Undertray/Splitter Modification

Magpie · Postby **Magpie** » Tue Jan 14, 2014 9:25 pm

There have been a lot of recent comments on the forum regarding overheating and the removal of the undertray. When I installed my splitter I did remove the undertray and never gave it much thought, until...

When the undertray is removed air is no longer channelled into the radiator, rather it will take the path of least resistance and go around it. The undertray is designed to channel air into the radiator.

This is a view from the passengers side, the gap is very large and it is obvious that air will go towards the gap and not through the radiator.

From the bottom looking up

Top looking down

The issue for me may not be as dramatic for some as I have a splitter, without the splitter or the undertray it is obvious that a lot of the cooling effect is lost around the sides and the bottom of the radiator.

Solution...

The old undertray is marked and cut

and then installed back in, reducing the previous gap. Cuts had to be made so to allow the splitter support to fit.

(the mount in the foreground is for a bullet camera and the white thing to the right is an air temp sensor).

Then I installed (rivets) a rubber strip to seal along the edge of the cut undertray and the radiator

Real world testing - whilst slightly lowered temps were recorded the biggest impact was the reduction in fluctuations of the water and oil temps. They were much more stable and not as prone to change as the car was pushed. All in all this is an improvement over previous and only took a few hours. However it also explains why it is bad to run a car without an undertray and why temps increase without it.

Snowmotion · Postby **Snowmotion** » Tue Jan 14, 2014 10:06 pm

So the under tray is not crucial under the motor but for sealing the gap in front of the radiator?

Magpie · Postby **Magpie** » Tue Jan 14, 2014 10:17 pm

I assume that the undertray gives the motor some protection, but, yes it would appear that it also contributes to making sure as much air as possible goes through the radiator to assist with cooling.

sailaholic · Postby **sailaholic** » Wed Jan 15, 2014 8:00 am

I think you will find it also helps pull air through the radiator by trying to create a low(er) pressure area in the engine bay by keeping the air flow going under the car from getting caught in the engine bay.

This would also help engine bay temperatures.

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Magpie · Postby **Magpie** » Wed Jan 15, 2014 8:09 am

sailaholic another valid point, hence why not a good idea to remove the undertray.

I will go through my data and see if I can find data where the air comming in was the same temp both before and after the mod (as well as other conditions). I can also see if there was a change in the engine bay temp and show the more stable water/oil temps.

Lokiel · Postby **Lokiel** » Wed Jan 15, 2014 9:49 am

This is a great article regarding ducting: http://www.stockcarracing.com/techarticles/general/scrp_0509_efficient_cooling_radiator/

- ducting will be my next DIY project once I get my car back; the vertical gaps on the left and right side of the radiator are huge so channeling all that air through the radiator should improve cooling (along with a bonnet vent behind the radiator like on magpie's Garage Vary hood.

deviant · Postby **deviant** » Wed Jan 15, 2014 10:55 am

It is worth noting that even the factory undertray can be a POS. I did have the factory one on my car but there was still a 2 inch gap underneath the radiator and plenty of places to the sides for air to get through. I ditched my factory undertray and made another one that seals from the bumper opening to the bottom of the radiator. I still need to do something at the sides.

I have also stuffed foam around the edges of the fan shrouds and the edges of the radiator so air cannot escape there. I have also taped over the holes in the panel in front of the radiator.

Magpie · Postby **Magpie** » Wed Jan 15, 2014 11:45 am

Lokiel wrote:This is a great article regarding ducting: http://www.stockcarracing.com/techarticles/general/scrp_0509_efficient_cooling_radiator/

- ducting will be my next DIY project once I get my car back

Geat article and in Danny's 20B PP build there are great photos of how he will be ducting air into the radiator.

Plan will be to get a fabricated solution to replace my work, however this will have to wait till the Accusump is relocated from the boot to the space in front of the radiator now that the air con has been removed.

Lokiel are you considering a splitter for your SE as I have had a PM regarding the mounting points that could be used and I could not help them

deviant wrote:It is worth noting that even the factory undertray can be a POS.

Agreed but it is better than not having one, hopefully people will consider what happens when it is removed.

Lokiel · Postby **Lokiel** » Wed Jan 15, 2014 11:56 am

Magpie wrote::
Lokiel are you considering a splitter for your SE as I have had a PM regarding the mounting points that could be used and I could not help them
:

Probably not but that may change later if I get really serious about trackwork.

I want to keep the car as a DD sleeper since I don't want to attract too much attention from the boyz in blue - an effective splitter is pretty hard to miss.

I'd like a solution that could be bolted on easily for track days and I'd also need a track-day wing too - it seems you can't really have one without the other for them to be truly functional. I suspect a track-day boot+wing would be the cleanest looking solution - also, if the boot started deforming I wouldn't really care.

I'll definitely be seeking advice from you if/when I do consider a splitter/wing.