Lagging exhuasts

[tristancliffe]

For best exhaust performance you want to keep the heat in the exhaust - look at F1 and Top Fuel cars - they do NOT lag their exhaust pipes. There might be a tiny benefit in lagging a closed wheel car as it MIGHT reduce the under bonnet temperatures sufficiently to give another horsepower or two, but I'm not a believer.

Exhausts scavenge better with higher temperatures. Lagging also increases the chances of the exhaust material becoming too hot and it softening/deforming.

[terence bower]

Which is exactly the reason we stopped lagging Manifolds years ago,got pee'd off with having to keep welding them up again!!

[Adam43]

Originally Posted by tristancliffe

For best exhaust performance you want to keep the heat in the exhaust - look at F1 and Top Fuel cars - they do NOT lag their exhaust pipes.

I am a little confused by this. I thought the point of lagging was to keep the heat in the exhaust.
I guess F1 don't do it because the inlet is quite separate from the exhaust and the temperatures acheived on the exhaust pipes are very high meaning simple lagging would be difficult.

There might be a tiny benefit in lagging a closed wheel car as it MIGHT reduce the under bonnet temperatures sufficiently to give another horsepower or two, but I'm not a believer.

I've often wondered about this. On our 6 cyl XJS the exhaust manifold was on the opposite side to the inlet. We wrapped the exhaust, but I did wonder if it was worth it.

Exhausts scavenge better with higher temperatures. Lagging also increases the chances of the exhaust material becoming too hot and it softening/deforming.

Originally Posted by terence bower

Which is exactly the reason we stopped lagging Manifolds years ago,got pee'd off with having to keep welding them up again!!

Never had that problem on the XJS, but it was a meaty manifold.
However the engine is out of the MGB at the moment, so it is the perfect time to lag the exhaust. I thought it was a good idea on this as the exhaust and inlet are on the same side and very close. This could help inlet temperatures?
So I split the thread because I was interested in everyone's views on this.

[GORDON STREETER]

Originally Posted by AdamAshmore

However the engine is out of the MGB at the moment, so it is the perfect time to lag the exhaust. I thought it was a good idea on this as the exhaust and inlet are on the same side and very close. This could help inlet temperatures?

That's a good idea on a non crossflow head and if you look here http://www.flickr.com/photos/16345037@N03/2469669739/
I used this to good effect in my car (although you can't see the lagging) in the mid 90s complete with cooling tubes for the inlet manifold after testing it on the dyno with an air line. I never had any trouble with cracking exhaust manifold tubes because they were all individual and sprung loaded into the head and the collector box.
All this attention to detail made for an engine that kept its HP throughout the race, and at the time was pretty unbeatable and gave me loads of class wins.

[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

[GORDON STREETER]

If anyone is confused on the start of this thread look here http://www.ten-tenths.com/forum/showthread.php?t=111697

[Adam43]

Nice set-up.

The MGBs inlet manifold is shielded well from the exhaust, but I will make sure the heat shield is as good as it can be before bolting back together.

I'd not considered cooling the inlet manifold. I'm intrigued that you chose to cool the manifold rather than provide cool air into the carbs. Is that because of the lack of space by the side of the webers?

When moving I have no problem with temperatures even on the hottest days, so putting in more ducting could b an option for us.

[GORDON STREETER]

I had tried a cold air box in the past, but the inlet manifolds were bespoke and built to the optimum length to compromise for power throughout the range. As you have rightly said there wasn't" a lot of room without major surgery to the inner wing (not allowed anyway) or canting the engine over enough. If I did that I might as well have had a downdraft head.http://www.flickr.com/photos/16345037@N03/2279860027/
We did make sure that there was plenty of cool air funnelled from the front panel.

[AU N EGL]

I know we all speak English, but WTH is "Lagging?"

[terence bower]

Insulating with a fireproof material,winding it around the manifold.
We have done a back to back on this,several years ago on a rolling road,one with,one without,the result? 0!!
I should add that the cracking occurs mainly in Stainless,not just Bs but also on Griffiths.The problem starts with condensation building up in the lagging and then being burnt off again.Cooling the inlet?,4in air intake to with-in 10inches of the carb will cure it,downside of in cooler weather the carb can start icing up.

[AU N EGL]

Ohhh Thanks Adam

Or what about ceramic coating your headers.

My headers are ceramic coated to move heat out the exhaust, not radiate into the engine bay

[Adam43]

It is exhuast wrap:

[bdwoody]

we do that to over here AU, its just the lagging route is cheaper .i m not sure how much benefit either has though...

[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.

[AU N EGL]

It keeps my engine bay and my foot well cooler and that is a big help. HP changes, I have no idea