intercoolers
- Thread starter bloat1992
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within reason the bigger the intercooler is and can cool the air without restricting it= more power.
That said the pump will have max fueling preset, so a better way of describing it would be power of a cool day on a hot day.
That said the pump will have max fueling preset, so a better way of describing it would be power of a cool day on a hot day.
Teflon
New Member
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The complexities of the thermodynamics are peculiar, but the variables go something like this:-
Turbo, compresses air, so more air can burn more fuel, therefore more power.
But, turbo also heats the air as it compresses it, and the more it compresses it the hotter it gets; like sticking your finger over the end of a bicycle pump.
At some point, you start getting pressure purely from the heat making the air try and expand, so you dont actually get any greater volume of air, just hotter air at a higher pressure.
So the idea of an intercooler, is to lower the air intake temperature, so that the pressure down-stream of the turbo is reduced..... but the density is increased, so you get a higher mass of air flow.
Down side is that once the air is trapped inside the cylinder, some of the extra charge you've crammed in is used to heat the charge back up to running temperature again....
So there are a lot of 'optimums' and balences in the factors going on....
And I havene't mentioned the 'plenum' volume and its effect on turbo-lag, or the added 'load' on the turbo from fitting an intercooler....
Basically, an intercooler has volume, so it takes longer for air to get from the turbo to the cylinders, which means a greater turbo-lag.
Also, the air from the turbo is split up and channeled through lots of smaller pipes in the intercooler to give it the surface area to actually cool the air, and that adds 'drag' to the air-flow, hence more Turbo-lag, but also more resistance to flow, which depending on the sizings of the intercooler in relation to the turbo, can mean that it 'chokes' the flow, which can mean that the air at the turbo out-put is heated more, for the same pressure, which is rather defeating.
There's also a thing called 'thermal stand-off' which is actually down to the intercooler design; basically, air shoved through the cooler shrinks, so teh air coming out of the intercooler has less volume than the air going into the intercooler, so to have a constant mass-flow, the speed of the air coming out has to drop an awful lot, and the effect you get is a bit like a queue of traffic and the cars at the front all sticking thier brakes on for road works, then the snarl at the end when the restriction is removed, and every-one's still traveling more slowly, even though theres now no restricion... complicated, but believe me, it chokes flow.
In the real world...... I have to question any-one wanting to tune a diesel, to be honest; I mean, it's fundementally an ecconomy engine, if you wanted power, why buy one?
But, for a few bhp, and without annoying insurance companies?!?
Better off, probably giving the thing a dang good service; old TDi's benefit hugely from new injectors, while long before they start belshing black smoke tired Turbo's will have lost a huge amount of efficiency from impella errosion and turbine's collecting deposits and pitting, and they nearly all manage to allow some of thier oil through the bearings into the plenum...
And timing pumps go out of calibration too.
Old rule of tuning, before looking for gains beyond standard, make sure you are getting what you should AS standard; chances are youre not, and it'll not be just in a peak or full throttle power you'll be loosing efficiency, but at part throttle and in throttle response. New hot-spots make a huge improvement there too.
So, unless you have a vert well fettled engine, a bigger intercooler wont do much for you, and probably wont even make up the losses from a tired engine.
But, if you want to go for a bigger cooler, well, in this country, we dont exactly suffer high ambient air temperatures, and we aren't at some inordinately high altitude above sea level..... and teh standard intercooler is sized to work in such extreme conditions as a high altitude desert, where you MAY get the sort of high inlet temperatures that would warrant a lot more cooling capacity..... but in blighty? For 3 or 4 bhp?
I'd buy a new set of injectors and get the hot spots renewed.
Turbo, compresses air, so more air can burn more fuel, therefore more power.
But, turbo also heats the air as it compresses it, and the more it compresses it the hotter it gets; like sticking your finger over the end of a bicycle pump.
At some point, you start getting pressure purely from the heat making the air try and expand, so you dont actually get any greater volume of air, just hotter air at a higher pressure.
So the idea of an intercooler, is to lower the air intake temperature, so that the pressure down-stream of the turbo is reduced..... but the density is increased, so you get a higher mass of air flow.
