Yes Malsal has got it...a few chaps in Australia are concerned about the replacement of the 1098 with 1 1/4" SU and peashooter exhaust but climbing off the coast to the tablelands was very slow and demanding on that 1098 even with 3.65:1 FD.

And, since I tend to drive the Minis with a vacation sized load on long trips over mountains, across deserts and with seasonal temperature variables these all impact on how I look at power unit, cooling etc.

I totally enjoyed that insight from Malsal:  ...a lot depends on what part of the country you drive in...

After 30,000 miles driving a 1275 + 2.76 final drive (and A+ gearing) I'd have to agree that 2.76 is, from a practical standpoint, too tall a gearing for a Mini. I personally am OK with it, and it is nice for long distance cruising near sea level. It makes a big difference in terms of noise, which is why Rover put that ratio in originally (though for drive-by sound measurements, not in-cabin noise.)

But fundamentally, a larger engine that has more torque at low revs (2-4000 RPM) is needed to truly exploit this gear ratio. Above 4,000 ft altitude, 70+ mph is pushing the limits of what the motor will pull - plenty of revs left on the tach, but the engine just won't pull higher in 4th. Even at sea level, I think 80mph is at the limit of what I can do. It would need to be able to pull those higher revs in 4th for me to call it fully "practical." My engine was dyno'ed at 53 hp (at the wheels) so it is in decent shape. Small motors need to be revved to get power out of them and it's hard to do that with a 2.76FD.

I like the cruising aspect of the 2.76, and at my home sea level altitude it works very well so I wouldn't change it. But if I were a manufacturer, I probably would use gearing that works well in broader cirumstances. If I get used to the increased noise, a 3.1FD might feel like I got a supercharger! The ideal would be a 5 speed that had a taller 5th than the ones available (so it would give something close to a 2.76 in 5th while actually using a 3.2 or 3.44.) But the boxes made today are more performance oriented and have more even spacing between ratios, instead of jumping to an "overdrive" 5th.

And I too have experienced aero drag as a major impact above 70mph. I've personally seen fuel mileage (along a similar route) drop by 20% going from a 65mph cruise speed to 75mph. Remember, we're talking a .49 cD here (.53 for Sportspack flared Minis.) A greater coefficient of drag than a VW hippie bus.

 

 

My 998 remained standard bore but aquired a 12G275 head, an MG Metro cam, duplex gears/chains & tensioner, a Hitachi 1.5" with K&N cone filter, a Sportex intake, a medium bore LCB into RC40, Pertronix ignition...and averaged 39.6 mpg (Imp) on the 7,500 mile transcontinental run in 2000 with a full load (+2,100 lbs.).

It was quicker than other 998s out my way and was faster than all but 1 Triumph in the Giant Slalom at PIR in 2002 (this might not be saying much).  In the hands of another driver it took 2nd place against 1275s in the autocross at MMW 2001 (though on a course short & tight enough to level things out a bit).  That factory original bottom end is still going in a LWB in the Fraser Valley...38 years later.

I did not have GPS in the car but the speedo was stock and so was the gearing.  Running on 165/70 10s it got up to some 95 mph when I pushed in on the divided Hwy. 1 in flattish Saskatchewan.

In Australia, I got a lift in a Mini with a Graham Russell 998 build...quiet, smooth (no rumpety rump) and pulled like the stock MG Metro 1275 on the like gears/wheels.

 

From my personal experiences i have found a lot depends on what part of the country you drive in and that applies to 1275's or 998's. In Florida we can get away with tall final drives due to the terrain or lack of it (2.76 under a 1275 and 2.9 under a 998). Now driving that same 1275 car in Virginia and North Carolina in the hills was a pia with having to downshift constantly to 2nd gear sometimes on the twisty hilly roads. My Clubman Estate runs fine all day long towing a camper trailer with a 1098 / 3.44 / on 10's at 65-70 mph.

Having the tall final drive in this crowd, I totally agree that tall final drives are not for 998s.  I have had one 998 with a 3.2 final drive and that was a sweet car.  If I was building a car for use only in town, it would have a 3.76.

While "There ain't no sustitoot fer cubes, boy" may be true for a lot of applications, there is always another way...

998s are more robust than 1275s, and will rev till valve-bounce quite happily.

