Weber 38/38 Outlaw Question

[kyreb1862]

Since the measurements of the Weber 38/38 and the 1.5 inch SU's are very close to the same, wouldn't the performance of the two be almost identical? I am currently running the Weber 32/36 on an unmodified B engine with very satisfactory results. However, this winter, I am pulling my engine to place it in a rust free body. While the engine is out I plan on up grading the cam, installing a new double row timing chain and gears, some head work and having the distributor recurved. These reasons are why I think a 38/38 would make a good performance upgrade and still give me the advantage of having one carb to deal with.

 

[DrEntropy]

I don't see ONE carb as an "advantage" John. :wink:

Twin SUs can be re-jetted (re-NEEDLED, actually) to accommodate the performance changes, with the real advantage of greater CFM flow on demand. The downdraught Weber has an accelerator pump as it's only plus.

A 40 DCOE on the other hand, wellll....

 

[jessebogan]

wouldn't that be a 45 on a B engine?? Still, the sentiment is the same.

 

[DrEntropy]

A 40 works fine on a mildly tuned B, Jesse. That extra 50 CFM at WOT on a 45 is kinda "Coals to Newcastle". :wink:

 

[billspohn]

Let's see- take a variable venturi carb and replace it with a fixed venturi carb (inherently less tolerant of air density , i.e. altitude changes) and then put it on a manifold that makes the mixture go around corners.

Nope, not a good move.

If you are doing enough to the engine to warrant a carb change (and most people don't because they don't want to spend them oney on gas flowing the head because it is a) expensive, and b) not 'showy) I'd look to the 1 3/4" SUs which look right on the car and give a decenmt power bump with a tuned engine.

 

[PAUL161]

I guess I'm prejudice on using the SUs. Their an excellant carb if you understand them. I have a Weber down draft that I took off the 79 and I use it for a paper weight! Works well for that! Sorry.

 

[DrEntropy]

:lol:

The manifold makes a GREAT doorstop, too, Paul. :smirk:

Seriously (if I may be excused for it): A pair of well sorted SUs will equal or outperform a downdraught Weber in most instances. The perceived "increase" in performance is due to the accelerator pump: Initial "wow!" If the engine is to be modified with higher compression, cammed, head CC'd & flow improved and everything balanced properly the DCOE Weber can offer a wider range of (readily available) tuning options than the SUs, tho time consuming and expen$ive...

BUT: with most road cars that's a LOT of money to spend on what Bill called "not 'showy'" stuff. There's no reason a set of SUs can't be made to supply a B engine in street trim with more than adequate flow. "Volumetric efficiency" is the SU's forte. No corners to navigate, metered flow across the RPM range, baby-poo simple to set up and maintain. That surrogate Fiat carb, not so much...

...was that too strong an endorsement?

 

[Roger]

Let's see- take a variable venturi carb and replace it with a fixed venturi carb (inherently less tolerant of air density , i.e. altitude changes)

That's not 100% fair. The downdraft Webers are really compound-choke carburetters. Sure, they start out as a fixed-choke when the first one opens, but the phasing of the opening of the second choke, until both are fully open, is variable.

 

[DrEntropy]

I reckon you like Fiats, don't-cha Roger!? :wink:

 

[Roger]

I reckon you like Fiats, don't-cha Roger!? :wink:

Dunno 'bout that. My daughter and son-in-law both have Fiats, but they live 5,000 miles away so not my influence! I do like Weber, though.

The only Fiat I really liked was a 1970 124 Special T, the 1600 Twin Cam that was a good match for the contemporary Lotus Cortina, if not an Escort Twink.

 

[MGZT260]

TRy dealing with 4 34 mm carbs! (on my Kawasaki 900.)

Incredibly they are easy to adjust as the linkages between are shorter and the carbs work more as a unit. Only reason I can think to go single carb is if you go 4 bbl Holley double pumper on top and work you rway down to an aluminum V8