The Stovebolt Site Forums The Shop Area Engine Shop Need help understanding Carburetors - the Good and the Ugly

Good day. I need GMC 270 carburetor education. Over the years wayward carburetors for GMC 228’s, 270’s and a few 302’s have populated my shelves.

In the photo below I lined up three keepable candidates for a recently completed 270 rebuild.

Left to right:

Zenith, Stromberg WW 2bbl, and a Holley.

I am biased toward Zenith’s but my knowledge is limited about the Pro’s and Con’s of a two barrel application and other manufacturers.

I am not interested in high performance and eeking out every last bit of power, air and fuel but looking for economy and reliability in stock configuration.

Can the experts help me decide, based on your experiences if either one of these is more preferable over the other. (I also know that opinions vary but still want to go down this slope) . What are your experiences in quality and what advantage would a two barrel have over a single barrel ? The engine will not be worked hard, but going in a one ton dump flat bed.

Thanks in Advance design. - Tom

I just had my 302 built and they recommended the Stromberg WW. It was selected because of the linkage and size because it came off a CHEV 305 displacement.

Yes. The Stromberg seems to match well on a 302. Curious to know why that is (I have my hunches but I am not an expert). I sold a 302 and threw in a Stromberg WW into the mix for that reason.

The one pictured is NOS. If I don’t use it perhaps someone here can.

(How did the rebuild work out for you?) gotta love those 302’s!

The pictures show:

Zenith single barrel
Holley two barrel
Holley single barrel

No Stromberg is pictured.

The KEY to whether to use a 2-barrel carburetor or a single barrel carburetor is the intake manifold. You DO NOT want to use a 2---->1 adapter.

Stromberg offered 477 different type WW carburetors for single carburetor applications from a 224 to a 401 (they also offered a dual 2-barrel set-up for the 702).

WITH THE APPROPRIATE TWO BARREL INTAKE MANIFOLD, several of these could be made to work on a 270 or 302 (and several of them could not).

The WW has one "design flaw" effecting longevity, an aluminum throttle body. Once the throttle body has bronze bushings installed, the WW is close to bulletproof.

Again, depending on the design of the intake manifold, probably not a lot of difference in performance in a SELECTED and MODIFIED Zenith single barrel, and the Stromberg WW.

While parts for neither are available at your FLAPS, more tuning parts are available, and less expensive, for the Stromberg than the Zenith.

Jon

And a wee bit of carburetor trivia:

Zenith had a two-barrel carburetor at this time (type 28ADA) but it was heavy duty and EXPENSIVE! For this reason, these units generally only were used in industrial applications, and heavy duty trucks (Autocar, Mack, etc.).

Zenith and Stromberg were owned by Bendix Aviation (Bendix was [past tense] to Zenith or Stromberg as GM is to Chevrolet or Pontiac).

In the mid-1950's, Zenith wanted a light duty 2-barrel carburetor.

So the engineers at Zenith and Stromberg got together, and settled on the upper 2/3 (air horn and bowl) of a Stromberg WW, and Zenith cast a new throttle body out of aluminum, with linkage differing from that of Stromberg. The new carburetor was called a Zenith WWZ-10. First production model was 1957.

Jon

Thanks for the clarifications, Jon. I’ll take a closer look at the middle carb when I get home in a couple days. Correct. Holley.

tom moore In the mid seventies I took care of a fleet that used all three of those,kits were easily available ,Don't recall many expletives about them just ocasional service as needed. that air cleaner clamp was pretty durable on off road trucks. Tom why don't you try all three,whichever fits your linkage best if trouble comes along pay carb-king to help you he doesn't have a semi-truck load of carburetors and 40 years of experiance for no reason !! Your lucky you can get away from all these warp-mobile carbs. You have brass floats too...try your luck be glad it's not ball and ball !!!

Yeah good to know. I don’t have anything to base this on… but it “seems Holleys get a bad rap. That middle two barrel Holley seems well made. Think I’ll stick with a single barrel.

The engine demand in CFM is not directly a function of engine size (if 7 or more cylinders use a common carburetor & manifold).
If less (L6), the demand is higher per cylinder, but less frequently. Add about 10%.

I'm not a carb expert, but I'm pretty sure that is a Bendix-Stromberg WW 2 barrel carb. Had one on my '57 GMC.

It had
Bendix
Stromberg
cast on the back.

Below from '57 GMC Maintenance Manual. The one on the left was for GMC 302 inline 6 engines and the one on the right was for GMC (Pontiac) 347 V8 engines.

Good to hear from you, Bill. I’m on the road - when I get home tomorrow or late tonight I’ll check it out in detail. I thought it was a Stromberg - but for all I will ever know… I am usually incorrect and it wouldn’t surprise me that it’s a Holley. Jon knows his business. I am easily confused… that’s the thing about constant learning (if done right) - it keeps me constantly humble.

Here I am near PA and NY with a new project:

Just to clarify:

The carbs pictured by Tom in post 1 of this thread from left to right:

Zenith single barrel
Holley two barrel
Holley single barrel

The carb pictured in post 2 by pdlightning is a Stromberg 2-barrel type WW.

As to what have might have been original; more information would be required. On different applications of the 270 in different years, G.M.C. used (in alphabetical order) Carter type W-1, Holley type 1904, and Zenith types 28, 30, 63, and 228.

All are single barrels

Jon

As to original carbs on the 302:

G.M.C. used Holley type AA-1, Stromberg type WW, and Zenith types 263 and 885.

The type 263 is a single barrel (size 4).

The others are 2 barrels.

Jon

Yep. It’s a Holley. I’ll have to change the writing on the box now. Lol! Thanks, Jon as always.

Tom

To answer the question, How did the rebuild go?..... My Stromberg WW was a "rebuilt" POS. Its now at a different carb shop but may be unusable. Now I have to find an equivalent good carb.

An L6 engine and a V8 engine of similar size are not as good a match as appears at first glance.
A single manifold (regardless of the number of carburetor throats) supplying a six-cylinder engine has fewer, larger, and more widely spaced intake pulses (each cylinder is 1∕6th or 16.7% of the total displacement, and has an intake stroke every 120°) than a V8 engine of the same total displacement (each cylinder is 1∕8th or 12.5% of the displacement, with an intake stroke every 90°). Each L6 cylinder is ⅓ larger, with vacuum pulses spaced ⅓ farther apart than a V8 of the same total displacement, thus increasing the amplitude and reducing the frequency of the vacuum pulses.
The L6 needs a carburetor about 10% larger than the V8 of similar size.

On the subject of intake pulses or signals……

In my mind, the stock Stovebolt manifold is sort of akin to a single plane manifold in the v8 realm. One big plenum.

Between that, and the siamesed ports, the intake pulses are probably not super distinct at the carb. At least not in comparison to something like a dual plane v8 manifold. Fairly chaotic things going on inside the manifold.

That’s just the way it works out in my head. Is that kinda close to accurate? Feel free to correct me……