messing about with engine air intake - Amin_{p}
Hi guys, a question, which borders on being technical but I hope will not raise the objection of the back room minders if I write is here. I have a diesel Citroen AX, and I have realised that the noise and general smoothness of the engine is highly dependent on the outside air temperature, even when the engine itself is hot. If the air is warm the engine is very nice, quiet and much more smooth. However when the air is cold, it sounds like a tractor engine, and is as smooth as an elephant?s backside. This lead me to think whether if I `heated? the air, or at least part of it, going to the engine I could make the engine perform better. I can do this easily by adding a bleed from the hot air blower to the air intake just before the air filter. I know some cars do this and warm a proportion of the air intake around the exhaust manifold, then bypass it back to the air intake, however I have not seen diesels with this feedback. Has anybody done this themselves? If I do this to the engine which was not originally supposed to have it, will I cause damage? And if no engine damage is caused, does it actually help things or am I dreaming things? Also is there a chance of pumping too much air back to the intake or is there self regulation in the chamber? I would be much obliged for your help and guidance and thank you.
messing about with engine air intake - Mark (RLBS)
Why would you want this in Discussion rather than Technical, assuming that you are serious ?
messing about with engine air intake - bazza
You are on the wrong track here. Heating your air intake will actually decrease the power output of your motor. Diesels produce more power with a cooled, denser charge of air. This can be quite noticeable on a nice cool frosty morning!
That's why manufacturers fit inter-coolers to most turbo-diesels these days, it's to cool the air down before it enters. This is very effective and gives a significant power increase.
Any air heating system you've seen is most probably associated with a cold start mechanism on a petrol engine - fine for those first few miles to improve fuel vaporisation but this is not the answer for your diesel.
messing about with engine air intake - Dynamic Dave
Hi guys, a question, which borders on being technical but I
hope will not raise the objection of the back room minders
if I write is here.

It all boils down to who you want your target audience to be.
messing about with engine air intake - Nortones2
Amin: what fuel do you use? Vegetable oil? Not trying to be funny, but your symptoms are at odds with my fairly long diesel experience. As said earlier, cool weather favours turbo-diesels. Other thought is: how far do you drive it typically? Does it get warmed up?
messing about with engine air intake - Amin_{p}
guys i definatly know where you are comming from, but honestly this is how it behaves. if you think that is funny about my car, wait till you hear this. you know how people say "if i drive like a granny i get 50mpg, but under normal condition i get 45mpg" (say, figures just an example), well my car is the opposite. if i change gears quicker, rev the engine less and treat it like a woman, it uses MORE diesel than if i rev it slightly and change gear later. also if i rev it, it doesnt smoke, but if i change into heavy gear quiker, i can see smoke coming from the back from my rear view mirror. what do you say about that? any ideas? time for new injectors?

about the hot/cold air. to be honest there is so much power you can squeeze out of an AX, and when i bought it i was aware of the performance limitations. my aim in what i said, was *not* to increase engine perfomrance. i was really after a way of making the car sound and behave less like a farm vehicle and more like a car. essentially to reduce the engine noise and roughness, frankly i dont mind loosing power in return. i have realised in cold air, yes the engine *is* more powerful (and feels like that too) but is too noisy and very rough.

and DD and Mark, i am sorry if i placed it in the wront place, but i thought `technical' matters mean if you are asking questions about something that has broken or gone faulty with your car. in this case the car is neither broken nor faulty, and i thought may be it would be more a discussion rather than asking form mechanical tips to fix something. however if i misjudged, my apologies to you both. i have no objection if you see fit to relocate the thread. thanks to all.....
messing about with engine air intake - Another John H
As others have said: what fuel are you using??

My old Peugeot Diesel 505 (RIP), was as agricultural as anything you might come across, especially when running on supermarket fuel.
BUT, it was significantly quieter and smoother on Shell.
(see numerous other threads about fuel quality/additives)
messing about with engine air intake - glowplug
Hmm, I'm not sure I can provide an answer but diesels do have various cold start devices, which I believe on some diesels alter the injection timing. On some PSA engines it's a waxstat kind of affair that links from the injection pump to the cylinder head. This could be playing up or the pump timing was wrongly set after a cambelt change. Pump timing can dramatically alter the tone of a diesel engine if it is wrong. This does sound about right to me, if the timing was say a tooth out then the engine would still start and run but as it warmed up the timing could alter pushing the injection further away from the ideal and so would cause more noise and smoke,powerloss, higher running temperature, etc. I've seen something similar on a perkins engine when the injection pump pulley had been fitted 180 degress out (same pulley on a turbo/non turbo but fitted 180 degrees different).
Just as a side note I was always 'amazed' at the difference damp weather made to the performance of an engine, I guess it's just a taster of what a water injected high performance turbo could be like.

messing about with engine air intake - Amin_{p}
Anthony, I use Total diesel, simply because Citroen recommended and still recommends Total. Having said that, you would think both being French they would help each others trade?. But I have used two other types, BP and ASDA. It might be just in my mind, but I thought BP diesel had more power but I got much less mpg than I get from Total or ASDA. ASDA seems to be the most quiet one I have tried so far, but I have not tied shell, so I couldn?t say anything about that. I will put some next time I go for a refill, but incidentally is it true that if you keep switching suppliers you can damage the engine?

Steve, I doubt there is a timing issue for this reason. The car has done 140k and 70k of that has been since the last belt change, During this time it has NEVER failed an MOT test for smoke related issues, also I have done at one point 95mph and it was fine ( I would think if your timing was out, you couldn?t get within 1 mile per hour of the specified maximum speed by the manufacturer, which I think for the AX, when it came out was 96mph). The reason I asked about injectors was that I know they are the original injectors (I think you are supposed to change them every 80k) and also the mpg is a bit low. I get about 430 miles out of 9.5 gallons, which works out about 45mpg which is about 10-15 mpg down on what you would expect from the car normally. Incidentally, if there is general consensus that dampness significantly helps the engine, what stops one pumping damp air back to the intake? Somehow the idea of a cheap DIY modification to the engine really attracts me. I am now in the process of installing a home made cruise controller to my car, which I think will make it the first AX with cruise control. The air intake modification was next one in-line once I am sure exactly what it is I will be pumping back?..

Also slightly off track, but what sort of modifications do you have to report to the insurance? Or for the log book? For example I have wired my car such that once the immobiliser had been deactivated, you can start the car by just pressing the horn, without the ignition key. Is this something which should be reported?
messing about with engine air intake - glowplug
You could be right about it not being a timing issue but I would say that if it's not had a 'belt for 70k fit one before it's too late. As for changing injectors the general consensus seem to be that it's not always mileage related and could be down to other factors. However if your MPG is down that much but the car still performs like it seems to then I think I'd be looking at all sorts to try to figure out what's going off. I'd be looking at the brakes, compression, injectors, timing (just to be sure!), etc. I know some of these may not make sense but I'd check for piece of mind.
As for dampness helping engines perform better, I think it really only becomes worth while when the intake charge temperature is getting seriously warm (forced induction). The dampness in the air will cool the intake charge and the induction tract making for a better bang. I would suggest a book such as Vizards 'tuning the A series' or an in depth turbocharging book. I remember reading of a modification to Uno Turbos that added water injection, the end result was that it could out accelerate some Ferraris at certain speeds. Other points to consider are that water causes corrosion and that more capacity taken up by non fuel and/or oxygen the less power the engine will develop. This isn't the whole story but thats where a good knowledge of thermodynamics comes in.

Keep us posted. I'd like to know what the outcome is.



Value my car