I am in the process of rebuilding my splitter and I'm curious what others are running theirs at and what would be a reasonable height for mine. Right now my plan is to try 3" with the car being 2650 race weight and 13k springs.

Whats your height at?
Whats your spring rate setup?
Whats your race weight?
etc

 

I drive to the track so I have some limitations. 5" extension on mine. I used aluminum flashing to make the air dam to cover the gap between bumper and splitter.

4" height
10K front springs
3000 pound "race" weight

I probably have another 1"-2" clearance at max compression. So the splitter could be lower even with those soft springs, but I already scrape it a little here and there on the way to the track (some gnarly backroads) so if I went any lower I'd probably need to readjust it at the track and then back again. I've considered adding a flexible lower dam on the leading edge of the splitter to simulate a lower height and have it survive scraping on the street.

 

Solid data point. Sounds like I should be relatively safe with a 4" extension as my tracks are relatively smooth.

 

Looks serious.

Also looks like you got the "Murica theme going strong. Long live the Red White & Blue.

 

A splitter should have a diffuser. Look at any of the ones from a major manufacturer (Viper, 1LE, etc.) or high-end race car where the rules allow.

This firm has probably the aggressive aero on a NASA ST or American Iron production-based car currently running: https://rhrperf.com/blog/project-crusher-part-3/

 

https://professionalawesome.com/prod...iffusers-pair/

 

Interesting. RHR has 3 different shapes, but is more expensive: https://rhrperf.com/vents-ducts/



They also have a huge hood vent.

 

Those are all pretty neat but ST4 rules don't allow a diffuser from my understanding of the rule book. The aerodynamic limitations they use are a big portion of why I decided to build for that class. They cap the complexity and cost at a level that I can sort of afford.

 

 

Sports racers typically run at 2-2.5". My guess is you will only find random anecdotal evidence. If someone has done a CFD it is hiding. Flat splitters generate enough downforce, or reduction in lift, to allow some rear wing and make the car feel more stable. But it still isn't a lot.

Years ago some had a porpoising problem where the nose would go low than seal itself to the ground and release. Higher end race cars have a heave spring or inerter to control that. It was a big thing in F1 about 12 years ago; when McLaren introduced the inerter they won 10 of the next 12 races.

Why not make your mount adjustable with spacers? That way you can test it.

This graph compares three alternatives. "AI" is for the American Iron class. The "ST4" is really for an STU Mustang. Ut doesn't address ground clearance.



These, from their post on rear diffusers, shows two different ride heights. Note that running low choked off air flow and some resulting downforce under the car.