Fuel overflow management

I have been hauled up on several occasions in my Westfield about fuel discharge during track days and sprint/hill climb events. This fuel overflow issues are exactly the same on the Sylva despite my previous efforts. This only happens when the tank is above half full. I fitted a Mocal valve which I thought would cure the problem as it has a dual function a) When the vacuum in the tank exceeds 0.5bar it will ingest air from outside. b) If however the tank pressure increases due to temperature effects (or sloshing) then the valve release in the other direction if that pressure exceeds 0.75bar. By this method the valve can act as a roll over valve and hopefully keep the fuel in the tank.

The problem occurs on track days when the fuel is warming up (so positive pressure) and the corners pull some g, if now the pressure release happens on a right hander then fuel is emitted momentarily till threshold of the valve closing is reached.

I have tried fitting a catch tank (fuel filter bowel) but this only delays the problem till the catch tank is overflowed. This results in dumping fuel from the catch tank onto the ground between sessions.

The answer may be quite simple, let the main tank overflow when positive pressure exists, collect the fuel and suck it back in when the fuel is used up and the pressure becomes negative.

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Brake bite

I have found the J15 as originally constructed has underwhelmed me in terms of the brake bite. In other words I am not getting the control leading up and into a hairpin in a Sprint track. I have had the need to emergency brake the  car and it did lock up the wheels fast enough but far too much pedal pressure for my liking.

The original brake design by Sylva Autokits specified HiSpec (on the front), my  brake setup is similar but uses 2 x 4 Pot Willwood midlights (on vented discs) on the front and 2 x VW Passat rears (Rally Design OEM handbrake callipers). The setup is common enough as I have something similar on my Westfield and I have no problems. I recently changed the front discs for X drilled and grooved discs similar to my Westfield. This had little improvement effect.

The master cylinders are the Sylva Autokits recommended 0.75" on the rear and 0.625" on the front with a balance bar configuration.

I decided to swap the 0.625" on to the rear callipers and fit a new 0.5" on the front. This by my calculation should increase the effectiveness by the change in the piston areas. This equates to 17% for the rear and 20% for the front.

I tried to get a Willwood part for the master cylinder but all I could get is a Rally Design copy at a reduced price. Apparently Willwood don't make them.

Only time will tell if I am on the right track. This is the third major change recently to the Sylva and I am beginning to feel I am at last getting somewhere.

The fourth and final change is to add ARB's - another winter project I think. I doubt I will get to try all this out properly before the spring. Early indications on a test day at Kames are promising. The effectiveness has improved but I still get a less than totally firm pedal. I think this may be due in some part to the pads needing time to bed in.

RD master cylinder

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Engine mounts re-design

Back in July 2013 I identified a problem with the stiff engine mounts as supplied by Sylva Autokits. It is a known problem with the Ford Sigma engine when you tune it, with a fast road cam, that will result in a resonance between 2-3000 revs. I successfully turned the right hand (offside) engine mount into a 6mm double rubber and metal sandwich with very little modification. The left had mount I was less successful with as the casting on the engine has very little surface area as it interfaces with the mount. My attempt to fit a 5mm steel plate at the bottom of the sandwich failed due to insufficient clearance with the chassis rail and the bottom of the gearbox.

After the near side failed recently I had a moment of inspiration. I decided to modify the Sylva Autokits mounting to give me adequate clearance for a full sandwich. This involved disassembling the bottom plate (next to the engine casting) with a 1mm cutting disc and removing 12mm from the fabrication and re-welding the bottom plate back on.

Failed sandwich rubber

New mount design note new base plate

Finished sandwich in place

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Throttle response

The next area of investigation was the Throttle response.  If you rev up my engine, esp when warm it currently rests at 2000rpm for a few seconds before settling back to the normal 900rpm tick over.

This has a dramatic effect on the ability of the engine to brake predictably going into a corner. In addition the Ford ECU has no feedback from the brakes so it makes it's own mind about the engine revs, emissions being the priority.

I have decided that the Idle Control Valve (ICV) is the culprit. If you pull the ICV during it's high idle the engine settles at a rate set by the butterfly end stop screw on the throttle body (usually about 500rpm). The ICV is a servo type valve controlled by the ECU, by changing the pulse width thereby modulating the current to it. By observing the waveform to the ICV on an ossiloscope it is about 150uS for a tickover of 1000rpm and increases to 300uS at 2000 rpm. By empirically adding a 33 ohm resistor you can slug the tick over response completely yet maintain a steady 1000rpm but will not surge. The down side is I suspect the emissions will be well out of order (thinking MoT in the future). I therefore decided to only add the resistor during braking. By adding a relay as follows you can force a specific idle during braking.

The down side of this modification is that  when the engine is cold the idle is well below normal when braking and can result in a stall.

An initial test drive with this mod looks extremely promising, returning drivability thru engine braking. However during a day out at Knockhill I came back with an engine that would not start properly. During subsequent troubleshooting I discovered that the ICV had failed almost completely but not badly enough once the engine was started but still displaying the erratic tick-over. Replacing the ICV with a part specifically recommended for the 1997 Puma 1.7 made a dramatic cure to the throttle response negating the need for all of the above. Lesson learned: Don't use cheap ICV's from ebay. However I have learned a lot about the ECU and it's control loop. Proper ICV's are adjusted to match the ECU for that model so you must insert the correct ICV part. Also the health of the closed loop system affects the throttle response. An air leak in the inlet or exhaust can affect the signal from the O2 sensor and therefore in turn affect the ICV setting and therefore throttle response.

Contents
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