Bones - a dual-duty Birkin S3

[Silber]

Time to start a thread about my journey with my car as I prepare for really diving into owning my 2009 Birkin S3.

 

 

My journey started about 20 years ago as a car-obsessed youth, memorizing statistics but having no idea what it's actually like to drive a car. I remember reading about the Caterham R500, smitten by the idea of a car that can do 0-100-0 mph faster than almost anything. Unaware at the time, but in hindsight very clear, the ethos of 7's has been central in what I find enjoyable in driving.

 

Fast forward to my early 20's, I bought a cherry '96 Mazda Miata from my next-door neighbor, that over the next nine years turned it from a completely unmolested street-car to a barely-legal autocross machine. Before its demise it was about 1950 lbs, with 108 whp from a stock 1.8L, and was just a blast to drive at autocross, despite being grossly underpowered.

 

Unfortunately I was one of those poor souls that had a major accident at an autocross event and crashed the car head-on in a 2.5 ft square concrete block. The car stopped in about 10 ft; the concrete block went about 40 ft.

 

That event led to trying out a couple of other cars over the next few years: a '99 Miata and a supercharged Subaru BRZ. Neither car possessed the same character as that first Miata. The NB was too slow, the BRZ was too big and lazy. I missed the rawness of that the NA, and after much pondering and introspection, I realized that yearning wasn't necessarily for something with more power, but something with less weight. Coming full circle back to my childhood, suddenly the idea of getting a 7 was forefront in my mind. I started searching the market to discover that Caterhams were out of my reach. I tossed the idea around of building an Exocet or other Miata-based kit car, but with two young kids.... that wasn't going to happen.

 

I joined the forum and started lurking and learning, and discovered that Birkins are very similar to Caterhams, but without the "name-brand" price. Then, after seeing a car for sale here on the forum, a chance to drive a 7 here in Utah (thanks @kayentaskier!), a couple of trips down to Las Vegas, and a year later, I purchased the 2009 Birkin S3 seen above. It has a 2.0L Duratec with Crower Cams and ITB's, and thankfully was fairly easy to get registered in Utah.

 

I've put almost 800 miles on it in the last six months, and have some key takeaways that I'll address in subsequent posts:

• Autocrossing it showed some shortcomings; needs an alignment, tires, damper and sway-bar adjustment, and brake bias adjusted
• The engine was not happy at the higher elevation in Utah; ended up getting it dyno tuned. Better but not perfect
• Going to address some maintenance items: fluids, harnesses, new wideband O₂
• Thinking about maybe getting some new seats??
• Going to use the original roll bar and windshield primarily, while keeping the roll cage the car came with for track use. Plan is to remove the windshield from the roll cage and make an aeroscreen.

 

Thanks for reading, look for more posts in the coming days/months as I learn more about the car, and enjoy a few more pictures of the car and from my first autocross with it.

 

[Croc]

Congratulations on your acquisition.  Its not surprising you have to do some work to make the Birkin meet your needs.  They all do for some reason.  A lot of people just never get around to dialing cars in.  I assume you will be mostly road use with forays into autoX and track? 

[panamericano]

Welcome.  Nice to see another Birkin.  Enjoy it.

[Silber]

8 hours ago, Croc said:

Congratulations on your acquisition.  Its not surprising you have to do some work to make the Birkin meet your needs.  They all do for some reason.  A lot of people just never get around to dialing cars in.  I assume you will be mostly road use with forays into autoX and track? 

 

Thanks Croc. I'm the third owner of the car. The first used it for autocross, but the second had no intent to race it, and thus had it aligned to very conservative street specs. I plan on road use, ~10 autocross events/year, and the occasional track day.

 

Autocrossing the car was a learning experience. I only did one event with the car to give it an initial shake-down, knowing that some major changes needed to happen before the final setup and tuning can take place. The car came with Bridgestone RE71R tires from 2018 with about 4k miles of street use. Tons of tread, not a lot of grip. I also still need to get the seating position just right. I'm not a tall person and find the reach to the brakes and shifter just slightly too far.

 

Takeaways from that one autocross event are as follows:

 

First, the car was severely lacking front grip. The amount of understeer was honestly very surprising, but makes a lot of sense considering the front camber was set to -0.5 degrees, the rear sway bar was on the softest setting, and the car likely has a rear weight bias with a driver (I'm guessing here though...). Looking at the photos from the event shows a good bit of roll on the rear of the car. The plan to address this is to start with an alignment with the following specs, and then fine tune with the rear sway bar, shocks, and tire pressures to get the handling just right. Any input on the alignment would be appreciated.

 

Front

Camber: -2.5 degrees

Toe: 1/16th inch Toe out

Caster: ?? As positive as possible ??

 

Rear

Camber: -1.5 degrees

Toe: Zero

20 mm rake

 

Second takeaway was the complete inability to trail-brake without the car trying to spin. My initial thought was brake bias, and subsequent testing confirmed the rear brakes locking before the fronts. I like to be able to carry some speed into a corner, having been brought up in the school of momentum-management with all those years in an underpowered Miata, so making sure the Birkin doesn't want to enter the corner backwards is a key point to address. There are two master cylinders and a bias bar for the brakes, so I'll be asking for some advice on best practices for adjusting brake bias later on.

