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Not arguing. I guess my point is that RWD benefits less than other drive configurations.
One thing you may not be aware of is that on (most) turbo cars, you lose vacuum assist when on boost. You really have to push hard on the brake pedal to get any effect. It can be a little scary until you understand what's happening and how to react to it.
Great point brother! I haven't had nearly the exposure to driving the array of vehicles that you have, so when ever you write on the subject, I'm taking notes.
I never thought about the brakes getting warmed up being a good thing for instance. Never thought about the boost creating complications either.
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I drive LFB in my wife's Ford Fusion to work and back many times a week, it's an auto & FWD, but with the heavy boost on the brakes & the ultra squishy suspension and automatic transmission, it never feels like a sports car. It feels like a pancake where as my 944 is a brick of cheese. I'll take the brick of cheese every time if I can.
"Double Deck" Diffuser. Figuring out how to blend the air from above the floor tray with the air below the flat tray at the point near the beginning of the rear diffuser.
"LFB is used by many divers of rwd cars. There are some that are very good at it. There are several that race sports cars that are very good. Today LFB is even more common because of the paddle shifting cars. Real three pedal guys that are good at LFB are getting old these days.
LFB is a skill or tool that you keep to use as much as is necessary to do what you want to do. Is it a tool you like to use more than others? possibly. Too much? possibly but Like I have suggested before racing skills are like tools in a tool box. Get and learn to use them all so that when you need them you have them. Can you use some tools more than others? yes. Do you like to use some tools more than others? yes. Can you get the work done with more different tools? yes.
Bottom line LFB is a tool that can be very beneficial to know. The amount and the extent to which you use this tool can be very different than someone else. Is it right or wrong depends on if you finish the race and whether you win.
One more comment on LFB. I used to say to people, as they argued with me on how to do things, beat me and I will worry about it. Well one very good friend of mine used to use LFB a ton but he was not really beating me. He had a 72 911E so we were in very different classes. Then one day he was way faster than me. Well I learned LFB. To this day he is one of the best unknown drivers I know. He is also one of the biggest LFBers I know. He forced me to use it but I never got to the point of using it like him. It is not quite a tool I use without thought. Now back in the day I used it much more but it was more of a situation where I was having an issue and figured that a LFB at the right moment is going to help so I did it. Where as there are other things that I do with out even thinking about it.''
John, that is very interesting! I love hearing about your experiences on the track
You are one of my heros & one of the people, like a angel over my shoulder... telling me "don't upgrade to a faster car, just learn to drive the one you got".
Okay, so I have the signature "Retro grouch", but for aero dynamics I'm focusing on elite cars 2013, 14, 15, 16... because the exhaustive research is far better today than yesteryear in this department.
The diffuser should extend rearward as the longer it is, the more effective.
Noah,
I love what you are doing with the undertray and diffuser. Great stuff! Hopefully it will give you what you are hoping for. The fab skills look good too.
Regarding driving techniques, etc. You are enthusiastic and open minded. I complement you on both fronts.
Thank you for your kind words. Regarding the under tray, I noticed at this regional stage rally, basically every car had hard plastic plates bolted to the underside... is that common practise where you are?
Thank you for your kind words. Regarding the under tray, I noticed at this regional stage rally, basically every car had hard plastic plates bolted to the underside... is that common practise where you are?
UHMW (or similar) plastic plates/panels are frequently used to protect suspension, fuel tanks, fuel/brake lines and other "less critical" components. They are usually used to deflect rocks and debris from damaging lines, hoses, fasteners, pivots, etc. Attachment is usually less sophisticated and not as critical as engine protection. It's not uncommon for zip-ties to be used to hold this protection in place.
Aluminum or steel plates are the usual choice for engine/sump protection. A rigid structure with ease of removal/installation are the primary criteria for these plates.
Have had the car out 3 times with the flat bottom. First with no rear diffuser. Did not find it settling. Very disappointing really.Then with my simple 2 rectangular partial diffuser and found it stabilized the car. Then needed to address the large cavity in the left rear quadrant under the floor near the muffler. The factory used a large steel heat shield and large muffler, but I removed the heat shield & run a small Dansk Sport muffler (fart box) for the last 2+ years. This leaves a big cavity that would allow air to either settle (static) or swirl and create turbulence - both which are not good. I now suspect the oem heat shield/big muffler helped negate the swirling or other by-products of under body air, but they are gone and with this new under tray I need to deal with the air above and around the car, but also the air above the tray and below the tray.
