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Old 23-07-2004   #1
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Airbox on mk2 45

Ive been cleaning my engine today, 1.0 Mk2, and thought id have a look at the airbox and realised the hose from the front bumper is blocked off at the grille, so not much air can be getting to the engine.

And i also realised that theres a pipe from the airbox which looks like it goes to the manifold. This is just for show and does nothing!

Surely because of this pipe, all the air in the airbox would dissapear out of this hole and not go through the filter and into the engine???

I am therefore thinking of moving the hose and re-positioning it more centrally in the grille and blocking off the hole in the airbox (that looks like it goes to the manifold) so that the airbox acts as a sort of 'forced' induction system.

Could someone tell me if i am right about this, and would my two modifications be worth while, or at least worth a go....???

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Old 23-07-2004   #2
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You can remove the pipe from the exhaust manifold during the summer, but in the cold winter months you will find that you can will stall a lot when its cold, as it uses the hot air to stop the carb 'icing up'.

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Old 24-07-2004   #3
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Yeah, the pipe to the manifold is the hot air intake, with out it, your car will run crap as in the cold. I thought I could get away with out mine, and it was fine untill it started getting cold. then it was an absolute bastard to drive untill the engine had warmed up...

but in the summer, pull it off, for sure.


Cheers,

Matt

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Old 25-07-2004   #4
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*I've just re-read this before posting and it sound more like a motor science lecture! But if you're interested, read on. Hope I don't bore you all....*

Chris,

If you mean the metal/ foil pipe from the exhaust manifold to the airbox, then yes, it does do a job and isn't just for show. If you feel the hole where it goes to the airbox, it will appear to be blocked off. This is because there is a spring loaded flap that covers this hole from inside the airbox.

This flap is temperature sensitive, and the idea is that when the engine is cold (and so is the air temperature in the airbox) it will allow hot air to be sucked in from the top of the exhaust manifold to help the engine heat up quicker. The flap also tries to keep the incoming air at a constant temperature, because if the air is too cold it will cause carburetor icing.

There is also the main cold air pipe going into the airbox, which is the main air source. This is balanced by the hot air inlet as mentioned above which helps keep the incoming air at a constant temperature.

Icing is a more common problem with carburetor engines, rather than fuel injection which tends to suffer less from fuel 'icing' problems. In fact, I read somewhere that multi point fuel injected engines don't suffer from icing. Also with multi point injection the more cold air going in the better, as most of the air temperature is controlled by the injection system. I think the fuel freezes less because it is pumped in under pressure rather than entering by a suction process, and the fact that there aren't small jets to get blocked as used in a carburetor.

However, the injection system in the Uno (non turbo) uses a single point injection system. This is really some kind of hybrid carburetor so it may be subsceptable to icing just as much as a real carburetor. The turbo uses multi point injection having four seperate injectors firing directly into the inlet manifold, so as far as I know Turbos never suffered from icing problems.

Carburetor icing occurs when moisture in the air/ fuel mixture is allowed to freeze. This causes ice crystals to form, which end up blocking jets. This happens gradually hence the problem of a car losing power the more it is driven on a journey in cold weather. The engine idle is also the first to be affected because the idle jets in the carburetor are the smallest so tend to get blocked first. This is why the first sign of icing is when the engine stalls when the car is brought to a stop after a run, yet fires up straight away with a bit of throttle but won't idle. Despite being injected, I think the single point system used on the Uno still has a number of jets inside the throttle body therefore suffering just like a carburetor.

It doesn't have to be freezing outside for icing to occur either, because icing can be formed by the wind chill factor of the speed of the air travelling through the intake. Just like in normal weather, it can be 5 degrees above freezing, but with the wind travelling at 10mph (this is a guess) it can actually have a chill factor of minus 5. The air speed travelling into the engine means the temperature inside the carburetor is below freezing despite the outside and engine temperature, causing it to ice up. This is why the airbox has a hot air inlet to try and stop this from happening.