 

Third takeaway was the definite need for some better tires. I'm interested in hearing other's thoughts and experiences with autocrossing their 7's and tires that they've used. As I'm looking to primarily autocross versus track time, I've been looking for tires that turn on quickly, especially considering the lack of mass with the Birkin. I came across a handy guide from Grassroots Motorsports that has helped me in learning about the current tire market: https://grassrootsmotorsports.com/articles/track-tire-buyers-guide/

 

My conclusion, considering my budget for tires (which isn't much) and knowing I'm going to be underprepped for my class and thus not competitive, is to get the Kuhmo Ecsta V730 in 205/50r15 for both front and rear. Supposedly turns on fast, wears well, and is not too far behind the fastest tires, while also being more affordable, checks all the boxes for me. Anyone have any experience with these tires on their 7? I'm also hoping moving up to 205's from 195's on the front will also help with the understeer.

[Silber]

For continuity and reference for anyone else with similar problems, I'll keep any further updates regarding the bogging/hesitation issues I first experienced in the other thread I started: 

 

But I did want to share the dyno results here. It's not the most powerful car I've owned, nor is it much compared to many of the other 7's on the forum, but it makes for a great power to weight ratio and I figure it's not too bad for nearly a mile above sea-level.

 

I don't foresee trying to get more power out of it, but rather I'd like to give my Birkin a weight-loss treatment. I'm planning on removing the windshield washer reservoir, getting a lighter battery, some smaller/lighter headlights, and possibly even removing the windshield wipers/motor and the heater core with its associated plumbing. I'd like to get the car as close to 1200 lbs as possible.

 

Oh, and one other quirk with this car: the throttle cable is actually a bicycle brake cable with the barrel style cable end filed down to fit in the lever for the throttle bodies. I can't imagine that's standard equipment on these cars....

[Vovchandr]

11 minutes ago, Silber said:

throttle cable is actually a bicycle brake cable with the barrel style cable end filed down to fit in the lever for the throttle bodies. I can't imagine that's standard equipment on these cars....

 

I carry a spare bicycle cable for my Zetec with me...

[panamericano]

Nice torque curve.  I like your approach.  Less weight.  

 

Maybe you should start a thread.  "DYNO SHEETS".  I bet the group has some interesting ones.

[D_Mac]

I think I have the same bicycle cable as well.  

You do have a nicer dyno sheet.  Show off. 

My weight loss strategy is to remove the passenger and skip breakfast.   

Fortunately my wife never reads anything that has a 7 in it.

 

 

[Silber]

This thread is due for an update. Sorry I don't have any pictures.

 

Over the last two months:

1. Installed new 5-point harnesses with pull-up style lap belts. So much easier to adjust.
2. Found out that the seat slider on the drivers side was gunked up and has much more range of motion than first observed. I've got the seating position almost perfect now.
3. Changed the oil.
4. Raised the rear ride height a smidge and stiffened the rear sway bar. The sway bar has five mounting points on each side, giving a wide range of adjustment, so I set it halfway (center hole on each side) as a starting point. The goal with these adjustments is to get the car to understeer less.
5. Took a look at adjusting the brake bias.... that's worth going into more depth about, see below.
6. Attended a low-key, test-and-tune style auto-x event to test everything out.

I knew the brake bias must have been off after the first autocross, but when I finally got around to adjusting the brake bias bar I was shocked with what I found. The lock nut on the bias bar was loose, and the bar was sitting about as far rear biased as it could go. There was my problem! I set the bar at an arbitrary point much more forward biased, didn't adjust the pushrods at all, and then didn't drive the car for a couple of weeks. Turns out it was still rear-biased. So several adjustments later, including fiddling with the pushrod lengths, I have it very close to ideal but still with the tiniest rear bias. I've almost maxed out how far the bar can be adjusted for front bias, so I'm a little perplexed as to why the car has such a rear bias, but now the car stops so much better and doesn't instantly lock the rear brakes under hard braking. Success!

 

Testing the car at the auto-x confirms that the adjustments helped alleviate a lot of the understeer, but I think it could still be better. A big part of it is probably tires, which I decided I'm going to burn off these old Bridgestones before getting new tires. Another contributor is probably alignment, but I'm also going to hold off on the alignment until I get new tires. Thus, I'll stick to shock and tire pressure adjustments and just enjoy the car as is.

 

Next step is to test it on a race track now that I have the harnesses, seating position, braking, and handling pretty close to where I want them. Looking forward to getting the car out on track at Utah Motorsports Campus to see how it does.

 

[Silber]

Took Bones to the British Field Day in Salt Lake City today. Met up with @Frankie and had the chance to really compare a Birkin to a Caterham side-by-side. It's interesting how similar the cars are, with really just very minor differences.

 

This car show also has a very little autocross course. I had the second fastest time, but was definitely hampered by a lack of steering radius on such a tight course. The fastest guy was a friend of mine who is a very good driver in a heavily modified bugeye Sprite.

 

 

[Frankie]

It was a wonderful day under the Elm, Cottonwoods and Pine trees at the Historic park in the center of Salt Lake. I didn't take an official count of how many cars were there but it had to be in the realm of 150 plus. We were parked next to a beautiful 2005 Morgan Aero 8.  Breath taking car! But the best part of the day was meeting a new Seven friend who I will be able to drive Utah's Wasatch's  canyons with.  I purchased a GoPro Max this year and have already driven four of our closest Canyons. Millcreek, Emigration, Big and Little Cottonwood Canyons.  As soon as i figure out how to use the damn GoPro and edit the film I will post them.