2007 Exige S Intercooler Air Flow Study

[fred2602]

Originally Posted by Pestodude

Anybody read French...would love to know if it works!

I have opened the post on elise.ch;, so our discussion in French was just about the solutions possible today. One member has found that pics but we don't have so much info about it, it's seems to be an alternative to the komotec kit.. I think it increases the contribution of air by taking it from the side pannels

Anyway, the post here on lotustalk is just awesome, very interesting to see that the cup roof only don't bring so much difference.$

Congratulations to apk919 and ready to read more stuff

[Ken Wright]

the set up with the standard roof intake and the side intakes is going to be great at circulating air in front of the intercooler and not pushing the air through it. The path will be: in the side scoops and out the roof scoop. The air will take the path of least resistance and this will be out the roof, not through the intercooler.

[qball]

Originally Posted by Ken Wright

the set up with the standard roof intake and the side intakes is going to be great at circulating air in front of the intercooler and not pushing the air through it. The path will be: in the side scoops and out the roof scoop. The air will take the path of least resistance and this will be out the roof, not through the intercooler.

Put some puller fans on it...

And I'm not sure I agree with your theory... that through the IC is less restrictive then the tiny roof opening...

[apk919]

Originally Posted by Ken Wright

the set up with the standard roof intake and the side intakes is going to be great at circulating air in front of the intercooler and not pushing the air through it. The path will be: in the side scoops and out the roof scoop. The air will take the path of least resistance and this will be out the roof, not through the intercooler.

Originally Posted by qball

Put some puller fans on it...

And I'm not sure I agree with your theory... that through the IC is less restrictive then the tiny roof opening...

I'm with qball on this one... air will flow from a high pressure area to a low pressure area... and I think that the fact that air flows from the inlet through the intercooler makes it clear that the inlet is at a higher pressure than the engine compartment. Yes, there's some inertial component here too.. but:

One of the parameters I'm logging is barometric pressure. Unfortunately my "fixed course" has a lot of elevation changes, and although I'm also logging elevation, I haven't tried to "normalize" the pressure readings yet (it may be possible to do that). But there is a clear trend in the data that shows that pressure behind the intercooler drops with increasing speed...

I'd have to guess then, that if both side ducts were combined with the roof duct, all the air would still flow through the intercooler. Maybe I'll actually find out...

[apk919]

Here's a small snippet of data taken from a part of the course that is relatively flat (so pressure should be related mostly to speed and not elevation). It seems the pressure sensor's resolution is in 1/100th's of an inch of mercury... so it's a bit "discrete". In any case I think it illustrates how pressure behind the intercooler drops with increased speed...

Note that the pressure sensor is behind the intercooler and a few inches above the engine's valve cover (see http://www.lotustalk.com/forums/atta...calibrate1.jpg)

[Smoky]

So what effect does blocking/redirecting the side intakes have on engine cooling? Anything at all? At a glance it seems like these side scoops may be the only source of cool air for the motor. But there may be more getting through the engine bay then I realize.

Great data apk.... Now you need to stick a sensor on each intake, scoop, and duct. j/k would be cool data though.

You are really covering a lot of the most interesting readings... great job!!

PS: What was actual baro pressure outside during the run?

[apk919]

Originally Posted by Smoky

So what effect does blocking/redirecting the side intakes have on engine cooling? Anything at all? At a glance it seems like these side scoops may be the only source of cool air for the motor. But there may be more getting through the engine bay then I realize.

Great data apk.... Now you need to stick a sensor on each intake, scoop, and duct. j/k would be cool data though.

You are really covering a lot of the most interesting readings... great job!!

PS: What was actual baro pressure outside during the run?

Thx! (and thanks to all who've kept me motivated...)

Well, there are the NACA ducts in the undertray... they're specifically designed to draw air into the engine compartment too. You're right though, I'd be concerned about blocking too much engine compartment ventilation.

Actual baro pressure varied with elevation... so without correcting for elevation I couldn't tell you what the actual was for that snippet of data. More work ahead!

