Holley 4780-2 or Q-Jet 7040202 - Chevelle Tech
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post #1 of 16 (permalink) Old Oct 20th, 19, 1:07 PM Thread Starter
 
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Holley 4780-2 or Q-Jet 7040202

Hey All,
My son and I have decided to do a 396 SS clone with our 68. Which carburetor do you think would be more "correct" for the project. I have both on the shelf in need of rebuild.
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post #2 of 16 (permalink) Old Oct 20th, 19, 1:38 PM
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Re: Holley 4780-2 or Q-Jet 7040202

The Holley double pumped never came on an SS 396.

Steve R
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post #3 of 16 (permalink) Old Oct 20th, 19, 1:47 PM
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Re: Holley 4780-2 or Q-Jet 7040202

I think whichever carb you use will be OK.It really depends on how the engine's set up but I think the Qjet is the most versatile carb ever. The thing to do would be to use a drop base air cleaner with the 396 350HP or 396 375HP callout on it so then whatever carb you use is kinda hidden under there.
So your real reason for picking a carb is how will you set that BBC up ?
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post #4 of 16 (permalink) Old Oct 20th, 19, 4:50 PM Thread Starter
 
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Thank you for the input guys. Greatly appreciated.
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post #5 of 16 (permalink) Old Oct 20th, 19, 9:06 PM
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Re: Holley 4780-2 or Q-Jet 7040202

7040202, 1970, 4MV,

Pass, 350/300 hp, A/T, Non-Ca.
Chevelle, 350/300 hp, A/T
Nova, 350/300 hp, A/T
Corvette, 350/300 hp, A/T

Holley LIST-4780-2 is the 3rd carburetor in the 4780 series (2 modifications past the original configuration), after market performance carburetors, and never was installed on a factory car, only as a performance carburetor over the counter addition.
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post #6 of 16 (permalink) Old Oct 20th, 19, 10:20 PM
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Re: Holley 4780-2 or Q-Jet 7040202

You guys do know that the 4780 is the same bores and boosters and all as the 3310-1 with pumps on both ends. I did the measurements this years and was surprised that the VS is a 780 and the 4781 is an 800 same main body.
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post #7 of 16 (permalink) Old Oct 20th, 19, 10:40 PM
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Re: Holley 4780-2 or Q-Jet 7040202

I always liked the factory calibration of the 4780-2. Very smooth transitions and excellent idle quality.

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post #8 of 16 (permalink) Old Oct 21st, 19, 1:45 PM
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Re: Holley 4780-2 or Q-Jet 7040202

780, 800 cfm, all depends on the vacuum depression the carb is flowed at. In essence, Holley didn't like the odd flow rates of the LIST-3310 carbs when they went into after market sales, so, they did what Chevrolet did earlier with the 302 Z28 engines, they simply flowed to get 750 cfm, and stopped. In the case of the 302, and a lot of the big blocks, they went to a set horsepower, and stopped going any higher. The 302 was restricted to FIA racing regs for its class in road racing to 305 cu/in maximum, and 300 horsepower, so, it made a solid 302 cu/in and was rated at 295 horsepower, although it made more power over the rpm level it was certified at.

We saw both 396 and 427 go to 425 horsepower, and, the 396 between 375 and 425 horsepower. These were factored to have a set power level, because of insurance regulations and limits too many horses, no insurance. A ZL1 was rated at 430 h/p, but a good one made roughly 565 h/p.

It was a sales numbers game, nothing else.
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post #9 of 16 (permalink) Old Oct 21st, 19, 2:25 PM
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Re: Holley 4780-2 or Q-Jet 7040202

The Qjet is the more "elegant" design of the two, and ought afford slightly better throttle response, particularly part throttle. The Holley is a bit simpler design.

sort of like an M16 and AK47 comparison. I'm wanting to rig up a "780" that is really a double pumper to support 600 HP> the "everyday carb, however, will be Qjet which ought meter out EFI -like driveability and economy. The 780 was a vacuum secondary carb, which is what GM used.

BTW, does the intake have both bolt patterns, square and spread bore ? It may force your choice if not.

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post #10 of 16 (permalink) Old Oct 21st, 19, 3:29 PM
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Re: Holley 4780-2 or Q-Jet 7040202

Yup-the original 396 "L78" was rated 425 HP at 6400 in 1965
The later L78s were rated 375 HP at 5600
..identical engines.


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post #11 of 16 (permalink) Old Oct 21st, 19, 5:04 PM
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Re: Holley 4780-2 or Q-Jet 7040202

I'm a big Holley guy but on a stock or slightly modified big block I would love to have a Quadrajet.

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post #12 of 16 (permalink) Old Oct 21st, 19, 8:34 PM Thread Starter
 
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WOW! You guys gave me lots to consider. To much maybe😂😂😂
Thanks a ton guys.
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post #13 of 16 (permalink) Old Oct 21st, 19, 10:42 PM
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Re: Holley 4780-2 or Q-Jet 7040202

There are things and places to look at when viewing a used Q-Jet, people do some very strange stuff to them along the way.
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post #14 of 16 (permalink) Old Oct 22nd, 19, 6:10 AM
von
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Re: Holley 4780-2 or Q-Jet 7040202

When you say "correct", if you mean correct appearing for a '68 SS396 then the Q jet is the choice for an L35 325 hp or L34 350 hp 396. The Holley would be closer to correct appearing for an L78 375 hp 396. If you mean "correct" in performance the Holley might have a slight edge in power over a properly set up Q jet but for street manners and versatility a PROPERLY SET UP Q jet is the winner IMO.
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post #15 of 16 (permalink) Old Oct 23rd, 19, 9:08 AM
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Re: Holley 4780-2 or Q-Jet 7040202

I was a naysayer of Q-jets in my younger years. ( due to lack of knowledge )

I recently took a 800dp off my 454 and replaced it with a 800cfm Q-jet. (I got Ruggles book and did some minor pin drilling alterations because of the cam size )
The Q-jet cold starts better, cold idles better, warm idles better, off idle throttle response is better, general drive ability is better, and need some track time to tell the full throttle difference because the butt dyno can't.

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