If you want to coax more power out of your car’s engine, a turbocharger is a great way to go about it. Taking waste energy from the exhaust and using it to cram more air into the engine, they’re one of the best value ways to make big gains in horsepower.
However, unlike simpler mods like a bigger exhaust or a mild cam swap, a turbocharger install on a naturally aspirated, fuel-injected engine often requires a complete replacement of the engine management system, particularly on older cars. This isn’t cheap, leaving many to stick to turbocharging cars with factory tuneable ECUs, or to give up altogether. In the 1990s, aftermarket ECUs were even more expensive, leading many to avoid them altogether. Instead, enthusiasts used creative hacks to make their turbo builds a reality on the cheap, and there’s little stopping you from doing the very same today.
Fuel and Timing
The reason a turbocharger install typically necessitates an engine management overhaul is due to the need to vastly change the engine’s fuel and timing map. A stock, naturally aspirated (NA) engine with fuel injection can measure the incoming airflow and load on the engine, and uses this information to determine the correct amount of fuel to inject and when to fire the sparkplugs.
However, with a turbocharger installed, the pressure in the intake, which is usually below atmospheric pressure for an NA engine, becomes positive under boosted conditions, and this can completely confuse a stock ECU. At best, it reverts to an “open loop” control method, ignoring its pressure or airflow readings into the engine. This uses a base table to decide how much fuel to inject and when to fire the ignition, based on engine RPM and throttle position only. With the turbocharger forcing much more air into the engine than expected by the ECU, the air/fuel ratio will be severely lean, likely leading to detonation, in which the air/fuel charge in the cylinder detonates instead of burning at a smooth constant rate. This can damage or destroy an engine in short order.
Thus, to properly run a turbocharger on a formerly naturally aspirated car, it’s necessary to inject more fuel to match the added air forced into the intake. This is where the power gains come from, after all. The best way to do this is by using a custom ECU that allows full control over the fuel and timing maps. This allows the engine to be tuned to deliver optimum performance right up against the limits of detonation and damage, and provides solid, repeatable performance. However, there are other more rudimentary ways to get the job done — increasing fuel flow and controlling timing — without going to the trouble of a full ECU replacement.
Fuel-wise, the cheap, low-tech solution is known as a rising-rate fuel regulator. Such a regulator increases the pressure in the fuel rail in proportion with the boost level. This is often done at a ratio — for example, a 10:1 rising rate regulator will deliver an extra 10psi of fuel pressure for every 1 psi of boost. The higher pressure causes the injectors to deliver more fuel for the same duty cycle. This makes it possible to increase fuel flow into the engine as the turbocharger spools up and delivers boost without having to make any changes to the fuel map in the stock ECU. These devices can be had cheaply, often with a variety of swappable diaphragms to change the ratio and tune the fuel delivery somewhat, though with far less finesse than a properly tuned fuel map.
Timing-wise, there are a few options available to avoid detonation. On cars where such adjustment is available, the cheapest method is to simply wind down the base timing of the engine to a lower level. This will keep timing lower across the board, hopefully avoiding detonation when running at high RPM and high boost levels. However, this means that at lower RPM and lower load situations, the car will be running with suboptimal timing, and will sacrifice power and drivability and likely cause the engine to idle poorly. This can be acceptable for cheap race builds, but may be frustrating for a street driven car.
Alternatively, a timing box, or ignition timing controller, can be wired into the car. These consist of a microcontroller that monitors signals like intake air temperature, RPM, engine position and boost. When the timing box detects boost, it intercepts signals from engine position sensors and spoofs them back to the ECU, offset so as to change the time at which the ECU triggers the ignition pulses. Popular models include the Bipes ACU for the Mazda Miata, and the Apexi S-ITC for a broad spectrum of JDM cars. Often, these timing boxes were also used to tune turbocharged cars running larger turbos and other major upgrades. Timing boxes usually offer some degree of tuning via DIP switches, LED displays, and knobs, which can be set to determine the exact level of timing retard desired to keep the engine out of detonation.
ECU Swaps Have Become the Preferred Hack
One thing you’ll notice when researching these devices is that the vast majority of forum posts regarding the technology date from before 2005. This is because as technology has progressed, aftermarket ECUs have come down in price enough to make them a more attractive option. The capability to properly dial in a fuel and timing map, versus trying to push and prod a stock ECU into delivering huge amounts of extra fuel and less timing, generally leads to a car that drives smoother, more reliably, and is less likely to blow up. It also is a lot easier to tune. However, these parts still have a place in the scene. They’re used for the absolute lowest-budget builds, such as the Broke and Boosted project, or in racing series like the 24 Hours of Lemons which feature restrictive budget limits. These techniques are also relevant to supercharging NA engines, as well as turbo builds on carburetted engines, though substituting rising rate regulators for boost-referenced carburettors and timing interceptors for boost-ready ignition systems.
