Wednesday, October 4, 2017

mini love - part 25

Now that the rainy season has started, I have time to begin think of a few enhancements that I may make to the Mini. Some of these are from my experience of driving the Mini on the track hard that I discovered something that I would not have otherwise.

First is the brakes and suspensions. I am extremely pleased with the modest investment in the suspension modifications. These upgrades not just made the car better on the track, but also improves handling and even ride comfort on the roads. I cannot say enough good things how spot on is the design of the Swift Sport Springs. The modest drop in ride height is just right given that our cars have to content with all sorts of challenges on public roads, and driveways.
  • Swift Sport springs
  • Koni Yellow dampers
  • IE fixed camber plates
  • Alta 22mm rear sway bar
  • Hotchkis rear lower adjustable control arms
For the rear lower control arms, I have left it at the same lengths as the factory fixed arm. My hunch and how the car drives tell me the modest drops in front and back ride height the alignment should not be too far off. I performed a rudimentary poor man’s alignment check and the front and back wheel cambers are very close.

In the two most recent track days, I have been braking later and harder at the end of the straights, and from higher top speed than any previous experience. In the last track day I use a set of Hawk HT-14 front racing pads. Because of all these the ABS activated a lot. I also experience rather strong front end shake braking so hard. I initially thought this was mostly due to pad lining transfer to the front rotors when I abused the stock pads. However with the Hawk pads which all but cleaned up any trace of the lining deposit on the rotors, I know the cause is something else.

I suspect the cause of this front end shake is due to two causes. The first is the factory rubber bushing for the front control arm. While there is no perceivable steering or handling shortcoming, I think under extreme hard braking the flexible bushings leads to temporary change in front wheel toe – resulting in excessive toe out. The shakes is probably the result of a sequence of toe change oscillations. While at the track I wanted to check the wheel lug torques for I was concern they may have worked loose. I didn’t because I didn’t bring the torque wrench with me and my friend who has one had converted to hex head lugs so I couldn’t use his.

When I performed the post track day inspection, I would found 2 of each front wheels lugs had loosen slightly – may be by 10 footpound max. This has never happen before.

In addition to the control arm bushing, I suspect the other contributor to the front end shake under heavy braking is the strut tower flex. I have no strut tower brace and I have been wanting to take a wait and see before investing in one. Over the off season I plan to install a set of Powerflex bushings for the front control arms. As for the strut tower brace, I would like to have some basic idea on the extend of the movement but that will require first invest in a brace to instrument up some sort of measurement.

I should mention I find the Mini’s electro-hydraulic assisted steering excellent on roads and especially on tracks. In turns at the edge of tire adhesion there is no shortage of steering feedback and the weight is just right for me. I do not feel there is any need to increase the caster to get more weight.

I set the Alta 22mm rear sway bar at the softest setting. The car has very little tendency to push though at time there is a hint. For wet road safety I have so far want to leave it at this setting especially to get over this coming wet seasons. Next season I would likely to experiment with the more aggressive settings (medium and stiffest) to get a bit more rotation tendency.

In advance of next season I plan to:

  • Replace the front control arm bushings with Powerflex
  • A good strut tower brace
  • Wilwood 11.75 inch front big brake kit
  • Steel braised brake lines for front and back calipers
  • More aggressive brake pads for the rear stock calipers
  • Milltek cat back exhaust
  • Configure a set of proper equipment for Harry's Laptimer

Powerflex control arm bushings

I have a set of JCW 380cc injectors that I am waiting to try out. However I want to install a wideband A/F gauge before I do that so I can find out the difference between the stock 330cc versus the bigger injector.

MTX-L Plus wideband A/F gauge

I have so far not mention the Exedy single mass flywheel and clutch kit that I install. For about the same price as the very popular Valeo I am very happy to have taken the road less travelled, while I have never driven with Valeo. The Exedy flywheel is a few pound lighter, and about 1/3 lighter than the stock dual mass flywheel/clutch all counted. The difference in the throttle responsiveness is very pronounce. The Mini engine now feels like a race engine as the RPM spools up so much faster, which is very important when you have to heel and toe from 113 MPH down 2 or 3 gears as fast as the brakes and tires can decelerate the car.

