Exhaust Manifold Heat Wrap

[Guest Chris Draper]

I'm thinking of putting insulating wrap on the manifolds to try to reduce engine bay temperature.

 

Is this sensible or does it lead to other problems? If it's worth doing, where should the insulation stop - where the manifold branches come together or beyond?

 

Thanks for any thoughts!

[malcolm]

I'm also interested in this.  My V8 FHC competition car has wrap on the manifolds down to just below where the branches come together.  It doen't seem to cause a problem, but then I've never noticed a problem with the DHC which doesn't have wrap, or any form of overheating issues.

 

Does engine bay temperature cause you problems then  ???

 

Malcolm.

[Guest Chris Draper]

I did manage to overheat my old engine very badly - & the bottom end then gave up about 4 months & 1,100 miles later (just after coming back from Switzerland which is something to be grateful for!).

 

I think water pump failure was the actual cause, but I replaced the radiator & water pump after the initial overheating problem & although it generally ran OK, the temp gauge would range between 1/2 & 3/4, occasionally going slightly above that. Enough to be a worry.

 

Anyhow, having now built up a 4.6 with a new short engine & the top end & ancillaries from the old engine, I don't want to take any risks & anything I can do to reduce overheating is good.

 

Thing is, I've heard that using the manifold wrap pushes the heat further down the exhaust system & I'm a little concerned about putting too much heat under the floorpan & next to the gearbox. Given that the gearbox is going to be additionally stressed with the torque of the 4.6, I don't want to do anything which might kill it off completely!!

[malcolm]

Can't say I blame you Chris.  If I'd built up a 4.6 I'd been keen on keeping my cool  :cool:

 

A TR7V8 installation with a decent cooling system need not be a problem.  A good high capacity rad and electric fan seem to be important.  A nice touch on my FHC is a twin fan system which can be manually activated in the car (one or both).

 

Manifold wrap?  Come one you V8 'experts' who post here so frequently - what do you think?

 

Malcolm.

[Cinnobar]

My response is don't do it. As a one time kit car owner and still loosely involved with them their have been several car fires attributed to heat wrap on manifolds transferring heat elsewhere and setting things alight. The exhaust boxes on my V8 on the noisy twin pipe system put enough heat into the boat to pretty much cook anything left in there. Heat wrap means they'll get hotter which is close enough to the fuel tank that I wouldn't want to do it. Also the system runs close enough to the body to cause probles if it got hotter.

 

Jim

[Guest ajttriumph]

I have raced my 8 for ten years without the need in up to 40 degree heat and never needed it, i doubt whether its worth the effort.

 

there are lots of little things that can be done if you have an under bonnet temp problem that will fix excessive temps

[andrewt]

Set your air intake up to draw air from somwhere not directly heated by the exhausts and bear in mind that the louvres above the headers are to vent excess heat. Note the heat haze you get out of them intraffic!.

Also wrapping the manifolds increases the heat effect on fatigue and will tend to trap moisture hence increasing the corrosion seen on your manifolds. Most exhaust manufacturers i have spoken to do not recommend it.

As per ajtriumph above i have run V8's for years and not had problems due to heat from the manifolds.

Andy

[Guest Chris Draper]

Thanks Guys, appreciate the responses.

 

Think I'll give it a miss then!

 

Cheers.

[SteveP]

<font color='#000000'>Thanks Guys, appreciate the responses.

 

Think I'll give it a miss then!

 

Cheers.</font>

 

Put it on all my race and fast road cars and it's excellent , reducing under-bonnet temps and increasing BHP. Rumours about fires are from the old product days . Properly fitted it's a definite bonus.

[tr7v8]

manifold wrap keeps tempreture within the manifolds, this keeps the gas 'expanded' as you could say which in turn increases the flow rate of exhaust gas, this incresses the scavaging rate of the cylinders for fresh fuel/air mixture, increrasing theoretical power, as the tr7 does not have an issue with hot floor pans as far as i'm aware i'd recommend wrapping tubular manifolds. As through my experiance in a FHC it ends up decreasing the cabin tempreture, which is too much to start with, plus's all round!

