FWD Drag Racing boost control strategies

[NOTORIOUS VR]

Looking to get a discussion started on boost control strategies for FWD Drag cars.

It seems like there are a few mind sets on what is best and I'm sure they all have the pro's and cons.

I would like to explore a few different ways to setup boost control and gain some input from people who have a good working strategy to manage wheel spin with a VEMS that controls boost.

From what I understand that popular strategies are:

-Time based (simple)
-Wheel speed based
-Gear based
-Differential wheel speed based (referencing driven/undriven)

Of course conditions are not always the same when drag racing and the amount of traction on the pavement is always changing.  So it seems an active approach seems to be the most logical approach (differential wheel speed).

I'm thinking that setting a base wheel speed or gear based ref table, and then any trim to act upon the base refDC if there is a deviation between driven and undriven wheel speed would make for a good setup.  Or what about a spark trim to reduce power based on differential wheel speed, even as a secondary anytrim?

Does anyone have any input to this (pros/cons, what to look out for), or maybe some solid data for personal achievements and setup/tests?

Thanks!

[gunni]

So my racing experience uses wheel speeds as you mentioned.

varying amounts of spark cuts based on slip error %, this would ideally be a non linear curve to control the torque reduction.
That is possible with VEMS by having a rev limit against undriven speed.

i.e. at 50kph you would normally be at 5000rpm, but if you are at 6000rpm you have 20% slip, I´m not sure if VEMS has the ability to somehow get a non linear torque reduction, i.e at just over slip you have very little say at 5200rpm, but you don´t want twice that at 5400rpm etc. I havent looked at the anytrim controls enough to be able to say if that is possible,

I have asked VEMS to implement a 0-5v based torque reduction so that torque reduction can be done externally or via their new smart bridge box.

[MWfire]

Here is example of good boost map. Car is 4x4, but lot of power :).

Spring pressure is 1.4bar of boost, so that is reason for that high boost in 1st gear. But in first gear traction control handle to much spin.
In 2 and 3rd gear boost control handle that.

On fwd cars i use abs sensor from rear wheel for traction control.

[MWfire]

So my racing experience uses wheel speeds as you mentioned.

varying amounts of spark cuts based on slip error %, this would ideally be a non linear curve to control the torque reduction.
That is possible with VEMS by having a rev limit against undriven speed.

i.e. at 50kph you would normally be at 5000rpm, but if you are at 6000rpm you have 20% slip, I´m not sure if VEMS has the ability to somehow get a non linear torque reduction, i.e at just over slip you have very little say at 5200rpm, but you don´t want twice that at 5400rpm etc. I havent looked at the anytrim controls enough to be able to say if that is possible,

I have asked VEMS to implement a 0-5v based torque reduction so that torque reduction can be done externally or via their new smart bridge box.

with anytrim ch you can remove boost, remove spark adnvace and give spark cut depending on voltage.

[Denmark]

Here is example of good boost map. Car is 4x4, but lot of power :).

Spring pressure is 1.4bar of boost, so that is reason for that high boost in 1st gear. But in first gear traction control handle to much spin.
In 2 and 3rd gear boost control handle that.

On fwd cars i use abs sensor from rear wheel for traction control.

3bar of boost take some good internals and fuel :)

[NOTORIOUS VR]

On fwd cars i use abs sensor from rear wheel for traction control.

I've seen you mention this before (traction control w/ VEMS).

Obviously there is no official/REAL traction control algorithm inside VEMS, but I suppose you're using a combination of any trim functions to mimic it?

Could you give an example?  As the only way I could think of would be spark trim (mult), and eventually spark cut (but I would assume this is very abrupt) with reference to speed1/speed2?

[gunni]

proportional spark cut is the means by why most motorsport systems operate their traction control along with spark retard, you do need ALOT of retard to fully control traction with that alone.

[Kamuto]

On fwd cars i use abs sensor from rear wheel for traction control.

I've seen you mention this before (traction control w/ VEMS).

Obviously there is no official/REAL traction control algorithm inside VEMS, but I suppose you're using a combination of any trim functions to mimic it?