However, as cold air is more dense than hot air, it allows the air fuel mixture to be more potent which actually equals more power through better combustion. That is actually how turbo cars produce more power by forcing a greater amount of air in (making it more dense through pressurising) for the ratio of petrol. With non turbo engines this is no-where near as noticeable, but if you've ever driven through a patch of fog on a late summer/ autumn evening you might notice that the engine seemed to be smoother and just a little more powerful for a few seconds! That's the effect of a greater air density.

As for losing all the air out of the hot air manifold pipe hole, that won't happen. On a norminally aspirated engine air is drawn into the engine by a SUCTION process caused by the air displacement of the engine pistons. The suction occurs at the carburetor or fuel injection throttle body. Therefore, this causes air to be sucked from the cold air and hot air inlets at the front end of the airbox.

A lot of people have mentioned that the cold air pipe going to the airbox appears to be blocked at the grill/ headlight end. My Uno (a carburetor model) originally had a pipe going to just below and to one side of the offside headlight. It was clipped into a plastic 'Hoover nozzle' type thing that exited at the front of the panel behind the front bumper. The idea here being that it takes an inlet of air away from the engine and also outside the engine bay, hence drawing in colder air.

On my car the blanking panel next to the radiator had a rubber flap that was supposed to be kept in place by the radiator, but due to air pressure coming through the front grill it kept blowing inwards and didn't seal against the radiator. This meant that when it rained, water and muck kept getting past it and all over my clean engine!

So while pulling an alternator out of a mk2 Uno in a scapyard, I noticed it had a different inlet arangement. This had a solid plastic panel with a cold air inlet pipe hole, that held itself securely in place next to the radiator and was a straight swap into my mk1. The cold air inlet hole IS partly covered by the front panel, but there is in fact plenty of space to allow air to enter through this hole from the front of the car.

Don't forget that this cold air inlet pipe is only supposed to be sucking in ambient air, and is NOT designed to be working like a ram air or forced induction system. It's only meant to draw in air from somewhere cooler than the engine bay, and the space behind the front grill is ideal. That's why it doesn't appear to be directly facing the cars airstream.

It is possible to fabricate some kind of ram air system for the Uno, but it is not without it's problems. The first issue is to have a big enough air scoop positioned so that it can catch a large amount of air at the front of the car. The mouth of the Uno's cold air inlet pipe is way too small to have any real effect. The scoop would have to have a much wider mouth to catch as much air as possible, tapering to the size of the inlet pipe to force the air in.

Then you would have to make sure the entire airbox and inlet pipework were totally free of air leaks. The idea here is that you are trying to pressurise the air intake system, and the slightest leak would cause the pressuring effect to be lost. You WOULD have to block off the hot air intake hole in the airbox, and also the engine breather tube inlet and the air bleed tube to the base of the carburetor/ throttle body. You would also have to make sure as well that the seal between the two airbox halves is completely air tight. It's designed to seal under SUCTION and is not meant to be pressurised!

Even silly things like the hot air flap sensor needs looking at, as on my car it is screwed in on the underside of the front casing. Where the screw hole is you would have to make sure this was sealed air tight too.

The cold air inlet pipe would also have to be much more substantial than the standard brittle plastic pipe originally fitted. The original pipe would be likely to crack under pressure, and in fact when they are a few years old they do a good job of cracking on their own anyway! Ideally a metal pipe would be best as rubber pipes tend to bulge under pressure.

Anyway, let's assume you managed to make an air tight airbox and inlet pipe, and placed the air scoop in a position where it can catch a large amount of air from the front of the car. You will now have one other problem, and that is a ram air effect doesn't work until quite high speeds are reached. There's a lot of arguments about exactly how fast you'd need to go, but some people reckon you'll have to be travelling well over 100 mph for any significant gain to be felt. It would also be dependant on how big and efficient the scoop is, and whether it is placed in such an area that isn't slip streamed by the cars aerodynamics.

