Olds With 4 Quadrajet Carbs: Madness or Hot Rodding At Its Finest?


Just about every passion essential to the spirit of hot rodding is embodied in the Quadrajet Madness project – a two-year tech odyssey that resulted in a wicked-looking 16-barrel, 3,000 cfm induction system for a 425ci Olds Rocket engine powering a ’66 Cutlass street/strip car.

The QuadQuad project makes its debut at the Olds Nationals.

Neill Gathings and Tom Cox, both engineers and inventive DIY’ers who found a second calling at the dragstrip, are the mad men behind the Madness project and fabricated the tall, individual-runner intake manifold that supports four Quadrajets on top.

“This was an all-out, gonna-do-it-no-matter-what effort,” says Gathings, “and it changed us forever. The journey and knowledge gained by the trials were worth more than the final destination, for sure.”

Even though this carb-manifold arrangement hasn’t been seen much since its debut at the 2006 Olds Nationals, and no one else has tried a similar concept, it’s a little premature to assume it didn’t work at all. As seen in the accompanying videos, the engine idled rather aggressively and responded to whips at the throttle in neutral. But it just wouldn’t drive and accelerate under load. The team narrowed down possible solutions, however, time and money became a factor and the project has been dormant.

Tom Cox, left, and Neill Gathings conceived the QuadQuad idea and handled all the fabrication.

Gathings’ introduction to the Quadrajet carburetor came many years ago when the high-dollar 390ci FE build in his ’73 F-100 rejected six different carbs. Cox suggested a Qjet.

“Tom had much more experience with cars,” remembers Gathings, noting that Cox had a head and intake porting business at the time. “So, you’d think I would have listened, right? Wrong. Another year passed before I took a trip to the wrecking yard to find what was the best carburetor I’ve ever had, a Quadrajet off a ‘72 Delta 88 455. That little 750 cfm carburetor got my mind flowing on what carburetors were all about.”

Starting over with Qjets

Gathings and Cox raced a ’66 Olds that ran in the low 12s and wanted more “crispness” on the street, so the 830 cfm Holley double-pumper was swapped out for a Qjet. Working from popular how-to books and growing experience with the carb, the car soon inspired a wild vision.

The team used Photoshop in the early stages of planning to envision what four carbs would look like on a cross-ram and tunnel-ram.

The team settled on a sectional design for versatility.

“We decided that it was time to jump off into the deep end and build something big, as if the Rochester division created an exhibition car using Qjets,” says Gathings, adding that he and Cox always believed the Quadrajet was unfairly saddled with a poor reputation due to poor tuning by the owners and lack of a strong racing promotion from GM. “We had a vision of what it would have been like to make a car that could bring attention to the carburetor like never before.”

That vision was a ’66 Cutlass named “Quadrajet Madness” that would be similar in concept to the famous Hurst car. Instead of a massive supercharged engine, this Olds would be built with a massive tunnel-ram “Quad-Quad” manifold showcasing a quartet of Qjet carbs on top.

“Thus, the system would complete a mechanical sculpture that both Archimedes and Bernoulli would have been impressed with,” beams Cox.

The team started by evaluating what was available, notably an early cross-ram intake, but then settled on a tunnel-ram.

“We mocked up the tunnel ram with four Qjets we had laying around to check height and overall fit,” says Gathings. “It was really starting to come together.”

CAD drawings also helped finalize the concept.

“The theory behind the QuadQuad is pretty simple actually. It began with the idea that dual-plane intake manifolds split a four-barrel carb in half, so each cylinder sees half of the carburetor at any one time,” explains Cox. “This being said, we began looking at what happens if we try to make the intake an independent runner and how it would affect the cfm per cylinder. While looking at the alignment we noticed that the runner spacing and thus the carburetor division would be identical to any dual plane intake. We determined it was clear that the pulse or signal would be incredibly strong with zero interference between cylinders. The engine would have all the flow needed to support 600-plus horsepower without being over carbureted.”

Quartet of restored beauties

Sparky's Qjet Restoration

Sparky’s Carburetor Service in Wisconsin handled the restoration, modifications and fuel-curve setup on the four Quadrajet carbs. Operated by Greg Kalkoff, Sparky’s specializes in Qjet carbs from the musclecar era and emphatically asserts that no Holleys or Edelbrocks will be accepted.

“Our success was dependent on getting the carbs matched exactly,” says Gathings. “We were moving into new territory for all involved. The technical details were discussed as to how the engine will have enough signal to keep the circuit active and what did that mean to the pulse generation on each carb.”

Sparky’s developed a rebuild strategy was that baselined the carbs similar to an Olds W30 model and completed the restoration process before returning the units.

For more information on Qjet restoration and modifications, visit sparkyscarbs.com.

The team found six Qjet castings that featured straight fuel inlets off salvaged Olds engines, and the four best units were sent sent off for restoration and calibration. Problem was, very little info was available on multi-Qjet arrangements. Will the engines provide enough signal to keep the circuits active? What parts of the carb will be affected by low and instantaneous vacuum created by the pulse? The team investigated other performance Quadrajets from the musclecar era.

