I am looking into the JB+ for my 2013 MCS and everyone seems to have great things to say about it but I haven't been able to find any concrete explanations about what it is actually doing. I have a fair bit of experience with performance mods and with opensource Subaru ECM tuning, and I am uncomfortable just plugging in something without understanding what it is doing.

It is advertised as increasing boost from 2-4 psi, which I'm assuming it accomplishes by decreasing the voltage coming from the MAF slightly thereby tricking the ECU into adding more boost to reach its target value. Since it is only plugged into the MAF, I can think of no other explanation for how it would increase boost.

I can see from the pictures on Burger Tuning's website that the unit consists of a potentiometer, a resistor, a few capacitors, and a flash microcontroller. My concern is that I can't figure out what the microcontroller is actually doing. If the unit is really just reducing the MAF sensor voltage, it seems that the same thing could be accomplished with a potentiometer, an adjustable voltage regulator, and a resistor. (I built something very similar to adjust MAP sensor voltage on my Jeep stroker engine, allowing me to fine tune the air/fuel ratio in open loop.) I would be curious to see what the voltage readings on the signal wire are at the various positions on the potentiometer.

Is there really no problem caused by adding boost in this way without also modifying fuel and timing?

I would appreciate any thoughts or comments. I just want to be sure I know what I'm getting into before I invest in a JB+.

Thanks.

 

I think you understand it better than me and most other JB users. Sounds like you just want to make your own and save some cash. Don't blame you, if I could I would have done up my own as well.

 

It's been tried and tested. For $300, it's worth it. If you can increase your octane over 93, you're safe to turn up the dial. I've read a few one-off's where the car didn't adapt. The JB was returned and a replacement was sent out, no issues. You're under warranty, I wouldn't experiment with anything that hasn't been tested and researched . Best of all, you can remove it in seconds before a dealership service. For me, that right there sold it. Get it and IMO, save your $ for a tune after your warranty expires if you want more.

 

I think that you're on the right track for what it does, and to answer your question about modifying fuel and timing I do know that the MCS runs slightly rich in stock ECU form. Also the boost varies a lot even just during your daily drive, as engine temps increase and decrease and loads vary boost is altered, fuel is added or decreased, and timing is adjusted. The factory even incorporated an "overboost function" so if its safe to add 5 psi in that way I'm sure 2-4 psi is well within limits for the stock tune and injectors to handle without leaning out the motor and damaging the engine.

Any mods you do you are taking away some reliability just because you are increasing the demands on the motor but this is such a minor increase on the internals that it's well within what the engine is capable of.

I might be mistaken but I think the microcontroller is to adjust for varying octane levels... not an expert on that by any means though.

Hope that helps in your decision.

 

Don't know how it does what it does, but I do know I like it!

 

I don't know how the JB+ works beyond what's been described above. However, there are ways the MAF sensor voltage output reduction could be mapped by way of a microcontroller that would be very difficult or impossible to acchieved via hardware. For example, one could create non-linear voltage modifications, cap the voltage modification at a maximum value, with or w/o rolloff, or have a peak modification that is once again reduced, and even use differnt such non-linear maps for different settings of a dial. my guess is that this is what the microprocessor does.
And as others have said, it's well worth the cost. Best grins per dollar to be had!

 

The MAF sensor in the MINI does not use 0-5 V. It actually uses PWM to carry the signal therefore it needs something more than a voltage divider type circuit hence the slightly more complicated internals to the JB+.

But like you said it modifies the MAF signal to trick the ECU into providing more boost but nothing is free and this is done at the expense of slightly leaner AFRs. The nitty-gritty "how" is proprietary and I'm sure that BMS isn't going to release that information.

I still think the JB+ is a great device and a value for people that don't want to get a tune.

 

Thank you cerenkov and Zephyr1. That is exactly the kind of info I was looking for. I figured there was something I was missing, otherwise there would be tons of DIY MAF mods floating around. I would be interested in seeing how the Microchip is programmed, but as you said, BMS probably isn't in a hurry to release that.

