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Discussion Starter · #1 ·
I am looking at some mods to improve rear downforce at speed.

First is an underbody venturi that flattens the underside of the car (now fuel tanks are removed) and seals it to the bumper, providing a rear air dam. This increases downforce and smooths undercar airflow. Also, a lower front panel to do the same.

Next is a Cusco twin blade rear aerofoil with gurney. If I have the venturi, will I still get benefit with this, or should I stick to the standard spoiler?
 
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Discussion Starter · #2 ·
On a related note have you got the Group A wing mirrors? Supposed to improve the aerodynamics quite a bit by reducing the front cross sectional area.
As for downforce at the rear then you probably need a better front splitter (lower) so less air goes under the car. Any air that does go under should exit out the back as fast as possible and as you say that means to smooth the airflow under the car. The faster the airflow under the car the more overall downforce it will create (rather the less lift to be totally correct). I think the standard rear wing is not too bad a design although there is a lot of it, any increase in downforce by a rear wing will also mean an increase in drag so you have to play one off against the other. I reckon you should sort the underside first and see what difference it makes and then adjust/renew the rear wing to suit.

Don't forget to tape up all the panel gaps if you are really serious ;)
 
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Discussion Starter · #3 ·
Tony

My favourite subject, aerodynamics! Much of what HH6 says is spot on. As mentioned many moons ago, the more you prevent air getting under the car, the better the downforce will be. Why do I use ? Because I doubt you would go as far as to actually create downforce but that you would only reduce lift. This is because to create downforce you would have to run a front splitter so low that it would not be practical. In addition, you would need a very special underbody, particularly at the rear to create a low pressure zone!

Back in the early 80's, German saloon car racing (cannot remember class) used to have these amazining turbo Capris with front splitters that not only ran literally about 75mm off the ground. They also had this big flat bottom edge that went out forwards of the car. The lines they drove were interesting because they couldn't go over the rumble strips. In addition, these cars looked different from the rear because they brought the undertray up to meet the rear valance but rather than leaving the valance as a dam, they remodeled the back to remove it!

Don't get me wrong. I would tidy up the bottom of the car and this should give you a difference. I would also change the wingAlthough I have only seen pictures and no dimensions, I would be very suprised if it didn't make a significant contribution to the aerodynamics, both in terms of downforce but also reduced drag. From the pictures I suspect that it would noticably tidy up airflow around the back of the car.
 
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Discussion Starter · #4 ·
On my old car (corsa gsi) my front bumper was only around 80mm off the road , i dident see any notacible benifits except being mashed around by the lack of suspention travel :) :) :)
 
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Discussion Starter · #5 ·
Speaking of downforce what was that motor that had fans in the front to suck it onto the road? I remember seeing it on the TV ages ago and reading about it previously, I think it was a 60'/70's UK car (MG, Jag or something). It may have run in a race series but my memory is a bit fuzzy.

I've got one,
You can't polish a turd :D
 
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Discussion Starter · #6 ·
Original Post:
Speaking of downforce what was that motor that had fans in the front to suck it onto the road? I remember seeing it on the TV ages ago and reading about it previously, I think it was a 60'/70's UK car (MG, Jag or something). It may have run in a race series but my memory is a bit fuzzy.
Not sure about MG or Jag, but Gordon Murray bunged a couple of downforce fans on the McLaren F1 in the 90s. Didn't he also pioneer it on Formula One cars in the 70s/80s?

Ian.
 
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Discussion Starter · #7 ·
If you remember Tony I was the first to suggest to you the route you are now taking,as far as the front splitter is concerned,as your car is for track use only ,Simons reasoning is'nt relevant.You can take it as low as is possible,remember I suggested run the car as low and as stiff as you can,fit an undertray and rear spoiler with gurney,DTM is the way to go.

The advantage you have is you don't have to follow regs,you can go as far as you wish.

GOOD LUCK
 
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Discussion Starter · #8 ·
yeh, wazzup, I remember :D

I have the extreme front skirt, which is more aggressive - think I will try to fit universal dtm corner spliiters and ears

the sides are quite low now too.
rear underbody venturi is a must I think

Just ordered the Cusco twin blade rear spoiler :D


yum yum yum!
 