A modern engine management system may be the most reliable, accurate way to tune a boosted engine, but it’s not the only way. However, don’t expect to get much help from the broader automotive community if you attempt such a build. The tricks and techniques have largely been consigned to the dustbin of history, so you may find yourself poring over old manuals and having to troubleshoot blind. But if money, racing regulations, or simply the sheer thrill of doing things the old fashioned way put you in that situation, we hope this guide gives you the best possible shot at success. Good luck, and happy wrenching!
56 thoughts on “How To Build A Turbo Car The Cheap, 90s Way”
Got me a megasquirt opensource ECU for my project car back in the day. Worked like a charm!
Yep, same here! Best learning experience to get into engine management systems! Excellent documentation for many vehicles!
Years ago I looked the Megasquirt .. some of the worst spaghetti code ever.
Yes, I remember your code was a lot cleaner and worked much better.
Mine’s still running happily after almost 20 years…
megasquirt is not opensource. megasquirt supplies source code only to the paid customers.
speeduino and rusEFI are two alive and active open source ECUs
megasquirt ain’t opensource, speeduino is tho! I’m running speeduino on a supercharged G13 Samurai as a daily, works great.
Megasquirt started out as totally open but as more money got made they have gradually closed shop – these days it may as well be full commercial as it’s near as makes no practical difference.
When mine dies I’m looking closely at Speeduino even though I am not a fan of Arduino.
MegaSquirt was never fully, GNU-style open source; the earliest version of the website had a FAQ about whether you could build a copy with no parts from Bowling & Grippo, and the answer was “Our lawyers can beat up your lawyers.” Most of what’s happened since has been being more specific about what the policy means rather than changing it.
Are you a fan of ARM? please look into rusEFI which is usually stm32 but can also run on kinetis and cypress
Speedduino or RusEFI. Maybe cheaper than rising rate fuel regulator and other crap that will give you poor output from your engine.
Those ECU’s only work in certain common engine “scenarios”, since especially 90’s ECU systems have a lot of quirks in design and implementations that require lots of effort and firing the parts cannon loaded with new sensors to compensate, coupled with pretty much redoing the wiring harness.
Rising rate fuel regulator and spark boxes are much cheaper, simpler and “it just works” to those not in the know of efi systems.
Though not a fun time to fine tune to make emissions compliant, but if you don’t know what you’re doing, then it’s something you should only be doing to your track day car anyway.
um, rusEFI has run everything from a kick-started 2 cylinder russian motorcycle to a dual drive by wire BMW V12. Along with tons of Miata 4cyl, volvo 4cyl, mercedes 4cyl and LS engines. 90s engines aren’t terribly more heinous than what followed with only a select few exceptions IMHO.
I think you’re taking guff there fella – those ECU’s will run almost anything, as will almost any aftermarket ECU these days.
Spark boxes & rising rate regulators on the other hand are sticking plasters at best, bodging around the problem rather than doing it properly with a new properly tunable ECU.
I think it is generally illegal to tamper with the stock ECU due to EPA regulations. If I’m wrong I’m sure someone here will chime in, and I don’t mind. The problem is that swapping out the ECU may change the vehicle emissions. Hacking the stock ECU software/operating system could also change the emissions. I have read that changing the ECU software also is illegal because of copyright law, but I doubt that since you aren’t distributing copies. BUT, it is highly unlikely you would get caught doing any of these things. A deputy performing a standard traffic stop would not look for such modifications, know how to investigate or even care. I wouldn’t worry about it.
Until an insurance claim happens. :)
Depends on where you live. Germany does have police officers who are trained for modifications, as an example. And all cars undergo a safety and emissions inspection every two years.
In Sweden its each year.
It’s illegal for STREET USE unless the modifications are EPA and/or CARB approved, but if it’s a dedicated track car you can do whatever you want, at least in the USA, other countries might differ.
The irony is that unless there’s an exemption, the track cars will then have to be towed to the track causing even more emissions. Perhaps it would make more sense to build an EV and not have to deal with emissions anymore…
Usually you can get registrations permitting you to drive to/from a track or organized meet, but it’s something that has to be planned and coordinated, bureaucracy and all.
Or have two tunes, a gutless but emissions compliant one, and the full send track one.
In my experience, law enforcement is willing to not kick up a fuzz about emissions and modifications if you’re at least trying really hard to not be a douche bag rulebreaker.
