Rear Diffuser

[spikep]

77racing said:

spikep said:

Have you got pictures of what's been done to the rear wishbones?

here you go took some finding in amongst thousands of pictures

white nearly finished 006 by flat chat, on Flickr

Thanks. After looking under an Audi R8 yesterday, I can see how that would make a difference.

[rev-erend]

Great thread ..

Suspect best results are circuit cars as stiffer strings stop air getting under the car.

[77racing]

Driver 61 seams a good reference point for fast car driving , it is track orientated as you would expect from me but none the less it contains a few useful bits and pieces for all drivers and if you are bored for an hour it's worth having a look round the site , I found one or two bits interesting. Jes i'm thinking your issue could well be suspension set up, maybe to hard on rebound on the rear ? Another question to ask is to understand what you did to change the car in the recent past before the over steer started then go back to that point again and start over slowly to see what change induced over steer if you get my drift.

this relates to over steer..............................

https://driver61.com/uni/oversteer/

Edited by 77racing on Wednesday 5th April 09:03

[rev-erend]

It could just be too much right foot too soon on corner exit.

I remember a great conversation on here a few years ago between Steve Heath who was a handy short circuit track day addict and another guy, Steve posted links of himself racing and said guy was pointing out some driving advice.

Que Steve not being happy until all realised matey was a Professional racing driver.

It's probably not well know but even pro racers have coaches.

[77racing]

well i'm certainly not a pro driver , my wallet is well and truly empty, bought my experience the hard way. Of course just because I say something don't make it true I agree. only trying to help out.

[77racing]

rev-erend said:

It could just be too much right foot too soon on corner exit.

it clearly shows over steer on corner entry on the video, but I could be wrong, no problem just my opinion.

[jesfirth]

77racing said:

Jes i'm thinking your issue could well be suspension set up, maybe to hard on rebound on the rear ? Another question to ask is to understand what you did to change the car in the recent past before the over steer started then go back to that point again and start over slowly to see what change induced over steer if you get my drift.

Edited by 77racing on Wednesday 5th April 09:03

morning perry. that video was taken in 2015 when it had a large front splitter - the car was definitely trying to kill me.. I cut the front splitter down to reduce front down force so it is better balanced now but still nervous at the rear when coming off the gas and hitting the brakes hard. I tend to set the rear shocks 2/3 clicks softer than the fronts maybe it should be slightly more or perhaps I need softer springs at the rear. I would have to check but I think I am on 725 front and 550 rear. I am interested in the way you lift off the throttle at speed. the problem with not being hard on the gas or hard on the brakes with sprinting is that either loses you time - but a spin loses a lot more!

Here are some photos of my home grown aero - not nearly as pretty as yours though. the fornt splitter extends to the underside of the fornt arches. the rear boot is a small lip and a gurney upstand. I have 77mm side skirts as well. Re the rear wishbone infills - your look smuch neater than mine!. I have 2 plates each side - both rectangular. the front one is screwed to the underside of the tub beneath the drivers seat and fills the gap between the floor and the wishbone plate. the 2nd wishbone plate extends in front of and behind the wishbone arms to create a complete flat floor. The photos don't show it properly flat as the car in on the jack so the suspension is at full stretch - it works when sat on the ground though.

[jesfirth]

for some reason the photos are not uploading - another try. what you see here is a photos of the near side rear looking forward with main plate below the wishbone and the smaller plate in front of it. they are set about5mm apart

Edited by jesfirth on Saturday 8th April 13:11

[jesfirth]

and the rear boot

[jesfirth]

perry - I found a photo of an early version of the rear diffuser - pre-blown though. This was in 2 sections one sitting either side of the exhausts - the final version had shorter exhausts with a centre plate as well.

[77racing]

jesfirth said:

and the rear boot

Morning Jes,

I firstly want to say, I most certainly am not trying to teach my grandmother to suck eggs if you under stand that old saying. I fully understand that you are a brilliant driver as seen in many of your video's and your results speak volumes. Any way moving on.

I have had a few thoughts about stuff. Your rear spring rate in relation to the front sounds about right to me. (From memory I have 1200 front 850 rear on mine) but i'm running much stronger aero than you which explains the high ish numbers for me. A standard race Tuscan no aero runs 550/600 rear 800 front, no rear anti roll bar. I don't run anti roll bar on the rear either .I am wondering about the rebound side of the shocks. Are you running an adjustable shock that you can take out some rear rebound just in case the rebound is to strong and returning with a shock. in extreme you would feel or hear shock locking out so to speak, that could throw car off balance once you unload rear under engine braking or using the pedal. I like the term "use the throttle as a wet sponge" not an on off switch. So I have to say the recognised way to initiate the braking faze into a corner is roll off the throttle and squeeze on the brakes till full on. Having had to think hard how to explain what I do I recon I do it right as it works for me but it is slightly different to what is considered to be the correct way. Coming up to the braking zone I left foot tap the brake pedal to get the pads up against the disc then I come off the throttle fair quick but not dump it off then I push on brake 25% get the weight transferring to the front then push 100% . Do you think you are trail braking a little as you turn in ? I ask as I do that for instance into Quarry at Combe to get the rotation going into the slight entry left as the bumps into there unsettle my car too much without some trail brake. If you are trail braking to hard it will send you into snap over steer. I maybe have 5% pressure on as I turn in but mostly my braking is done before turn in.