“Those carbs omitted the power piston and rod on the primary side due to vacuum signal loss and the inability to control the circuit properly,” says Cox. “The factory used jets only for the primary side of the carbs and plugged the power piston completely, thus negating the issue of vacuum signal abnormality.

The carbs were returned fully detailed and in concours condition with the re-curved fuel settings, so attention was then directed at designing the intake. The team considered the pros and cons of different intake manifold designs, including single- and dual-plane.

“There are two parts of this Quad-Quad induction system that make it unique for an American engine,” says Cox. “First, the intake manifold is an independent runner (IR) design with no common plenum. Second, we’re utilizing a carburetor that incorporates a high-cfm variable venturi.”

Challenges of individual-runner intake

Their strategy focused on the concept that the carbs on an IR intake could be tuned without regard to pulses from other cylinders.

“Our investigations looked at early examples of IR systems using Weber carburetors on V8 engines, which are known for good throttle response and torque, especially when off the cam, but are usually limited in air flow ability,” says Cox. “This is where the Quadrajet would perform above the rest.”

Mockups with four carbs on top of a plate positioned on a tunnel ram were also studied.

The also considered the disadvantages of such an arrangement.

People’s disbelief at the show was humorous, to say the least.–Neill Gathings

“There are significant drawbacks to a Quad-Quad style induction system. The first is cost. There are more carburetors to build and maintain, especially when you consider eight of everything — eight matching jets/secondary rods and four hangers, and so on,” says Cox. “The second is complexity, more parts to tune and elements to go wrong. The third is the added complexity of valve timing.”

Long-duration cams can generate reversion, but manifolds with common plenums have a tendency to cancel out most of the ill effects. On an IR intake, that reversion can travel all the way to the carb and actually have a “stand-off” with the incoming charge. The reversion can even go through the carb, as seen in one of the accompanying videos.

The advantages of an individual-runner intake still convinced Gathings and Cox to pursue a design for the 425ci engine, starting with the original crankshaft in Gathings’ first Olds, a ’66 Delta 88. It was teamed with .030-over flat-top Ross pistons and factory 7-inch rods upgraded with ARP hardware. Other short-block treats include Clevite bearings and a Cyco Pro/Race damper.

An Offy tunnel-ram intake was machined down to provide a level access to the individual runners, then the machined billet blocks were mocked up on top of the intake.

There were challenges in setting up the camshaft. The team wanted to use .921 roller lifters from a diesel engine to utilize as many Olds parts as possible. An early mockup revealed the lifters were too long for the block’s lifter bores, which led to oiling issues. Lunati came through with a custom roller profile billet cam ground on a smaller base circle to reposition the lifters, which were modified by Jack Rhoads to bleed off some duration on the low end to improve drivability. Even with that effort, the block had to be modified with 1-inch bushings, relocated oil-feed holes and high-pressure/high-volume oil pump to make it all work.

The base section is welded in place and the top surface is machined for a level and straight support for the remaining sections.

Lunati helps with custom-grind camshaft

“We tapped into the main galley passage as the main source for the lifters and plugged the crossover lifter valley to keep the engine from bleeding to death through the factory lifter oiling holes. Even this part was challenging to get all the copper tubes run, and make sure it all worked,” explains Gathings. “After all that you might ask ‘Why this cam and lifter setup versus something else?’ Well, we wanted to stick to something we knew, which was the factory W30 cam of the day and use stock part combinations, not a $1000 set of lifters.

The cam spec’d out at 244/244 at .050 with a .350-inch lobe lift and 114-degree lobe separation.

A custom Lunati camshaft, new lifter bushings and extensive oil-feed routing was needed to adapt the Olds diesel roller lifters to the block.

“No one could advise us on an IR profile,” sighs Gathings, “and I mean no one knew what to choose.”

Cox prepped the Edelbrock heads with a valve job, bowl blend and port matching the gaskets. He added Harland Sharp 1.7:1 rockers teamed with Smith Bros. pushrods to optimize valve-lift area.

The strategy for fabricating the intake focused on machining solid blocks of aluminum and welding the pieces to the base of a modified tunnel ram for flexibility, as opposed to a sheet-metal desgin. CAD representations were studied and height possibilities were debated.

View of the intake during fabrication and after sand blasting.

“We settled on two removable spacers in the mid section under the main top piece,” says Cox. “The purpose of these was to have the ability to tune the runner length to achieve the best characteristics if we deemed it necessary.”

When the machined parts were assembled, the team realized a considerable amount of metal needed to be “hogged out” to form the individual runners. Cox handled all of the port work by hand, including the external shaping. The manifold was then sand blasted with heavy grit to provide a vintage cast appearance.

RC tricks contribute to linkage design

With the carburetors in place and using hex shafts, couplers and heim joints produced for an Enderle fuel injection manifold, the team designed the throttle linkage. They also had the help of a friend well versed in setting up intricate linkages for RC aircraft.

“After several different configurations of angles and lever positions, we settled on what gave the right mechanical advantage for four carburetors moving in unison without over travel,” says Gathings.

The intricate linkage was designed with Enderle fuel-injection components and a few pieces from RC aircraft.

