Morris Minor Owners Club

I've just been given an HIF 38 carb that came off a 1 litre metro. Would this give me much extra oomph if I fitted it to a standard 1098 minor? I'd want it to give me an extra 5bhp minimum for it to be worthwhile. Are there any other advantages to the HIF-type carb?

I realise I'd have to buy a different inlet manifold, but what would I do for the exhaust, given that the Minor manifold is cast in one piece? Bear in mind I don't want to spend lots of money or scare the insurance company.

Any suggestions gratefully received!

it is possible to carefully saw through the standard manifold so that you
keep the old exhaust part of it but can fit a different inlet manifold. if you
are definitely using a different inlet then you can cut off the original inlet part
leaving a good margin for error and then shape the exhaust section until
there is just room for the new inlet. Seems a fiddley job considering that
you are already changing the inlet side which necessitates notification to the
Insurance!!!

The alloy inlet manifold from an MG Metro will be ideal. Last 2 I got were £5 each on ebay. Then as above - cut off the old inlet and use this. It will help the 1098 - part due to eliminating the exhaust heat from the inlet manifold (3 bhp), part due to the better flow of the new inlet manifold (2 bhp) and some due to the bigger inlet area of the carb (~ 3 bhp). There would be more if the head could be swapped for a better 12g295 ex MG 1100. Note - lack of exhaust heating to the inlet will make the car more crisp all the way up, however - the flow + carb will only be apparent at full blast!

OK, that sounds like a worthwhile improvement. I might be able to lay my hands on a K&N filter so that would give a few extra bhp I suppose.

I've looked on ebay and it seems like the MG metro manifold is for an HIF 44 carb, not HIF 38. Are the fittings the same? Also if it's a bad idea to heat the inlet manifold, why are most of them water heated?

Just another thought - will all this affect my fuel economy much?

Thanks for your help.

Some Mini 1000 were fitted with cast one piece manifolds (virtually identical to Minors) that took a 1.5" carb (same size as HIF38) and the exhaust pipe was the same angle and size as a Minors.

As with any fuel-related swaps it's very important to get the car set up by an expert. This sort of conversion especially so. The standard exhaust is small for even a standard 1098 so you don't want excess emmissions fighting to get through the exhaust system.

chrisd87 wrote:Also if it's a bad idea to heat the inlet manifold, why are most of them water heated?

For economy. But if you are tuning for power then don't connect it to the water supply.

Just another thought - will all this affect my fuel economy much?

Depends on your right foot! It can give you slightly better economy or worse depending on how you drive.

Great! If the insurance are OK about it, I'll start to acquire some bits.

The MG manifold takes both carbs. The water heating is for good emissions at idle - use it if you wish. The effect of water heating is very much less than the exhaust heat from the combined manifold - DO NOT use one of these if you want more power. With the correct needle your economy will be the same - provided you don't use the extra power! If you do use it - then you are obviously going to use more fuel.

I get better economy with the HIF38 and MG Metro inlet, but I fitted a larger bore s/s exhaust at the same time which would help efficiency. I've also got the Metro air filter which will limit power but has the advantage of taking in warm air from the exhaust manifold via a bi-metallic flap and that's stopped the carb icing up in winter as the old one used to do. If that's not a concern then a K&N would give more power but they can be a bit noisy.

Also if it's a bad idea to heat the inlet manifold, why are most of them water heated?

It also avoids carb-icing...

Regarding economy - I agree with the comments above - a mildy tuned engine is more efficient therefore when driven at the same speed it will give similar or better economy. When dirven faster, it will of course use more fuel.
When engines get highly tuned they can start to loose economy and performance during mild driving, but give a lot of fun when driven hard.

Water heated manifold does NOT stop carb icing - it's down stream of the carb and the heat will not travel back up stream. Only way if this is a problem is as per Stig - heat from exhaust manifold going in with the air.

OK thanks for the help. I'm keeping my eyes skinned on ebay at the moment for an inlet. I don't think the economy will be a problem as I don't race around - I just wouldn't mind a bit more go when I need it.

Had a slight change of plan - instead of tuning my current engine, I think I'm going to buy another engine, overhaul it and tune that as there's no point in tuning a knackered engine.