JPSC Forum

Has anyone fitted a rear diffuser to a live axle Phoenix/Fury (or Striker) and did it make any difference. I can't help thinking a enclosed rear would help the aero of the car at high speed which, with a flat floor in the engine bay, would help reduce drag.

Thoughts?

I have a flat diffuser on my car and also on my last one. Both cars were not live axle but i do think it made a difference on my old car, not just on straights but also when thrown into a corner for me it just felt more planted. Maybe its all in the mind but it did work for me.
I do not see why your car would be any different as all mine did was give me a flat floor to the end of the car,it did not seal the backend of the car in like you would need to do for a full shaped diffuser. You also have to be carefull with a sealed diffuser in that you do not get an air pocket in the rear bodywork.

On my old car l had a 7 degree angle upswept from below the diff to the rear body, i had some 20mm spacers from the body to the diffuser so that the air did not get traped in

When a friend of mine fitted an Elise rear diffuser to his Westy , it sucked the rear down so much that he had to modify the rear arches because the Tyres melted on them It was virtually flat till 18 ins from the rear then tipped up about 6ins plus flared out with 4ins vanes . I've been in his car on track which could be thrown into really tight corners at 100 plus mph but then it did have 5lts of TVR engine highly tuned under the bonnet . The most hilarious fun Ive ever had in any car

That will be a yes then Rob

jeffw wrote:That will be a yes then Rob

Yes would have been the short answer but I thought you may recognise my description of the car ----- at Odiham he was in your class and had a bonnet looking like a Union Jack
I considered doing it but am just too lazy to remove it all every time I want to check underneath for any problems ( which I do before every event I go to)

I've got a diffuser. Been on since I built it so can't say whether it improved it or not but the theory is sound so it should be doing something. It's flat floored, apart from the sump sticking through and a few NACA ducts feeding air to my charging regulator and diff. The diffuser turns up from the diff cage and protrudes out the back 30mm. It's got pillars between the back and the bodywork to givea 2-3" gap that air can escape from the tunnel.
I did notice a big difference when I put corner splitters on my bonnet though, both to how planted it felt at high speed and front grip through higher speed corners.

Got any pictures Adi ?

Not got any taken to show them specifically, but they can be seen in these...

I would guess the reason for more stability once you'd put the front splitters on was due to the rear undertray removing any static rake you may have had , so at high speed it would balance out. .

Possibly, but i'd be loath to claim that much rear downforce without evidence and I'm not convinced the mountings would handle it. I think most of it is reduced front lift, as I believe the shape of the bonnet forces/allows air over the front wheels creating lift.The splitters reduce that. Before at high speed on motorways if you hit a bump it took a bit for the front to settle down; Now it plants itself back down instantly. It's fairly stable right through 120+ then gets a bit light beyond that but not enough to worry. I was also getting a bit of understeer in high speed corners both on entry and exit and thats mostly gone now... but it might be me using my right foot more.

Extending the fins the full length to the front would improve drag by reducing the air spilling out the sides. It'd be a pain to do and they'd regularly get bent though.