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Holley 770 CFM Truck Avenger
Bigger IS Better!

By Jack Brinks

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Some of you will remember reading the article “Holley’s Cure for the Carburetor Blues” here on Rockcrawler.com last year. You may also remember me wishing for a larger Truck Avenger to go with my “warmed over” AMC 401. Well, that wish has come true! Holley has begun producing the new 770 CFM Truck Avenger carburetor, which is 100 CFM larger than the original!

Holley 770 CFM Truck Avenger
Holley 770 CFM Truck Avenger

Externally, the 770 CFM version looks almost identical to its younger brother. It has all the off-road modifications just like the 670, such as the one-piece fuel transfer tube, clear fuel level sight plugs, spring-loaded needles and seats, etc. The only difference I noticed was a large vacuum port had been relocated. Other than that, you won’t notice any difference until you check out the size of the bores or “barrels.” As you can see in the photos, there is a significant difference!

Holley 770 CFM Truck Avenger
Holley 770 CFM Truck Avenger


Installation
Unlike the changeover from an old QuadraJet to the 670 Truck Avenger, the process of installing the 770 took all of 15 minutes, since everything hooked up just like the 670. If you’re swapping from a QuadraJet (or another carb, for that matter), be sure to check out the article referenced earlier. It will save you considerable time depending on your application.

Once installed, I cranked the engine over to fill up the fuel bowls. Before I could even pump the accelerator to give my 401 a squirt of premium and set the choke, the engine fired and fast-idled at about 1,500 rpm. I let it warm up a little while checking everything under the hood, and tapped the throttle to knock the idle speed down. The engine came down to a pre-set 900 rpm or so and I then adjusted curb idle speed to 700 rpm where I like it. I messed with idle mixture just a bit, but found myself putting it right back where it was when the carb came out of the box!

With everything looking up to snuff, I installed my Holley PowerShot air cleaner and headed out for a little on-road testing.

Holley 770 CFM Truck Avenger
Holley 770 CFM Truck Avenger

Road Testing
It was like this carburetor was made just for my engine! It worked well in every aspect, from light to hard acceleration. One thing to note, was I had switched out the spring for the vacuum secondaries to the lighter one (as I had on the 670), which allows them to open sooner. On the larger 770, they came in a bit too soon. Switching back to the heavier original spring worked well. Compared to the 670 Truck Avenger, the 770 definitely has the edge. Compared to my old QuadraJet, the 770 is about neck and neck, especially when you put your foot flat on the floor. Off-road however, the Truck Avenger, either the 670 or 770, leaves the QuadraJet in the dust!

Off-Road Testing
My first opportunity to test the 770 CFM Truck Avenger was at Barnwell Mountain Recreation Area (BMRA) near Gilmer, Texas. I put the carb through its paces - extreme off-camber positions, steep inclines and declines. I put my CJ-7 into an extremely off-camber ravine, scraping the right rear fender flare in the process with not one hiccup.

Incline and decline operation was tested on the Fun Country and DeWoody trails. Fun Country is a level 4 trail (on a 5 scale) with a good ledge near the top of the last hill climb. With the exception of bending my driver’s side mirror (which was folded in!) on the tree you see in the picture, I made the climb with no problem. In fact, at the top, a fellow Jeeper asked what kind of fuel injection I was running! I thought I was going to have to raise the hood to prove it to him! (Please note: The tree you see in the picture was left standing intentionally as a safety measure to catch vehicles that might get sideways on the ledge as part of the trail building process.)

Holley 770 CFM Truck Avenger
Holley 770 CFM Truck Avenger

On DeWoody, a 5 rated trail, (which is really just a very challenging hill climb with numerous ledges on the way up), things got a little more interesting. I ended up winching up the last few feet, after I put the front tires a foot or two in the air on a ledge. This had nothing to do with the Truck Avenger, just my driving style! Even the rough terrain and the extreme angle didn’t stall the engine. While I was sitting waiting to get hooked up to the cable, the engine did begin to run a bit rough, but I was sitting at a good 45+ degrees! I had no problem keeping it running, though.

Bottom Line
On hill climbs, rough terrain and off-camber ravines, the 770 CFM Truck Avenger performed just as well as the 670 CFM version, which is exceptional. For sand or mud, there’s no question the greater CFM will come in handy. While I wouldn’t replace a fuel injection system to run any carburetor, there’s no doubt in my mind that the Holley Truck Avenger carburetor is the closest thing to fuel injection you’ll find! The toughest choice you’ll have to make is which one to get, the 670 or 770. If you’re running a stock 350 cubic inch or smaller V-8, I’d recommend the 670 CFM model. If your engine is modified or you’re into the bigger cubes (like me), the new Holley 770 CFM Truck Avenger is for you!

RESOURCE
Holley
1801 Russellville Rd.
Bowling Green, KY 42102-7360
Phone: (270) 782-2900 or (270) 781-9741
www.holley.com

 

Jack Brinks

Jack Brinks is an avid four-wheeler and a contributor here at ROCKCRAWLER.com. Jack resides north of Houston, TX and frequents many events in the Southwest.

Contact Jack at jb77cj7@aol.com


 
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