Undertray

[Casgar 21]

Just found this guy and thought it would be an interesting topic to discuss since it seems to be a reasonable easy thing to construct with apparently many benefits. He have more videos discussing undertrays in detail, among other interesting topics.

 

[Midlife 814]

Kinda hard to change the oil, don't you think?

[dream car 12]

" Its quieter on the road with less wind sound"  Just want to hear the rumbling of exhaust, window open with wind blow through my hair ( Oops window open I guess that defeat aerodynamic).

"Early testing of MPG is showing about 4 MPG increase"  Gas is Cheap down here in Texas, I'm happy with my 10-12 MPG.

I'm glad Nate's is happy with his result. ( does his engine get overheat ? )

[Casgar 21]

On 10/3/2020 at 1:47 AM, Midlife said:

Kinda hard to change the oil, don't you think?

If you mean on the car in the video in question, then yes. Just cut a small hole around the drain plug and the problem is solved.

I realise that I may have created a somewhat vague topic, so I will try to make it more focused on what I'm acually interested in, namely how a undertray apparently can increase downforce and reduce drag, and thus increasing the performance of the car.

On 10/3/2020 at 3:19 PM, dream car said:

" Its quieter on the road with less wind sound"  Just want to hear the rumbling of exhaust, window open with wind blow through my hair ( Oops window open I guess that defeat aerodynamic).

"Early testing of MPG is showing about 4 MPG increase"  Gas is Cheap down here in Texas, I'm happy with my 10-12 MPG.

I'm glad Nate's is happy with his result. ( does his engine get overheat ? )

I can understand those arguments, especially the rumbling exhaust, and the performance aspect isn't necessarily relevant if someone mostly use the car for the street. On the track however I don't really see any big reasons why this isn't something you could try (except rules of course). More downforce can't be a bad thing, especially since these cars have a tendency to get light in the front at higher speeds.

The engine overheating might be the biggest problem, but you won't know unless you try. A smoother underside should make the air flow faster and at a lower pressure, so the suction effect might compensate for the reduction in engine bay exits. Personally I'm contemplating some hood vents similair to the -67 and -68 Shelby cars since I have to cut and repair my current hood anyway.

 

Some more videos that triggered my initial interest. Notice how the undertray in the first video is pretty short, but apparently made an improvement anyway.

 

 

[RPM 1,190]

I'm all for improving aerodynamics, but where will the air that comes thru the grill go? Seems to me you'd need to vent it out somewhere, thru the inner fenders or louvers in the hood. 

[GypsyR 32]

I don't this guy tossing out any actual qualifications other than he authored a book and stood in front of a camera. Plus I might be inclined to give him a tad bit of credit if his personal cars weren't a generation one Prius and a Honda Insight. Jeremy Clarkson once spoke of the Insight as wanting to crash it into a tree just so he wouldn't have to drive it anymore. That and in the one video he claims he wasn't aware of how the curve at the front of "undertrays" had and aero effect. Reading between the lines this tells me this boob has absolutely no qualifications in the field of aerodynamics. Just no way.

But as the saying goes "Just because the biggest fool in the world says the sun id shining doesn't make it dark outside." I long since have been quite distracted but about 15 years ago I stocked up on some PVC sheet to do essentially the same sort of things. It and the car are still out there but I'm still quite distracted.

Though it may not be clear on every video, allowances are to be made to vent air from underhood. A side effect he mentions of all this that the air directed under the car this way has a bit of venturi effect and will draw that warm out through smaller openings than one might expect. If you do things right. Do a big lower like he shows on his Prius on a Fox Mustang and you will have an overheated engine PDQ. Because those cars draw the air for the radiator from up under the front bumper. I bet he has no clue about that. Aero stuff isn't a one size fits all science. For what little I know about it anyway. Far from an expert me, but I've tried to listen while smart people talked.

[EastYorkStang 63]

At what speed would these be effective? Probably over the posted limits.