Exhaust wrap - why?
Discussion
Why is exhaust wrap used for performance gains?
In my ignorance, I would have thoght that if the exhaust gas was allowed to cool it would reduce in volume, and hence improve the effective flow rate of the pipes.
Conversly, keeping it hot makes the exhaust system more restrictive as it has a greater volume of gas to get rid of.
I'm obviously missing the point in regard to the performance claims made in wrap / coating adverts.
In my ignorance, I would have thoght that if the exhaust gas was allowed to cool it would reduce in volume, and hence improve the effective flow rate of the pipes.
Conversly, keeping it hot makes the exhaust system more restrictive as it has a greater volume of gas to get rid of.
I'm obviously missing the point in regard to the performance claims made in wrap / coating adverts.
I would say that keeping underbonnet air cool was my motivation. Also to prevent excess oxidation. I suppose that the rate of heat loss is relatively insignificant to the density of the gas, temperature, speed of shockwaves, etc. It may help but only decimal places of a %, that's a rough guess. I'd also look at what other means of achieving it are, glass tape comes in less expensive forms.
I do it because it reduces the heat into the engine bay. The manufacturers also claim that it increases the exhaust tuning effect, and I can see in principle that it might help to have more momentum in the exhaust in some cases, but I don't know how much difference that makes in practice.
The science behind the alleged performance gains is dubious at best.
Yes, gas flows faster when it is hotter BUT is also occupies more volume and so HAS to flow faster. Any improvement would come from reduced under bonnet temperatures and at speed even this effect would be minimal.
I fit it to stop me and my Dad burning our hands on the race car when it has broken again, and to stop the exhaust melting everything nearby, including the starter motor.
Yes, gas flows faster when it is hotter BUT is also occupies more volume and so HAS to flow faster. Any improvement would come from reduced under bonnet temperatures and at speed even this effect would be minimal.
I fit it to stop me and my Dad burning our hands on the race car when it has broken again, and to stop the exhaust melting everything nearby, including the starter motor.
Hotter gasses do take up more volume but accelerate out the exhaust system much faster, the faster the exhaust gasses get out of the cylinder the better scavenging you get, I.E. more intake charge is allowed into the cylinder on the following cycle (the quickly exiting exhaust gasses can actually suck the intake charge into the cylinder) and that will get you some performance gains. The wraps tend to rust out headers fairly quickly though.
Edited by Trooper2 on Wednesday 18th October 04:34
So, apart from the under bonnet heat reduction, there doesn't seem to be any support for the claimed power advantages then.
I understand the claim that hot gas accellerates faster - don't know why, maybe it's because it's less dense. BUT since there's more of it 'cos it's hot that even the whole thing out.
I wonder what the effect would be of having an oversized cooled manifold and system would be. The gas entering the manifold would contract, which would aid port scavenging. No practical application of course, due to the weight/complexity of cooling the exhaust system!
Anyway - can anyone tell me how exhaust manifold heat retaining wrap gives power gains?
I understand the claim that hot gas accellerates faster - don't know why, maybe it's because it's less dense. BUT since there's more of it 'cos it's hot that even the whole thing out.
I wonder what the effect would be of having an oversized cooled manifold and system would be. The gas entering the manifold would contract, which would aid port scavenging. No practical application of course, due to the weight/complexity of cooling the exhaust system!
Anyway - can anyone tell me how exhaust manifold heat retaining wrap gives power gains?
Paul Drawmer said:
Anyway - can anyone tell me how exhaust manifold heat retaining wrap gives power gains?
It is the same mass flow rate but has a higher velocity because it is hotter. The higher velocity means it has more momentum (mass x speed) which means the pressure pulses are greater, which means it tunes more strongly (and at different rpm) than the cooler exhaust. This is how it can, in theory, produce more power. Can't say I've noticed any difference to the engine running characteristics on mine, but the rate of under-bonnet electronic failures dropped off dramatically with it fitted, and the whole engine bay runs a lot cooler. Mine also hasn't suffered any significant corrosion.
wadgebeast
As a B these were Peter Burgess comments
Exhaust wrap.....
I am not convinced of the effectiveness of heat wrap...Keeping the exhaust isolated from the inlet manifold/induction system is great....use a physical barrier. Keeping the heat in the exhaust system could lead to extra heat being trapped in the cylinder head, reducing efficiency...in the same way that I understand stainless steel exhaust manifolds tend to keep the heat in the head. I have had two negative experiences with heat wrap....
