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MG MGA - Twin Cam Carburettors

I am fitting a Derrington Head to my 1600 engine and have tried some different H6 SU's (1.75") to the manifold to test the installation. Short body SU's foul the bonnet strut when it is clipped up. I have a longer body one which clears the strut and also thanks to the cutaway in the bonnet introduced for the twin cam clears the bonnet.

Can someone please confirm what the body length between the manifold flange and the air cleaner flange of the twin cam carburettors is. Is is 5 3/8" (136mm)?

Thanks

John

John Francis

John,

My H6's measure as yours - 137mm flange to flange.

Post a picture of your setup when your done!

Cheers,
Ben
B Rollo

Hi Ben

Thanks, John
John Francis

John,

I have H6 SUs on my HRG head and they fit under the bonnet without any problems. The only issue is clearance for air cleaners. I have 'trumpets' with foam socks to get around this.

The strut was on the other side of the bonnet on twin cams - perhaps you could adopt this approach as an alternative.

regards,
Mark
M Wellard

Hi Mark

It would be great to see some pictures of your set up. The installation has a few marginal aspects, carbs and bonnet, air filters and starter switch and of course the heater trunking.

John
John Francis

John,

I turned the heater around and reversed the intake/fan - as in the twin cam (actually it's a triumph herald body with the holes in the right place.

Heater ducting is just on the other side of the engine. I didn't have to alter the starter switch position. The front trumpet has a section cut out so that it clears the inner guard.

Let me know if you need any pics from other angles.

Cheers,
Mark


M Wellard

Hi John,

Heater pic in this message.

The carby linkages are just a copy of the twin cam set-up.

Regards,
Mark


M Wellard

Hi Mark

Thanks, the pics are helpful. With the Herald heater did you have to move the hole in the body? I was planning to use a twin cam heater until I learnt that the twin cam has a different scuttle hole for it to keep it central in the engine bay. I assumed a twin cam heater would probably hit the bonnet opening or the wiper motor using the 1600 hole. Yours looks quite close too.
John Francis

Hi john,
I didn't alter the body - using a t/c heater would produce the same result as I have, it's just that the triumph heater was more readily available. While it is close to the wiper motor, there is no interference.

Regards,
Mark
M Wellard

John I wonder if the manifolds can be different,can some be longer? Mine is steel and have never seen another one.
Mark what did you do to mount the heater valve like a twin cam?
gary starr

Gary,

The Triumph Herald heater body had the requisite fittings and it just bolted up.

my head came with manifolds for and MGB HS4 and I had to get the flange changed to match the H6. Length could certainly be an issue.

Mark
M Wellard

Here are some measurements I went out and got off my set up. Please be advised that I have never installed the head or carbs. I have 1 3/4" HS's that measure 102mm flange to flange. The manifold which is steel measures 97mm across the top and 117mm across the bottom. What head gasket are you all using? I need to have all new valve seats installed,exhausts need hardened ones and the intakes have been cut too much. Head has had to have some heavy welding done to repair freezing cracks,this all on a "excelent condition" head from a company in Darlington UK !


gary starr

Top view-


gary starr

Hi Gary

Yours looks very similar to mine. Its not nearby at the moment so can't take a photo or measure. I will be using the composite gasket as recommended by Barney. Its sold for one version of the MGB engine but I can't remember which version.
John Francis

I have some of the manifold variants on my page here
http://www.rhodo.citymax.com/HRG.html

The stock carbs are adequate for any street tuned MG engine, although the 1 3/4" do look nice.
Bill Spohn

You may want to try going the Weber route with your HRG head!
Mike


Mike Ellsmore

Is someone making manifolds for webers Mike? Just curious.
gary starr

The Weber manifolds were fabricated back in the early 1990s for my car - not sure who made them but I can supply basic dimensions if anyone is interested.
Mike
Mike Ellsmore

Hi Mark

I have a couple of other questions. The choke cable has to be longer I think and the fuel pipe has to be re-routed. How did you do both of those things? It looks like your fuel pipe has been cut off shorter al la twin cam with a filter. Did you use a twin cam choke cable?


PS Peter Burgess made the following comment a while ago. Webers will give absolute maximum power, ideal for racing, but SUs will give better mid-range torque. So the latter are probably better for road use.

Thanks

John

John Francis

John,

I used the same choke cable. The fuel line was cut and I used a fuel filter to join the shorted fuel line fitting to the flexible hose.

HRG made manifolds for webers - if you plan on using them and look long enough, a pair may turn up.

Regards,
Mark
M Wellard

This thread was discussed between 25/04/2012 and 29/04/2012

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