Technical Removing Cylinder head

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Technical Removing Cylinder head

Will it not decrease performance? If you keep the gases hot they occupy more volume - so you'll put a higher gas flow rate through the cat and create more backpressure?

Also, if not carefully maintained and you get oil spillage on it it can become a fire risk.
 
The cold air box will combat the decrease in performance caused by the under bonnet temperature. Exhaust wrap is used in some* race cars but remember this is for out and out performance and unless you are seriously** preparing your car for competition use it won't make any difference. Back pressure is irrelevant, exhaust gases leaving the cylinder are dictated by the pressure wave effect.

*'Some race cars' does not include F1 which is the height of engine technology - bare that in mind.

**'Seriously' means an entire strip down, blueprint, head work, new con rods, pistons etc.
 
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Well I've known several people wrap the manifold and at least one who's proved a small performance increase on the dyno. Of course the benefits will vary by car and other mods.

I've got a friend who's involved in the design of CATs and he said it should work better, or at worst the same.

I really don't think your going to crack the manifold, perhaps on a modified turbo........

In terms of fires: most of the sellers claim the wrap actually reduces the chances of a fire as the exhaust wrap is designed to be fire retardant.

Here's some advertising about why it's good and how it effects the gasses: http://www.autoinparts.com/Heat_Shield_Products-Exhaust_Wrap/c868_869/index.html

Please note, I'm not claiming to be an expert, I'm just trying to add to our discussion :)
 
Is the heat shield just human protection type thing or does it really serve a purpose - radiator was mentioned?? Basically if the heat shield falls off, what is the consequence? I was thinking under bonnet temperatures would rise in traffic but maybe that is just a minor thing.....

Matt, this is the purpose of forums, constructive discussion, I love it!!
 
Of course, clean it, now why didn't I think of that? :D

As to the heat shield. I'd always thought it was partly there to protect the radiator which sits opposite it. However, driving without it didn't seem to effect some people on the forum. I also noticed that when my car had it's accident and the radiator was pushed so it was almost touching the bottom of the heat shield the car still seemed fine, even in 25 degrees.

Another reason to think the radiator isn't an issue is that my MR2 has one and the engine is at the back and the radiator is at the front! Of course they may have left it on as the engine is a "standard" unit.

I would therefore hazard a guess that it's to keep engine bay temperatures down.

I wouldn't have thought it's to do with protecting people as a mesh would be cheaper and protect it enough.
 
well I will give it a bit of a clean but dont really want to get into changing anything other than I need to to get it to run again, remember I havent actually driven this car, it has no history and may be a dog (then again it may be a gem!).

Anyway, result 1, ordered a new head gasket set from ebay - advertised as bankrupt stock, and just the head and manifold gasgets, it arrived today as a complete set, all gaskets, sump gasket, camshaft oil seals, valve stem seals etc - all for £20 rather than £80 at other places so that should keep the rebuild costs a bit lower!
 
The cold air box will combat the decrease in performance caused by the under bonnet temperature. Exhaust wrap is used in some* race cars but remember this is for out and out performance and unless you are seriously** preparing your car for competition use it won't make any difference. Back pressure is irrelevant, exhaust gases leaving the cylinder are dictated by the pressure wave effect.

*'Some race cars' does not include F1 which is the height of engine technology - bare that in mind.

**'Seriously' means an entire strip down, blueprint, head work, new con rods, pistons etc.

Ah, but with higher backpressure won't you end up with less scavenging effect?
 
Exhaust gas scavenging occurs when the pressure wave from the fired cylinder 'bounces' off of the closed exhaust valve of the next cylinder in the firing sequence.

I didn't mention anything about a high back pressure HP, you did in post 21.

By all means wrap your exhaust, its your car. I'm just giving some advice. Also the heat shield prevents the exhaust manifold radiating heat into your radiator.
 
I was thinking of wrapping the pipes because firstly I want to get another induction kit and secondly because the cover already in it is beginning to break...
 
