Dyno Mapping Part 3. Boost-By-Gear

The Golf has been on the Dyno at EFI-Parts twice since I fitted the DTA S80Pro ECU. The first time was with the TD04-HL19T Turbo and then a few months later year when I swapped to the GT2868HTA ex BTCC Turbo.

After the engine failure and subsequent rebuild I did quite a bit of road mapping to get the fuelling somewhere close then let the ECU do the fine tuning on closed loop fuelling. This was only a temporary measure so I could take it to DN24 as Chris didn`t have any slots available before then.

Before we put the Golf on the Dyno, Matt wanted to see how his S54 powered E36 was performing so that was strapped on first for a couple of runs

 

Not the most powerful S54 in the world but for a stock engine he`s pleased with that. We did another run afterwards and the temps were getting a bit high, the ECU cut a load of timing and the power dropped from 322 to 288 ! Just shows how important good cooling is 

 

Next up was the Golf whilst we were strapping it down Chris was asking what I actually wanted to get out of the session. To me this is almost as important as the mapping ! having the tuner who understands your requirements and how the car will be driven rather than setting it up to give an early torque delivery hump that tapers away as the revs rise. I explained there were a few things I wanted to achieve.

-Fix the Cold start, warmup map and part throttle response

-Tune the fuelling

-Optimise the Spark map

-Find the limit of the Turbo then wind it back a bit.

-Do a power run for each of the Boost-By-Gear maps

 

Strapping it down was a bit tricky as the new side skirts are deeper than before but we managed to get it strapped around the subframe.

 

Whilst idling Chris tuned the warmup map and then asked if this was the same ecu map as before. I asked why and he said he was surprised the idle control loop wasn`t setup.

The last time I was here we only had a limited amount of time. We could easily spend a full day fine tuning everything in the ECU but that costs money and it’s all about prioritising what’s important and what is a “nice to have”. As the actual fuel tuning went quite quickly this time, Chris was able to spend time on the other bits and pieces

The idle control uses spark angle to control the tickover speed, advancing timing as much as necessary to stop a stall. If you watch the highlighted box on the short clip below you can see the ignition timing changing to maintain the idle.

 

After setting this up the car idles better than it has ever done. Even from stone cold, I turn the key and it starts and idles with no throttle requirement. The only reason to blip the throttle is to excite the alternator and start it charging 

 

Chris then spent a lot of time on the tip-in throttle tuning. This is to remove the slight stumble that was present at certain revs when I applied more throttle. After he`d done this I did a trackday at Croft in the damp and I was delighted with how snappy the engine response was to small pedal changes. This sort of tuning takes time but it is so much better to drive than it was. I didn’t actually think it was that bad until I drove it afterwards. It’s surprising how you learn to drive around small niggles and then don’t even notice them.

Once the mid table part throttle tuning was complete it was time for some power runs. 

I’ve dropped the wastegate spring by 0.1Bar since the last visit. This dropped the power on Wastegate pressure as expected from 309HP to 291. Peak torque is only 5 ft lb lower.

 

As Chris was going through the power runs I noticed the torque seemed to fall more than before and for the same boost figures it was making less power than last time. Initially this was a surprise but he pointed out the compression ratio was lower with these pistons and whilst that is ‘safer’ from a knock point of view, it will make less power for the same boost so this wasn’t he wasn’t surprised at all.

A slight boost increase of 0.15Bar saw power jump 20BHP. This is almost identical to the run last time on this pressure as can be seen by comparing the 2019 and 2020 graphs below. .

 

2020 with 0.05Bar more boost.

 

One of the main things I`d changed in the ECU settings was to enable Boost-By-Gear (BBG). The option was always there but issues with my wheel speed sensor meant I never turned it on.

It’s all controlled by the ECU but has turned out to be one of the best features I’ve found. Quite simply, it controls the amount of boost the Turbo generates in each gear, so in 1st and 2nd where you are traction limited it keeps it almost at wastegate spring pressure, then it is increased in 3rd where traction is less of an issue, but kept at sensible limits to protect the CV’s. As I then move into 4th it supplies more power and finally more in 5th and 6th.

This is the table to ECU uses to control Turbo boost on the normal setting. The solenoid is kept open until 2,500 which keeps the wastegate closed allowing no exhaust gases to bypass the Turbine. This aids spool. Once it starts coming on boost the valve starts to close, allowing gas through the wastegate as necessary to generate the required boost.

