Twin hs2 carb v single hif38

[andrew.searston]

Hi everyone
In currently have a hif38 carb on my morris engine (1275 head 1098 block, Maniflow exhaust system), is there anymore gain to be made with twin hs2 carbs over the single hif38? Or even twin hif38?
Thanks
Andy

[philthehill]

There is nothing to be gained in fitting a pair of HS2 1.25" SU carbs over a single HIF38.

Twin HIF38s on a 1098cc engine even with the 940 head will be too much and there is a very good chance that you will loose power.

You need to refer to the Vizard book on the 'Tuning The 'A' Series' if you want to know more and in more detail especially as regards air flow in and out of the engine when fitted with various tuning equipment and having had improvements to air flow carried out.

[Monty-4]

Smaller twins may have a very slightly faster throttle response, something to do with smaller pistons as I vaguely recall reading.

Otherwise - as phil says - single larger carbs are generally better in terms of power and efficiency. If memory serves, Vizard explains it in his big yellow book as being due to the "siamese" port design - with twins setups any given cylinder will only ever "see" a single small carb and not get the benefit of the flow of both. It seems the "balance" tubes on the twin manifolds don't make up for this vs. a single larger carb and introduce a flow restriction t'boot.

Also changing needles, re-jetting and servicing will cost twice as much.

... but I have twins anyway because they give a bit of a "period tuned" look. ;)

[andrew.searston]

Thanks guys think I’ll just keep my money and stick with the hif 38 setup I have