My turbo is on its way out and Iv order a jmtc 45 extreme k04 turbo to replace it. Will I be ok to do a straight swap and run it for a few months until I get it mapped? I already have full exhaust system,intercooler and air intake. I don't want to cause any damage to existing parts but unfortunately I can't get the turbo fitted and map done all in one so looking like I may have to go down this route?

 

You can fit a t88 turbo from a thousand horsepower supra and be fine. The key is not to go on boost or if you do, make sure and not hold the throttle down for more than a very short period.

 

But in terms of like the Ecu, will it adjust itself to run the k04 until it gets mapped? Or will it run low on boost or just be normal and take a while longer to spool up?

 

I expect the ecu will still seek the originally desired boost pressure figure. The issue is that 10psi on a stock turbo is different than 10psi on a bigger turbo and it may not add the extra fuel and it may not retard the timing if required. All in, whilst u may be looking for someone to tell u it will all be okay, nobody should tell u that as it isn't them paying for the engine rebuild if u hold it at 6500 rpm in 6th gear on a hot summers day.

Thus my original response which is it will be fine if u stay out of boost. It will probably be fine if u do a small amount of in positive boost driving and it will probably not be fine if u go hunting top speed records.

Good luck

 

Steve is pretty much right on the money. I ran the exact same turbo on an N18 for about a month and a half a few years ago before getting into tuning. Boost still topped out the same, maybe a little lower and AFR's were the same as before.

The ECU will adapt the PWM signal to the pressure controller that regulates the wastegate to control psi in order to get the desired amount of airflow into the engine. In addition pulse width to the injectors is driven by RPM and airflow measured by the MAF sensor in a load based system like ours. In other words 250 g/s of air will still need the same amount of fuel for the same lambda whether it gets there at 10 psi or 15 psi. The load based ECU is also why many of the common modifications like intake, exhaust and intercoolers make very little difference on our vehicles without a tune. There is a short term gain only and then the ECU adapts. I had to dig through some old dyno sheets but the N18 mentioned above had full bolt-ons to include intake, 2.5' exhaust, intercooler, catless DP with the KO4 and made a whopping 171 whp on the stock tune.

What I would not recommend is combining the KO4 with a JB+ and then driving it like ya stole it. Treat your Mini good and she'll do the same to you.

 

Out of interest, on this particular point, how do we think the ECU decides what load it is providing? It doesn't have a cylinder pressure measuring device, that I know of.

Is it using some sort of clever measure of the effort taken to produce a spark in the chamber?

Cheers

RW

 

You are correct our ECU does not measure cylinder pressure. The term load based could better be described as torque based. Load i.e. torque is a function of the air mass entering the engine, RPM of the engine and a scalar. Altering the torque map alters the boost curve up to the mass limit contained in the map or the boost limit set elsewhere, whichever occurs first. There is a torque map for each gear which is how the first two gears are boost limited. With our load based system you will see higher boost levels on a hot day vs a cold day as the ECU is targeting mass airflow to reach a given percentage of absolute load.

Boost based tuning utilizes the MAP sensor to calculate air mass based on engine RPM and manifold pressure. Call it a refined speed density method. Of course with this system the air temp, altitude, etc all affect the amount of air mass entering the engine. Placing a larger turbo on this type of system without retuning will result in higher AFR's.

 

Interesting. This will explain why when the guy altering the map tried to adjust the duty cycle to the vacuum operated actuator it didn't quite do what he was expecting. We moved to manual boost control on a more standard pressure controlled actuator. It just made things more simple.