The high rpm numbers increase which forces the turbo to supply more boost as redline approaches to maintain good torque at the top end.

 

It is very easy to setup BBG, click the ‘Use Gear PWM Modifier’ in the Turbo parameters page which then uses the second table. This looks at what gear you are in and then simply applies a percentage correction to the percentage table.

eg, in 4th gear it is 0% which means the solenoid is operated as per the table, but in 5th and 6th the whole table is multiplied by 4% to give a new value of 51.9% * 4% = 53.98% boost solenoid duty. This 2% increase is enough to lift the boost and generate an extra 8HP which is very small. But the -9% in 3rd gear reduces power by 36HP   A correction factor of 1% is an increase or decrease of around 4HP at peak power.

 

It sounds complicated by it isn`t. Once setup it never needs touching again unless I decide I want more power in 5th or 6th. In that case I simply change the 4% to 5 or 6% to give more torque and power.

Whilst driving the difference is noticeable. 3rd feels like it is pulling well, which it should do with 332BHP.. When you change into 4th it feels like it is pulling just as hard as it did in 3rd ! I know this isn’t the case but there is certainly less drop that with this feature disabled and the power the same in each gear.

This is the 3rd gear pull.

 

This graph shows it quite well. The Green trace is the turbo boost and each run generates more boost than the previous one.

 

By now Chris was fully into the 1Bar and above tuning and apart from fuelling he was also tuning for EGT and spark advance. As the EGT sensor feeds into the ECU which is then displayed on the Dash, he was able to do a pull, change the timing and see the difference it made to power and also EGT at the same time. He commented that the engine responded well to timing at low boost but as it increased the advance changes had less of an effect. I explained he’d said exactly the same last time we were here.

This meant he was able to setup the timing to keep EGT’s low whilst also having no knock. Chris commented that with the lower compression pistons I now run, even though it makes less power it is also even less prone to knock than before. He never  heard any engine knock during the entire dyno session. This gives me a huge amount of confidence knowing that whatever the weather the engine will be safe.

The cooling system is well up to spec as we know already and it meant Chris never needed to stop and let the engine idle and cool, the water temperature which is usually a limiting factor sat at 75degrees between runs and peaked at only 79Degrees during a high boost pull.

 

Fourth gear was starting to see some big numbers but still maintaining the linear delivery I want.

 

We left 5th and 6th to be slightly more than 4th. We could have lifted it to around 400BHP but that would reduce the effectiveness of the high boost overtake button and I decided I’d rather run less boost most of the time with the extra 60HP available at the push of a button when I wanted it.

 

The overtake button is a steering wheel mounted button that when pressed immediately switches to the second Turbo map which generates 1.5Bar and gives this torque curve. I use it when I’m chasing something faster than me if I need some extra help to keep up on the straights. It puts a smile on my face everytime I press it, why wouldn`t it ? Press the button and instant 50+HP increase !  It is limited to 1.3Bar in 3rd which allows me to deploy the extra power in 3rd but not the full 432HP

 

When setting this map we tried raising the boost to 1.7Bar across the rev range. Whilst that did give a nice rise in power from 5,700 to 6,500, it dropped down to the same power as 1.5Bar as it approached and hit Redline which immediately told us that whilst the fuel system could supply more fuel, we’d hit the limit of the Turbo efficiency so it was dropped back to 1.5Bar at the top end as the extra 0.2Bar made no extra power.

 

All this talk of boost and settings. You really just want to see the video don`t you 

Finally, all the plots overlaid which hopefully make sense if you’ve read the explanations earlier.

 

The Croft trackday was 2 days later and all the mapping and tweaking meant I didn’t have to touch the laptop all day. The boost by gear worked just as I hoped and the overtake button gave a big push when needed. As I’ve already mentioned, the actual driveability of the car is much improved over what I thought was a good setup already. Just goes to show, it’s the little things and attention to detail on the part throttle mapping that makes all the difference.

In an ideal world, Chris would have had time to do all this on my last visit but we only had 3 hours and setting up fuel and spark on full throttle then optimising the power delivery was more important. I know the part throttle mapping needed a bit of extra dyno time and that was successfully completed today. 

 

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