The present focus is to blend the air above the tray with the air below and then eventually blend BOTH with the air behind the car. The transaxle in the rear and the torsion bar and exhaust and the fuel tank makes for VERY VERY "dirty" air. So, the priority last night was to somehow guide the dirty air into the diffuser... but there's very little room!
Fortunately, Wilson the unstoppable has a "spare wheel well delete" (flat bottom) which is used to mount the 2 rectangular partial diffuser, but there are so many shapes to contend with. The best I can do is to try to smooth the edges & guide the above tray air into the diffuser.
So I made this. Car test drive #3 was the best yet. No word of a lie-I can literally feel the car being sucked to the ground when at hiway speeds. And this is just the tip of the iceberg as they say. Much more to do. This is a powerful tool... the underbelly of a sportscar is underestimated by many, yet holds the key for aero improvement with less drag then the topical downforce solutions.
I am for the first time in years running out of aluminum, otherwise I'd try to make the main diffuser body out of 1 large panel, then add the fences and strakes, but I'll be lucky to have enough supply to finish this job with the scraps that remain in Wilson's Garage.
This piece will connect the under tray to the 2 rectangular partial diffuser. It spans the ENTIRE width of the body in an effort to streamline the problematic disruption to the air caused by the tires compressing the air as the vehicle goes forward.
Notice the cut outs for the tires to keep it close as possible to the rubber.
Question:
-Is flat bottom necessary?
-What role does the diffuser play and will the diffuser work without flat under tray (just diffuser)?
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Answers in the order of the questions:
Flat bottom might not be the best. It might be second best. The first best looks like the underside of a wing. As shown on this 78 Lotus. The car literally generated huge downforce.
In fact that design was so effective that it was banned in F1, and flat bottoms were mandated. So then designers manipulate the front end and back of the cars so that it functions similar to the "ground effect" as shown on the 78 Lotus. The principles and goals remain identical, though the turbulence is probably higher & more challenging to "get right". With flat bottom you need a method of hi air pressure into the under side of the car/then squeeze that air close to the ground which lowers the air pressure and increases the velocity. We do this to generate downforce because the air over the top of the car is high pressure & with very low pressure under the car it gets sucked to the earth. (As opposed to "pushing" the car down with wings and things, this ground effect sucks it down because of pressure differential). The rear diffuser's #1 job is to extract as much air as possible out from under the car. It is part of a 3 part system: One:the method of bringing high pressure air in. Two:the method of squeezing the air close to the earth. Three: Open up/expand the underside air. The more air you can extract equals the more downforce you will have.
So, how would the 944 perform with the factory front/middle pans & oem diffuser? My guess is OKAY. Will it be as good as something like what I'm hoping to achieve? I think not. Just popping on a diffuser will align stray gases but will it suck out extra air? To answer that, I'd ask myself if the car has a good front and middle design to draw in and then squeeze the air, because a diffuser relies on those.
"Diffuser" we all call the oem porsche 944 panels on the S2 and turbo a diffuser, but I think the tail end of the car, where it lifts up as an integrated diffuser by definition; the bodies are a diffuser at the rear, but the transaxle/spare tire well/torsion bar/exhaust is such a cluster that the so-called diffuser is just trying to align the expanding gasses. So it's really a horizontal "strake".
"People who are attaching these wings or other aero aids to street legal vehicles are either using them only for decoration, or are modifying their vehicle with the intention of using it for racing. In some rare cases they are built into the design of a street legal sports car. Of course those vehicles are designed from the start to be street legal, but fully capable of competing in races right from the factory.
Many racing car manufacturers however are looking at the shape of the underside of their vehicles either to maximize downforce, or to minimize fuel consumption. The real racer will work on this area first before attaching any wings to his car.
"
-Formula1-dictionary.net
I have been thinking of these two elements.
Obviously a good car has both.
By increasing the downforce on a car it'll corner better.
By stiffening the suspension the car will corner better.
Duh!
On a street driven car, stiffening the suspension upgrade will make for a more uncomfortable ride.
By simply increasing downforce the car's comfortable ride could be retained and the centre of gravity is lowered at speed.
In a cornering situation the suspension will be less dangerous and more predictable - more reliable.
Whereas the risk with any aero aid is it can STALL. For example if you have to apply brakes to decelerate the car rapidly, then your additional downforce is drastically reduced and this will upset your balance considerable at an inopportune time, and when driving at slower speeds you loose the benefit of aero whereas the suspension upgrade will still perform.
...so I'm guessing a balance between the two is the best choice.
... just brainstorming from a guy who has yet to drive his car on a big track.
11-08-2016, 11:44 AM
