I am beginning a rebuild on my 1977 L82 engine. My goal is to increase the performance over the original specs. Has anybody had any experience replacing the Quadrajet Carburetor with a Holley 0-80555C 650 CFM 4175 Spread Bore carburetor (Manufacturer's Part Number: 0-80555C). Is this a better performing carburetor? Thanks.
Question: Holly carburetor for a 1977 L82 rebuild
- Thread starter vrnole
- Start date
Hib Halverson
Technical Writer for Internet & Print Media
For a stock, near stock or even mildly modified 350, the Rochester Quadrajet, with changes in calibration appropriate for the modifcations, is the best choice.
I'd only go to a Holley is the engine is significantly modified which, in the case of a 350 would mean, "beyond the 425-hp level".
The QJ is a far better carburetor than the Holley as far as drivability and fuel economy are concerned. Up to 425-450 horsepower, the two can provide comparable WOT performance.
I'd only go to a Holley is the engine is significantly modified which, in the case of a 350 would mean, "beyond the 425-hp level".
The QJ is a far better carburetor than the Holley as far as drivability and fuel economy are concerned. Up to 425-450 horsepower, the two can provide comparable WOT performance.
motorman
Well-known member
spread bore vs Q jet
as carb rebuilder i would tell customers that brought in their holley spread bore for rebuild i would ask if the still had their original Q jet. i told them i would rebuild their Q jet and if they did not like it better than the spread bore i would rebuild the Holley free. never had to do a free rebuild.
as carb rebuilder i would tell customers that brought in their holley spread bore for rebuild i would ask if the still had their original Q jet. i told them i would rebuild their Q jet and if they did not like it better than the spread bore i would rebuild the Holley free. never had to do a free rebuild.
Hib Halverson
Technical Writer for Internet & Print Media
"Motorman" is spot on.
For a street-driven application, even those which are race cars but are also street driven, I would not go to a Holley until the mods get the engine to a point that it's airflow-restricted. Typically, a QJ will support up to 700-750 cfm.
Once you do get there the Holley--but the 4150 series not the "Spread Bore"--is the way to go.
Now...there are exceptions and one is road racing. If the car is also modified for significant increases in cornering and braking, the Quadrajet, by virtue of inferior fuel control in the float bowl during high lateral acceleration in cornering and high deceleration under braking, becomes a limitation. In that situation, you need a Holley with center-hung floats no matter what the power level.
In fact, one reason the 70-72 LT1 used a Holley was not so much of the air flow but the better fuel control in cornering and braking.
For a street-driven application, even those which are race cars but are also street driven, I would not go to a Holley until the mods get the engine to a point that it's airflow-restricted. Typically, a QJ will support up to 700-750 cfm.
Once you do get there the Holley--but the 4150 series not the "Spread Bore"--is the way to go.
Now...there are exceptions and one is road racing. If the car is also modified for significant increases in cornering and braking, the Quadrajet, by virtue of inferior fuel control in the float bowl during high lateral acceleration in cornering and high deceleration under braking, becomes a limitation. In that situation, you need a Holley with center-hung floats no matter what the power level.
In fact, one reason the 70-72 LT1 used a Holley was not so much of the air flow but the better fuel control in cornering and braking.
After 3 Q-jet on my "78 I went to that Holley. I must say I a bit old school to begin with. BUT I'll NEVER GO BACK TO THE Q-jet. The Holley runs and preforms great. After a little tuning I'm getting 18 mpg hiway. This on a 4-speed & 4.10 rear gears. I LOVE MY HOLLEY.
Gary
SAVE the WAVE
Hib Halverson
Technical Writer for Internet & Print Media
I'm doing some Holley tuning myself and could use some pointers on part throttle tuning for better fuel mileage.
18.9 highway with a 4.10 axle is astonishing.
Tell me the different things you did to you Holley to achieve that. I'd like to try some of them, myself.
18.9 highway with a 4.10 axle is astonishing.
Tell me the different things you did to you Holley to achieve that. I'd like to try some of them, myself.
I use an Action + intake; 14 in. X 3 in. air cleaner; #60 main jets. There are other things I've done with the exhuast and timing. The Holley and intake made the big difference in the drivablity - performace - fuel mileage. Turning 3500 rpm's and 70 mph had to do something. :W Guess I should also state I running the original L-48 350.
Hope that answered some of your questions.
Gary
Hope that answered some of your questions.
Gary
Hib Halverson
Technical Writer for Internet & Print Media
Actually, that kind of fuel mileage is an amazing feat. I've worked on Holley's for 20 years and if you can get that mileage with a 4.10 axle, I must have some "tricks" left to learn.
It's a Holley 4175, correct? What's the "R-" number on the choke horn?
What did you do to the sizes of the primary IFRs? Also, where are you as far as the ratio of main jet number to power valve channel restriction sizes?
Tell me more about the spark timing you're using?
Lastly...there's much I have to learn, I admit, so....tell me more about an "Action + intake".
That's correct it's the old model; # on the choke horn are, 80555 then under that is D579. The primary metering plate has 7445 stamped on it.
The intake is a Weiand Action Plus tht I picked up with a box of other SB parts at a sale. Only paid $75 for a whole box full of stuff; Dist. carbs and this intake. I got the carb off of E-bay for $59; but it took awhile to find a kit for it. Got that from a New - Old stock sale for $25. Put the kit in it; Bolted it on and it ran great. She ran a little rich, so jetted it down to the #60s.
As for the timing, I'm not sure of the actual degree; I set it by ear. (old school) Advanced til it kicked back but would run - then backed it off until it start good. She idle a little high, about 1000, but sure run good.
The last trip I got with her was over the North Cascade Hiway here in Washington State. It's a 2 lane Pass , only open in summer, going up to about 7000 ft. I got 18.4 on the trip. NOT BAD. I was a Happy Camper.
Before with the stock intake and Q-jet the best I could get was around 14 mpg. I do have to admit that if I get into a bit, burning the tires or pushing it through the gears the mileage does drop a bit.
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