The Stovebolt Site Forums The Shop Area Engine Shop Carburetor Swap - 1959 GMC 100

Greetings! I recently bought a 1959 GMC 100 with a Pontiac 336 and a dripping Stromberg WW carburetor. I’m just looking for some guidance on whether to rebuild or swap the carburetor out for a Holley 4412. The factory manifold includes an odd offset bolt pattern with an adaptor for the Stromberg carburetor. If I go with the Holly, I would need to place an adaptor on top of that to match the Holly mounting flange. Do you see any issues with two adaptors? Thanks for your guidance!

Wouldn't the adapter already be standard GM two barrel to whatever the Stromberg is? In other words, have you tried simply removing the adapter to see if the Holley will bolt to the manifold itself?

The Stromberg is one of the top 3 or 4 2-barrel carburetors ever made !

The only problem is that Stromberg used an aluminum throttle body. Like so many other carburetors with aluminum throttle bodies (think Q-Jet), 50k miles and the throttle body needs bushings. Once the throttle body has been bushed, 250k miles are not unreasonable.

I would highly suggest rebuilding the Stromberg (unless you own stock in Shell Oil )

Jon

Tronman:

Thanks! I read online that GM used an offset bolt pattern unique to these trucks with the rear bolts closer than the front. Just pulled the carb and actually measured the bolt spacing - which I should have done before! The back is spaced the same as the front. Just goes to show:

1. The simple answer is most often right;
2. You can’t believe everything you read on the internet; and
3. I can be a dope - especially when I’m in a hurry!🤪

Thanks again!

Carb King:

Thanks for this. Makes the most sense and will be easier than changing everything else to fit the carburetor. Much appreciated! Best regards!

Just wanted to close this out. I got a rebuild kit and rebuilt the Stromberg. It looks and works great. Thanks again for the advice!

The smaller GMC engines such as yours used the Stromberg type WW, with the normal rectangular flange bolt pattern.

But the type Stromberg type WW has a "big brother", the type WWC used on larger GMC engines. The type WWC used by GMC does have a trapezoidal flange bolt pattern. These were used on most GMC 351, 401, 432, and 478 CID V-6 engines. Many of these carbs have an internal governor.

Stromberg also built WWC carbs for the Chrysler 383, which has a rectangular pattern, but larger than the pattern on your carburetor.

Jon