1) MGB standard race car with heat wrap....after the end of the season the engine was replaced with next years' engine...only the owner rang up to say the new head was faulty as the studs didn't line up with the manifold ( standard CI)....after much head scratching (
) it transpired that the manifold had warped by some 1/4 of an inch or so.....we wondered where the extra heat 'lived' under running conditions.No heat wrap from then on!
2) Ford Capri 2.1 Pinto with twin 45 Webers, hairy cam and monster cylinder head.....belonging to a friend...we relayed the story about the MGB ex manifold....bravely, our friend ripped off the wrap (about £30 worth!)....result 4 bhp increase, which seems to be attributed to removing the heat wrap. The engine is a x-flow so no heat was being saved from direct contact with the inlet manifold as in the MGB scenario, the benefit of having a cooler underbonnet area was more than wiped out by whatever was happening inside the head with the reduced heat rejection.
Overall, I get the feeling we can cause more problems than we cure with using heat wrap.
Peter
Interesting read
www.centuryperformance.com/heatwraps.asp
As a B these were Peter Burgess comments
Exhaust wrap.....
I am not convinced of the effectiveness of heat wrap...Keeping the exhaust isolated from the inlet manifold/induction system is great....use a physical barrier. Keeping the heat in the exhaust system could lead to extra heat being trapped in the cylinder head, reducing efficiency...in the same way that I understand stainless steel exhaust manifolds tend to keep the heat in the head. I have had two negative experiences with heat wrap....
1) MGB standard race car with heat wrap....after the end of the season the engine was replaced with next years' engine...only the owner rang up to say the new head was faulty as the studs didn't line up with the manifold ( standard CI)....after much head scratching (
) it transpired that the manifold had warped by some 1/4 of an inch or so.....we wondered where the extra heat 'lived' under running conditions.No heat wrap from then on! 2) Ford Capri 2.1 Pinto with twin 45 Webers, hairy cam and monster cylinder head.....belonging to a friend...we relayed the story about the MGB ex manifold....bravely, our friend ripped off the wrap (about £30 worth!)....result 4 bhp increase, which seems to be attributed to removing the heat wrap. The engine is a x-flow so no heat was being saved from direct contact with the inlet manifold as in the MGB scenario, the benefit of having a cooler underbonnet area was more than wiped out by whatever was happening inside the head with the reduced heat rejection.
Overall, I get the feeling we can cause more problems than we cure with using heat wrap.
Peter
Interesting read
www.centuryperformance.com/heatwraps.asp
) for these coatings to be applied? The way I read it he is saying wrap is bad because it keeps heat in and the coatings are good because it... keeps the heat in. I can understand why he is frustrated by talking to "engineers". I have a similar problem with talking to "experts"!
I had some wrap which I gave away as I didn't like the idea of it accelerating the corrosion of tubular manifolds but I can see it as being extremely effective method of engine bay heat control.
I had some wrap which I gave away as I didn't like the idea of it accelerating the corrosion of tubular manifolds but I can see it as being extremely effective method of engine bay heat control.
MGBV8 said:
wadgebeast
As a B these were Peter Burgess comments
Exhaust wrap.....
I am not convinced of the effectiveness of heat wrap...Keeping the exhaust isolated from the inlet manifold/induction system is great....use a physical barrier. Keeping the heat in the exhaust system could lead to extra heat being trapped in the cylinder head, reducing efficiency...in the same way that I understand stainless steel exhaust manifolds tend to keep the heat in the head. I have had two negative experiences with heat wrap....
1) MGB standard race car with heat wrap....after the end of the season the engine was replaced with next years' engine...only the owner rang up to say the new head was faulty as the studs didn't line up with the manifold ( standard CI)....after much head scratching ( ) it transpired that the manifold had warped by some 1/4 of an inch or so.....we wondered where the extra heat 'lived' under running conditions.No heat wrap from then on!
2) Ford Capri 2.1 Pinto with twin 45 Webers, hairy cam and monster cylinder head.....belonging to a friend...we relayed the story about the MGB ex manifold....bravely, our friend ripped off the wrap (about £30 worth!)....result 4 bhp increase, which seems to be attributed to removing the heat wrap. The engine is a x-flow so no heat was being saved from direct contact with the inlet manifold as in the MGB scenario, the benefit of having a cooler underbonnet area was more than wiped out by whatever was happening inside the head with the reduced heat rejection.
