11 replies to this topic

[Clubby1275GT]

anyone know what sort of power were talking of when twin su's are fitted and tuned to the engine?? getin bored of the hs4.
anyone know the best size for a 1275 stage 1 with aspirations of taking it to a stage 2?
twin 1 1/2's 1 1/4 or even maybe twin 1 3/4???

[Wil_h]

The gains to be had over a 1 1/2 Su on a pretty standard 1275 would be zero.

but they will look better. But this is pointless unless you have a glass bonnet.

Wil

[wobblybob]

while on the subject what r they power gains with one on a 1293 with stage 3 head??

[Bluemini]

Twin carbs are a waist of time, they take more time and effort to set up than is worth and you get little if no power increase.

Stage 3 head depends on the rest of the spec of the engine.

[Wil_h]

It's all to do with flow.

Generally the biggest restriction in the intake system will be the head, and usually the at the valve end.

I guess if your head is so good that it 's flow exceeds that which the carb can flow then you need a better flowing carb. Also, a better head and cam will allow the engine to rev higher, using more air per minute. This again may cause the need for a better flowinmg carb.

However, a Webber or a 1 3/4 HIF is a better choice than twins IMO (for the reasons Bluemini stated).

If you think about it, there's plenty of turbo minis out there with over 150 BHP using 1 3/4 HIFs.

Wil

[stormduck]

The main point of using twins is to get equal amounts of fuel/air mix in each cylinder, maximising the fuel consumption. A single carb cannot get equal amounts in each cylinder because of the curve in the inlet manifold. Based on this you should get a better and equal burn in each cylinder, maximising fuel usage, which should give you a tad more oomph, and in theory a smoother running motor.

[miniboo]

i am fitting twin carbs soon. dunno what power i have now but will let you know after i have had it rolling roaded.

[floatintoast]

Am fitting a 1 3/4inch SU carb and maniflow exhaust system to a 998 any ideas to sort of power gain i can expect? will be fitting an uprated air filter soon. cheers






[SIZE=1][COLOR=orange]998 79' Mini City

[Wil_h]

Don't bother fitting a 1 3/4 carb on that spec motor, a 1 1/2 will work much better.

You're baically fitting a stage 1 kit, so expect 10 to 20% increase over a standard engine.

Wil

[floatintoast]

what advantages does the 1 1/2 have over the 1 3/4, i have been previously told the 1 3/4 was the best i could fit to it (within reason), (my 998 is from an 87 mini)

cheers again,

[Dan]

A normal 998 Mini does not flow enough air fast enough to effectively use a 1 3/4" carb. If you fit one you will probably get a performance reduction rather than an increase as there will be a rather weak venturi, you won't be able to get it into tune properly. If this was a racer that spent all its time up in the 8-9000 rpm range then it would work but otherwise it won't.

Twin carbs do not by themselves increase the power produced by your engine. They can help you to liberate the full power available from any modifications you do make. Generally they will help you to reduce port biasing of the mixture, as described above giving a better fuel distribution. They will pick up faster than a single as you can run smaller chokes in twins and not suffer a lack of top end, smaller chokes will have a greater venturi effect and so respond better to light changes of throttle, which also means the piston will be more responsive in turn.

They do not go out of tune faster than a single carb, and do not require much more maintenance. If they are fully and properly setup and tuned to begin with they won't give trouble, the only extra tool you will need to tune them is a three foot length of narrow rubber tubing.

[floatintoast]

thanks for the advice!