Using a HS Carb as a throttle body
Turbo Mini Forums

Jb I considered the wet manifold route using an injector in the carb body, but after looking at the HS4 the injector would need to be placed up stream of the butterfly ala the SPi mini and be visible

Paul just working through the final mad cap details, in theory I believe we can get it work and hide the install

Hardest bits to hide is the fuel hoses and pressure regulator. Looking into disguising the fuel return to look like the carb overflow pipe and fit the regulator on the front subby with return line going down the driver side

Ordered my MS2 chip, Jim stim and 4 channel driver board yesterday. Already prepared the MS for the changes and removed unused components.

Been a slight change on the engine front as it'll now be a 998 due to a lack of 850 pistons.

998 +20
12G295 + larger valves
MG cam

Twin HS4 throttle bodies are now to be used as it'll help to hide the fuel rail and injectors. A bung will be machined to replace the dash pot piston, holes welded and then they'll be bored to remove the bridge, welding etc to provide a smooth air flow.

Just need to find a suitable fuse/relay box to hide now and then the loom can be built, going to check out the local bike place later on

Run into an issue with the alloy used to cast the HS4's and not being able to weld it

I could

Make a body to look like a HS4 and install the butterfly and dash pot

Try brazing the carb to fill the bridge gap before line boring it

Leave the bridge gap and live with the airflow restriction

There's not enough material in the carb side walls to install a sleeve down the inside of the body

Any other ideas

I'm surprised it won't weld - what method are you using ???

The only suggestion I can think of as an alternative would be to drill out the whole bridge section from "underneath" ie, just keep enlarging the jet tube hole until the bridge has gone - a fairly large hole, probably about 1" - then thread it and screw some threaded aluminium in then bore the body out and shape the outside how you want.

A LOT of work but probably less than making a whole body from scratch....

Schrödinger's cat - so which one am I ???

I guess the compromise of wanting to use the SU as a TB is that you end up with a restriction. I'd leave it.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Were you asking the welder to try and fill the angled bits from the inside ???

Schrödinger's cat - so which one am I ???

Yes, the troughs either side of the bridge that are cut into the lower body

That's probably the issue then - to weld that sort of alloy properly needs AC TIG and a separate filler wire.

I can't imagine anyone being able to get a TIG torch down inside an HS4 body at the right angle and being able to see the filler wire.....

The welder may have been expecting to use a different (easier) method and used the alloy as an "excuse".

Has he/she actually tried welding on the body, ie, on the outside of it, to see if it is a genuine materials issue rather than an access issue ???

The alloy they used for the inlet manifolds is perfectly weldable (I have one that has been repaired to prove it) and I can't imagine the alloy for the carb itself is too much different (although you never know with Leyland....).

If so, the build-up you want can be done externally by a good welder just by cutting slots through from the outside and back filling them. You would get a lot more distortion but it would give you what you want.

Schrödinger's cat - so which one am I ???

Space could well be the issue, although the dash pot hole is quite large.

Do you think the durafix easyweld would be up to the job?

I've never used the Durafix stuff myself but I think a couple of people on here have.

If you can make it flow it will be fine as what you're doing needs little structural strength.

I think you will still struggle with access and even the Durafix requires a large heat input - possibly more than a common plumbers blowtorch on a large casting (which will really suck the heat away) - can provide.

But certainly worth a try if you have a spare/scrap HS4 body.

Schrödinger's cat - so which one am I ???

that durafix / techno weld stuff should do the trick,

I seem to remember wasming up an old SU with a blow torch years ago and it turning to a puddle on the floor pretty easily, they may be a funny alloy that won't tig.

After being laid up due to an accident, I needed chearing up so I've bought a mill and I'm going to try and make my own replacement SU bodies :)

Also Brett has completed the engine build so I'll be going down next week to take a peek

Edited by Ratty on 18th Aug, 2011.