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Discussion Starter · #9 ·
Make sure to brace the front spoiler because it deforms quite a bit at high speed. You can feel the difference the bracing makes.
The 2 wing type spoilers are more difficult to tune vs the single wing.
I have found that the base and the arms holding them are usually not stiff enough and they start to bend or flex.
The loss of power thru running 2 wings is not worth the additional downforce achieved.
Also if you are running with panels under the engine make sure that the engine will have somewhere to ventthe additional heat that is built up because of a lack of airflow.

Robert VanLane
TakeTomboRacing
 
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Discussion Starter · #11 ·
What u need is a big hoover under the car just like the Mclaren F1. Dont think a dyson will be sufficient though.....shame ;):)
 
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Discussion Starter · #13 ·
I rivet the bumper to the body and then use half inch wide steel bars and then screw them to the frame in a W shape. Rivets are pretty permanent and make a mess when the bumper is ripped off. Use removable Nutserts or whatchmacallits (clevits , dcuz can`t remember what you call them).
The cheapest way to improve the front spoiler is to use the stuff that is used on overfenders for 4wd trucks. It is usually black rubber 12-15cm wide and comes in rolls of 5m or so. It will bend and absorb blows better then a lower lip spoiler will. Get the type with the wire in the lip , it`s rubber but still quite stiff.
If you are going to race the car I would keep the bumper stock because you will spend alot of money replacing them. I try to keep my car as stock as possible , because then I can go to any scrapyard and pick up a stock bumper (well not any scrapyard but it will be easier then getting XYZ bumper).
There seem to be so many things that jump out and attack my car on courses . If I spin off and run into the side and have to back out and rip my bumper of in the process , I don`t worry because it is not so expensive to replace.
I just have to go home and tell the wife . Ooooooooooh that is painful and expensive.

Robert VanLane
 
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Discussion Starter · #15 ·
Blade,

don't forget the cooling aspect. not just of the engine but of the whole drive train if you fit a full under body kit that covers the gear box, centre diff and rear axle.

Personally i'd try to run with as low a front splitter as possible. That way there will be so little air going under the car that a venturi won't be worth it. I seem to remember some magazine fitting a splitter that was braced using screw fittings. These could then be screwed in and out to adjust the angle of attack and road clearance. This might allow you to drive on the road and still have low clearance for race days. You need to balance out front and rear downforce. Its easy to get the rear with a wing, front is more difficult. get them out of kilter and the handling will be skewed at speed.

The main thing on the underside is to make sure it is smooth particularly if you have removed the fuel tank. You don't want to leave a massive hole for the air to get trapped in.
 
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Discussion Starter · #16 ·
The original fan sucker cars were the Can Am Chaparall cars circa 1970. I believe they won a handful of races before being banned. Idea resurrected by Gordon Murray with the Brabham fan car.
 
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Discussion Starter · #17 ·
The Brabham fan car is in the Donnington Museum as is the other F1 idea of fitting brushes all round the the front of the car to prevent any air going under the car. The regs had to be changed b4 they could ban this idea.

Jeremy
 
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Discussion Starter · #18 ·
On a similar vein to my stupid questions some time ago:-

I remember in Chemistry at school you could create a suction effect by running water through a hose with a T piece attached - this would create suction at the exposed end of the T piece - I hope I am makink sense here! would the same principles apply if air was passed through the hose at high speed? If so could this principle be used suck the car onto the track?
 
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Discussion Starter · #19 ·
I checked with my sponsor about your car.
His suggestion was to go with a piece of aluminum under the front bumper and another on top of the radiator. The biggest problem with street cars on race courses is that they overheat.
The aluminum under the car shouldn`t go pass the frame and should screw to the spoiler to stiffen it.
The reason for the two pieces of aluminum is to focus the air to go thru the radiator.
He suggested taping around the radiator so that no air can go around the radiator , only thru it.
He showed me some front spoilers for racing and some for looks. The difference was the racing ones focussed the air to go into the radiator and IC much better then the sports type. Lowering the front spoilers helps but he was not too excited about the Venturi on street/track cars because it will quickly get bent up. He said the rear stock spoiler is better then most of the aluminum types , stiffer. There are some good ones he said but they tend to be mostly for looks . And the best investment is too reduce weight , especially in the frontend.

Robert VanLane
 
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