THSCC Forums

I started this discussion here

http://thscc.com/forum/viewtopic.php?f=23&t=14022&start=45

after the April HPDE @ VIR.

For those that don't know, the Gen1 Mazda6 (like mine) ran in the Speed World Challenge Series. Tri-Point Motorsports fielded two cars with factory support. I assumed they figured out a way to get the cars past the 120mph speed limiter. I called Mazdaspeed Motorsports last week to see what they could tell me. They said I really needed to talk to Mike the ECU guru, but he was at Laguna Seca for the week (tough job).

I talked to Mike this morning explaining what I had and what I was doing. He seems very willing to help. He said, as he recalled they had done it without a re-flash back when they were racing the Gen1s. Said he could dig up the details and call me back in a few hours. In the meantime he requested pics of the car and youtube links from VIR. Sent!

Just got off the phone with him again. He explained the VSS came from the ABS system which also controlled the TCS and brake bias (I already figured this out). He said they were never able to get it to work thru changes to the PCM (that's what Mazda calls the ECU). Whenever they eliminated the speed limiter, they would lose brake bias too (I experienced the same thing). Their solution was to run the ABS power thru a normally-closed, momentary-contact pushbutton on the steering wheel. As the car approached 110mph, the driver would press the button, the speedo would drop to zero, the ABS & TCS lights would come on, but the car would continue accelerating to 140mph. At the end of the straight the driver would release the button, the ABS/TCS lights would go out and the brake bias would work.

SERIOUSLY!? Are you kidding me? This sounds like something I would do, not a pro team with factory backing!

He said later they had the idea of placing a switch under the throttle pedal so the ABS circuit would open at WOT (this sounds a little better). They never did it because the drivers got used to it on the wheel.

I still think Ricky's idea of removing every other ABS tooth is better.

So what do you think?
Cash

_________________
09 Bullitt - DD
11 Fusion - Wife's DD
03 Mazda6 - Track car
00 PSD Excursion - Tow rig
67 Firebird - Don't you still own your 1st car?
61 F100 - Dad's truck
90 Moto Guzzi Calif III - Tourer
00 Cagiva - Adventure bike
00 DRZ400 - Woods bike

So, the ABS module is sending a message with speed information to the PCM that is then applying a speed limit? There isn't a dedicated signal?

Short of reprogramming the PCM another option might be to install a filter on the can-bus between the abs and pcm module. You would need some type of sniffer to figure out the address and packet layout. Theoretically you could take any incoming message from the abs computer that is broadcast for the pcm and limit the speed data to less than 120mph. Leave all the other CAN traffic alone. Of course, this would take a bit of specialized work.

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2001 Honda S2000 - SOLD
2012 Boss 302
2003 BMW 330i

I think putting the switch under the pedal might be the most practical solution to this one. I'd also put one under the brake that closed the circuit no matter what the throttle is doing just in case you end up in a stuck pedal situation. Maybe just tie a relay in with the brake lights.

You should mount the button on the steering wheel but label it BOOST or NOS.

Really! As if MazdaSpeed doesn't know how to recode their own ECU, err PCM?

('tho I like their ghetto solution... "above 110mph, who needs ABS")

I think this is the elegant solution, but as noted it would take some specialized CAN knowledge and work.

Other than the above idea, this is what came to mind...

I am not an ABS expert, but I assume they use some type of hall effect sensor with a toothed wheel on each hub. First option is to intercept the signal off each wheel and cap the output that is sent to the ABS ECU to show the car not going any faster than 120 MPH. Basically read in the sensor pulses and create an adjusted output. Does the ABS ECU use averaged data from all wheels, or just one wheel to determine speed? Second options is similar to the first, but instead of capping the output, a threshold is set so that when the car approaches 120 MPH, you disable (via relay) the ABS ECU. So you still read the pulses and calculate speed, but you don't output a new pulse, you just turn off the ABS ECU. As the speed is reduced below second threshold the ABS ECU is turned back on. Having a threshold for off and on prevents issues when your speed hover around a single threshold. Both options would require some type of microcontroller. You would also have to have some type of master switch to defeat when not on track.

Also, if this car is dual purpose (street/track), I think there might be liability issues with having this type of modification in place even if you had a switch to turn it off/on at will. If I was to do this, I would find a way to make it easy to install at track and then remove once done. For example is there maybe a single harness that has the four speed sensors input into the ABS ECU? If so, I could see a small custom harness that could be injected at that point and then removed afterwards.

But... frankly as fun as it would be to do the above, I have to wonder if it would just be easier to do a WOT switch or a push and hold switch on the steering wheel.

Richard

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

I think at the end of the day it would be easier to put an LS swap in the mazda6

_________________
2011/2012 Autox VP
2013/2014.5 President
2013 Top Gun

2015 Fit

22R-EC => 4G63 => D16Y7 + D16Y8 => EJ255 + K24Z2 => K20Z3 + K24Z2 => K24Z2 + M54 => L15B

Transverse mount, though.

This. Definitely this.

What if you wire up a dead man switch to the brake peddle so that ABS is only active when you are on the brakes?

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9' 5" noserider

Currently AWD, that just makes the RWD conversion easier

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02 Focus SVT
STF 9

What? Cash's 6 is NOT AWD.

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Vincent Keene
'06 Ford Mustang GT (track rat)
'15 Dodge Charger R/T (yeah, it's got a HEMI!)
'07 Ford Fusion SE (205,000 miles and counting)
'98 Chevy Z-24 (retired)
'93 Acura Integra (Team SWB 24HOL Car)

I say mid-engine. It may cause problems with rear seating and increase interior noise however!

Richard

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Actually mid-engine would be a good idea since the weight distribution on his 6 is 65% F/35% R (or worse).

Mid-engine FWD, though.

There you go. Be different. The engine still has to be in the back seat however.

Richard

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Sadly, that's correct - no single wire to clip.


Yeah - I think that's a bit beyond my backyard engineering skills.


Good idea.


Love it!!


Yes.


I had exactly the same idea - kind of a pulse converter - take in two pulses, output one. It would take some work, but I think this is doable.


Fortunately the car is a dedicated track car.



I like this idea too. My only concern is the constant powering-up and powering-down the ABS module - can't be good for it. Additional comments from MSMS, they said don't interrupt the main 30A line to the ABS module. There is another smaller wire that is only hot with ignition - that's the one you wanna interrupt. Apparently interrupting the main power wire causes the ABS module to reboot and the ABS can't recover fast enough to give you effective brake bias when you release the button at the end of the straight. Good tip! Glad I wasn't in the car to test that mode.


Correct the AWDs came out 3yrs latter with the Mazdaspeed6.


61/39, thank-you very much.



You're right - this is likely where I'll start. CANbus Hack V1.0

Cash

_________________
09 Bullitt - DD
11 Fusion - Wife's DD
03 Mazda6 - Track car
00 PSD Excursion - Tow rig
67 Firebird - Don't you still own your 1st car?
61 F100 - Dad's truck
90 Moto Guzzi Calif III - Tourer
00 Cagiva - Adventure bike
00 DRZ400 - Woods bike