getting to know my jtd 8v. - Alfa Romeo Forum
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Hmmm getting to know my jtd 8v.

hi alfa owners,

ive only had a quick look at my engine bay but its so much different to anything i have owned, have only owned 2 other cars and they were both 1.4 engine, very simple !

where is the air box located ?

how does the intercooler and turbo configuration go ? all i know is a pipe from the intake on top of the engine goes into the intercooler and thats it lol...
i know the turbo goes onto the manifold then does the turbo have another inlet and outlet ?

im not thick when it comes to engines just diesel engines and turbos lol, do they not intake air the same way as petrol or something aswell, no throttle body ??

any other usefull diesel information would be handy

thanks, rob.
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Hi, im new here, but am used to Turbo's.

On a none turbo car you have an air (induction pipe) which draws cold air in from the edge of the engine bay (usually near the bumper or wing) and into the engine. To stop dirt getting in to it there is a filter housed at some point in the pipe.

On a turbo the induction pipe starts the same, at the engine bay edge. Again there will be a filter close to the start of the pipe. The pipe then goes straight in to the turbo.
all the air in this pipe is being sucked into the turbo. The turbo which consists of a fan is sucking the air into it.
The air goes through the turbo and as it does so it is compressed it is then blown out the other side of the turbo through another pipe.
These are boost pipes because the air pressure is much higher because the turbo is forcing air through them.

remember how we said the turbo was compressing the air. Well this unfortunately creates heat as the air is squished together.

An engine needs cold air as cold air is denser, meaning if you had say a cup full of air you would have more air molocules in a cold cup than in a warm cup. this is because in a warm cup the air molocules will be spread out more and take up the same amount of room. In the cold cup you would have much more tightly packed in.
yet occupy the same omount of space.

Therefore the air exiting the turbo is now warm which is very inefficient.
So it needs cooling. The air is then passed through an intercooler. A radiator for air which has a good surface area. The intercooler as with a radiator is cooled by being positioned so that its exposed to the outside air that passes over-through it. Thus cooling the high pressure air being passed through it.

After leaving the intercooler the air is sufficiently cooled and travels under pressure into the engine.

The turbo itself sits in the exhaust. As exhaust gas passes through it spins a turbine wheel (a fan blade)
this is connected by a spindle, the spindle passes through a sealed part of the turbo and on the other end of the spindle there is the compressor wheel (another fan blade)
this compressor wheel is the one that sits in the induction. It sucks air in as it spins and blows it out the other side into the boost pipes.

This might help,

so the turbo is driven entirely off exhaust gas. this is why there is a delay in turbo pick up as it needs to have enough exhaust gas passing over it to spin fast enough to draw in cold air via the compressor wheel (usually at about 1400rpm on a diesel.

the smaller the turbo the easier it spins as the blades turn more easily. Therefore bigger turbos take more engine revs to spin them.

Hope this helps,


Last edited by rrbridges; 20-10-10 at 06:22.
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(Post Link) post #3 of 3 Old 24-10-10 Thread Starter
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wow some great info there ! thankyou mate !!!
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