MPH = 3686 RPM.

As it just happens, yesterday morning I revised my gear ratio web page to include engine RPM at 65 MPH in fourth gear with 32 inch diameter tyres for all the standard Series transfercase and LT230 versions and 4.7:1, 4.1:1 and 3.54:1 R&P ratios. At a glance you can see all the combination 4th gear ratios and the engine speed at 65 MPH for each combination of transfercase and R&P.

I also linked the web page with the RPM calculator I used to help people get numbers for different size tyres.

http://www.expeditionlandrover.info/gear_ratio.htm

Again thinking about the engine swap issues here and know my Merc 300D motor should be good for over 4000 rpm. So theoretically, I'm trying to figure out what this would equate to as my highway crusing speed if I left the gearing alone.

May I suggest an alternative? Find out the RPM range where the 617 engine is happiest and provides its best fuel mileage then choose gearing to get as close to that engine RPM as possible at highway cruise. It is going to take a great deal of work to get a 617 Mercedes engine to fit into a Series bay. It seems a waste to couple it to the wrong gear ratios. There's lots of bolt in combinations to choose from so don't settle only for what sorta works but stresses the engine every time you hit the highway.

Data is your friend
TeriAnn@ nerds are us

[BackInA88]

Run it up to 65 without the overdrive this morning for you.
Looks like 3500 RPM's.
Looking to get me a 4000 RPM tach the 8000 RPM unit I had setting in the garage just doesn't cut it.
To me it was screaming for the overdrive.
Mine runs nice and smooth at around 3000 RPM's and can still pull itself up a small grade without loosing speed.

[Jim-ME]

I have always been under the impression that max rpms the same rpms that peak HP is achieved. If I read the RN catalog correctly a 2.25 L petrol engine peaks at 4,250.

[yorker]

If you like to crunch #s this site has some useful calculators:

http://www.grimmjeeper.com/gears.html

[TeriAnn]

It could be on TAW's page but for some reason every time I start reading her site, I have the uncontrollable urge to just get in my truck and drive, or wrench or kiss it.

Funny, me too!

A lot of that web site was written just after I came back from a trip or just after a Land Rover wrenching session when I wanted to document something before I forget for the next time I have to do that task. Some of it was written in leu of driving when the fuel tank and my pocket book were both empty and some when I just decided it was too cold or wet to work on my Land Rover outside.

My next computer will be a portable. I suspect I will end up writing a big photo & text journal covering my travels. I don't know if anyone would bother to read it other than myself though. If nothing else I could continue to write my book while on the trail.

Actually, I've seen my truck at some unbelievable highway speeds and am really wondering what engine speeds I should be looking for in reality.

While I'm a firm believer in the concept that reality is what you make of it, I've noticed that reality is strongly influenced by physics. Why not put a tach in you Land Rover? A couple of wires, a couple of screws and about an hour or less and your questions are answered more accurately than taking a poll of people with different configuration Land Rovers.

Honestly, have you ever seen your truck read 85+ (very close to 90) while it was wearing 33" tires and in Roverdrive high? I think my numbers and experiences are probably acts of god, rather than what the truck was designed to do.

The Land Rover engineers detuned the 3.5 V8 they put into production Series IIIs because they wanted to discourage drivers from driving faster than 65 MPH in a Series Land Rover. You were driving outside the safety design parameter envelope

When I had a 2.25L engine in The Green Rover I mostly cruised along at 55 MPH. Now that I have a 5L V8 and taller gearing, I mostly cruise down the highway at 60 MPH. The nice thing is that now I do it in the mountains as well. I think the fastest I've ever taken the Green Rover is 75MPH.

But getting back to 2.25 engine RPMs, having driven for a couple decades with a tach & 2.25L engine, I have noticed that a 2.25L engine seems happiest between about 3000 and 3400 RPM with 3200 being the sweet spot. With 32 inch tyres this means between 50 and 60 MPH.

My 5L V8 likes to loaf around in the low mid 2000 RPM range so I have raised my gearing accordingly. I bet a Mercedes 617 diesel also prefers to cruise at lower RPMs than the 2.25L petrol engine.

Be nice to your engine and your engine will be nice to you ... hopefully

[Tim Smith]

Run it up to 65 without the overdrive this morning for you.
Looks like 3500 RPM's.
Looking to get me a 4000 RPM tach the 8000 RPM unit I had setting in the garage just doesn't cut it.
To me it was screaming for the overdrive.
Mine runs nice and smooth at around 3000 RPM's and can still pull itself up a small grade without loosing speed.

Thanks so much for testing that for us! I had no idea the motor was actually going so slowly at that speed. It sounds so much faster when you are behind the wheel.

[BackInA88]

Yeah it sures sounds like it is screaming!