Thread: Biggest Intercooler for Isuzu 4BD1T

Originally Posted by slug_burner

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I do not understand the reference to the speed of sound. I think the time it takes to get a volume up to pressure will depend on the volume rate that the turbo can push air into the i/c and hoses. I don't recall the detail, it could be something inperceptible for all I remember.

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The effect that John was referring to is, I believe I can say, when there is a change in pressure at the outlet of the compressor, a pressure pulse will travel at the speed of sound to the inlet manifold.

So it will take that long for the pressure to change at the manifold.

The air does not travel at the speed of sound, just the pressure.

You might like to think of a molecule 'X' at the compressor pushing against it's neighbor, and so on until molecule 'Y' get pushed into the manifold. So the pressure reaches the manifold long before 'X' gets there.

Like others have explained, frontal area of core (for cooling air) has more beneficial effect on the heat transfer than thickness.

Another consideration is enough cross section area for the air flow from the compressor, for acceptable pressure loss. This (pressure loss) is related to what slug_burner said

... go for wide and short not long and skinny

Taken from the book Maximum Boost Designing, Testing and Installing Turbocharger Systems By Corky Bell. Chapter on Intercooling.

Design criteria for creating an intercooler are many and varied. These criteria will outline the considerations for building an intercooler that maximises heat removal and minimise boost-pressure loss and any lag increases.

Heat Transfer Area. Heat transfer area is the sum of all the plates and shells in the heat exchanger core that are responsible for transmitting heat out of the system. Easy to see that the greater the heat transfer area, the more efficient the intercooler. This is not a case, however, where twice the area doubles the efficiency. A 10% increase in core will net you about 10% of the amount you did not get out the first time. Therefore , every 10% increase will become less and less important. For example, if an existing intercooler core measures 70% efficient, 10% core increase should yield about 10% of that remaining 30%, or a new efficiency of 73%.

Internal Flow Area. Streamlining inside a core is bad design. The harder it is for air to find its way through a core, the more likely it will give up its heat-obviously the major objective. But the bad side is that this poor steamlining can cause large boost-pressure drops. To compensate for bad streamlining, the internal flow area must be made large enough to really slow the air down inside the intercooler, so as to reduce flow drag and keep pressure losses to acceptable levels.

Internal Volume. All of the volume internal to the intercooler system must be pressurized before that amount of pressure will exist in the intake manifold. Although this volume is not a large contributor to lag, it is nevertheless a design factor to optimise in the process of creating a good intercooler system. It is a good idea to keep track of the volume and constantly attempt to keep the excess down. A reasonable judgement of of the volume's relationship to lag can be made by dividing the internal volume by the flow rate through the system at the rpmat which throttle is applied and multiplying by 2. (The factor of 2 results from the approximate doubling of airflow through the system when going from cruise to boost.) The approximate lag time is given by

Time = (V/flowrate) X 2

Example:

Let volume of intake = 500 cu in. and flow rate = 150 cfm at cruise speed of approx 2000 rpm.

Then

Time = (500 cu in/150 cfm) X (60 sec/min/1728 cu in/cu ft) X 2 = 0.23 sec.

Now this book does not deal with diesel engines however I think that most of the information would still apply. Not sure about the factor of two though as this suggests to me that at cruise you would be running at atmospheric pressure then the boost would come on to 14.7 lb./sq in. (one atmosphere). For diesels I think that even at cruise they still run some boost (I don't have a boost gauge on mine so I don't know for sure), not necessarily max boost but definately above zero boost.

I put it out there because like most engineering problems the law of diminishing returns applies. Like in the example given previously a 10% increase in core the first time around will get you 3% improvement, the second time you increase by 10% you will only get 2.7% and so on. SO there is a stage at which it will not be worth increasing the core any further.

John and Bush65,

I can see how the pressure pulse might travel at the speed of sound however I think that what we might be interested in is the steady state value and how long it takes to establish that as opposed to the transient condition.

Using Bush65's terminology you want all the little Xs at the boost pressure, without the volume of the intercooler and hoses you could just use the linear distance of the pipe work connecting compressor and intake and with the speed of travel you could work out how long it will take for the pulse to travel the distance. However even if the compressor was able to produce a nice square edge the volume of the intercooler system will cause an exponential rise in pressure, much like the voltage across a capacitor rises exponentially in response to a step change in voltage.

Originally Posted by Brian Hjelm

As with your water radiator, frontal area is the major item. Increasing the core thickness eventually causes flow restriction, ask M.A.N truck people about this. They tried to improve their truck's suitability for tropical road train service by increasing core thickness and rows of tubes to the ridiculous extreme of of 10 rows. Actually ran hotter past a certain point. Their cab design precluded increasing frontal area.

If they'd used two 5 row cores and run the hottest air through the back, then second pass through the front they would have done a lot better.
Still not ideal, just better than a single 10 row.

Originally Posted by Dougal

If they'd used two 5 row cores and run the hottest air through the back, then second pass through the front they would have done a lot better.
Still not ideal, just better than a single 10 row.

Their archaic cab design had major space problems. They were really clutching at straws. The Oz division was desperately trying to increase sales volume and they had made no headway at all in the road train market. Underpowered and overweight, they were always going to struggle against the North American marques. Like other European and British truck makers, they thought they knew it all because they sold into rough usage markets in Africa and the Middle East. They had no idea of the distances and speeds travelled in Australia, no appreciation at all of the dust problems, and the effects the constant slap,slap, slap applied by even our good roads had on cabs and componentry.

Originally Posted by Brian Hjelm

Their archaic cab design had major space problems. They were really clutching at straws. The Oz division was desperately trying to increase sales volume and they had made no headway at all in the road train market. Underpowered and overweight, they were always going to struggle against the North American marques. Like other European and British truck makers, they thought they knew it all because they sold into rough usage markets in Africa and the Middle East. They had no idea of the distances and speeds travelled in Australia, no appreciation at all of the dust problems, and the effects the constant slap,slap, slap applied by even our good roads had on cabs and componentry.

The comment I saw was talking about cars not trucks, but the same applies - "Nowhere else but in Australia do drivers travel as fast for such long distances on rough roads" . Most places either they slow down when it is rough, or the distance (of rough roads) is not very great.

John

Originally Posted by JDNSW

The comment I saw was talking about cars not trucks, but the same applies - "Nowhere else but in Australia do drivers travel as fast for such long distances on rough roads" . Most places either they slow down when it is rough, or the distance (of rough roads) is not very great.

John

Or stop five times a day for prayers, chase a gazelle, have a sing-sing.

We have underpaid owner-drivers trying to make a mile and a dollar to keep their truck and their home from the repossessors.