Could you give an example?  As the only way I could think of would be spark trim (mult), and eventually spark cut (but I would assume this is very abrupt) with reference to speed1/speed2?

dont forget boost trim :)

[MWfire]

On fwd cars i use abs sensor from rear wheel for traction control.

I've seen you mention this before (traction control w/ VEMS).

Obviously there is no official/REAL traction control algorithm inside VEMS, but I suppose you're using a combination of any trim functions to mimic it?

Could you give an example?  As the only way I could think of would be spark trim (mult), and eventually spark cut (but I would assume this is very abrupt) with reference to speed1/speed2?

No any trim for that.
launch rpm curve option. Works very good on rwd and fwd cars, also i use that in hillclimb races
http://www.vems.hu/manual/vemstune/help/examples/curve-launchRPM.html

Denmark: audi v6 3.0 engine. It was 80mm turbo, now for 2016. is 91mm turbo.
So far 8.49@278km/h. One of runs
https://www.youtube.com/watch?v=MfXsKDxXDu8

[NOTORIOUS VR]

No any trim for that.
launch rpm curve option. Works very good on rwd and fwd cars, also i use that in hillclimb races
http://www.vems.hu/manual/vemstune/help/examples/curve-launchRPM.html

Very cool.. Does this mean for this table to work Launch = always on and Speed input either Wheel speed 1 or 2.

As for the table setup:



Does it mean that if wheel speed exceeds any given RPM for the speed (ie 8k RPM at 40 KMH) which would indicate wheel spin, the ECU will apply the launch limiter?  If this is the case I'm curious as to why this wouldn't cause too much of a power lost? Because it is a large retard of ignition?

[MWfire]

If you configure that table good, on every wheel spin ecu will reduce power to control that wheel spin.
Here is example on my every day car, fwd normal tyres. 0.5bar of boost in first gear. That gives 60feet of 2.0-2.1s with normal tyres on normal road.
https://www.youtube.com/watch?v=XbMX2I_8Qr8
speedo is connected to rear wheel, also vems.

[NOTORIOUS VR]

If you configure that table good, on every wheel spin ecu will reduce power to control that wheel spin.

Am I right to assume the amount of power cut is always the same?  For large or small wheel spin, there is no difference in power reduction with this method?

[MWfire]

If you configure that table good, on every wheel spin ecu will reduce power to control that wheel spin.

Am I right to assume the amount of power cut is always the same?  For large or small wheel spin, there is no difference in power reduction with this method?

not the same.

[NOTORIOUS VR]

not the same.

Alright, good to know!

Thanks  :)

[RazOn]

Ok, I've played with this and it looks like it has some limitations when using the launch curve method.
The problem is caused by some kind of delay in road speed reading.

Everything seems to work good when testing at "low" rates of acceleration, but when the acceleration is very fast, the ECU sees the rise in RPM but no rise in wheel speed... causing rev limiter to kick in unnecessarily.

I noticed this while trying to set up the RPM vs speed ramps. So I don't have to do high speed runs, I changed the launch control input selector to the driven wheels sensor and put the car up on jack-stands.

I used first gear to take speed readings at idle and at 6000rpm and I plotted the points on the curve, then raised the limits as follows to allow for some "slip" and prevent false limiter engagement:
I raised the idle rpm limiter from 1000 to 2500 then extrapolated the 2'nd point to 8100 (my normal redline) and added 100rpm for safe margin. With these settings I should've had plenty "safe zone" and traction control should have never kicked in.

When accelerating slowly, I can rev all the way up to my launch rpm without hitting the limiter at all.
However, when I stepped on the throttle a little faster, the rev limiter kicked in. This means the ECU saw too much RPM at too low of speed.... something that in reality is not possible since there is a fixed mechanical connection between engine and speed sensor (sensor is on the differential).

Maybe you guys have an explanation for this.

Here's a screen shot of the log. RPM and wheel speed on 1'st row, spark cut on 2'nd row.


And here's a couple screenshots showing bad relationship between rpm and speed.