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.