Coweling and engine bay aero

The Convert

Captain
Jun 4, 2017
1,433
Its got nothing to do with casting and I wont reveal my involvement as its none of your business.

Here is another endurance built f20 engine bay, I'm posting cars that totally contradict your theory about engine bay aero that use stock hoods and delete
the factory cowl plastics, even purpose built race cars get rid of it but they also include extra heat venting so its not a direct comparison.


View attachment 41700View attachment 41701
This one is just on dyno. So, hard to say if this is full time running gear.
 
Here is a e92 race car for sale with a stock hood


1220.jpg
 

The Convert

Captain
Jun 4, 2017
1,433
Here is a e92 race car for sale with a stock hood


View attachment 41706
What about the giant vents in the low pressure zones in the hood? The lack of cowel is interesting though. Would be curious to know what the intent is.
 

The Convert

Captain
Jun 4, 2017
1,433
They looked like reflections to me but they wouldn't have much of an effect on aero at speed except the extraction of heat.
And under hood pressure...which is key for drag/aero. Certainly interesting to know why they would choose cowel removal AND hood venting, unless they’re trying to extract heat by adding air at the windshield and then remove from vents.
 

fmorelli

Major General
Staff member
Aug 11, 2017
3,027
Virginia
I cleaned up this thread best I could, over coffee this morning. Posts moved to the Octagon. If there is content that got swept up in the mix of personal stuff, and you feel the content is beneficial to other readers, please feel free to post the content part on the thread.

Guys do me a favor - I realize folks can get passionate about stuff. It happens. But when the commentary starts to go personal instead of subject-based, it's a pretty good sign that you should not press the "post reply" button. I spent about 20 minutes this morning cleaning this up - 20 minutes I'll never get back ... so help a brother out :sunglasses:

Filippo
 
Ok after doing a lot of research basically by removing the cowl you are turning the bonnet into a hood scoop by using the highly
pressurised air at the bottom of the windscreen.

Removing the cowl altogether basically allows leaves and water to enter the engine bay and that is why you should trim it and not remove it.

It has its pros and cons but in our case and 99% of most its a pure pro.

It has some aero effect at 130mph and at 150mph and beyond where it starts to get dangerous by positively pressurising the engine bay.

Here is the formula 0.0000176 x air speed in mph² = ram pressure increase in pounds per square inch (psi).

But that will only be a problem if you cant get rid of the pressure.

Without specialist equipment or a wind tunnel there is no way of measuring this.

But for most people and street driven cars its a pure pro, if you intend to track at 150mph through a corner use the factory cowl.

Do your own research and make up your own mind but in most case its a huge benefit.

Like I said earlier the cowl also has other purposes but not aero in most part on our cars.
 

The Convert

Captain
Jun 4, 2017
1,433
Ok after doing a lot of research basically by removing the cowl you are turning the bonnet into a hood scoop by using the highly
pressurised air at the bottom of the windscreen.

Removing the cowl altogether basically allows leaves and water to enter the engine bay and that is why you should trim it and not remove it.

It has its pros and cons but in our case and 99% of most its a pure pro.

It has some aero effect at 130mph and at 150mph and beyond where it starts to get dangerous by positively pressurising the engine bay.

Here is the formula 0.0000176 x air speed in mph² = ram pressure increase in pounds per square inch (psi).

But that will only be a problem if you cant get rid of the pressure.

Without specialist equipment or a wind tunnel there is no way of measuring this.

But for most people and street driven cars its a pure pro, if you intend to track at 150mph through a corner use the factory cowl.

Do your own research and make up your own mind but in most case its a huge benefit.

Like I said earlier the cowl also has other purposes but not aero in most part on our cars.
I agree with most of this, but am not yet convinced that the high pressure windscreen air is not adding lift by adding more air under the car via the trans tunnel, as well as increasing drag.

I agree that increased pressure on the underside of the hood is not likely to cause problems at normal enthusiast speeds.

Now, I’m sure the vast majority of us would never notice the difference in feel or lap time (we’re likely not good enough drivers), but that doesn’t take away the fun of the engineering challenge to improve the car’s capabilities by improving aero. It’s likely the least bang for your buck mod on these cars, but is a fun challenge nonetheless.
 
I really don't think it will cause any lift what so ever as the formula was designed for cars with no under tray.

With undertray the only thing it might add running one is drag and a positive engine bay pressure which will help with boost and running cooler.

With the extra cooling and added engine bay positive pressure the turbos will have less strain and the engine will produce
more power and offsetting the losses somewhat.

Mind you this is only past 150mph anything under that you don't even have to worry about it.

How many of us except maybe the lucky Germans on their autobahns will ever see those speeds for more than a few seconds at the track.

Conclusion there might be some drag but aero or lift highly unlikely on our cars, every car is different so if you really want to test it to see
how much there will be if any, go hire a wind tunnel and play with the cowl as I wont be going any faster than 150 mph any time soon as our national
speed limit is 68mph and most euro countries are 80mph and which is the recommended national German autobahn speed limit but its not mandatory.

So for most a properly trimmed cowl is far more beneficial than having it sealed or totally removed.

Correct me if I'm wrong.
 

MrBlah

Private
Aug 31, 2019
31
LT1 baby!

-- I found it kinda funny reading Felix's thread on his temp measurements and shock load measurements, and realized the stock data recorder in my camaro has all of that built in.
I've never seen shock load measurements in the GM data logger, nor can you do temp sensors outside of what's built into the car like he is doing
 

Davidwarren

Corporal
Nov 6, 2016
199
Louisville
I've never seen shock load measurements in the GM data logger, nor can you do temp sensors outside of what's built into the car like he is doing
You're right, I don't add additional temp channels. But the transmission and differential temps are already built in. And they don't have issues overheating, so no need to monitor the air temp around them. The magnetic dampers all log displacement and can be added as a channel in the Pi Toolbox. I added one as an example here:

Annotation 2020-08-03 144359.jpg
 

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