I had posted this inquiry before in the garage but I suppose I really should have posted it here...
I've a Sheridan standard wide-body that I'm having some floating issues with (no doubt due to the sbc anchor out back) and so I've decided to build a splitter in the hopes of keeping things a bit more stable.
As you can see I have a duck tail but it's useless for any kind of real downforce nor can I say I'm keen on building a wing as this car is also streeted, but I think a splitter may help.
Let's see what ya'll are building/have built!
Thanks
David
Click to view attachment

David,

I would suggest you leave it be and work on your alignment. I have run a v8/ls car with a splitter and no wing = not pretty. Chase the problem back to tweaking the rear toe - makes a huge difference. The car will be far worse if you just run a splitter of any magnitude.

Tony

Tony,
Well that surprises me.
I just had my four wheel alignment and corner balancing done by a well known shop for 914's who are associated with Summit Point Motorpark! And when I complained about my front floating in the triple digits, all the go fast guys told me I should add a splitter :-(
That said,
Rear Camber Toe
L -1.64 1/16
R -1.54 1/16
Front (best that could be achieved w/o camber plates)
L -.94 1/16
R -.65 1/16

Caster was set to 5 1/4

Corner weight
Rear 700 both
Front 480 Both.

I sometimes wonder if more weight should have gone to the front?
Or perhaps having a (stock) rear sway bar as well as a (stock) front sway bar, although I can't see where that would create float :-/

I'd have to agree that having a splitter without a substantial rear spoiler or wing seems like it would be de-stabilizing at speed. What symptoms are you seeing and when? On track, street, autox?

Scott

My front end is starting to float just above 90mph in all environments.

Splitter will help make sure it goes all the way back to the rack cover plate. This will smooth out air flow under the car. I would start with 3" past the front bumper. Anything bigger than that and it will pull the car down significantly at 100+ MPH. Which will mean brace (tension rods) tied to the chassis or you will rip the whole thing off and run it over.
If you are doing a bunch over 100 MPH GET A FRIGGIN WING.

No, my entrance to turn one will be right at 100 and on the back straight I can't imagine being over 120 (my skill level isn't high enough to go faster.)
I had planned on using braces and yes, going back about midway between the wheels.
But now I'm concerned about not having a big wing (previous posts).
Need to get with my track mechanic, someone I trust implicitly).
The recommendation from my mech was to go out 5" and test. Easier to cut material off rather than add material to something to short.

Let me put it this way...I broke by first splitter early one weekend at Road Atlanta. I then went on to set the fastest lap and speed I have ever done in a 914. I went 164.3 mph around T9 with no splitter - you do not need one. BTW: I run a 3.5" splitter reveal and have a massive rear wing - if you do try to add a splitter the 5" you are thinking is way too big.

Tony

I would add more negative toe in the rear - try .100" per side and O-toe in the front. You also have to add more - camber... I run 2.35 in the front & 2.40 in the rear.

I think given that my fronts are maxed out going to -2.40 in the rear wouldn't work. And I suspect for the same reason -.100" toe in the rear and zero in the front wouldn't work. Your numbers hinge on using camber plates so my fronts can get more negative camber, right?
Front (best that could be achieved w/o camber plates)
L negative.94 Toe 1/16
R negative .65 Toe 1/16
What's your corner weights? Mebbe I can remedy the problem with added front weight until I get camber plates?
As an aside, the numbers you're recommending are for an iron v-8, right? 2360 is my total weight.

LF 553 RF 534

LR 777 RR 758

This includes my weight with fuel...LS7 all-aluminum engine.

2622 Total

50% cross weight and 42/58

So your carrying a tad more in the front than I am...
Makes me wonder if I could find some improvement that way?

Wandering can happen for multiple reasons. I'd be surprised if a splitter is needed to fix your situation, since you don't have a large rear spoiler or a wing. A couple things I'd check before making a splitter:
- As stated by someone else in this thread, I'd add some rear toe-in. 914 rear trailing arms and their mounting points are very flexible. A little extra toe is needed to keep you from going to positive toe at the back. If you are going positive by chance, that could cause wandering.
- Have you bump steered the front suspension? Most lowered 914s need to be bump steered. When I first set up my 914 racecar, I took it to the track for a shakedown before I had time to bump steer it. It wandered ALL OVER THE PLACE at speed. Set the bump steer, and voila, problem gone.

Scott

I did add a bump steer to it. Thinking the toe in is creating most of the problem but wondering about how much I can adjust given I don't have camber plates and have the front maxed out at this point...
Not sure how much more adjustment I can go given that fact :-(
Mebbe adding a bit more weight in the front could add a lil more stability?

Tony,

Are those numbers with you in the Dr seat or empty?

Seems pretty heavy.

EDIT: NEVERMIND!

You can do what you want but you did ask for direction...I don't know nearly as much as allot of folks around here but very few have gone faster in a 914. It has taken time, trial and error to figure out what make these cars tick. Best of luck.

Tony

Andyrew - How'd you do on reading comprehension on the SAT??? JK!

T

[quote name='Andyrew' date='Sep 13 2017, 01:55 PM' post='2527217']

This includes my weight with fuel...LS7 aluminum engine.

2622 Total

50% cross weight and 42/58
[/quote]

Tony,

Are those numbers with you in the Dr seat or empty?

Seems pretty heavy.

EDIT: NEVERMIND!
[/quote]

One more suggestion...some trial and error on your part to find the happy place. Adjust the front toe to +.5 and test...the more positive you add the more stable the car will be at speed. Of course, there are downsides too but first just try to get a handle on it and then back out the toe.

Tony

Huh?
I wasn't being argumentative. Quite the opposite, but if you took it that way....(shrug).

So, can anyone else chime in? Can I go with more rear toe and zero toe in the front if I can't get much more negative camber out of my front (due to a lack of camber plates)?
I'm a bit hesitant not knowing what effect that could make (without getting what's been noted as a need for more negative front camber)

Being maxed out on camber should not influence how much toe you decide to go with, in front or in back. Zero toe in front should be fine. I use toe out personally, but my car is track only. You can try .1" toe in back. I use more than that to counter flexing, but it should be a good start. Don't worry about the camber for now. More would be better, but I don't think that's going to be the source of the wandering.

You mention above that you added bump steer. Do you mean that you added a bump steer kit? If that's what you meant, you still need to measure your bump steer to make sure it's really been minimized. It varies widely from car to car depending on ride height, tire/wheel sizes, and other factors.

In case you're not familiar, here's an article on Longacre's site about how to do it => http://www.longacreracing.com/technical-ar....aspx?item=8162. Of course, they want to sell you an expensive tool to help measure it. You can DIY it and get pretty close with string and a tape measure, or make a tool yourself similar to the one soe vendors sell if you are handy.

Re: adding weight, I would not choose that option. Your car is at a nice weight at 2360. That should not be your issue.

Scott

Thanks a bunch Scott!
I'll try setting the toe in front to zero and the rear to-.1
And yes, it was a bump steer kit. I had no idea their was a measurement or that they even came in different thickness's. The article was helpful!
Again, thanks!

Oh, and for the purposes of clarification, I wasn't thinking about actually adding weight, rather changing the corner weighting to reflect carrying a lil more weight in the front.
Currently 480/480 700/700. But I was thinking changing a lil could help.
Something like 490/490 690/690.
Not sure if I was unclear or not about weighting.
D