Build

Kevin See of Redline American Muscle installing the quieter (and torquier) BBK Varitune exhaust.

As the Rockingham track has a drive by noise sensor, I was forced to change the SLP Loudmouth exhaust for the BBK Varitune exhaust, otherwise I would have been disqualified. However, apart from the uninspiringly quieter sound, the BBK also loses top end power, which would be very useful at Rockingham.

The old straight through SLP Loudmouth exhausts

The previous front towing bracket was removed to make way for the intercooler radiator when the supercharger was fitted. Therefore Redline had to fabricate new parts to fit a new towing bracket to a different location on the chassis.

Mike Thompson of Redline fabricating the new front towing bracket.

Redline always carry out a complete check of the car before every race and they found that the oil seal on the differential was leaking, so they replaced this.

Kevin See of Redline changing the differential oil seal.

Performance

I was very surprised to find that although the BBK exhaust produced less high end power, it gave considerably more low end torque. Lack of low end torque has always been the bane of the Mustang 4.6 modular engine (unlike older traditional american V8s). The Supercharger had gone some way to improving this, but now the BBK exhaust made the car much more driveable, with better acceleration coming out of low speed bends.

However, a problem developed with the clutch slipping, which became significantly worse on each lap of the track – to the point where my initial practice lap was my fastest. On the video you can hear me fighting for power as the revs rapidly rise coming out of each corner as the clutch slips.

Another new problem I experienced was significant body roll coming into the tighter bends at high speed, resulting in fighting to control the car and making a poor exit from the corner. I suspect that this was due to the front suspension ride height being raised during the investigation of the supercharger pulley rubbing on the bonnet. Hopefully this can be lowered again by an inch with no more problems. One concern is that we found that by raising the front of the car relative to the rear and making the body more level than the traditional Mustang “nose down” stance, was that understeer into tight bends was considerably reduced. I just hope the change don’t reverse this improvement.

The other problem I had was the long term issue of the brakes being ineffective on long braking from high speed. The good news is that we have now identified the cause in a non-OEM master cylinder which allows fluid to leak past its seals, particularly under sustained pressure. The plan is to replace this along with a Mustang GT500 servo which provides 30% less assistance. This should produce a firmer pedal feel and inspire more confidence.

Results

Pulling away from the line I had to feather the throttle to avoid just sitting there with clutch slip, however I got a reasoable bit of traction and my 60 foot time was comparable with other cars in my class. I changed to 2nd gear just as I entered the chicane, but couldn’t be as aggressive as I was on the first practice lap where I rode both the left and right kerbs of the tight corner.

Pulling onto the banked section I am unable to use the full potential of the Mustang – you can hear the revs rise sharply as the clutch slip and then when it gets grip I am fighting for tyre traction and cannot put the full power down until the car is pointing straight. Once the car is lined up, speed rises rapidly and the Whipple supercharger is screaming down the straight as I head towards the kink in the banking. During practice I had to brake hard at this point to avoid carrying the massive speed out of the corner and colliding with the wall on the exit (which some other competitors did, with one completely wrecking their car). However, I have now mastered the line and just lift off the throttle, getting back on it as soon as I dare. The revs now hit the limiter in 4th gear as I exit the corner down the short final straight meaning I am now doing 140mph. I have learned in the past that it is quicker to stay on the limiter rather than try and change up to 5th which will take to long on the agricultural Tremec 3650 gearbox.

I then hit the brakes as late as I can as I approach the Deene hairpin, gritting my teeth as I can feel the loss of contact with the discs, due to the inefficient seals on the master cylinder. I have judged the distance well within the limits and I hold a good line (unlike in practice when I ran over the outside kerb trying to slow the car). As I line up on the straight I gently apply power and the car responds picking up speed towards Yentwood corner. I aim for a very late apex but the car is a real handful under braking with a lot of bodyroll due to the high front suspension settings. I manhandle the car round the corner keeping within the kerbs and put the power down one – two – three – four times I try before the clutch engages and I am already onto the Chapman curve. Another three times I have to try and coax the car forward into the Pif Paf chicane. The speed builds as I come onto the Steel Straight and come into Gracelands corner. The tight bend is very difficult for the Mustang with its current suspension setup, so I run wide to turn the corner into a triangle and put the power down as soon as I can get a straight line through to the exit. Fortunately the clutch grips first time and I accelerate across the finish line with a speed trap reading similar to my competitors.

Conclusions

I did some practice on the simulator which helped a great deal with track familiarity and racing lines on the day. However, the slipping clutch and body roll made the car almost undriveable and looking at the video, the lap looks pathetically slow, particularly on the infield section. I had hoped that the fast track at Rockingham would enable me to close the performance gap on long term rivals Gordon Peters and Bill McKenna. I managed to get up to 140mph on the banking (red lining in 4th gear), but could have gone considerably faster if the clutch hadn’t been slipping. The limitations of the brakes was understood before the event and I wasn’t surprised when I had to run wide, nearly leaving the track at the hairpin at the end of the main straight as I couldn’t scrub off enough speed on my first practice lap. After that I just had to brake earlier and more gently.

Overall, despite the mechanical problems I think I did quite well to beat some credible opposition. My only concern now is the time (and cost!) it will take to get the replacement parts and have them fitted. This is likely to mean the car will miss some events which will impact my championship chances after only the first event of the season.

1st Gordon Peters Nissan 370Z 82.08secs	2nd Bill McKenna Porsche GT3 82.82secs
3rd Scott Hughes Porsche Boxster 87.78secs	4th Alex Peters Ford Mustang 90.98secs
5th Tim KIRKHAM MG ZS 180 91.37secs	6th Marc HANSON MG SV 92.69secs
7th Nick ATTRIDGE Aston Martin DB7 MC 102.60secs