Poor Man's Ride Height Sensors: some (more) data

[masraum]

I would think and it seems that I've read that a bit of push is preferable at speed. Oversteer at 100+ is generally not the best feeling.

Also, what about an adjustable splitter?? or (can't remember the name) the little wings that go at either end of the front end?

I would think these observations would be what I often read about when teams have to tune the suspension for low speed stuff and then tune the aero for high speed stuff and balance the two. Not necessarily getting the front rear balance exactly even.

Originally posted by gestalt1
[B]Jack, i find this testing to be fascinating. i am amazed that the wing has such and effect on lap times considering what the measurements are showing. i would think that the wing is making the 60% rear weight bias of the 911 worse at higher speeds.

On the contrary. By adding more down force in the rear Jack is not increasing the mass which is what causes our "problems". He is increasing the traction which is like adding more rubber. More traction in the rear means the mass in the back is not able to throw it's weight around like it wants to. Especially in the 911 a bit more downforce in the front at speed may be just what the doctor ordered to make the car more stable.

[svandamme]

how does BB2's current front track spoiler look like ???

[randywebb]

I agree w/Sherwood.

Jack, have you ever taken a multivariate statistics class? I think it's time...

Also, a simple minded way to do things is to generate some X-Y plots from your data.

But I suspect the next step is already clear -- and it involves the front.

[Jack Olsen]

Originally posted by 911pcars
Solution? Introduce more front end rake and/or increase the effectiveness of front splitters, air dams and/or aero add-on bits.

That's actually the one thing I did change. I was worried that my 5.5-inch splitter height was letting too much air under the car, so I lowered it down 1.75 inches:



Although it's not an apples-to-apples comparison, it doesn't seem to have made very much of a difference.

Originally posted by svandamme
ride height would also be affected by fuel tank contents,air temp , air pressure, tire temp , and resulting tire pressure...

That's a good point, and my notes include some of that stuff. But all these tests were done within 30 minutes of each other, so conditions are pretty constant.

[svandamme]

how flat is your bottom , and do you have extra rocker extensions to trap the air

ideally , that spoiler plate would just blend over with the belly pan , and be one flat bottom... till it reaches the diffuser

bit tricky with the fan in the back doing exactly the reverse of what you need. eg , blowing air under, instead of sucking it away... but you could just as well use that to get more downforce in front, it wouldn't matter what happesn in the back, if the front is what you need to improve

[Jack Olsen]

Originally posted by gestalt1
Jack, i find this testing to be fascinating. i am amazed that the wing has such and effect on lap times considering what the measurements are showing. I would think that the wing is making the 60% rear weight bias of the 911 worse at higher speeds. The splitter seems to me to be of more benefit than the wing.

Actually, I believe you want to add a disproportionate amount of downforce to the rear because of the car's weight bias. Keeping the rear end from breaking loose in high speed sweepers is where aero helps the most. Push isn't so much of an issue at those speeds.

My goal here isn't to increase downforce in absolutely equal amounts front and rear. But I'd be happy if I could increase downforce in the back without making the situation worse up the front.

I may resurrect my front wing project. Or my underbody diffuser project.

As a side note, I did a lot of searching for a street car with a front wing on it, and I couldn't find any. That wing on the Lamborghini probably isn't doing any good, but it's interesting to see that someone tried.

[svandamme]

horn grills are they used for brake cooling ? looks like you got ducts in the spoiler ? if so , consider blocking them , you got air flow going into the wheel wells, which is technically "under" the car, and you don't want positive pressure there, but vacuum...

all the little bit's help..

EDIT , forgot oilcooler... timmeah

[Don Plumley]

Would stiffer rear springs help counteract the see-saw effect and help translate more of the downforce into traction?

If you had four-way adjustable front shocks, you could stiffen low speed rebound?

[svandamme]

how about if you took 2 hoods?

1 for daily driving, regular
1 for track use


center mounted oil cooler, get air from below, dump the air above the bonnet.... 906 style....

then remove the horn grills
and make a front plate that extends from the front spoiler , to the wheel wells , could even be made to be removable

flat bottom, and as little air under the car as possible, and trapping that vacuum, should do the trick better then any amount of "wings" in the front...

