Acceleration Tuning - High MAP & Low RPM

[ever_green]

Hi i'm a tuner that mostly deals with Subarus and Mitsubishis powerplants. From Naturally Aspirated to Turbocharged, My customers independent of how much power they make always monitor their fuel economy. So it's important for me to give them best possible mileage on the streets. One possible area is for the automatic folks to have the drivebywire and transmission tuned in a way that will short shift and keep the throttle open wider (and sooner). This sometimes can lead to open loop enrichment (although it does not always occur, but if it does the ratios will be about 5% more rich). So with this low RPM high MAP tune the engine will usually shift around 2000-2700 RPM and keep 13 psi of MAP (roughly 90% engine relative load as referred to here).

In contrast the DBW & Transmission can be tuned to shift about 500 RPM higher but with lower MAP of about 11-12 PSI (75% Load). However chances of hitting open loop enrichment is much smaller this way, so you spend more time running as lean as possible.

Several things:
- This tune does Not affect cruising efficiency, it's just for acceleration
- Peak VE on these cars is usually around 4000 RPM
- Closed loop target AFR is roughly 14.5:1
- BSFC sweet spot is at very high MAP and wide RPM range according to manufacturers, yet i'm not sure this is trustworthy as they usually overestimated the 'boundaries'

I think I should go with Higher MAP, open thorttle, lower RPM strategy despite chances of enrichment (up to 5%) ?

[pgfpro]

Nice post!!!

The light acceleration is one of the hardest things to tune, and every car is a little different it seems to what it likes and dislikes.

IMO I think it has a lot to do with the ignition maps and the fuel octane.

I have seen some strange cells in maps that can't handle a higher load and have to have a lot less ignition advance. I think it has to do with poor air velocity that creates a poor fuel atomization and to some degree some fuel fall out.

On my car I can have it shift at a 1000rpm if I want (control over TCU) but what I have found is my car likes to be shifted at 2800rpm for the best FE results.
This took a ton of hours but it now way better fuel mileage then it did before.

[Mustang Dave]

Accelerating @ 100% load (MAP = BARometric pressure) and shifting @ 2500 RPM seem to work fairly well for my 4-liter Mustang. YMMV

[ever_green]

Yes almost every car I tuned tends to knock somewhere between 1000-2000 area under load. So yes timing is retarded under low RPM and high MAP areas. Fueling is not rich, since enough air is not flowing past the MAF sensor to trigger open loop.

Currently with ~18% throttle opening (25% pedal angle)
1-2 : shifts at 2700 RPM
2-3 : 2400 RPM - Torque converter locks up
3-4 : 2000 RPM - Torque converter stays locked

AVG RPM since time to top gear is 1850 RPM and average MAP is 12.5 PSI or 85% LOD just shy of open loop. Car hits top gear at 40 MPH doing 1500 RPM.

Also the transmission slips much less with a slightly more aggressive drive by wire, so shifts are noticeably quicker.

[pgfpro]

One thing I forgot to mention that you brought to my attention is on my auto I have a full line pressure switch.



I'm also running John Deer Hygard gear oil in my auto. This really tightens up the torque converter before lock up. Even getting up to freeway speed it helps a ton with torque converter slippage. It also tightens up the stall speed by a 400 rpm. So this is why I'm decide to build my turbo compound system to make all the torque I want for awesome 60' times.

[H-Man]

Your car doesn't count as something that needs to worry about air fuel ratios. Your car would run off of the exhaust gasses of my dad's corolla in place of fuel without misfiring. (Yes, I wish I could get away with that kind of setup in cali, I can get E85 real cheap vs E10 so if a CR bump made up the efficiency loss, my $/mi would be way lower.)

[ever_green]

Thanks I just bumped up the line pressure using the drivebywire system. Basically you use higher scale for requested torque numbers while rescaling throttle settings to match previous setup. This tricks TCU into thinking that full throttle is requested at part throttle and so it shifts fast similar like in full throttle. Shifts are very quick. ~400ms vs 600ms stock from logs and the converter no longer hesitates when locking/shifting.

I'll post a vid tomorrow but people think it shifts like a DCT and torque converter is virtually locked at all times unless exceeding 40% pedal angle. It gives a woody feel to driving experience but more controllable. If anything customers can switch to sports or sportsharp mode to get more unlocking.

[pgfpro]

Originally Posted by ever_green

Thanks I just bumped up the line pressure using the drivebywire system. Basically you use higher scale for requested torque numbers while rescaling throttle settings to match previous setup. This tricks TCU into thinking that full throttle is requested at part throttle and so it shifts fast similar like in full throttle. Shifts are very quick. ~400ms vs 600ms stock from logs and the converter no longer hesitates when locking/shifting.

I'll post a vid tomorrow but people think it shifts like a DCT and torque converter is virtually locked at all times unless exceeding 40% pedal angle. It gives a woody feel to driving experience but more controllable. If anything customers can switch to sports or sportsharp mode to get more unlocking.

Sound great can't wait to see the vid!!!

[ever_green]

here is the video, i installed a scangauge 2 in the second part for load reference:

https://www.youtube.com/watch?v=LJ_dD6iriho

There is already improvements of about 0.4 L/100km on this tank same commute to work despite dropping temperatures and more active weather. High Map and Low RPM is the way to go. Now a manual transmission swap with a longer final gear and drive is next modification. I think gearing that allows cruising at 1800RPM @60 MPH will be ideal in this car.

[Joggernot]

Can't see the video.