Remember that a carburetor/ fuel injection throttle body can suck in very large volumes of air very quickly, so the amount of air travelling into the airbox would need to be much greater than that to be able to create a pressuring effect. And as soon as you opened the throttle wide open most of the pressure would disappear very quickly into the engine giving a momentary 'turbo' effect.

On top of this, you would no longer have the hot air inlet and could well end up having icing problems in colder weather! You may also find that as the intake/ air box side is now totally sealed, in wet weather water might enter into the carburetor/ throttle body from a combination of being forced in through the ram air effect AND the suction from the engine. Apart from making your air filter go soggy, it could cause rough running problems if it mixes with the fuel.

On the normal cold air intake, air is sucked in and the inlet pipe travels upwards towards the airbox. This is so that any water/ rain that may enter the inlet pipe will just drain out as the suction isn't great enough draw it up the pipe into the air filter. If damp air is forced in by a ram air effect then it may be possible to have water ingress problems. That's also why a lot of cold air inlet tubes are of the ribbed type, as air travels through no problem but foreign objects or water droplets are more likely to get stuck in the ribs. Water is way heavier than air and is less able to travel upwards over the bumpy ridged surface of the tube.

Assuming that you did get a ram air system to work you also face yet another problem. If you force more air in than normal for the ratio of fuel, you make the mixture weaker. That in turn causes 'pinking' or pre-detonation, which can lead to burnt valves, holed pistons and overheated engines. That's why turbo or supercharged cars have knock sensors to detect this, and they adjust the fueling and timing when it happens to stop the pinking and weak mixture problems. A bog standard non turbo Uno can't do this, so will continue with a weak mixture pinking away merrily until something goes bang!

To cut a very long posting short, yes, ram air DOES work, but only at very high speeds that allow more air to be forced into the air box than is needed by the engine hence keeping it pressurised. This theory was kind of proven by a bike magazine when they tested a Kawasaki with a ram air system (I think it was a ZZR or ZXR 750, going back over a decade). They did some top speed runs, and found that going by the measured power of the engine, the weight of the bike and also taking into account aerodynamics the bike went much faster than it should have done.

As they measured the power on a dynometer where the bike was static on a rolling road device, they concluded that the ram air effect was coming into play and making the engine produce greater power at higher speeds. Obviously, on a dynometer no ram air effect was happening at all as the bike was effectively standing still. It is worth bearing in mind that the bike was reaching speeds well over 150mph where a ram air system is likely to start working, a speed way more than a non turbo Uno can ever hope to achieve......

Also worth bearing in mind, is that if a ram air system really did work on the average road car then car manufacturers would fit it. The fact that they don't says it all really. Then again, they fit spoilers, but the laws or aerodynamics say they have no effect until speeds of over 90mph are reached. And most factory fitted spoilers have hardly any effect at all as they are designed to look good rather than create downforce.

To make a ram air system for a standard Uno is really a waste of time. It might look good, but is unlikely to have any effect at all. Best to keep the standard airbox and make sure the hot air pipe from the manifold is in place. That way you can drive all year round without any problems.

If you really do want forced induction on your Uno, go find and fit a supercharger. Or to save the hassle, go find a Uno Turbo which has all the hard work done!

Think I'd better get to bed now after the science lecture......

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Old 25-07-2004   #5
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Phew took me a few days to read the last post! :p

Thanks for all the replies.

Right ive come to the conclusion that the hot air intake from the manifold is to be kept.

But im also still thinking of relocating the main cold air feed more centrally in the grille so that it doesnt look like its being obstructed.

Im thinking (correct me if im wrong, i normally am!) that when im travelling at speed, because there would be no obstruction at the grille, air would be able to enter the air box more freely, meaning that its possible more air would get to the engine.

Also i thought the air-fuel mixture on later mk2 Unos was self adjusting? Meaning that if more air did enter, the engine would adjust the fuel accordingly...

And if the hot air intake helps to prevent 'icing', replacing the airbox with a cone filter would make the engine run awful in winter.