Exhaust gas scavenging occurs when the pressure wave from the fired cylinder 'bounces' off of the closed exhaust valve of the next cylinder in the firing sequence.

I didn't mention anything about a high back pressure HP, you did in post 21.

By all means wrap your exhaust, its your car. I'm just giving some advice. Also the heat shield prevents the exhaust manifold radiating heat into your radiator.

No offence intended fella, just asking questions as I'm not too sure about it myself. Some of the talk on the advertising pages don't seem to make a lot of sense.

Had a search, Guy Croft suggests it's not such a good idea:
http://www.guy-croft.com/viewtopic.php?f=13&t=759&hilit=exhaust+wrap
 
Hey HP, sorry buddy I didn't mean to sound edgy I only had a few minutes to spare. I have guys Fiat/Lancia twin cam book so your definitely on the right track with that website. Nice to know other people share the same interests. You can't go wrong with Guy's advice.
 
Sorry to post so late after your pics...been busy upsetting mods:D That is a lovely MG and VERY big respects to you for taking on this huge job. May the force be with you:worship:
 
Thanks for the messages of encouragement. I have only embarked on the first half of the job so far, i.e. taking the head off, I imagine the other half will be much harder. What I can say is that I am by no means a qualified mechanic, yes I tinker with the MG, yes I know how everything works in principle but I have not rebuild 1000 engines or anything like that!! Taking the head off took about 11 hours in total and most of that was spent thinking (at different stages). The only thing that was remotely difficult was getting the bracket that supports the inlet manifold to the engine block off, it needed a bit of arm bending, everything else was quite straight forward. I would imagine all in all this would cost over £1500 for a garage to do (including the head rebuild) which would more than likely mean that most poeple would think of selling for spares (especially one like mine that isnt perfect and has no history). For me, all in all it will have cost about £500 (rebuild head, new gaskets, oil and filter changes, new head studs, new tensioners, new cam belt, cam locking tool) which is much more in the relms of it being worth putting the car back on the road. The car having cost me much less than £1000 means that I can justify spending £500 and a few weekends to put it back on the road.

Anyway, lets not get ahead of ourselves, it isnt running yet and I still have a long way to go but loving every minute of it so far! (apart from the initial engine noise when the tensioner fell to pieces!)

Regards

Chris
 
Interesting link, this Guy Croft thing that is. Don't know who he is though :)

I would certainly not wrap a turbo'd car, especially one with an after-market turbo. From experience of a turbo on an MX-5, the manifold is already under more stress.

Having said that, it looks like the increased temperature in the manifold of a lightly tuned NA car with an exhaust wrap is less than you'd get from adding a turbo.

The only dyno proved gain I know of, was on a tuned Mini 1275 which got up to 120bhp using carbs (the wrap added around 10, if I remember rightly). I would expect a lot less for the Barchetta, unless you are using a cone air filter. In that case the reduced under-bonnet temperature should help a lot.

Otherwise the only benefit I can see if that you could run without the heat shield. This could save a bit of hassle as they have a tendency to break and then rattle!

In terms of any cracking problems: LRB, how long ago did you fit your and have you had any problems?
 
Matt, the improvement on the mini could be bigger as the exhaust and inlet manifolds are on the same side of the head. I'm guessing really, but I'd think it'd reduce heat transfer to the intake if wrapped (and the joining piece cut off!)
 
I wrapped my manifold about 16 months ago and have had no problems at all - just to clarify that my manifold is a std FIAT one, if it was stainless I would not contemplate wrapping it.

I wrapped mine as I was fitting the Green cone filter and wanted to keep the temp down while in traffic, I have to say that wrapping the exhaust worked a treat and has made a big difference to the temp under the bonnet.

One tip is if you are going to wrap it do it while its off the engine otherwise its a bloody nightmare!
 
Matt, the improvement on the mini could be bigger as the exhaust and inlet manifolds are on the same side of the head. I'm guessing really, but I'd think it'd reduce heat transfer to the intake if wrapped (and the joining piece cut off!)

Good point!
 
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