I am looking at making my own splitter and diffuser from alloy sheet.
Couple of questions for anyone who's done the same.

Front splitter--- is it worth running it to the bulkhead to create a flat floor. If so, what about the prop tunnel as this is still open to the ground. Should I cover this also.

Rear diffuser--- I'm thinking of covering all the open area from behind the seats to just past the rear of the car. Looking underneath their is the problem of the lower wishbones. The diffuser would be flat from the leading edge then kick up at the rear lower wishbone mount . What has others done when allowing for wishbone movement.

TIA Brad.

Both are only cosmetic without a full floor.

Mind you with a full floor they're probably just cosmetic

A full floor will affect your cooling though.

Not done it but been looking in to it.

You will need a flat floor for it to work well as the idea is to balance the forces. It will be very hard to create downforce without measuring the pressures but you will be able to create less lift.

You don't say what car its for so I'll assume Fury.

The below are items which I think would work but would have to be tested to assess whether they do.

Having little deflectors in front of your front wheels will help deflect the the air away from the wheel face and would be beneficial at reducing lift.
Having a full flat floor will be beneficial, this includes covering the tunnel bottom. This should help preserve the air flow.
Having a rear diffuser start as far forward as possible would also help, the angle shouldn't be greater than 8 degrees sloping up to the back of the car. You could go steeper but you'd have to test. 8 is a maximum rule of thumb.
Having the whisbones in the air stream of the venturi won't be too much of an issue, maybe try to make them aero section if youre that bothered.

Putting side skirts on the car underside to try to trap the air might not work. As this video will tell you, listen to the German engineer
https://youtu.be/PZxC-knQmkM 2:40 in "skirts didn't work"

You wouldn't go far wrong watching a few Julian Edgar videos on youtube or reading his books (I've not read them yet) or reading some of his autospeed articles
starter for 10 https://www.autospeed.com/cms/a_113177/article
He's very much into testing and not following trends.

If you pop over to the JPSC site I did a small mod which worked for me.
https://jpsc.org.uk/forum/viewtopic.php?f=4&t=1878&hilit=fury+cooling

Without measuring something (ride height, drag, air speed, etc) you'll never know. You could argue I was using the water temp as a measure and I was happy with my results.

Best of luck

If it doesn't work youre just adding weight.

[Edited on 10/5/21 by pigeondave]

[Edited on 11/5/21 by pigeondave]

Brad
See my little build diary for my Ali/Carbon rear diffuser I made last year.

http://www.locostbuilders.co.uk/viewthread.php?tid=216560

I'm not sure if it increased the downforce, but it's made the car quieter, could be due to smoother airflow or boxing in the diff area. Cost was 27 quid and weight was 4 kg.

ETA..My lower wishbones on full droop were still above the lower chassis rails, so I was able to cover the entire rear floor area.

[Edited on 11-5-21 by Slater]

Thanks for the info fellas.

Great info Dave. all taken on board.

I think I will try a short front splitter/undertray first and see how things go.

Brad

Thanks Slater. I missed your post.

Although I enjoy working with ali. I've always felt you can't beat marine ply and GRP as it's a lot easier to work with more forgiving if it doesn't go right first time.
There's a thread just up the page about building a GRP body onto a Se7en type chassis which may be of interest.
http://www.locostbuilders.co.uk/viewthread.php?tid=218429

[Edited on 14/5/21 by pewe]