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Old 25-07-2004   #6
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1986Uno45S; well done, seriously good advice there and good knowledge....

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Old 27-07-2004   #7
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The hot air hose from the manifold can be thrown away and never used again. Have been driving without it in -30 C without problems. Not even startups. The cold air is "obstacled" with the plastic cover. I removed the cover and drilled a big hole in it. Worked fine - more cold, dense air through the filter.

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Old 27-07-2004   #8
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I wouldn't advise anyone to run a carburetor version of the Uno without the hot air pipe Mort, as carburetor icing is a well known problem on UK Uno's. Most times people have found that the metal pipe was missing, and simply replacing it solved the icing problems. Of course, in the summer months it will probably run fine without it, but once the weather gets cold icing problems can occur.

On fuel injection it is less critical, but I'm not sure exactly how the Uno's SPI system works. If it it doesn't use jets like a carb and also injects the fuel under pressure then it is unlikely to suffer from icing problems. Therefore, once the engine is warmed up the colder and more dense the air going in the better. But don't forget that the hot air pipe is also meant to enable quicker engine warm up, which in turn aids fuel economy! That's normally what engine manufacturers are looking for rather than out and out performance.

And ChrisUnoman, it's not just about getting more air INTO the airbox. The amount of air needed by the engine is dictated by how much is sucked in from the inlet side which is the carburetor/ throttle body. The biggest obstruction to inlet air flow is the air filter itself, which is why a lot of people replace them with free flow sport items.

So you could make a huge inlet for your airbox and remove the air filter, but the engine is still only going to draw in as much air as it needs. As the filter is known to be restrictive, replacing it with a free flow item will allow the engine to breath better. But it's not a huge difference in air flow.

To make it flow more air you'd need to have a free flow exhaust system and would probably have to have the cylinder head gas-flowed with bigger valves put in. That, along with the performance air filter would then reap some gains in the power department.

So it's not just about getting more air into the engine, but also how much and how quick you can get it out of the exhaust. If the exhaust and/ or cylinder head are restrictive then the best air filter and air inlet in the world are going make very little difference.

Remember that a lot of people fit performance air filters because a: they look good and b: they sound good. On their own they don't make much difference to the power of an engine, but they SOUND like they make the engine more powerful! And at the end of the day, they aren't cheap and the manufacturers make a nice profit out of selling them!

Check out some of the car tuning magazines where they've tested some of these performance add ons. Quite often a performance air filter will be lucky to raise the power by 1 or 2 bhp, but can increase torque a bit more. In conjunction with a performance exhaust and cylinder head work only then can the power output rise significantly. Any kind of engine tuning needs to be done through the whole engine, from both the inlet to the outlet. The only exceptions are 'chip' conversions which allow Turbo cars to produce higher boost hence much more power very easily. But of course, this is at the expense of engine life!

The only real way to see if modifications make any difference is to have the car rolling road tested before and after the modifications were made. I can remember one issue of Classic Ford magazine where they tested some readers cars, and despite all the performance mods some actually produced LESS power than standard!

Fitting a perfomance filter onto a carburetor does often leads to the mixture running weaker. The only way to check this is to do a plug check and see how how they've been running. If they're running weak then it is normally a case of upping the main jet size or in extreme situations fitting colder spark plugs.

On fuel injection it depends how good the system is. If it has a knock sensor which detects pinking, then yes, it will automatically adjust the air/ fuel mixture ratio. However, I have a feeling that the SPI system on the Uno is very simple and does NOT adjust the mixture, only the idle speed. I could be wrong about this, but I have no technical info on the Uno SPI system. A lot of older SPI systems don't self adjust, though all modern cars with catalysts do. The giveaway is if you can adjust the timing. If you can, then the air/ fuel mixture is set by the throttle body. If you can't, then both the timing and mixture control is done electronically.

