aerodynamics

[pieperz06]

shit i could make that

 

[STEVE_POE]

foolio, man thanks for the info. anymore pics would be great if you couold post them up .

anyone notice the r888 toyo . poor bastard. lol I thought they switched back to ra

 

[foolio2k4]

Yeah still using r888. Pirelli guy i talked to said they switching to pirelli slicks next year. Also should be releasing full slicks for the consumer market

 

[Philostang]

THANK YOU! How sweet is that. Thanks for the pics.

shit i could make that

Yeah, a diffuser isn't super complicated in itself; just a few basic principles to apply. The tough part is getting it really optimized with the rest of the undercarriage. If you run an IRS you're blessed with a stationary differential. Our damn things keep moving around on us, and that means you have to take into account clearance at full droop (one way or another). You're either going to run out of ground clearance real quick, or end up cutting a clearance hole and either living with the detriment or trying to fight it with other aero tricks. FWIW, I'm in favor of fighting it.

Of course, you could build your diffuser only up to the rear axle, but then you're not really integrating it well with a total under-car aero package. You're just adding stuff.

Best,
-j

 

[foolio2k4]

we cant have the same style of diffuser as the WC mustang cuz we still have rear exhausts unlike the side exhaust WC mustang.

 

[STEVE_POE]

great pics and info. not much left of that car to call it a 2010 mustang . thing almost looks like a tube chassis inside a mustang tub.

pretty much exactly what I'm building now.

 

[Philostang]

great pics and info. not much left of that car to call it a 2010 mustang . thing almost looks like a tube chassis inside a mustang tub.

pretty much exactly what I'm building now.

Great! So let's see your under-car aero pics. =)

Sorry if I'm coming off like a leech, but I've had stuff on my mind for a while now and the usual mayhem and money (too much of one, too little of the other) have prevented their development. I envy those who are actually grinding away on making their projects a reality.

Anyway, back to the rear diffuser, sure we can't do exactly what they did, but you can do most of it in the middle between the exhaust exits. This turns out to line up pretty nicely with the axle's lower control arm bracket (which you'll have to get around anyway), so it's a natural place for the rear diffuser. If you have a can-style muffler or straight pipe (like the mid-muffler guys do), then you can actually go up and over it or even enclose it, though I worry just a tad about heat build-up. A louvered insert here that you could test and remove as needed might be nice... just thinking out loud.

Best,
-j

 

[STEVE_POE]

my car is far from needing a under tray.. just now got the rear quarters,roof,package tray and tailight section cut away and removed. Car sits about 3ft off the ground . only thing it has is a tub and frirewall and shock towers. getting ready to cut the spare tire well out and the trans tunnel out.

 

[ocpony]

Philostang,

Here is a few shots of my under carriage pan that I did for running the Texas Mile this spring. I don't have any wind tunnel testing numbers or even a real before and after thing as I added about 100hp since my first run at the mile when I ran 160.3 mph. This time I ran 180.3mph. Each time I went to the mile I attained my target mile per hour (160 and then 180) on my third runs. So at least I am getting my speed calculations accurate. I did also remove the factory rear wing on the last run in order to help reduce drag. Ibelieve I currently hold the record at the Texas Mile for fastest speed in a s197 Mustang GT now with the 180.3 mph run. The previous highest speed in the records was 178 mph.

 

[foolio2k4]

Hmm.. it doesnt look bad. But its not completely flat at the bottom right?

 

[ocpony]

Hmm.. it doesnt look bad. But its not completely flat at the bottom right?

It bowed slightly from rocker to rocker where it goes over the frame sections in the middle just behind the tranny. It then bends up at the rear starting directly under the axle in order to give clearance for axle travel. When changing tires the diff comes thru the rectangular hole in the pan. I need to enlarge it still a little bit as it hit and pushed the pan down when I was changing the tires so I had to be very careful not to damage the mounts or the pan itself. It is my first attempt and I will be making some adjustments to the rear section for the run this fall. I want to fully cover the rear to the bumber lips but I may extend the bumber down first in order to clear the mufflers. I am also looking at using different mufflers. I mainly wanted to reduce any drag under the car due to uneven surfaces and to smooth the airflow as it exits the car. I had a pretty good rake on the car also using my H&R adjustable struts and rear springs. I couldn't lower the rear any more due to the fact that the tires would contact fenders on any bumps. It was very stable at full speed which was a concern of mine since I had never used a pan before. I didn't know if I would make it better or worse.

 

[pieperz06]

Philostang,
Ibelieve I currently hold the record at the Texas Mile for fastest speed in a s197 Mustang GT now with the 180.3 mph run. The previous highest speed in the records was 178 mph.

i think you are correct. but i think i have the record for an all motor S197 GT

 

[Philostang]

OC, thanks for sharing! And congrats on the speed record! I have mostly the same goals for my aero considerations - I just want greater high speed stability, basically combating the lift inherent in all production car designs. I'm not looking for some sort of huge gain in downforce.

Anyway, we have a concrete piece to discuss! And I have questions!

