NineMeister

The temp sensor is in the airflow meter itself and is fairly slow to react to air temperature change, I see the same effect on the dyno and with our fans running have to idle a 964 for 10-15 minutes before the intake temps reduce. Bills work reflects an earlier thread on the same subject confirming that for town driving the best air intake location is under the open grille, whereas for track driving at full throttle most of the time the intake position is not sensitive due to the volume of air consumed.

wsybert

I noticed the slow temp change while driving too. I will have to get the car out on the interstate where I can open it up more to see if I can get thte temps closer between the two setups.
Bill

Red rooster

Bill,
Well done. This all fits with common sense ! Every time I have seen a cone put straight on the flap unit and so buried in that hot place I cant resist wondering how much power is being lost !!
Just as an example ,your two temperatures of 60F and 105 F mean that the motor is loosing 4% power ! or around 10 bhp at the higher temperature.

People pay good money to try and gain that .

The drilled Cup car airbox may have been a way to get more noise ! There is a small element of show business in higher level racing . Just a guess because I dont see any meaningful performance benifit .

All the best and good luck with the other tests.

Geoff

N51

I do not believe the cup airbox was only a noise machine, and refer, again, to Bob Scotto's dyno work that showed a gain with it over the standard box. I've no recollection as to whether he tested a cone filter.

Has anyone tried routing the AC into the intake? Just joking!

Noah

wsybert

I may have access to a good data logger that I can use for future tests. Better temperature response and will have a differental pressure transducer onboard. Would also like to get a speed input for reference too... any suggestions welcome.
Need to figure out how to get both probes in the intake. There is the port on the AFM (upstream of the flap) that I can tie into for one. Would like to get them both at the same location.

NineMeister

Here is the difference I found on a 964RS on Motec through the standard airlow meter between the standard air filter and lid and with it removed.

Red rooster

Colin,
That almost falls into the " experimental error " area ! Maybe the answer lies somewhere between effective intake length and intake area ? The next step would be a lid with a much larger intake trumpet , especially at the filter end , to see which effect is dominant ?All good stuff .

Geoff

deep_uv

Bill, Drilled airbox lid on its way. PM Sent.

Steve

NineMeister

Respectfully disagree Geoff, tested on same car/day/dyno within 5 minutes of each other.

Your old Sun dyno may not have been this accurate though!

wsybert

Got your PM's. Thanks for sending the drilled cover.
Look forward to the tests... I know there is probably little to be gained, but every little bit counts.
I understand that on the track there is probably enough airflow to make the location a non-issue. For daily driving, however, these is a difference. Just nice to know how much. Will post as soon as I get time to do the tests. I am most likely going to do the air temp only, as I won't be able to get my hands on the data logger for a few weeks.
When I do, I will post the pressure drop for the straight vs elbow intake piping.
I am off most of this week, so if the weather holds out, may have some data after the holidays.
Jeez... with 5 configurations to test, I may be driving all day!
* Short Cone filter on AFM
* Cone filter with longer tubing and 90 deg bend WITH heat shield
* Cone filter with longer tubing and 90 deg bend WITHOUT heat shield
* Standard airbox
* Drilled standard airbox

Red rooster

Colin,
Cheeky bugger !!! ( Joke !! )
So now your telling me that your dyno has 0% error ? and an air cooled 911 motor doesnt change in 5 minutes during power testing runs !!!!!!
Come on Colin , you know better than that .

Still be interesting to know whether its induction length or area that could cause a tiny power drop .

All the best

Geoff

-CD-

What modifications have been done on the RS?
Thats a lot of power!!!

Thanks for info!

Greetings Christian

NineMeister

The dyno is fixed inertia, so the only measurement required for the calculation is roller speed, why would the sensor change between runs? OK, the absolute accuracy may be debatable, but the relative difference measureed is real. With repect to the car, since the engine was runnning on Motec and me being particularly thorough on the day, I started each power run with heads at the same temperature, all other factors (AT, BAP, tyres, etc) the same.

I believe the difference measured to be real, but I am afraid that anyone else must believe what they want, simply because I am sick and tired of debating this every time I post a dyno graph.

This particular comparison only shows the advantage on this car of removing the standard paper air filter and lid, there were no other changes that would affect the resonant length of the intake.


Christian,
This car is a 964RS CS fitted with a 9m Motec conversion, final power gain for the system was around 35hp from the 302hp as arrived. There has been a lot of discussion on here regarging this conversion, so if you are interested please do a search under Motec and you will find the best threads, here is one for starters:
https://rennlist.com/forums/showthre...ight=964+motec

Red rooster

Colin,
Sorry if I caused offence ! That old Sun was a Maha !!

Getting past that stuff , we are still faced with the filter cover off at high speed and back on at low for best overall performance ,due to thermal effects at low and another problem at high.

Its interesting that the two plots have a slightly different shape across the rev range.
If we were looking at a simple flow obstruction there would be a nearly fixed % torque drop across the range.
I wonder if the intake snorkel is just too comparable in diameter to the intake system and so effectively lengthening the intake. That would do little at low speed but would be a negative at high.
How about a filter lid with a much larger diameter intake picking up from the spoiler . Would that give the best of both worlds ?and so fix this for ever !!!!!!!!!!!!!!!!!

All the very best

Geoff

wsybert

Finally got my hands on a sensor with enough accuracy to check the difference with and without the elbow (pressure drop).
To recap the thread.... I added a 90 degree bend to the intake to position my cone filter closer to the spoiler, then added a heat shield under it. During street driving, the temps were cooler under the spoiler, but a question of whether or not the 90 degree bend in the intake now caused more pressure drop and therefore negated the affect of the cooler air.
So....
It definitely has an affect on the pressure, but not much.
I used a Rosemount Differential Pressure cell, with an accuracy of 0.05%, and a range of -250 to +250 inches H2O.
I did not have a means of calibrating the device, but all I was after was the difference, so this should be good enough. (They come from the factory pretty close already).

I installed the low side of the transducer to a port just in front of the AFM, the high side was at atmosphere.
I ran the car at idle (800 RPM), 2000 RPM, 4000 RPM, and 5000 RPM, for about 5-10 seconds each.
At 5000 RPM the differential pressure difference with and without the elbow on the intake, is about 0.17 inches H2O or 0.0063 psi.

I am going to get a run at 6800 when I can. This was done in the garage with the equipment on my bench, and I did not want to run the revs up that high with no load for any length of time. Maybe not an issue, just makes me uncomfortable.

I also had a chance to run some temperature tests on the different intake setups.
I have to say, that I screwed up a little, and took the temperature on the standard airbox, a little prematurely. Meaning, I did not let the car warm up fully before starting the test. I say this based on how the graph looks, and knowing I only ran the car for about 15 minutes or so, before I started to capture data.
I do believe it would be the coldest of all, due to the fact it draws all of its air right below the spoiler.
I left the data in just to show it.
So, as far as the temps go, the drilled airbox is the worst, followed by the cone with no heat shield, then cone with heat shield, the stock airbox the best. (Go figure, Porsche did it right.)

Bill