I have tried finding flow/power limits for twin SU carbies off a 180b sss

Would they be suitable for a high compression l20b with a cam? Also what would be the rough power limitation.
I will eventually go to twin weber or simular, but on a budget atm

Thanks

they will be fine

From my expiriance there to small for a hi comp l20b and and with a cam would be a pain in tha ase. There borderline with a stock l20b.

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I recently went up to 1 3/4" SU's (stock are 1 1/2") on my hi-comp L18.

Much better performance, not as breathless. I'd suggest they are borderline for an L20B.

Even Datsun themselves fitted the larger SU carbs (44mm) when they went to a 2 litre engine on the Fairlady.

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1970 ex Group A Rally P510
1971 P510
1972 180B SSS
1965 SP310 Fairlady
1966 SP311 Fairlady

Ok I had a feeling that they might be too small.
After browsing last night I found this image.

I don't disagree with what anyone has said on here, but, I just wanted to highlight the part mentioned in the original post regarding "being on a budget at the moment"..... budget being the key word.

We all know power costs money. Webers make power, so clearly they will cost money.

if twin su's is what the budget allows (or you already own them), then they will work fine. Will they make as much power as a twin side draft weber assembly? No (not even close). But, the car will run on them and it will still perform quite admirably.

Out of interest, what is regarded as high compression? I would consider 10.5:1 as being high for a every day driver, but for a race car its nothing.

Definitely agree

Will the smaller SU's work ? Yes

Are they ideal ? Nope

Whatever you get, make sure they are in good condition with no air leaks around the throttle shafts. SU's seem to get a bad name, but only becasue people are fitting worn out, 40 year old ones and expecting them to work like new.

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1970 ex Group A Rally P510
1971 P510
1972 180B SSS
1965 SP310 Fairlady
1966 SP311 Fairlady

I ran some good condition well set up jap su's on my daily l20b flat top pistons big cam ( unknown specs ) and it ran but only just
same engine with sss cam ran well at idle and ok mid ( still better than the down draft weber ) but a little lean up top.
same engine with sss cam and ported w53 head ( now thats hi comp ) forget it. (but goes like stink with twin dellortos )

so it may work depending on set up but as said don't expect them to be good.
also I have found with the su's the float level is critical!!! as is with most carbs but more so with the su's.

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Thanks for the recommendations guys.
I have both the standard carby/manifold and also the twin su's

Im looking at building a 2.2L l20b probably around 10.5:1 CR with a 266deg seat to seat cam .510 lift with 44mm intake valves.

Im restoring a 200b Aspen for a mate for his 30th bday (as in my build thread)

I budgeted for the engine build and body resoration but didnt take into account the carbs. So worst case scenario I should at least be able to get it running before I give it to him if I cant afford new carbs.

Would it be better to stick with std carb and manifold or go with the Su's?

I think the SU's(Hitachi) will be better (subject to below) than the std Carb, which I would describe as a crude early anti polution "gizmo".

I agree with Dave that the SU's need to be in good condition to be tunable. Minimal wear/air leaks in the butterfly shafts and/or the mixture tubes (the outer tube the needle sits in). SU brass floats can also get hairline cracks in the wall and sink after 40 years, but you can still buy new, improved, replacements from Nissan. If this is to be a daily driver and if the SU's are in good repair use them on a stock/mild L20, or get them reconditioned - this is a simple and relatively cheap fix by "SU Midel".

However if the engine specs are as you described (L22 overbored Cam etc.) forget the stock carb or the SU's, they aint gonna work.

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RichardC
SSS016