Lagging exhuasts

[GORDON STREETER]

Originally Posted by Dave Brand

A few years ago a couple of riders were disqualified from Aprilia Mille Championship races (bikes, for the uninitiated!) for lagging their exhausts. It was said to give a 1-1½ BHP gain.

Dave. Out of interest were they 2 or 4 strokes ?

[Al Weyman]

Its not just about performance though is it, it also keeps heat away from starter motors and wiring and makes the engine easier to work on while still hot.

[GORDON STREETER]

Well if you will run those engines with exhaust manifolds on both sides then that could cause a problem !

[Al Weyman]

Yeah and bloody hot they get too!

[tristancliffe]

Originally Posted by AdamAshmore

I am a little confused by this. I thought the point of lagging was to keep the heat in the exhaust.

An interesting point, which caused me to re-read my post. Amusingly, it seems I've gone mad. I don't like lagging because it keeps the heat in the system, and I meant to say that exhausts work better if they can get rid of the heat through the tube walls.

I'm not quite sure how I managed to write essentially the exact opposite in the middle of the text!, especially when I then state that lagging keeps heat away from the engine bay. I guess I must have been thinking about the counter-argument as I wrote it, and accidentally wrote that instead

Sorry guys. Start again, but discuss what I meant not what I wrote

[Dave Brand]

Originally Posted by GORDON STREETER

Dave. Out of interest were they 2 or 4 strokes ?

Four-stroke V-twins.

[dtype38]

On my straight six I've lagged the exhaust manifolds down to the silencer. Worked wonders for underbonnet temperatures... no idea what its done for the performance, but now I don't melt my aluminium bulkhead or bubble the paint on the bonnet when I stop!

[AU N EGL]

Originally Posted by Al Weyman

Yeah and bloody hot they get too!

I though that may be I could carry my Lunch with me.

You know heat up the left overs wrapped in aluminum foil by putting them in the passenger side foot well.

[S14GJC]

Hi all,

Jusr reading abou this lagging/heat wrap. Recently I had heat problems with my Astra VXR done at Thorney Motorsport. It's pushing out just over 300BHP huge amounts of torque but we had problems with heat. John recommened a cermaic coating he sells from Zircotec, which we had done on the manifold, turbo housing, downpipe and half the system.

BIG difference I can tell you! There is much less heat now the performance is better, we put my car on John's rolling road and found the turbo performing better. Engine bay temp was down too which helps for the induction too. Another plus is it's so much nicer than the wrap, you hardly see it there and John tells me I won't need to worry about it again for as long as the bits are working! It wasn't the cheapest solution but it certanly makes a difference, well worth investing in!

[TomBE]

from what i have heard / made up from it / tought about:

- atmo. engines: wrapping keeps heat in the exhausts, which means it has a larger volume, therefore a higher velocity and by that draws (a small) underpressure at the exhaustvalve when it opens, which should result in (a small) hp increase. plus it keeps the (radiation-) heat from the headers from giving it to the engineblock, therefore keeping it cooler.

- turbo engines: wrapping the headers keeps the heat (which is converted to pressure in the turbo) from escaping, therefore having more energy to give to the turbocompressor, and thereby increasing pressure thus power.

downside is ofcourse the immense temperatures of the headers.

if you have any toughts or confirmations, please note!

[Adam43]

As I said on the previous page we did this on our Jags and have now gone for it on the MGB. I can't see a downside, so worse case is no gain. We put it on at the weekend:

The engine and gearbox have just gone back in and it was the ideal time to do it. Of course we forgot and just as I finished tightening the prop shaft bolts engine mounts and I said "you know what we didn't do...". Cue scrapped knuckles. It would have been so easy when the engine was out!

Still wondering whether to have a go at Gordon's cooling inlet manifold suggestion.

[tristancliffe]

I can't remember which Lotus is was that tried it - might have been the Esprit - bug lagging the exhausts caused the metal to melt! Plus it was down on power as the gasses weren't allowed to cool quickly - and you do want them to cool quickly. As I said before, professional teams, be it F1, GP2, DTM etc don't use it because they want more power.

At a push I'd consider ceramic coating, not to improve performance, but to stop bodywork/wiring melting and paint blistering.

TomBE - hot gasses have a higher pressure which means they travel more slowly. Low pressure = fast flow velocity

[Adam43]

Lagging an F1 or DTM exhuast is a little different. These are made of exotic materials and run at different temperatures anyway. GP2 is a spec. series. I dare say that in some applications it is unwise, but for our MGB, I'm pretty confident there isn't a down side. There is plenty of exhuast under the car to lose heat; I'd prefer it to do it there than in the engine bay between my Webers.

[Chris Y]

I wrapped my exhausts a few years back - thinking there weren't any downsides.

Then, after two engine rebuilds (different engines) where the exhaust manifolds had warped and wouldn't fit back onto the heads, I stopped doing it! These were cast iron manifolds though. I think the headers you have there Adam are more suitable.

[BertMk2]

One thing to watch out for with exhaust wrapping - if you have any oil flying about under the bonnet the wrapping soaks it up nicely and eventually starts a small but persistent fire. It takes ages to cut off charred oil soaked wrapping too.

Not that this has ever happened to anyone of course