Well some of you guys may be aware of this one, but for those that havnt heard, this is going to make you chuckle.
I was asked 4 months ago or so to build an ECU for a Mk2.5 VVT engine.
Simple, I hear you say.
Well yes, pretty much, but as we got on to specifics I found out that the engine was not in a 5 and the loom would not be present. Still, nothing serious, just another kit car yeah ?
MX5 powered hovercraft!
So anywho, the ECU was built to a marine spec.. aka properly sealed (except the connector for now, while testing was being done) and the ECU sent off for installation.
Anywho, everything went well and the engine fired up on the 2nd attempt.. 1st attempt it would have if the auto leccy had listened to my instructions carefully but hey ho.. he got it right eventually, but then proceeded to melt a capacitor through the previous incorrect wiring.
I put this right and at the same time hooked up a lovely stack rev counter and got that working.. ECU back to norfolk, fitted, running! and then I was asked... would you mind tuning this thing for me?
Now the fun started.. how the hell do you put a hovercraft on the dyno ??.. how do you hit every load cell ?? Does AE matter ? Idle control ? Cue 1 very awesome and quick learning curve.
So myself and Roger(along for the giggle mostly) headed up to Norfolk with just a laptop and usb/serial lead.
This is where we met up with Gary for the first time in a snow covered farm and got a first glimpse of the beast.
So anywho.. we got on site and after some banter found out that Gary's calculations meant we needed to get 200lbs of thrust for the hovercraft to work safely and successfully. Anything more was a bonus, and the engine weight, HP and big spinny air pusher had been speced to reach 200 or there abouts... so the target then.. not 200bhp... but something to aim for.
First run we started off with about 130lbs and an engine that would not get passed 4krpm. A little adjustment to the fueling and we managed to up the power and reach 5krpm and the target of 200lbs was beaten as we hit 220lbs... never realised how much power you needed to turn a fan.
Gary at this point was looking quite impressed and pleased. We could have left it here really, but I suggested we needed to get more revs to reach the engines peak power band.
5 degrees of adjustment was made to the blades and we tried again. This time we were hitting different cells in the map, much less load for a given rpm. suddenly 5krpm was only 200lbs or there abouts, but we were able to push through the revs and reach somewhere close to 6800rpm.. Much more optimal and tuning progressed.. Some healthy fueling adjustments and a little work on the ignition timing and you could feel the attitude of the strapped down craft changing.. It start creeping and we had to tie it to a car to hold it back a bit better and we kept on tuning.
Finally I reached a point after about 2 hours where I was happy that the map was as good as it could get working out in the snow.. my feet were cold, the fueling was within 2 % of perfect all over, and the ignition timing was where the craft seemed to feel the most aggressive.. I'd not seen the gauge at this point but was happy to suggest we had a decent amount of power and a nice reliable setup.
This was when roger piped up with exactly how far passed our target we had achieved.
The gauge read to 330lbs.. our needle fell off the gauge by a lot.
Gary was in shock.. and very pleased. We discussed changing the pitch of the blades around which would alter the way the power was delivered and that he would experiment with this in the future, but for now he was happy that he had enough power to make the craft safe out at sea and that now we needed to test it out.
4 up we went off into the field.. cue several minutes of intense sideways fun in the snow. Turns out that this is the best the craft has been in all its years ( last engine was a bike engine ) and that we had really achieved everything we set out too, and then some.
Long drive home.. sleep!