More on the vct system

Here are a few additional graphs showing the operation of the vct system in just an on/off mode.

• Run 3 is with VVT on all the way
• Run 4 is with VVT off all the way
• Run 8 is with VVT on up to 5500 and off after, plus final tweaks on fuel and
  ignition.

What really stands out is the additional mid range that it fills, and clearly the cam is capable of making power high up the rev range (normally compramised with the mid and low down).

Will try and writ some more on this interesting subject when I get chance.

Engine set up - Does VCT work?

Friday was a big day for the Sylva J15. It was time to get the engine tuned and ready for IVA.

I have used Northampton Motorsports many times in the past, and find them nothing but perfectly professional, pleasant to deal with and talk to and most importantly...bloody good at their job. You also know that the power you end with is real and not just beefed up pub fodder.

We kicked of at around 12:30pm, and the engine was all over the place. It would not idle, and there was something not quite right...we ended up tracing the issue down to a TPS sensor not allowing one of the butterflies to close, and the bleed screws leaking. Once sorted, we had a good tick over, and the car was ready for mapping.

Now, this was always going to be an interesting one. There has been many, many threads about the function of the variable valve timing system on the st170 and puma 1.7 engine. The system used by ford is continuously variable, but the Omex 600 in the J15 will only do on/off control. The question really is, will this work?.

The answer is yes, and it worked very well. Troy at NMS, did some power runs with the VCT fully on, and with it fully off.

• With it on, the tick over and first 2000 rpm were compromised, but mid range looked good, with power trailing off beyond 6000rpm
• With it off, tick over was fine, but the mid range was low, but top end power looked good with the engine puling right up to 7200rpm.

So, with these two plots overlayed, it was very clear where to turn the vct on, and where to turn it off again. This is done via the alt function in Omex, and also you can specify the throttle load, so if your are cruising gently, you can have the vct off.

Anyway, what was the result of all of this. Headline figures were a stonking 155bhp, but decent torque in the mid. You can see the plot shows the kick at 5800rpm, where VCT is disengaged. The curve is smooth, and the engine is bog standard apart from the Throttle bodies, and exhaust. so up from the 125 hp of the puma by 30bhp. Very pleased...I took the car for a sneaky drive down the industrial estate and it felt suitably fast. The next step was the emissions ...and with the addition of the CAT, it sailed through without any further alterations to the fuel map. All in all, a great day out :-)