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Apexcarver
Apexcarver PowerDork
1/4/18 12:11 p.m.

 

A lip like that is going to be the easiest improvement, beyond that for rear aero, you would be looking at more $$ and perhaps making your own out of fiberglass based on foam cores available in the aviation community. (CF is out of stated price range.)

as far as front, mustangs are bottom breathers, it can be done, but doubt the reward will be worth the effort.

I will warn you, I have friends running a DP miata and the aero difference (splitter and large dickbill) has been tenths in a 1800lb car.  I expect improvements to be less on a 3100lb car.

 

Tires are most CERTAINLY holding you back more than anything.  Azenis are several generations old at this point and 245 is just way too small for the car.  Problem you will run into is getting anything decent for a 17 inch wheel (I have 255/40/17 RS3V2 on 17x9 and need more).   With some work you can fit 315's all the way around (break out the fender roller, it takes some effort 275's fit no problem whatsoever, I ran them in V710's years ago).   I faced it with my car, I have the 17x9, but couldnt find the 275's I wanted in good rubber.  Down the road I will have to upgrade to 18x10 or 18x11 (11 is TIGHT custom fit) to be able to be in the tire fight.   

 

Areo is a tenth, tires will be a second or more. Even 200tw to 200tw as you are both not on the best compound and undersized.  

 

I understand the budget thing, try the ducktail, but start putting away for a set of 18x9 or 10's to fit 275+ widths in a better compound (RE11R, RS3V2, ETC...  watch for the tire tests, the differences can be big)

 

I am on a similar setup except H&R race vs super race and I dont have the PHB or rear LCA's (next items, well, when I stop being distracted building something else), what about swaybars?  I worked with Sam Strano on mine and I have a huge Addco front bar with the stock cobra rear. Its counter intuitive, but the big front bar reduces understeer by combating camber loss and made a difference for mine. 

 

 

 

rslifkin
rslifkin SuperDork
1/4/18 12:17 p.m.

Isn't the 615K+ the ZII Star Spec compound instead of the older compound in the 615K?  If so, it's not the fastest tire out there, but it's not multiple generations behind either.  I do agree that 245s are too small though.  

jj
jj HalfDork
1/4/18 1:12 p.m.

He drives a Focus RS.  I have a better tire than he does, but there is lot that car can do it seems.

jj
jj HalfDork
1/4/18 1:44 p.m.

Apexcarver, thanks for the input.  I have 18x9s with 30mm offset but I was concerned that 275s wouldn't fit at first.  This car is a bit of a hack, so I have no issues with rolling fenders.  The biggest I can get in RE-71 is 275, but the RS4 I can get a 285 with the right height.

I actually never thought of a front roll bar.  The car feels ok as is, and at 34 psi, the fronts aren't close to rolling over.  Did it help you change direction better?

I think at least for now I will try the rear spoiler to see if it helps with the high speed sections.  Also, a plain front air dam seems too easy not to try.  I can make something to wing nut to the lower half of the front bumper that sits really low and just put it on at the event.  Like the miata in this pic, but made out of plastic. 

Apexcarver
Apexcarver PowerDork
1/4/18 3:54 p.m.

Well, with an SN-95 there will never be great turn-in.  Between the weight dist and the roll axis inclination, its not in the cards.

That said, I feel like mine works pretty well. I also have an STS miata (coilovers, bars, exhaust, etc) and the mustang will never turn in like that. If you abuse corner entry it will understeer, if you approach correctly it will stick and have good balance through the turn.  The bar was put on at the same time as a total suspension overhaul, so I cant really tell you what it was as a single change. 

