The Chevrolet Cosworth Vega Engine with Weber Side Draft Carburetors

A restored Cosworth vega
A restored Cosworth vega
Webers with air cleaners
Webers with air cleaners
engine head
engine head
weber 42DCOE side draft carbs
weber 42DCOE side draft carbs
engine head
engine head

 When you paid around $6000 in 1975-76, for a Chevy Cosworth Vega, you could have bought a Corvette Stingray, or just about. The Cosworth Vega was the high end Vega, although it looked racy, it was not really the case. It had a computer to regulate the electronic fuel injectors, mag wheels, better interior. The engine was a twin overhead cam with 16 valves, so it was totally different than buying a non-Cosworth Vega, which was also a 4 cyl engine without a computer or fuel injection. Its engine was a 140 cu. inch, which generated around 90 hp. The Cosworth was 122 cu. in and generated 110 hp at 5600 RPM. In comparison, a 1967 Corvair Monza with two single carbs and six cyl generated 110 hp also. The Corvair Corsa of 1965-66, with four carbs produced 140 hp, its Turbo edition, 180 hp.

Because the Cosworth engine was totally different than the non-Cosworth vega engine, GM produced a totally different repair manual for it. For tune ups, the Cosworth noted these differences:

Compression: 170 psi

Plugs: AC R43LTSX with .060 gap

Timing: 12.0 deg BTC

Valve lash: .014

Idle speed: 1600 RPM

Fuel pump, in gas tank: 5.5 psi at 12.8 V; external pump: 6.6 psi at 13.5v

Air cleaner: A505C

Many Cosworths were modified using Weber Carbs, usually 2  two barrels, model 42 DCOE Side Draft or similar (the models ran from 38-45). The models in this class were similar. Weber carbs are more expensive and had to be synchronized (much like in the Corvair) so that all opened and closed at the same time and all had similar air flow. If this was not correct, the car would not run very well. The use of a Unisys for air flow still are available. The reason for changing to Webers, which remain fickle devices, is interesting. The standard Cosworth was fuel injected, no carburetors, controlled by a computer. As long as they worked, they were easy. Using Weber carbs meant no fuel injection, no computer needed.

If you have Webers on your Cosworth, the carbs may need adjustments and proper specs for the carb.

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Comments 2 comments

stephen 5 years ago

Q: What is the expected hosepower with a well tunned

Weber 42DCOE side draft carbs -- 2 x two barrels?

DB511 5 months ago

Your horsepower ratings don't take into account the Cosworth rating is net horsepower, the Corvair's are gross ratings. The Corvair's engines also did not have to meet the much more stringent emissions standards. The 1975 Chevy Monza 265 CID V8 was also rated at 110HP.

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