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Even the best built and dyno-tested engine will not perform as good as possible unless it is properly tuned for the vehicle it is in. This owner of this kit car (LEFT) had fuel supply problems caused by fuel tank venting problems and lean off-idle driveability problems that were cured by tuning the carburetors air/fuel mixture curve.

Customer satisfaction is every bit as important as the quality of your work if you expect to be a successful engine builder. You see, even when you build your customer the perfect engine, your customer must be happy with how their engine performs or your business and reputation will suffer.

Far too many good engine builders have had the quality of their work questioned when an engine they built does not perform like the customer expected, but more often than not, these performance issues are the result of tuning issues that should have been addressed by the person that installed the engine in the vehicle.

Many engine builders offer engine dynamometer testing, tuning and engine break-in services so they can supply their customers with an engine that has been performance tested. However, just because the engine runs well on a dyno does not mean it will perform as it should once it is installed in the vehicle without additional tuning to accommodate the specific application.

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The air cleaner of this modern fuel injected engine that is in a vintage car supplies the engine with hot air that has passed thru the radiator. This hot air will cause a loss of potential engine performance and it will also cause the engine control computer to retard the ignition timing as it senses the high inlet air temperatures.

The flow of the exhaust system, the air density, the inlet air temperature and how the air flows into the carburetor in the dyno room is often quite different from the conditions that the engine will see once it is installed in the engine bay of the vehicle for which it was built.

These changes in the engine’s incoming air charge and the flow of the exhaust system can mean the tuning package that worked on the dyno will not always be correct for the needs of the engine once it is installed in the vehicle.

If your company offers dynamometer testing services it would be a good idea to supply your customer with a dyno data sheet that includes the engine’s horsepower and torque output readings along with the air/fuel mixture readings and ignition spark advance curves that were used during testing.

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The air inlet package of this vintage carbureted ­vehicle supplies the engine with the cool outside air that it needs to make maximum power.

Even if you are not dyno testing the engine you built for your customer, it would be advisable to supply the guideline that helps them determine where the base timing and total spark advance curves should be set at plus what the air/fuel mixtures should be at idle, part throttle/cruise conditions and high load/power so they can perform a final tune to the engine so it will perform its best.

Another strategy for success, and as part of the conditions of the engine warranty, you may want to consider supplying the customer a checklist that they would fill out and return to you with what the ignition spark timing settings are and what the air/fuel mixture curve readings are once the engine is installed.

If the air/fuel mixtures and the ignition spark advance are not correct for the needs of the engine, the engine’s power, driveability, fuel efficiency and reliability will suffer.

If the engine is not properly tuned for the blend of gasoline the ­customer will be using, the ­engine you built for them could be damaged by ­problems such as bearing failure, piston/ring problems or cylinder wash down problems if the ignition spark advance or air/fuel mixtures are not correct for the needs of the engine.

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The most important tools of a tuner include a timing light, a weather station and the equipment needed to read the air/fuel mixture of an engine.

This both allows you to prevent damage and poor performance plus it protects you from falsely taking the blame.

Timing is Everything
The first step to take when you are performance tuning an engine or diagnosing any performance related issue is to check the base ignition timing and the amount of advance from the mechanical and vacuum advance curves.

The reason you should always check the ignition timing first is because any air/fuel mixture readings you get will not be accurate if the ignition advance is not correct for the application.

The accuracy of any air/fuel mixture readings will be hurt anytime the engine is misfiring, even a slight misfire can cause a wide-band oxygen sensor based A/F meter to supply you with false readings.

The total mechanical timing a typical vintage engine needs for maximum efficiency has not changed by very much, even with the newest blends of reformulated unleaded gasoline, but the initial timing and the amount of additional timing from the vacuum advance has changed due to the removal of lead from the gasoline and the changes in gasoline formulation that have been occurring since the 1970s.

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A programmable fuel injection system tunes the engine with key strokes on a laptop but any tuner is only as good as the data they/ it uses to make the correct tuning changes.

One of the best guidelines for determining what initial timing works best for a vintage or high performance carburetor equipped engine I have seen is in a Barry Grant/ Demon carburetor selection guide.

It recommends 10 to 12 degrees of initial timing when the camshaft duration is less than 220° @ 0.050˝, 14 to 16° of initial timing with less than 240°. @ 0.050˝ and 18 to 20° of initial timing with a cam with less than 260° @ 0.050˝.

The amount of total ignition spark advance should always be checked and the amount of mechanical advance from the distributor should be reset whenever the initial timing is changed because too much spark advance can cause the engine to run too hot or lead to engine failure from detonation related problems.

