WooHoo! Mod Day!

So today I made the pilgrimage to Thomasville, NC to “Mini Mecca” of the Carolinas – GrassRoots Garage. I had an appointment to have my two remaining pre-Dragon mods done – a 15% pulley install and a one-ball exhaust mod. I’ve done EVERYTHING else to Blimey myself. But these two are beyond my skill level… They are DEFINITELY not beyond Dan Zipkin’s…

If you’re not familiar with Dan and GrassRoots – Dan is a highly certified and highly rated BMW technician who was selected to be the first MINI technician in North Carolina, back when Flow BMW acquired their MINI franchise. Dan got MINI trained and certified, and performed prep and dealer option installs on almost all of the first year’s MINIs delivered in North Carolina. As Flow grew their staff of MINI technicians, Dan trained and supervised the team. Eventually Dan took an opportunity to move on to the area’s Bentley dealership – but remained in high (and growing) demand for off-hours work for the area’s MINI community as one of the most knowledgeable and experienced MINI mechanics around. Eventually Dan opened his own garage – GrassRoots – to service the growing MINI community. It’s now sort of a rite of passage for a MINI enthusiast here to go spend a day with Dan, have him take you for great barbecue for lunch, and leave with a more capable MINI.

Grassroots Garage – note the three MINI race cars in various states…

Blimey Lift

Here’s the man, the legend, Dan Zipkin…

Dan Zipkin

So – after that brief pause for a commercial interruption –

The Pulley!

Dan prefers CravenSpeed pulleys. Craven produced some special, very cool pulleys for Dan, laser engraved with the GrassRoots Garage logo. And RED – which we all know is the fastest color.

GrassRoots Pulley

After much consideration, I opted for a nice, conservative 15% pulley – this pulley is 15% smaller in diameter (and thus circumference) than the stock supercharger pulley. As a result, for any given engine RPM, it turns the supercharger (and water pump) 15% faster than stock. I’ve never heard of anyone having engine problems with 15% pulleys – but there have been some folks who have reported issues with smaller pulleys.

An interesting sidebar – Dan had a JCW pulley in the shop that had been removed to fit a smaller pulley. We took a pair of calipers to it and it was – hold onto your pants – 10.4% smaller than stock. NOT the 14.something% commonly thrown around as fact. The Craven 15% pulley measures 15% smaller than stock.

So… a pulley install is a bit more involved on an automatic transmission MINI than on a manual – and after watching Dan do it, I’m darn glad I didn’t try it myself. To access the pulley, Dan puts jacks under the engine and transmission, disconnects the mounts for these, and lifts the engine to expose the supercharger and pulley. Then a pulley puller is used to remove the stock, pressed-fit pulley from the supercharger shaft.

Here’s the stock pulley with the puller attached:

Pulley Puller

And here’s the engine with no pulley:


And here’s my nice, new, engraved, RED 15% pulley, with belt and tensioner re-installed!
Pulley Installed

See how easy that was? hehe

Dan did a LOT of steps before, after and in between these photos. One thing we did: there is a rubber grommet in the bottom of the stock airbox, with a hole that enables the airbox to get a bit of cold air from the cowl area. With the Dinan intake, this is still in place. The hole is probably 25% as large as it could be – the rest is covered by a useless rubber membrane that restricts flow. Dan cut away the extra material to effectively open my Dinan intake even more. Extra cold air for $0 – I like!

Next up….

The One-Ball Mod!

After a lot of studying available exhaust options, I chose to go with the aptly named “One Ball Mod” of the stock MCS exhaust. In the stock exhaust system, exhaust gases flow out the exhaust header, through the catalytic converter, through an almost-straight pipe to the rear of the car. Gases then flow through a resonator on the passenger side, through a muffler on the driver side, and out twin tailpipes. This modification removes the resonator (the big, heavy can on the passenger side of the exhaust system) and re-routes the exhaust pipe to the remaining muffler. The result is less weight (about 20 pounds), a little more volume and “growl”, less backpressure, and better flow resulting in more power. And MAYBE less “drone” at low RPMs and highway speeds. And the only cost is some labor to perform the cutting and welding required.

