Interesting...anyone else experience this? Options

[Cracker]

So in my last session on track last Sunday (Happy Mothers Day if one is reading!), I noticed allot of heat - like I really felt it! I actually looked to see if something was on fire - nothing. So yesterday I drove the 914 to the Home Depot - I felt some heat again - just not as hot.

My rear window is plexi - not glass. The pressure from the engine bay/targa rear is so great it blew the seal on the panel. At least half of the entire length was flopping-in as I drove down the road.

I realized the "air" funneled back towards the cockpit - I just didn't realize it did so with so much veracity. Another bit of info to file away in the 914 bank.

Tony

[veekry9]

Yeah,I have been scratching some shapes down to make the needed wide tire fenders retain a 914 look.
A massive bubble of air behind the targa makes the drag penalty gargantuan.
I agree that the rollcage should be of that scale,the power so large.
The track setup is no overnite sensation,some flogging needed.
The dynamics of the rear trailing arms must be studied to ensure stability.
A cellcam vid of the moves under track conditions is good info.
Use led pen lasers securely fastened to the swingarm,aimed at targets inside the fender.
Aim the cameras at the targets,record the motion of the swingarm in several axis.
A toe transition under accel and braking can be mapped and solved.


https://www.youtube.com/watch?v=BHYYlTZIZQ4

Stepthru and observe as the car snap oversteers.

https://www.youtube.com/watch?v=dIm7UVqy840
https://www.youtube.com/results?search_quer...che+914+v8+race
https://www.youtube.com/results?search_quer...race&page=1




Unlimited
Jeff MacPherson took Second in his green Porsche “914-8,” which you can guess means a pretty wild V8-powered 914.
Time Attack 1 was dominated by Jeff Zwart, with his twin-turbo, all-wheel-drive Porsche 911 with a 9:46.243.
Perfect timing and a time to better.
(IMG:style_emoticons/default/happy11.gif) heh heh.
http://www.hotrod.com/news/1507-2015-broad...-climb-results/
/

[Cracker]

Good ideas...thanks.

T

Yeah,I have been scratching some shapes down to make the needed wide tire fenders retain a 914 look.
A massive bubble of air behind the targa makes the drag penalty gargantuan.
I agree that the rollcage should be of that scale,the power so large.
The track setup is no overnite sensation,some flogging needed.
The dynamics of the rear trailing arms must be studied to ensure stability.
A cellcam vid of the moves under track conditions is good info.
Use an led pen laser securely fastened to the swingarm,aimed at a target inside the fender.
Aim the camera at the target,record the motion of the swingarm in several axis.
A toe transition under accel and braking can be mapped and solved.


https://www.youtube.com/watch?v=BHYYlTZIZQ4

https://www.youtube.com/watch?v=dIm7UVqy840
/

[Dave_Darling]

The air going forward along the rear deck lid has been something that anyone who has studied 914 aerodynamics knows about. For quite a while now. The strength of it is a bit surprising to me, but tuft testing has always shown the direction.

Other stuff that might be interesting, as far as aero goes:
- The base of the windshield is a high-pressure area. That's why the fresh air inlet is there.
- There is a high-pressure area low on the face of the front deck lid. Oil cooler (or radiator) exhausts into this area tend to work very poorly.
- There is a low-pressure area higher up on the face of the front deck lid. Cooling air exhausts in this area tend to work rather better.

--DD

[ThePaintedMan]

Tony,
It is my experience after studying many race-bred 914s before delving into mine, that the rear windshield should be mechanically reinforced, as Rich said. If you use Lexan, like I have, then you can run two vertical aluminum straps from the bottom to the top and riveted into the plexi itself.

This not only helps the plexi/Lexan from blowing out like you experienced, but if for some reason you ever spin that thing backwards at speed, it'll REALLY come in handy. The same is true for the front windshield. It should be reinforced with some aluminum tabs bolted/riveted into the body. I'll send you a picture of how I did it when I get my car back this month. Not to contradict Rich, but I would in no circumstances remove the rear window. It is part of your "firewall" and if you were to ever get an engine fire at speed, think about how the back of your neck will feel with those flames.

[r_towle]

No,argument on the fire issue.
Seems early race cars removed all glass except the windshield.
Also have seen some tweaks to the roof by lifting it, and some have added wind tabs.

Somewhere there is a cool study of 914 aerodynamics on the Internet done by a professor at a college over the course of a few years. The results are out there online still, and kinda a cool read for those interested...

[r_towle]

Here
http://www.cassidy-online.com/porsche914/aerodynamic_aids/

[veekry9]

https://www.google.ca/search?q=air+flow+win...Uf02m3UHLlYM%3A

Well,the 'granularity' of the test scale masked the result's detail.
The model was far too crude to differentiate from a childs's fabrication.
Testing airfoils is done on a much finer resolution.
So,model the 914 on a larger,more accurate scale.
The skin surface of the model should represent actual roughness.
The road surface is involved so therefore modeled too.
Make your mods after a baseline run,repeat until satisfied.
Take it to the oval,do 1000 miles in testing the mods.
Airfreight it to the Nordschliefe,attempt to match the factory's results.
(IMG:style_emoticons/default/laugh.gif)
heh heh
/
Proving the results yourself assures you the truth of the matter.
/

[stownsen914]

Simple reinforcement of the rear window should do the trick, as suggested.

