Running without an undertray

[SiH]

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.

Have a read of the links I\'ve posted dude - Undertrays can make a huge difference, and the flow through the bay doesn\'t work the same way as a lot of people think

[redgti]

yeah i\'ll give it a read later i think. i wish i\'d done a study like this for my dissetation.

[suba]

Well - here\'s what I\'m going to do.  Go for a blast and check the Water / charge temps on the Power FC with the tray on, and then with it off - that should settle this one!

[SiH]

You need to get a lot more enpirical data than that if you want to fet some conclusive results dude. Repeated runs in tne same conditions, with the same exrernal temps etc at the very least.

[suba]

I dont agree - same day conditions, run the car from 2,000 rpm to redline in 3rd and see what the temps do.  if the airflow over the V-mount is compromised without the tray then the charge temps should reflect it noticeably - if they dont then I dont see that there is an issue.

I asked a friend of mine about the articles posted earlier in the thread - this was his response:

Aerodynamics is something of an art besides a science.
The pressure gradient across the rad front face to back face would give more indication of air flow through the rad. Also there will be a pressure variation at different places on the face of the rad. So the whole story would not be so simple.
The 25% variation in the under bonnet pressure would not translate to a 25% air flow change through the rad.
Temperature measurements in conjunction with the pressure measurements would give a better picture of what is happening.

[suba]

Ok - temps wise there is s*d all difference with the tray and without it on a moving car.  

The only bit left to decide on is whether the stability is effected at high speed, which is a little more difficult to test!:3Confused

[batman]

i have a v mount without and under tray and have had many a high speed run 150 160 mph and no issiues with stability

[rx jamie]

the undertray acts as a kind of venturi which helps remove hot air from the engine bay. id doubt that a clipped/screwed on piece of plastic sheet could massively effect stability at speed a huge amount as the engine sub frame and sump take up a lot of space which would keep the air flow smooth enough. might be a different story if the sheet was made of strong aluminium and was incorprorated into making the entire bottom of the car as flat/smooth as possible. id guess that would make a lot of downforce. but im no aerodynamics professor.

[CharlieP]

I havent got round to making my undertray fit back on after my v-mount set-up, temps have been 20-40air and 82-85 water...so no drastic (if any affect so far)
 
But, I will be making the undertray fit again....as I don\'t really want to risk high speed instability...do you??

[ashc]

i\'ve not noticed any instability either over several track days
the way some vmounts are done (like mine) the rad fans would be totally obstruced by an undertray, my rad is only about ten degrees slant from the floor- i don\'t think i\'ll be putting it on again, no probs with temps either. The mot common style vmounts with the intercooler mounted 90 degrees to the floor and the rad at about 45 degrees would probably benefit though i suppose.

[suba]

OK - have you had any issues with gravel traps on track days...:Thumbsup!

[ashc]

most of my track experience has been at nurburg, no gravel traps there lol

[davyv]

A stone took out my aircon rad and radiator when i had no undertray when my car was stock.

[suba]

just trees and other stuff to hit then!:Thumbs-up

[overboost]

I have a V-mount set up with no undertray. Both temps are decent. As for high speed stability can\'t really comment as I have a RE style diffuser and it plants the car to the ground on motorways.
 
I guess for those people changing their front bumper the undertray will have to go anyway. My plan is to get a feed front bumper and get one custom made to match it.