Cosmo Kramer

I will never discount your progress you have made racing! I am glad you keep using the 928 platform. However I also will not discount someone that has designed and then tested a splitter in a wind tunnel and also currently holds the land speed record in a 928!

And you aren't lucky Mark, it's the Amsoil!

NoVector

We now pause for OT: Carl, it'd be great if you updated the Wikipedia 928 page with your record. It has the 1986 Bonneville run, but not yours.
We now resume to the thread already in progress...

Andre Hedrick

Any chance of a model for street like the skid plate guards?
Also is there an option for adding titanium pinch plates which are replaceable?

mark kibort

Thanks!

but, lets not confuse my critiquing of why it works, to that it works.
My thoughs here are only help him with a better design and to help keep him safe at 200mph+
Lets also not discount that windtunnel only helps with some of the factors, especially since some of the tests didnt include pressure tests on the top of the splitter , or below. I did pressure tests at the speeds carl has had in the wind tunnel. just because my way is cheap, doesnt mean it isnt as valuable. in fact, much of the stuff ive found (and i havent shared it all here ) carl hasnt. tufts, pressure guages, and soon to be movement guages, folllowing traffic, etc. all will add to the knowledge base here.
remember, wind tunnel doesnt = real road dynamics. its close, but not everything, right up to the floor of the wind tunnel not moving, but the air above it is. another factor with measureable effects , NOT detected.
also think about that moving splitter. has it been testing on the track with turbulence? or getting airborn off a hill at 100mph? what if it folds up ?

DO YOU want to be the one that tests that spliter at Watkins Glen or cal speedway on the banking going 170mph. have a car spin in front of you. send a turbulent flow of air your way, and have that think kick up? what do you think that wall will feel like? before i put my life in that "good" idea, im going to test it on the street, with a video camera and changing environments. (things a wind tunnel is useless in doing) What i might be able to provide, is a hint to Carl, to make that "trailer friendly" function, use a manual locking pin. just a thought! and im the bad guy here??

And, what if im right about the cross flow on the splitter face? the splitter will be plenty strong with the mod i suggest, get better functionalitly AND it will look better.

again, this is a forum to chat about these things!

brutus

For a number of reasons Carl's run is not an official record run it is however the fastest recorded speed for a 928 but not by all that much. If he exceeds 131 or so in two directions (backup run) to eliminate wind then he would have set a recognized record. Also would then be invited to join the red hat 200 mph club.

Carl Fausett

Yes and no.

Yes, it was not a new Bonneville Land Speed Record for BGMS (Blown Gas Modified Sports) cars, and will not be until I exceed 231 MPH twice in two consecutive runs (only FIA world record attempts go down and back)

but YES, it is an official record run of a Porsche 928, setting a new record for this marque.

I think I am saying the same thing as brutus did, just differently.

jbrob007

Guys... Would Carl's splitter be beneficial to a NON-track car? I drive mine plenty fast (at times) and havent tracked it (YET) other than autocross... which I know isnt fast enough for even a standard spoiler to have any effect ( other than deflecting orange cones before they dive under the front end

Most DONT track our cars, but if the splitter will help direct air around and not under the car at speeds approaching 90 - 100 + mph then it may have some application for the rest of us Mind you I would NEVER exceed a posted speed limit...

Carl Fausett

Makc Kibort:

does this picture help? (yes, the chin splitter is under there in this picture)

Reading some of the posts, two thoughts come to mind:

1) it would be exceedingly difficult to separate the chin splitter from car, and I am not sure you want to. True - how much of the downforce produced was splitter, and how much was car is a valid question. But as this is a 928 chin splitter, we wanted to know how much down force it makes when mounted to a 928. The combination is what was valuable to us.

2) we need to talk vocabulary here just a bit. A Chin Splitter and an Air Dam are not the same thing. Even the competition rule books define them differently.

Now, I have used a number of different air dams on the top of this chin splitter over the years (I can post pics if you want) and at the wind tunnel, I tested the chin splitter with 3 different air dam options mounted above it. And, have posted the 3 different down force numbers attained with the different air dams so the reader can make an informed decision.

