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We had been using the Evora 400 undertray a while back to help with engine bay temps.

Getting it was problematic and then we had to modify it to clear headers.

Then it was expensive.

Then it got impossible to get.

So we took what we liked about it and changed what we didn't like about it.

The design we came up with cools the same, but is much easier to install (especially so in the field) since it engaged with the leading edge receiver groove in the chassis where the Lotus 400 part does not. It also has the air kickups where they don't hit headers. It has fewer spacers and the bolts are better at staying captive to the spacers. We also take the time to "glue" the stiffening ribs to the tray in addition to rivets to eliminate rattles. We've been real happy with the part.

This is a great mod for any Evora with an engine. lol. Seriously, the engine bay temps in the Evora from NA to wild are just horrendous. We need all the air back there we can get.

Have a look!

Evora Cool Tray

Cheers,

Phil
 

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What exactly is the horrendous engine bay temperature? Has anyone measured it with an infrared camera right after a heat?
 

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What exactly is the horrendous engine bay temperature? Has anyone measured it with an infrared camera right after a heat?
It's nothing to see overall 150F engine bay temps.

Lotus struggled with this and designed several different scoops for undertrays/diffusers over the years until they just gave up and did the 400 style undertray.

Not to mention the air kicks are a big deal to get some air to the forward bank of the motor. The exhaust proximity to the trans is an issue too. As is the boiling clutch fluid. There's simply very little air relative to the heat that's generated. The aim is to get the air to the parts getting the abuse.

Another good tip is to swap the boot lid glass for a vented unit. Not everyone prefers that swap though... for the race cars, you do both the undertray and the boot lid for sure...


Phil
 

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What exactly is the horrendous engine bay temperature? Has anyone measured it with an infrared camera right after a heat?
I swapped my undertray to a 400 style about a year ago when my car was mostly stock and I did notice that the car runs much cooler in general. In traffic alone I used to go to 3/4 on temp and now I'm about half.

Asfar as track days are concerned I don't have any data and if I did it wouldn't be consistent as my setup gas changed a bit since my last track day(100% stock)

In any case, more cooling is definitely better. As mentioned there have been slight variations to the Evora undertray to begin with. Mine was NA so completely flat. Then the S had a small drop by the transmission. And now they run a full drop the entire length.
 

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My car like most NA Evoras has the "Hot Climate Kit" which is a small fan mounted on the passenger side of the engine and it vents up behind the car. It apparently will only come on when ambient temperature is above 80F.

Two questions:

1. Is there a setting to make the engine bay cooling fan come on at a lower temperature?
2. Why not cut some NACA style ducts in the stock undertray to help air flow?
 

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Illegal Alien
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My car like most NA Evoras has the "Hot Climate Kit" which is a small fan mounted on the passenger side of the engine and it vents up behind the car. It apparently will only come on when ambient temperature is above 80F.

Two questions:

1. Is there a setting to make the engine bay cooling fan come on at a lower temperature?
2. Why not cut some NACA style ducts in the stock undertray to help air flow?
1. Per Services Notes Section KJ, Page 8, The Hot Climate Kit (all USA market, Middle East and other hot climates) is activated by coolant temp, not ambient air. Fan only operates with car stationary as part of Heat Soak control:
a) car at idle or ignition off; and coolant is > 100 deg C, fan runs for 3 min, or
b) coolant over 103 deg C within 90 secs of sign turned off, fan runs for 2 min.
c) fan restart is activated, fan will remain off for 2 min t protect fan from overheating.

Additionally if water temp exceeds 108 deg C within maximum of 20 mins after engine shut down, water recirculation pump will activate and run for 8 min.

Nothing really to gain with changing trigger temps (Phil's/ BOE Fastworks tune could change these ECU maps, but why). My 410 seems to be using a bigger fan than what was on my S

2. S cars, at least come with 3 NACA ducts, plus Trans air scoop .. not enough, bigger scoop and covered hatch provides more air. Remember just opening intakes without bigger outlets just fills a 'box' with stagnant air, you need to extract air into a lower pressure zone to get air flow.
 

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My car like most NA Evoras has the "Hot Climate Kit" which is a small fan mounted on the passenger side of the engine and it vents up behind the car. It apparently will only come on when ambient temperature is above 80F.