Looking at your rear boot as above and the front splitter pictures, I do have a few thoughts that might interest you. Firstly would your regs allow you to extend the boot ramp and gurney over the rear arches. you could still have it so that the ramp is part of the boot lid over hanging the rear arch if you get my meaning thus extending the gurney and ramp by another7" either side, that might/probably will, put on more rear force.

You are spilling air off the sides of your front splitter by not having end plates that will keep the air on the front of the splitter and make it much more efficient . I happen to have my front splitter off at the moment in my garden as I am at Combe in the GT race next weekend so have taken some pictures to help us understand what I am talking about. This is my front splitter as I use now. The "ski jump" on either side I hope helps to direct air up and over past the front wheel arch ( less drag) by stopping air entering the wheel arch.


DSC_0733 by flat chat, on Flickr

DSC_0734 by flat chat, on Flickr

DSC_0735 by flat chat, on Flickr

DSC_0736 by flat chat, on Flickr

OK now I need you to have a very very open mind on this next thing. I have been thinking about how you can get a lot more rear down force on the griff with out changing the silhouette of the car there by staying with in your series regs. This will sound way out of the ball park but just have a think about what i'm about to suggest as I can seeit in my minds eye and how it would work.

Here you have it.................Put a rear wing in the boot.................................................................. Ok stop laughing now, i'm been serious .Put a standard boot lid back on and put a row of knacker ducts or one long scoop vent duct like the 70's custom car in the boot lid to feed air into the boot. then mount a rear twin element wing cut to size onto the floor of the boot. increase the size of the rear number plate and open that up to get the air out . you could even mount a fan to suck extra air into wing . Stranger idea's have worked in the past. Just think of the "FAN" car that Ken Tyrell ran for a race until they banned it for been too quick for every one else that was in the 80's I think way out there for it's time.

[jesfirth]

perry thanks - lots of useful advice it is all very much appreciated - we can all learn and I am far from perfect - if we were better I guess we would be driving as a professional not spending our own money on it.

I see what you mean on front splitter wings reducing airflow into the front arches. I will try that - thanks.

Your idea on the wing in the boot is barking mad but I love it - you could have something there but sadly there are 2 problems.

the first is that i drive to and from the events complete with a full tool kit, stuff for the day a tent for my gear, chairs changes of clothes, fuel cans etc etc so the boot and car is always full!

I suspect regardless of the silhouette rule that steve would take a dim view of it. I guess our real issue in the speed champs is that if one person does something and it gives them an advantage then to keep up so does everyone else - I know that's racing and we all have decent shocks, brakes, corner weighted cars etc etc but it is supposed to be entry level motor sport to keep the cost down and so that people can use "standard" road cars. some of us have just taken a perfectly good road car and ruined it. to quote one passer by at an event last year "jesus jes I saw that car in 2010 and it was lovely what you have done to it" beauty is clearly in the eye of the beholder.

when are you guys next out to play - if its local to me I might try and come along to watch.

[Matthew Poxon]

Regarding the silhouette rule I wonder if you would get away with a little lip spoiler like Andy Race had on his Monster Griff?

I know Andy said it actually helped out more than you would initially think. You can see the affect it has in the below photo.

[Matthew Poxon]

Precat said:

I ran the rear SC power rear diffuser on its own for a few years and although it improved rear end grip and stability on long fast bends, the down side was the front end felt light and unstable in a straight line. This led to the fitment of my home made front splitter which works by counteracting the high pressure area between the forward leaning radiator and the ground. Now that high pressure area is between the radiator and the top side of the splitter resulting in a downward force on the front end of the car. The difference is amazing and the car feels a lot more balanced and stable above 90mph when compared to how it was without the aero aids. Tested on tracks and in Germany.

I never noticed the cheeky front splitter on yours, very nice. I did notice the lack of driving lights, I also noted you have properly reprofiled the nose intake to get rid of the light pod recesses looks really good.

[77racing]

Matthew Poxon said:

Regarding the silhouette rule I wonder if you would get away with a little lip spoiler like Andy Race had on his Monster Griff?

I know Andy said it actually helped out more than you would initially think. You can see the affect it has in the below photo.

Hi Matthew,
That picture shows graphically what you don't want from a rear spoiler. Clearly shown is all that air sticking to the back of the car which is massive drag holding the car back.