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MG MGA - MGA Exhaust Manifold or Header for MGB Engine

There are conflicting comments on the web and in print on whether one should use a stock MGA exhaust manifold or an aftermarket MGA exhaust header on a transplanted MGB 1800 engine in an MGA.

The MGB stock manifold is not practical to use in a left hand drive MGA as it requires many modifications.

I am putting a MGB 1800 five main engine in my 1958 MGA and would like to hear which exhaust I should use.

I only plan to use the car for street driving and MG club runs.

Thanks in advance.

Reed Hayes
Reed Hayes

I have the stock MGA manifold (and entire exhaust system) on my 1800 5-main-powered '58. It seems to work just fine for the sort of driving you and I do. From what I understand, headers can increase horsepower at high rpm at the expense of low speed torque, making the car less pleasant to drive on the street. Maybe someone has done a dyno run with the stock manifold and again with a header?

Ken
k v morton

If it was mine I would use an MGA big bore header. Do not use the MGB version as it will be too short to go under the chassis. Otherwise do as described by Ken, although I have never used a header as you refer to them that has caused my engines to loose torque and become awkward to drive?
Robert (Bob) Midget Turbo

I am the same as Ken. Absolutely everything external on my 5-bearing 1800 was transferred from my 1500 MGA engine.

Steve
Steve Gyles

Note my post on MGB general re historical trivia.

FRM
FR Millmore

Unless you really tune your engine you can use the stock MGA manifold. I've been using it for years with a mildly upgraded 5-main 1800 and the car's still plenty quick. Now I've added some head modifications and want it to breathe better so I'll be adding a header and larger exhaust.
Mark J Michalak

Thank you for all your replys. It appears that for street and club run driving the the stock MGA exhaust manifold will work on stock MGB five main engine in my 58 MGA.

Reed Hayes
Reed Hayes

I put a 3 main MGB iron manifold on my A in the '60s. The only modification required was grinding the manifold for the steering clearance and welding a patch cover to seal it. The down pipes fit if pushed up a bit and bracketed. I did not bracket them well enough, so they sagged a bit, so speed bumps take some care. Sounds great, works well, gets too hot!
I have had good results with Maniflow LCB headers from England on my Cooper. Great sound good torque and power range for street. I would be interested in how their system works on MGAs. See link:

http://www.maniflowonline.co.uk/index.php?section=mg

Russ
Russ Carnes

Let me add that port matching with a good competition gasket makes a good bit of difference as well. Compare the gasket to the open ports on the manifold and head, grind so they are the same with no offset or restriction.
Russ
Russ Carnes

This thread was discussed between 14/01/2010 and 20/01/2010

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