Building a Diffuser - Page 3

Ludikraut · Oct 21, 2009, 03:55 PM

Quote:

Originally Posted by bchappy

sure there is.... right out the side skirt...

Not enough ground clearance that way. In order for it to work for me, it could not go any lower than the rear diff and even that is less than optimal.

l8r)

griceiv · Oct 21, 2009, 03:56 PM

Quote:

Originally Posted by bchappy

sure there is.... right out the side skirt...

or have it blow on the bottom of diffuser. basically end it right at the rear diff.

sscottttt · Oct 21, 2009, 09:16 PM

Another awesome project Jid2, looking forward to seeing the result of your efforts. Does anyone have any info on making the diffuser wider towards the back and angling the strakes so that they are further apart at the back than the front. It seems to be done this way on prototypes and f1 cars, I think this would "diffuse" the air even more, creating an even greater low pressure area and more downforce. Being that the diffuser needs to be narrow at the front anyway to clear wheels and suspension components I don't see why this couldn't work out. I think you can see what I'm talking about in this F1 Pic

... and here's a pic I found of a diffuser for a C6 Vette where you can really see how the tunnels start narrow and get wider towards the rear.

sk8terdude929 · Oct 22, 2009, 06:52 AM

I have been following your threads and love your ideas I really like your full body undertray too and would like to build one myself if possible. I’m sorry if I missed this but didn’t see it in there, What size and thickness material did you use for the diffuser? That is if you dont mind sharing

Ludikraut · Oct 22, 2009, 09:00 AM

Quote:

Originally Posted by sscottttt

...Does anyone have any info on making the diffuser wider towards the back and angling the strakes so that they are further apart at the back than the front. It seems to be done this way on prototypes and f1 cars, I think this would "diffuse" the air even more, creating an even greater low pressure area and more downforce. ...

It's a possibility, but ... a diffuser does not generate downforce by "diffusing" the air. It helps to reduce drag by slowing the (hopefully) fast moving air coming from the undertray before it exits from the rear of the car into the car's wake. The effectiveness of the diffuser is directly related to how fast the air coming into it is and how much of a wake (determined by type of rear wing, shape of car, etc.) is behind the car. If you get it just right, you will gain a little bit of downforce in addition to the reduction of drag. I think the reason for the shape of the pictured F1 diffuser is to get the air spread out (diffused) evenly across the width of the rear wing to maximize the reduction of drag. I would also think that if you're running a big wing on your Evo, then you'd want a slightly steeper rear diffuser, and possibly tapered out slightly - whereas if you're just running a duckbill or trunk lip, then you'd want a flatter, straighter diffuser. The other potential issue with a flared diffuser is the air from the wheels, as it will be harder to keep it out from under the sides of the diffuser.

l8r)

Ludikraut · Oct 22, 2009, 09:02 AM

On a separate, but sorta related note ... did anyone see the Mythbusters episode with the golf-ball dimpled car? One of the coolest episodes eVar.

l8r)

jid2 · Oct 22, 2009, 09:13 AM

^^^ Crap, I missed it, maybe they have it online or on-demand. I saw the duct tape last week.

Material for the diffuser is .032" 5052 Aluminum, the diff-plate is .065" 5052.

MATT@WORKS · Oct 22, 2009, 11:11 AM

Quote:

Originally Posted by Ludikraut

Not enough ground clearance that way. In order for it to work for me, it could not go any lower than the rear diff and even that is less than optimal.

l8r)

That might work even better than you think. That would be called jet streaming-- you can increase downforce by doing it. Look at the F1 exhaust exits under the rear wing. The only problem is that your downforce will change depending on the throttle position which is one of the main reason why F1 and ground effect cars stopped mixing jet streaming and the ground effect by dumping exhaust on the diffuser. I doubt you'd have this problem since you have half the engine and probably a tenth of the downforce they had.

