dual z carbs on a L20b

[sdsurf]

Will su carbs off a z work on a L20B with the proper maniold? would it be worth it to get them from a yard? I saw some but want to find out more...

[datsunfish]

Yes they will work but may require some mods for the 4 cyl mani. I would avoid the flat tops but if cheap enough its worth it to give it a shot. 4 cyl su manis often go for over $100 on ebay. You can modify the 6 cyl mani but it would be a big pita.

[zerow]

They may be too much fuel/air for a 4 cylinder 2.0 liter motor. The Z carbs are dual 44mm carbs spread out over 6 cylinders, whereas the smaller 4 cylinder carbs are dual 38mm spread over 4 cylinders. Also, the 44mm Z carbs rotate opposite the 38mm, so you have to fabricate a new linkage that will allow the new carbs to open (not a big problem if you are cable driven).

 

There was a write up about the pitfalls of using 44mm carbs on a smaller L-series motor:

 

http://www.jetlink.net/~okayfine/su/zsus.html

 

I thought the same idea for my L20B, but thought twice. I will reserve that for my LZ22 build in the future:D

[Jason]

42mm Roadster SU carbs off the U20 would probably work better, Datsun claimed 135hp out of the U20 with those mounted up. Cable pull linkage and custom manifold work required for this to work though....

[ppeters914]

U20 flows a lot more than a L. Even they ZTherapy guys say 38's make more sense on a street-driven L20b. Better low-end and mpg than the 44's. The only downside is you'll run out of carb on the top end, which isn't a problem for most folks.

 

OTOH, if you're building the badazz-SR Killer L..... :lol:

[Jason]

Depends on the head/cam/exhaust Pete, I run the float bowls dry with the 38mm SU's on my l20b on long, uphill pulls and any long pull over 5500rpm. I've got the floats set at 23mm also..... For a stock cam and head you should be OK with the 38's.

[ppeters914]

Depends on the head/cam/exhaust Pete, I run the float bowls dry with the 38mm SU's on my l20b on long, uphill pulls and any long pull over 5500rpm. I've got the floats set at 23mm also..... For a stock cam and head you should be OK with the 38's.

Agreed. I shoulda said STOCK street-driven L20b. :rolleyes: That's also what the Ztherapy guys say, and they're making money saying it. :D

[zerow]

42mm Roadster SU carbs off the U20 would probably work better, Datsun claimed 135hp out of the U20 with those mounted up. Cable pull linkage and custom manifold work required for this to work though....

 

Agreed, the 42mm carbs would theoretically work better, but, the nature of them attached to a pushrod motor versus (IMHO) an overhead cam motor might reduce their overall fuel economy. If ZTherapy states that the 38mm carbs are more efficient for a L-series street motor, then I would say that is close enough to gospel. They would know best.:)

[Jason]

At this point if I keep my foot out of the throttle I run about 10-11 litres per 100 km. If I have a really heavy foot I run about 13-14.5 litres per 100 km. This is a stockish L20b with a .507 lift cam, 38mm SU's and a 2" exhaust. I would be guessing at this point that if I switch up to the 42mm SU's I would run about 10% lower fuel economy, but, I would gain the ability to pull longer on hills and above 5500 rpm. It's a tradeoff, one which I don't feel up to doing at this point.

[datsunfish]

Nothing about a 507 cam is stockish. That would be more than enough for twin 2 barrel 40s. The L motors get the large majority of performance increases from head work.

[Jason]

Well, springs and such in the W58 head have been upgraded to handle the cam, however, the head is unported and still has the steel exhaust liners in also. Seems to help with the emissions (smog) test that I have to pass up here. Bottom end is stock so I'm pretty much limited to 6500rpm or so....

[ppeters914]

I would be guessing at this point that if I switch up to the 42mm SU's I would run about 10% lower fuel economy, but, I would gain the ability to pull longer on hills and above 5500 rpm.

Yup, that's what Bruce told me when I started researching SU's to replace the Weber on my L20b.