THE QUADRAJET MPG SECRET
“HOW TO FIND AND BUILD THE PERFECT QUADRAJET FOR ANY ENGINE—WITH MINIMUM TUNING AND MAX ECONOMY.”
Would you pay $10 for a carburetor that produced excellent fuel economy and great performance? I did.
I know the Rochester Quadrajet has earned a bad reputation among Gear Heads. But what if I told you there’s a secret to avoiding problems?
With that secret I developed a system to target, rebuild and tune for maximum mpg a Quadrajet for any engine. The secret is simple: Although QJ’s look the same, internally they are vastly different. Rochester changed fuel and air restrictions, tuning each serial number to a specific engine.
The bad reputation came from mechanics trying to install high flow models on small engines, or the other way around. With ample time and money Quadrajet gurus can make any QJ run well. But do you want to spend days installing and removing a carburetor to drill passages? My system eliminates 95% of the hassle. Heck yes, give me the easy way.
That is where I stop the book. Of course I go on to explain why the Quadrajet is the best carburetor for mileage, how to target the correct one for your engine, and how to rebuild the one you do use. I also explain the tricks to modifying and getting the max performance as well.
Take a look at the book on Amazon Kindle if you're interested. I'll post a link to the book as soon as it goes live. In the meantime, here is a link to a youtube video I did about the Quadrajet and my book: https://www.youtube.com/watch?v=hRhAP4b4K7c
I plan to post snipets of books about efans, Beefing up the Ford 300, Inline six, The Autolite 4100.
I plan to post snipets of books about efans, Beefing up the Ford 300, Inline six, The Autolite 4100.
THE MIGHTY SIX
How to get 50% better mileage and keep the horse power
I have a 1975 F-250 named DD. Each summer as my son grew up we would drive her deep into Mexico, over deserts and mountains. And each September when he returned to his mother overseas, I started working on DD, making her safe for our grand travels, the boys on the loose.
When he stopped coming I noticed DD’s tired 390 was burning two quarts of oil a week and eating me alive at the pump, getting seven mpg around town and 10 on the highway. I needed to immerse myself in a project and make a change.
Then I found the Clifford Performance site, and my memories turned to dust when I saw the monster Ford 300 they build to order. It’s definitely not the inline six my Grandma had.
That image sparked an idea that set the course of my life for the next year: By using a high performance inline six, would it be possible to obtain the hp of my 390, yet achieve 50% better mileage? I had to find out!
My son was 20 and no longer spent his summers with me. Now I had so much more free time to build the engine I always wanted, with polished aluminum valve cover, hp carb, and header. I wanted to feel good when I opened the hood. I needed the project to take my mind off my son.
My 390 with a 2v carburetor came from the factory with 265 hp. However, the 300 inline came rated at a whopping 140 hp, and I wanted to achieve close to 250. Being a backyard mechanic meant I needed to educate myself about building the Ford 300. I started prowling the net for information. Forums like Ford Truck Enthusiast, and Fordsix performance became my classrooms where experienced guys educated me about the build without making me feel ignorant … most of the time. During four months of research I kept a file so I could copy/paste useful items, parts numbers, machinist terms, how many thousandths to shave off the head, and bits of advice from guys around the country, people helping a stranger, America at its best.
I learned that building an inline is completely different than a v8. Building a high performance 300 is the Wild West of engine building. There aren’t any books available for building an inline 300. Every builder is trying different parts, pistons out of a 390, the head off a 240 for higher compression, EFI plugs in models from the sixties, seventies, and eighties, EFI exhaust manifolds on all models, and even Chevy rocker arms for more valve lift. The guys on the forums are writing engine building books one thread at a time. And because there are so many variables and a lack of literature about it, each engine is unique, making it a part of the builder, the sum of his choices.
|The Clifford 300. It should be on a center fold.|
As boxes of parts arrived, I felt intimidated and ended up hiring a professional mechanic who would work out of my garage. He was a childhood buddy down on his luck. I should have known something was wrong when he showed up the first day with a twelve pack of beer. And he knew I didn’t drink.
At first I thought he was psychologically unbalanced because of his obsession with cleanliness. But I just rolled with it and learned. He set up the garage like a hospital operating room, wire wheeled EVERY bolt, empty beer cans clicking on the concrete floor as he worked, used bottle brushes on the newly machined block, and washed it with soapy water, then blew it dry and covered every working surface with oil. I learned to custom fit each set of piston rings in their own cylinder, to measure main and rod journals, apply molly lube to each end of the head bolts. Piece by piece it went together.
Five months later, after shipping delays, problems with cash flow, waiting for the rebuilt transmission, the engine stood ready for installation. More than 1,200 guys saw the photos I posted online. Enthusiasts all across America, connected by the forums, gave me their phone numbers in case I needed help. People wanted to be there to hear my masterpiece fire up.
The engine started on the second crank. It sounded great and strong, and took two days of tinkering and adjusting to get it dialed in. And then diaster struck. I noticed the oil pressure dropping. I spent $70 for a new gauge, but the psi continued to decline. I became frantic, searching for an answer, posting notices on my forums. Guys all across America tried to help. I started losing sleep, going over every detail of the engine in my mind. I changed filters and oil several times. It was more than just an engine failing. It had been part of my life for almost a year. If it wasn’t there I’d start thinking about my son.
