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

[Randal]

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.

Tony

Very interesting!

If the seal won't hold then some windshield stays might be in order for the back window. I mean that vacuum could carry some very hot water in case of a hose failure. (IMG:style_emoticons/default/sad.gif)

I never noticed this on 222, but then no windshield or back window might have had something to do with it.

[Cracker]

Yes Randall - it was noticeably hotter - could be worse should a failure occur. I'll most likely rivet it in place. Its nice to know the source of the buffeting hot air. Salesman step up? (IMG:style_emoticons/default/blink.gif)

T

[veekry9]

A cooling breeze thru,for to make 'smooth'.
(IMG:style_emoticons/default/biggrin.gif)
[
In the '30s,aero studies were reaping results.
https://en.wikipedia.org/wiki/Meredith_effect
https://en.wikipedia.org/wiki/North_American_P-51_Mustang
http://www.historicracer.com/aviation/p51-...ect-lee-atwood/
https://www.google.ca/webhp?sourceid=chrome...+radiator+scoop
]
/

[Cracker]

What is that big "hunk of engine" in your diagram? A big-six? (IMG:style_emoticons/default/lol-2.gif)

T

[Rand]

What is that big "hunk of engine" in your diagram? A big-six? (IMG:style_emoticons/default/lol-2.gif)

T

Dude, never mock a p51. ;P
Squirrelly pants.

[veekry9]

It might be a Blown Caddie Northstar!

SplinterCaddie
[
http://www.joeharmondesign.com/
https://jimsgarage.wordpress.com/2008/04/06...-you-will-like/
http://www.houston-imports.com/forums/show...r&p=9243212
https://www.google.ca/webhp?sourceid=chrome...engine+for+sale
http://www.northstarperformance.com/sgstuds.php
Well,it was a Caddie,now LS7.
]
(IMG:style_emoticons/default/happy11.gif)
Pressure differential,the source of the drag at speed.
Feed the low with air ducted from the highs at the front of the race car,or the windshield base.
A 'tunnel' up the middle of the floorpan would work too.
The compromises Porsche made in development,discarded for applicible solutions.
A set of giant scoops set into the doors would feed the drag turbulence.
The smooth transition of air to the rear and the wing would speed things up,being cooler.
(IMG:style_emoticons/default/smile.gif)
/

[veekry9]

Now,the frp isn't the same but,the ducts will fill the drag.
The nose should be smoothed out some ,the lips of the frunk and lite covers create turbulence and drag.
Eventually a shape resembling a ah..Fiero will reduce drag and make fast.
You have an abundance of hp+tq,a trip to the speedway will sort out the small changes to the slippery stuff.
Scrape the track clean down low,test the pressure below with a manometer.
Empirical data and the tuft testing,chicken feathers or yarn using cellcams.
https://www.google.ca/?ion=1&espv=2#q=f...20cfd%20testing
The same o same oh will repeat the other's results.
Remember the Superbird.
(IMG:style_emoticons/default/biggrin.gif)
/
http://www.buildyourownracecar.com/race-car-design-software/
A 7L modified class means the side windows should be flush.
Build a scale model of the side of the 914,turn face up and run a stream of water over it to discover the drag penalty.
The flow means go.
/

[r_towle]

Probably need to use a mechanical method to hold the window in place.
Or, remove it all together for the track.....

[Cracker]

I remember that car - ugly. It was a Pikes Peak effort and was all over the place. Very loose everywhere. Just sayin.

T

[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..