Perhaps the best compromise is to run a performance filter in the summer and the standard air box with hot air pipe in the winter. This would be especially so with a carburetor, and less so on a fuel injected model. Besides, in winter you don't want to have more power when your wheels are sliding on the cold/ damp/ freezing roads! And in winter you want the engine to warm up quicker to get better MPG and also to keep the inside of the car warm!
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Old 28-07-2004   #9
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1986Uno45S

My Uno from 1993 has a Bosch SPi. Looks like carburettor, but really - it doesn't ice. The little pre-warmer hose did nothing good (or bad). It was just a gadget that really didn't work - and yes, the thermostat switch was operational, deciding what to let in, cold or hot air.

The SPi on these models do not self adjust and do not have an anti-knock sensor. The distributor is of a breakerless type, and pinking is mainly due to a trashed vacuum advance unit or wrongly adjusted igntion timing. No adjustment is possible. There is an injection ECU getting info from the lamda sensor, air temp etc. but not a digiplex or microplex.

I've installed a K&N filter (custom ordered by size etc.) and it works very nice. A bit louder engine noise, but not very noticeable with the hood closed. But there is a higher torque at high speeds. I've just returned from holiday after driving over 1000 km each way in one session. At "Salty Mountain" in Norway I was doing 120 kmph (100 kmph equals 60 mph) and still having torque (which was more or less absent with the old air filter box).

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Old 29-07-2004   #10
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Hi Mort,

Ok, from the information gathered it appears that the SPI system is NOT susceptable to icing, but the carburetor engines are. However, when fitting a performance air filter to any car it is worth doing a plug check to just make sure the mixture isn't running weak. Better safe than sorry!

By the way, can I ask how you know that the hot air pipe doesn't work on your car?

From what I know all it is supposed to do is enable quicker engine warm up in cold temperatures and to stop carburetor icing on carb models. On SPI engines, once the engine is up to operating temperature it looks like icing isn't a problem, therefore the colder the air the better.

Your experience with the K&N filter shows what can be expected by changing from the standard item. Torque is more likely to increase than power, which is a good thing because it makes the engine more driveable. Top speed will probably stay pretty much the same, but the mid range driveability can improve. Many people find that fitting a performance filter makes the engine feel more responsive, the throttle response more 'crisp', and the car just that bit better to drive.

But some people expect noticeable power gains and are disappointed when top speed appears to be unchanged. Increasing torque is more likely to make the engine respond better in the middle of the rev range, not the top end. That sounds exactly like what you have experienced.

Oh, and I'm not sure on this one, but I'm sure I read somewhere that carburetor icing is more likely to occur at temperatures just above freezing than when it falls below freezing. Something to do with fuel mixed with moist air having an optimum temperature for freezing that only occurs at a certain temperature range. Also it's something to do with the amount of moisture in the air, which is more likely above freezing than below, because below freezing most of the moisture has already frozen and turned into ice crystals.

No, I don't understand it either! But I guess fuel mixed with air freezes under different circumstances to water. Probably what happens is that if there is a lot of moisture in the air, which happens as soon as it gets damp and cold (about six months of the year in the UK!) and the outside air temperature is below about 7 degrees then carb icing can occur. If it is cold but the air is dry then carb icing is less likely to occur because there aren't enough water molecules in the air to freeze.

However, I'm no scientist so can't confirm this 100 %, though I do remember reading about it back in the days when there were a lot of carburetor equipped cars on the road.

I do know that my first Uno suffered badly from icing problems until I realised what exactly the problem was! I changed distributors, carburetors, spark plugs and spent ages trying to work out what the problem was until I got it sussed. And yes, on my car the hot air pipe was missing and the hot air flap in the airfilter was jammed shut. I rectified those and the problem all but disappeared.

Took me about a couple of minutes to write that last paragraph, but solving the icing problem took me about two months! Back then there wasn't a forum like this to ask people for advice!

Chas
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Old 30-07-2004   #11
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Quote Quote:
Originally posted by 1986Uno45S
Hi Mort,

By the way, can I ask how you know that the hot air pipe doesn't work on your car?