 

A straight on, linear, proportional change to a PWM signal could be done via hardware w/o microcontroller (i.e. with a 555 timer type circuit), hence my guess that there is some non-linear mapping for which a MC would be ideal. Another thing that could be done is to build in some hysteresis.

 

I think it tricks the car into thinking it's running at higher elevation, where it has to add more boost to achieve the same load based goal. The engine runs on the lean side, even under boost, going rich at high RPM. The limit of the JB+ is the stock maps which is why you need higher octane in order to turn up the dial. A tune would lower engine temps, richer the AF allowing more boost and timing.

 

Yesti,

I agree that the JB+ is modifying the MAF signal to show less airflow so the ECU adds more boost to get to the same load target, but that means there has to be a MAF sensor downstream of the turbo so the ECU can calculate the proper fuel to add, otherwise the engine would run dangerously lean. But so far as I can tell there isn't a second MAF, so maybe the ECU is using the MAP (manifold pressure) and IAT (intake air temp) sensors to calculate the air mass delivered to the intake, and determining fuel from that?

As I understand it the ECU will set a code for a boost leak when MAF before the turbo is greater than the effective MAF (determined from MAP and IAT?) delivered to the engine. But for the JB+ to work the ECU must not check for the opposite case, instead it takes the MAP and IAT data and calculates fuel and doesn't check that the air mass delivered is greater than than what the pre-turbo MAF said.

If my speculation is correct, that's an interesting loophole in the design.

 

Terry (from BMS) has hinted at what it does and that the trick used does not work on the N14 engine.

https://www.northamericanmotoring.co...ml#post3833309

https://www.northamericanmotoring.co...ml#post3848876

https://www.northamericanmotoring.co...ml#post3816619

 

Does it matter if it's used on a factory JCW version of this engine? I remember one person saying they used it on their fJCW and it was fine, they turned the dial down to 30% I think. Just curious.

 

The user manual says you may want to turn it down to 30-40% unless you are running higher grade fuel (91+), race gas, E85 mix, or meth.

http://burgertuning.com/instructions/mini_jbplus.pdf

 

Don't all MCS require Premium grade 93 octane anyway??

 

Require? No. IIRC the manual recommends 91 w/ a min. of 89.

 

FYI it does run the car lean. Up to 16 AFRs at mid RPMs at 60%.

Otherwise it's great for all reasons above.

 

What is the advantage or disadvantage to car running lean?

 

Pros for running lean: more power!

Cons for running lean: burn through a piston.

 

I put 93 octane. I have set at 50%. The instruction says to leave it at 100%.....???

 

Sure enough the instructions have been modified. Maybe Terry will chime in.

The S has always previously been 50% and the JCW was 30-40%. Both my JB+'s were at 50%. I've attached the jb+ pdf that I downloaded on 5-11-2015 which is when I purchased the last one.

 

I noticed the same thing a few weeks ago, thought it was a type-o but wondered if maybe more testing was done? It seems too obvious to be a mistake. I bought mine around December and remember the instructions saying it came shipped at 50%. Weird

 

I emailed Jon at Burger, he replied and said that there is a newer unit now out. If your JB came preset at 100%, that is equilivant to an older until being preset at 50%. So you still need higher octane on the older units to be safe turning the dial up. I guess I'll have to blame California on that one, glad I got an older one!!

 

I took a chance on this when it first came out. It was just so easy! I have a modded 2013 JCW that has,among other things, a JB,a sprint booster,and I love that stupid SPORT button and the car just RIPS ***.

ISAMIN

 

If all it is doing is scaling the readings downward, the same could be achieved with a larger MAF housing. These cars use a 60mm inside dimension MAF. Plug in a 70mm unit and see if the results are the same.

But as the OP observed, the ECU will have to adapt its fueling map tables for the altered readings. This could easily throw a code for an implausible signal. Perhaps the JB unit somehow circumvents that.