Overall, I get the feeling we can cause more problems than we cure with using heat wrap.
Peter
Interesting read
www.centuryperformance.com/heatwraps.asp
As a B these were Peter Burgess comments
Exhaust wrap.....
I am not convinced of the effectiveness of heat wrap...Keeping the exhaust isolated from the inlet manifold/induction system is great....use a physical barrier. Keeping the heat in the exhaust system could lead to extra heat being trapped in the cylinder head, reducing efficiency...in the same way that I understand stainless steel exhaust manifolds tend to keep the heat in the head. I have had two negative experiences with heat wrap....
1) MGB standard race car with heat wrap....after the end of the season the engine was replaced with next years' engine...only the owner rang up to say the new head was faulty as the studs didn't line up with the manifold ( standard CI)....after much head scratching (
) it transpired that the manifold had warped by some 1/4 of an inch or so.....we wondered where the extra heat 'lived' under running conditions.No heat wrap from then on! 2) Ford Capri 2.1 Pinto with twin 45 Webers, hairy cam and monster cylinder head.....belonging to a friend...we relayed the story about the MGB ex manifold....bravely, our friend ripped off the wrap (about £30 worth!)....result 4 bhp increase, which seems to be attributed to removing the heat wrap. The engine is a x-flow so no heat was being saved from direct contact with the inlet manifold as in the MGB scenario, the benefit of having a cooler underbonnet area was more than wiped out by whatever was happening inside the head with the reduced heat rejection.
Overall, I get the feeling we can cause more problems than we cure with using heat wrap.
Peter
Interesting read
www.centuryperformance.com/heatwraps.asp
Cheers fella. I've had no problems with the head, but then again I've not had to take the thing off for a while. Might take the lagging off and test it, although the biggest improvement I've ever found to make the car go faster is to get rid of wife weight....
leorest said:
The way I read it he is saying wrap is bad because it keeps heat in and the coatings are good because it... keeps the heat in. I can understand why he is frustrated by talking to "engineers". I have a similar problem with talking to "experts"!
I had some wrap which I gave away as I didn't like the idea of it accelerating the corrosion of tubular manifolds but I can see it as being extremely effective method of engine bay heat control.
I had some wrap which I gave away as I didn't like the idea of it accelerating the corrosion of tubular manifolds but I can see it as being extremely effective method of engine bay heat control.
I thought that wraps are on the outside of the exhaust, coatings on the inside? So with a wrap, heat from the exhaust gas gets into the exhaust system, can't escape, so it all gets hot and conducts to the head. With coatings, heat from the exhaust gas stays in the gas, the exhaust metalwork runs cooler. With a turbo, keeping the exhaust gases hot before the turbo means you get faster spool up.
I put some wrap on the brand new manifolds I fitted to the 350i as I was concerened about under bonnet temps. It did seem to keep the engine bay cooler, but 18 months later, the manifolds started blowing. When I removed the wrap ( at first I thought it was the gasket, but had to remove some wrap to get access to the bolt ) I found both manifolds completely rotted out. I complained to the manifold supplier as I expected new manifolds to last more than 18 months, and the first thing he asked me was whether I had used wrap, so obviously he knew there was an issue with it. The replacement manifolds were a) stainless and b) not wrapped! When I bought new manifolds for the Griff they were a ) stainless and b) ceramic coated ( still worried about under bonnet temps ) but as they are not fitted yet, I cannot say how good they are.
If I was buying new manifolds I'd think about having them ceramic coated. Having the insides insulated from the hot corrosive exhaust gases seem like the best move. But I would say if the exhaust literally rusted out from the inside that quickly there's something funny going on. Did you have a lot of corrosion on the outside too?
Manifolds were rusty from both sides. I think the wrap had got damp during periods of non use ( I now have a dehumidifier in the garage ) and this held the water against the metal causing the outside to rust. I accept this was not the manufactures fault. However, they were also rusty from the inside, which I was VERY unhappy about. In fairness, the supplier ( A well known TVR specialist ) did give me a discount off the replacement stainless ones I bought ( other wise I would have taken my business else where ). Just for the record, I have used this company on & off for 10 years now, and other this have never had any cause for complaint.
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