Im building an l20b which ive dropped a fair amount of money on and going to run twin 45 webers. The question is will the standard fuel pump give the webers enough fuel and if not what larger mechanical pump would suit.

Ps not interested in electric pumps

My mechanical fuel pump runs my l20b stroker with twin 48 dco carbs, I'm now running e85 and although it's not fully tuned it is running that fine as well, and I'm running f2 emulsion tubes and 200 main jets(lots of fuel).

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When the sign says "don't feed the bears", man you better not feed the bears.

And thats with the stocko pump?

My stock pump puts out 4.5 psi pressure. Webers seem to only need 2 psi ish each.
I know another member was using 4.5 psi in his stroker L and that has serious power too

Ok, so i should see similar figures from a stock l20 pump? Is there a way to measure it?

Fuel pressure Guage and t it in line to the carbs.
Try it on another motor first if you can and your worried

Ah yea, thats easy enough. Ill have to find a guage

It's not pressure, it's flow you should be interested in. Dcoe webers should only have 2 psi going into them.
Pressure is potential energy where as flow rate is actual energy. Too much pressure in these carbs can force the carbys needle open causing drive ability issues at low revs. I run the std pump on my worked l18 and I don't have any fuel delivery issues but I do suspect my pressure is a tad high as it fuels up a bit when idling at the lights but nothing a quick blip of the throttle can't fix.

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Chris Thomas

1971 1600, mild L18, 5 speed

All I want is less to do, more time to do it and higher pay for not getting it done.

We set our pressure on webers to 1.5 PSI
Note that the needle & seat should be sized to the power output.
Thus 150 HP FW needs a 75hp NS per carb.

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A little knowledge is a dangerous thing.
www.datsport.com

"R.I.P. Baz. 29 April 2022. Thank you for all your contributions to the Datsun community over the years. You will be missed." - OZDAT

Is that 1.5-2psi each? So id want 4psi total out of the pump and what sort of flow figures would i be chasing?

No you would still only want 1.5 too 2 psi for both carbs.

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Chris Thomas

1971 1600, mild L18, 5 speed

All I want is less to do, more time to do it and higher pay for not getting it done.

Ok, and what flow figures roughly?

An elegant sufficiency.
As RR stated when asked the HP of their engine.

_________________
A little knowledge is a dangerous thing.
www.datsport.com

"R.I.P. Baz. 29 April 2022. Thank you for all your contributions to the Datsun community over the years. You will be missed." - OZDAT

As a rough guide - the factory service manual says a stock 180B mechanical pump flows enough to fill a litre bucket in under 1 minute when running at 1000 rpm. Therefore could drain the entire fuel tank in under an hour at a touch above idle speed. Not sure how this relates to your engine's fuel needs, but that's a fair bit of fuel the standard pump can move in under an hour.

BTW, manual states 3.6 - 4.4 psi as standard pressure of the pump.

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