Track forum general chit chat.

[Bartledoo]

Originally Posted by ThunderMoose

My quarantine project. I lost my BimmerWorld diffusor at the beginning of the year. This one is made by AJ Hartman. I think it came out pretty good. It add some additional winglets but I am not planning to install yet. My garage is pretty small and I think they'd take out my wife's ankles.

[roastbeef]

well, naturally, i have questions. is there any science as to how long to make it? how far does it extend under your car? did you mount it as high as possible (close to the car body), or did you have it at a specific height? how far out can it get before it has a diminishing return or drag?

long and low, or high and short? i'm curious about aero theory here.

[roastbeef]

Originally Posted by Shmelgy

I'm not sure about the tuning, I'll have to ask Racewerkz.

The fan is wired to a switch, I turn it on when I start the car, then leave it on for a few minutes after coming off track. Their website says 1298 CFM, but no idea what the stock fan's CFM is

i see. so i'm assuming since the fan is on your track car, you're not too worried about it being variable or necessarily more powerful, just weight and the ability to cool the car when its off?

i would theorize the oem fan has a high cfm. i have a 3,300 cfm flex-a-lite efan on my desert truck and when that thing powers on, it "feels" or "seems" to be about the same or maybe a little more than our oem fan in the e9x m3. i know its not exactly a scientific observation, but you get the idea.

[ThunderMoose]

Originally Posted by roastbeef

well, naturally, i have questions. is there any science as to how long to make it? how far does it extend under your car? did you mount it as high as possible (close to the car body), or did you have it at a specific height?

I am sure there is science on how to do it. You can review wind tunnel data on AJ Hartman's web site to study the results. https://ajhartmanaero.com/blog/project-crusher-part-2/

However, I was limited on how far I could practically move it forward and how high and low I could make it. So basically, I used the underside of my diff as the reference point. The leading edge of the diffusor sits <1" behind the diff and is essentially flush with the bottom of the diff cover. This puts it at about 4" off the ground (as measured from the bottom edge of the tunnel sides) and the trailing edge at 8" beyond the rear most part of the bumper. I chatted a bit with AJ via e-mail and he didn't see any issues with it.

It will be interesting to see how it performs. I am suspecting that I will be able to take out some of the rear wing and still have as much downforce as before.

[b4hand]

Originally Posted by ThunderMoose

It will be interesting to see how it performs. I am suspecting that I will be able to take out some of the rear wing and still have as much downforce as before.

Any plans for a flatter floor leading up to the diff?

[ThunderMoose]

Originally Posted by b4hand

Any plans for a flatter floor leading up to the diff?

None

[roastbeef]

ThunderMoose does drag reduction feel the same as more downforce when it comes to trades like this in terms of cornering?

[b4hand]

Originally Posted by ThunderMoose

None

Will the diffuser help that much alone? I thought you needed to channel the air smootly to the diffuser and then it would work better

[Bartledoo]

Originally Posted by b4hand

Will the diffuser help that much alone? I thought you needed to channel the air smootly to the diffuser and then it would work better

The AJ Hartmann testing showed that you can still smooth it out with a legitimate diffuser and get substantial results with no flat bottom leading to it.



The data shows 2-3" height being more effective than 1" also. Flat floor numbers are reported to be double what is shown in the graph above.

I'm guessing a negative rake value means sloping down to the rear, as this would make sense to me, slightly squeezing the flow at the entry, cleaning it up, and attaching it to the surface

[Shmelgy]

Originally Posted by roastbeef

i see. so i'm assuming since the fan is on your track car, you're not too worried about it being variable or necessarily more powerful, just weight and the ability to cool the car when its off?

i would theorize the oem fan has a high cfm. i have a 3,300 cfm flex-a-lite efan on my desert truck and when that thing powers on, it "feels" or "seems" to be about the same or maybe a little more than our oem fan in the e9x m3. i know its not exactly a scientific observation, but you get the idea.

Yes sir, figured I might as well lighten it up while we were in there doing the power steering pump conversion. It's also quieter than the stock fan, if you care about that sort of thing

[roastbeef]

its probably just fine for a track car. keeps the temps down around the pits/paddock. i'd guess the fan doesn't run at all at track speeds.

[tdott]

Originally Posted by Bartledoo

The fact that most of us are still dumping the heat exchanger flow out of our undertray is really bothersome. I wonder what the lift difference is with it blocked off vs open. That would be a cool test.

Wouldn't that negatively effect cooling?

[ThunderMoose]

Originally Posted by roastbeef

ThunderMoose does drag reduction feel the same as more downforce when it comes to trades like this in terms of cornering?

I am not sure I am a good enough to "feel" the difference. When playing with the wing, I'll look at data to see if I pick up top speed. I'll do the same with the diffusor as I have a ton of data with my old setup.

When it comes to cornering it's often very difficult to quantify the difference as so much goes into maximizing corner speed - tires, position, suspension, braking/weight transfer, and aero of course.

That being said, I am certain that the diffusor is in the direction of goodness. It's substantially better that stock rear diffusor and much better in form and theory than the BimmerWorld diffusor I had for last 4+ years.

Will keep you guys posted if I ever get back to track.

[kayha12]

Looks mean Dennis! Can't wait to see it on track

[Bartledoo]

Originally Posted by tdott

Wouldn't that negatively effect cooling?

Yep. That's why we still have it open. The exchangers need to be ducted out of the hood for a permanent solution. It could be sealed for a quick test though.

[b4hand]

Originally Posted by Bartledoo

The data shows 2-3" height being more effective than 1" also. Flat floor numbers are reported to be double what is shown in the graph above.

Well damn. That is quite good!

[roastbeef]

the jpmarketing full underbelly diffuser is a pretty good value... $1,850 for the system, but i'm not sure how "plug and play" it is. there is some fit and finish to be done to adapt it to your own car, but much of the work is done.
https://www.jpmarketingllc.com/produ...r-recaro-racer

[ThunderMoose]

Originally Posted by roastbeef

the jpmarketing full underbelly diffuser is a pretty good value... $1,850 for the system, but i'm not sure how "plug and play" it is. there is some fit and finish to be done to adapt it to your own car, but much of the work is done.
https://www.jpmarketingllc.com/produ...r-recaro-racer

That's a great deal!

I've seen Jens' car up close a few times and his is perfectly done with respect to aero. Zero compromises.

[roastbeef]

-0.7 ounces today. Free mod (plus titanium hardware). Gutted the rear exhaust hanger.

[Kelse92]

Is anybody out there using the Bimmerworld rear spring perch?
I have KW's currently and their perch is a real pain to do any ride height adjustments with. I would like to find a solution without spending a ton of $ if possible and this looks to be the best priced one out there so far, but wondering if maybe one of the other two Ground Control options is a better way to go?

https://www.bimmerworld.com/Suspensi...g-Perches.html

[tsk94]

Originally Posted by Kelse92

Is anybody out there using the Bimmerworld rear spring perch?
I have KW's currently and their perch is a real pain to do any ride height adjustments with. I would like to find a solution without spending a ton of $ if possible and this looks to be the best priced one out there so far, but wondering if maybe one of the other two Ground Control options is a better way to go?

https://www.bimmerworld.com/Suspensi...g-Perches.html

The articulating ones from GC are really nice. I had them on my E36 race car and was very happy with them. That being said, they are double or more the price of those BW ones. If you can justify the price difference they are worth it imo.

[//steve\\]

Originally Posted by roastbeef

-0.7 ounces today. Free mod (plus titanium hardware). Gutted the rear exhaust hanger.

What does your car weigh currently?