Stovebolt.com Forums The Parking Lot '73-'87 Trucks -- "The Rounded Line" 1973 454 Edelbrock tuning

I’m thinking I should have gone with a 650CFM instead of 750 and possibly it’s simply too much carb for a stock rebuild with headers, sensible mufflers and a 90’s era automatic overdrive.

I’ve tried a dozen variations of jets and metering needles included in the 1407 tuning kit, first going lean and then going towards rich and it is still a dog off the line and gets the same 9mpg since we got it in 1981.



[img]https://www.instagram.com/p/CNk8dqjArvB/?utm_medium=copy_link[/img]



I’m not expecting anyone tune my carburetor by description over the internet but maybe someone has experience with a similar combination and might have some ideas.

I’m ready to order a 650 edelbrock or even rebuild the old Quadrajet but unfortunately dad modified it to idle on the cam he was running before I rebuilt the engine and went back to the stock lift.

Thanks in advance for any helpful comments!

One well-built Qjet is worth more than a truckload of Carter AFB "clones". Edelbrocks in general are sort of a "one size fits none" copy of a Carter, with a bunch of manufacturing shortcuts taken that make them virtually impossible to tune without a flow bench, a pile of replacement parts in various sizes, and a few decades of carburetor building experience. I've only been building carbs and teaching the subject since the late 1960's- - - -and I don't feel qualified to do it.

What's your rear axle ratio? It's possible you're working on the wrong end of the vehicle. A little lower gear ratio to let the engine wind up and get into a better torque range might solve the low end bog, and improve the gas mileage by letting the manifold vacuum stay in the "cruise" area more frequently.
Jerry

I believe it has the standard 3.73 differential.
But you make a good point. I put 32” BFG all terrains on it so that didn’t help either…

Install a temporary vacuum gauge and tuck it under a windshield wiper so you can watch it while you drive. I think you'll be surprised how often it stays down in the sub-10" of mercury "power" range with the metering rods in the full rich position. Lower gears allow the manifold vacuum to stay high enough to keep the metering rods pulled down in the leaner ranges.

With an OD trans, performance and fuel economy would probably be better with a final drive ratio somewhere in the low 4's.
Jerry

Windshield wipers? This beast has one vacuum powered wiper motor and the arm stays in the glove box so it won’t get lost!
Heheh!
I’ll just watch it from the access door in the firewall!


Low gear on the TH 400 was 2.48
Low gear on the TH 700r4 is 3.06 so I “think” that probably helps to correct for the oversized tires. These gear ratios make my head spin so my thinking may be 180 degrees off!

Your initial advice about resurrecting the old Quadrajet is probably the first thing I’ll try. I really miss the distinctive sound of those secondaries kicking in!
The mileage is really not an issue for me If the performance level goes back up.
I’ll revisit the differential ratio situation after that issue is straightened out. I’m basically using it as a farm truck since I rarely take it camping any more. I usually pull a ‘47 Tour-ette teardrop or a 1965 Mobile Scout 13’ canned ham, both of which are easy to pull although the canned ham has more wind resistance.

I really do appreciate you sending me in the right direction Jerry, thanks much!

Those huge secondary barrels do have a distinctive sound, but if the secondary air valve torsion spring is adjusted correctly you shouldn't be able to feel a difference in acceleration as the transfer from primary to secondary air flow happens. There should just be a smooth change in RPM, but with that big block it should plant your spine firmly into the seat back!

That 454 should be able to pass anything but a gas station! Yes, the 1st. gear ratio on the 700R4 is lower, but the tall tires probably still need a gear somewhere in the low 4's. The rock crawler guys love those 4.56's and 5.13's to go with their big wide, tall tires.
Jerry

My 1984 C20 crew cab had the factory 454 Th400 3.73 rear end. The Q-jet was rated at 800 CFM for that application. I got a consistent 10 MPG no matter what. I would put a good Q-Jet together, get rid of the headers and tune it as close as you can to stock.

It’s always been scary fast and a lead foot runs in both sides of my family, I always did my best to stay out of the secondaries but dad had it set up his own way, where you pretty much had to stomp on it to get them to kick in.

The only thing I hate to lose with that Edelbrock is the manual choke. I guess I’m a control freak and use the choke sparingly.
I was thinking eventually going with 4.11 gears since “the brakes are good and the tires are fair”… but how much would 4.56 gearing take off the top end?

