Author Topic: Ram air pressure measurement (Read 8968 times) Tweet

MJ Williams · « **on:** August 05, 2011, 02:34:41 PM »

Has anybody measured what the airbox will get pressurized to by the ram air? Assuming stock displacement, stock air box and perhaps 150 mph or whatever speed you got a pressure reading at.

wildphil69 · « **Reply #1 on:** August 05, 2011, 11:25:56 PM »

I was wondering this the other day... Wondering if all of the expensive seals and tube extensions were worth it?

ZX10Hef · « **Reply #2 on:** August 06, 2011, 12:43:32 AM »

I had a friend of that has a dynojet dyno he put a vacuum Gage on is are box and at 6 grand it would go a -30 inch of vacuum I would like to what it would a 150mph

Oz Booster · « **Reply #3 on:** August 06, 2011, 04:17:40 PM »

aviation stuff is easily found to see what the actual wind pressure is at speed but what the airbox pressure is could be entirely different
i saw a chart for airspeed indicator calibration not long ago that suggested .388 psi at 150mph sea level,

glenn71 · « **Reply #4 on:** August 06, 2011, 06:03:22 PM »

When i was running my 1441 at the strip 13 on the dyno
Was 13.5:1 a/f in 4th gear.it was running blackbird
Injectors at 60psi,so if you needed 5% more
Duty cycle at approx 5.25cc of fuel per hp
On this dyno,it was making approx 12-14hp
More in 4th gear from ram air and the correct
Fuel addition,this with a large airbox mod so
Imagine the difference in 6th.id think 16-20hp
On a 1400+cc engine would be realistic.

sportbikeryder · « **Reply #5 on:** August 06, 2011, 09:07:09 PM »

Might be a good idea to get a 0-1psi or so range pressure transducer and hook it up an see. Especially for the land speed guys. I woudl imaging some are measuring the ram air pressure for landspeed. If not, it woudl be pretty easy to do.

At high speed I would imaging 15-20 in h2o or should be able to be generated with a modern ram air system. Probably quite a bit higher with the extended "tube nose" landspeed bikes of late.

Nosgsx1300 · « **Reply #6 on:** August 08, 2011, 04:15:49 PM »

I did at Maxton one year
I got .92PSI

Nosgsx1300 · « **Reply #7 on:** August 08, 2011, 04:16:05 PM »

on a gen 1 at 192mph

wildphil69 · « **Reply #8 on:** August 09, 2011, 10:49:21 AM »

Quote from: Nosgsx1300 on August 08, 2011, 04:16:05 PM

on a gen 1 at 192mph

with the stock plastics and box?

Warp12 · « **Reply #9 on:** August 09, 2011, 03:18:04 PM »

Quote from: Nosgsx1300 on August 08, 2011, 04:15:49 PM

I did at Maxton one year
I got .92PSI

How did you log it, and how did you smooth out the pressure pulses for logging purposes?

Nosgsx1300 · « **Reply #10 on:** August 09, 2011, 03:53:40 PM »

ramair seals, screens removed
a gm 2 bar map sensor wired to my innovate LM-1
smoothing required in the software was minimal

made .72psi at 120 mph then slowly built from there

Warp12 · « **Reply #11 on:** August 09, 2011, 04:46:52 PM »

Quote from: Nosgsx1300 on August 09, 2011, 03:53:40 PM

ramair seals, screens removed
a gm 2 bar map sensor wired to my innovate LM-1
smoothing required in the software was minimal

made .72psi at 120 mph then slowly built from there

Interesting. That seems on the high side, especially at 120 mph, if you are talking above ambient.

What was your baseline pressure reading, without the bike running?

Nosgsx1300 · « **Reply #12 on:** August 09, 2011, 05:21:37 PM »

I calibrated idle to 0 psi

Nosgsx1300 · « **Reply #13 on:** August 09, 2011, 05:36:55 PM »

the reading seemed to climb to .5 thru .75 very quickly
then from there up it was real slow

I wish I still had the logs but 3 computers later things got lost
I did this on the recommendation of DaveO, and he seemed to agree with the findings
this was with a large box mod, ramair seals to the fram rails. the screens out of the vents
I never tried those snorkel thingys. I would have but didn't have them the weekend I was doing this

Warp12 · « **Reply #14 on:** August 09, 2011, 06:08:51 PM »

Quote from: Nosgsx1300 on August 09, 2011, 05:21:37 PM

I calibrated idle to 0 psi

Ok, so then it should have been below atmospheric at idle. Your zero point was below atmospheric and your positive measurements are in reference to that, right?

That is opposed to looking at the actual ambient, and then looking at the rise above that number.

I'm just trying to get a picture of the methodology.

Nosgsx1300 · « **Reply #15 on:** August 10, 2011, 04:57:15 PM »

why would it have been below atmospheric at idle?
I did not have it commected to vaccum
it was IN the airbox

Warp12 · « **Reply #16 on:** August 10, 2011, 07:13:12 PM »

Quote from: Nosgsx1300 on August 10, 2011, 04:57:15 PM

why would it have been below atmospheric at idle?
I did not have it commected to vaccum
it was IN the airbox

Why would it not be below atmospheric pressure at idle? The engine was sucking air out of the box; in that respect it was connected to a vacuum, right?

Nosgsx1300 · « **Reply #17 on:** August 10, 2011, 09:30:20 PM »

maybe but I saw no difference between my zeroed reading with the bike running or not, so I dunno

glenn71 · « **Reply #18 on:** August 11, 2011, 04:24:43 PM »

i did some measurements the other night and the
snorkel size through the frame rails is basically
the same size as the 4 46mm throttle bodies.
my question is,if the airbox pressure rose to 0.75
psi quickly and then slowly afterwards and wind pressure
builds in an exponential manner,it suggests a restriction
as airflow and injector duty cycle generally
peaks around 9000rpm,so if the engines appetite
for air then decreases but the road speed
increases still,logic would expect the airbox
pressure to build quite well beyond max injector
duty cycle point.a differential pressure gauge on the intake snorkels
other side of the frame rails and comparing that to the
airbox would be a good start.

Nosgsx1300 · « **Reply #19 on:** August 11, 2011, 07:26:22 PM »

I have since gone tubo, so I can put sensors anywhere and get postive pressure

MJ Williams · « **Reply #20 on:** August 14, 2011, 09:05:50 PM »

Thanks for your comments. Always food for thought.

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Author Topic: Ram air pressure measurement (Read 8968 times) Tweet