Next on the development list, is to make a custom Stainless exhast system and a rear diffuser (in time, we will also completely flat bottom the car).
Why are we looking to make a rear diffuser ?
A properly fabricated rear diffuser is like an upside down wing. It will help create downforce to give the car more grip. Whereas a wing on an airplane such as a 600 odd ton 747 gives it lift !
Before we can start all of that, we need to move the exhaust. Currently it sits too low along the length of the car, and the rear box and exit are in the way of where we want the rear diffuser to be, as you can see from the photos below. At the lowest point, we probably have 2 inches or ground clearance.
So, first step, was to commission Redmetal Fab to make us an exhaust. It will be made from Stainless steel and incorporate V Bands. These guys are real artists when it comes to their work. The specification for this exhaust was a combined effort to make something functional, yet also look like a wonderfully crafted piece.
The current exhaust on the car is made by HKS from the cat back, with a Japspeed de-cat silencer, and a generic mild steel down pipe. Both have an internal diameter of 75mm.
The rear housing on the back of the Garret 4094R turbo is also 75mm exhaust.
The current downpipe was removed.
The exhaust wrap was removed
A flexi was added in, for 2 reasons. To allow some flex in the exhaust, and also to allow for some ‘damping’. As the engine moves around a little in the bay under load and deceleration, some of this will be taken up by the flexi and take the pressure off the exhaust manifold. The downpipe was also shortened so it sat closer to the chassis of the car.
New heat wrap added. This was about 10 metres worth with such a tight wrap.
Now to start on the main exhaust section. First off, many pie cuts. This is to help give the exact angle of the exhaust we want.
Welded in to radius sections (this is for the back box).
Beautiful welding I’m sure you will agree. The whole exhaust will be completed with TIG (Tungsten Inert Gas) welding.
Some of you might be asking, why use pie cuts instead of mandrel bends ? Valid question. A Mandrel might possibly flow air a little better than custom pie cuts. Which would you rather look at ? Personally, we love the work and effort that is going in to this exhaust, like the car, it is an art form ! Also, it is easier to be more accurate on fabrication positon. (I'm not saying you cannot be accurate with mandrel bends. Without vast expensive equipment, pie cuts are a good way to be accurate easily).
New back box completed. This runs from a single 75mm and neatly branches in to twin 75mm.
The completed article. A wonderful piece of work ! You will also notice 3 x 75mm V bands. This is purely to give us the option should it be needed in the future to remove small sections, instead of the complete system.
Time for fitting
Plenty of clearance now ! We now have around 90mm ground clearance at the lowest point.
A little trim needed to the Nismo 400R Rear bumper.
There we go, popping through the rear bumper. Twin 3 inch pipes. We left the tail pipes longer than we knew they needed to be. Until we had the exhaust fully in place, we weren’t entirely sure on how long or short we wanted them.
What we were now left with on the 400R Rear bumper is a hole where the exhaust used to exit (bottom left).
Time for some fibreglass ! This is not something we have tried before. How hard can it be, in the words of Jeremy Clarkson !?
Firstly, the plasti dip needed to be removed
10 minutes, easy peasy ! All we did, was made a gentle cut with a blade to score the plasti dip, then peeled it off.
This is the area we needed to fill.
Filling a flat piece would be easy, but this was a tapered curve !
We bought a pre made sheet of fibreglass
Yes, that is tin foil, it says non stick on the packing, and yes, it is !
Time for some filler and lots of sanding.
Bit of spray paint as a mist coat. This makes the area we are working on all the same colour to allow us to see any further areas that neded work
Considering we haven’t done this before, not a bad job. Certainly some room for improvement. We’ll let it go off for a few weeks then look to address the areas to make it a perfect finish. Add some plasti dip, for the finished result.
Once it had all dried properly with a few more coats of plasti dip. Fit it back on with the newly trimmed tail pipes for the overall picture of what we have achieved.
Pretty good we think !
Has this new exhaust changed the power delivery of the car I hear you ask ?!
Time for the dyno to tell us ! We took the car back to Abbey Motorsport to find out.
The answer is yes. It has given us some more mid range torque, and a little less top end power. Less than 5% difference respectively either way. Being a track car, already with plenty of power. We would much rather even out the torque to increase the overall top end BHP, to allow for smoother power delivery.
Now we have a bench mark on the exhaust. We can start with modifying it. So the section before the rear box section is going to be changed, then we can come back on the dyno to test again.
How does the new exhaust sound ? Have a little listen and let us know.. The old exhaust was 104db based on normal track day measurements of 1 metre away, measured at a 45 degree angle. The new exhaust comes in at a mere 96db, which is great, as it gives us access to a few more tracks in the UK we can now visit. We are planning on an additional muffler on the tail pipes should we need it to take the sound lower for some of the super quiet tracks.
(Lets not mention the screamer pipe just yet, that obliterates most track day sound meters when it comes to drive by limits, so we will look at adding a silencer there too!! :) )
We are now off for a track day at the Nurburg Ring, see you soon !