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MG MGB GT V8 Factory Originals Technical - SU carbs heigth problem

Im building a V8 roadster with a Rover SD1 V8 and SU carbs.The engine is as low as possible (3 mm space between steering column and exhaust manifold) but the SU carbs are about 20 mm too high for the standard bonnet.I think I can find 10 mm in machining the inlet manifold further down but then there is another 10 mm to go.
Is there a difference in heigth between the SU type's? Ore is it possible to lower the top of the dashpot cover's of the SU carbs??

V8 regards,

Arno
Arno van Dulmen

Arno,
I am assuming that you are still using the "penthouse" inlet manifold that positions the carbs on top of the centre of the engine. I don't think you will ever get them low enough. Look at a picture of the inlet that MG used - it places the carbs right at the back of the engine, just in front of the heater. Even there, they only just fit.
Mike
Mike Howlett

Mike,
I also have my carbs faced rearwards like the standard BGT, and I knew that there would not be much space left.I have used the standard MGB cross member and maybe the gearbox is a bit higher than standard but it fits perfect and I don't want to change that.
regards,

Arno
Arno

The factory and conversions had the top of the dahpots machined down.
Ian Sanders

I can back up what Ian says. My Factory GT V-8 uses special HIF6 carbs with a shorter "chimney" on the dashpot dome, and also a damper rod that is flat on the top. The difference in overall height is pretty close to that 20mm you are looking for. Ordinary (Rover P6 type) HIF6s and the later HIF44 carbs do not have the shorter domes and damper rods.

You might check with some of the V-8 parts suppliers in the UK like Clive Wheatley to see if they have the original style carbs.

Cheers,
Paul Kile
Paul Kile

This BBS is so-o-o-o useful! I am still at the planning stage of a V8 conversion and I had no idea that the SUs were different on the factory MGV8. Does this mean that if I keep the chrome bumper crossmember, I won't be able to get the engine low enough to accommodate the SUs up by the heater?

If I swap to a rubber bumper crossmember and rack, can I get back to the original ride height with modified springs without compromising the suspension travel?

Mike
Mike Howlett

Mike,
In answer to your question regarding height of SUs with a chrome bumper crossmemmber. If I'm not mistaken, Costello, using that setup in his B-V8s had to have a bulge put into the bonnet. I'm using the stock suspension in my '68 GT, modifying only the steering shaft with an additional u-joint, and the bulkhead and tunnel for more clearance. Everything is pretty close, and I anticipate needing a bulge or scoop, which in my opinion, if functional isn't a bad thing.

Regards, Joe
Joe Ullman

i got round the problem by cutting small holes in the bonnet felt to give me extra mm's !!
Brian Marshall

Joe, Brian, et al,

The Costello V-8 needed that large power bulge because he retained the original Rover pent-roof carb placement, like on the P5B and P6 cars. Those need much more than 20mm to achieve clearance in an MGB.

The Factory MGB-GT V-8, even with its lower dashpot chimneys and damper rods, used cutouts in the bonnet felt to aid in clearance.

There is also the story that the Factory GT V-8s used a different bonnet with a slightly higher curvature, much like the MGAs used on the Twin Cam and later cars. This bonnet may have been commonized on all MGBs starting with the rubber bumper cars. Part number differences seem to bear this out, but past threads on this BBS discussing this, along with actual measurements, don't seem to bear this out.

Cheers,
Paul Kile
Paul Kile

Paul,

could you give met the heigth of the dashpot's of you factory V8?

regards, Arno
Arno

Arno,
I'll try to remember to measure them this weekend. I even have a later HIF44 carb for my 1275 engine that is going into my MG 1100. It has the "tall" dashpot and damper rod. I will measure both and post the results here.

Cheers,
Paul Kile
Paul Kile

Mike,

No you can keep the CB cross member - my V8 has lots of room under the front of the sump (at least 1 1/4 inches) and the carbs fit just fine. I took 1/8 inch off the top of a standard HIF6 dashpot and use the flat top dampers.

Also, did you know that the later bonnets have more curvature than the early ones ? I gained another 3/16 inch clearance after having to change my bonnet.
Chris Betson

I have just finished putting a V8 in my 1964 (chrome bumper) MGB. I used a Clive Wheatley plenum chamber and machined down a Rover manifold to duplicate the factory setup. I used HIF6s from a Rover and compared the dashpots with the factory ones at the time. The Rover ones I used are only 5mm higher than factory MG ones.
There is a critical measurement quoted in the book 'How to give your MGB V8 power' from the top of the rocker covers to the lip where the front mudguards bolt on. It is 50mm +/- 2mm. Place a straight edge between the mudguard lips above the front of the rocker covers and measure down to the covers. should be 50mm plus. There are many handy measurements in this book. I had to use them all because I converted a narrow transmission tunnel car.
cheers
Ian Buckley
Ian Buckley

In my earlier message I forgot to add that I have used a standard bonnet (hood to some of you!) and there are no clearance problems. I was very interested to read that some bonnets are different.

cheers

Ian Buckley
Ian Buckley

I just went outside in the 40 deg (C) heat (No ice in the carburettors here!).

Using a straight edge, I measured from the top of the dahpots to the top of the rocker covers. 153mm.

Ian Buckley
Ian Buckley

This thread was discussed between 12/02/2002 and 19/02/2002

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