Ideal front splitter length?
 

The vehicle in question is an '04 MSM where we threw everything away and put in a K24Z3 (~205 whp), BMW 6 speed, & 3.909 Getrag diff. Xida Race 800/500, replaced everything else in the suspension, front BBK, welded & de-powered rack, etc. Aero is probably going to be a 9LivesRacing Big Wang in the rear and a splitter in the front (but I'm restricted to stock bumpers). Splitter is likely going to made out of wood sheets or alumalite panels. Base alignment is going to be about 4.825" high & -3.0 deg front, 5.0" high & -2.5 deg rear, with adjustments made based on how the car drives and tire temps. 205 to 225 width super-200TW tires (no slicks).

Does anyone know what's an ideal length for a front splitter if I'm forced to run a stock bumper/dam? I think 2.0"-3.0" is a good length, but I don't know if bigger is better.... At a certain length, it is just going to keep getting ripped off. Since the vehicle needs both autocross and track days, I'm probably going to keep the factory bumper. I don't think something like the 9LivesRacing Dam is legal for autocross after reading through the rules. I've got to have the splitter extend no further than the body/wheel lines on the sides, so not as ideal either but its what I got to work with.

I'm waiting on backordered parts for weeks due to COVID supply chain issues, so going to have some time to work on this. Since I've never done this before...I assume that if I feel like I need more/less front aero grip, I just shorten or lengthen the splitter? Building an aero setup is new to me.

What class are you running? Those rules will really determine what route you should go on front aero, like air-dam, splitter ramps, splitter size, cannards, etc.

On CFD with the standard air-dam we saw diminishing returns past 5". Not too sure how that will come out as with OEM bumper though. The standard medium kit front aero package is 3" out from the air-dam, which is the very outside lines of the bumper.

In a perfect world, you'd have your aero balance matched exactly to your weight balance. Fortunately, the aero loads we see with our cars and the typical aero components we're talking small numbers in terms of force. So getting aero balance within 15-20% of weight balance is just fine.

I'm likely going to be in SSM for autocross, and just HPDE / open track night type of events. Nothing actually competitive, just need to learn how to drive. Diffusers are explicitly forbidden. I just reread SCCA 2021 Solo Rules;16.H seems to permit replacement of the front bumper with an air dam. Huh, could have sworn otherwise. Front splitters are limited to <6.0" and my not extend past the widest point of the bodywork.

Might just be easiest to use 9LivesRacing Dam and Sturdy Boi (hehe), then make a custom splitter that's narrower.

If you are running ssm- install up your 9lives wing. Build yourself a 6” wood splitter, and go to a test and tune, with the tools to cut. (I also brought a 7” length of 2x4 with holes drilled every inch just big enough to slide a pencil into to mark the next line. Make a run or two and see how it feels -cut the splitter back (if it’s too much grip up front)- until you are happy with how it handles. You can make a better version once you have it dialed to handle how YOU like.

My BBFW spoiler would probably be perfectly balanced with a 3” front splitter for solo- but I prefer the tail go first so mines 4”, I’m guessing you’ll be 5 or 6” if that wing works as well as I’ve heard. Especially if your doing solo wood is the cheapest and most durable material. If you don’t hit at least a few cones with it you are going fast enough.
https://cimg5.ibsrv.net/gimg/www.mia...6c324fd40.jpeg

Ideal length is usually whatever class rules allow.

Following and providing my very little experience. Still learning tons.

I have been building my car around SSM rules. I am running a 9LR double element kit and a homemade wood front splitter 5.5". I am still running a stock bumper and an eBay front lip. Xidas 800/500 and 205 RE-71R.
The rear wing was neutral and the balance felt great. This year I'll be on 245 proxy RRs when running in SSM and my RE-71R for running in XS-B. 91' turbo 1.6 at ~2500lb with a full tank of gas.
Camber Front -3.2/-3.1 Rear -2.4/-2.3
Zero front toe
1/16 in rear toe
Corner balanced and ride height is 4 5/8” 4 5/8” 4 5/8” 4 3/4”

It was night and day difference between aero and non-aero at my local auto-x track that is ~1 mile long and we see peak speeds of ~70 Mph.

The 2x4 with pre-drilled holes is brilliant! Perfect way to get a clean line across it to cut. I'm definitely stealing this idea. I like neutral with a hint of oversteer at low speed with aero giving stability (tiny hint of understeer) once you pickup some speed.
Well, there is such a thing as too much front grip...especially with whatever your rear spoiler is. If I don't have enough angle on a rear wing with a 6" spoiler on a track night, I might end up in a gravel trap. Hehe.

Yeah, that's my opinion on non-aero too. I really need some in my Fiesta for SMF, but I've got shitty coilovers with too much turbo on that car.

Good to see my starting alignment is similar to what others are running on the Xida 800/500. I'm starting off with more rear camber (corner grip), but also twice the rear toe in. K24 is a lot of instant torque for a Miata, and its been a while since I've been playful with a RWD car...'08 Mustang GT, '94 Viper (UGH). I *feel like* you need slicks to run something like an LFX V6 or larger NA motor on a car this size just from the toque...or I just need to learn to drive better.