SU Carburettor Conversion

[bob46320]

I have a '32 RN box saloon with front gravity tank (No pump).  I am thinking of fitting an 1 1/8"  Side draft SU carb.  The standard 22FZ is updraft and lies below the fuel level in the tank (Hence no need for a pump).  I see that most of the SU conversions use the later Manifold (1933 onwards) with an adaptor plate,  but that may not work without a pump to deliver fuel as the carburettor fuel bowl is above the bottom of the tank.

I am thinking of making a 90 degree adaptor to fit on the existing inlet manifold and using a 90 degree copper (plumbing) elbow to a new flange for the carburettor.  This would keep the SU fuel bowl below the bottom of the tank.

Would it work, or is the bore of the existing pre '33 inlet manifold too small? 

What would the gas flow be like adding an extra bend into the inlet manifold ?

Bob H

[Austin in the Shed]

I have a '32 RN box saloon with front gravity tank (No pump).  I am thinking of fitting an 1 1/8"  Side draft SU carb.  The standard 22FZ is updraft and lies below the fuel level in the tank (Hence no need for a pump).  I see that most of the SU conversions use the later Manifold (1933 onwards) with an adaptor plate,  but that may not work without a pump to deliver fuel as the carburettor fuel bowl is above the bottom of the tank.

I am thinking of making a 90 degree adaptor to fit on the existing inlet manifold and using a 90 degree copper (plumbing) elbow to a new flange for the carburettor.  This would keep the SU fuel bowl below the bottom of the tank.

Would it work, or is the bore of the existing pre '33 inlet manifold too small? 

What would the gas flow be like adding an extra bend into the inlet manifold ?

Bob H
Sounds like it would look horrible,Bob.I fitted a 1 1/8 SU using the original manifold turned upside down,cut the vertical bit off and made a flange for the SU and had it welded on.Then had to make a cranked rod to meet the butterfly arm.

[Nigel was in Brittany]

On My RN, I am using an 11/8 SU, SU Pump and later manifold with adaptor made by Stuart Palmer.

[bob46320]

Austin, was that on a gravity fed front tank ? And what sort of bore reduction was there from the original to the 1 1/8" SU ?

[Nick Salmon]

Does anyone supply off-the-shelf-adapters to be able to mount an SU on an A7 manifold?

[Nick Lettington]

Like this one Nick? Ok not quite off the shelf...

http://rally200022.wixsite.com/austin-7-...C-to-order.

[Charles P]

Does anyone supply off-the-shelf-adapters to be able to mount an SU on an A7 manifold?

I thought that John Barlow did

C

[Austin in the Shed]

Austin,  was that on a gravity fed front tank ?  And what sort of bore reduction was there from the original to the 1 1/8" SU ?

I  don't understand your question Bob.There was none of the original vertical part of the inlet manifold which is the most restrictive part left.The 1 1/8 bore from the SU flows straight into the branches for 1-2 and 3-4. There was a photo of this but it's on the old forum.
Yes it's on an RN scuttle tank.

[bob46320]

last question - Did you have to fit a pump to the SU on your RN as I have read that the float chamber would be above the bottom of the tank

[Chris KC]

Bob, I can't answer who may have the adaptors in stock (yes, try John) but there are certainly plenty of these around.

Concerning flow restrictions my own experience has been that it's not all that critical.

As for fuel supply, I think you are right in saying the float bowl will usually end up above the base of a scuttle-mounted tank, so a fuel pump of some kind is recommended.