Because It's Awesome, I'm Putting Carbs On A Miata.
Carburettors vs. electronic fuel injection (EFI): automobile enthusiasts of a certain age will be familiar with the distinctions. While early EFI systems had flaws, the technology introduced a new level of control and dependability. Carburetors were phased out in the early 1990s as the great majority of automobiles were offered with EFI.
The Mazda Miata wasn't any different. It was released in 1989 and featured multiport fuel injection as well as a distributorless ignition system. The system was highly sophisticated for its day, especially for a budget sports vehicle, consisting of two coilpacks in a wasteful spark arrangement with computer-controlled timing.
Despite the Miata's technological prowess, modified vehicle enthusiasts choose to go their own way. Evan happened to be one of these people, and he chose to do just that, ditching the EFI system in favor of a classic carburetor configuration. It was during this time that I became interested in mechanical tinkering.
But why is that?
True, the Miata's factory EFI system is fully capable of performing its duties, and it can also handle certain minor engine changes with ease. Those aiming for higher power levels will often change the ECU, injectors, and fuel pump over time, but the system's overall design will be preserved.
The engine, which is equipped with twin Weber carburetors. Below is a comparison of the standard engine bay. The engine compartment of a standard Miata. The original manifold, intake, and air flow meter all take up a lot of room.
This is not to imply, however, that carburetors are without merit. Because of the Miata's engine architecture, a set of dual carburetors may be installed with the correct manifold and a very short intake runner length. This offers the dual benefit of enhancing throttle response while also eliminating intake limitation for more power. There are huge improvements to be gained here, given the limitations of the typical intake and air flow meter. Furthermore, such a configuration may significantly boost induction noise, which is a significant benefit.Those who prefer the melody of a naturally aspirated engine will appreciate this. Finally, even in the face of pricey Italian competition, having a distinctive build is a wonderful way to get some solid attention at Cars and Coffee, and this should not be overlooked.
Alternatively, simply look at the article's title!
However, this engine was not built to use a carburettor.
Fitting carburettors to a car that wasn't built to have them requires some effort. The computer-controlled ignition system on the Miata adds to the complexity. This implies that the alteration will necessitate adjustments to both the fuel and ignition systems.
Norman Garrett chronicled the labor necessary in the Mazda Miata Performance Handbook at a time when paper still ruled supreme (pages 79-82). The first step is to decommission a large amount of obsolete gear. The stock intake manifold, intake pipe, and air flow meter have all been removed because they are incompatible with the carburettor installation.
After that, the carburetors may be installed on the engine. This necessitates the use of a custom manifold created expressly for the task. Mazdaspeed makes a component for both the 1.6 and 1.8 litre Miata engines that allows for the installation of dual Weber carburetors, which we employed in our project.
An EFI car's fuel system often operates at 30 to 70 PSI, significantly more than the 7 PSI required by the normal carburettor. To address this, a fuel pressure regulator developed exclusively for carburettor use must be installed. With the old intake hardware gone, there's plenty of room in the engine bay for this to be fitted near the carbs.
An op-amp inverter circuit in its most basic form. Only one of the LM324's op-amps is utilised. Mazda Miata Performance Manual (c) Mazda Miata Performance Manual (c) Mazda Miata Performance Manual
Then there's the issue of ignition. Timing advance is regulated by a computer and is based on information from the cam angle sensor and the air flow meter, which allow the ECU to determine the engine load. The ECU can no longer determine how much timing to run since the air flow meter has been removed. This may be left alone, but the engine will lose performance without a suitable timing curve.
Normally, a distributor would be in charge of this. Switching to a traditional distributor-based configuration is not practicable due to the nature of the Mazda B6 and BP engines. Instead,There are two popular ways for spoofing the air flow meter signal to the ECU so that it can manage the timing accurately. A throttle position sensor can be mounted on the carburetor's throttle linkage, with the throttle position acting as a load signal for air flow.
Alternatively, a manifold air pressure sensor that detects the vacuum in the inlet port can be fitted. This signal can then be reversed, imitating the original air flow meter accurately enough to serve as a reliable engine load reference. You may choose the mechanical intricacy of the throttle position sensor method or the electrical complexity of the MAP sensor approach, depending on your preferences. The author preferred the former, while the owner preferred the latter,As a result, we started working on an automobile inverter circuit.