Wind tunnel time is so expensive I couldn't spend a lot of time testing other air dam/splitter combo's - thats not what we were there to do. Our primary focus was lowering our Cd (Coefficient of drag) and we had way more front down force than we needed/wanted.

All I can say with some certainty is, on the 928, as we opened the air dam up to allow more air to enter the radiator opening, we lost down force and increased drag.

mark kibort

the answer is no. you will NEVER realize the benifits on the street. if you do, you are driving way to fast and more than likely will kill someone or yourself.

put it this way, I installed the splitter to cure a push in some high speed corners (80mph) , and it did work and you could feel a differnece, but even still, the differnce was small. I was still able to drive my car , stripped of any aero, on worse tires, to a lap time of only 1.2 seconds off my best time at thunderhill.

Carl Fausett

Depending on the application (Street, street/race, or track) I've seen some very nice air dams made and placed above the chin splitter.

Here are a few:

mark kibort

Ok, Carl. Hmmm, where to start.

I guess at the top. first of all. with the air dam (thats what I would call what you show in the picture) you DONT HAVE A SPLITTER. yeah yeah, i know its under the air dam, but its not a splitter anymore, its a under carrige plate now.
with the BIG air dam, flush with the front of the nose of the car, the air can still go under the car, but as it hits hthe flat plate front, it naturally goes over and to the sides and under. to what proportions, is given by the pressure differentials in those directions. in otherwords,, you need less of a splitter with that configuration than you do witha nose like the 928 has.thats why nascar can use the air dams and still get a lot of downforce vs that stock car's nose configuration.

so, nothing you posted is a surprise, right? you opened your vent, you lost downforce, increased drag. this is because the air flow is now entering the radiator area, exits under the car, adds to the lift under the car, and adds to the drag as that air exits the rear of the car. no surprise, right. the bigger the hole, the worse the drag gets and the downforce is reduced as well. you dont need a wind tunnel to know this, but you do to find out the degree that you get and lose downforce and improve drag to hit your top speed target.

it is very complicated and you need a ton of time, almost infinite, to find the resutls of all the possible permutations. you got great base lines and now you can use a simulator to determine other effects of changes you might make.

rake is very important, and my point earlier was that you probably didnt lift the rear or drop the front to see the effects on downforce front to rear. i would bet A LOT, that you would be surprised of the increaseed downforce , vs angle of dive of the car. this is why you saw a huge change in ride height at high speeds.

The problem with some of the air dams and splitters, is that you are trying to be a little too intuitive in your design. air flow is funny, in that it doesnt do the things you think it would do. your final splitter is a little off, though still very nice and effective, is the tapered air dam removes some of the effectiveness .

mark kibort

all those splitters are nice. the brackets will stop flow to the sides which is a critical element of the flow characteristics with a splitter. but a hood vent will take that air, and vent it upward to the low pressure zone in the hood area.

splitters are splitters. bigger is ususally better and so is lower.

Carl Fausett

Joel, two possible benefits for the street:

1) A chin splitter on a street car will get more air thru the radiator and bring the coolant temp down. Not at speeds under 30 MPH, but on anything above that, it helps divert more air through the radiator. This assumes you NEED to bring your temps down. If you dont, then this is not a benefit.

2) in the broader view of "benefits" if you think it looks cool. I' have seen (and now have posted) some chin splitter/air dams that look pretty good on the street. Sometimes, its an option as opposed to buying a replacement "S" chin spoiler.

Otherwise - as to down force produced, I agree with Kibort, you wont go fast enough legally to receive effective downforce in a street application.

Carl Fausett

Actually, we specifically played with ride height and rake angles in the wind tunnel a LOT. It was integral to our quest for more rear down force.

mark kibort

what did you see when the nose was dropped and the rear was lifted? should have seen a lot more downforce over all. the rear , the wing would be more effective, and up front, the nose would have a lot more downforce as well. drag should have gone up too.

The splitters do look good, i must say! seem to be a natural for the early cars.