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Hi there, I'm just aquiring parts for my project engine build (Shorrock supercharged 1098 for road use) and was wondering if anyone here can help me out with SU carb choice - what are the pro's and con's of an SU H4 compared to an SU HS4? Is the main difference to do with the choke setup with the HS presumably being an improvement over the H version?

Thanks very much,

Paul.

If you are making the manifolds yourself then there is little to choose between the two carbs. But if you are using original Shorrock manifolds the flange will only take an H series carb.

For a standard Shorrock "suck through" type set up there is nothing to choose between the two carbs you mention. For a conventionally aspirated engine, as you say, an HS series choke mechanism works better, but the H series has a longer body improving mid range torque. This is on no consequence in forced induction.

Hi Mark,

Thanks for that - sorry my first post might of been slightly missleading, I had forgotten that the mountings for the H4 and HS4 are different - I'm actually looking at using an H6 or an HS6 (which have the same 4 bolt mounting flange) on a Shorrocks Triumph Herald manifold as the engine is for my Ogle and I'm using an Austin/Morris 1100 install kit with the supercharger mounted in front of the engine in place of the dynamo. The Mini install kit meant the bonnet wouldn't shut by about 2". I just thought there would be more experience/knowledge on H4's than H6's on here (caught out again I should have known better). The original install kit uses a Solex down draught carb but I want to use an SU carb as I think they are better and more tuneable - it should also fit better as there is only about 1/2" clearance between the open intake of the Solex and the underside of the bonnet. The HS6 being shorter than the H6 should give me more space for a filter.

Anyway thanks again, so I've got the choice of either depending on space.

Regards
Paul.

No worries

My comments above still stand for H6 v HS6 The efficacy of both carbs would be about equal in a forced induction engine. Funnily enough my Dad used an H6 on his Shorrock blown 1100 in the 60's.

M

I think it was settled that Shorrock didn't make a kit for the ADO16....???

I think it was settled that Shorrock didn't make a kit for the ADO16....???

I don't think it was

See columns 4 & 5 in the table below.

Mark - I don't suppose you have any engine bay photos of your dad's 1100 with supercharger from back then do you?

Vegard - also page 11 of the same Shorrocks catalogue shows a photo of "a typical conversion kit" which is the kit for an 1100, There is also an under bonnet photo of one installed on page 26 of Jonathan Peck's "The ABC of Shorrock Supercharging" document.

Regards
Paul.

Do they have a by-pass valve for overrun?

I would be looking for a carb that heat had as little as possible effect on mixture, so no wax stats, or bi-matallic strips. I had some mixture issues when the damper oil got too hot but I was running a Toyota charger.

Good luck with the build cant wait to see some pics.