There are a slew of other jobs to complete in order to get everything up and running, as with any large engine upgrade. The throttle cable had to be modified on this design, and the brake booster was no longer as efficient due to the loss of suction from the carburettor manifold. Expect snags along the road, as with any large endeavor.
Electronic Mistakes: Connector on the Wrong Side
The schematic in question, which shows the connections to the car's air flow meter. The author had considerable difficulties reading this backwards. Mazda Miata Performance Manual (c) Mazda Miata Performance Manual (c) Mazda Miata Performance Manual
I worked mostly on the electronic side of the project, designing an op-amp circuit to invert the MAP sensor signal, based on Norman Garrett's idea. The task is done by an LM324 op-amp, according to the schematic. Only one of the four available op-amps is used, and it is configured in an inverting configuration with a gain of one; that is, basic inversion without amplification. This is designed to work with a standard GM 3-bar map sensor, which is widely available new or used and has been installed in millions of vehicles globally.
We struggled to get things working reliably after whipping up the circuit on perfboard. We gave up trying to power the circuit from the air flow meter connector's 5 volt wire and instead utilized a 7805 regulator with the Miata's 12 V auxiliary supply in the engine compartment. Despite this, we continued to have problems. Rather than neatly inverting the MAP signal, the circuit merely produced either 0V or 5V all of the time.
With no understanding what was causing the problem, the circuit was reconstructed with scrap components and an LF356 op-amp. This worked in limited bench testing, but when linked to the car, it started acting up again. As is customary, we were frustrated for several hours until we realized we'd read the schematics backwards. The AFM connection is taken from the side of the air flow meter itself, not the wire loom in the car, as described in the Mazda Miata Performance Handbook. We were able to get the circuit operating and the signals inverting well after correcting this error. It was impossible to evaluate how big of an influence the circuit had without a dyno or other high-end diagnostics accessible on the Miata ECU,However, we went ahead and took the automobile for a test drive.
The Engine Soars Because of Your Footwork
In summary, driving a modified Miata is a lot of fun, even if it isn't as fun as the standard one. Of course, there's a little more power available. The snap of the throttle, on the other hand, is addictive, with the engine blasting forward with the tiniest twitch of the foot. Induction noise is also there, and the raspy bark is to die for when paired with a decent exhaust system.
Obviously, there are some significant disadvantages to the setup. It's doubtful that emissions regulations would pass in places where they matter, and cold start performance would suffer in locations where frost and snow are common. A short flat area in the powerband about 4000 rpm was also an issue. We were unable to identify a clear cause due to a lack of time to do appropriate A/B testing. The carburettor intake arrangement may be trading mid-range torque for top-end power, or the op-amp substitution may be producing problems because the LF356 is not a rail-to-rail part like the LM324.
Regardless of the compromises, the end result was a joy to drive, with the undercarriage aesthetics and audio to match.It might not be the ideal choice for everyday driving, but for weekenders looking to impress at local car events with some old school flair, it's a great way to go.
The Next Theme Has Been Announced: Engine Hacks
Over the last few weeks, we've had some fascinating High Voltage postings. The next topic will be announced today: Engine Hacks. For the next two weeks, we'll publish a new post every day about an interesting engine project. We'll present projects in which engines are created from the ground up, engines are adapted to function in new ways, or engines are used in ways they weren't designed for. Please contact us via our tip line if you or someone you know has an intriguing project that you believe would suit nicely in this area.
An EVIC (Electronic Valve Internal Combustion) engine is seen above. The valves are not actuated by a cam shaft in this sort of engine. Instead, solenoids are employed, which are combined with a tiny CPU and sensors to calculate when and how long the valves should be opened. This sort of engine allows you to perform things like change the quantity of gasoline that enters the cylinder on a regular basis. You could even make the engine run in reverse if you combined this with electrical ignition!
VN SS, ready for the Drag Challenge, with a nine-second time.
In the present day of turbo LS mills, a CARBY-FED, 383-cube Holden V8 seems like something from another age, but Street Machine Drag Challenge competitor Michael Ryder couldn't picture his VN SS any other way. Who can blame him, considering the car's 650 horsepower, nine-second timeslips, 9000rpm gear changes, and impeccable street manners?
The original version of this article appeared in the November 2021 issue of Street Machine.
Michael had previously worked as a panel beater for HSV in Perth, so applying a fresh coat of Alpine White to the VN was second nature to him. "It was all original paint," he adds, "but then I struck a wall at Heathcote a few years ago, and we had to rebuild the entire front of the vehicle, and then I gave it a new lick of paint."
