Who uses the Boost by gear feature and how...
 

Hi,

back from the race track with the experience of a 360 comming out of a 90deg 3rd gear corner with a little patch of different tarmacs - I started thinking about the boost by gear feature.

ATM I am running ~17-18 psi (210 kPa target) in all gears and with my flimsy 205/40-17 tires this is struggeling for traction quite a bit in lower gears.
(I will be swapping to 8x15 wheels with 205 or maybe 225 tires next season)

So I really would like to see if any of you is usingthe Boost-by-gear and what kind of settings you are running....

Thanks

I have not set up boost by gear, buy I have played around with the speedo function on my MS3x. One thing that I noticed was it always seemed to read 1 gear low until you got into the higher gearing. I have a 6 speed and 4.10 rear end, I usually start in 2nd so that may be what throws it off.

What settings are you usig, mine is set to 4000pulses per mile snd working spot on.

You might want to try boost by speed instead.

Did you set up boost-by-TPS?

Won't that increase the boost when he starts spinning the rear wheels? It would only work well with a front speed sensor.

The boost table ist TPS depending, maybe I should review that....

Getting back to this - what would a good boost target table for my 210 kPa max boost target look like?

I would like to see some of your tables, please, mine is surely set way too high on low TPS values.

https://www.miataturbo.net/attachmen...ine=1412597718

Yes, it would require a non-driven wheel speed sensor.

No one else has your exact setup, chassis, alignment, wheels/tires, etc. Start low and increase boost until wheelspin, then decrease it.

O.K. thanks!

LOL why would anyone want to go from 0 to full boost when going from 0 to 10% throttle? You a drag racer? :D

The objective of your boost target vs RPM and TPS is to maximize DRIVEABILITY. You want the throttle to feel natural and progressive, not like a switch.

What I do is run mechanical boost, then create a 3D graph of boost vs. TPS vs. RPM. What you will find is that for any given RPM, boost tends to flatten above a certain TPS. If I were to chart said TPS it may look like this:

3000: 25%
4000: 30%
5000: 40%
6000: 50%

Something like that.

And then if you plot max mechanical boost vs RPM, you may get:

3000: 6 psi
4000: 7 psi
5000: 8 psi
6000: 9 psi

something like that.

What I do then is take the above 2 plots and do this. Let's say full boost target is 15 psi.

For 3000 RPM, max mech boost is 6 psi. It pretty much reaches 6 psi at 25% throttle. What you want is to linearly increase boost target, from 6 psi, to 15 psi, from 25% to around 95%.

For 4000 RPM, max mech boost is 7 psi. It pretty much reaches 7 psi at 30% throttle. What you want is to linearly increase boost target, from 7 psi, to 15 psi, from 230 to around 95%.

And so on.

You get better driveability from a low-boost wastegate can than a high-boost one. This way your right foot sees maximum "resolution" - small throttle openings can more finely adjust boost pressure.

@Jason- thanks for the very throughout answer. I think I will have to read it two more times to wrap my head around that setup process. (Not so easy in an foreign language☺)

Zaphod, this is somewhat off point but you did mention it.

Just for your reference, going to a 225 tyre (semislick) from a 205 is a MASSIVE difference in traction. I would say it feels like a 75% improvement.

My lap times dropped nearly 2 seconds from that change alone and the car felt like a totally different vehicle. I tried going back to the 205's a few race meetings later and it felt like it was a wet or icy day...I vowed to never drive my car on 205's again!

Which was expensive as I had a good used set AND a brand new set waiting to be used.....

Here's my actual datalog of MAP vs TPS, (Y and X axes, respectively) at various RPMs (color) with my 5 psi wastegate can.

Looking at just the steep part and ignoring the slow climb of boost with RPM, MAP starts to flatten out between 25 and ~38% throttle depending on RPM. So my boost targets start at 125 kPa, and ramps to 200 kPa at 95% throttle (just below 100% throttle). The point where it starts at 125 kPa, depends on RPM. At low RPM, it starts at 25% throttle. At high, 40%.

https://www.miataturbo.net/attachmen...1&d=1412783762

Here is, what mine looks like from my last long log:

https://www.miataturbo.net/attachmen...ine=1412837351

I take it this is with your existing setting in post 8?
You get a step increase in boost at 20% throttle. That's terrible for driveability.
Can you make a new log with EBC disabled?
And can you make the dots bigger? The colors are hard to see on individual dots.

Will do some log with wastegate only and try to get a better screenshot, though I don't know if I can make the dots bigger in MLV...

I will be installing my electronic boost controller soon but in the mean time I turned on the gear detecting and from the logs I've checked it's pretty much spot on while driving.

O.K. here are the new scatter plots:

Wastegate pressure only:
https://www.miataturbo.net/attachmen...ine=1413357330

And here is the EBC one with my changed boost target table:
https://www.miataturbo.net/attachmen...ine=1413357330

This is the new boost target table:
https://www.miataturbo.net/attachmen...ine=1413357330

@Jason: sorry, there is no way to change the size of the dots in MLV.