 

RS4 would likely be a good option. The only rubbing I ever had with the 275's was on my aftermarket exhaust and it was mild and also without a panhard. 285 should likely fit fine and at worst need a little rolling. Heavy mustangs generate a LOT of tire heat when driven right and a tire that tolerates it helps immensely. I get the feeling that he RE71R like to run colder. Feel out your tire temps and bring a sprayer either way if you are going for the last Nth.   When I say driven right, to get a good time out of my car with the RS3's you always want to have some slip angle, ideally as a slight (not outwardly noticable) 4 wheel drift.  It takes finesse. My time in my miata was a good education tool for the mustang as its easy to learn some bad habits in the mustang.  Be smooth, but smoothly approach the limit where you are just at that edge of grip to have a slight slide.   Its hard to describe in words, easier to feel riding in the car.  Takes awhile to get the right feel for it.  

 

Video is from a small lot with a tight course, so you can get a feel for what turn-in and midcorner balance is.  

 

Diagnostically, what diff are you using and if stock, when did you last replace the clutches?  They dont last too long until they give up and you one wheel peel.   Mine last 2-3 years at best and have eaten one in 1 year before. 

 

I have also been considering the Steeda X2 balljoint to help with the roll axis inclination, but need to research it a bit more.

 

 

 

wvumtnbkr
wvumtnbkr UltraDork
1/4/18 4:21 p.m.

Airdam and spoiler are easy.  They helped us drop 2 seconds on the same track yoy.  Would be less at autocross.

jj
jj HalfDork
1/4/18 6:04 p.m.

In that video, it does look flatter than mine.  Mine does lean more toward oversteer I think, especially when trailbraking.  Your car sounds good.  

These tires also seem to like some slip angle.  Mid corner I will go right up to the edge of understeer, but not push past that.  On entry to some corners I can get it to drift down to the apex karting style but its hard to always judge the speed correctly.

My diff is a 2.73 with worn out clutches.  The ratio works really well for my local club as I can go 75 in second if I need to, but peak power is 1000 rpm below that.  The course speeds usually range from  60-75 max.  I spent so much time last year doing suspension and various other maintenance things I haven't been motivated to change the clutches in the diff although I need to.

Apexcarver
Apexcarver PowerDork
1/4/18 7:26 p.m.

pretty sure you mean 3.27 for the ratio, which was stock for pretty much all the V8's (though in SCCA SP you could update/backdate to 3.55 from the Cobra R).

 

The 4.6 DOHC (modular cobra) I have doesnt really develop oomph below 3krpm, so I want to swap for the 3.55's at some point   If I recall correctly, I can reach 76 in 2nd and the 3.55's would make it more reasonable. My case may be different to yours, I can spin to 7k RPM.  (are you 302 or 4.6?)

As far as sound, catted BBK X-pipe with Flowmasters.  I have a catless H that used to be on the car, very different sounds and its surprising how much the cats quiet it down, the X is smoother and the H was much more harsh. I havent dyno'd but I think the x with cats makes more power than the H did.   

sleepyhead
sleepyhead HalfDork
1/4/18 8:29 p.m.
Apexcarver said:

I will warn you, I have friends running a DP miata and the aero difference (splitter and large dickbill) has been tenths in a 1800lb car.  I expect improvements to be less on a 3100lb car.


(and in another post)
That said, I feel like mine works pretty well. I also have an STS miata (coilovers, bars, exhaust, etc) and the mustang will never turn in like that

A couple things to think about:  The Mustang's fastback should allow cleaner flow to enter into the spoiler... and the size of the mustang's trunk should allow for a larger "wing area" for the spoiler to make downforce with, and possibly will act with a larger moment arm from the rear axle?  (I don't have either car, so I can't make the measurements).  Also, I'd think the front to rear weight imbalance would be greater for the mustang vs. the miata, so the mustang could benefit more from adding rear downforce?

otherwise, I've enjoyed reading and learning from the posts already here

Tom1200
Tom1200 HalfDork
1/4/18 11:11 p.m.

JJ I'm assuming you don't have an easy way to adjust the corner weights, even so I would have them checked anyway just to make sure the isn't way off front to rear. 