Don't just remove it. The inward airflow you mentioned sounds like more of an annoyance than anything, but imagine of you had an engine fire or hot fluids spraying from the engine, and THAT started blowing into the cockpit. That would suck pretty quickly.

The best fix to the poor airflow over the back of the 914 would be to build a hatch to slope down from the roof to the decklid. Of course this would be a significant project, would ruin the 914 shape if you're looking to keep that, and also not be legal with at least some racing organizations.

Scott

[mbseto]

...I just didn't realize it did so with so much veracity.

Proving the results yourself assures you the truth of the matter.

(IMG:style_emoticons/default/smile.gif)

[naro914]

Tony
FYI I have lexan in Papa Smurf, we screwed it in along the top and bottom. Opted for sheet metal screws instead of rivets so we could remove it if we wanted..

[veekry9]

The rotating flow also occurs laterally,a huge drag penalty that increases with speed.
A simple aero test in the car on the freeway can be done with talc powder and cellcam.
Or a hair dryer on a scale model in the shower.
/

[veekry9]

Oops,my bad,did read the cpr long ago.
Do use the link to the site's tests,valid args made.

(The model from above),constrained flow area,disregarded below 12".
The rotating bubble at approx 20mph.
The mirror moving the flow below the fenderline.
The tumbling flow inside the cockpit is drag too.
The affected airmass is much larger than that depicted.
At the rear,the flow's direction is reversed as is the top's,tumbling into a bubble that grows with speed.
/
These are not the only aero pix we have read of over all time,hence my faux pas,selecting their stuff.
Thanks for pointing that out.
/

[Cracker]

...this topic really resonates with you! Very good. (IMG:style_emoticons/default/beerchug.gif)

T

[r_towle]

If you follow the link I posted, you will see the original data and analysis that goes along with the pictures the Veekry is posting from the original scientific research.

His opinion aside, it might be worth noting that the site is copywrited, and the author has a pretty specific claim to not reprint his research.

That is why I posted a link to the entire research, it puts it all in context with some very detailed and pretty valid conclusions.

It also give credit where credit is due.

[veekry9]

About to Snap.

The other thing,that inside rear looks way wrong,the roll excessive,the angle of the dangle too steep.
It is true that the relocation of the suspension is a large task,lowering the rear to racetrack heights changes the geometry dramatically.
A raised pivot is the way,when using larger dia tires and a stance lowered to (4-4.75") 10-12cm.


When everything changed.
Note the roll is reduced,the front wheel steering into the slide.
Still slipping,on the trailing throttle,clutch engaged.

https://www.youtube.com/user/maicy123/videos
/

[Cracker]

I've got a less scientific explanation for what occured (I've watched that video two-dozen times), "In way over his head". The first indication of that was his lack of car control and poor instincts...the second was, he kicked the car upon exiting". Bush league and amateur written all over both.

T

[Cracker]

Rich - Thank you. I am aware of the professors "assignments" and have actually designed a few things within the build around the data. Thank you for the link.

T

[Dave_Darling]

John Rogers over on the Bird Board put a diverter across the back of his roof. It was a simple ~quarter-round bent piece of metal, which took some of the air going back along his roof and pushed it down toward the engine bay opening. He did it primarily for cooling, as I recall.

It would be interesting to see if it had any significant effect on aero.

--DD

[veekry9]

Agreed,though I tried to not be so harsh,and thought the lift and steering input may have been to avoid the halfwit in the blue shirt.
I too would be a little pissed,not saving the slide,tee-boning a boulder in Colorado.
I didn't notice a Hans device,that was a good jolt,and anyone on the tracks should use them.(He did)
That is the fun part of putting your favorite theory on the track,to prove out or crap out,costs too.
It's all good to analyze later what happened and make the preps to attenuate such wiggly behaviour,like riding a sidewinder.
A fast pace requires fast inputs,lock to lock,here's a few vids I chose that demonstrate.


https://www.youtube.com/watch?v=w6Thomd4BQg

https://www.youtube.com/watch?v=VKHnJ8kojKA

https://www.youtube.com/watch?v=MpwpRQ6Vouc
https://www.youtube.com/watch?v=yeZiEfswGX4
Ask any racer if they have crashed.
I had a chance to see Mario hit Roberto Roberto Guerrero's stopped car here in Toronto.
He later said in an interview that the car's construction is what made survival possible.
He stood for a few moments on the far side of the chainlink,I would suppose,in wonder.
https://www.youtube.com/watch?v=-_cc9MXdE6A...be&t=18m35s
/

[Cracker]

Dave - I've thought about something like that...was even thinking about yesterday again (ala the old BMW 3.0 CSL batmobiles). I see allot of drag for the sake of cooling...in MY application, it does not seem worthwhile. Thanks.

T

John Rogers over on the Bird Board put a diverter across the back of his roof. It was a simple ~quarter-round bent piece of metal, which took some of the air going back along his roof and pushed it down toward the engine bay opening. He did it primarily for cooling, as I recall.

It would be interesting to see if it had any significant effect on aero.

--DD