First, I'm glad to see your diffuser is placed more or less where I had mine planned. I think we followed similar principles, 8-9 deg rake, clear the diff at ride height, and the rest just follows suit. Everything's hunky-dory at ride height, but then that damn differential droops on us. ARGH! At least I'm glad to see that the cut out doesn't need to be as large as what I had thought was needed (I was thinking MUCH larger).

I had planned a small grill out back between the diffuser and bumper, mostly for looks but also to ensure that air on top of the diffuser can escape. Have you considered adding in vertical blades? If you break up the area that the air sees as it exits the rear you'll speed it along and get less disruption of flow.

I think new mufflers are in your future. That's going to make the rear bumper area much easier to deal with, but personally I do worry about heat build up. In fact, I worry about this everywhere (oil pan, cats, trans, exhaust piping). Sounds like you're doing top speed runs, so I imagine your runs offer different cooling opportunities/liabilities than what I'll get (typical 15-20 min. runs on a road race track). Any thoughts? Do you drive her on the street with that undercarriage treatment?

Also, with regard to heat management, have you seen the Nissan GTR bottom? They go almost full belly pan, but theirs comes right up to the exhaust tube (effectively making the bottom 1/3 of the tube surface part of the pan). I think (*everybody duck!*) that the faster air under the car is going to do a pretty good job of cooling this part of the tube...but the other 2/3rds are still up inside the pan...and that's just got to get hot. Thoughts on heat?

One thing that intrigues me is your treatment of the front splitter-to-belly pan transition. I'm assuming you're raked up front on the belly pan to capture pent up air in the engine bay and give it a smooth path to a low pressure zone, yes? Or am I thinking of what you did in the wrong way? I'd really like to hear your thoughts on this area, as it's a major concern for me. I feel pretty confident in applying what I know of aero to the rest of the car, but this area seems a bit confusing to me. I've seen a lot of different approaches, and many of them use a similar design as what you executed. I've also heard of some safety concerns here with catching air under the nose and possibly flipping the car. Do you know if this "dip" helps combat that possibility?

Last thought, have you considered doing some tests with yarn tufts and a Hero cam? You can tape up short 3-4" strands of yarn along any area you want to study, slap a Hero cam under there and take a run (use a stopwatch and keep track of what time in the video you hit what speed). Maybe you could find a trouble spot or see what doesn't need attention? Just a thought.

Again, thanks for sharing!

Best,
-j

 

[ocpony]

OC, thanks for sharing! And congrats on the speed record! I have mostly the same goals for my aero considerations - I just want greater high speed stability, basically combating the lift inherent in all production car designs. I'm not looking for some sort of huge gain in downforce.

Anyway, we have a concrete piece to discuss! And I have questions!

First, I'm glad to see your diffuser is placed more or less where I had mine planned. I think we followed similar principles, 8-9 deg rake, clear the diff at ride height, and the rest just follows suit. Everything's hunky-dory at ride height, but then that damn differential droops on us. ARGH! At least I'm glad to see that the cut out doesn't need to be as large as what I had thought was needed (I was thinking MUCH larger). You just have to be careful when you jack it up. On the street it was not a problem unless you hit a large bump on one side. I tried to keep it as high up as I could to keep the pan as flat as possible. My lowering springs were as low as I could go without major tire contact issues. My 325/50/15 DR poke out about 1/2 inch and will only hit on hard bumps.

I had planned a small grill out back between the diffuser and bumper, mostly for looks but also to ensure that air on top of the diffuser can escape. Have you considered adding in vertical blades? If you break up the area that the air sees as it exits the rear you'll speed it along and get less disruption of flow.
I designed and installed this in about a week right before the Mile. The last piece was the rear section and I was out of time so I just sort of made a simple section to cover the middle of the car where the most of the airflow is going according to some basic flow designs I have seen. I plan on redoing this area and adding the vertical fins on the revision 2. I have a lot more to do in this area but I am not sure how much I will gain. I think adding the vertical will do me the most good.

I think new mufflers are in your future. That's going to make the rear bumper area much easier to deal with, but personally I do worry about heat build up. In fact, I worry about this everywhere (oil pan, cats, trans, exhaust piping). It did get very hot around the tranny area and you need to make sure all wires to the tranny shifter and O2s are kept as far from the exhaust pipes as possible. I cooked the loom on the tranny wires but not the wires thankfully. Sounds like you're doing top speed runs, so I imagine your runs offer different cooling opportunities/liabilities than what I'll get (typical 15-20 min. runs on a road race track). Any thoughts? Do you drive her on the street with that undercarriage treatment? I only leave the front piece on for the street due to the heat and it gets very noisy when the road debris kicks up on the pan.