I believe the initial post said the car has Koni yellows; I can't remember they do or not but If they have a separate rebound adjustment try a couple of clicks stiffer and a couple of clicks softer and see what that does. It's remarkable sometimes what a small adjustment will do. On your Mustang I'd be looking to slow the wheels down (read hold the weight forward or aft for a split second longer) 

If the limited slip isn't 100% you need to fix it straight away, it's clobbering you more than you think; it's changing how the car turns in and also likely limiting your ability to balance the car mid corner. Depending on how bad it is that alone may be costing you over a second.

jj
jj HalfDork
1/5/18 12:11 p.m.

They are actually 2.73.  My peak power is at 4500 RPM (nearly stock 302), and my self imposed redline is 5500.  It seems to work well.  If it was shorter I would have to do a 2-3 shift a couple times per run.

My Konis are at full stiff front and 1/2 rear.  The front springs are stiff enough that I was getting some skipping/bouncing on bumpy turns until I turn them up.  

Any reason that a NASCAR style spoiler is any better than a drag race flat style one?  

Apexcarver
Apexcarver PowerDork
1/5/18 12:37 p.m.
sleepyhead said:
Apexcarver said:

I will warn you, I have friends running a DP miata and the aero difference (splitter and large dickbill) has been tenths in a 1800lb car.  I expect improvements to be less on a 3100lb car.


(and in another post)
That said, I feel like mine works pretty well. I also have an STS miata (coilovers, bars, exhaust, etc) and the mustang will never turn in like that

A couple things to think about:  The Mustang's fastback should allow cleaner flow to enter into the spoiler... and the size of the mustang's trunk should allow for a larger "wing area" for the spoiler to make downforce with, and possibly will act with a larger moment arm from the rear axle?  (I don't have either car, so I can't make the measurements).  Also, I'd think the front to rear weight imbalance would be greater for the mustang vs. the miata, so the mustang could benefit more from adding rear downforce?

otherwise, I've enjoyed reading and learning from the posts already here

The referenced DP miata had its windshield removed...

 

 

Apexcarver
Apexcarver PowerDork
1/5/18 12:45 p.m.
jj said:

 

Any reason that a NASCAR style spoiler is any better than a drag race flat style one?  

Angle of attack will dictate a lot of things, but I think the drag style ones are more about drag reduction than they are about downforce. The flat ones (I think you are talking about at least) allow a less turbulent wake for less aero drag from whats behind the car.

What you are after is creating a high pressure area on top of the car and if you couple with a diffuser, utilizing the low pressure wake to create a low pressure area underneath the car.  Problem is, autocross speeds are lower, so its difficult to generate a lot of force and as I mentioned earlier, the mustang is a heavy car, which will need more force to give effect than a lighter car. 

 

this is what I think you are talking about

and its all wrong for the goals you have. 

Apexcarver
Apexcarver PowerDork
1/5/18 12:54 p.m.

if you wanted the true ultimate in autocross aero, it would be carbon fiber multi-element wings like the AM guys run

 

 

but you are looking at a lot of time, work, and money in supplies to build a wing like that.   (carbon fiber isnt cheap, design tolerances are critical)

THAT wing and car combo, yeah, the aero is worth seconds (car weighs like 800lbs). 

The earlier referenced one is much much more feasable with your budget constraints and stated goals.

Tom1200
Tom1200 HalfDork
1/5/18 8:55 p.m.

JJ I must admit to being a bit surprised by the fact that the Konis are full stiff front (admittedly to control the 1000lb springs) and the rears are midway but you still have snap / sudden oversteer on the brakes. I know little of Mustangs, especially this generation, is this typical of this generation of Mustang?

I also forgot ask are you comfortable with big oversteer? If not it might be worthwhile to find an empty lot and get comfortable with a high level of corner entry oversteer. I only bring it up because in my leaf spring beam axle Datsun oversteer = faster lap times. Typical of leaf spring cars it moves around a lot, if you drive it with smaller slip angles it less edgy but it's also results in slower lap times.

Regardless of current set up I think the aero is worth trying.