[Jesset100]

[svandamme]

i'de go for the floor pan , should be pretty easy to optimize the air flow up front, no engine , tranny , exhaust , the floor pan is allready pretty flat, under the cockpit ,but not flat enoug for turbulence


if you take a big sheet of 2 mm aluminiym , and hang it under the nose , all the way to the tranny mount maybe some spacers so the whole thing hangs maybe an extra inch closer to the ground

then cut away where it interferes with the front suspension....

technically , you could probably make it so you can unbolt it again , so it wouldnt' compromise non track driving... it would complement the rear diffuser, then it would only be a matter of fabricating some ducting for the engine cooling, so it vents out backwards, instead of downwards...(unless you can change the airflow the opposite way , like Bernie Ecclestones suck fan F1 car in the old days )

in anyway ,the flat floor pan in front would not be affected by the fan in teh back, you'de get downforce right uptill the engine , behind he axle..

the weight should not be to bad, and it's down low anyway

[masraum]

Jack's already got the floor pan smoothed out.

[svandamme]

Originally posted by masraum
Jack's already got the floor pan smoothed out.

any pics of that?? i remember the diffuser thread, but haven't seen anything of that floorpan flattening work

[dougn1]

this is just a thought that my not be of use but is interesting.

increasing the front spring rate should reduce the lift......seems contrary to logic at first

[dougn1]

i shoud say it will reduce the amount of ride height change due to lift

[911pcars]

Stiffening the front spring rate would have little effect on the cantilever-effect created by the rear wing; at least that's what I'm interpreting from the posts. I think Jack realizes there's a need to balance both ends so they act harmoniously.

That means either reducing the downforce of the current rear wing and/or increase the downforce of his front end (or perhaps reduce undercar air flow to prevent front end lift).

I believe Jack has tried vehicle skirts, that in conjunction with the air tunnel experiment which, as I recall, created some engine airflow issues. If skirts around the periphery helps (I don't know), they should be made from a rubberized material (Jack used?) to increase longevity. There are too many inflexible obstacles on a track (or off-track) surface to expect a rigid, metal material to excape damage.

Sherwood

[Jack Olsen]

I previously had a flat undertray, although more recently I cut a section out for airflow for the AC. Flattening the bottom out helped reduce turbulence under the car, but there was no attention paid to the actual angle of the flat surface relative to the ground. If the big plastic sheet actually contributed anything significant to negative lift, it would have been pulled off.

My next big project is to do a more sensible aluminum undertray and diffuser. It will be removeable.

Today I'm going to get the sand bags out again and try to get some real calibration for the amounts of actual ride height change that's taking place relative to the numbers the sensors are giving me.

If I get the time, I might try another run with the side skirts in place, and also a run with a skirt/air-dam hanging down even lower in the front. I have a skirt piece that can attach to the underside of the splitter and reduce (by another inch and a half) the amount of air getting under the car.

Here are some pictures of previous aero efforts. I wish I'd had the ride height sensors back then. If I put all that stuff back on for tests now, it'll cost me another Saturday.

[svandamme]

Jack, instead of holes in the tray for the cooling air exit , how about a duct to the back

lower the diffuser a tad, and have an opening for the cooling air to come out in there, the fan would push it out anyway ,so for cooling flow , it wouldn't matter, but the cooling air would not arrive below the car (opposite of Bernie's F1 hoover) and it wouldn't upset the flow of air from the front...




think of a somewhat reverse air shroud at the bottom

[911 tweaks]

I am by no means trying to be a wise guy...however...has any thought been given to what the current NASCAR stock cars look like for instance the current Monte Carlo, etc...they have some VERY fluid looking front, side rear and allaround body mods to allow 200+mph at some tracks!! Is suggesting this a no-no in the Porsche world?
just trying to help... What may be best to know, if not already stated in thes thread, what are the tracks, places that a"911" will be driven that want these aero body mods? strip? oval? enduro? street?... all of these type of road courses will require different set ups to achieve best "overall" performance/lap times... just a thought

[porcupine911]

Jack -

i haven't followed your aero progress completely and it might be a little off-topic from your ride height experiments, but have you contemplated the use of strain gauges on the wing struts to measure drag vs lift? it might answer some of your questions regarding the rear wing's effectiveness.