WTB..su carbs

[NCLNDYM]

FINALLY BOUGHT A GREAT SET

 

 

Looking for a good set of su's, including the intake, linkage etc. Would like at least 38mm. Local pickup preferred. Im in Socal.

[73GTV]

Moved to another Post Thanks

[NCLNDYM]

Look good, have one other guy gettin me pics of his, let ya know.

[73GTV]

Moved to another Post: Thanks

[NCLNDYM]

Finally picked up a set of sss su's

[crackerjack69]

Feel free to trade me that stock manifold for the ported one I ended up getting when I bought my SU's <lol>

[NCLNDYM]

The intake mine came with is 1.5"

[ggzilla]

All the Datsun factory twin carbs are 38mm (1.5") from all engines from 1200cc to 1800cc. For the 2-litre and larger engines Datsun fitted the 46mm hitachis (including U20 and L20B and the sixes).

[crackerjack69]

So my 38mm SSS carbs won't feed an L20B very well?

[datzenmike]

They will work just fine on a 2 liter. Remember the rule about carbs? Never over carb. I suppose a very slightly larger would be slightly better but a 46mm is fitted on L24 motors and larger. That's too big in my opinion. 38s would idle and run best....

 

From SU Tech Page

 

"Theory Why don't Z-car SUs work on smaller 4-cylinder L-series motors?

 

Both the 38mm and 46mm carbs should be able to setup to provide the same venturi air velocity. This is not the problem as I see it. Lets say you are accelerating a L20B full throttle from 2000 to 4000 RPM. Do this first with a small 38mm SU setup, there will be upward movement of the slide piston and fuel needle to meter fuel to this changing volume of air. Lets say the needle of the 38mm SUs rises 20mm during out 2000 to 4000RPM test. Now do the same 2000 to 4000RPM acceleration test with a set of 46mm SUs. The 46mm SUs with larger diameter venturi will need to raise the piston/needle assembly less than the 38mm setup in order to flow the same amount of air. Lets say the 46mm SUs needles only raise up by 15mm. In each test, metering the same amount of air, the larger SUs will rely on less upward movement of the needle to meter the fuel so there are fewer "fuel flow mapping points" on the physical surface of the needle and accuracy of the air/fuel ratio is reduced . (think of the physical surface of the needle like the electronic bits of information in the fuel map of an EFI brain).

 

The overall situation is also analogous to the factory sizing of EFI airflow meter, where a small airflow meter is used to provide more accurate info to the EFI brain for better emmisions control."

 

 

[mr68gts]

Ive been running 38mm su's forever on a l20.

no problems with it whatsoever.

paul

[ggzilla]

Yes, no problems. A little small but will run FINE. Nissan fitted 46mm to the U20 four-cylinder, but you don't need carbs that big.

 

Why don't Z-car SUs work on smaller 4-cylinder L-series motors?

The L20B is the LARGEST stock 4-cylinder L-series motor.

 

THEORY is fine, but doesn't always hold up.

 

FACT is that Nissan didn't fit 38mm twins to 2-liter JDM/US engines, but instead fit 46mm twins. They did fit twin 38s to the L20B in Europe, and as everyone says that will work fine.

 

You should have no problem with twin 38s on an L20B.

[docbainey]

I had 46s on my stock l20 610 for awhile off of a 2000. It ran a little rich with no tuning, but really made a big difference. Dumb ass me sold them years ago and have just finally re-aquired some to go back on. This time I'll put a mild cam and header on and it should be singing sweet. The stock roadster cam is nowhere as crappy as the smogy 610 cam. Plus the roadster has 1 3/4" intake ports and big valves + 9.5 to 1 compression, it breathes really well. The U20 was good for 135hp from the factory. If I put a 30% power increase in the 610 I'll be lookin for some better brakes for sure! Ah not to mention the 5spd & 3.90 LSD.