This option pleases me, I’m reminded of the famous VW dieselgate models of a few years back. If anyone purposefully builds a Jeckell and Hyde setup please use a large red button to initiate beastmode. :)
@Troy K Ryckeley – my 2004 opel astra has “sport” mode button which does nothing, I would gladly hook up some real function to that.
Swapping out ECM if and when it is possible shouldn’t affect emissions as the ECM must measure O2 in the exhaust, however there is some software obtainable for some systems to make modifications such as remapping the timing and fuel maps, adjusting transmissions shift parameters and tweaking RPM limits. Most factory ECM’s have speed controls which can be over ridden. Many times the re programming changes the engine temp operating range for improved performance, engine temp is a critical factor where it comes to keeping the intake air temp down which helps control detonation. When an engine is expected to make more power it makes more heat so lowering the operating range give a margin of safety when more heat is being made. Hacking vehicle ECM’s only becomes a problem when that vehicle is in a dealership and someone runs a scan of the ECM, since to hack a controller requires a license pass code, there are some software programs out there that you can purchase for various vehicles giving access to the EEPROM to re flash them. One example was when Ford came out with their earlier EFI small blocks the factory ECM could be adapted to about any V8 engine as it would supply fuel to any displacement simply by reading air flow, vaccum, throttle position, air and engine temps, and RPM. Also early GM systems like those found on Oldsmobiles with the none fueled throttle bodies could be adapted. Those were bank fire, meaning half the injectors were fired at the same time then the other half, only 2 channels and a really simple system. The MegaSquirt MS3 system, a DIY has so much customizable options and is about the best budget you can find. MegaSquirt has expanded their offerings to cover about every design out there when it comes to building an aftermarket system. They can work with throttle body in about every cylinder configuration invented including rotary engines up to 4 rotors. They can be configured to run fuel only or fuel and timing, sequential and in 2 stage with coils on each plug. The software that runs on their processors is about the most advanced there is. None of the EFI systems for aftermarket as far as I know are approved for on road use but since most are being slated for vehicles which are not under the Federal Emissions Regulations anymore on account of their age and intended use. When engines are swapped from a later year model the installed systems from the factory usually go into the older vehicle which the Government will accept, it’s when an older engine that doesn’t meet newer standards goes into a newer vehicle, that doesn’t usually happen. The neat thing about some EFI control setups, is that there are companies that make systems that just piggyback into the factroy ECM’s so if you live in a place that requires inspections, the performance box can be removed and the system goes back stock, you just run a risk of getting caught in between inspections such as was mentioned in foreign countries. Now when it comes to Germany, they are so into hi perf to start with, even stock vehicles run a cut above the rest of the world. You can have your choice of old lady cars or sports versions but we all know that. The nice thing about being able to re flash an ECM is the police will have a harder time picking this out since nothing gets changed under the hood that makes it stand out unless you dress everything up, but that can be done without altering any emissions.
As someone who has worked in the performance aftermarket tuning cars for the past 15+ years, I have to take issue with much of what you say.
Megasquirt is old and tired. They have not kept pace with advances in technology. If you really think their software is “about the most advanced there is” take a look at the Motec M1 build environment, allowing more or less full customization of both the algorithms used to manage the powertrain but also CANbus vehicle connectivity for integration. MS can’t even touch the feature set of some of the more advanced open source projects. It’s tired. It still works fine for many setups – but those setups haven’t changed.
Reflashes (and altering the tunes on factory ECMs in general) almost always have an impact on emissions. Recently, organizations like the SEMA Garage have made it possible for smaller/independent entities to rent time in a facility that is capable of making all the measurements necessary to comply with CARB/EPA testing. The amount of work in the performance aftermarket is huge compared to the tiny sliver of truly emissions compliant aftermarket tunes that happen. Not attracting attention of law enforcement or other compliance entities and actually being able to walk the walk and pass a test are two very different things.
When teaching EFI tuning classes, one of the points that I hammer into students heads is that the optimal conditions for fuel economy, emissions and performance are NOT THE SAME. The possibility of performance gains in almost every factory car (and current performance aftermarket) exists because the priorities of the original manufacturer are almost guaranteed to not be optimal performance. Change priorities, change conditions, change results.
Some aftermarket ECUs (ProEFI/Woodward, etc.) are used by smaller manufacturers for things like marine applications and powersports. Some companies like Bosch who make ECMs used in major manufacturer’s vehicles use the same/similar technology in products they sell for motorsports. (Bosch Motorsport MS4/ME7, etc.) It’s entirely possible for a “non-OEM” ECU to pass emissions compliance but I’d be shocked to see it happen because of the different priorities of automotive enthusiasts and the amount of work required to get emissions right far, far, far exceeds what is required to make a car “drive right” and make power.
