Rolling Road

Rolling Road Session

The “Westfield World” tells you, that once  having completed the construction of your car and successfully passed SVA you will need a session on a rolling road, with an expert tuner, to dynamically set up the carburetion or fuel injection of your car. It’s true; our car had only rudimentary tuning by us, to balance the carbs and set them up so that the engine ran, and passed the SVA emissions test.    On the morning of SVA, once on the open road,  we discovered our car had a massive flat spot at 2000 / 2500 rpm. Beyond that it accelerated well with plenty of power at the top end.  We spent a little while after SVA trying to diagnose the problem. After some road testing, we were convinced the carburetors needed re-jetting and tuning on a rolling road. 

Our 2.0 l. Zetec was fitted with the Webcon Zetec Performance kit. 3D mapped ignition system and 2 x DCOE45 Carbs. We did some checking using Dave Andrews, Jetting program, Westfield’s recommended Jets (courtesy of Chris Masters), a standard Weber DCOE45 and the Webcon performance kit. The table below shows the comparisons

Jetting Comparison

Dave Andrews Jetting Program

Westfield

Weber

 

Performance

Flexibility

Recommended

Standard

Zetec Performance Kit  (Our Car)

Model

DCOE45

DCOE40 -45

DCOE 45

DCOE45

 

DCOE45

 

Part Number

19600.???

19600.???

19600.???

19600.060

19600.200

Main Venturi (Chokes)

38

36

34

36

40

Aux Venturi

4.5

4.5

 

4.5

4.5

Main Jet

155

145

120

145

150

Emulsion Tube

F9/F16/F2

F9/F16/F2

F16

F16

F4

Air Corrector Jet

190

180

125

155

155

Idle Jet

50F9

50F9

65F8

55F8

50F8

Pump Jet

40

40

50

45

45

Pump Bleed

 

 

45

40

40

Needle Valve

 

 

 

200

200

Float Level

 

 

 

 

12

ß                        Idle Air Jets                        à

Weaker                   Normal                     Richer

F3 F1 F7 F5 F2-F4 F13 F8-F11-F14 F9 F12 F6

Idle air jets  in common use, weak to rich: F2 F8 F9 F6

Armed with this data we booked a rolling road session with Ray West at Thruxton.

Andrew called in with the Westfield just after 8:00 a.m. We set off in convoy, with me leading, I took the shortest route through Andover to the A303. Thruxton is just 2 junctions down the road from Andover. Andrew took over at this point because he had been to West Tuning before.  We arrived at about 8:40 a.m.  Outside was an Alfa Romeo Giulia Spyder and inside a Fisher Fury. Andrew had indicated that at the back of the workshop was an engine clean room completer with Dyno and this could be seen through the glass panel in the back wall.  Ray wasn't there, but Colin was expecting us.  Ray West  turned up shortly and we explained about the specification of the car, the Webcon performance kit and the flat spot. We showed Ray the table of jetting (above)  to give him a basis from which to work, but it was clear he would use his own judgment based on testing the car and then see how to get the best performance.   We showed Ray where the ECU was mounted and how to hinge it down to get access to it.  Ray wasn't ready to start on the car straight away, he indicated probably about 11:00 am, so we took ourselves off for breakfast at the nearest Little Chef. With a couple of hours to kill we found ourselves heading for the Army Aviation Museum at Middle Wallop. We spent a thoroughly enjoyable 2hrs browsing the museum. Well worth a visit if you are in the area.

We returned to Thruxton and West Tuning at around 12:30. Ray was just finishing off. I asked him how it was going, "Not too well was the reply". I can’t eliminate the flat spot entirely without it being much too rich".  He had achieved a good compromise. He had tried several combinations of jets and emulsion tubes and settled on pretty well back at the start point except for changing the idle jets to 65F8. The originals were much too weak.  65F8 idle jets are the ones recommended by Westfield. He was of the opinion that the cure would be to replace the “chokes” for weaker ones. If this was a racecar tuned for performance he would have been happy.  During this discussion Ray was complimentary about the car; Saying “that they see all sorts but ours was one of the nicer ones”.   Once again we have received a seal of approval from the experts, which makes us feel good. 

The printouts from the tuning session are shown above. The flat spot can still be seen at around 2000 rpm.  However Ray said it was much worse before changing the idle jets. The peak power output was 168.6 Bhp at 6224 revs. Webcon data claims 165 Bhp, Peak torque was 154 lb ft at 5017 rpm. The effect of weakening the chokes would be to reduce the power output by some 10 -12 Bhp. Ray spelt it out; on carbs, we had a choice performance or flexibility and we would always have to compromise.  Weaker “chokes” are, not common amongst racing engines, and if they were, they would usually bore them out to a larger size. So Ray did not have any we could try.

With that, Ray took the car out for a test drive - minus bonnet. On his return he said that the flat spot was improved but present momentarily at 2500 rpm in 5th gear. 

Ray invited us to road test the car - still minus the bonnet, to see what we thought. The difference was obvious immediately. Most of the popping and banging on overrun had gone. There was a smooth pick up in all gears below 5th. the car would pull away in 2nd from standing still. The flat spot was still there but nothing compared to before Ray tuned it.   Whilst Ray was doing his test drive we had formulated a strategy to obtain some “36” chokes and get Ray to re-tune it. Having driven the car, we changed strategy, to driving the car for a while to assess the performance. and revisit the tuning in the winter. Do we sacrifice 10-12 bhp for the sake of a minor flat spot?  Ray also said that the weaker chokes would probably bring the torque lower down the curve.  Ray pronounced the car 95% fixed and we agreed.

We were impressed with Ray who has run cars in the German Touring car Championship but is taking a sabbatical this year. He does a lot of work for Swindon Racing Engines. In the garage was another touring car and a Lotus (3.6ltr) Carlton. The company Volkswagen Van, a West Tuned, 150 Bhp Turbo diesel.   Ray charges  £35 per hour and we considered our 3 hours well spent.   We left happy with the rolling road experience and the improved performance of the car.

 

We rounded off the day by dropping in on Thruxton circuit, next door. Ian Taylor Racing were holding one of their corporate touch and try days or experience track driving day.  The opportunity to drive a selection of a Formula First single seater, MGF, Porsche Boxster, Ferrari 355, Lotus Elise.  Nothing much inspiring going on we made our way back to the Little Chef for coffee. Following behind Andrew, it was clear the car was performing much better; just by the way that Andrew was driving.  After coffee I came home and left Andrew to enjoy of driving the car back to Thatcham.