1275 tuned Marina engine, better twin or single carbs

[MMT1968]

Hi,
I’ve got a 1275 Marina engine in my Traveller and tuned it to a powerful street engine. It has a raised compression ratio to 10,3:1 by differnt pistons, a fully ported head with polished and enlarged combustion chambers, 38inlet/31outlet valves, a Kent 266 camshaft, duplex chain, 41mm Maniflow exaust including LCB-manifold, and double HS4 carburettors.
I‘m not sure if the double HS4 will be much more effective than a single HS4 exept in higher revs. David Vizard said they don’t. It’s running well and powerful but I wonder if it would be a big difference when running under just one HS4. I‘ll have the needles adjusted on a dyno in the near future and that would be easier if just one carb is concerned.
What’s your opinion, should I go for just one carb or leave it on twin HS4?

Chris

[Blaketon]

I'd leave as is and see how the dyno goes. If you go single, I'd go HIF44. What inlet manifold have you got?

I have a 1275 Midget engine in mine and it runs an HIF44 (MG Metro carb and manifold). I also have a 1275 Midget, with the same head, LCB and straight through exhaust (Similar to the Minor) and that runs on twin HS2. The two give roughly the same power, on the same rolling road but the Midget pulls much better low down.

[MMT1968]

Inlet manifold

IMG_0189.jpeg (36.78 KiB) Viewed 413 times

Thanks for your reply,

I’ll stay with the twins until to dyno appointment. Following David Vizard there is not much difference in hp and torque between a single carb and twins. It’s about 5 to 6 hp at 5500 revs and hardly 1 hp at 2000 revs but the twins do need more fuel. That’s what I recognized also, mine needs 12l per 100km. That’s a lot for a small engine in a 850kg car even if the needles are not correct. It’s running on BJ needles now and so too rich as the carbs came out of a Healey 100. My Morgan +8 needs just 11l with a 3,9 l engine and 300hp. So this engine is much more effective in burning fuel to power than that small Marina engine. That‘s why I am asking.
I don’t expect that tuned engine to take some 8l or so but 12 is a lot to my opinion.

Chris