MG Metro Inlet Manifold

[pauly45]

Hi,

Has anyone ever replaced the two steel water inlet and outlet pipes on an MG metro aluminium inlet manifold ?

They look like they were cast in at time of manufacture, so I guess it's a machine out job.

Cheers
Paul.

[bmcecosse]

Why would you? It works best without the water heating!

[pauly45]

It would mean I've got to re-do the piping however.

It really works better without it ?
I thought these manifolds were "the ones to have" as it were, and that the heating helped. (in some way !)

[bmcecosse]

Yes - good manifold, but don't bother with the heating. After all - twin carb manifolds don't have any heating - very often their only advantage over a single carb on the old std single carb manifold - with exhaust heating!!

[IslipMinor]

Another view. An unheated inlet manifold in theory can produce slightly more power as the incoming charge could be cooler, thus denser - no factual evidence has been produced for a Minor as far as I know? On the other hand an unheated manifold can ice up in cold/damp conditions (i.e. the UK), which is why they incorporated heating in the first place, and an unheated manifold will need more choke during warm-up, until it gets warmed up from the engine itself.

We have a water-heated manifold and an SU HIF6 on our 1380 - it produces very good power and is very driveable from cold. I fitted a Weber DCOE45 a while back for a rolling road back-to-back comparison - it was on an unheated manifold and was a pig to drive during the warm-up phase. Not a proper comparison I know, but for 4bhp in 106bhp more power, I reverted to the HIF6 quite quickly. With a couple of tweaks, the HIF6 now produces 6bhp more than the Weber using the same rolling road!

I am due to do a rolling road session later this year, so will clamp the manifold heating feed hose at some point to get a proper comparison.

[bmcecosse]

Since the water is cold during 'warm up' - it can't hope to heat the manifold! Let the manifold ice up - won't do any harm. The problem is if the carb ices up - but don't imagine that a heated manifold can help that - the 'heat' has no hope of travelling to the carb against the incoming rush of freezing cold evaporating fuel and air. And the carb is mounted on a phenolic insulating block - specifically to isolate it from the manifold. The manifold heating probably improves fuel consumption when driving gently - by flashing off any fuel clinging to the walls. The only way to stave off carb icing is by drawing in HOT air from close to the exhaust manifold (Minis had little 'stoves' on the ex manifold to make this more effective - or of course to have electric heating element in the carb - as fitted to some cold country export cars.

[IslipMinor]

From experience with making a steel manifold for twin SU's on a Sunbeam Rapier many years ago, I started without heating (for maximum power) and it was awful to drive until warmed up, and then had a hesitation on quick throttle opening. I put this down to the fuel dropping out of suspension and condensing on to the cold manifold walls. Even so the performance and economy were far better than with the twin downdraft Zeniths before.

Fabricating a water jacket, fed by the heater bypass system in exactly the same way as a Minor does, transformed the 'warm-up' phase and eliminated the flat spot as well. The fuel economy seemed even better and I can't say I noticed any reduction in performance. Definitely converted my thinking about having a water-heated inlet manifold!

[bmcecosse]

Well - can't deny your proof there Richard! I made 'long' steel inlet pipes for twin 1.5" SUs on my racing Mini - it was terrible until warm anyway (S head and 544 cam on a 998) - but it went well when hot! To get back to the original subject - I would not attempt to renew that pipe - I suppose you could slide a slightly smaller pipe through inside the cast-in pipe - if you really want the water heating - how effective that would be I'm not sure. My 1098 engine has the Metro manifold - and water not connected. The 'choke' goes in most of the way as soon as it starts - and right in by the end of the street - and it's only a v short street... Plugs are light beige - so not running rich.

[katy]

To replace "the two steel water inlet and outlet pipes" you could possibly drill them out, then tap the manifold w/the appropriate size pipe thread tap and get hose barbs to fit.

[pauly45]

Actually, thats not a bad idea.

A nice brass hose barb threaded in might work.
There's not a huge amount of aluminium around it, so I need to find out what the hole diameter would be to take such a thing.

Cheers
Paul.

[Biggles1957]

Paul - I've just fitted one to my traveller together with an HIF38 and connected up the heater pipework. The steel pipes on the manifold were a bit on the short side I thought -probably been cut off due to corrosion I think - and I found that two short lengths of 15mm copper pipe would fit rather nicely with the aid of a tapometer to make ideal pipes to fit the hoses to. I flared the ends of the original steel tubes a little and smeared the ends of my copper pipes with sealant adhesive to help them knock into place -they are a really snug fit. This way I didn't have to drill out the old pipe and have achieved a completely water tight solution if you use the same fix make sure you clean up the inside of the steel pipes and the outside of the copper to ensure a good fit and seal.

[bmcecosse]

Big risk of wrecking the thing with the drilling/tapping - and if the glue comes unstuck????? Just run without the 'heating' - honestly - it's fine.

[Biggles1957]

The copper pipes were such a good fit that the main function of the sealant adhesive was as a lubricant to help knock them in. I'm really happy with the results

[bmcecosse]

Until the day one pops out on the M'way and wrecks the engine.........