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John V · 04-09-2016, 07:53 AM

The beginning:

Starting chassis: This car started life as a Japan Red no-sunroof 2002 BMW 330Ci 5-speed with sport seats and no other options, and the picture above is how it looked when we picked it up, at Nationals, in 2011. It was dirty as all hell when we got it. The previous owner had built a racetrack out at his ranch in Wyoming, and it's very dusty out there. I spent about a week cleaning it when I got home and it still isn't really clean. Being a non-sunroof car was important; the sunroof adds about 40lbs high on the body shell.

Differential, Suspension, Wheels and Tires

SCCA Street Prepared lets you do lots of stuff to the car, but the bang for your buck starts here, so it's what I wanted to focus on first. Here's the thing. You can build a 90% complete DSP car by getting these three things correct. Everything else is great for a top-tier car, but if you do these three things your car will be capable of amazing feats in the hands of a talented driver.

The differential is the item that makes these cars so magical. Stock non-M E46s come with an open differential. Plenty of aftermarket companies sell performance differentials. The diff that came with this car was my first lesson learned about buying competition cars that someone else built. It was supposed to be a custom Metric Mechanic differential with 40/90 ramps - essentially making the differential lock up very hard on acceleration and open on deceleration.

Unfortunately, that was not what I found in the car when I tore into it. What I had was a roadrace differential, also known as a "one way" differential. It was locked up hard on both acceleration and deceleration. On a track this makes the car stable. On an autocross course this makes the car pushy on turn-in, which is undesirable. You can see this ramping in the picture below.

I ended up swapping this out for a used Jim Blanton-built diff that would serve me well for many years.

Because of the SCCA rule set, many rear end ratios are available. Stock for this car would have been a 2.93 rear end. When I bought the car it had a 3.46, which would have come in an automatic 330. I ended up swapping it for a 3.15, which when paired with 285/30/18 hoosiers and a 7,000 RPM redline gives about 66MPH in second gear at redline, perfect for most Solo courses.

Setting up an E46 differential is not hard, but it requires some special tools. I started a thread here which details how you do it.

For shocks, I run custom-valved Moton Motorsport adjustable dampers with remote reservoirs. They're adjustable in a relatively narrow window around my base valving for high speed compression and low-speed rebound. They have aluminum bodies and are very light. If I were to do this all over again, I would run Ohlins shocks. They're much more durable and offer the same performance. These need to be rebuilt every couple of years and it's getting harder to get parts. I run 60mm I.D. race springs that are 140mm long and use a variety of rates. Most of the time I have 140n/mm springs up front and 120n/mm springs out back. I don't run a rear sway bar, but I do have a large, hollow Hotchkis bar up front. The front camber plates are from Vorshlag.

Wheels and tires: Prior to 2016, I ran 285/30/18 Hoosier A6/A7 tires all around on 18x10" wheels. This size is readily available in the aftermarket and they can be made to fit under a 330 with very lightly modified fenders. The fenders of this car were originally flared using fenders from an E46 M3 so that the tires had plenty of clearance.

Back in 2014 I actually bought a pair of 18x11 wheels and borrowed a pair of 315/30/18 Hoosiers to see just how much modification would need to be done to fit these tires.

The answer is "a lot" and so I shelved that idea. But I revisited it a few months ago after the 2015 Solo Nationals.

04-09-2016, 07:53 AM	#2
John V No more BMWs Join Date: Apr 2005 Carmudgeonly Ride: Ram, MS3, CX-5, RX-8 Location: Glenwood, MD Posts: 14,753	The beginning: Starting chassis: This car started life as a Japan Red no-sunroof 2002 BMW 330Ci 5-speed with sport seats and no other options, and the picture above is how it looked when we picked it up, at Nationals, in 2011. It was dirty as all hell when we got it. The previous owner had built a racetrack out at his ranch in Wyoming, and it's very dusty out there. I spent about a week cleaning it when I got home and it still isn't really clean. Being a non-sunroof car was important; the sunroof adds about 40lbs high on the body shell. Differential, Suspension, Wheels and Tires SCCA Street Prepared lets you do lots of stuff to the car, but the bang for your buck starts here, so it's what I wanted to focus on first. Here's the thing. You can build a 90% complete DSP car by getting these three things correct. Everything else is great for a top-tier car, but if you do these three things your car will be capable of amazing feats in the hands of a talented driver. The differential is the item that makes these cars so magical. Stock non-M E46s come with an open differential. Plenty of aftermarket companies sell performance differentials. The diff that came with this car was my first lesson learned about buying competition cars that someone else built. It was supposed to be a custom Metric Mechanic differential with 40/90 ramps - essentially making the differential lock up very hard on acceleration and open on deceleration. Unfortunately, that was not what I found in the car when I tore into it. What I had was a roadrace differential, also known as a "one way" differential. It was locked up hard on both acceleration and deceleration. On a track this makes the car stable. On an autocross course this makes the car pushy on turn-in, which is undesirable. You can see this ramping in the picture below. I ended up swapping this out for a used Jim Blanton-built diff that would serve me well for many years. Because of the SCCA rule set, many rear end ratios are available. Stock for this car would have been a 2.93 rear end. When I bought the car it had a 3.46, which would have come in an automatic 330. I ended up swapping it for a 3.15, which when paired with 285/30/18 hoosiers and a 7,000 RPM redline gives about 66MPH in second gear at redline, perfect for most Solo courses. Setting up an E46 differential is not hard, but it requires some special tools. I started a thread here which details how you do it. For shocks, I run custom-valved Moton Motorsport adjustable dampers with remote reservoirs. They're adjustable in a relatively narrow window around my base valving for high speed compression and low-speed rebound. They have aluminum bodies and are very light. If I were to do this all over again, I would run Ohlins shocks. They're much more durable and offer the same performance. These need to be rebuilt every couple of years and it's getting harder to get parts. I run 60mm I.D. race springs that are 140mm long and use a variety of rates. Most of the time I have 140n/mm springs up front and 120n/mm springs out back. I don't run a rear sway bar, but I do have a large, hollow Hotchkis bar up front. The front camber plates are from Vorshlag. Wheels and tires: Prior to 2016, I ran 285/30/18 Hoosier A6/A7 tires all around on 18x10" wheels. This size is readily available in the aftermarket and they can be made to fit under a 330 with very lightly modified fenders. The fenders of this car were originally flared using fenders from an E46 M3 so that the tires had plenty of clearance. Back in 2014 I actually bought a pair of 18x11 wheels and borrowed a pair of 315/30/18 Hoosiers to see just how much modification would need to be done to fit these tires. The answer is "a lot" and so I shelved that idea. But I revisited it a few months ago after the 2015 Solo Nationals.