Also, with regard to heat management, have you seen the Nissan GTR bottom? No, but I should have looked at them when I was at the mile, as there were 2 pitted near me that ran 200+ and got booted for no roll bar. They go almost full belly pan, but theirs comes right up to the exhaust tube (effectively making the bottom 1/3 of the tube surface part of the pan). I think (*everybody duck!*) that the faster air under the car is going to do a pretty good job of cooling this part of the tube...but the other 2/3rds are still up inside the pan...and that's just got to get hot. Yes it gets hot on WOT runs! Thoughts on heat? I run an auto and did not have time to switch to 2.73 gears like I planned and had to use 5th gear (0.71 OD) which did last for the event but I had to replace that OD drum and band after returning home. I am sure I was getting extra heat from this fact. I did datalog 2 of the runs and the tranny temps didn't spike to bad IIRC ( 190* or so). I run an extra B&M supercooler in line with the stock cooler.
I do not run the cats and I would not reccomend it with the full pan as mine was very hot even without the cats. I only run the cats on the street.

One thing that intrigues me is your treatment of the front splitter-to-belly pan transition. I'm assuming you're raked up front on the belly pan to capture pent up air in the engine bay and give it a smooth path to a low pressure zone, yes? Correct, at least that was the thought and it appears to have worked well but I will need to verify it. That was to also give the engine and headers a place to relieve some heat. Or am I thinking of what you did in the wrong way? I'd really like to hear your thoughts on this area, as it's a major concern for me. I feel pretty confident in applying what I know of aero to the rest of the car, but this area seems a bit confusing to me. I've seen a lot of different approaches, and many of them use a similar design as what you executed. I've also heard of some safety concerns here with catching air under the nose and possibly flipping the car. Do you know if this "dip" helps combat that possibility? I was concerned with this also but with the car racked as much as it was it did not appear to have any stability issues. The Dip mainly came from the undercarriage shape as the rockers are higher up on the chassis and I didn't have time to design a half in spacer for the length of the rocker area.

Last thought, have you considered doing some tests with yarn tufts and a Hero cam? You can tape up short 3-4" strands of yarn along any area you want to study, slap a Hero cam under there and take a run (use a stopwatch and keep track of what time in the video you hit what speed). Maybe you could find a trouble spot or see what doesn't need attention? Just a thought. Thanks for the great testing ideas. I have a GOPro already so I will try out this for sure.

Again, thanks for sharing!

Best,
-j

I also drag race this car and do some road racing but mostly been DR. I have Pinks All Out in Topeka and then straight to Mustang Week in Myrtle Beach scheduled for July. I am switching the suspension back to the drag setup next week to get the car ready. I need to try to get it diled in for Pinks. I am still not getting full boost. I will be switching the suspension back in Sept. for the Mile in Oct. and will be reworking the rear pan then and swapping the rearend out so I can run the mile without OD. So I may not have much to add until then on the revisions. I also hear someone is going after my record so I may not post everything until after the next mile run.

 

[pieperz06]

I also drag race this car and do some road racing but mostly been DR. I have Pinks All Out in Topeka and then straight to Mustang Week in Myrtle Beach scheduled for July. I am switching the suspension back to the drag setup next week to get the car ready. I need to try to get it diled in for Pinks. I am still not getting full boost. I will be switching the suspension back in Sept. for the Mile in Oct. and will be reworking the rear pan then and swapping the rearend out so I can run the mile without OD. So I may not have much to add until then on the revisions. I also hear someone is going after my record so I may not post everything until after the next mile run.

did you ever run the mile N/A

 

[ocpony]

did you ever run the mile N/A

Yes back in 08, I ran 150.914mph ! j/k
I ran in the fall of 08 with the standard 2.4 KB on 10# boost and ran a 160.3mph on street tires 27 inch KDW's. I made 3 runs the first was 4th only at 145mph bouncing off the rev limited from the 1/2 mark.
Second was using 5th gears with a late shift.
The third run was 160.3mph with a more timely shift into 5th.
Also these runs were on the lowering springs but with no aero mods other than taping the corners of the hood and lights. THis is more for holding the hood down since I don't have hood pins.

 

[pieperz06]

Yes back in 08, I ran 150.914mph ! j/k
I ran in the fall of 08 with the standard 2.4 KB on 10# boost and ran a 160.3mph on street tires 27 inch KDW's. I made 3 runs the first was 4th only at 145mph bouncing off the rev limited from the 1/2 mark.
Second was using 5th gears with a late shift.
The third run was 160.3mph with a more timely shift into 5th.
Also these runs were on the lowering springs but with no aero mods other than taping the corners of the hood and lights. THis is more for holding the hood down since I don't have hood pins.

i damn near shit my self when you said that. its weird that you went to 5th when i was shifting to 5th i slowed down by like 5 mph but i had lots less power.

 

[Shotokan1509]

THis is more for holding the hood down since I don't have hood pins.

Stock hood? The flutter at 80 is scary, can't imagine doubling the speed without pins.

 

[Sleeper_08]

You should see it at 135+ with a cross wind!

Am I pushing my luck relying on the stock hood latch in the 135 to 140 MPH range?

 

[pcdrj]

You should see it at 135+ with a cross wind!

Am I pushing my luck relying on the stock hood latch in the 135 to 140 MPH range?

YES! Hood pins!