 

Tom

[anthonyt]

sorry but my memory of the combined gas law would say that as the gas cools it would take up a smaller volume and have a lower pressure which would increase the scavanging rate rather than vice versa, but i could be wrong.

 

First year engineering physics was a long long time ago!

 

You will probably find something on wikipedia or elsewhere on the web re the law if you are interested.

 

I am at the racetrack many weekends each year competing or watching and i cant recall the last time i saw a wrapped exhaust other than on areas where a driver can burn himself geting in or out of the car, if it really did present any marked advantage every competitor would do it.

[knortech]

Has anyone tried ceramic coating on their headers.You can get an internal and external coating from the link attached. Not a cheap option.

www.camcoat.u-net.com

[Nick_nl]

The heat wrap is used quite often in turbocharged cars.

As Tom said, it keeps the heat inside the exhaust.

For a turbo this means more energy available more energy comes out.

Downside is the overall temperature increases.

 

Isn't it a idea to use a heat deflector shield ?

Some aluminium plate could do the trick.

[marvmul]

sorry but my memory of the combined gas law would say that as the gas cools it would take up a smaller volume and have a lower pressure which would increase the scavanging rate rather than vice versa, but i could be wrong.

That's correct. Applying the gas laws would show it. Gas is flowing from a high pressure area to a low pressure area. But 2 fenomenons are responsible for the gas flow and scavenging : the pressure differential (and wrapping does harm to it), and the pressure waves : when a pressure wave from the exhaust valve is arriving at an aperture or a wider section or a merge in the exhaust tract, a pressure wave is starting in the other direction, to the exhaust port : it depends on what moment in the engine cycle this pressure wave is arriving at the exhaust valve to make it beneficial, harmful or indifferent (and this depends on the rpm and other things like T° etc) : wrapping the exhaust could improve or make worse this scavenging by pressure waves: it's a matter of coincidence. I guess no one can do the math's, or at least it will be easier to do it on an engine dyno by trial and error. (by changing the length and diameter of the primary and secondary exhaust tubes etc.)

[dblenk]

HI

 

just read about the wrapping as i was thinking of it for the 6, however i too have heard the problems of fire and found Zircotec on the web they ceramic coat the manifold so i am thinking that way they reduce the temp by 30% ?

its about £20 per 1" pipe per linear foot £35 per 2" per linear foot

 

regards

 

david

[Rassilon]

Vaguely on topic - My exhaust downpipe sheared in the middle today, just near to the gearbox mounting.

 

£40 inc shipping (£10) for a NOS one from ebay.

[RogerH]

Hi Guys,

as Tom stated by keeping the gas hot the volume does not reduce thus keeping the gas velocity high.

If you allowed it to cool the volume would reduce and the gas velocity would then decrease thus reducing the scavenging effect.

The maths for this problem is very complex and there are nummerous formulea that come into play -

Boyles (first law), Charles (Second Law), Avogadro's law, Poisson's law et al. Within this bunch they cover Pressure, temperature, velocity density etc.

 

However there is a more practicable point to insulation. Firstly it will keep the engine bay temp down but more inportantly where you have so many unknowns going on within the manifold it is probably best to keep certain things as known values.

In an uninsulated manifold the temperature drop of the front pipes would be greater than the rear pipes.

This will cause the gases from each pipe travelling the same distant to get there at different times.

Thus if you had an extractor manifold (Not an Ex-Tractor manifold) one needs to get the gases at the extraction point at the correct time. With all this varying cooling due to poor insulation going on how can the lengths be calculated for best effect. By using ceramic coating on the manifold pipes this will remove one serious variable.

 

Although F1 and other fabulous cars don't use fabric insulation they probably do use ceramic or twin skin manifold pipes.

Ever wondered why the pipes don't melt - ceramic insulation on the inner diameter as well as outer diameter.

 

I'm not an expert (or even an amatuer) on exhaust manifolds but I do play with gas tubine engines for my sins and there is some commonality.

 

Roger