A simple pop generator is pretty easy, though, but colouring it to fit the exhaust sound can be tricky. Luckily I generate mine directly, so I just feed the pops etc. through the same "colouring" system as the exhaust itself (it sounds cohesive, if not necessarily realistic; a better "system" would help...). Crackles, fluff and other subtle effects are harder, and probably more important - especially for carburettors, where the various excess fuel sounds are effectively a performance indicator at part throttle.
I was going to discuss the difficulty of doing a race car soundset properly so that it sounds authentic, as you have tried several times to do. The above Raceroom video is a great springboard for that.
It does sound really good. But one thing that people don't grasp who have no experience in the area of sound design, are all the little aspects of noise a car makes just in the decelleration stage - and yes it's not a real word, but I want to change English to where it makes more sense. I also use "perplexion" in my writing, and no one was aware that it's not a proper English word yet either. Bloody Oxford braintrusts, meh. But I digress.
Listen closely to that Porsche in that video and focus intently on the sounds it makes solely when it's braking for turns. It makes an astonishing number of distinct sounds. A real sound designer has to mike up a car like that right to start with, and that's a bear in and of itself. I discovered this firsthand when I tried to mike up a drumkit for my Jewish-Christian friend, and what should have been a 30 minute doddle ended up being a few hours of torment and grouching from him. Miking is NOT that easy. It just isn't. ESPECIALLY on a car, and ESPECIALLY when you want to mike it racing around a track like that. It's a recording engineer's worst case scenario.
THEN You have the fact that every decelleration the car goes through sounds different. Every single one. The car creaks, pops and bangs. It backfires. The transmission whines, and it lurches over track undulations. There's wind noise to filter. And every single recording is completely different. All those little noises have to be isolated and filtered out, but saved so that they can be added in, possibly, so they blend in right. But of course with each one, the exhaust note will be different, the tranny whine will be a unique pitch, the wind will be at a different level and timbre... Sometimes it just won't work.
It takes dozens, sometimes hundreds of recordings just to get a pure exhaust "performance." You have to sift through all these recordings and splice together all the two second or less bits to get a pure accelleration/decelleration cycle, and make it sound like it's not spliced together at all. And then pitch-match all those little elements like backfires, pops, bangs, creaks, tranny lurches to match what's going on on-screen. Because if you just use a best sample, it sounds canned and fake because you use the same thing every time and it comes across like a rap song with the same loop every two seconds. And if you use more than one, you have to have an intelligent way to have the game engine pick the right one for what the car is doing.
Get the point yet?
As an audiophile and recording engineer, I can hear where the splices are in the Raceroom beta video, but the quality is so high I don't care. It sounds plenty immersive and authentic. But at the same time, HOW long has it taken game developers to get to this point?
You guys who think this is no big deal have no clue.
What if it has authentic sample and realistic sound recreation - no dramatic effect like in FM4 + added more intake and exhaust sound details - backfire etc. And most importantly accurate sound field physics inside the cockpit and other cam position, we'll hear it as if we are in the real car, not loud brutal sound effect as if you are in front of engine bay with popped hood and exhaust going out the front bumper 
Which I will explain.
I mean, even given the fact that they use common soundsets for roughly similar cars which get people complaining they aren't right, it's really ludicrous to think you can get the same quality in one-seventh the time. Want to try and get a week's worth of work done in a day? Not me!
