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2007 Exige S Intercooler Air Flow Study

152785 Views 697 Replies 81 Participants Last post by  gfelber
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.


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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.
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 :)
Maybe at a dead stop there is, but not sure that matters unless your car idles at 8K rpm ;)
Glad I'm not the only one that has dented their IC with that stupid placement of a hood latch. It would be 1000X better if they had simply attached a small locking arm to either side of the hinges -- it's like the chassis design team and the body design team came from different pubs!
Very interested on how the fans workout.

Any chance you wiring guru's could share info on where I might be able to find an RPM signal in the center wiring harness inside the car?

Thanks, Rob.

Was hoping to get a wire color.

thanks, Rob.
Could I get a link to where I can download/purchase the Lotus Exige S service manual and TSB? Is this a service manual or a shop manual?

I'm used to paying $300 for shop manual downloads.

Thanks, Rob.
Your data is about what I expected. And I agree, fans on the IC will not help -- fans in a race car are only used when there is no air flow (aka not driving at speed) -- when racing (if you have fans) you turn them off, only when you come into pits or doing cool down laps do you turn the fans back on (aka low speed).

Does anyone have a charge cooler? Would be nice to get their numbers -- but my hunch is that a charge cooler's benefit is with more stability and consistant temps under load and non-load situations -- I don't think it would necessarily reduce the air/gas mix tempurature that ultimately goes into the cyclinder chamber.
Maybe we need to ask Casey at FF how he got 85F for intake air on their 380 turbo car?

I still think the location of the IC is horrible and the primary cause of it's lack of efficiency. Has anyone thought about moving it forward and up a little and then isolating the engine area using the side ducts to flow are into the engine bay?

I would think trimming the plastic duct a little and removing some of that angle while raising the IC higher -- could probably gain 3-4" up and back. Isolate the engine bay with 3 pieces of aluminum (CF if it actually works) that can be easily removed/installed with rubber gromets around the necessary IC tubing. It might require some new IC tubing that is slightly longer (not much) -- but keeping the tube length short is a BIG plus.

Think I might take some measurements and pics.
As has been said, Air to Air is definitely more for street driving and/or drag racing with plenty of cooled down.

Having just got back from a miserable day at ButtonWillow, the air to air IC just isn't gonna do anything, just extra dead weight.

Don't know the street to track ratio for the Lotus, but there were A LOT of Loti at the track and they seem to be a very popular car for track days, even at other none Lotus related events.
I'm going to experiment with home brew kit. It looks well thought out and the power draw is only 50 Watts (about the same as my Nav/Stereo).

The water spray kit

Take a look at some of the data readings that were taken with this setup. However it appears the pump will not do well in continuous operation. Max is about 1 minute then needs to cool down. Anyone have alternate pump solutions? Higher pressure the better.
You could be correct on the rules - I didn't see anything in the rules that prevented this, but there are many pages and I didn't necessarily digest every detail.

Charliex, not great data, they do post more data on other links. But after reading more about the water pumps, there doesn't appear to be a really good pump to accomplish track type situations -- one would have to set a long delay between triggers to keep the pump from overheating with the high PSI needed to create the mist.
From what I've heard, direct water/meth injection isn't helping these cars much either -- the heat soak is just too much.

I believe I was seeing 176F at ButtonWillow for IAT (according to EFI software and that was 15 minutes after I had been out on track) -- which is WAY hot. I had to let the car sit for a long time before I could even touch the pipes with a rag and gloves ON!

I hope someone comes up with a good solution for track worthiness. But I would have to say the large roof scoop appears to be more about looks than function. I'll continue on the sprayer and relocating the IC up and back and opening the mail slot as much as possible, but I'm honestly not expecting much.
Is that a dent I see in the IC??? Hehe...does anyone not have a dent in the IC?

I'm hoping to be a protoype for a new solution to these extremely high IAT values.
I just finished opening up my mail box on my 07 S today. I also found a good misting spray nozzle and installed that. Now for the bad news, the GM water pump used in the windshield spray tank is a joke -- tested with it and all I got was short pulse of next to no pressure, it was beyond pathetic.

