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MG MGB Technical - Manifold: CI or Tubular

What is the considered opinion of the troops on choice of manifold.

Is the old Cast Iron best, or should I opt for the tubular sort.

This is for a normal spec car, and I would like to use the most efficient and effective solution.

Alex

I'd vote for the original CI piece. It's a reasonably efficient design and comes with none of the headaches of a tubular manifold (fitment, leaks, more noise, higher underhood temps...) If your car is otherwise stock there are better places to start when looking for HP, such as making sure the engine is in top shape and proper tune, less restrictive air cleaners, and others amply discussed in the archives.
Rob Edwards

There are a raft of problems with tubular such as alignment and warping that cast-iron don't suffer from - if you can get them. Dunno about efficiency being one of the benefits, though.
Paul Hunt

Alex-
Tubular headers radiate more heat into the engine compartment, warp readily, and are far noisier than the cast iron manifold which is an excellent design for use on a stock engine. If you want to improve its flow characteristics a bit, just have it electropolished. It will then flow about as well as any 1 3/4" tubular header. You might even consider having it coated with a ceramic material to reduce operating temperatures inside the engine compartment. Taken together, these two modifications should cost less than a tubular header. Whatever you do, don't switch to a 2" Big Bore exhaust system if you're leaving the engine in an otherwise stock state of tune. The reduced backpressure can cause problems, some subtle, some more obvious, but will garner you little in the way of a performance increase without making other modifications.
Steve S.

Alex,

Ceramic coating is available in UK but fairly limited and fairly expensive but try Camcoat if going this route.

Paul
Paul

Glad I hung onto the Cast Iron manifold, as it seems to be the preferred choice.

What is electropolished exactly, I'm sure its not just
having it plated. I can't imagine how the manifold internal bores can be polished.

Also if the manifold is to be electropolished, does it also have to be coated with a ceramic material, or is it one or the other, or half and half.


Alex

Alex-
Electropolishing is an electrochemical process used to smooth metal, usually prior to plating. It is commonly performed on a precision casting (such as a window winder handle) or on prepolished sheet metal after it has been formed to shape (such as a bumper) prior to plating it. The item to be electropolished is thoroughly cleaned, then emersed in a chemical bath. A current is then run through and the highest points on the surface of the metel are removed. In a sense, it's the reverse of plating in that metal is removed instead of deposited. Because the item is completely emersed, the polishing reaches into every crevice, so it will polish the interior of an exhaust manifold quite nicely, making for reduced turbulence in the exhaust gas flow. Be sure to instruct the firm to protect the gasket surfaces with plater's tape. Once the manifold has been electropolished it can then be given a ceramic coating. If you do choose to have the exhaust manifold ceramic coated, be warned that if only its exterior is coated, the heat will build up inside of it until it warps, just as if you has wrapped it in insulating tape. Have it coated inside and out or don't bother. If you choose to not have it ceramic coated, simply paint its exterior with a good quality thermoconductive paint.
Steve S.

Alex-
Electropolishing is an electrochemical process used to smooth metal, usually prior to plating. It is commonly performed on a precision casting (such as a window winder handle) or on prepolished sheet metal after it has been formed to shape (such as a bumper) prior to plating it. The item to be electropolished is thoroughly cleaned, then emersed in a chemical bath. A current is then run through and the highest points on the surface of the metal are removed. In a sense, it's the reverse of plating in that metal is removed instead of deposited. Because the item is completely emersed, the polishing reaches into every crevice, so it will polish the interior of an exhaust manifold quite nicely, making for reduced turbulence in the exhaust gas flow. Be sure to instruct the firm to protect the gasket surfaces with plater's tape. Once the manifold has been electropolished it can then be given a ceramic coating. If you do choose to have the exhaust manifold ceramic coated, be warned that if only its exterior is coated, the heat will build up inside of it until it warps, just as if you has wrapped it in insulating tape. Have it coated inside and out or don't bother. If you choose to not have it ceramic coated, simply paint its exterior with a good quality thermoconductive paint.
Steve S.

I remember somewhere reading an article about using heat tubing on the exhaust manifold for similar reasons (less heat in the engine bay). The person who did it ran into much worse problems and finally realized it was from heat being transferred back into the engine instead of radiating out of the manifold. I suspect ceramic coating would produce a similar result.
Steve Simmons

Never had any personal experience, but I've always been intrigued by the Extrude Hone process:

http://www.extrudehone.com/
Rob Edwards

I don't know about you, but I'd like to know what this is...

http://www.extrudehone.com/jpg/intakewputty.jpg
Steve Simmons

Steve-
Reread the last part of my previous posting. If the exhaust manifold is coated inside and out, the hot exhaust gases just pass through it. The coated manifold is sealed by the ceramic coating so that it can't absorb the heat from the exhaust gases, thus no heat retention problems. If only the exterior of the manifold is coated, you'll have all the heat retention related problems that you can think of.
Steve S.