EDIT: Just FYI... barometric pressure decreases by about 1" of Hg per 1000' elevation, from sea level to about 5000'... and the elevation of my course varies by ~340' from minimum to maximum... so I'll be trying to pull a relatively small signal out of a much larger one...

[Drmike]

Just thinking/musing out loud:

As we are concerned with heat transfer shouldnt we be looking at mass flow rate of the air not just pressure?



Air pressure P1 entering the scoop depends on vehicle speed and its aerodynamics
Air pressure P2 in engine bay depends on vehicle speed its aerodynamics engine bay vent pressure and resistance for flow to exit the bay




Flow through scoop depends on all the losses in the system

- Roof scoop dimensions, length and shape
- Resistance to flow from the intercooler matrix
- Difference between roof scoop air pressure, P1, and engine bay air pressure P2 (exit resistance)


So all things considered we should see the following:

at low car speeds air pressure P1 and P2 is high but flow is low
at high car speeds air pressure P1 and P2 is low but flow is high


The mass flow rate is a function of pressure (density) and flow rate


So you can have a low pressure high flow air giving same mass flow rate as high pressure low flow air



Nothing ever moves from low to a high pressure zone. its physically impossible, Its always the other way around


The only way you will get reverse flow out the scoop is if the air pressure at scoop entrance is lower than the air pressure in the engine bay AND if the engine bay has high pressure flow entering into it. It doesnt matter how high the pressure or temp is in the engine bay if its not moving/being fed it wont flow anywhere and will instantly balance with scoop exit pressure. As the only air entering the engine bay is coming from the underfloor engine bay vents then I would assume that air would be lower pressure than roof scoop pressure at speed due to aerodynamics? That being the case I cant see how reverse flow can ever happen - but I could be talking bollocks

bottom line I think we need to measure mass flow rate. so we need to record air pressure (in scoop) as well as flowrate (or velocity) through scoop



opss clearly the coffees kicked in


all things being equal:

flow rate through scoop depends on total resistance to flow through scoop

How much the front part of the scoop size contributes to the total resistance to flow through scoop is the question. My guess would be the intercooler matrix is far larger a contributor - which would suggest ading fans after the intercooler wouldnt be very effective

Measuring air velocity, V, after the intercooler may not highlight small changes in flowrate, Q, as the 'area' A is huge (Q=VA) so small changes in flow rate may not be apparent. It might be better to mount the velocity meter inside the ducting before the intercooler if possible or in a duct attached to the front and encompases all the outlet from the intercooler

[apk919]

Originally Posted by Drmike

Just thinking/musing out loud:

As we are concerned with heat transfer shouldnt we be looking at mass flow rate of the air not just pressure?



Air pressure P1 entering the scoop depends on vehicle speed and its aerodynamics
Air pressure P2 in engine bay (non moving air not from scoop) depends on vehicle speed its aerodynamics and resistance for flow to exit




Flow through scoop depends on all the losses in the system

- Roof scoop dimensions, length and shape
- Resistance to flow from the intercooler matrix
- Difference if any between roof scoop air pressure, P1, and engine bay air pressure P2 (exit resistance)


So all things considered we should see the following:

at low car speeds air pressure P1 and P2 is high but flow is low
at high car speeds air pressure P1 and P2 is low but flow is high


The mass flow rate is a function of pressure (density) and flow rate


So you can have a low pressure high flow air giving same mass flow rate as high pressure low flow air



Nothing ever moves from low to a high pressure zone. its physically impossible, Its always the other way around




opss coffees kicked in

I agree that the mass of air flowing though the intercooler is more important, that's why the most significant graphs are those which show the volume of air (in cfm) vs. vehicle speed. The pressure drop in P2 with speed (which is the significant measurement with regards to volume) seems to be quite small (only a few hundredths of an inch of Hg).

On the other hand I'd say that P1 increases with speed (since the scoop is actually flowing less air than it would be if the ducting presented no resistance... imagine sticking a tapered cone vs. a tube out in the airstream). That's significant when considering how air will flow when combining ducted air from other sources (i.e. the side scoops).

