What is the stock boost of the Cooper S?

 

It's about 11.5psig peak.

 

Thank you..and one can assume that a 15% reduction pulley would increase the peak number by 15%?

\Newbie Q

 

No. The "15%" is the supercharger pulley diameter reduction. From that, there is a change in the drive ratio of the blower, but it is not 15%. The stock blower drive ratio is 2.11:1, whereas with a "15%" s/c pulley the drive ratio is 2.49:1. When you have a stock MCS and only add a "15%" supercharger pulley, you'll see about 16psig peak of boost.

 

I see 10 psig on my early '02 with ~50k miles. No adjustments have been done on my bypass valve and I bet I'm loosing a little there.

 

How much boost are the stock internals of the R53 capable of handling without fear of detonation?

As stupid of a question as this next one is; I feel compelled to ask it anyway.

Gas prices are through the roof. Has anyone successfully run lower octane gas, without detonation?

 

With a 15% pulley you should be able to get away with 91 octane, but in hot weather you might see some detonation. I don't have a pulley but there was a thread on which gas people use, and those who have 17%/19% always use at least 93 if possible.

I always put 93 in, no matter what. It all comes out in the wash when the miles start adding up.

 

I don't own a MCS *yet*, but hope to soon. A lot of the interior pictures I'm looking at on Ebay Motors, don't show a boost gauge. I was under the assumption that all 1st Gen MCS R53s, are supercharged. Is that not correct?

If this is correct, why the lack of boost gauges?

Thanks for helping a newbie out.

 

Some enthusiasts add aftermarket boost gauges. For most folks in street driving, it's more bling than function - OK, great, now I know what my boost is, but how does that help me? How will I drive differently? etc. And if something's wrong and it's not making boost, I'll feel it (and probably get a Check Engine Light) and will get it checked out. Unlike oil pressure, temps, etc. which can be silent but deadly killers...

 

They are all supercharged (pos. displacement). As for the boost gauge- some people buy aftermarket ones. I'm not sure it would be a very profitable or popular option. I'd venture to say that most people don't really care what kind of boost they're getting. I can't speak for everyone though. Saabs and the new Acura RDX (which I have) has a boost gauge, but it doesn't have any numbers on it.

 

The actual boost pressure will probably vary from car to car and if a boost gauge is added there will a variable just due to the gauge. My boost gauge shows ABOUT 10 to 11 lbs and I also had it on the dyno a few days ago and it showed 10.3 lbs boost at redline of 6850 RPM. I am getting a 2% crank pulley Tuesday and a 15% sc pulley. After that I will go back to the dyno and let you know.

 

Please do post your results when you get them. I am anxious to see how much of a power increase could be expected from the extra boost.

No one has commented yet on how strong the pistons, connecting rods, and crank shaft are. How much boost can the stock internals of the motor handle?

 

Boost does vary.

Some report 16 to 22 psi after mods-
https://www.northamericanmotoring.co...ad.php?t=46346

That's alot of increased boost. Hope it doesn't blow up.

 

I do not recommend going over 22 PSIg on 93 octane [R+M/2] unleaded. I also do not recommend anything less than "premium" unleaded. That said, the Cooper S will knock as low as 14 PSIg with the stock supercharger, depending on the situation and components involved. The Cooper S ECU ignition program pulls timing the instant it sees knock, so it's not a huge concern. When you start running twincharge setups though that are untuned, that's when you'll blow up the stock internals pretty easy.

Cheers,
Ryan

 

I thought our R53s uses the roots supercharger, i associate positive displacement with the twin screw type.

 

I'm hitting 15 PSI max with my 19%. Hoping it will go up when the air gets colder or it might be time for a crank pulley too.

 

Visited Randy Webb in Denver Tuesday. Installed Alta 2% pulley and Webb
15% pulley. Indicated boost now 15lbs. but it keeps blowing pressure hose off so I need to fix that problem.

 

I am hitting about 15% on a regular basis on my 05 JCW MCs. I have a 2% crank pulley ready to go on and am curious if I would see any more gain by going to a 15% or 17% supercharger pulley. I kinda think I should just leave it alone at this point. It runs strong and my mileage is decent. Has anyone changed out their pulleys on a Cooper Works car?

 

you mean 15 LBS not 15%. I just installed a boost gauge today and I'm hitting 16lbs with a 17% and 2% pullies.

 

ahh yes, the dangers of typing while tired. Yes, 15lbs boost. JCW full kit with filter upgrade is the only thing that I would think would be effecting my boost. I have M7 DFIC and heat shields, and and MSD wires and distributor.

 

So I got my Autometer boost gauge installed today. I get around 20 in/hg on strong deceleration and around 15 in/hg cruising. But some of you guys said you saw around 12 PSI WOT (stock). Today in 90 degree heat I only saw 8 PSI max. Not sure if that is normal with the heat or if I have a boost leak or gauge line has a hole etc.

Car still feels great..but just wanted to check w/ you guys.

BTW- I am at around 5800 feet above sea level in Denver

Cheers

cp