Weber 40 DCOE (dual) vs 45 DCOE--- good enough for an L20b?

[Grimlid]

Setting up to rebuild my l20b with a mid level perfromance rebuild. nothing too heavy and obviously running on high octane pump gas but im spending a few grand at leaset though im kinda at the mercy of my mechanic....

Found a set of 40 dcoe in good condition. I had beenthinking 45s but is 40 dcoe big enough ? Im guessing yes but would like the opinion of someone whos run these or been around longer than me. I dont want undersize it but also dont want to be wasting unburnt fuel and have a shitty mix that cant be consumed.....

a lot mixed arguments with no real conclusions on line and didnt see any datsun owners saying much. 5mm is a lot when I consider its a circle circumfrence so its exponentially larger....

Thanks for any feed back

Russ Grimlid

[datzenmike]

 Largest L head port is 1.5" so 40mm is plenty. Size doesn't automatically run richer, even 45s can be tuned.

 

How high will your compression be? 

 

As for mechanics... they are there to be told what you want done.

[banzai510(hainz)]

for the street I like my40mm Mikinus better that 44s

12 hours ago, Grimlid said:

though im kinda at the mercy of my mechanic....

I say listen here first unless this guy has L motors all over his garage and then that still might not mean nothing(just a collector)

 

 

Contack Byron on the 510 realm (hes in the Vancouver BC area)and he can get the most bang for buck out of a L motor with bolt on stuff.To get the last 5 HP out of these might cost thousands.

Edited April 11 by banzai510(hainz)

[Grimlid]

10 hours ago, banzai510(hainz) said:

for the street I like my40mm Mikinus better that 44s

I say listen here first unless this guy has L motors all over his garage and then that still might not mean nothing(just a collector)

 

 

Contack Byron on the 510 realm (hes in the Vancouver BC area)and he can get the most bang for buck out of a L motor with bolt on stuff.To get the last 5 HP out of these might cost thousands.

Thanks

 I appreciate the insght on the 40 vs 44. I think Its an opinion ive heard before....

I know \byron a bit i tried emailing him but hes been busy I guess.. My mechanic is super busy and focusses mainly on z models (its the z shop ) Hes gonna rebuild my l20b with a bunch of components he put aside. He told me to pick a carb set and go with it so thats what Im doing basically seeking more assitance when google doesnt have an answer.

Edited April 11 by Grimlid

[banzai510(hainz)]

soem one said Mikunis are better cause they have a low, mid,high circut.  Weber more on off the numbering sytem is weird for them.

 

I had 2 st of Mikunis 44s and sold them for 1200. wheich really was a good price with the Datsun Bigport manifold already to bolt up

[Stoffregen Motorsports]

To get performance out of dual carbs, you at least need a cam, a header and a good exhaust. The non-siamesed cast manifold would be good too.

 

You also need to have someone set the curve in your distributor. This is one of the most overlooked mods to a Datsun L motor. A simple recurve, which costs only $150, will allow you to run more base timing without the worry of having too much timing on the top end. Different springs are also installed to get the timing in quicker than stock, which builds torque.

 

Head porting and big valves would also be great, but you're into real money there.

 

Also be sure to get some sort of soft mount for the carbs. The o-ring type are the bare minimum, but you can now get the previously unavailable Nismo style rubber vulcanized soft mounts with studs on both ends. There's a guy on instagram who is making them, but I forget his name. SOft mounts help keep the fuel from bouncing around inside the float bowls. I'd also do a heat shield under the carbs, but above the manifold/header.

[Stitebunny]

21 hours ago, Stoffregen Motorsports said:

 

 

You also need to have someone set the curve in your distributor. This is one of the most overlooked mods to a Datsun L motor. A simple recurve, which costs only $150, will allow you to run more base timing without the worry of having too much timing on the top end. Different springs are also installed to get the timing in quicker than stock, which builds torque.

 

 

How does one go about recurving? Is it a matter of just trying different springs until you get what you want?

Is there a good base line timing for doing this that you might want to aim for?

[Stoffregen Motorsports]

I used aftermarket springs a few times, but I found that if you removed one of the two springs, it worked great. Be careful that the spring preload is right. If it's loose, then the distributor cam can float around causing timing flutter at low speeds. You can add/remove preload by simply bending the tab that the spring attaches to. I set it so that there is almost zero preload, but no slop either.

 

Base timing varies from motor to motor, but 12-15 at idle is great. Same with total timing. 32-35, or (depending on compression ration and cam) maybe less. I had a 12:1 2150cc motor with a big cam that I had to run 25 degrees. It ran fine but worried about cracking a piston, we lowered the compression ratio to just around 11:1, then we could run 32 degrees timing.

 

Every motor is different, but the above should get you in the ballpark.

[Stitebunny]

Cool thanks for the info!

Might try messing around with this. 
Sorry for the thread derail. Though slightly related!

Im running 40’s on L20B.  

[Grimlid]

On 4/12/2024 at 10:13 AM, Stoffregen Motorsports said:

To get performance out of dual carbs, you at least need a cam, a header and a good exhaust. The non-siamesed cast manifold would be good too.

 

You also need to have someone set the curve in your distributor. This is one of the most overlooked mods to a Datsun L motor. A simple recurve, which costs only $150, will allow you to run more base timing without the worry of having too much timing on the top end. Different springs are also installed to get the timing in quicker than stock, which builds torque.

 

Head porting and big valves would also be great, but you're into real money there.

 

Also be sure to get some sort of soft mount for the carbs. The o-ring type are the bare minimum, but you can now get the previously unavailable Nismo style rubber vulcanized soft mounts with studs on both ends. There's a guy on instagram who is making them, but I forget his name. SOft mounts help keep the fuel from bouncing around inside the float bowls. I'd also do a heat shield under the carbs, but above the manifold/header.

Thanks, First Ive heard of recurve but IM putting money into the motor now and possibly the head also if I can get a knowledgable machine shop. Like you say Im currently running 2" exhaust (upping to 2.5" next) . heat shield is in the mail.  I was planning just to use a matchbox dizzy or other electronic ditributor. I havent heard of recurve and will spend some time with that thanks.

 The Porting may also come now but Im thinking it will wind up waiting for awhile since everyone I talk to is so busy and wants my motor in and out , I finally found a recommended guy in Mission BC who is willing to spend some time with me so I will see waht I can work out with him on the rebuild.