[Drmike]

Originally Posted by apk919

On the other hand I'd say that P1 increases with speed (since the scoop is actually flowing less air than it would be if the ducting presented no resistance... imagine sticking a tapered cone vs. a tube out in the airstream). That's significant when considering how air will flow when combining ducted air from other sources (i.e. the side scoops).

Yes a tapered inlet will reduce losses and enable higher flow rates.
Given the aerodynamics at speed Im wondering if air flowing over car and towards roof scoop is going to see reducing presssure as car speeds up.

[lwein]

Has anyone ever thought about putting a scoop,or maybe better,a NACA duct on the Drivers side "sail" panel--not unlike a 1967 GT -350 scoop? IC should get better airflow,and the top could be removed? I know it involves cutting into the body,but just an idea??

[apk919]

So, given a decent 20% increase in flow due to the first fettle, I thought I'd see how much more fettling was possible, as well as sealing leaks and smoothing flow.

There wasn't much more material to be removed, given the size of the ducting (see pics). There were gaps between the opening in the clam and the duct work though, and I sealed them with silicone caulking. Also, I worked on making the roof gaskets (for both the Cup and stock S roofs) seal more tightly with the clam opening. It's interesting that Lotus designed the gaskets differently... the Cup roof gasket goes over the top of the duct, the stock S roof goes under. On my S, there was a gasket attached to the clam to seal the gap above the duct. I don't know how a Cup car's clam gaskets look (pics anyone?). So I removed the gasket from the clam, and added a gasket below the duct for the Cup roof, and above the duct for the stock S roof. See pics...

Now I need to road test... maybe tomorrow...

Pic #1: After completing the fettling.
Pic #2: After sealing the ductwork with silicone.
Pic #3: Cup roof mating gaskets.
Pic #4: Stock S roof mating gaskets.
Pic #5: Replaced the crappy hose clamps (Jubilee?) with decent slotted band hose clamps (Tridon). They're much easier to take apart, put together, and tighten down on the snorkel to the ductwork. Highly recommended if you ever take it apart.

[Mag]

Originally Posted by robains

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!

lotus stopped using these because over time it warped the hatch.

The hot air from the radiator is an issue. Just stick your hand on the roof on the highway, you'll notice the air there is quite a bit hotter than if you raised your hand into another airstream. Crude thermometer I know but the difference can be felt. I've heard of a splitter added on bottom of front of roofs similar to cup roof along the windshield top edge that supposedly splits the hot air and runs it in a different direction allowing fresh air in the scoop.

Really Really interesting post by the way.

I am in the camp that thinks that fans is the only way to go. Either roof, the bottle neck is still at the fettle location. Even with fettling, the opening is just... ridiculous. If fans are used, just a theory but I think the non cup roof would be a better combo here.

[Smoky]

Would love to see pics and a writeup of how the fans are located, installed, and wired-in to function. Are they always on when the car is running? Are they strapped to the i/c? Or elsewhere? Do the fans replace the function of the roof scoop, or supplement it?

I've seen several references to using fans on this forum but have never seen evidence of anyone actually doing it.

apk: where exactly are you sealing the duct? it is difficult to tell from the photos. From what I can tell, there is a bead of silicone on the inner lip of the body-portion of the scoop (as opposed to the roof scoop, which appears to be removed in your pics, with the photo showing a view into the body-portion of the scoop). If you have a moment, could post a few more angles, and then maybe an external pic showing arrows pointing to what exactly is sealed? I just can't tell if you're improving the seal of the roof scoop to the body scoop, or if it is a better seal within the body scoop and has nothing to do with the roof scoop.

Thx!

[lwein]

Originally Posted by Mag

lotus stopped using these because over time it warped the hatch.

The hot air from the radiator is an issue. Just stick your hand on the roof on the highway, you'll notice the air there is quite a bit hotter than if you raised your hand into another airstream. Crude thermometer I know but the difference can be felt. I've heard of a splitter added on bottom of front of roofs similar to cup roof along the windshield top edge that supposedly splits the hot air and runs it in a different direction allowing fresh air in the scoop.

Really Really interesting post by the way.

I am in the camp that thinks that fans is the only way to go. Either roof, the bottle neck is still at the fettle location. Even with fettling, the opening is just... ridiculous. If fans are used, just a theory but I think the non cup roof would be a better combo here.