Two questions:

1. Is there a setting to make the engine bay cooling fan come on at a lower temperature?
2. Why not cut some NACA style ducts in the stock undertray to help air flow?
The cooling fan on the passenger side also only comes on when below a certain speed IIRC.

The stock NA undertray has NACA ducts; I'm guessing they're not nearly as efficient as dropping the leading edge and ramming air into the front.
 

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I'm a little confused here, does NA Evora mean naturally aspirated or North America? And is the heating problem now less of an issue with 400? I'm use to hot engine bays as I added superchargers on my R8's and Huracan
 

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OK, the chance of coolant temperature going above 100c is higher when ambient temperature is over 80F. The stagnant air argument is not valid in this scenario due to negative air pressure under the car in motion. Even if it is true, it applies to the proposed cooling tray design as well.

What about the additonal drag this cooling tray will produce? The whole point of NACA scoops is to intake air with minimal disturbances to flow on the boundary layer. I do understand that it may not work well in a neutral or negative pressure area such as the flat underbody. Wind tunnel data has shown that the under-body makes up to 30% of the vehicle's total drag. Smooth underbody with strategically placed holes in the stock undertray will probably outperform this as the negative pressure area under the car will suck hot air out of the engine bay.

Without evidence of mathematical modeling, number crunching, or some basic wind tunnel testing. It is hard to validate the claims.

I like how this guy is approaching the problem.
Aerodynamics of Engine Cooling ? Part 2 « omgpham?
 

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Discussion Starter #11
Always amazed how a forum can take theory and get it all jumbled up...

In any event, you don’t need a calculator or a wind tunnel at the level of modification in question here for a streetable application.

The underside the car is not terribly productive to downforce on a “streetable” track toy. The cars are simply far too high and have significant spill over air, etc. There’s a list to be sure.

As for the stock naca ducts, again, no calculator needed. In the easiest form of the discussion, it’s a simple function of area. The entire leading edge vs a few small ducts. Once you drop the leading edge into the airstream (creating scoop), there’s a high pressure zone to the scoop and provides for substantial airflow. NACAs are great for significant airflow with minimal air disturbance, but to compare to a scoop, and a significantly larger scoop to boot... well, there is no comparison.

As pointed out, Lotus tried to resolve the heat issues with small scoops. They tried a few different styles of it.

With the 400, they simply did what needed to be done early on, they made a scoop the size of the leading edge like we did here.

The other option is to delete the entire undertray like a “normal” car and then there’s plenty of air to keep parts in check... we’re spoiled and love the “hope” that the undercar aero makes a difference at road going heights and we like the lower drag of a smooth bottom (even if it has a scoop through part of it;))...

There’s plenty of data collected on the race track with Evora’s and from Lotus to support these “claims”... It’s not like we were looking for something to stay busy when we built these. Lol..

-Phil
 

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For a naturally aspirated Evora on street duty, I am not seeing a real reason to worry much about engine bay temperature.

All I am saying is that I am not seeing any absolute numbers being quoted. There is no quantification of the problem in the form of an engine bay heat-map before and after the modification with identical environmental conditions. There is no list of parts that could have shortened life due to elevated temperatures in the engine bay.

A calculator cannot do computational fluid dynamics analysis and Lotus does not need to try many designs physically if they have a proper model of the car in a CFD simulator. Please do share the data from the race track if you can. That will answer all my questions.

On the plus side, I do see what you mean by this is exactly what Lotus did to the Evora 400. Thanks for making this mod available for the older Evora owners.
 

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For a naturally aspirated Evora on street duty, I am not seeing a real reason to worry much about engine bay temperature.
Says the "new guy" :wink2: who probably hasn't experienced the master cylinder failure. These like to fail because of cooking fluid. This is due to the assembly/lines running at the front of the engine near the cats (stock car) w/o much cooling. There are several of us on here, myself included that have had to deal with this heat related failure....on street car. For some cases, more than once.
 

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The other option is to delete the entire undertray like a “normal” car and then there’s plenty of air to keep parts in check... we’re spoiled and love the “hope” that the undercar aero makes a difference at road going heights and we like the lower drag of a smooth bottom
Yes. I've kept my undertray off for years because it's not practical on a car with 5.1" of ground clearance.