I’m big on factory original too with the exception of this Frankenstein dad built. We used to have many heated debates about stock vs original. My argument being that you can wring more HP out of it but at the cost of longevity, expense and simplicity.

That said, I’m curious as to what the disadvantages of headers are? I always believed the common assumption that improvements to exhaust flow was a good thing for both economy and performance. I hope I don’t sound argumentative or unappreciative, I’m just curious about the advantage of going back to cast iron?

You can run the Q-jet with a manual choke, they used to make a kit to do just that. Mr. Gasket or some other aftermarket venders had them. Hotrod Lincoln will gently give you his thoughts on headers. Depending on how the internals of your engine have been massaged you may be killing horsepower and economy with the headers.

At one time I had over 30 years' worth of dyno run documentation, some of it recorded by my father, and some I did myself, from the high school auto mechanics shop where we both taught from 1971 to 2010, with a 7-year gap between us. That shop was equipped with a chassis dyno, a water brake bell housing dyno, and all the equipment needed to build high performance engines except a crankshaft grinder. During my tenure, an over-zealous assistant principal discarded a filing cabinet full of "obsolete" paperwork that included dyno run documentation on at least 100 engines! He didn't get a Christmas gift from me again!

Those runs proved one thing beyond the shadow of a doubt- - - - -headers, compared to stock cast iron exhaust manifolds are good for three things- - - -increasing the under hood temperature, blowing out gaskets, and burning up spark plug wires. They also rust out in a hurry unless they're stainless steel. The only measurable power gain is achieved at RPM's far above anything the average street engine ever sees, and to get a power gain that's worth the effort, each header tube must be exactly the same length from the exhaust port to the collector. The best way to achieve that is to use a collector about 6" in diameter, and let the pipes from the last three cylinders extend into it. I ran a 460 cubic inch "440" MOPAR pull truck engine with that setup, and sized the diameter and length of all the header tubes to hold exactly one cylinder's volume of exhaust gas. The tubes were about 6 feet long each. We won several pulls in the Super Stock class with that engine- - - -running one carburetor and gasoline, and producing just over 700 HP at 6500 RPM.

BTW- - - - -that "one carburetor" which was required by the pulling class we were running was not a big Holley, Edelbrock, or Carter- - - -it was a Qjet for a 455 Buick with a little bit of jetting change to accommodate the "Street Tunnel Ram" intake, radical roller cam, and ported heads were running.
Jerry

That’s a lot of references material lost to the landfill.
Thanks for teaching what you learned from it. That information is not entirely lost in a way but that’s still a tragedy.

I’ll pull down the cast iron manifolds out of the barn and give them the business!
Then they will be ready to go back on when these pipes eventually cause trouble.
Meanwhile I’ll rebuild the Quadrajet and get it a manual choke linkage.
I appreciate you guys helping with a game plan!

Does the engine still have the spread bore Q-Jet manifold or had it been changed out to a square bore? If you use the Q-Jet you'll want an intake to match.

I went all in with the hype and put an Edelbrock manifold on it. I still have the factory intake somewhere.

"I love it when a plan comes together!" Good luck! If you want to dress up the engine with a little eye candy, an aftermarket manifold for a Holley "Spread Bore" carburetor has the same footprint as a Qjet. I'm not even sure if those manifolds are still available, except maybe at a swap meet somwewhere.
Jerry

As it turns out that Aluminum doesn’t age well If you don’t keep it polished. I will just repaint the factory manifold eventually when I make the swap later on.
I think changing the gear ratio (as you suggested first) would be the best performance modification for a stock setup anyway.
Thank you kindly for the help!

Check which Edelbrock intake you have. If it's a single plane, it's a high RPM manifold & will be a dog at low RPM's. Your dad may have gone that route to match the cam he installed back then. For a low end torque application you want a dual plane intake.

Google it for more info. Also, have you dug into the ignition timing any? That might be something to look at, depending on what your dad might've done . Does your distributor have a vacuum advance? Is it hooked hooked up & working off of a manifold vacuum port?

I put a Gen V 454 with a modern Edelbrock dual plane in my C10. I checked with Edelbrock tech dept about which carb I should use on my mildly built 454 & they recommended the carb you have. Just saying that a 750 is not too big for that engine.

The Holley intake Hotrod Linc mentioned had a great reputation back in the day but is no longer made.

Do you realize you're responding to a zombie thread that hasn't been active in the past 18 months? I doubt if the OP will see your comment, since he hasn't been around since then.
Jerry

No, I didn't. Usually I look at the posting date. Thanks for pointing out.