Next came routing the fuel lines and establishing a vacuum source for the gauge as well as keeping the TH400 tranny happy. They tee’d off from the constant velocity port in each carb.

Carbs installed, fuel line and linkage hooked up and ready for the show.

“Functionally, it did work,” adds Cox. “However it was very difficult to get a smooth vacuum needle due to the pulsing action.”

Fuel is fed via a 110 gph electric pump. There’s an -8 AN tank line to dual -6 AN outlets supplying each side of the carbs.

“The theory was that each carburetor will only get pulsed every 720 degrees of crankshaft rotation, so fuel demand on all four should not be any different than a single,” says Gathings, noting that they sandblasted the blue off the AN fittings. “We wanted to keep the old school look going all the way to the fittings.”

The design and fabrication had taken nearly two years, but the team had just two days to wrap up all the details before the car was to debut at the Olds Nationals in Dallas.

“We fired up the motor for the first time and it ran like crap,” says Cox. “Timing was so far off, but luckily there was enough room to move the distributor to get it to fire around 35 degrees.” (see video)

The engine was running in time to load the car for the show. Unfortunately, the team didn’t find time to modify the hood, so it was left off for the show.

Sounds good but drives rough

“People’s disbelief at the show was humorous, to say the least,” remembers Gathings, noting some people asked how many of the carbs were fake.

While the engine exhibited a very high idle, it revved easily. However, it had never been driven.

An opening in the hood was cut to showcase the QuadQuad manifold and carbs.

“This where things got very interesting and the education began,” says Gathings. “The car ran perfectly as long as the secondaries were not cracked open. As soon as the secondary air door saw enough pressure differential, all hell broke loose and the motor became unstable.”

The team tried a variety of tuning adjustments to no avail. Cam timing, especially too much intake duration, was deemed the primary culprit.

“The roller cam timing event began about two to three degrees before the piston was done traveling upwards, thus it backflowed up the intake runner and caused atomized fuel to fog the windshield,” theorizes Cox. “We also thought the fuel standoff may also be accentuated from the fast air moving across the top of the carbs, since we didn’t have breathers while driving.”

But driving with air cleaners produced paper elements saturated with fuel vapor. Gathings then fabricated custom velocity stacks to help control the air. The team also noticed the secondaries moved violently when pulsed.

Getting ready for a rebirth

“This means that the dynamic energy and the pulse strength hitting the carbs was so intense that the air doors basically slammed open and slammed shut with very little transition in between,” says Gathings. “The carbs were later modified to add a shaft between air doors across the driver and passenger pairs in an effort to help regulate the intense slamming and opening of each one.”

Individual airhorns wouldn't fit, so Gathings fabricated conjoined twins for the front and rear sets.

Another direct vacuum port was added to each venturi to help gauge exactly what was happening in the manifold, not the carb where the other vacuum source was made. Finally, the hood was fitted with an opening to give the car a cleaner appearance.

Unfortunately the team couldn’t improve on the car’s performance. The QuadQuad manifold was swapped out for a standard tunnel ram so Gathings and Cox could reevaluate the carb circuits.

Getting a true and consistent source of vacuum was always a frustration after installation.

“Thinking back on it now, it would have been better to run the single Qjet, then duals, then the Quad-Quad,” says Gathings. “But I’m sure we would not have ever completed the task if done that way, just because we were on a journey.”

After the QuadQuad project was shelved, the Olds ran with a dual-quad setup for awhile.

Based on the experience and advice from experts, Gathings made adjustments to the dual-carb setup that improved performance, including using his RC buddy’s ideas to modify the accelerator-pump linkage. He also changed the fuel pump and utilized a RobbMc bypass regulator to better maintain the pressure down the track.

“The latest status with the car is that it was raced until last year as a dual then single Qjet car,” sums up Gathings, adding that it will receive some needed TLC during the next restoration to prepare for the 2016 Olds Nationals. “The rebirth of the car will be all racecar, no street bruiser. And it’ll be a tribute to the Hurst Hairy Olds but with differences that will include Qjets – if fate and patience allows.”

The Olds Cutlass is awaiting its next rebirth. Should Gathings and Cox try the QuadQuad setup again? Leave your comments below.

About the author

Mike Magda

Mike Magda is a veteran automotive writer with credits in publications such as Racecar Engineering, Hot Rod, Engine Technology International, Motor Trend, Automobile, Automotive Testing Technology and Professional Motorsport World.
Read My Articles

Horsepower delivered to your inbox.

Build your own custom newsletter with the content you love from EngineLabs, directly to your inbox, absolutely FREE!

Free WordPress Themes

We will safeguard your e-mail and only send content you request.



We'll send you raw engine tech articles, news, features, and videos every week from EngineLabs.



We will safeguard your e-mail and only send content you request.



Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

Late Model LS Vehicles
Drag Racing
Muscle Car & Hot Rods


Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • LSX Mag Late Model LS Vehicles
  • Dragzine Drag Racing
  • Street Muscle Mag Muscle Car & Hot Rods



Thank you for your subscription.

Thank you for your subscription.


Thank you for your subscription.

Thank you for your subscription.