9 replies to this topic

[Tinkerbelle]

Hello all,

As the title suggests, what should I look for in terms of wear in used sus especially HS4s?

I want to replace my twin HS2s as I feel they are holding my 1275 back a bit, but don't want to buy new and have bought a few sets of poor ones before I bought these HS2s new.

Also, if I do go for new are these what I would want:

http://www.sucarb.co...l.aspx?id=27734

They seem a lot cheaper through SU than say, Minispares?

Does anyone have experience of a direct twin HS2 swap to twin HS4s, as I am wondering what effect it has on the low end torque?

Thanks

Matt

[bmcecosse]

The beauty of the SU design is the variable venturi - therefore the larger carbs will work just as well at lower revs - with extra air flow available at higher revs. However - the standard BMC inlet manifold is a poor thing, and you will do MUCH better with a long branch manifold with no balance pipe ie - like a weber inlet! Of course the larger carbs will only benefit the engine if it is capable of drawing in the extra air - so a decent cam and an optimised cylinder head should be top of your list!

[Tinkerbelle]

Thanks for the reply. That is very helpful, of course the venturi only opens as much as is necessary so the larger total diameter HS4s should in theory act very similarly to the current HS2s,, but with better top end potential.

The engine is a 1275 with flowed etc MG metro head (stage - who knows, 3?) and I always use sw5 cams. They seem to always give good results and its too much hassle to change if I experiment with another! Mind you at 185 gbp now I may have to rethink.

Matt

[olly917]

I was thinking of using a sw05 cam in my 1275! How do u fi d it n what alt was u thinking of using? Olly

[twrminisport]

If you tune the HS2's to vizards bible, slimming down spindles and angled butterlys you can make them perform like a standard set of hs4's anyway. Just by modding the spindles with a file and by angling the butterflys with a file and a couple of other bits which is all FREE i gained 5 bhp.

Twin HS2's in good order modified can be used up to about 90bhp effective working range

Edited by twrminisport, 22 March 2011 - 11:56 PM.

[Ethel]

Regarding wear, a piston drop test is the only really critical bit, all the other bits can be replaced. Though leaky throttle bushes would probably make it worth passing unless the carb is near enough a gift.

http://www.jcna.com/...h/tech0006.html

[MiniMonty]

Slight hi-jack...

I've got a nice pair of HS2s but have been told there is no point fitting them to my 998 because of shared ports.
"the engine can only breathe through one port at a time so twins are a waste of time"

This thread seems to have experts at large - so is the above true or false ?
All and any advice much appreciated as the Mini is about to be taken off the road for three months of TLC.

Best wishes
Monty

[Tinkerbelle]

Olly917,

I have used the standard MG metro cam that was in that engine and a MD276. The SW5 just seems to give better torque than the MG metro one and plays more nicely than the higher duration cam. If I remember correctly the SW5 has a low duration like a standard a series cam but is ground to be on full lift for a longer duration, which creates the good idle etc.

Monty,

I believe it is all about the siamese, not lady boys, but the shared ports. Your man is correct in that only one of the siamese ports and 'paired' cylinders linked can breath at any one time but with a single carb you get uneven charge distribution in each of the paired cylinders due to length of runs and shape of pathways so you can not get really good tuning, i.e. weak in one of the pair rich in the other. The twins make each path length and shape the same for all cylinders (with the caviate that if they are not set up equally the two pairs of cylinders served by the different siamese ports will be out of balance, which causes problems also)

Above all though, the look really good and seem to give good torque characteristics (its all about the torques for me). If they are no good, why did Special Tuning use them in rally cars and why were they fitted to the performance models i.e. Coopers.

Hope that helps, I'm a full time Geologist and only a part time Mini enthusiast

TWRMinisport,

Thats a great help and could save me a lot of money, I didn't know you could mod them that far. I don't expect to go above 90 hp.

Matt

[twrminisport]

Yeah they are good if you tune them
have you got a copy of tuning the a-seies by David Vizard? all the mods are in there

Seriously mini monty i had an otherwise standard 998 with twins and RC40 and that made 53bhp at the rollers. So much more torque aswell. Big increase and well worth it when standard is 38bhp.

Edited by twrminisport, 23 March 2011 - 09:38 PM.

[Tinkerbelle]

Got the Vizard book, its coverless and thread bare, must have a read through and pretend to be working, like a beano inside the bible at sunday school:)