Thank you, those are some great tips for ECU products. I’ve been working with EFI-Ignition which is based on the mega squirt but is more of a rounded product. Have been looking into different manufacturers for the next project.
I was surprised to find maybe fiver years back on the market, devices to spoof the O2 sensors so you didn’t have to purchase new sensors or something I didn’t quite comprehend if otherwise.
Tell that to Volkswagen… No tampering!
Depends on the country.
Here in the UK its legal on older cars, grey area on newer cars as the annual MOT inspection has an incresingly strict emissions test that would be very hard to pass with any significant modification.
I might have a few corrections to that.
With the installation of a turbo, most airflow meters will happily tell the ECU the right airflow since they’re sitting just after the filter box. It’s just that the Fuel-Tables (3-axis table) don’t have target values for the measured airflow. It will top out at maximum available airflow values and just apply the fuel target values for that, which will result in a very lean mixture and therefore a blown engine.
Then the fuel thing…a turboed engine will need higher fuel pressure depending on boost levels. Basically the only way to get that is a boost referenced fuel pressure regulator, which you refer to as “rising rate fuel pressure regulator”. It’s not an option, it’s the only way. Additionally, you’ll also need uprated injectors since the N/A ones won’t be able to flow the necessary amount of fuel, no matter how much pressure they get. And an uprated fuel pump which is able to provide both the pressure and the flow. Without those three things, the mixture will be lean and the engine will knock its rods out.
Changes to the fuel map are a must as a result of all of that. But then again, they’re highly recommended even if all you do is install an aftermarket intake (Cold-Air-Intake) since it will result in the airflow sensor providing incorrect values.
Many older or simpler engines only have a manifold absolute pressure (MAP) sensor and no Mass Air Flow (MAF) sensor.
It’s those configurations that rising rate fuel regulators and “spark” boxes excel at manipulating.
In fact, I’ve only seen MAF sensors on gasolines with aggressive lean-burn capable ECU’s and direct injection, but those also has “internal” EGR, so plenty of reason to include a MAF.
1989 Ford Mustang 5.0. Mass air flow model, basic ECM.
1986 GM 5.0/5.7 TPI. Mass air flow. Incredibly ECM.
(I could go on)
No lean burn, wideband, direct injection, turbochargers contributing to backpressure and internal EGR. Basic, primitive dinosaur pushrod engines, arguably barely removed from the first generation of electronic controls at all. And MAF.
Most Japanese cars from about 90 to mid-2000s also go on this list of MAF, port-injection, no wideband, no EGR. Even the turbocharged ones, though they do use boost-referenced mechanical fuel pressure regulators.
Watching 24hr Lemons is the best!
Change or blow out all the dust in her air fliter, your car will breath much better
Is an intercooler mentioned? you will need to fit that into the intake airstream, cools the hot air down somewhat… Get a Renault Fuego…. they did it right
Intercoolers are heavy and introduce turbo lag – Colin Chapman, in his Lotus Esprit Turbo
from what for I know about turbos, Renault invented ’em , they still might could be makeing them inFrance , but only Germany has the Autoban
Stupid question; why not place the TB, it’s maf and it’s temperature sensor before the turbo? In 1973 I put a huge SU carburetor In front of my old corvair turbocharger and water injected it through a football inflation needle. Then I built a water cooled, adjustable waste gate. The car was stupid fast. I drove that car that way for 9 years crossing the entire US 4 times flat towing cars planes and campers at a?steady 80 mph. So, if it worked before the turbo so well, why wouldn’t it be the same for modern stuff. Granted the FI pressure would have to be bumped up to over come boost. I don’t see it done, but this old hotrodder can’t figure out why. Please help me understand.
I’d definitely put the temperature sensor after the compressor or charge-air cooler if equipped with that (since hot air is less dense, and in edge cases be part of the causes for detonation), preferably in the intake manifold itself.
Though with the carburetor (or throttle body if efi) in front of the compressor instead of after the compressor means you can run a purely Mass Air Flow setup (no MAP), since no blow-off (either venting or recirculating kind) is needed, though there’s a small risk of boost spikes in rare Scenarios.
Generally there’s a lot of nervousness about having significant volumes of fuel/air mix because of the explosion risk if there’s an intake backfire. My friends who have done carb-supercharger builds are quite definite about intercoolers being totally unsafe with this topology, so if you really want a charge cooler you’re stuck with fuel mixing downstream of the compressor. (Where it’s somewhat of a better fit as the fuel evaporation helps cool the incoming charge more when it’s hot.)