Down side is that once the air is trapped inside the cylinder, some of the extra charge you've crammed in is used to heat the charge back up to running temperature again....
So there are a lot of 'optimums' and balences in the factors going on....
And I havene't mentioned the 'plenum' volume and its effect on turbo-lag, or the added 'load' on the turbo from fitting an intercooler....
Basically, an intercooler has volume, so it takes longer for air to get from the turbo to the cylinders, which means a greater turbo-lag.
Also, the air from the turbo is split up and channeled through lots of smaller pipes in the intercooler to give it the surface area to actually cool the air, and that adds 'drag' to the air-flow, hence more Turbo-lag, but also more resistance to flow, which depending on the sizings of the intercooler in relation to the turbo, can mean that it 'chokes' the flow, which can mean that the air at the turbo out-put is heated more, for the same pressure, which is rather defeating.
There's also a thing called 'thermal stand-off' which is actually down to the intercooler design; basically, air shoved through the cooler shrinks, so teh air coming out of the intercooler has less volume than the air going into the intercooler, so to have a constant mass-flow, the speed of the air coming out has to drop an awful lot, and the effect you get is a bit like a queue of traffic and the cars at the front all sticking thier brakes on for road works, then the snarl at the end when the restriction is removed, and every-one's still traveling more slowly, even though theres now no restricion... complicated, but believe me, it chokes flow.
In the real world...... I have to question any-one wanting to tune a diesel, to be honest; I mean, it's fundementally an ecconomy engine, if you wanted power, why buy one?
But, for a few bhp, and without annoying insurance companies?!?
Better off, probably giving the thing a dang good service; old TDi's benefit hugely from new injectors, while long before they start belshing black smoke tired Turbo's will have lost a huge amount of efficiency from impella errosion and turbine's collecting deposits and pitting, and they nearly all manage to allow some of thier oil through the bearings into the plenum...
And timing pumps go out of calibration too.
Old rule of tuning, before looking for gains beyond standard, make sure you are getting what you should AS standard; chances are youre not, and it'll not be just in a peak or full throttle power you'll be loosing efficiency, but at part throttle and in throttle response. New hot-spots make a huge improvement there too.
So, unless you have a vert well fettled engine, a bigger intercooler wont do much for you, and probably wont even make up the losses from a tired engine.
But, if you want to go for a bigger cooler, well, in this country, we dont exactly suffer high ambient air temperatures, and we aren't at some inordinately high altitude above sea level..... and teh standard intercooler is sized to work in such extreme conditions as a high altitude desert, where you MAY get the sort of high inlet temperatures that would warrant a lot more cooling capacity..... but in blighty? For 3 or 4 bhp?
I'd buy a new set of injectors and get the hot spots renewed.
Teflon
New Member
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- 683
Diesel 'Spark-Plug'....... its a chunk of brass in the combustion chamber with a carefully machined groove in it, designed so that the hot spot holds heat, and when the charge is compressed, the groove catched a bit of charge that gets a lot hotter than the rest and ignites, the flame shooting out of the groove and setting the rest of the combustion chamber contents on fire......
Like a petrol spark-plug, electrodes, over time the groove gets erroded and gunked up.
Means the burn initiation gets a bit tardy, like petrol ignition retarding, and the combustion 'pattern' isn't as crisp as it should be, and start up isn't as easy as it could be.
A 'good' TDi, with sharp hot-spots should start almost instantly, with hardly any cranking........ if it takes more than one 'lurch' of the starter, good indication new hot-spots would be big bonus to performance.
Teflon
New Member
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No, glo-plogs are a coil of resistance wire in a spark-plug housing that get hot when you put an electric current through them, and are used as a 'pre-heater' to het a little warmth into the cylinder head when cold to aid starting.
Hot-spots are a chunk of brass, shrink fitted into the cylinder head to propogate ignition during normal operation.
They aren't a 'user serviceable part'.
You have to take the cylinder head off, take it to an engine reconditioners; they will probably remove the old hot-spot by milling it out the hole, then fit a new one by heating the head up, and freezing the hot-spot before pressing the two together, and letting the frozen hot-spot expand and the heated head contract to get an effoff tight interferance fit between the two, so it wont drop out during use.