Looks disgusting, doesn't it? I think that is the abrasive paste being forced through an intake plenum and runners. For those that don't know, the process works by forcing the abrasive paste through something like a manifold, and the paste wears away the high spots, roughness, etc. By the nature of the process the points of maximum restriction are abraded the most whilst the least restrictive receive the least material removal. It allows you to port and polish complex castings that would have previously required to be cut apart, worked on, and then rewelded...
Rob Edwards

Thanks Steve S for your comments, I understand now.

The question now is does anyone in the UK know any vendors who can do electropolishing, and others who can do ceramic coating.

Also, any idea of what the cost should be.
Alex

Alex,

www.camcoat.u-net.com About £60 - £150 depending on finish.

Paul
Paul

sorry to throw a spanner in the works, i just changed my exhaust system for one with a tubular mnanifold and must say i would recommend it to anyone!

I havent noticed a very great cabin temp, perhaps the passenger side is marginally so, but never venture that side and besides its my first summer with car so i dont really have much experience to go on....

My car is 72 BGT, its fitted with unleaded head and K&N's i have just learnt its had a rebore, but is not heavily modded.

The increase in the willingness of the engine to rev was very very noticeable indeed as soon as the system was fitted. I was rather sceptical at first on fitting the system but am now hooked - i would definitely recommend it over the standard manifold which i dont think allowed the exhaust gases to exit quick enough from the engine using the standard system.

In the UK you can pick up a tubular manifold for less money than the top price quoted by paul for the coating you would need on the cast iron original to make it as smooth inside and then you have to take into consideration that the tubular manifolds are still usually free-er flowing with less severe exit angles from the engine block to main pipe than the original system... I would still say that even with a standard engine (as mine nearly is) there is a noticeable rise in the useability of the engine with the new system that far out ways any of the lesser points that have been mentioned.

IMHO ~PHIL
phil earl

Paul's estimated prices came as something of a shock,very pricey indeed.

At between £60 - £150, depending on finish, it certainly makes a canny Scot think twice about the comments of phil earl who seems to rate the tubular route.

I was expecting a price closer to say £ 25, but those prices certainly make me think.

Also what does depending on finish mean, surely there is only one finish.
Alex

It appears that to use the CI manifold, a lot of money has to be spent in order to bring it up to the performance of a tubular manifold.

As with all things, there are quality products, and duffers, so all these problems about fit etc surely come down to purchasing a top quality tubular manifold, one that actually fits properly.

In addition, there is the question of bog standard mild steel or stainless.

phil earl may be able to enlighten us on the brand of his manifold, or failing that the name of the vendor, and how much he paid for it, and anyone else for that matter might care to chip in.

Re mild steel, has anyone considered nickel plating in order to protect, and possibly save against the cost of stainless, just an interesting comment made to a friend of mine.
Fred

Protect against what? They get so hot that corrosion isn't likely unless given very little use. I painted mine with silver high-temperature paint several thousand miles ago and apart from one or two very small areas where perhaps prep wasn't perfect or I inadvertantly touched the surface between prep and spraying it is still sound. Unless one gets one of the latest manifolds with the correct flanges stainless steel are likely to be as mismatched to the head ports as mild steel.
Paul Hunt

Sure guys

I bought a double S stainless steel tubular manifold, bomb middle silencer and supersports rear silencer for a bit more noise and flow from the rear end.

Cost me £202 all in from the Welsh MG centre here in UK, which is a little cheaper i think than the current MGOC price which would make me think that different specialist garages can get different discounts (i know Welsh MG bough a bulk of exhausts when they ordered mine, hence i might have benfitted through them sharing the discount)

I think current MGOC prices for just the stainless steel manifold is £75 - £100 but i havent looked at just that so i could be a bit off

I am feeling a bit gutted though having just bought peter burgess' excellent MGB tuning book, as he rates only the Peco HDR performance exhaust for max BHP increase.

I was going for the Double S HDR system but was talked out of it. However i discounted the Peco system as its mild steel and has only a 1 year warranty. The double S is stainless steel and the warranty is valid for the length of time the purchaser of the exhaust owns the car...

You pays your money - you take your choice

Regards ~PHIL
Phil Earl

Just though re: increase in BHP...

THe increase i get from my system is about 5 BHP across a wide rev range.

According to P Burgess, the max increase through the Peco is quoted as 14BHP but this i believe comes with a lot of other engine mods such as high lift cam/rockers and high comp ratio etc

My engine is +60thou overbore and K&Ns but little else.

Just some thoughts..... ~PHIL
Phil Earl

Oh dear, dare I say this, in view of Peter B's recommendation.

A little fairey, no not George Michael, whispered in my ear that PECO was not very hot, and that the stuff to go for was MANIFLOW.

The reason given was that whilst PECO was prone to warping and other ill fitting tantrums, MANIFLOW was a class act which did the job to perfection.

Perhaps I was dreaming and the above was during a telcon with MANIFLOW's sales manager.

What do you think.
Fred

This thread was discussed between 05/07/2002 and 13/07/2002

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