Chas
Chas.

When we bought the car the pipe was missing. I was absolutely clueless about cars at that time, and didn't know it was missing. I took the car to a FIAT garage one year later after reading the haynes manual a couple of times asking about this pre-warmer hose I had read about. He said it I didn't have any problems last winter, I didn't need one. I got one anyway just to see if it helped. I waited until winter came and put it on. The car did not warm up faster, and did not run better. So I tossed it.

When I rebuilt the engine after a headgasket change I didn't replace the hose's bracket on the manifold either. I used an extra shim on those two bolts instead.

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Old 22-12-2004   #12
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Re: Airbox on mk2 45

Im from Ireland and have a 1990 Uno45S. This is my second Uno and experienced the same problems with both of them. The car drove perfectly in summer but come the cold frosty weather the car would stall. I changed everything plugs, carburetor, leads, filter but didn't solve the problem. I was convinced it was a carburetor problem and was perplexed when even that didnt solve the problem. I knew that if there was a bite in the air the car would give problems so eventually I came round to the idea that it had to be something to do with the fact that the carburetor didnt like cold air. So I disconnected the air inlet pipe from the front grill and twisted it so that it points towards the engine thereby taking the bite out of the air. It seems to be going perfect now. I noticed that there was a metal pipe going from the manifold to under the air box but it fell off. I dont think even when it was on it was doing much because it was loose and rattly. Just wondering what other people think of moving the cold air inlet so that it is warmed by the engine.
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Old 23-12-2004   #13
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Re: Airbox on mk2 45

It's alright, you just don't get that cold air to the engine. Replace the hose to cold air feed during spring and summer.

I've got a KN on top of the SPi. The airbox is thrown away. During summer a large flexible hose feeds cold air. During winter it's simply pointing down under the engine, so engine warmed air goes through the filter. Works great.

Morten.
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Old 23-12-2004   #14
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Hi All (1.0 IE),

Nice posts 1986Uno45S!!!

I do a lot of short distance driving; so the faster the engine warms up, the better (oil and cat’ life etc).

I noticed my air box’s temp sensor was not connected to the diverter flap, so I screwed it back on (very tricky! – 3 hours) and now she warms up faster. This means the demisters work faster at shifting ice and warming me. Morten, at –30 this would be a big bonus? Wouldn’t you’re hands stick to the steering wheel when if its that cold?

Chrisunoman,
Don’t forget to check the air box “feet” are attached (see attached). If missing the holes underneath will leak air – they tend to brake off with age. You might like the whistle (Turbo blag?). They were a lucky find at scrap yard waiting to be fitted, well one spare (for now).

Joesod,
Don’t do it in the summer if you get a warm ambient temperature. My 903s’ (non supper) both suffered from overheating in the summer (round air box in summer position). I think my head gasket went shortly after fitting a new (non FIAT) hot air intake pipe. An AA guy later told me to poke a few holes in it to cool the air for when running normally, but by that time my air box was filling with oil pushed up through the breather (student neglect). I never trust them now re points gap, but that’s on another thread.

BTW I once clocked 102 MPH in her (uncelebrated 1986 D reg standard 903 - 45 Formula) down hill towards Sheffield Fire Duct on M1 with wind behind us. She was still going for it but traffic got in our way!!! I wish I still had her.

Its well known the carb`ed FIRE engine suffers from icing. My friend’s used to stall on the motor way at 90 MPH too often on cold days. – Death trap!!! His hot air intake pipe was in position, but I now wonder about the box feet.

Regards,
Louie Bee.

Sorry Morten, you kind of already answered that one. This thread is large and takes a long time to reply to (for a dyslexic). Glad I refreshed before posting. I am after that extra toque too. I don’t think ill be trying the ram. I think a new air filter (Do I block the breather off?), then have her tuned on a Bosch rolling road as I get a bit of pinking after about 50 MPH at the moment. Just learning about consequences from this thread as a friend blagged me it didn’t matter.
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