View Poll Results: do you drive your car without the engine trays installed?
I run with the trays installed on my steet car at all times
26
53.06%
I run with the trays installed on my track car at all times
4
8.16%
I run with the trays if Im not feeling too lazy or tired to put them back
6
12.24%
The laws of physics and 951 ownership require them to be removed too often, so I dont bother
13
26.53%
Voters: 49. You may not vote on this poll
engine under tray poll...
12-20-2006, 02:04 AM
#1
Quit Smokin'
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Thread Starter
engine under tray poll...
after helping a fellow 'lister with his clutch the other day I got to thinking about the engine trays. My frined always takes the extra 15 minutes to reinstall both trays under the car. How much do these actually improve the performace of the car (either cooling, or ground effects)? I have all the parts to install them on my car, in fact they came in a nice plastic bag from my car's PO, who informed me that they were "the first thing most owners removed". I remembered thinking to myself that I would put them back on, but I never have. All the other heat shields and the batwing are in place, just not the large trays. Curious how many of you guys actually use them.
12-20-2006, 04:53 AM
#7
Drifting
actually the under trays were for DB testing nothing more, nothing less. the car had to pass strict drive by sound tests when new and these trays help muffle engine noise.
for an undertray to be benificial to aerodynamics the tray would start at the leading edge of the car and pertrude at least a foot beyond the rear of the vehicle. otherwise no effect. undertrays need very clean air to work properly, and unwanted turbulance would destroy the whole effect.
for an undertray to be benificial to aerodynamics the tray would start at the leading edge of the car and pertrude at least a foot beyond the rear of the vehicle. otherwise no effect. undertrays need very clean air to work properly, and unwanted turbulance would destroy the whole effect.
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12-20-2006, 05:55 AM
#8
Burning Brakes
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Interesting info on DB testing 
That said, however, the factory went to great lengths to engineer some effective undercar lift and drag mods into the 951...including the rear diffuser, the side skirts and the two damnable plastic panels under the front footwells. Diffuser makes a noticeable difference in tail lift and buffeting at higher speeds.
Agreed that classic "ground effects" need a smooth, long boundry layer for full impact, but any aero tweek that decreases undercar turbulence can make a contribution to fighting lift and decreasing drag, especially at critical places like exiting under the tail and places where positive pressure air barriers build up.
That said, however, the factory went to great lengths to engineer some effective undercar lift and drag mods into the 951...including the rear diffuser, the side skirts and the two damnable plastic panels under the front footwells. Diffuser makes a noticeable difference in tail lift and buffeting at higher speeds.
Agreed that classic "ground effects" need a smooth, long boundry layer for full impact, but any aero tweek that decreases undercar turbulence can make a contribution to fighting lift and decreasing drag, especially at critical places like exiting under the tail and places where positive pressure air barriers build up.
12-20-2006, 06:26 AM
#9
Drifting
your probably more right then myself. i can imagine porsche would use all these panels to the greatest effect they could. i guess im trying to say the impact on ground effects may not be noticeable, whereas drag could be effected. ive had my car up to 250km/h a more then a few times with and with out the undertrays and noticed very little, well actually nothing.
but one good side effect of removing the undertrays is it gets the heat out of the engine bay. which helps in longevity of seals, hoses etc.
but one good side effect of removing the undertrays is it gets the heat out of the engine bay. which helps in longevity of seals, hoses etc.
12-20-2006, 06:36 AM
#10
Burning Brakes
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You're right. Put all of these aero "fids" together, perfectly installed and the difference between having them and not having them would not be easily sensed. I've run with an without engine undertrays for varying periods and never really heard or felt any change in performance. The diffuser, however, I would move into the category of "noticeable difference" because it changes the amount of total air noise and definitely helps secure the tail against crosswinds and high speed lift.
12-20-2006, 07:09 AM
#11
The trays helps keeping the engine/bay clean...
It only takes 5 min to remove them and ( I`ve read ) That they direct air backwards to cool the tranny.
Either way, The clean engine is reason enough for me to keep them .
It only takes 5 min to remove them and ( I`ve read ) That they direct air backwards to cool the tranny.
Either way, The clean engine is reason enough for me to keep them .
12-20-2006, 07:12 AM
#12
They are on all the time. it only takes 2 minutes to install and remove if you change all the bolts to 10 mm. Not to mention the fact that the metal one has the vertical heat shields for the rear caster blocks. This is especially important for the driver's side where the exhaust pipe comes close.
12-20-2006, 07:25 AM
#13
Drifting
but also when driving the rear caster blocks are in the airflow, so really no heat effect, but by having the tray there they dont really get that colder air anymore and are exposed to the radiant heat from the exhaust.
12-20-2006, 08:04 AM
#15
Drifting
but really whether its parked or not it will get radiant heat from the exhaust. the heatshield will work up to a point until it gets heat soak(probably 5 minutes) and then transfers the heat through it.
i guess this issue is more of a personal preference. everyone is going to have their owns ideas on it
i guess this issue is more of a personal preference. everyone is going to have their owns ideas on it