Not posted in a while so Hi guys!!
Pondering at work how crucial input air temperature is to a normally aspirated engine.
Take my TVR for example, the intake is ducted from the very front of the car in a thin walled flexi pipe which runs inches from the enormous and very
lengthy exhaust manifold thus gets quite warm...
Now I can appreciate that a stonking great V8 probably sucks through a lot of air so the air isn't in the pipe for too long to get really really
hot but I would hazard a guess that by the time it reaches the throttle body that it must be a good 20+ degrees above ambient.
If I could somehow get the intake air to ambient would I see any noticeable change in performance?
As an aside I am pretty sure I need a bigger air filter on the front of the car, I can hear the engine "sucking" through which can't be
good for flow!
[Edited on 19/12/13 by tegwin]
A bit non scientific but I feel my car seems to sound, feel and run crisp when I drive out on early morning blats. On the flip side I can often feel
almost a lean AFR feeling when its a mega hot day.
The difference in intake air in this analogy must be 20deg or more.
On my hairdressers there was a noticeable (but as yet unquantifiable) improvement in power by enclosing the air filter in an ali box open towards the
ambient air flow.
This is because the s/c is hot side and was drawing hot air from around the exhaust.
Space only allowed a single thickness ali sheet but it surprised me there was such an improvement.
As for normally aspirated the same applies - see threads on MX5nutz where owners achieve more power by drawing air from the front of the car.
So subjectively the answer is yes - shield the air intake and pipework from hot air and you will notice an improvement.
HTH.
Cheers, Pewe10 
quote:
Originally posted by pewe
(but as yet unquantifiable)
I made an airbox over the regular sausage type filter and ducted it right to the front with an intake scoop. Whether it's the cooler air or a
slight bit of pressure (i know that's been questioned on many forums as impossible....) going in i don't know but i do know it made a very
very noticeable difference 
As above, i also find it's not as 'sweet' when it's very cold/freezing though.
Ian
We did a back-to-back test, bonnet on, bonnet off, on my mates Westy on the rollers and the difference was less than one hp.
Zetec engine, MBE ecu, Jenveys, lambda and air temp sensors, so the fuelling should have been correct for both runs and this was confirmed by the AFR
plot.
We were surprised too.
I would have thought on your Tiv when running with 'the taps open' ;-) the volume of air consumed would struggle to be warmed by radiated
heat from the flexi induction tubes. Its highly likely it will make more actual difference and more perceived difference, when going from steady state
(idle, small throttle opening) in traffc to wide open throttle as the air has much greater time to be warmed and then when you boot it, the engine is
seeing warmed air for a few seconds.
certainly this is true in sprinting/hillclimbing, where the cars sit idling in the paddock queue and then are flat out off the line. On the data
logger date from my ecu, the induction charge temps are affected initially, but a 200yards into the run (at WOT) the air temps have dropped to a point
where they aren't affecting power again.
id exh wrap the exhausts manifolds and downpipes, and use thermo barrier around the induction tubes at least, but a slight redesign would be best
really in addition to the wrapping/thermo barrier imho
Air intake temperature does indeed make a difference. How much I'm not sure...
But if you look at the density of air vs temperature, air has about 7% more mass at zero degrees centigrade compared to 20 degrees centigrade.
Assuming your ECU compensates for it, that means you're also injecting 7% more fuel to keep the engine running at (or close to) stoimetric.
More fuel and more air = more power 
Not sure if you'd see a 7% increase in power as my limited knowledge falls apart at that point...
Scientific answer (if you want it).
At the temperatures we are talking about air behaves like an "ideal gas".
Therefore PV=nRT (http://en.wikipedia.org/wiki/Ideal_gas_law)
Where P is the pressure, V is the volume, n is the number of Moles of gas, R is the ideal gas constant and T is the temperature in Kelvin.
So, given that P (air pressure), V (volume of gas sucked in) and R (Gas constant) are all constants in your system the amount of air (and hence
oxygen) that you engine will draw in is related to n.
So working through the numbers
nT = PV/R
So if you increase T from 293K (about 20degC) to 313K(about 40degC) then the decrease in n is about 7%.
So assuming you have the same AFR at both temperatures, then you could get a 7% power increase. In reality it is probably lower because you get
better fuel vaporisation when things are hot.
Matt
It isn' just AFR. lower intake temp allows increased ignition advance, but on most engines the real gains are when the ambient temp is down to
close to 0c. Best power is developed on freezing cold foggy morning, the moisture provides evaporative cooling and thefllashing off of water
droplets to steam provides additional power.
You read the IAT sensor from OBDII on most tintops it is surprisingly high but as this helps achieving a higher exhaust gas temperature this helps
emissions by getting the cat working.
There was a thread about this recently with a link to an American RR test of a Skyline with the air intake in various positions, suprisingly it made hardly any difference.
Some seat of the pants stuff on bike engines from racing experience. Highly tuned two strokes had to be jetted up in cold weather or they would seize
at the end of the straight. Whether they were any quicker was hard to tell as the tyres at the time hated cold weather.
Riding in 24 hour races (750 four strokes) the difference in performance somewhere like Le Castellet (Paul Ricard where they used to hold the Bol
d'Or) was very noticeable between early morning when it was cold and humid (around 0-5°) and mid afternoon (25+°). In the morning sessions the
bike would easily pull an extra 300 rpm down the straight. When you've got a 1.8km straight it gets a bit boring so you had a load of time to
check out the revs and ponder on such things....
Later on, again with bike engines but this time in sidecars running GSXR 1000 motors, we had a very clear indicator of what a decent cold air intake
was worth. We were running prepared motors at the time (lightened, balanced, prepped heads, programmable ignition and injection) but our air intake
was badly plumbed and leaking between the naca duct and the airbox. We eventually got the intake sorted on a Friday evening after a days testing and
before Saturdays warm-up and qualifying.
In the warm up the bike was flying. And then before we could get a time it blew up. Dropped valve. 
Our spare engine was a stock road bike motor which had never had the lid off. No choice so in it went. No set up, nothing. Again the bike flew but
with a motor that should have been 15 brake down? Our times were the best we'd ever recorded at that particular circuit (Ledenon) but above all
the bike was so much easier to ride. Super clean linear response made everything so much easier. Only at the very end of the straight did we see a
very slight deficit to the tuned motors they other guys were running. Finished third and no one believed we were running a stock motor.....
The point of all that is that you may not see a huge power increase with a decent cold air intake but the motor (providing your set up is near enough)
will be so much more pleasant to ride/drive you'll be quicker and safer and that is so much more important than a bhp number...
When i was going on excavator licence lesson and other sstuff I've learned that in cold air u have more oxygen for better mixed with gasoline.
That is why turbo engines have IC.
And I remember one day on 400 yards competition in my capitol some of tge guys splash with cold water front mounted inter cooler before racing.
To. put some numbers on it I took some figures this morning. ambient temperature was 4 to 6c.
After start during initial running the IAT stayed within 10 degrees of ambient until the coolant temperature reached thermostat opening temperature
88c.
The IAT then increased seadily to. 49c. in stop start urban driving after parking for 10 minutes the temperature reached 55c and only dropped
very slowly back to 51c on restart.
When using full throttle and high revs the IAT decreased but. at a much slower rate than might be anticipated.