While working as a tradie doing bathroom renovations during the day, Michael spends his leisure time at home building really difficult street and drag vehicles under the MR Racing Fabrication moniker. "That means I've built a ton of turbo LS cars, RBs, and everything else you can think of," he explains. "So I could've done it with this automobile just as easy,But I adore my old Holdens, which is why I like the VN in its current form."
Michael has owned the car for around ten years and competed in Drag Challenge with a different combination in 2018. "That was the old 383, and what I didn't realize at the time was that it had been running on a broken piston for the previous week!" That's why we only did 10s that week, but we had a great time anyhow."
At the 2021 Tuff Mounts Holden Nationals, the 383 finally let go on Michael in dramatic manner, providing the ideal reason to swap in the new 383 that the vehicle presently runs. "The small block was completely constructed and ready to go, and when the old engine let go, it practically demolished everything," Michael explains.
The VN is equipped with 28x10.5 radials on the rear and 26x5 R17s on the front in racing trim; Michael uses a separate set of wheels and tyres on the street. Wilwood stoppers with four wheels are also used to keep items safe.
Michael and his friend Chris from Chris's Porting Service collaborated on the new donk. Thanks to a Scat steel crank, Callies Compstar H-beam rods, and Diamond flat-top pistons, the VT-generation Holden block has been stroked up to 383 cubes. A Comp mechanical roller stick specced at 268/272@50 and.686in lift, as well as a Savy Motorsport stage-five dry sump, round out the bottom end. Michael explains, "We required the dry sump since we'll be spinning this thing to 9000rpm at the track."
Michael drives on the street with a 38L fuel cell and adds a 20L cell for methanol at the track.
A set of hand-ported –9 Yella Terra heads seal the bottom end, together with a custom Torque Power intake manifold and either a 1050cfm alcohol Dominator for racing or a second 1050cfm Dominator that sips 98 for street use. "I used E85 at Drag Challenge in 2018, but for street miles today, I switch to 98 since it's simpler to get and makes the car more streetable," Michael explains. "As for going carby, we tried injection on the old combination for a bit and discovered that we ran faster with the carby set-up," he says.
The new engine is based on a Holden VT-generation 5.0L block that has been stroked up to 383 cubes and produces roughly 650 horsepower at 9000rpm.
Michael expects that the new engine will produce roughly 650 horsepower, but he doesn't know for sure because he conducts all of his tweaking at the track. "I take all of my other customer engines to an engine dyno, but because this one has a dry sump, it's a lot of work, so I simply do it in the car for convenience."
A transbraked Turbo 350 'box with a Dominator 6200rpm converter backs up the enraged iron lion, sending power to a nine-inch rear end with 4.56:1 ratios. That could make it seem like there'd be a wild animal on the street, but Michael assures us that it's not the case. "On the street, it's a breeze to drive, and on the track, it's a dream." Over the years, I've spent a lot of effort really getting stuff out and testing it. It never gets hot, the exhaust is really quite quiet for what it is, and even with the converter, it'll idle off the lights and cruise about without a hitch."
Michael was set to compete in Drag Challenge 2021 for the second time with his own vehicle. Unfortunately, COVID has struck once more, ruling DC out for 2021, but Michael has a plan in place for when the time comes. "This combination will be fantastic for low nines," he adds, "but for Drag Challenge, we'll scale it back a bit and aim for mid-nines all week."
Let's hope that in 2022, we'll be able to see him achieve precisely that.
Michael (center) is surrounded by his friend Nathan (left) and brother Jake during Drag Challenge 2018. (right)
Pacemaker Radial Aspirated is a kind of pacemaker.
SPECIFICATIONSEngine: 383ci Holden Torque Power Pro is the inlet. Paw Yella Terra –9 Yella Terra –9 Yella Terra –9 Yella Terra – Comp Cams roller camshaft Diamond flat-top pistons Callies are the rods. H-beam Compstar Scat steel crank MSD grid, ICE dizzy, and leads are used for ignition. MagnaFuel ProStar fuel system Alloy radiator, FG Falcon fan for cooling Turbo 350 transmission 6200rpm Dominator Converter Extreme 9in diff, 4.56:1 gears
The best DC 2018 pass was 10.69 at 125 mph.
Link - https://bit.ly/3DfH7Bj(Copy and Paste URL to the Browser)