Hey,

I've read extensively how much more modified the engine of a JCW is.

The question I have is, due to reworked head, pistons, turbo, clutch and transmission, is the JCW more "moddable" than a regular N18 Cooper S?

I'm planning on putting a tune on my S to bring it to around 220WHP 250WHTQ and am wondering if it's safe to do so without strengthening the engine.

 

220 whp should be nowhere near the limits of your engine.

 

The JCW N14 is well understood and can make GOOD power,,,
the JCW N18 is pretty new...and even MINI held off on installing it in the JCW for a bit...it does hold promise though IMO.
Biggest issue seems to be it is MUCH harder to tune than the earlier versions which were just getting well understood....it seems you will be at the forefront of modding a JCW n18....

 

I don't have a JCW N18... Just an MCS N18

 

The reason for the stronger head and pistons is because the factory JCW runs at a much higher boost pressure. The S runs at 13psi boost, but the factory JCW runs at 19psi. The turbo is a similar design, but larger for higher air flow. The uprated clutch and transmission are to handle higher engine output. The exhaust system flows better than the S version.

My assumption was that raising the power from S level to JCW level used up enough of the safety factor that BMW designs in and forced them to uprate the internal engine parts.

Also, you might do some searching around regarding mods to the ECU. I thought that the '13 models had the ECU code encrypted, thereby making mods very very difficult

 

Please clarify...Does the current 2013 JCW have the N18 engine? I have seen N14 and N18 thrown around so much, I cant tell if all models have the N18 or just the S and base models.

Thanks for clarification.

--Chad

 

Yeah, 2013s have the N18, I'm pretty sure the 2012s have it too. I think it was the first year of the new engine (2011) where only Cooper S' had the N18 put in them. JCWs still used the N14

 

I was under the impression the 2012s had the N14 engine.

Edit: I see you qualified that, the 2012 JCWs had the N14, which is what I was saying, this being the JCW forum.

 

I have to correct this a little bit. The S and JCW have different compression ratios. It's not as simple as i'm going to make it but since basically since the JCW has lower compression ratio when boosting more PSI the internal combustion pressures are not that much higher then the S with a lower boost pressure. So essentially you could have an engine with a higher compression ratio and lower boost and have the same combustion pressure as an engine with higher boost and a lower compression ratio.

 

The difference in compression ratios is only a half point; 10.5 for the S and 10.0 for the JCW. For a fair basis of comparison, if would be the original Gen2 S of 172hp versus 208hp for the JCW as both are not full VANOS equipped. Many factors go into the 36hp difference: improved intake flow, improved exhaust flow, somewhat more aggressive ECM settings, etc. However, I would have to think that the biggest part of the 36hp is due to increased turbo output (bigger turbo than the S) and the increase in manifold pressure. The increase in manifold pressure is almost 50% (46% to be exact).

Just to take a SWAG, if you look at air flows through an orifice...

I'll arbitrarily assume that the turbo outlet is 1.5" dia and compare flow at 15psi and at 20psi (using tables). At 15psi you get 727scfm and at 20psi you get 885scfm. That's a 22% increase in air flow due to a difference of 5psi. Now this obviously doesn't adjust for the specific shape of the turbo exit or the temperatures involved, but it does point up the relative difference. Anyway, I would have to think that in this case, a significant increase in air flow trumps a loss of half a point of compression.

 

Of course It does. Like I said, that was very simplified. Just wanted to people to know that. The other thing is the JCW turbo is larger. So less PSI will more flow can come out to the same volume of air. I just wanted those things to be said. Now knowing that, the differences in drivetrain components really doesn't matter. The chances of making enough power to break any component from power alone is very low.

 

Err, yes but. I had to turn around and ask the guy behind me who's fresh out of formula SAE since I come from big naturally aspirated engines but the primary reason for lowering compression in forced induction is lower combustion temperatures and reduced detonation.

 

Lower pressure = lower temp = less chance of detonation. You are correct.

 

It also has the effect of reducing the octane requirement. The next step would be even more expensive 93 octane. Beyond that would be racing fuel or avgas.

 

Brake Mean Effective Pressure (BMEP)

BMEP is the average pressure which, if applied to the pistons uniformly from the top to the bottom of each power stroke, would produce the measured power output. With various conversion factors applied and 4-stroke factored in, the equation is:

BMEP in psi = 150.8 x (Torque in lb-ft) / (Displacement in CuIn)

Displacement = 97.5 CuIn
Justa Torque = 114 lb-ft
S Torque = 177 lb-ft, 192 lb-ft overboost
JCW Torque = 192 lb-ft, 207 lb-ft overboost

BMEP Justa = 176 psi
BMEP S = 274 psi, 297 psi overboost
BMEP JCW = 297 psi, 320 psi overboost

What this says is that the turbo MINI engines breathe very well. One point should be noted, however. The JCW routinely runs at a power level that the S only reaches in the time restricted overboost mode. I think this is the real reason for the upgraded parts.

 

Well put. I'm sure you are aware that the octane rating of gas is its ability to resist detonation.

 

Yes, sort of the reverse of how we think of the Cetane scale for Diesel fuel.

Anyway, my earlier point was that if you didn't do anything else to prevent pre-ignition, you would need to raise the Octane requirement. 93 Octane would be the next step beyond the current requirement of 91.