Running without an undertray

[suba]

Since fitting of a V-mount the undertray on my FD has not gone back on yet - what do you guys commonly do....run with or without?

Are there any issues regarding running without one?

[CharlieP]

I\'ve heard they are important for air flow out from the engine bay!

[suba]

Well - I was advised by a well know specialist that airflow was improved by running without one.....

Has anyone had any issues with grit or stones flying into belts etc.?

[CharlieP]

Who was that??
 I was only saying what I\'d heard....not being a know all

[BlitzBoy]

depends on how you intercooler is setup, on FMIC I ran without one for a while I put back the undertray and got better cooling for the water rad.
On a V mount it may be different

[SiH]

My car runs a shedload cooler with the undertray on.
Also feels a lot mroe stable. That\'s an FRP one though.

I really would put it back on if at all possible, they make a big difference.

[ashc]

mine was taken off by reworx when they fitted the vmount, and not put back on as the rad projects lower, they said it wasn\'t necessary anymore - haven\'t had any probs over the last year, although i cr**p myself over speedbumps. With a standard engine, it does make a difference though.

[FlikstRR]

ive been drifting for most of the  season on a V mount setup with no undertray...

trust me.. run with one!  temps are ALOT higher without one as the air hs a path with less resistance to run..  I\'d advise the undertray at a minimum if not.. additional ducting if your running a V-mount.

[AshRX]

dont run with one and have no intention of running with one. Temps are all good whatever conditions.

As above it all depends on setup of rad and IC

[suba]

hmmm...lots of different opinions.  I may try and rig something up that caters for the lower radiator on the V-mount.

I\'m more concerned with stability at speed, and I can\'t imagine that gravel traps do it much good either.

[SiH]

Some intersting stuff for you :
http://www.autospeed.com/cms/A_2159/article.html
http://www.autospeed.com/cms/A_2160/article.html
http://www.autospeed.com/cms/A_2162/article.html

There\'s some stuff of relevance in there Worth a read, anyways

[Nik da Greek]

That\'s a really fascinating read, excellent links, SiH. Especially interesting the way that his intercooler "scoop" actually worked as a vent, sucking air up off the radiator and blowing it the wrong way through the IC! Then you read the third part, and it\'s obvious that the vent was in the worst possible place for it to act as an intake, the area of lowest air pressure across the bonnet. It shows with startling clarity that the shape and direction the vent faces is almost completely irrelevant compared to the pressure gradient involved.

Those experiments show that vented bonnets like the Mazdaspeed/KnightSports style ones where the vents are right forward between the headlights should work much better than the FEED style ones where the pressure measurements imply that if anything, their vents are more likely to be sucking air back into the engine bay rather than exhausting it out. That\'s exactly what the Yanks discovered forty-odd years ago with things like the cowl induction hoods on Camaros and Pontiacs where they utilised the high-pressure wave at the base of the windscreen to force air back under the rear of the bonnet to feed the carbs.

[SiH]

Exunctly It\'s the link that I dig out when people post up pictures of their bonnets raised at the back \'drift spec\' because it \'makes it run cooler\'

It could also go some way to explain why my AD9 bonnet didn\'t really seem to make much of a difference to cooling at all - I see FAR better temps with my MS undertray and stock bonnet. Goes to chow that you don\'t neccessarily need a vented bonnet with a V mount

It\'s a shame I never got round to actually doing a test like that with my old bonent, I just measured intake temps etc.

[redgti]

I have been thinking about this and i don\'t see the need for the undertray with  a v-mount. As long as the v-mount is properly boxed in and ducted from the front bumper.
 
If anything would this undertray not keep extra hot air in the engine bay as the rad fans blow air in to the undertray and not directly out of the bay.

[Nik da Greek]

I have been thinking about this and i don\'t see the need for the undertray with  a v-mount. As long as the v-mount is properly boxed in and ducted from the front bumper.
 
If anything would this undertray not keep extra hot air in the engine bay as the rad fans blow air in to the undertray and not directly out of the bay.

Evidently not.....

I think it\'s down to the undertray keeping a nice, fast, smooth stream of air flowing under the car that a) sucks air out the rear lip of the tray due to moving faster than it and therefore creating a pressure drop at the rear and b) not being all messy and turbulent, thus making it easier for airstreams from the engine bay to merge with the airflow around the car.