Damn - great thread if I say so myself. Looks like we just put a premium on 998's, sorry. Several tried n true builds documented in one place. Anyone want to trade my project 1275 for their useless but running 998?....

The current engine in Betty is +.080", MG Metro cam, 12G295 head, MG Metro inlet, HIF38, std exhaust manifold with a magic pipe and twin-box RC40, 123 dizzy, std bottom end & flywheel, std gearbox with a 3.105 fd.  I have a naughty photo taken of the speedo off the clock while going up hill.
Even before the project slipped and she ended up non-standard (I was only changing the gearbox main bearing...) she would cruise at 75-80.
Once I get the FI fitted and fettled, I'm expecting some smile-inducing numbers on the dyno.

Tubbs would do 75 all day with a 3.44 under a bog standard 998. 
The replacement 1100 engine in Tubbs allowed me to waft past Guido on the M40 like he was standing still (speedo off the clock), and the one I'm building now will be better again.

Elrond would cruise with the needle nearly off the clock and max out well past IGN - 731 cam, 12G295 head, the same inlet and carb that are now on Betty, LCB and twin-box RC40, but a standard 998d bore, std everything else including the 3.76 final drive.

I'm utterly convinced that the A-Series needs to rev freely, and that long final drives are actually a bad thing.
Sitting at 4500-5000 rpm all afternoon poses no problems as long as the cooling system works and the oil pressure is good.  Indeed, I have seen it written by one of the BMC development engineers that a smallbore motor on the test bed will pretty much run forever if you keep the fluids topped up.

 

Now that 1275cc engines are harder to find in stock form, 998cc engines are becoming more sought after

I sold most of mine out at $750.00 with working trannys- But if you really want the best, then, there is one, totally rebuilt, locally for $9K with a tranny and all the ancillaries mounted- BIG AL

I'll add to it also -

Yep - a decent 998 is a really good cruising engine.  Mine, with 997 Cooper cam, 1.3 roller tip rockers, duplex chain, Luminition Optronic ignition, HIF38 on MiniSpares intake, K&N in drilled plastic housing (3 holes taped over, so only 2 holes of 5 being used), Maniflow freeflow exhaust with RC40 side-exit twin-box, lightened flywheel and 3.44 FD feels right at home at anything between 70 and 90 mph.  Between 50 and 70 mph, it doesn't really feel like it's settled; but above 70 it's smooth as silk and eager to go.

On a trip last summer to Jutland to attend the Classic Race Århus, covering around 400 miles, I averaged 33 MPG.  When I was a bit late for the ferie boat crossing, I had it up to 145/150 kph (90/93 mph) and it had plenty more still in it but I can't afford the ticket so I brought it back down to around 80 (ish).  T'was lots of fun. 

I thought the comment that inspired this was very incorrect.  In my own experience, a stock spec Canadian mini 1000 with or without the air injection system connected is good for 84 mph.

My own road trip car has a + 0.020 998 with a 1990 era unleaded head.  SW5 cam, minispares intake, maniflow header, RC-40 exhaust.  Duplex timing chain, stock clutch and a 1-2-3 mini ignition system.  The single HS4 SU has a stock air filter housing with a K&N filter.  All crankcase vents are plumbed to the carb.

This is on a remote transmission with a 2.95:1 final drive.  3rd is sometimes needed for steep hills, but mostly the car is comfortable at modern highway speeds.  It cruises at 75 most of the time.  It was a noticeably faster car when it still had a stock cam and a 3.44 final drive.  It gets better mileage than a friend's near perfect MK I Cooper S.

Sorry to intrude, but I'll put mine in here.

stock bottom end. Kent 256 cam. 12G295 head w/ 1.25 intakes, stock exhaust. stock rockers. MiniSpares Stage 1 kit. K&N filter in stock (but drilled) air cleaner. single HIF38 carb. 3.1 final drive. Stock rod change trans.

I can cruise at over 70 no problems. No issues on CA freeway traffic. I can also max out the speedometer, for whatever that's worth.

The more people that are in the car, however, the performance does suffer on inclines.

 

Alex, what's your 998 specs? 998's are a bit easier to come by out here sometimes as I have been passing them by. Wish I hadnt now. Spoke to someone recently that was entirely satisfied with their 998's - started a thread on this