67/68 427/390 Carb change.

[Richard S.]

What was GM thinking, what was the reasoning, for changing from Holley to Rochester Quad in 1968 427/390 Corvettes....thanks for the help.

[Joe L.]

Re: 67/68 427/390 Carb change.

What was GM thinking, what was the reasoning, for changing from Holley to Rochester Quad in 1968 427/390 Corvettes....thanks for the help.

Richard-----


I do not know, for sure. However, I do know this:

GM spent "megabucks" developing the Q-Jet for use across all of their car lines. From its first use in 1965, it was rapidly phased into use for virtually all 4 barrel applications. The Corvette was actually a "hold out" because by 1968 the Q-Jet had taken over for all other GM applications except a few SHP applications.

Holley carbs were (and remain) very problematic in many areas. I'm sure that GM had a lot of customer complaints regarding these. In fact, in 1968 I had a new Chevelle SS 396 with L-78 which used a Holley carb. I had HUGE grief with this carb. When the car was less than a year old, I took it on a trip to Los Angeles and the carb failed on me. I took it to Citizens Chevrolet in Eagle Rock (Los Angeles), CA as the car was still under warranty. They told me that GM did not warranty Holley carbs after the first 30 days and I'd have to take it up with Holley.

I think that the switch to the Q-Jet carb for most Corvette applications for 1968 was a GREAT one. No matter how folks malign them, the Q-Jet is a GREAT street carburetor. In fact, I think it's the absolute best street carburetor ever designed. The do have a few trouble spots but these can be easily and permanently fixed. The thing with Holley carbs is mostly about "cache".

Plus, the Q-Jet is not only a great street carb, it's also a great performance carb. Most Q-Jet models deliver about 800 CFM, which is competitive with the biggest Holley carbs of the day. Their small primary/large secondary configuration provides excellent street performance and fuel economy. The air valve secondary provides smooth secondary operation.

Besides everything else, a Q-Jet is FAR technologically superior to a Holley. Not even in the same ballpark.

For all-out performance and racing, a Holley is probably better. However, the VAST majority of folks don't use their cars for all-out performance and racing.

Q-Jets are funky looking; Holley carbs are "cool" looking. I think that's why lots of folks think Holley carbs are great. They're wrong.

[Duke W.]

Re: 67/68 427/390 Carb change.

What was GM thinking, what was the reasoning, for changing from Holley to Rochester Quad in 1968 427/390 Corvettes....thanks for the help.

There were two reasons:

1. Emissions, which was the primary reason - GM knew that more precise fuel control would be required to meet future emission requirements. This is the reason for the small primary throttle bores. They provides more precise fuel metering in the range of normal load that make up the emission certification test. The early models had a plant only off-idle mixture adjustment, which was sealed after it was set, but this feature was dropped from later models.

2. Cost - use an inhouse manufactured "standard" carburetor for all four-barrel applications.

Beyond that all the reasons Joe stated regarding the Holley design were (and are, today) certainly valid, and I agree that the Q-jet (along with the old AFB) are much more reliable and trouble-free designs. Look at all the "Holley problems" that are reported versus the WCFB, AFB and Q-jet, even though Holleys make up a relatively small fraction of Corvette carburetor use from the fifties to eighties.

The late Dale Pearman referred to Holleys as a "packaged leak", and I consider myself blessed that I never owned a car with a Holley carburetor.

Duke

[Lyndon S.]

Re: 67/68 427/390 Carb change.

And they just sound so cool when you kick a Q-jet in on a big block well hell that sound is even cool on a small block when you get on it.