engine bay temps

[s4marsh]

when i got back from a drive earlier i was under the bonnet doing my routine checks as you do and started thinking about the heat that was in the boost pipes, airbox and all the pipework onwards from there and was wondering how much of the heat will have been generated by the flow/friction of air inside the pipes and how much was heat soak from the engine bay temps as the car was parked up with no airflow..leading me onto the idea of some home made pipe covers and heatsheilds especially round the turbos + downpipes and insulate the airbox and intake as best as i can from the radiated heat or is the majority of heat from the air flow itself and would i be then trapping the heat in making the intake temps rise even further? i have a load of glass cloth blanket that i use in the furnace building industry which will be identical if not better than some of the stuff motorsport places selling. any thoughts on the idea??? i was maybe thinking of bonding it to some aluminium foil with the special fireproof glue thats used with the cloth to make rigid heatshields too and can make all sorts of shapes like doing fibreglass work. i have plenty if anyone wants to try something like this???

 

[Matt82]

on my golf i decided to remove the rubber seal between where the bonnet meets the bulkhead. worked a treat. easy to reverse if you dont like it though

 

[s4marsh]

so its helps hot air escape up the windscreen you mean???i can see that working yes.. you could fit a little extractor fan and ducting between your wiper arms down into the bay too..lol

 

[Matt82]

it wont need any form of extractor, the edge of the bonnet will make a good low pressure area, that alone will suckplenty of air out when youre on the move

my golf has an under tray etc a couple months back we arrived at a meet, parked up and later on we wre looking under the bonnets. mine was roasting hot (mainly due to the undertray i think)

with the rubber part missing, that doesnt happen anymore

 

[s4marsh]

that sounds very good for what it takes to remove and re fit if no improvement.. i was only joking about the extractor tho matt.....lol i was also thinking about cutting some air feed holes and ducting from the undertray like an upside down bonnet scoop,
i've just tested my home made heatsheild material too, i glued 2 layers together and then glued foil over that and then held a lighter directly underneath my hand to see how much heat protection it offered....it managed a good 25 seconds with my fingers touching it before it got too warm compared to a third degree burn un protected i'm guessing so the exhaust manifold next to the airbox is getting shielded along with insulating the airbox and intake i might also make 2 sleeping bags for the turbos...lol

 

[s4marsh]

well i've made a heatsheild that goes along the side of the airbox,under the pipe leading to the y pipe which is right above the turbo and also around the intake at the front of the engine bay and is all one peice with 3 layers of fireproof glass cloth bonded together like fibreglass and coated with tin foil facing the engine it should be good for 800c easy and should stop the airbox and pipes getting super heated but the proof is in the pudding,i'll post a picture when fitted 2moro so you can all have a laugh and call me names......this is what happens when i'm out of work i always have a pointless little project on the go

 

[Matt82]

ive not got an s4 yet, but i think vagcom should be able to log the intake temps. that would be great for a before and after test

with my car, science wise, i went as far as to open the bonnet after a thrash with the rubber strip in, and it was hot and without the strip it was a lot colder

i think i only gained 50cc though

 

[jcb]

remove the undertray, the engine cover and depending on the model the flat plastic panels behind the vents.
my tqs had things that looked like vents but were closed off at the back.
all adds to air flow

 

[aragorn]

From past experience the airflow thru the bay is pretty substantial while actually moving, its just that it tends to heatsoak pretty quickly once you pull up.

I would bet you'd see very little difference in IAT's before and after the above mods.

In my old nova with its 16v motor i placed a temperature sensor in the engine bay, strapped to the side of the cone filter. While driving, it never showed anything other than ambient temperature, however pull up at a set of lights or park up for 5 mins and, especially on hot days, it could quickly climb to 40-50c and would go off the scale of the guage if it was really hot or you were sat for a long time in traffic.

You also need to bear in mind that the standard airflow arrangements are designed to allow the most efficient flow of air thru the radiator and intercooler assys, and removing things can have undesired side effects. The rubber strip for instance, if missing, can allow fumes and suchlike to be more easily drawn into the heater and blown inside the car. Removing the undertray could (i'm not saying it will, just giving an example) alter the aerodynamics at the front of the car such that you have reduced downforce on the front wheels at high speed, which probably isnt worth it for a tiny bit more airflow that may infact not be helping anything...

 

[Matt82]

remove the undertray, the engine cover and depending on the model the flat plastic panels behind the vents.
my tqs had things that looked like vents but were closed off at the back.
all adds to air flow

the undertray is a good thing... keep that.

if i get an s4 without one, will you let me have yours?

 

[aragorn]

Ye i notice the undertray has naca ducts in it, so its obviously doing something under there in terms of aerodynamics and airflow.

 

[s4marsh]

that was my original point really. is the majority the temps heatsoak once parked up?? i wouldnt remove the undertray maybe run some air ducts from it as your spot on about the aerodynamics especially at motorway+ speeds however the shielding would help reduce heatsoak when stopped at traffic lights and so on which has been pretty noticable on a warm day i've even turned my boost down to compensate a bit

 

[Markey]

I have been playing about with this in my Silvia. I fitted an intake temp sensor and once moving the IC does a very good job of cooling the air to be low 19C. And the car spends most of its time sideways. Once you stop the temp goes up but not that much 26C or so. In my experiance unless your going for big power then its not going to make a difference to you. Water injection would if you had big HP.