Morris Minor Owners Club

Posted: **Sun Mar 22, 2026 6:50 am**

I watched one of Stef's videos. Someone had tuned her Minor. He drilled large holes in the air filter box to allow more air to get in, and the car went much faster.
Shall I get my drill out?

Posted: **Sun Mar 22, 2026 8:32 am**

My experience of having my car tuned on a rolling road (a standard 1098 like Steph’s) was that the mixture went lean at higher rpm. Rather than not enough air my car had not enough fuel. They’re all different so case by case basis I’d say. I don’t like seeing original air filter housings butchered. If more air is needed you could fit a high quality (not the cheap ones which actually seem restricted) pancake filter.

Stephen

Posted: **Sun Mar 22, 2026 9:27 am**

Could you please post a link to Stef's tuning video.
It is quite possible that the max air flow through the standard air box is not equal to the design max air flow through the carb which may effect the fuel/air mixture.

Posted: **Sun Mar 22, 2026 9:49 am**

I don't have the technology, but the youtube channel is Idriveaclassic.

Posted: **Sun Mar 22, 2026 10:09 am**

It's in this video but this isn't the main video which I haven't seen. I've watched this one though. AC Dodd uses "on the road tuning". Tuning in real driving conditions not tightly controlled rolling roads. I believe he uses exhaust sensors fitted temporarily during the test drives. Not sure what he measures whether CO or O2 or what.

Stephen

https://www.youtube.com/watch?v=wIjpLwyk-o0

Posted: **Sun Mar 22, 2026 10:37 am**

stuffedpike20 wrote: ↑Sun Mar 22, 2026 6:50 am I watched one of Stef's videos. Someone had tuned her Minor. He drilled large holes in the air filter box to allow more air to get in, and the car went much faster.
Shall I get my drill out?

We need more info. Why were holes drilled to allow more air? What else was done that required this 'modification'? I don't think drilling holes in a standard air filter casing in a standard car is going to improve things on its own.

Posted: **Sun Mar 22, 2026 12:12 pm**

myoldjalopy wrote: ↑Sun Mar 22, 2026 10:37 am
stuffedpike20 wrote: ↑Sun Mar 22, 2026 6:50 am I watched one of Stef's videos. Someone had tuned her Minor. He drilled large holes in the air filter box to allow more air to get in, and the car went much faster.
Shall I get my drill out?
We need more info. Why were holes drilled to allow more air? What else was done that required this 'modification'? I don't think drilling holes in a standard air filter casing in a standard car is going to improve things on its own.

The video that Stephen has put up is not the Idriveaclassic one that I saw.
Mr Dodd did not just drill holes in the air box, he did other stuff too.
Steph was very pleased with the results.

Posted: **Sun Mar 22, 2026 1:33 pm**

Surely if the carburetor is set up for the standard air filter it would need re tuning to accommodate the extra airflow.

Posted: **Sun Mar 22, 2026 1:50 pm**

Here's the video he did with Steph, not showing her Minor but explaining what he did on a Mini

https://www.youtube.com/watch?v=zLShDtFAm9M&t=22s

Posted: **Sun Mar 22, 2026 3:40 pm**

In the one that I saw, Steph takes her Minor out after tuning and is surprised by the extra power.

Posted: **Sun Mar 22, 2026 6:15 pm**

Had a look at the video above and as I hinted in my post above the air flow through the inlet pipe of the standard air box is insufficient to cope with the size of the carb and the modifications carried out to both carb and engine. It appears the Steph's Minor is modified (1172cc if I remember correctly) so it may well have been that the air box was not allowing max or adequate air to get to the carb so required the additional holes in the air filter housing. As regards a standard engine I would not drill any extra holes in the air filter box because of the following - on cold days you need the ability to swivel the air cleaner to pick up warm air from the manifold to avoid icing of the carb, drilling the extra holes will create additional engine noise and your air filter element will get fouled quicker.

