Forced induction - again

[Petrus]

Much has been written about is and more will be.

Me, I have been fascinated by it ever since ´turbo´ became  fashion in the mid seventies. I delved into it for a project I had to present for automative tech school.
I was bowled over by it being akin to something for nothing; using exhaust gass energy that had to be dissipated otherwise, to compress the intake air.
Since compressing gas = increase in temperature a cooler of the charge was an inherent problem creating solution.
Since the exhaust turbine and intake inpellor anr sitting next to eachother heat exchange is another issue, partly adressed by the intercooler. This was no addressed till the Mercedes F1 energy recovery unit separtating the two with an extended axle.

Then there are the mechanical compressor and the mechanically/electrucally driven centrifugal
ones.
These do suffer from compression = temp. increase but not from exhaust heat transfer but at the price of the exhaust gas not driving it.

The relation between increase in psi and degrees temp is about 1 to 10: 2 psi boost = 20 degrees F increase in temp. In C it is ca. half but still rather a lot really.

Back to the intercooler.
Appearing a cool solution it has an inherent problem: It is restrictive to flow. That restriction hás to be compromise because the temperature transfer between the intake gas and the cooling medium nééds time and contact. The faster and less impaired the flow, the less heat transfer.
The thus unavoidable restriction means that the boost needs be higher, increasing temp. through pressure.
Another thing is the cooling medium. Water is by far the most efficient and as such a air to water can be much more compact but more complicated and with inherent disadvantages.
Thus the charge cooler size/design needs be matched to the amount of boost and cooling medium system.

All in all the appearant something for nothing again does nót exist. Aaarrrrggghh.

Ok, and a comparative graph between the various superchargers. Do NÓT look at the amount of pressure! Thát is a match/design issue and easily shifted. The comparison is the shápe of the graphs.

[shnazzle]

Think about it in wider cause-effect terms;

First, power:
2.5hp loss per 10deg increase in temp. 

First and second laws of thermodynamics already puts a stop to "something for nothing" so no point even trying.
You can convert energy but at a cost of heat. 

10psi = 100f = 38deg C
That doesn't include heat soak though, so call it 50deg.

So that's a little under 12.5hp loss by the rule of thumb and normal atmospheric pressure.

A bit of a bummer in road car but hardly end of the world. Motorsport world a bit more impact.

Second, knock:
High intake temp = more chance of knock.
Now you have a solid reason to cool.

Intercoolers work two ways right; surface area and volume.
And importantly, volume is not flow capacity.
Restriction is not the issue. Lag is. A big thick intercooler only flows effectively when it's pressurised. So basically you pressurise the intercooler and piping before you pressurise the engine. Lag.

Smaller thinner intercooler = pressurises very quickly so no lag, but less total cooling capacity.

Matching it all up is where the magic is.
Right size intercooler for the right size turbo for the engine's CFM and properties.
Cooling location then further tweaks it.

Personally I always thought a long thin front mount intercooler with a slightly bigger turbo would be the way to go on the mr2. With 2in pipework max.

[Petrus]

Think about it in wider cause-effect terms;

First, power:
2.5hp loss per 10deg increase in temp.

First and second laws of thermodynamics already puts a stop to "something for nothing" so no point even trying.
You can convert energy but at a cost of heat.

10psi = 100f = 38deg C
That doesn't include heat soak though, so call it 50deg.

So that's a little under 12.5hp loss by the rule of thumb and normal atmospheric pressure.

Correct ofcourse.
Very important to keep in mind with charge cooling this inherent loss by simply raising charge pressure.

Second, knock:
High intake temp = more chance of knock.
Now you have a solid reason to cool.

That and /or other measures.

Intercoolers work two ways right; surface area and volume.
And importantly, volume is not flow capacity.
Restriction is not the issue. Lag is. A big thick intercooler only flows effectively when it's pressurised. So basically you pressurise the intercooler and piping before you pressurise the engine.

Smaller thinner intercooler = pressurises very quickly so no lag, but less total cooling capacity.

Matching it all up is where the magic is.
Right size intercooler for the right size turbo for the engine's CFM and properties.
Cooling location then further tweaks it.

Personally I always thought a long thin front mount intercooler with a slightly bigger turbo would be the way to go on the mr2. With 2in pipework max.

Your reasoning has two ´yes but´s.
The appearant quick boost build up is not boost at the inlet but between turbo and intercooler.
Long tubes, long channels, have a lot of surface. That indeed gives heat exchange but also surface drag = the more pressure drop. Another downside is that the longer the travel, the longer the lag at the inlet. Length to tubing is also volume.

Theorising/dreaming about the MR2, you´d want a Rotrex with the outlet straight up through the engine lid.
Connecting to a 2.5" alloy duct with longitudonal vertical baffle inside and external finning sitting traverse, an inch or so above, the deck.
Then back through the lid to the inlet manifold.


Back to the beginning, to an n.a. engine (or sc); one could also mist water in the filter box.
All you need is a nozzle in the box, pressurised water bottle, solenoid, throttle position actuated micro-switch and an on/off on the dash.

I fitted something akin to my turbo diesel. Upped the boost with an mbc and fitted a butane tank instead of a water tank. Nozzle in the inlet manifold. Was about 30hp on the button and full throttle.