Im just purchased a used full stock MCS and planning out my mods. Im considering a 15% or 17% pulley. I understand I would get better boost from the 17% but I'm just not sure if i should go there or go to the 15%.

Any thoughts or suggestions....

 

Go with the 17%, you'll love the extra power.

 

Are you just wanting to add a little pep to the car or just want some extra power when you feel like you want to use it?

 

17% and one step colder plugs.

 

im leaning to more power so looks like 17% may be the way to go.

 

I actually ran the 15% for a few years before moving to the 17 and I regret not doing it sooner. You get more power lower in the rpm range. If you are not going to track the car, the 17 will run just fine, even with a stock IC.

 

17% for the street is great imo...more usable power and better drivability where you need it in a mini...downlow. it does limit you a bit in rpm's if you want to play it safe, or have outgrown the "boyracer" way of driving and rarly redline (or just don't want to break stuff), it is fine. If you are a trackie, or redliner, go for the 15% .

 

Remember, a 15% will make more hp on a dyno, at redline, so more bragging rites, but a 17% gets you on boost at lower rpm's, so for typical intown driving, it is more of a benefit.

 

This is not correct, Zippy. 17% makes more power at redline--I've done the apples-to-apples on our dyno.

 

Ok...just going by jan/rmw's info from when i was putting mine together, but the person with the hands on wins!!

 

Just an FYI, but you might want to get a leak down check done to get an idea on the health of the engine before you start to mod it. Best to get it checked before you start adding more pressure.

 

Sounds like you have your answer, just make sure to get the smaller belt and you're set!

 

i doubt that would be critical ... most people add pullies without even checking anything and it all works great.
But if you want to be very careful then and leak down test and a pressure test can be done


Personnally id go with the 17% that way you are never left thinking "what if"

 

I would if I bought a used car especially if I was going to mod it which is what he is doing.

 

A 17% will make more power. If you are going to track your MINI where it will live at high rpm for long periods of time I'd recommend a 15% for better longevity. How many miles are on the MINI you plan to modify? Is it up to the extra loadings it will see? Best check the engine over closely. Compression & leak down tests would be good insurance.

 

What constitutes high rpm for long periods? I drive long back roads where I doubt I drop below 4k rpms for more the a couple seconds at a time over a 40-50 mile drive.

 

Is the shorter belt just the JCW belt, its time for a new belt anyways for me so I might as well do the pulley at the same time.

and would I maybe be better off with a 16% pulley for a autoX and HARD back road street driving

 

I do not plan on tracking the car. Of course as soon as i say that.....

the Mini is bone stock at over 100k miles. Best I can tell the previous owner just drove the Mini and took care of general maintenance

 

So what would be the better if one wants the Zippy probably won't track and would prefer not damaging any other parts due to pulley. Car has over 100k miles.

 

My choice was the 17%....
Folks say to go 15% if you track cause both heat issues from the sc getting overspun (lack of efficiency, and beyong the desgin speed) and possible water pump cavitation (tinny bubbles that forn around a pump spinning too fast)...can lead to higher temps and possible a spike in oil temps (stock oil cooler uses a coolant loop to cool the oil).....from running ON REDLINE like some folks do in auto-x....
4000 rpm ish is imo the upper end of the middle "cruising" range....so no worries of the above imo...heck, with the elevations out west, the 17% is imo a nobrainer!! One cavat...with over 100,000 miles, the water pump might be nearing the end of it life anyway...and the same for the SC....they might last till 200,000+, or die in two weeks, but BOTH are kinda wear items...have seals, etc that do wear, and are generally NOT considered to be parts good for most cars lifetime.
At some point you just have to say you will enjoy the car, and consider a slight increase in $ in mx to be the cost of the extra fun. Whatever you decide, have fun!!

And to the poster that asked is a shorter belt was "a jcw belt"....that was used in the early days, but would stretch and slip with a bit of age....
Most folks use a 535 or now more commonly a 532 length belt...both nice and tight with a 17%.....

 

I put a 17% on mine at 104,000 miles and drove it to 165,000 miles before I sold the car with zero issues on the supercharger. i was nervous at first but the 17% is definitely the way to go IMO.

 

So how critical are the cooler plugs. I recently changed the plugs to NGK stock replacement platinum .

 

Fairly critical. You are going to be increasing the heat which can cause early detonation. Cooler plugs help prevent that.

 

It really only comes into play when tuning the car. When adding timing and raising the rev limiter, I've seen stock plugs misfire with an aggressive tune. On a stock tune, we have not observed any changes in power, knock activity or misifiring by changing plugs.

There's another issue which would actually argue for stock plugs, and I don't have the time or energy to fully detail it here, but let's call it the 'canary in a coal mine' engine protection. If you put aggressive pulleys and tunes on your car, you do risk pre-ignition detonation (pinging), especially with varying qualities of fuel available. Pinging is very bad for your car. On R53s, excessive pinging can damage your motor's internal mechanical componenets, specifically, it can crack the piston ring landings. If you have the less durable stock plugs in the car, and for some reason have excessive pinging, it's the plugs that will take the damage, not the ring landings. Plugs are inexpensive and easy to replace. Pistons are expensive and hard to replace.

Obviously, if this were to occur, you'd want to figure out what's wrong with your tune before going to 'colder' plugs.

*Big note--so there aren't any misconceptions*: This is not typically an issue with moderately modified cars, like pulleys, intakes and exhausts. It's more of an issue with highly tuned cars.

 

In a nutshell:

17% for a street car
15& for a tracked car
One step colder plugs, when ever you like, hear pinging, or have the car tuned.

And everything should be fine as long as it is now.