Posted: **Sun Mar 22, 2026 7:58 pm**

Well, Mr Pike,
If you've a unmodified 1098cc engine like me then you'll find that with the ordinary air box that there's about 6.5 inch of water depression in it (before the filter) when at full throttle and max engine revs all under load. (In top gear that's about 74/5 mph on the flat with a Traveller.)
As 33.8ft of water pressure equals one atmosphere, then if you can eliminate the 6.5inch of water pressure drop by drilling holes in the airbox you'll gain about 1.6% power. (Mind you, the noise increase will make it sound much more!)
One way you can try this for yourself is to remove the airbox and hold the filter in place with a large washer using the airbox bolt plus a spacer. And then you really hear the noise! That's why they use an airbox. (And to protect the fragile filter.)
MikeN.
PS The filter itself contributes about another quarter inch of water pressure loss.

Posted: **Sun Mar 22, 2026 9:05 pm**

I'm going to leave well alone.

Posted: **Mon Mar 23, 2026 12:51 pm**

Good thinking !

Posted: **Mon Mar 23, 2026 1:39 pm**

MikeNash wrote: ↑Sun Mar 22, 2026 7:58 pm Well, Mr Pike,
If you've a unmodified 1098cc engine like me then you'll find that with the ordinary air box that there's about 6.5 inch of water depression in it (before the filter) when at full throttle and max engine revs all under load. (In top gear that's about 74/5 mph on the flat with a Traveller.)
As 33.8ft of water pressure equals one atmosphere, then if you can eliminate the 6.5inch of water pressure drop by drilling holes in the airbox you'll gain about 1.6% power. (Mind you, the noise increase will make it sound much more!)
One way you can try this for yourself is to remove the airbox and hold the filter in place with a large washer using the airbox bolt plus a spacer. And then you really hear the noise! That's why they use an airbox. (And to protect the fragile filter.)
MikeN.
PS The filter itself contributes about another quarter inch of water pressure loss.

Please.....call me 'stuffed.'

Posted: **Mon Mar 23, 2026 1:55 pm**

Fitting a K&N element will reduce the pressure drop too.

Posted: **Mon Mar 23, 2026 7:00 pm**

It has to be remembered that the factory fitted air cleaner is an all round compromise as regards noise, filtering ability and performance requirements.
The Morris 'A' Series in standard form was never considered a performance engine and it was not until the classic Mini Coopers came along that the 'A' Series engine was able to produce some sensible factory bhp/performance.
The Minor later air filter housing could be rated as a performance filter when compared to the oiled mesh air filter fitted to the likes of the A30/A35.

Posted: **Tue Mar 24, 2026 6:36 am**

The minor set up is designed for torque and cold operation not power, aside from the restrictions, its got an exhaust heated manifold and the air cleaner often picks up of the exhaust manifold. A 1098 sprite with twin cabs, better exhaust and mild engine tweaking went from 45 to 60hp, this is what we are aiming for. (I know the sprite had 2" mains , I'm putting my faith in modern lubricants, balancimg and limited use!)

Posted: **Tue Mar 24, 2026 9:24 am**

Only those 1098cc 'A' Series engine numbers prefixed by 10CC had 2" main bearings (and special flywheels).
Generally the 1098cc 'A' Series does not like being tuned but with the balancing of every moving part and careful assembly you will probably get away with upping the power of a non 10CC 1098cc 'A' Series engine.
The whole lower end that is - starter dog, damper pulley, crankshaft timing gear, crankshaft, flywheel and clutch cover must be balanced as one assembled unit. The rods and pistons must also be balanced as separate units and as assembled units. The rods must be balanced end to end.
To get the engine properly balanced can be time consuming and expensive.
Good luck
Phil

Posted: **Fri Mar 27, 2026 7:41 pm**

My 1098 has been mildly warmed - Kent cam, Hif 44 carb and LCB exhaust - it is probably now similar in performance to a 1275 engine.

Would it benefit from having a harmonic damper pulley fitted?

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