Hey guys,

I went to dyno my F20C today just to make sure it's all ok. It's installed in BMW 2002 racecar body, sorry about that ;-)
It's a JDM spec engine I bought for the swap from Holland.
In dyno run rev limiter came up at 7500rpms and at that point we had no idea why, so I ended up having about 220hp at 7500rpm.
Well, couple of hours later my dyno guy figured out it must be a Japan spec speed limiter at 180km/h. Which seems to be true.

I was able to find few threads about by-passing it but they are all rather old. Most of the talk is about piggyback boxes such as Greddy speed limited cut or HKS speed limit defencer. https://www.nengun.com/hks/speed-limit-defencer
But what do those boxes actually do? Alter the speed info going to ECM by dividing pulse frequency?

I'd like to know about homebrewed solutions without spending +100€ for something pretty simple. I'm not that much into electonics that I could design it myself but it should'n be more than couple of components to achieve.

In one thread I found this very interesting reply from Chris. Has anyone tried if this works? It would be perfect.

 

Don't see why it wouldn't work as long as the signal from the dash is the "same" as what the ECU expects: same voltage levels, same pulse-shapes, just half as many pulses. Of course you also have to have the S2000 dash (or at least the electronics) in your racecar.

As chris_barry noted, in a street-driven car there might be unintended issues with ABS, EPS, etc., so in general people should be very careful if they try this. But I agree, for your racecar it sounds perfect.

 

Couldn't you just buy a USDM ECU, key, and ignition module from eBay from a wrecked one?

Its not home-brew...and it will probably cost a bit more than 100 euros...but...

 

Thanks for your replys!
I looked into diagrams and it looks that the dash output might work. It seems that it's a grounding output just as the VSS sensor. VSS might need pull-up resistor to VCC2 when disconnected from ECU.

But then I started thinking what does ECU, or ECM in Honda language, actually do with the VSS signal? Shows the speed in OBD? Enables speed limiter actuation. I can't figure out anything else.
Engine runs without car moving. So does the speed info actually have any effect in engine control or could it just be left out?
I realize it's needed for EPS, ABS etc, but I don't have any of that stuff. The dash I have and working speedo is nice but not necessary (never had one before the swap).

I guessed that someone will suggest US or Euro ECU, but I think that would bring me more and bigger issues than I have now. While the JDM engine has higher CR and more power, I would assume there's some difference in engine control too.

 

^Lol possibly also windshield wiper speed?

I for one am ready for you to just do it already and tell us what you find out!!

 

Yeah, I think I can just barely manage without connecting windshield wiper to ECU in my racecar ;-)

I think I'm gonna just try removing the signal from ECU. To test the effect I would need to go to dyno again, or to a fast enough track. I'm afraid that will have to wait until next spring since the season is pretty much over here. I'll keep on watching if someone can provide better info here but eventually I'll let you know how it ended up.
Hmmm, what's the worst that could happen if I run 190kph on jack stands...

 

An update to the issue. I tried without VSS signal but after couple of pulls to higher revs ECU went to fault mode. It limited revs to 4000 and shut off throttle completely until revs dropped to 2000. My universal OBDII-reader indicated P0412 (secondary air solenoid malfunction), which sounds a bit irrelevant and I never had such connected. After resetting ECU it worked again for couple of accelerations but not further. Anyway after reconnecting VSS it worked fine again. No long enought straight for 180kph on that track.
Next I will try the instrument panel output, pin C1. I measured with oscilloscope and found that, yes, it gives speed related frequency, but the divider is much higher than /2, something around /37 from values what I got. Well it's lower frequency anyways, let's see if it works.

 

Allright, though my investigation doesn't seem to raise a lot of interest here, I'm updating the situation. Simply, it didn't work. With lower frequency signal I'm still ending up in the same fault mode cutting my throttle response and limitting rpms. Somehow the ECU must be comparing engine rpms's with the speed information because otherwise this would be impossible. It lets me run two warm-up laps, and that's it. I was sure it would be happy getting any pulse signal
Now I'm trying to figure out a pulse divider by 2 that I could build up from off the shelf components at my work, in two days. Then I could still test it on Wednesday and sign up the first race. Not likely to happen.

 

Well I'm interested, thanks for the update.

You might want to see if a Modifry Yellow Jacket would work for you -- I think it can adjust the VSS signal by up to 50%.
https://modifry.com/index.php?route=...&product_id=61

 

Seems like the above mentioned box might very well do the trick. Negative for me though, is that it would take probably a month and double the price to get one in Finland.

But I have good news. On Sunday night I called to my collegue and friend. Monday morning he designed me a circuit, using HEF4040B binary counter + transistor output, that divides the frequency by two. I found the components on Monday, built and installed it in the evening, today went to track and bought an hour of track time - and it works! No more fault mode and there's no way in hell the ecu could know me going too fast before 360kph! So it seems like success finally, woohoo