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This is one of those "is it worth it" things, that I don't know would fit into the same category of cello-taping over panel seams to improve aerodynamics, or into the category of adding a barn door spoiler to a bicycle to improve traction in corners.
(ie, pointless, or downright silly)

Would wrapping a manifold make any (positive) difference to a non turbo road / slight track car ?
 

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We can argue about performance benefits, but in theory keeping the exhaust gasses hot means they are light and fast and flow better. But the main benefit for me would be keeping the temp in engine bay lower thus protecting the wiring from heat that makes cables and plastic fragile over time. Cooler intake temp might be benefit too. Wraping the pipes also makes them stiffer and less prone to resonances so the exhaust note might change as well, its more damped and not so metallic.
 

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........ snip...........

Would wrapping a manifold make any (positive) difference to a non turbo road / slight track car ?
Yes......... BUT............. it's hard to say if it's worth it or not.

I used do do some road racing with small, hatchbacks (VW Golf mainly). The rules allowed a few modifications including the exhaust system. Everyone, including me, wrapped the exhaust system, but only as part of many other modifications. As far as I know, dyno data for just exhaust wrapping alone is VERY scarce for obvious reasons. But since I had the engine out more times than I care to think about, wrapping the exhaust fell into the category of not overlooking any potential legal performance improvement, no matter how small. But that was racing, which is different from the real world.

I think most folks would agree that any performance improvement associated with wrapping the exhaust is going to be small. Will you notice it on a street car? Doubtful, in my opinion. It's cheap though.

Problem is, you gotta remove the exhaust manifold. I think I would do the wrapping only if I had the manifold off for some other reason. And I'd do that only after I made relatively inexpensive (and reversible) changes which are more likely to produce genuine performance improvements. I'd first think about stiffer/lower springs, different anti-roll bars, better dampers, improved wheels and tires, strut braces, better intake system, improved exhaust components, better brake components and/or brake cooling, improved driver restraint and/or drivers seat (don't underestimate the performance improvement associated with a good 5 or 6 point harness and a real racing seat), etc. You can expect these changes to make track days a lot more fun.

I would also be concerned about the tendency of the wrap to absorb moisture and cause increased manifold corrosion.
 

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I wrapped mine in my 155, no noticeable difference in performance, but engine bay temp was a lot lower though.

I use a racing seat with a 6 point harness and feedback it gives from the car is amazing :)
Depends on how far you want to go though.
 

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I wrapped the manifolds on the 155. The wrap reduced noise from the engine bay marginally (v6) but it also reduced the temperature in the engine bay a little, particularly at the back.

The second bank of cylinders is right up against the bulkhead so I get a slightly cooler cabin in the summer (no air-conditioning in my beast)... plus hopefully it'll give an easier time of it to the starter motor and alternator which are all packed in the back there.

I wrapped the front manifold too for consistency.. but apart from it looks better than the rusty manifold pipe, I didn't notice any hugely beneficial side-effects on the front.

If you have a T/Spark it may be worth lagging the pipe where it passes under the sump.. since that extra heat does (according to legend) bake the big-end for #3 cylinder... :)


Ralf S.
 
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I'd again echo the sentiments above, may produce more power but the main gain is cooler under bonnet temps which be fits the longevity of everything else.

It's not a nice job though and you need to ensure thy are wrapped evenly otherwise the manifold can crack due to localised heat spots. This isn't much of an issue on a tspark but on a v6, replacing the rear manifold is fairly laborious.
 
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