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Go Back   Pelican Parts Technical BBS > 1- Porsche Technical Forums > Porsche 944 Turbo and Turbo S

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Join Date: Sep 2003
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Turbo rear diffuser

Can anybody tell me what the rear Turbo diffuser actually does?
And by that i don't mean what it does, but at what point does it actually do something.

I would imagine that below certain speeds it's mostly just some weight hanging off the back, right?

So at what point does it start to work, and how much difference does it actually make ?

I would also imagine it's more effective at a lower ride height then at a stock ride height? anybody has some actual data or experience adding or removing it and then noticing different handling?
Old 07-01-2012, 05:49 AM
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As far as I understand it, the only thing the "diffuser" does is visually distinguish the 951 and S2 cars from the earlier models. As I recall a couple of the magazine articles on the 951 when it first came out commented that the part was strictly for looks.
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Old 07-01-2012, 10:25 AM
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well that's kinda what i'm guessing, but i'de be interested to hear if anybody thinks it has a real function, and if so, at what speeds it starts to work.


Just bought a 944S with blown valve train, it has the turbo diffusor on it.
But I'm thinking about tossing the thing.. It's not factory original for the 944s (the diffusor is OEM Porsche tho).. and it personally think it doesn't look all that nice on a car that doesn't have teh turbo or s2 nose..


+ there's some value in those things.. if i sell it i get added budget to fix the engine...
Frankly i care more bout the engine then about the looks.

So unless the thing has a real function, for what i'm going to do with that car(drive the chit out of it on country roads)... I'm going to remove and sell it.
Old 07-01-2012, 11:03 AM
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Is the diffuser the OEM part or fiberglass? I'd be interested in it if its fiberglass.
Old 07-02-2012, 03:36 AM
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I'm in Europe.... doubt it's worth for you to cover the shipping cost, i'm sure you can find em locally
Old 07-02-2012, 03:57 AM
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Everything I have read says it is indeed functional......it is basically an upside-down "spoiler" that creates downforce as the air flowing along the underside of the car passes through the gap between it and the rear bumper. I think Porsche even put out some numbers on how much downforce it creates at certain speeds, but I can't remember what they were. Porsche engineers are not big on adding things that aren't functional.
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Old 07-02-2012, 08:20 AM
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But if so, i would think it's more a stability thing for higher speeds (that the Turbo can achieve and a regular 44 or 44S can't)

I've done 245 in my previous S .. it was stable.. without the rear diffusor .
And i don't think i'll ever go faster then that in the project S i dragged home.
It's just to much work, and to risky for my driving license..

I'm doing mostly narrow country roads.. different kind of game.. i want acceleration , not top speed. So that diffusor, i think is just unwanted weight for my purposes..
Old 07-02-2012, 09:08 AM
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if you just want acceleration, a Porsche isnt the car to drive in the first place.

a diffuser (which is not what our cars have), takes under body air, and because it was kinda squeezed to get under the car, the diffuser opens up without adding more air, so the pressure drops. this gives you good rear downforce.

we have an under-body spoiler, which yes, also add rear down force, but it it doesn't do it by diffusion. it does it by not allowing the air to separate from the bottom of the car and get turbulant. by keeping the boundary layer attached, drag is induced, which creates the down-force. notice the under-body spoiler is tilted in the same manner as an above body spoiler is ...
Old 07-02-2012, 10:16 AM
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i never said i want "just" acceleration
i said i prefer acceleration over top speed.

What i really want is handling, which is why i want to shed weight, since that will give me more acceleration , later braking and better cornering.

So that underspoiler, or diffusor or whatever it's called, at this point i still haven't heard anybody saying anything that would indicate to me that it has a valid use.. sure it adds more downforce but do i really need more downforce on a 944s?
I've never had any issues with lack of downforce on my previous 944S, even if i loose 250 lbs, i don't think i'll need more downforce then either. It'll still have plenty of weight on it's own then.
How much downforce does it produce anyway ? Can't be much at low speeds.
Old 07-02-2012, 11:59 AM
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Quote:
Originally Posted by svandamme View Post
i never said i want "just" acceleration
i said i prefer acceleration over top speed.

What i really want is handling, which is why i want to shed weight, since that will give me more acceleration , later braking and better cornering.

So that underspoiler, or diffusor or whatever it's called, at this point i still haven't heard anybody saying anything that would indicate to me that it has a valid use.. sure it adds more downforce but do i really need more downforce on a 944s?
I've never had any issues with lack of downforce on my previous 944S, even if i loose 250 lbs, i don't think i'll need more downforce then either. It'll still have plenty of weight on it's own then.
How much downforce does it produce anyway ? Can't be much at low speeds.
depends on how fast you plan on cornering. on a high speed road track, i defiantly see a need for it. on a low speed autocross course, not so much. the 944 is not a zero lift car, at speeds above 60-80 mph, the car will make lift. anything to reduce that will increase cornering speed.
Old 07-02-2012, 12:17 PM
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Quote:
Originally Posted by white944cup View Post
Everything I have read says it is indeed functional......
Road & Track sure didn't think it was functional when they tested the 944 Turbo in November of 1987.

"The 944 Turbo is recognizable by its shapely front-end cap and rear undertray spoiler, useless as such. Scuttlebutt is that marketing demanded the spoiler for product identification: 944 Turbo owners needed something to identify themselves to traffic they'd just passed."
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Old 07-02-2012, 06:34 PM
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all spoilers don't function until at least 45 mph. at 75mph, they actually start to generate any force that is meaningful. that's the fact.

how much does that thing do is really not important unless you drive over 100mph which few of us do anyways.
Old 07-02-2012, 08:32 PM
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gonna chuck mine... get some money back for the engine instead.
And frankly i don't like em cosmetically.. + it'll probably end up getting ripped or damaged if i hit some rougher country roads... or have to put a wheel in the grass by the side of the road to pass a tractor or something.
Old 07-03-2012, 03:49 AM
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it's a hard rubber material, similar to the deck spoiler above, yet finished to be painted. Might be slightly harder...or could just be more internal reinforcement.

Mark
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Old 07-03-2012, 05:57 AM
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Call me weird then, but I like how it looks. Agreed, I rarely go over 100mph...

My car is devoid of any "turbo" badges or anything. I like how thee distinctive nose and that spoiler sets the cars apart from N/A models

But to be perfectly honest, I like the N/A nose style more, a more classic look.

Jeff
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Old 08-01-2012, 07:48 AM
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it hides the spare tire well nicely.........
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Old 08-02-2012, 08:57 AM
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rear valence

im pretty sure it lifts the car a little bit in the rear at high speed for stability and better handling at high speed. not 100% sure though. i dont work for porsche.
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Old 08-02-2012, 10:16 AM
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