So I'm searching for a high pressure water pump for 12v DC and the only thing I've found is a Shurflow which can only do 130 psi max. After searching the net some I'm finding out that true mist systems (multi-nozzle) are running at 800-1000 PSI, weigh A LOT, very large, and some want 230 v 10amps+

I'm thinking I could probably get away with 200 psi unit for a single mist nozzle, but there are none to be found for 12v DC.

So in a word, external water mist on IC doesn't appear to be a workable reality until someone can produce small efficient light weight pump.

I've been made aware of a "yet to be released" alternative ... stay tuned.
From the pic of the unit, that pump looks to be exactly like the GM pump used in the Lotus washer unit -- for long repeated spray durations it'll just burn out the pump. I couldn't see any specs on the pump at all.
1 or 2 Mist Jet Application for Maximum Coverage and Effectiveness
1 or 2?? Errrr...that isn't gonna do much good -- assuming it can even generate a "mist".

70 PSI 12v DC Flojet and this is about 12X larger than the pump you see in your link.

I've seen some smaller high pressure pumps, but that can't run for more than about 9 seconds and MUST cool down for a period before. I've also used a Shurflow 45 psi pump on an 04 STi and it wasn't able to really product a mist.

I've been searching and the more I search the less I find of intercooler misting systems that are viable for track duty.

The closest kit that might work (intended for home use) is this Unit from EZ Mister

The pressure is needed so that you do NOT just spray water on the IC (this does more harm than good), the mist style nozzle doesn't "flow" a lot of water, it mists (very very small hole). The high pressure is needed to be able to atomize the water as much as possible thru this tiny hole -- as that is what truely cools the IC -- the mix of cool water vapor with the air flow -- best case is you can drop air temp over the IC by 35 degrees F. But misting takes pressure, lots of it.
The Harm it does:

1. Doesn't actually cool the air flowing over the IC, in fact, it will most likely just generate more heat as the water turns to steam once it hits the hot IC and or engine which will generate a burst of hot steam to make things even hotter.
2. Rear tires (Hoosiers in my case) don't react well to water dripping on them and probably wasn't too good for anyone who might be following.

The water spray ultimately just heats up the IC and can cause the engine to start to detonate -- this has happened to my OLD 04 STi and to a friend's 03 WRX until we both removed the water spray and the detonation went away. Spraying with more water doesn't help either, I went thru 3 gallons per track session on my STi and it didn't help heat soak at all -- my lap times didn't change much with or without water spray.

When you go into a Sauna and want to generate some heat, what do ya do, you take a cup of water next to the heater and dump it on the hot rocks which in turn generates a ton of steam with heats up the Sauna more. This is exactly what you are doing if you just spray water on a hot IC and/or Engine.
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All ears if you folks would like to provide details.

For any benefit, you want to cool the air going over the IC, not spray water on the IC. Have you stood under a misting system in 100+ degree ambient, it does indeed cool the air, and those systems run 800-1000 psi (10 nozzles).

But try it -- I sprayed water on my IC and my IAT went up, not down. Only when I really hosed down the IC with 4 gallons (aprox) of water continously from a garden hose did I seem IAT go down. So lets be realistic, unless your drive with 100 gallons of water in your car, a water sprayer isn't helping.
if you spray water on the IC it converts to steam which is then pushed thru the IC which in turn does NOT cool the IC.

Misting is performed on the incoming air to cool the air which then cools the IC.

I agree with you is some ways but you are removing the air flow from the equation/context -- yes you convert the heat into steam and reduce IC temp, but the steam immediately then flows over IC increasing it's temp.

The Subaru sprayer is manual, not automatic, and it wouldn't be the first time a gimic device has been but on a car...happens all the time.

I do have an idea, the water went thru the IC onto the hot engine which then converted the water to steam which raises up towards the IC which in turn heats the IC, not cools it.

The key here is to mist the air flowing OVER the IC, not to spray water ON the IC. You want the air to be cooled and water free by the time it passes thru the IC.
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