(Relatively) Low cost Big Turbo upgrade for E89 N20 versions

[biZ4rreMids]

The torque looks mighty impressive, slightly better than a stock 35is (336ft lb v 332ft lb). What were your initial thoughts on your drive back home?

 

[R.E92]

That's a good result. Hopefully it drives OK at part throttle.

Wastegate tuning is pretty tricky, they are controlled in 2 parts, a standard base map that acts as a starting point for the wastegate and then a PID loop that adds or removes depending on how far under or over the target boost the pressure is. Getting a bigger turbo fully dialled in is tricky because the base map and the PID loop both need completely reworking. Usually takes a lot of road testing.

 

[Anonymous]

The torque looks mighty impressive, slightly better than a stock 35is (336ft lb v 332ft lb). What were your initial thoughts on your drive back home?

The drive home was slightly unusual in the sense that the top was up as the weather was squally and showering..most of my high speed hooning has been top down..

The slight loss of bottom end sub 2500 rpm torque was surprisingly noticeable in typical low speed shuffle type traffic..it felt very muscular in the penultimate tune state so a slight loss as can be seen from the graph..

Once it got going it felt very powerful, first time I’ve started to have the back step out despite a Quaife limited slip diff..

The feel with the top up felt less refined, more brutal and less turbine whoosh..

So yes more powerful but for the money spent, with the benefit of hindsight not worth it for me..the previous version was the best cost/drivability/performance compromise...

Once again that ZF box just seems to rise to the challenge of the mods and has always been part of the solution not the problem..

So yes, great performance noticeable improvement despite relative small percentage change..

Glad I upgraded the brakes, the acceleration from say 55ish to 120 ish is pretty impressive so slowing down becomes more of an imperative..

You can see why many see the 35i as a handful

 

[Anonymous]

That's a good result. Hopefully it drives OK at part throttle.

Wastegate tuning is pretty tricky, they are controlled in 2 parts, a standard base map that acts as a starting point for the wastegate and then a PID loop that adds or removes depending on how far under or over the target boost the pressure is. Getting a bigger turbo fully dialled in is tricky because the base map and the PID loop both need completely reworking. Usually takes a lot of road testing.

As far as I could see on the 75 mile drive home part throttle was perfectly behaved....thanks for your comments on the set up...that accords with how they described their ‘struggles’ to get it set up properly....I reckon they did about 10 hours of dyno time..they had it for 4 whole days..

I’ll see how it adapts / settles in..I need to test it on similar conditions, top down, same roads etc

It’s got more of a rumbly feel now rather than silky smooth but that may be the effect of driving top up for the first time with this and the previous tune...

As I said you can see that you’re trading more flow on the turbo against a small loss on the bottom end torque

Clearly making the LSD work for its living now..

 

[Anonymous]

Had a chance to try the car top down on a sunny day on familiar roads in various modes today.

So in comfort mode the relative small reduction in torque at low rpm is what I picked up...it’s empathised by the auto box’s short shifting on low throttle settings..

Larger throttle settings show a wave of aggressive grunt still supported by the box preferring to short shift..

Putting it into Sports + mode and pressing the pedal hard starts to overwhelm the wheels..it will spin the wheels on an exit out of a junction despite the LSD..

It’s now reached the point where the brake upgrades and chassis mods just contain the extra power..

The lighter front end and better balance means mistakes are forgiven in a way that a stock 35i telegraphs you not to try..

It runs up to 120mph in a short distance given its head...at some point I’ll get a data logger on it to quantify it..

So for me, at this stage, it’s got to the point where enough is enough..

The de-cat exhaust adds an aggressive growl which is what I picked up transmitting sound/vibration to the cabin with the top up..it’s lost when the top is down..

Part throttle/ off throttle the engine is as well behaved as stock..

 

[MACK]

I'd not spotted you had this fitted till today and saw your other thread with N20 remap tables. Good, honest appraisal as ever Pete. I have to agree it does seem a bit of a disappointing result given what some are achieving with mods on the standard turbo and I'm not keen on the idea of the turbo having more lag. One of the best features of this engine for me is its relative lack of lag.

Looking at this and your table in the other thread, I'm being to think you might be on to something with your PWG vs EWG theory. Unless there's other differences between the earlier and later cars we are missing, but Realoem doesn't list any.