Single to Twin SU Worth It?

[Tornado99]

I have an '88 Mini with a 1275cc engine, unknown internal mods (maybe a hot cam as some local Mini mechanics suggested). Has a single HSU4 carb with stock manifold and K&N gauze intake filter.

Is there much to be gained by converting to a twin SU setup? If so, what carb size should I be looking for?
Thanks.

[timmy201]

Depending on the modifications to the engine you might be better off with a single 1.75” carb

If you wanted twin SU carbs then for a relatively tame engine you’d pick twin 1.25” carbs, and for highly tuned 1275 engines you’d pick twin 1.5” carbs

Regardless of the direction you chose, you need to have good condition carbs that are matched, built correctly and tuned for the performance of your particular engine

[Exminiman]

Suppose question is what do you want to use the car for…..fast road, competition ?

If its road? and you are not concerned about every last HP, then I would stick with the single SU and a decent manifold

Single SU is smoother, easier to set up………….and cheaper

[johnv]

But twins look soooo much better...

[Tornado99]

Suppose question is what do you want to use the car for…..fast road, competition ?

If its road? and you are not concerned about every last HP, then I would stick with the single SU and a decent manifold

Single SU is smoother, easier to set up………….and cheaper

Ya not looking for top power and performance. It is a street car to ride about in for fun.
I have a classic motorcycle that I converted from single to dual carb and found bike much more lively in mid range, so got me thinking the cooper S setups might be worthwhile. I use a dual vacuum guage setup to balance my bike carbs and a colortune to help with setting mixture. Are these used on dual carb mini tunes?

[Cheeser]

For your use I would suggest single HIF 44 on good inlet with proper air filter. Once that is sorted get it set up on a rolling road by someone who knows about SUs.

[mk1]

Couldn't agree more with Cheeser.

The HIF44 is a very good carb & you are unlikely to be able to detect any improvement using twin HS2's over an HIF44 on a decent manifold. The single is cheaper, easier & will stay in tune longer.

If all you are bothered about is decent reliable performance, then the HIF is the way to go, if you want something that goes about the same but looks much "cooler" then twins is a great option. But they will cost more than twice as much be less reliable & will certainly go off tune fairly frequently.

As ha salso been said, whatever option you go for an initial dyno session is essential.

[UHR850]

I had a Hif44 carb on my MG Metro engine but changed it to a twin Hs2 setup. I was not happy with that so did put the Hif44 back on it, happy again.

[Peter Laidler]

I am like you Tornado. I use a colourtune to set my mixtures. but I use my sensitive ears and stethescope to set the air intake.

Nothing wrong with a refurbished - or known good - HIF44

What is your classic bike? Me too......

[tweedy998]

I'd probably echo what others have said and in your case suggest sticking with a single, probably a HIF 44.

Twins do look very aesthetically pleasing, but do need quite a lot of things to be right, are quite high maintenance and expensive, as others have highlighted.

[Tornado99]

I'm in BC Canada and do not know of any rolling road facilities in the region. So not likely it will ever be possible to get that level of tuning done.
This twin idea came up bc I came across a complete twin SU setup for mini on a used parts lot for sale. With the input here and other forums, seems the wise option is to stick with what I have and avoid introducing more complexity than I can sort out.

[mascher]

If you're still using the original intake and exhaust manifolds, I would say keep the HS4 and change to an alloy intake manifold and a Cooper free flow exhaust manifold. Cleaning up the HS4 throat should help a bit as well. This works well on an engine that you're not going to rev much above 5500 rpm.

Kelley

[De-hira5729]

I didn't feel like using HIF very often in Japan, so it's very fresh.
I would love to try it! !

[MiNiKiN]

I'm in BC Canada and do not know of any rolling road facilities in the region. So not likely it will ever be possible to get that level of tuning done.
This twin idea came up bc I came across a complete twin SU setup for mini on a used parts lot for sale. With the input here and other forums, seems the wise option is to stick with what I have and avoid introducing more complexity than I can sort out.

Not having access to a rolling road is no excuse. Simply fit a broad-band O2-sensor (Lambda-sensor) to the LCB manifold connected to a black-box or A/F-Meter. Such you can set-up the carbs on the road - better than on many rolling roads.

I have a Zeitronix System that even records the AF-Signal along with other sensor signals (rpm, throttle pos, temperature, etc - many optional input signals ). You could define a certain test track and navigate it with defined throttle positions - so you see how the AF-ratio behaves over the revs and correct it en route with different needles to match. e.g. https://www.lambda-tuning.de/zeitronix_ ... sonde.html

[Herbert]

I'm not sure if anyone has told you this on this thread but if you go from single carb to twins, you have to not only change the inlet manifold but you need a new exhaust manifold and all the rest of the exhaust system. It will give you more power, better torque and higher revs which can't be used with benefit unless you change the gears to S ratios. Good luck! R

[Alex]

I am like you Tornado. I use a colourtune to set my mixtures. but I use my sensitive ears and stethescope to set the air intake.
......

I'll bet you a slab of beer that your carbs aren't balanced.
Suzy's were done by a professional using a listening tube, and a listening tube with a whistle in, and they weren't even close - I checked them with several different airflow meters afterwards.

[Peter Laidler]

Just PM'd you with my qualifications to say what I did

[Tornado99]

I am like you Tornado. I use a colourtune to set my mixtures. but I use my sensitive ears and stethescope to set the air intake.

Nothing wrong with a refurbished - or known good - HIF44

What is your classic bike? Me too......

Cheers. Bike is a '74 Norton Commando. Came to me with a single Amal carb fitted. Ran ok, tended to be lean overall, bluing on the headers etc. Now has the original setup dual Amal's. Goes like stink.

[Peter Laidler]

Hi Tornado, I'm another Norton Commando man. Glad to meet another man of taste. Have you tried an SU?