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InvisibleFrisbee New Reader
10/12/22 10:08 a.m.

I've been lurking here for a while, mostly following along with the LS1 Kart build. I have my own Kart based on a C4 Corvette. I autocross and do HPDEs with the car. The bottom of the car is pretty flat with the exception of the drive shaft tunnel between the front and rear wheels. I'm considering building a rear diffuser to get more downforce. Considering that the bottom is flat, and doing some search on how diffusers work, my understanding is that built properly it should do something...but I'm also fully aware of how ugly the airflow around the top of car is. 

Even if the air above the diffuser is extremely turbulent, will the principals of a rear diffuser work as long as the airflow below the car is relatively clean?

stafford1500 Dork
10/12/22 10:28 a.m.

Welcome and the answer to your question is a solid yes. The diffuser will work even if the flow over the top of the car (and above the diffuser is messy. Consider that the diffuser is driven by the low pressure BEHIND the car. Turbulent air in that region is typically fairly low pressure, since it is a large component of the drag force.

The expansion angle of the diffuser may need to be tweaked to get the most out of it, but for a starting point anything is better than nothing. Note that the rear overhang is short since the fuel tank/bumper extension is gone, so dont be afraid to run the diffuser out past your cage structure. Exhaust will likely give you a challenge.

My current challenge car is a C4 and I have built a fairly large and aggressive diffuser for it. The front end is tied to the floor at the bottom of the seat pans, so it extends the floor into the diffuser as much as possible.

InvisibleFrisbee New Reader
10/13/22 1:33 p.m.

In reply to stafford1500 :

Have you run a plate below the trans tunnel? The exhaust is in there with the transmission...I'm worried that might trap too much heat in that tunnel, but it would be nice to get the bottom really flat.

stafford1500 Dork
10/14/22 11:37 a.m.

I did not cover the bottom of the driveshaft tunnel. There is already a lot of heat in the trans tunnel and closing it off flow underbody flow won't make that any better.

Johnny_at_NineLives Reader
10/24/22 9:14 a.m.

i bet that terrible body will generate a ton of diffuser flow. Lots of area for the diffuser to fill. 

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