Your question has a couple of parts that you seem to have intermingled.
F1 in the 80s *did* run throttles on the inlets of the turbochargers. I think this was to try to keep the shaft velocity up on the turbos but I’m not 100% sure. The larger volume of air between the intake valves and throttle plate with a pre-turbo throttle would probably make for rather different transient dynamics than the small volume with a more traditionally placed EFI throttle. Independent throttle bodies (which have incredibly SHORT distance between intake valve and throttle) are known for having very fast transient throttle response. As a driver, transient response is generally desirable.
MAFs typically end up closer to the intake manifold in order to only meter air actually going into the engine. One of the “weaknesses” of most MAF systems is that the assume that ALL air which travels past the air meter will eventually end up in the combustion chamber. If you let the air escape after being “metered” but before entering the chamber, the ratio of fuel to air tends to be richer than intended because the computer calculates fueling from ALL the air it inferred was going into the cylinder. You could move the MAF pre-turbo (and this is sometimes done – see Nissan SR20DET for an example) but it is usually paired with a recirculating compressor bypass valve so that the system remains sealed. So why not put sensors pre turbo? Flexibility in plumbing bypass valve, time lag between sensor reading and air arriving into the combustion chamber.
Water injection is still used with fuel injected vehicles. The NACA reports documented its use with piston aircraft engines rather well. Many aftermarket water injection systems are available today.
As a young(er) EFI guy, I’d love to see more pictures/details. Draw through carb setups are still seen rarely today. Sounds like a neat setup.
Water injection to provide non-oxygen in the cylinder to prevent detonation for lean fuel-air ratios?
Mostly thermal. Huge specific heat, huge heat of vaporizatoin. Formation of H3O+ and OH- ions is a rate limiting reaction for a lot of the larger combustion reactions. 2H2O + a whole bunch of ionizing energy (spark) equals a whole bunch of hydroxide and hydronium. The NACA reports and their meta analysis cover it fairly well.
These predictable worried lawful neutral comments….this is hackaday. Stop worrying so much about the law.
What law? Here in the UK, I just need to have no visible smoke at idle.
^ this, on a lot of classics going EFI from a crappy old carb setup you can gain power, economy, and have better emissions than the car ever did from the factory.
Plus slow down before the blatantly obvious speed traps.
>ECU for full control over fuel and timing, but this can be cost prohibitive
$200 ECUMASTER DET 3/EasyEcu MICRO say what? btw both made in EU/Poland.
Screw EFI. Carburetors in my opinion are better.
When running a rising rate regulator it is also good to run a bleed valve ( boost controller) on its signal line so you can bleed the boost signal at full boost to tune the amount of fuel. Some times a rising rate regulator will be just too Ritch.
“The best way to turn what would ordinarily be a high-mileage naturally-aspirated internal combustion engine into a piece of junk in less than seventy-five thousand miles. Reliability is right down there with that other internal-combustion-engine engineering marvel foisted on the general, clueless, car-buying public–the rubber timing belt.”
Remember the Mercedes 300D? Non-turbo. Regularly achieved >500k miles with no maintenance other than routine oil–and other ‘consumables’ –changes. Darling of European taxi drivers. Mercedes issued BADGES to be placed on the cars’ grilles, to advertise every new 100k-mile increment achieved. There were a LOT of 300Ds, here and abroad, sporting ‘500K Miles’ badges.
[…but, with a turbo, one DOES GET a healthy increase in power over the non-turbo version..for the short time the engine lasts. Turbocharged engines are the only type engine Volkswagen knows how to build, nowadays. Tell you anything?]
I had a 1982 Fiat 2000 Spyder (124) turbo’d from the “factory”. Fiat outsourced it to an aftermarket company who literally put a boost controlled switch in the coolant circuit that would trick the ECU into thinking the car was cold for cold start enrichment. It would just dump fuel in. Not efficient, but safe for the engine. A common improvement to this system was to remove it and just run NA.
“At best, it reverts to an “open loop” control method, ignoring its pressure or airflow readings into the engine.”
Open loop is where the ECU stops looking at the Output Sensors.. It still needs the Gross Input Sensors to approximate How much Air has been injected at what RPM, so it can delver the ‘Proper Fuel’ and a Spark it timing delivered from it’s Base Map , with no feedback from the Output Sensors.
This so reminds me of wanting to EFI for starters one of the Briggs & Stratton engines… probably one of the opposed twins and then see what else I can do to not waste money and improve fuel and lifecycle performance.
53 comments and no mention of Sloppy Mechanics eBay turbo madness? What has hackaday become?
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