Gear Ratio's

[benmagoo]

Got myself a 56' Splitty with a 1275 sprite engine running a single SU, a 5 speed type 9 ford box and a 4.22 ratio diff.

Acceleration is brisk enough with plenty of low down torque but up at 60 - 70 mph she runs out of legs and have ended up doing 70 at what sounds like halve revs but nearly full throttle.

My question is about the gearbox; are there any markings etc that will relate to the gear ratio's in the box?

I know that the two real options are more power and / or change the diff ratio but I really want to do this propperly and not jepardise drivability for the sake of a bit of top end.

Thanks in advance for any help or info.

[MoggyTech]

Only other diff that would improve top end is the 4.55 from (I think) the LCV version, aka van or pickup. The 1275 should be plenty to drive 5th gear on the T9 box, so maybe you just need a good tune up.

[Packedup]

What carb are you running? It could simply be you're using something too small for full power (which would still flow well enough for low end grunt).

[benmagoo]

I had concidered the state of tune, its an HS4 - am gonna call local rolling road for price on tune.

[Packedup]

I had an HS4 on the 1275 Midget lump in my now deceased Minor, and it did start to run out of steam but not as bad as yours sounds. I'll have to try and remember to check what needle/ spring combination is in the carb, as it certainly worked fairly well.

[Kevin]

Only other diff that would improve top end is the 4.55 from (I think) the LCV vers

Thats the wrong way round that will give better low end acceleration but will run out of steam at a lower speed.
The combination quoted is quite normal and should give good performance as the 4.22 axle with the type 9 is the normally accepted combination with no need to go for a 3.9 or 3.7 diff as the five speed is like an overdrive box.
If the carb definately an HS4 what manifold is it on, as it needs to be on a larger one rather than the standard Minor one. With your setup an HIF38 or even better an HIF44 would be the ideal combination. One other thing what sort of air filter has it got on it as this will restict things as well.
As an aside I used to run a 1275cc engine with an HS4 on the correct mini manifold with the standard filter housing opened out to suit and it didnt start to run out of steam until around 90 mph.

[benmagoo]

She's booked in for a dyno session next Wednesday, on closer inspection (actually looking this time) its running a HIF44 with a standard air box on a mini sports manifold and an LCB manifold.

I think I will wait for the dyno tune before making my decissions on further action as I had my Mini done three years ago and remember the change being like driving a different car all together.

Thanks for the input, looking forward to my dyno graph now - what bhp / torque should I expect to see at the wheels? 55 / 60 ish?

[Packedup]

A HIF44 should be fine, but what do you mean by standard air box? The HS2 Minor one won't fit, and will flow quite poorly anyway.

Factory spec is 65hp (give or take) for the 1275, you might be looking at 70 at the flywheel if you're lucky. So 55 at the wheels sounds about right if the engine is in good condition and tuned up right.

[Matt]

Using the elbow off a marina hif44 allows a standard minor airbox ;)

[Packedup]

What a hideous concept. The Minor box is barely adequate for a low powered Minor!

I've got a one half of a pair of HS2 Midget filters on the pickup, still not great but they were kicking around and I needed a filter.

For a 1275 with a HIF44 I'd be wanting something somewhat more efficient though.

[benmagoo]

What a hideous concept. The Minor box is barely adequate for a low powered Minor!

I've got a one half of a pair of HS2 Midget filters on the pickup, still not great but they were kicking around and I needed a filter.

For a 1275 with a HIF44 I'd be wanting something somewhat more efficient though.

It's running the plastic doughnut thing

Ultimately efficiency is the aim, serious thought is being poured into the Canems (www.canems.co.uk) semi-sequencial mappable ecu jobbie on bike throttle bodies. Theres a feature on it in this months Mini World and sounds quite interesting whilst keeping that distinctive A-series burble

[youngun]

You mean the one that surrounds the carb leaving the dashpot visible? Maestro style i think!

[benmagoo]

Thats the monkey, the classy looking generic plastic doughnut

[Matt]

Im sure you mean a mini one? AFAIK the maestros tended to use a flat panel?

[benmagoo]

Very possibly although this is the BMC parts bin, it's probably the same housing as used on most SU applications - metro's, mini's etc

[IslipMinor]

I would check the airbox/filter set up. On a recent rolling road session I 'found' 8 bhp by simply removing the 'cleaned up' MG Metro airbox, which already had a K&N filter element in it. Now has a round, deep K&N and 'stub stack' - haven't yet had the opportunity to check the power output.

[benmagoo]

What a difference a dyno tune makes!!!



That’s 55.2 bhp (46.9 At The Wheels) and a full 66.3 ft lb of torque!

Turns out she was running dangerously lean; the guy said he was amazed that she hadn’t burnt out any valves!

She started the day at 49.6 bhp (41.5 ATW) running very lean, with a good tune and new needle they found a full 5 bhp which doesn’t sound like much but is actually over 13% increase in power.

On the road she is like a totally different car, she accelerates much more smoothly, around town is a little more drivable and on the dual carriageway 70 is easy and prompt with plenty left in reserve.

Thanks for the advice and tips etc, I would still like to find out about the type 9 ratio’s but maybe that’s a long term project for now

[IslipMinor]

There are a number of different gearsets in the Type 9, but the most likely one is:

1st 3.610 4.51 27

2nd 2.080 7.84 47

3rd 1.360 11.98 72

4th 1.000 16.30 98

5th 0.830 19.64 118

The 2nd column is the gear ratio, the 3rd colum is the mph/1000 with the 4.22 diff and standard tyres and the 4th colum is the speed at 6000 rpm engine speed.

[benmagoo]

Thats super cool, and looks very close.

Driving her this morning was brilliant, 55 to 70 in 5th is 5-6 seconds! she then motors happily on to 80ish on the speedo

Gonna wait til after our holiday to Ilfracombe in September before deciding about diff's etc.

Well Chuffed

[bmcecosse]

Try the car with NO air filter fitted - just to be sure. Could judt be completely wrong needle (what is it ?) - or very possibly that the fuel pump can't keep up enough supply at the high revs. May also be ignition timing - is the mechanical advance working ok - and how much advance is it giving ? Also check vacuum advance working - although not used a full throttle - if it's jammed it can cause you to set the idle advance wrongly - and then it does mess up the full power setting.