Apexcarver
Apexcarver PowerDork
1/5/18 9:48 p.m.

My car is slightly more softly sprung in the front and similar in the rear (if I recall the rate difference between the race and super race, lost the reference for them) and I run koni yellow single adjustables.   I usually run one half turn off full stiff all the way around.  

 

I am kinda surprised that you are having the sudden oversteer on entry as well. That said, it all depends on what you are doing with the momentum of the car as I could just about make mine do whatever I want, but would have to flick a bit to go full tail out under brakes.  That said, I likely have a completely different brake package with the cobra PBR setup and it might even be a different generation of ABS.

 

Oh yeah, a peeve from mine.  SEATS!  the stock ones suck for keeping you in place. Too squishy, too slidey for the leather. Make you hang onto the wheel for dear life, which makes you less responsive and have less feel for the car.  Consider changing at least the drivers to something more positively locating.  (my seats are rebadged Cobra Monacos and the driver is mounted on a modified passenger slider)  I am guilty of being overly vocal about ergonomics and how it changes driver performance, but it made a difference for me. 

Carbon
Carbon SuperDork
1/6/18 2:39 p.m.
Apexcarver said:
jj said:

 

Any reason that a NASCAR style spoiler is any better than a drag race flat style one?  

Angle of attack will dictate a lot of things, but I think the drag style ones are more about drag reduction than they are about downforce. The flat ones (I think you are talking about at least) allow a less turbulent wake for less aero drag from whats behind the car.

What you are after is creating a high pressure area on top of the car and if you couple with a diffuser, utilizing the low pressure wake to create a low pressure area underneath the car.  Problem is, autocross speeds are lower, so its difficult to generate a lot of force and as I mentioned earlier, the mustang is a heavy car, which will need more force to give effect than a lighter car. 

 

this is what I think you are talking about

and its all wrong for the goals you have. 

One of those that pops up like a supermod wing (active aero)might be cool. Reducing drag at speed and adding downforce and drag under braking and at low speed. 

Appleseed
Appleseed MegaDork
1/6/18 8:36 p.m.

Active aero. Wasn't Keith working on something like that for the Targa Miata?

loosecannon
loosecannon Dork
1/6/18 9:09 p.m.

I hired an aerodynamicist to analyze and model my car in CFD. Going from no aero to good aero made to the limit of EMod rules would get me a 2% decrease in lap times on a course with an average speed of 90 km/h. This is with an 1800 lb car and the lighter the car, the more effective aero is. So, to answer your question, aero will probably only drop tenths of seconds for you, not 2 seconds.

jj
jj HalfDork
1/8/18 4:05 p.m.

I don't know if I would call it "snap" oversteer, but its close to that.  I'm not flicking it or being overly aggressive on turn in.  just breaking while turning.  I've always been able to catch it, and I am comfortable with oversteer.   I think it hurts me on decreasing radius braking zones because I cant brake as late as I want and have to find a way to straight line the entry.  The transitions and not so sharp turns are ok because I can get back on power if I need to.  Really the mustang is very easy to control a slide.  It's even easier than a NA miata I had.  It could be the PHB needs adjusting.  It might be 1/4 to 1/2 degree from level.  Not sure if it would matter that much.

At the least, I think the 8-10" spoiler is worth trying just to help with that.

Loosecannon:  That sounds great to me!  2% at my last event would be 1.36 seconds on 68.2 second lap.  Even if I got only 1% that would get me .6 seconds.

wvumtnbkr
wvumtnbkr UltraDork
1/8/18 4:07 p.m.
jj said:

I don't know if I would call it "snap" oversteer, but its close to that.  I'm not flicking it or being overly aggressive on turn in.  just breaking while turning.  I've always been able to catch it, and I am comfortable with oversteer.   I think it hurts me on decreasing radius braking zones because I cant brake as late as I want and have to find a way to straight line the entry.  The transitions and not so sharp turns are ok because I can get back on power if I need to.  Really the mustang is very easy to control a slide.  It's even easier than a NA miata I had.  It could be the PHB needs adjusting.  It might be 1/4 to 1/2 degree from level.  Not sure if it would matter that much.

