DCOE 40 vs OER 47 Triple setup

[Reese]

Hey guys,im about to make a dission on if I get OER 47mm carbs vs the Weber DCOE 40mm carbs. Im running a stock L28 block (for now) w/E88 Head, MSA Stage 3 cam with other performance items. Is it overkill to run the 47mm carbs?? thou Ive been told i can downtune the OER's to run better for my weekend warrior car. What you guys think I should run..?

[Lazeum]

You should go and search on the forum for people with Webers & other triples to compare your setup with the ones' from others. You'll find the answer to your question.

You'll see that we do not always agree about what would be required.

 

As far as I'm concerned, with stock engine and supportive mods, you'll be fine with DCOE40.

The risk of having too big carbs is low torque at low & mid range => not fun

Too small carb and you won't get HP at high load but engine would be fun at low & mid RPM => still fun

 

Afterwards, you can run big carbs with small venturi/chokes, so it trully depends on your hp goals on the long range and how you expect to run your car (street / Track....?)

[Tony D]

Are you sure they are 47's and not 45's?

 

There is a BIG difference in what you will do with a 48/50 versus a 45.

 

Not so much between a 40/45.

 

Generally 48/50's are not considered 'street' carburettors. Simply because the size venturis used to optimized power above 7000 makes down-low transitions iffy. They only make them so small for that size carburettor.

 

A 40 or a 45 would be far more at home on the street, as you can get almost identical main venturis for low speed drivability.

 

Either a 40 or a 45 would work fine on the street. Really without forged slugs, either would work with little sacrifice on top end power, there is only so much you will make a 7500 or below.

 

I'd get straight on what OER you really will be using, as a 48/50 is a whole different animal than a 40/45. I personally have never heard of a '47' so this needs to be clarified first.

[SHO-Z]

From what I have heard the OER are a new version of the SK Racing carbs, weber jets and Mikuni floats. It partialy depends on how much you want to spend on other parts for your car. Used webers are going for around $600 and the OERs could cost twice that amount if you can fine a used set, I have never seen any. I have not seen any SKs for sale in a long time.

[djz]

OER make 45s, 47s and 50s.

 

OER Japan website

[Tony D]

Everything I posted is directly applicable, nothing changed. Read the website (venturi selection choices in particular)and make up your mind.

 

For the semantically challenged, substitute '47' for '48' in my original post and not one whit changes.

[SHO-Z]

I think anything larger than a 45mm is way too big for a Z engine. Four 45mm carbs are used on a 350 ci V8, do the math! You would need to install chokes about the same size as a 45mm to get the jets to flow properly. At anything less than full throttle it would fall on its face.

[Tony D]

No, 55mm Webers are suitable for use on L28's, depending on what you are doing. Arguably and dyno proven they will give power under the curve.

 

But this is a relatively mild street engine and 40 or 45's will be fine.

 

You simply won't get power above 7500 with 45's, and if you are operating in that area, it becomes a very hard decision to go with 48(7), 50 or 55's as they take an entirely different manifold due to the massive port sizing.

 

Or, you can go with 45mm ITB's and pick up RPM range and horsepower over the 45mm Webers you formerly ran.

 

45mm ITB's will run power levels unheard of in anything but 50mm or larger Carbs. But in ITB's you don't need vacuum to make the petrol flow. So pumping losses are reduced, and power levels rise. We made 20HP more at 7500 rpms on 45mm ITB's compared with 45mm DCOE's. We also had a continued rising power point to 8250rpms (where it was making 40+hp more!) using 45mm ITB's over 45mm DCOES. All on the same head, same manifold (match-ported to the head) and same cam.

 

The cost of 50mm Mikuinis and a new manifold (or gowd forbid the 55 mm DCOE Weber Monsters) was compatible with the E-Motive TEC2 at the time, so we went EFI since our racing class did not disalow EFI for cars that came with EFI from the factory (woo hoo 280Z!)

 

For the street in the USA, 45DCOEs are more than enough. If you are serious about power and can give up the lower end of the rpm band...then go bigger. But in this case, 45's are more than enough. And likely the 40's will work fine, if not be a little restrictive in the useable RPM range of the engine package.

[JSM]

The other thing to consider are part replacements. I had a set of older 45 OER and I couldn't find parts for them. Webers from my research were much easier to get parts for.