Why not lose the 8 lb undertray (Elise and Exige), increase airflow across the transmission case and oil pan, and allow for faster oil changes? The drag and downforce penalties on the street are negligible.
 

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For a naturally aspirated Evora on street duty, I am not seeing a real reason to worry much about engine bay temperature.

All I am saying is that I am not seeing any absolute numbers being quoted. There is no quantification of the problem in the form of an engine bay heat-map before and after the modification with identical environmental conditions. There is no list of parts that could have shortened life due to elevated temperatures in the engine bay.

A calculator cannot do computational fluid dynamics analysis and Lotus does not need to try many designs physically if they have a proper model of the car in a CFD simulator. Please do share the data from the race track if you can. That will answer all my questions.

On the plus side, I do see what you mean by this is exactly what Lotus did to the Evora 400. Thanks for making this mod available for the older Evora owners.
Do you have a S1 Evora? How long have you had it? Ive noticed in the summer with mine my temps would climb and that cooling fan on the passenger side would run when stopped. Think the lack of airflow plus the cats were creating alot of heat..
 

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OK, the chance of coolant temperature going above 100c is higher when ambient temperature is over 80F. The stagnant air argument is not valid in this scenario due to negative air pressure under the car in motion. Even if it is true, it applies to the proposed cooling tray design as well.
My stagnant air statement relates to air pressure inside an engine compartment, or wheel well, or any box without large exit venting will be high that pressure of incoming air. example a 5 sided box (say 2 ft sq) with open face to air flow will be filled with stagnant air, cut a small hole on back face (say 4 inch dia.) and airflow will improve but not greatly, same box with open face aft, still filled with stagnant air, cut same hole on (now) front face .. air flow will improve greatly.

What about the additional drag this cooling tray will produce?
My Evora exceeds a claimed 190 mph with a real draggy 400 underpan scoop, I guess I'll file suit with Lotus that I wanted lower drag car with a 5% lower Cd so it would exceed 200 mph, or give me 18% more hp to get to the same spot.

The whole point of NACA scoops is to intake air with minimal disturbances to flow on the boundary layer. I do understand that it may not work well in a neutral or negative pressure area such as the flat underbody. Wind tunnel data has shown that the under-body makes up to 30% of the vehicle's total drag. Smooth underbody with strategically placed holes in the stock undertray will probably outperform this as the negative pressure area under the car will suck hot air out of the engine bay.
. except Lotus is feeding in air from the underside as by the time the air has reached rear wheels it has slowed down, and thus increased pressure. Purpose of a well shaped (not cosmetic) diffuser is to accelerate the aft air flow and drop the pressure back down to create a down force. As Phil states we have too much air gap AND diffuser shapes will most likely cause flow separation and the transition line, defeating the whole purpose.

Without evidence of mathematical modeling, number crunching, or some basic wind tunnel testing. It is hard to validate the claims.

I like how this guy is approaching the problem.
Aerodynamics of Engine Cooling ? Part 2 « omgpham?
I have spent a career with based on a sound study of aero and hydrodynamics up to Masters level and years involved with wind tunnel testing and CFD modeling. Without such testing/modeling guess what a scoop will bring in air and the larger the exits the better flow (My car has the 400 under tray scoop and 410 louvered hatch), if you want to spend 100's of thousands on testing ahead, but outcome goal will be to reduced drag coefficient by maybe 2% while maintain same inflow.
 

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I am just trying to reason out my future purchase guys, cool down. I recently did the clutch master cylinder job so I know what a pita that is. Don't take it personally.

In the mean time, should I just remove the under tray and leave it open?
 

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Says the "new guy" :wink2: who probably hasn't experienced the master cylinder failure. These like to fail because of cooking fluid. This is due to the assembly/lines running at the front of the engine near the cats (stock car) w/o much cooling. There are several of us on here, myself included that have had to deal with this heat related failure....on street car. For some cases, more than once.
Have you wrapped your clutch lines with something like this to reduce the chance of having the same issue again? [ame]https://www.amazon.com/dp/B002R51AFA/[/ame]
 
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