2007 Exige S Intercooler Air Flow Study

[apk919]

I've been trying to get real data on how much air actually goes through the intercooler on an Exige... I'm using a GPS to record position, and speed over time, and a datalogging weather meter to record air flow through the back of the intercooler (as well as temperature, humidity, atmospheric pressure, etc) over time.

I first calibrated my air flow readings by forcing air through the roof scoop and taking readings across the face of the intercooler. While the meter reads in fpm, given this calibration and the area of the intercooler you can then convert fpm to cfm (without getting into the nitty-gritty, multiply the fpm measurements by 0.4606 to get cfm).

I established a fixed "course", and gathered data with both the stock Exige S roof, and the Cup roof... processed all the data generating scatter plots, histograms, and linear regressions.

The bottom line is that there is no significant difference in intercooler airflow between the stock S roof and the Cup roof. How could this be? It seems that the inlet is not the limiting factor. Most of us have suspected the bottleneck where the end of the roof and the beginning of the clam meet is the limiting factor... my next step is to attempt to minimize the bottleneck and compare the results to the baseline.

First: a graph of vehicle speed vs. intercooler air flow speed, for both roofs, showing both the linear regressed results and the average value histograms.

The next two graphs are scatter diagrams of the raw data for each roof.

[Pestodude]

I love this f**k'n guy!!! Great work!

[Jack]

Let the "fettling" begin -- I love that word.

Keep up the good work.

[djo715]

Great data!!! One comment - perhaps the cup roof starts to make a difference at higher speeds? The histogram data seems to show some larger differences starting at around 65mph.

If you just included samples at 65+mph - would the regressions still match up?

Cheers,
-Darryl

[robains]

great work on the data, but it would probably be more relevant if the readings are taken at speeds 60-160 mph. It's pretty rare that on track one is going slower than 60. Also, it's more critical to know the flow above 60 since that is where one would start feeling the affects of heat soak.

Was this data extracted from street driving or track driving? Guessing street?

Great work, would like to see more, maybe from a track day as that is where the heat soak issue is most relevant.

[EliseAtLeast]

Originally Posted by apk919

... my next step is to attempt to minimize the bottleneck and compare the results to the baseline.

Great work . Would love to hear the result of your findings.

[Bgwilly31]

cup roof makes no difference.....

makes no sense.

[Jack]

Originally Posted by Bgwillyelise

cup roof makes no difference.....

makes no sense.

He didn't say that...and it obviously makes some difference as can be seen from the graph. As Robains already mentioned, my bet is that the difference between the two roofs is even greater at speeds above 80 mph, which appears to be the maximum speed at which the test has been conducted so far.

[apk919]

Thanks for the encouragement everyone...

Yes, there's not much data above 65mph... and it's not clear that the slight increase in flow with the Cup roof is significant above 65... not many data points. I'd love to get data at higher speeds, but as you have guessed, my "course" is on local roads... and I might have problems if I tried to take too much data above 75mph

EDIT: The "fixed course" is close to a square, with approximately equal legs in each compass direction... and I tried to avoid taking data on windy days, but a sudden gust of wind could always be responsible for data points above or below the regression line.

I wanted to make sure I could reproduce the conditions somewhat reliably so that the data could be compared properly.

I've just started "fettling"... I'll post more results when I've got them...

[robains]

Great data, even at lower speeds, I'm surprised the Stock S roof flows that well. Now, how do we determine drag of the two types of roof scoops?

But yeah, higher speed data may change the dynamics of that chart considerably. Get your car on a track with a good long straights

[apk919]

Originally Posted by robains

Great data, even at lower speeds, I'm surprised the Stock S roof flows that well. Now, how do we determine drag of the two types of roof scoops?

But yeah, higher speed data may change the dynamics of that chart considerably. Get your car on a track with a good long straights

Yes, I think it's at least possible to say there's no "reverse flow" through the intercooler... I had heard rumors to that effect previously.

[robains]

Maybe at a dead stop there is, but not sure that matters unless your car idles at 8K rpm

[Smoky]

This is excellent! Very good job! Keep the data coming!

Also, can you post a scatterplot with the datapoints color coded according to which roof produced them? And then overlay the regression line against the scatterplot. Would be nice to see how the datapoints group or don't group around or to either side of the regression line.

Thx! Can't wait for more.

[qball]

The cup roof is still ineffective because the opening at the top of the rear clam is still too small. (fettled or not)

Doesn't matter how big the roof scoop is or how far forward it is, we can't compress air and increase airflow that significantly at these speeds we need the intercooler to work.

Your best option is to get airflow from another area and have some fans to add in in the process.

[apk919]

Originally Posted by Smoky

This is excellent! Very good job! Keep the data coming!

Also, can you post a scatterplot with the datapoints color coded according to which roof produced them? And then overlay the regression line against the scatterplot. Would be nice to see how the datapoints group or don't group around or to either side of the regression line.

Thx! Can't wait for more.

How's this?

EDIT: Only data points with vehicle speeds > 5 mph and air flow speeds > 0 fpm were used in the regression analysis...

[shoco]

Great work! I notice a dip in the points of both graphs at 45 mph. This is where I noticed "reverse flow". Do you find any significance to this trough in the data points? Would you consider testing my intercooler ducts that take airflow from the side scoops and funnel it through the intercooler from the back? I'm sure many people on this forum would love to see the comparison data.

[apk919]

Originally Posted by shoco

Great work! I notice a dip in the points of both graphs at 45 mph. This is where I noticed "reverse flow". Do you find any significance to this trough in the data points? Would you consider testing my intercooler ducts that take airflow from the side scoops and funnel it through the intercooler from the back? I'm sure many people on this forum would love to see the comparison data.

I wouldn't be surprised if there are transitions in the flow around the body that affect either flow into the scoop, or pressure in the engine compartment. That could easily lead to dips/peaks around the regression line. I'd love to have a full scale wind tunnel, but none of the F1 teams with those facilities returned my calls .

I read your solution with interest... I've been considering a hybrid solution that incorporates your side scoop ducting, but feeds it into the front of the intercooler in conjunction with the flow from the roof scoop. There's not alot of room in there though... My first mod will just be to fettle out the bottleneck and perhaps seal/smooth the flow from the roof scoop.

EDIT: Also, one of my planned tests is to measure air flow at each of the side scoops to get some idea of the potential volume of air available...

EDIT 2: Calibrating the air flow sensor... yeah, OK... it's not NASA or McLaren. But it works.

[shay2nak]

is that the stock IC? looks pretty tall.

[apk919]

Originally Posted by shay2nak

is that the stock IC? looks pretty tall.

Yup, that's the one that came with my car... 14" x 6.25" (cross-section to ducting)...

[Mr. Know]

Reverse airflow and improper intercooler operation was one of the sticky points that made me have a hard time choosing an 07 vs. an 08 car. I'm glad of my decision...from what I see so far.