NZ Flat Bottom & Diffuser

[NZGTRA17]

Finally got around to fitting the flat bottom and diffuser to the car. Not made easy as I dont have a hoist so had to do all the work with the car on axle stands and only 18" up in the air. Got a very sore neck and arms a few times.........

I used 4mm alumalite to flat bottom the car. Attached this direct to the chassis with 5/32" ally rivets. Tried to keep all cutouts to minimum size to prevent to much "leakage" & drag.

View of flat bottom around engine bay and rear of LF wheel.


View from LH rear looking forward. Note I have left trans tunnel uncovered at this stage to promote some airflow for engine/clutch/trans cooling. May cover this in at a later date post more testing. You can see that I have also left the front "bottoming pad" on. This will disturb airflow somewhat but we have some highspeed ripple strips on my local track that we occasionally "crest" so could not afford to remove in case sump got damaged by a hit.


Diffusers are Stillen oversize Ford GT items. They are 100mm longer than a standard GT diffuser. I have designed these to be able to be fitted to the rear of the car without the need for jacking. The front edge of the diffuser mount panel slips into a receptacle attached to the chassis and then bolts on to the rear cross bar where the rear tow point is. Having this panel detachable was a must for me as otherwise getting the car on and off the trailer would be impossible without damaging the diffusers.


The diffusers maintain the standard 4" ground clearance. This means that they basically conform to std ride height. I have found that we use most of our available ground clearance at my local track so didnt want to go lower at this stage. Rear edge of diffusers is pretty much lined up with the rearmost part of the bodywork.


Rear view.



With any luck I will be track testing within the next couple of weeks. Wont have a good feel for lap time improvement for a while though as need to scrub tyres at this session. We have also made around 3 key changes at once (usual story for those on a budget......). More hp, change to 18x10"s with 285/30/18 DOT's and of course the flat bottom and diffusers.

Kel.

[wirewheel99]

Despite how it looks the RBR Exige diffuser is in line vertically w/ the rear body work.

[NZGTRA17]

Brian had previosuly asked what weight the flat bottom and diffuser added. The rear diffuser panel with the 2 diffusers mounted on it is by far the heaviest part (diffusers are a rubberised compound) and weighs approx 14lbs.

The remainder of the weight is just the flat bottom sheeting which I would estimate at no more than an additional 20lbs.

Kel.

[panozracing]

that's a nice chunk of weight. How are you going to find out if your aero additions have been more beneficial then being lighter?

[NZGTRA17]

Originally Posted by panozracing

that's a nice chunk of weight. How are you going to find out if your aero additions have been more beneficial then being lighter?

Easy Brian, we log every lap we run. The stopwatch is king as far as we are concerned. If the car is not faster (or there is another worthwhile benefit) then off it comes. We have yet to make a change that has not seen the car go faster but there will come a time when this will happen of course.

As an aside Brian, given we burn 28 gals in an endurance stint (around 180lb weight change never mind the 5lbs the driver loses........!!) a 30lb weight change is no big deal. For sprint racing yes. If the car was more settled with a full or empty tank allowing it to be pushed consistenly harder (remember we are racing up to 6 hours on DOT's) then the weight gain may perhaps be worth it for this alone.

Will let you know how it goes.

Kel.

[NZGTRA17]

Track tested the car a few days ago with new wheels, flat bottom and diffuser. After 5 laps scrubbing new tyres I immediately went 1.2 secs under my previous best lap time from our last race on the track in November (where we were runner up in the DOT class of the NZ Endurance Championship).

Car is now super stable on high speed corners but requires some adjustment now to maximise grip on mid/lower speed corners. We need to take camber out due change from 40 series to 30 series tyres so we expect to see the times come down further as we maximise lower speed corner grip via set up, and get to know the limit on high speed corners.

Could'nt be happier with the transformation of the car, so well worth the effort in my books.

Kel.

[PanozDuke]

Kel,
That is a massive improvement once you get a car to the level you had already taken it. I'm anxious to learn how it does after you do the alignment and then the race results. When is the enduro?

Mike

[NZGTRA17]

Originally Posted by PanozDuke

Kel,
That is a massive improvement once you get a car to the level you had already taken it. I'm anxious to learn how it does after you do the alignment and then the race results. When is the enduro?

Mike

Yes it is Mike. I was pretty pumped when I got out of the car thats for sure. The improvement is a result of 2 key changes though as the wider rims will also be contributing. We have only gone up from 275's to 285's but mow that we are on 18's I have fitted 10" rims so in reality we have picked up perhaps 12 - 14mm of useable tread width.

We are aligning the car this weekend then will do another track test day to make sure all is well re tyre temps, pressures and low speed handling.

Next race we are doing is on 12 May and is a 6 hour enduro. We are hoping to be outright contenders but that will depend of course on the field and how the cards fall for the front runners. There will be a number of GT3's and there are now a few cars getting NASCAR engines fitted so challenging to compete with up to 830hp on the straights albeit that DOT tyres are a bit of a leveller.

Kel.