Originally Posted by F104
My 2 cents worth:.
With an open intake, there is now two paths for the air getting into the filter:
- thru the bit of original piping one has have left, but which has a fair degree of resistance through the 'hump' and direction changes
- thru the radiator and intercooler, which represent an enormous surface compared to the intake, and which simply results in warmer air
An 8+ minute idle test doesn't prove anything. The engine hardly burns enough fuel to heat the thousands of gallons of air going out thru it on idle in 8 minutes . My 320d actually cools down when idling after a motorway run, simply because the massive amounts of non throttled air going thru it.
The acceleration tests would prove something, if you measure the right things. Just showing OBD intake temperature after the intercooler is as valuable as showing the temperature on the moon. Although I agree we're not talking massive differences here, it is simply not correct.
So why would these test show similar intake temps after intercooler. For each degree in turbo inlet temp, the turbo outlet temp goes up a bit more than one degree. That causes additional expansion, which has to go thru the same turbo charger paths and intercooler piping. That means less molecules get thru it. Or in other words the turbo pressure ratio stays the same, but air mass flow decreases.
And then the intercooler sees hotter air coming in, but also less off it. Easier job cooling it down. So yes intercooler out temp will not change much, but now there is less air mass too.
There's no free lunch in science, if you start less efficient there's no way of improving on it.
And my guess is at 70mph constant speed the 335i engine takes in some 30-40 ltrs or air/second. The theorethic free air flow thru the intake channel after the hump (60cm2 cross section) at 70 mph is some 180 ltrs second (in easy rounded metric numbers, 108kph is 30 mtrs/second. That is 300dm/sec thru a 0.6 dm2 intake, or 180dm3/second).
Even if you reduce that by up to 50% due to friction losses (as it isn't exactly a straight inlet) , the OE intake can flow more cold air than 99% of driving conditions require.
Thanks my fellow belgian landsman
That is what i call a: very good and solid answer
If the open intake is so much better, why don't all performance car have them instead of those hyper-technical closed intakes???