Bigpower

Well, after a year off with no track action due to a new arrival in the family and the fact i've sold the engine out of the golf, i'm now getting itchy feet again. So a new engine has been sourced and an update will follow soon.


Anyway I'm planning a few changes and toying with the idea of fitting a diffuser. The question i'm asking is, would I notice any difference in the handling, or just wasting my time?


Cheers Steve

If it is designed and fitted properly, you will notice it, yeah. Do some research on ramp angles, lengths etc and you should be laughing.

Same old thing with aero, you'll need a few bits done like front splitters, dive planes and such to get the full benefit.

Good to see you back............I missed out on a Mk2 earlier so I may be back into the fray as well.

Taken from another thread.


The downforce comes from two aspects.

Reducing the resistance of the underbody increases mass flow under the car. Given that the size of the channel is effectively fixed and we're well away from Mach number effects, the more air flows through the faster it has to go and, by Bernoulli's principle, the static pressure has to drop. Lower pressure under the car gives you the downforce.

Secondly, the upsweep of the diffuser means you're changing the momentum of the flow and giving it a vertical component. Action & reaction means air goes up = car goes down. More downforce.

With respect to the original question, 7-10 degrees is about the limit, depending on how smooth you can keep the floor all the way along the car, where your cooling air exits (hopefully not underneath), whether you have deepend/sharpened/extended sills, what rear wing angle you're running, how close it is to the back of the car and whether you run proper endplates or strakes in the diffuser.

even it it produces no down force it should reduce drag, on my pulsar the rear bumper was like a parachute, the main reason I fitted one

Plus it looks cool

I have one in the workshop that I have been meaning to fit for over a year. I bought one for Lotus Elise and modified it to fit.

Must get round to fitting it soon.

Hi Steve,

Long time no-see congratulations on the new addition!

In my experience there are greater performance gains to be had in different areas than aero.

After dabbling with a Ginetta at Donnington last month it is really apparent that vehicle ride height is paramount to making the diffuser function effectively.

To achieve anywhere close to the ride height that would begin to work the Golf would have to be very low indeed. The VW arrangement of wishbones and pick-up points move the roll centre significantly when lowered, therefore by lowing the vehicle a lot would have a very detrimental affect on handling unless spacers and new pick-up points were implemented.

The floor of a MK2 isn’t very indicative of creating a nice flat surface as the rear-beam mounts and “chassis rails” are unhelpfully large.

If it was me I’d be looking at fabricating some solid-top mounts and bottom arms to find some scope to add camber and caster. Also spacers on the rack to try and remove some of the inherit VW trademark bumpsteer before going down the aero route.

Cheers for all the advice and pointers from everyone, Its early days at the moment, but I should be making some progress soon!!