Exedy single mass flywheel

Exedy friction disc

Exedy clutch installed

One reason that I chose Exedy over Valeo is I was hoping for a heavier clutch pedal. It turns out the Exedy is very close to the stock Luke clutch. Despite the pedal being lighter than I’d like there is no shortage of clutch grip. In retrospect now knowing the rather light duty of the MINI’s plastic release bearing I can understand why, stock, Valeo and Exedy all have light pedal. The only aftermarket clutch/flywheel kit that I know that has a strong release bearing to go with the race performance clutch is OS Gekin. The Exedy clutch engages noticeably more crisply than the OE Luke clutch which feels vague. It is too bad the Exedy single mass flywheel and clutch kit is not more recognized due to some incorrect information (unintentionally) disseminated here on NAM. Before I settled on the Exedy kit, I was looking at $1000 clutch kits and I am very glad of my final choice.

What I especially like about the Exedy clutch kit is the feedback of the drivetrain vibrations as well as the pleasant kind of sound. The Mini just feel more communicative to me. There is ever slight increase in vibration on the steering wheel but far from triggering rattles of the interior. Turning on the AC in the hottest summer day does not induce unpleasant vibrations. It just adds the right amount of rawness to the Mini which it deserves. Together with the excellent suspension and brakes, and the modest increase of engine output all comes together as a very balanced whole, on roads and on tracks. I now seldom drive with the car audio on as the Mini is such a treat to drive.

Milltek cat back muffler is coming, before the winter comes. The soggy season has started here right on time on the first day of autumn.

There is nothing that I do not like about the factory cat back with the one-ball modification. If I were to pick one thing I dislike the most about the Mini design, the soda can tail pipe tips win hands down. I have always like the Milltek exhaust but taking off a perfectly good muffler is such a waste. I am however at the quandary of if I want to put nice parts into the Mini it make more sense to do it when the car is in its prime. The sportier tone of the exhaust would give the Mini a bit more character especially on the track.

The 10% off promotion sealed the deal and I ordered the non-resonated version. I think it is a better choice not to have a big lump of red hot cylinder under the gear shift mechanism.

Such a shame that I put so much work into the one-ball exhaust. The truth is I grew to really like its sound. Who knows. May be I would grow to like the Milltek more since I rarely drive the Mini in long trip.

non-resonated Milltek
the weather outlook is excellent just when the shipment arrives

I can only wish for is a trouble free installation and fitment. With aftermarket exhaust system you just never know. There is nothing more annoying than exhaust parts rubbing against or hitting any part of the car.

I want to capture properly the difference of the exhaust sound of the on-ball and the Milltek. To do so when the vehicle is station is quite easy. To do so with it accelerating and cruising is much harder without some careful planning and setup. While smartphone is the obvious choice since I don't have a GoPro action camera, I don't feel it being a good choice. I plan to use a Minidisc recorder with a Sony external microphone. The Mini Disc recorder is less aggressive in managing the exhaust sound as noise instead of main audio of interest. The down side of using a Minidisc recorder is more work to get it from the recorder to a computer. Also there will be no video unless I record the video with the iPhone and then try to sync the sound track during post processing.

The exhaust kit arrive. I carefully checked every part and the weld joints as well as weighting all the pieces for to compare against the stock system. Hours later just before I proceed to mate the two flange joints that I discover one flange on the Milltek main pipe was welded crooked. It is the one that mates to the stock header. This is the most unpleasant experience.

the longer segment is the pipe in question that has the crooked flange

Before I begin installing the Milltek exhaust, I carefully weighed all the components. I also weighed the stock exhaust.

muffler - 20 lb 3 oz
straight pipes (2) - 9 lb 1.5 oz
misc hardware - 2 lb  (not include two pre-05 hangers)
Total: 31 lb 4.5 oz

resonator - 20 lb 14 oz
muffler and pipe - 27 lb 4 oz
hangers - 14.6 oz x 2 = 29.2 oz = 1 lb 13.2 oz
Total: 49 lb 15.2 oz

So Milltek is 18 lb 10.7 oz weight saving. Additionally I did a simple seat of the pants flow restriction comparison. I blew as hard as I could through the mufflers and the resonator. Both the stock resonator and the muffler are clearly noticeably more restrictive than the Milltek muffler. Note that the stock resonator and muffler are in series. Because of this I would expect the Milltek muffler to run significantly cooler, as well as allow the engine to breathe freer.

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