I have also felt the hot air that comes over the windscreen,it is from the heat of the radiators in the nose,and it is suprisingly hot.
I looked into fans a while ago,and the tiny fans that would fit don't come close to pulling enough air,pushing is not a good idea,either. the only place where fans might help on this car is when it is in traffic,but how much horsepower do you need in traffic? I am still thinking that a scoop on the drivers side "sail" panel(opp side of the fuel filler door)--or a NACA duct ---run into the stock air duct along with the roof might be the answer. It could be replaced with another gas filler door(screwed shut)if desired should the need arise. If you wanted to remove the top,you would still get air into the IC from the top scoop on the clam and the new sail panel air inlet. All of this is just mental masturbation on my part until somebody gets temps and meaningful data. Where is Jim Hall (Chaparral) when we need him?

[apk919]

Originally Posted by lwein

Has anyone ever thought about putting a scoop,or maybe better,a NACA duct on the Drivers side "sail" panel--not unlike a 1967 GT -350 scoop? IC should get better airflow,and the top could be removed? I know it involves cutting into the body,but just an idea??

Originally Posted by lwein

I have also felt the hot air that comes over the windscreen,it is from the heat of the radiators in the nose,and it is suprisingly hot.
I looked into fans a while ago,and the tiny fans that would fit don't come close to pulling enough air,pushing is not a good idea,either. the only place where fans might help on this car is when it is in traffic,but how much horsepower do you need in traffic? I am still thinking that a scoop on the drivers side "sail" panel(opp side of the fuel filler door)--or a NACA duct ---run into the stock air duct along with the roof might be the answer. It could be replaced with another gas filler door(screwed shut)if desired should the need arise. If you wanted to remove the top,you would still get air into the IC from the top scoop on the clam and the new sail panel air inlet. All of this is just mental masturbation on my part until somebody gets temps and meaningful data. Where is Jim Hall (Chaparral) when we need him?

I've always liked the way those sail panel vents looked... but that mod is a bit over my head at this point...

I am planning on getting flows and temps from the inlets of the roof scoop and the side scoops. I'm also tempted to get another logging meter so I can do them simultaneously (so there's no chance that different conditions will affect a comparison). All I need to do is spend more time and money

[apk919]

OK, this is about as far as I think I can get by fettling alone. Altogether, it looks like a 25% increase in airflow through the intercooler compared to the flow before fettling. In addition, the distribution of flow across the face of the intercooler is more uniform now than after the first fettle.

I'll try to get the same data with the stock S roof, and topless as well. Then... hmm... what should I try next?

[turbophil]

Since you've now proven that the stock IC doesn't get near enough airflow evern after fetteling, try adding NACA ducts on the c pillar behind the rear class and directing more air to the IC...

Cheers,

Phil

[apk919]

Originally Posted by turbophil

Since you've now proven that the stock IC doesn't get near enough airflow evern after fetteling, try adding NACA ducts on the c pillar behind the rear class and directing more air to the IC...

Cheers,

Phil

What do I do with the right side C-pillar? The fuel filler tube is in the way... asymmetric ducting?

I'm considering increasing the size of the side ducts (there's at least one source of CF side ducts that has a larger intake cross-section than the stock ducts). And do we really need the mesh? All on the list of potential experiments...

[turbophil]

Originally Posted by apk919

What do I do with the right side C-pillar? The fuel filler tube is in the way... asymmetric ducting?

I'm considering increasing the size of the side ducts (there's at least one source of CF side ducts that has a larger intake cross-section than the stock ducts). And do we really need the mesh? All on the list of potential experiments...

I'd seriously consider putting a duct on the drivers side c pillar and see if that helps. I think it would look pretty cool. You can't see both side of the car at the same time so whycare about symetry

Frank found that the mesh blocks a heck of lot of air on those side scoops, so I would certainly remove that jazz...

The reality is that you need a lot more air to really get some good efficiency out of those ICs and I think you've shown that the big issue is that little opening. If you can double the size of that hole, you'll probably double the air... If I were you, I'd start doubling

Best,

Phil