Heat under bonnet

[ChrisF]

I wrapped my exhaust about 500 miles ago.  It definately had the benefit of reducing under bonnet heat. It may solve your concerns.  

I have not experienced any exhaust problems so far and like you, will worry at the time if a weld breaks.  

My alternator has a metal heat shield fabricated to protect it....my starter motor has no heat protection and again no problems.

Regarding the claims for increased bph with exhaust wrap....I found it hard to notice any difference, if at all.   It certainly has done no harm.

[Kit Car Electronics and Essex AO]

Please be careful with metal heat-shields.

I lost a Ford prototype car that caught fire inside a covered car transporter - the bouncing caused the exhaust heat-shield to touch the alternator live terminal, which then welded to it. The short melted the battery cable, set fire to the fuel lines and the truck driver was flagged down on a French Autoroute with smoke billowing out the back.

Believe it or not, he OPENED the rear door of the truck, at which point the car exploded, blowing matey backwards and the bonnet onto the opposite carriageway!

Luckily no-one seriously hurt, but driver was locked up by local Gendarme for driving without shoes and travel documents!  

If it can happen to Ford...

[fordy]

Why would exhaust wrap increase BHP - ive never heard of this claim???

[neilwillis]

It's hocus pocus about air intake temperature being lowered because the engine bay is cooler.

IMHO, not a jot of difference in reality.

[S8ight]

it may give you a very slight increase in power if you reduce under bonnet temp considerably, ooh say maybee about 1-2 BHP. unless of course you are an avid Max Power reader, in which case you can claim to have gained an extra 40-50 BHP.

[fordy]

It's hocus pocus about air intake temperature being lowered because the engine bay is cooler.

IMHO, not a jot of difference in reality.

Would make no difference to mine then, i have a big hole in my bonnet for cooler intake air.

Although there is some formula for BHP to air intake temperature - i seem to remember that every increase in degrees C above ambient can cost you about a quater of a BHP or something - i.e reducing air intake temp by 10 degrees can gain you 2.5BHP - oooh

cheers

Chris

[neilwillis]

Could always take it out in the winter only, just think of the power gain!!!

     

[Turbowestie.co.uk]

The other "benifit" to wraping the exhaust it to insulate the downpipes so to reduce the exhaust gas temperature loss, therefore the hotter the gases exiting the downpipes, the larger the volume they take up and the faster the exhaust gas velocity, the higher the velocity the higher the gas inertia, the more charge being drawn in to the combustion chamber on the valve overlap stage of the combustion cycle. Or so the theory goes........

[oilman]

I would have thought that high gas temps would have lead to high temps and then a higher pressure drop across the exhaust system.  As we can't control the pressure of the outside world then the pressure within the engine should go up.  This would imply that you would need more energy to get rid of the exhaust gases and therefore less energy would go into the drive.  And yet people keep on telling me that wrapping the exhaust increases power.  Insulating very hot surfaces sounds like a good idea to me from a safety point of view.  ( I hear cables don't like being cooked very much).

[fordy]

Its probably one of those marginal things that makes such little difference either way its not worth worrying about - i agree with Oilman though, wrapping for safety is a good idea - think i might get some.

cheers

chris