When the psi got below six at a hot idle, I took action. With the help of the mechanic I dropped the pan and pulled a couple of the main bearings, and a rod cap. The once shiny bearings looked like a cat had clawed them. Some contaminate had gotten in the oil. Without hesitation, I changed the rod and main bearings, and swapped the stock oil pump for a high volume. That helped for a while. But after a short time the psi started dropping again.
I made a rash decision and started building a new engine. I spent a lot of money building the same engine AGAIN.
What happened to the first engine and the bearings remains a mystery. I’d like to blame it on drinking mechanic, but I had been watching over his shoulder, checked the tolerances with him. I thought it might have been polishing compound under the valve cover oil baffle. I had it professionally polished, and that was the only part put on the engine what was not cleaned inside. But because the first filter was tossed without cutting it open, I’ll never know what got in the oil. The original filter would have trapped any foreign particles. I learned that with engine building never assume something is clean. If you don’t KNOW it is clean inside and out, clean it! It is much cheaper that way.
We were anxious to break down the first engine to find out what had happened, and were surprised and disappointed when everything looked good, and was within tolerances. We checked the mains and the rods, the lifter bores, and searched the block inside and out. Nothing. I can only blame the dropping oil pressure on an internal crack in the block.
Regardless of the added cost and labor, it turned out good, and was a lot of fun learning so much about this low end torque machine, and also making contact with so many fellow backyard mechanics.
Like every other engine, better performance required improvements with intake/exhaust flow, raising the compression, better ignition, and adequate, well-turned carburetion.
The first thing I needed to do was stay on regular gas, and that meant keeping the compression ratio just above 9.0 to 1. Part of me really wanted the power more compression brings, but I didn’t want to pay for it every time I filled up. So instead of having the machine shop shave the block and head the amount Clifford recommends, I only took .020 off the block and the same off the head.
The one place I did follow Clifford’s blueprint was the head. Everywhere I looked on the internet I found articles on how restrictive the original head is. Go on any of the forum and you’ll find posts about how to make the head breathe better. But be advised, this is only for pre-EFI heads. So I paid a professional to port the runners, clean the bowls, and install larger, small block Chevy valves.
I know the Ford purists are shouting right about now. And while researching this project I learned more than I wanted to about engines and this country too. Most people know America was divided during the civil war. But what most of main stream America does not realize is that there is another division: Between Ford and Chevy lovers!
The reason I went with the Chevy 1.94” intake valves (SUM-V8000-8), and 1.6” Chevy exhaust valves (SUM-V8010-8) is because finding Ford length valves that size is nearly impossible. These are slightly longer than the ford valves. I had to use a longer push rod to compensate and get the proper valve/rocker/ p. rod geometry. The larger valves gave me another jump in horse power. I should mention that I also had a 30* back cut done on the intake valves.
Improving performance, adding horse power, means allowing the engine to flow better. To do that I added the four barrel carburetor intake, ported the head, added larger valves, and installed a header to help the flow coming in exit just as quickly. It is a river of air.
Now, to help the valves ‘gulp’ more air I added an Iskendarian cam shaft (#331256). Along with came Isky valve springs (#6005B). Those springs turned out to be a mistake. They rendered 134 psi. That was way too much for a 300, so I removed the inside spring and ended up with 117 psi. Also, remember to get spring keeper and retainer for a Chevy valve.
While the head was at the shop getting larger valve seats installed, I had them remove the factory push in rocker studs and replace them with ARP screw in studs to handle the added stress on the valve train, (#ARP-134-7101).
Greg Koesel, a retired Ford engineer and 300 racer, who has built several of the big block inlines above 300 h.p., says that “between two and three hundred horse power is where the cost begins to add up.” One of the items he is referring to is forged pistons. But forged pistons for a 300 are expensive. Guys are keeping that cost down by boring the engine .050” over, and using 390 v8 pistons. But since I wanted to stay around 250 h.p. I didn’t need to throw big bucks at it, and went with hypereutectic .030 over pistons from Federal Mogul, #H519P30. I wanted performance, dependability, AND economy.
Because of fuel economy concerns I chose the Offenhauser DP intake manifold (Summit Racing part #OFY-6019DP) over the ‘C’ type. Below that I bolted on a Hedman header (#HED-89300). The header caused me the most concern. It required grinding quite a bit off the alternator bracket and reshaping the heat sheild. Not only that, but installing this header meant the starter would be sealed in place. It is possible to use an EFI year smaller starter to avoid sealing in the starter.
My main issue with the header is mpg. That is correct. It raises the temperature in the engine compartment a lot. So the air entering the carburetor is now heated, and that produces less mpg and less power. I am now changing to EFI manifolds, and running dual pipes out the back, each 2.25”.
Whether using headers or EFI manifolds, install with Mr. Gasket #260 gasket, (MRG-260). Your install will also be easier if you use 2” grade 8 studs and crimp nuts, not the type with the nylon insert. Because the header flange is slightly thinner than the intake, I had to grind 1/16” from each of the thick factory washers that hold the intake and exhaust to the head.
I ended up with more than a 50% improvement in mileage. Also, every time I get on the freeway I play like I’m back in high school and stomp on the pedal so I can feel the rush of power when the toilet flusher size secondary butterflies open and the engine starts the old Quadrajet moan.As soon as I stopped working on the engine I started missing the summers spent with my son, roaming and fishing Baja, so I just kept doing mods on the truck, but each of those is another article.