Ludikraut · Oct 22, 2009, 11:22 AM

^ I was talking about a side exhaust, where the 3" pipe would have to cross over to the side - underneath the undertray/diffuser. Dumping the exhaust into the stream isn't a bad idea and would probably work really well at race speeds, but I'm not sure how streetable that would be. <cough> <cough>

edit ... just did some rough estimates for exhaust flow, and, yeah, I'd have maybe a third of the exhaust flow compared to a 2.4L F1 V8 @ 18000 RPM.

l8r)

donour · Oct 22, 2009, 11:38 AM

Quote:

Originally Posted by jid2

^^^ Crap, I missed it, maybe they have it online or on-demand. I saw the duct tape last week.

http://dsc.discovery.com/videos/myth...y-vs-clean-car

Apparently there is a company that makes a vinyl skin you can apply. They claim a 15% drag reduction at 65 mph with only a few extra pounds of weight.

d

kwlevo · Oct 22, 2009, 12:40 PM

i havn't seen anyone posting anything about the CBRD evo

i'd like to see more pics of this one.
i am in the process of buying a EVO X and using as a GT car in Canadian GT Sprints and looking to making some good Aero for the car.

MATT@WORKS · Oct 22, 2009, 12:52 PM

Quote:

Originally Posted by kwlevo

i havn't seen anyone posting anything about the CBRD evo

i'd like to see more pics of this one.
i am in the process of buying a EVO X and using as a GT car in Canadian GT Sprints and looking to making some good Aero for the car.

I don't remember his name (forgive me if you're on here!!!) but the guy that built and runs Paul Dala Lana's BMW is really good at race setup. He builds some pretty amazing cars for Canadian TC, I'm sure a good GT car wouldn't be difficult for him to bang out with amazing performance.

turbotime · Oct 22, 2009, 01:00 PM

I was looking at trying to make something similar to ^.... they haven't said much about it though, keeping it under wraps I guess.. I did read they said it was make from balsa wood core with carbon wap outer.

sscottttt · Oct 22, 2009, 01:30 PM

Quote:

Originally Posted by Ludikraut

It's a possibility, but ... a diffuser does not generate downforce by "diffusing" the air. It helps to reduce drag by slowing the (hopefully) fast moving air coming from the undertray before it exits from the rear of the car into the car's wake. The effectiveness of the diffuser is directly related to how fast the air coming into it is and how much of a wake (determined by type of rear wing, shape of car, etc.) is behind the car. If you get it just right, you will gain a little bit of downforce in addition to the reduction of drag. I think the reason for the shape of the pictured F1 diffuser is to get the air spread out (diffused) evenly across the width of the rear wing to maximize the reduction of drag. I would also think that if you're running a big wing on your Evo, then you'd want a slightly steeper rear diffuser, and possibly tapered out slightly - whereas if you're just running a duckbill or trunk lip, then you'd want a flatter, straighter diffuser. The other potential issue with a flared diffuser is the air from the wheels, as it will be harder to keep it out from under the sides of the diffuser.

Ludi, respectfully I'm not sure I agree with you on exactly how the diffuser works, I agree that it helps the flow of air under the car exit smoothly and works in conjunction with the rear wing of a car to create downforce and reduce drag. However, I think the diffuser itself adds downforce by creating an area of low pressure under the rear of the car "sucking" it to the ground.

Side note: Mythbusters episode was awesome, something I've always wondered about and had several arguments that it would be possible for a "dirty" car to have less drag than a clean one.
More info on the topic: Racecar Engineering Article

hamflex · Oct 22, 2009, 02:06 PM

Quote:

Originally Posted by Ludikraut

^ I was talking about a side exhaust, where the 3" pipe would have to cross over to the side - underneath the undertray/diffuser. Dumping the exhaust into the stream isn't a bad idea and would probably work really well at race speeds, but I'm not sure how streetable that would be. <cough> <cough>

edit ... just did some rough estimates for exhaust flow, and, yeah, I'd have maybe a third of the exhaust flow compared to a 2.4L F1 V8 @ 18000 RPM.

l8r)

What if your exhaust dumps?

My exhaust dumps right were the cat would be. So for a flat bottom, should i route to the side? Or would just having a hole in the flat bottom and having the exhaust continue to dump be that big of a negative effect on the under aero?