Here’s the “before” photo – with two “balls”:

Two Balls

Dan marked the exhaust at the location to be cut. then removed the cabrio-specific bracing under the rear of the car, the exhaust hangars, and unbolted the exhaust from the cat. Then he removed the exhaust from the car. Then the scary “point of no return” part – Dan started hacking up my exhaust with a reciprocating saw! I knew this was coming – but it was still a LITTLE unnerving… The first not-easily-reversible thing I’ve done to the car…

After the initial cut, Dan re-installed the straight pipe on the car, to assist in lining up parts to be welded. I bet this would sound NICE…
No Balls

Then Dan cut off the resonator, and cut out some pieces of pipe to use for the re-routing. Here’s the now-worthless resonator…


He then placed the muffler/tailpipe assembly back on the car and spent a while test fitting and modifying a couple of sections of pipe until he had the fit “just right” – then he tacked everything in place with the welder. REAL men fearlessly weld inches away from full plastic gas tanks…
Dan Welding more

Then he removed the whole assembly from the car, completed welding the joints, let it cool, and reinstalled the system. Here’s the result. Dan did a fantastic job getting this to line up – it’s straight, the tips are centered, and it’s solid.
One Ball

The re-routed, welded pipe – no holes, plenty of clearance in all the right places. Not as pretty as a brand new $700 stainless system – but for $100, it’s a thing of beauty to me!
One Ball Welds

I love the way this sounds – more growl, a little more volume, it amplifies the burble a bit, but it’s not obnoxious and not at all “ricey” sounding.

While Dan was working, UPS delivered a shipment of 12 rare, previously unobtainable Non-BMW-branded-or-priced NGK “JCW” plugs. Here’s proof:

NGK Plugs

These are the same plugs sold as JCW – just without the JCW price. They’re NGK number BKR7EQUP. These cooler plugs should help prevent pre-ignition and/or fuel “dumping” with the pulley. Soooo…. now Dan has 8 plugs left. The first 4 are installed in Blimey!

And, while I was there, I had Dan download my ECU to have an MTH tuner file generated. I have my first scheduled dealer service after the Dragon – after that, if they don’t flash the ECU, Dan will have MTH generate my tuner file and I’ll stop by for an extra “boost”… more to come on that later…

I drove the 2 hour route home – over some moderately twisty, open country roads. The pulley and exhaust, combined with my existing Dinan intake, are AWESOME! There’s significantly more pull and power from about 3000 RPM up to redline. And I LOVE the sound – both the added supercharger whine, and the improved exhaust sound. It’s all good! Blimey loves more throttle!


  1. You sooooooo could have done the pulley. Need friends who have the special tools, but it really is a DIY project.

    The exhaust mod? Yeah, not DIY. But cool. Very cool.

  2. You seem to be a real solid mod guy… I like your clean and tidy approach to your work! Man after my own heart!! really sweet MINI! Was very interested in reading the thread and your blog regarding the one ball… Mine is an 06 MCSa as well with Alta 15%, MyMini CAI, cold plugs, etc… Been thinking exhaust for a while now, but worried about highway drone as spouse does NOT like noise… Have you found any additional noise at, say, steady 2500rpm on the highway?? Would really like to hear a one ball first hand!

    Thanks… Steve (Speedee)

  3. Speedee –


    Different folks have had different experiences with the One-Ball – I think it actually turns out differently on different cars and with different approaches to the cut and weld…

    In my case, it’s definitely louder – but not a lot. I really wish I had used my sound pressure meter to test it BEFORE with various RPMs – but I didn’t – so comparisons now are meaningless – I’d guesstimate that it “sounds” maybe 30-40% louder. Not twice as loud. But louder. It’s NOT obnoxiously loud like some catbacks, and it’s NOT “ricey” like 90% of the tuner boy hondas that pass you on the highway. My wife does NOT like noise either, and she hasn’t complained… and I think she would, or at least make faces at me…

    Before the mod, I had a DEFINITE drone as you describe – a WUHRRR…WUHRRR…WUHRRR… kinda fading in and out about 30 times per minute. Painful at cruise control speed on the highway. Now, I THINK it does it a good bit less. Maybe a little. Hard to tell whether the exhaust is just loud enough consistently now that I don’t hear it, or if it was more related to the resonator that is now gone… but, to be honest, I haven’t cruise controlled since I got it – I HAVE driven about 6 hours on the highway and haven’t noticed the drone – but I’ve been driving, er, enthusiastically, so no nice, steady 2500 RPM… I’m driving to MOTD tomorrow with the family, so that will be a good test.

  4. Nice write up.
    Can you get the NGK part number for those spare plugs your using?

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