At the least, I think the 8-10" spoiler is worth trying just to help with that.

Loosecannon:  That sounds great to me!  2% at my last event would be 1.36 seconds on 68.3 second lap.  Even if I got only 1% that would get me .6 seconds.

I would be looking at brake bias.  Our car does this with overly aggressive rear pads.

jj
jj HalfDork
1/8/18 5:58 p.m.

Ok, i uploaded some videos I had.

First one is an example of the oversteer under braking.  I was able to catch it though. https://youtu.be/s3ObushyMNM

Second is my best run that day.  https://youtu.be/rFTw4cbqrmI 

loosecannon
loosecannon Dork
1/8/18 6:37 p.m.

In reply to jj :

But you won't get 1%. I got 2% by eliminating a windshield and adding headlight covers to give air an direct shot to the spoiler, blocking off all air through the grill, cutting out the front fenders behind the wheels and having a flat floor. Your heavy sedan cannot get the same aero affect as my 1800 lb open top car,sorry.

[URL=http://smg.photobucket.com/user/loosecannon/media/MGB-GT/IMG_7928_zps3nyfnafe.jpg.html][/URL]

Tom1200
Tom1200 HalfDork
1/8/18 9:52 p.m.

Loose Cannon while he may not be able to generate the same downforce level but in the case of his car it may be enough to change the balance to,the point that he can more use of the car attributes. Also this generation of Mustang actually has a pretty low Cd, that long sloping roofline may do well or at least well enough. On a different note I have to say I'm impressed that you had someone do CFD for your car. 

jj the videos are very enlightening;  the S curves at around the 30 second mark are where I noticed what you where talking about, especially the right handed before the 90 degree left. The other thing I noticed is the way the car reacts to transitions; in the slaloms it appears the dampers lag behind (the body roll is on a Mars Rover kind of delayed reaction) as if the rebound damping isn't quite right. It's like the rear of the car lags behind relative to the front.

On your fastest run there's a 90 left (I think it was just before the 90 right with white line down the center) where you onvioulsy focus on unwinding the wheel trying to get the car to flatten out and get a better drive. 

Obviously we can't see exactly what your doing from outside the car but you look pretty smooth and the front end isn't bouncing up and down (typical of people who are rough with a car) so overall I'd say you drive it pretty well.

In one of these posts I mentioned about focusing on the most glaring issues; I'd try playing with the brake balance. Get the corner weights checked, if nothing is way off then start with an aggressive rear spoiler and or wing (cheap spoiler gets my vote). At the same time come up with an easy to install splitter. If the spoiler balances the car then add the splitter, if that unbalances the car then take it back off. You can reduce the splitter size and try it again. After that try fine tune things I'd back off the front dampers 1 click (provided the front chatter doesn't return)

Short of doing the CFD like Loose Cannon did you're going to have to do the trial and error method. I'm looking at a diffuser for my Formula 500 that I run as an F-Mod autocross car, it's the same deal; I've got a lot of rake in the car to combat the inherent low speed understeer (they have no diff, uses a kart axle) at higher speeds it oversteers a bit to much even for me. The rules don't allow a larger spoiler, so a diffuser is the only option. 

GameboyRMH
GameboyRMH MegaDork
1/9/18 7:40 a.m.
loosecannon said:

I hired an aerodynamicist to analyze and model my car in CFD. Going from no aero to good aero made to the limit of EMod rules would get me a 2% decrease in lap times on a course with an average speed of 90 km/h. This is with an 1800 lb car and the lighter the car, the more effective aero is. So, to answer your question, aero will probably only drop tenths of seconds for you, not 2 seconds.

Well you did already have a splitter, spoiler and diffuser before you got CFD done. This car has none of those.

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