lart951

Well, let me ask you something, when I drive my car in cold weather why does it feel more powerful? I know cold air is more dense, is it one of the purposes of intercooling keeping the mixture cooler more dense?

User 41221

Yep, thats pretty much the entire purpose. Hot air contains less 02 than cold air given the same volume, and engines are basically nothing more than air pumps, the more air you can run through it, the more work it will produce. Depending on the barametric pressure, cold air at 0 degF can be about 22% more dense than warmer air at 100 degF, hence the additional power on cold days. The intercooler is working to try and accomplish the same thing, altho it isn't going to be nearly that effective.

lart951

So the greater source of heat exchange (hot to cold) happens within the compressor area/

User 41221

Thats certainly one place where it occurs, yes, which is one reason why turbo lubrication and cooling is so important. If you wanted to put a heat shield around the hot side of the turbo, you'd get no question from me on its effectiveness for underhood heat control. Relative to the original postulation that started this whole silly conversation, I'd venture to say you'd get more bang for your buck by wrapping the headers with a thermal blanket after ceramic coating them instead of polishing aluminum.

If you want my bench racing advice on the subject, the best practical combination for thermal control on a 951 would be doing the aforementioned hotside wrap and header/crossover coating and blanket, leave the cam tower and intake rough to maximize surface area for cooling, and mount a rear relief vent for the intercooler (ala 968 Turbo RS). Bonus points for cooling fins on the intercooler pipe running from the turbo to the intercooler to disperse heat and some sort of thermal treatment on the intercooler pipe running from the intercooler to the intake to try and reject as much heat as possible (thats the one place I'd say polishing might help). if you do all that, I believe you'd feel a noticible underhood temp difference, altho I wouldn't expect much of a power gain from doing so.

I'd be all for getting 67King to see what kind of composite intake he could design for us.

lart951

me too

Chris White

As much fun as it is to ‘bench engineer’ (like bench racing but with more pen and paper!) the ‘real world’ answer is that the entire system is dynamic enough that there is no single correct answer. You will find times that the temp inside the pipes / manifold is greater than the ambient air in the engine compartment and then you will also find the opposite a minute later. So if you want to be a serious ‘bench engineer’ you will have to specify what running condition you wish to optimize.

Personally I am not concerned with rush hour traffic….first I just don’t live in an area where that happens and secondly you rarely need max power in a traffic jam. If you normal MO is to cruise around slowly and then suddenly require full power you might be more at home in a Corvette….

At full load you will see significant temps inside the turbo to intercooler pipe, just above exterior (outside engine bay) temps in the intercooler to throttle body and intake manifold. You also will not see very high air temps around the intercooler pipes and intake manifold. While the intake manifold is connected to the head the stock type gaskets are actually decent insulators and the only conduction heating is through the bolts – not very much. The colder intake air inside the manifold is enough to cool the manifold down quite a bit. Typically the intake manifold is actually cool to the touch when you come off the track – a lot cooler than the cam tower!

Convection heating is minimal when the car is moving at speed due to air moving around the engine bay, Radiation heating near the turbo can be an issue – especially in a modded engine at full power. This is the one area where polishing may help – if you have removed the stock heat shield and forgot to wrap anything!

So just to get the ‘bench engineering’ terminology correct we should be tossing out the following terms so we can seem intelligent to the rest of the interworld (after all – isn’t that the point of the internet – to have a platform to appear more intelligent that we really are?)

Conduction (including static and motionary (Mass Transfer))
Convection
Radiation

In the end….the polished stuff looks ‘cooler’(non temperature related) so that’s why I like it. The only thing that I like better than polishing is the look of a finely machined part. Sand casting comes in 2nd to last only slightly better than a badly welded/grind part!

OK – anybody have any good ways to ‘bench engineer’ a good excuse to make something look ‘cool’?

BTW – as a disclaimer – I used to race a Ford…..! But that was a car/engine from back in the day that Ford really wanted to go racing!

Chris White

Hmmm…first ‘bench engineering ‘ victim…..
Heat exchange is not quite right for this situation. Significant heat is created when compressing air (see Combined Gas Law). At 1 bar of boost you can see a temp increase of well over 100f and double that if you are not using your turbo in its peak efficiency range. Heat transfer due to conduction, convection and radiation is very minimal due to the length of time the air is inside the compressor. In fact the heat ‘flow’ would change inside the compressor housing – at the intake annulus (you get to use cool terms when ‘bench engineering!’) the compressor casting would be hotter than the incoming air but at the compressor outlet the air charge would be hotter than the casting. Hmmm…heat energy flowing out and back in from the same gas….!

BTW – the heat from compressing air is the main heat enemy of your engine – it will cause power loss and then detonation if not controlled. Be careful operating your turbo outside of its efficiency range and make sure your intercooler is up to the heat ‘rejection’ task.

When it comes to turbos entropy is just not cool enough….

Chris White

Back when I was a little more extreme about tweaking 944 turbos I started working on a Peltier based intercooler pipe system…..but then I had my son (he is 10 now) and concept of ‘relative time’ suddenly dawned on me…..

Power gain would have been minimal put the ‘coolness’ factor would have been very high!

User 41221

Sheesh, way to ruin all our fun, Chris! lol

Fine, if you insist on being a curmudgeon about this, please understand that the only real world benefit that I expect anyone would gain from a practical application of my bench racing suggestions is that the electrical connectors and wiring would get a little less brittle over time, due to reduced underhood temps. I won't postulate (again with the big words to impress people with!) the impact the vent might have on engine performance due to potential temp drop of the intercooler, as there are a lot of variables in how one would execute said vent since the hood latch/crossbar interferes with the installation. Fair enough?

I'm a Ford fanatic as well, having owned a number of classic Mustangs in my younger days.

lart951

Oh no, another Ford engineer.

lart951

You guys are just envy.