The additional timing from any vacuum advance system in most cases should be limited to a maximum of 10 to 12 degrees of advance since today’s gasoline burns somewhat faster since it no longer contains lead.

Your customer should be made aware the ‘original’ timing settings may not be correct and indeed may cause damage.

Once the ignition timing curves are properly tuned the next step is to check the air/fuel mixture curves the fuel system is supplying the engine with.

If the customer happens to have a dyno sheet with the air/fuel mixture readings, it is always nice to compare the air/fuel mixture readings that were recorded when the engine was on the dyno with the air/fuel mixture readings now that the engine is in the vehicle. It is not uncommon to see air/fuel mixture readings quite different from what was recorded when the engine was on the dyno.

The real world operating conditions that are seen after the engine is installed in the engine bay are often quite different from the ideal conditions the engine was tested at while it was in the dyno room.

Additionally, most dyno testing only determine maximum full throttle output which is only a part of a typical engine’s operation once it is the vehicle.

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Proper tuning decisions will help you avoid problems like the damage that was done to this piston that was caused too much ignition spark advance.

The air density that really matters to an engine is the air that it is getting thru its air cleaner package during the dynamic real world operating conditions it will see in the ­engine compartment of the vehicle the engine was built for.

The air ­density and the flow patterns of the air as it enters a carburetor is often quite different from the static temperature controlled conditions that were seen in the dyno room which will often cause the air/fuel mixture to change once it is installed in the vehicle the engine was built for.

Tools for Reading the Air/Fuel Mixture
The two most common tools used to check the air/fuel mixture are a 5-gas exhaust gas analyzer and a wide-band sensor based digital air/fuel meter.

The readings from a 5-gas exhaust gas analyzer method are more comprehensive and accurate, plus the readings can help determine what air/fuel mixture the engine needs for maximum efficiency, but the reaction time is slow (6 to 10 seconds).

The readings from a wide-band sensor based digital air/fuel meter are basically in real time plus the tool is very affordable – but the user needs to know what air/fuel mixture readings they are tuning for.
Many of the digital air/fuel meters have recording capabilities allowing the air/fuel mixture data to be combined with inputs such as throttle position, engine vacuum, engine rpm and vehicle speed.

This data can be played back so you can what areas of the air/fuel mixture curve need tuning attention. The wide-band “oxygen” ­sensor would be better named as a Lambda sensor because it does not ­really read the oxygen content in the engines exhaust – it actually creates an output voltage that the digital air/fuel meter converts into an air/fuel mixture reading when it exposed to the unburned combustibles in the exhaust.

The downside of the digital air/fuel meter method is that the output data from its “oxygen” sensor will supply the user with false readings if the air/fuel mixture is not properly burned in the engines cylinders.  Anytime the air/fuel mixture readings indicate you need to make a major tuning change it would be wise to confirm the readings with an exhaust gas analyzer before you make any major changes because the “oxygen” sensor can easily misread the exhaust and supply the digital air/fuel meter with false lean or rich readings.

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This carburetor shows evidence of a backfire problem, but the real question is was the problem caused by ignition or air/fuel mixture tuning problems. Whenever you are trying to solve a lean air/fuel mixture problem during high engine load conditions, don’t forget to check the fuel pressure while the engine is under load and experiencing the lean mixture problem.

The readings that are available from a 5-gas exhaust gas analyzer provide the user with the information needed to determine the engines air/fuel ratio, misfire rate, combustion efficiency plus the readings can be used to see if the engine has any detonation issues.

These readings can allow an experienced tuner to determine what air/fuel mixture an engine needs for maximum engine efficiency and the readings can help in the tuning of the ignition spark advance systems.

The gases the exhaust gas analyzer looks at are:
1. CO (carbon monoxide): The reading that is used to determine the air/fuel ratio, a low reading indicates a lean a/f mixture and a high reading indicates a rich a/f mixture.

2. HC (hydrocarbons): The amount of unburned fuel or an indicator of an engine misfire, the best air/fuel mixture and the best spark advance setting will give you the lowest HC reading.

3. CO2 (carbon dioxide): The product of complete combustion, the best air/fuel mixture and the best spark advance setting will give you the highest CO2 reading.

4. O2 (oxygen): A high O2 reading indicates a lean mixture, an exhaust leak, an engine misfire problem or an engine with a high overlap camshaft at lower engine speeds.

5. NOx (oxides of nitrogen): This gas created by excessive combustion chamber heat, in many cases a high reading may be related to excessive ignition timing creating detonation that can result in engine damage or an engine that runs too hot.

Reading the Air/Fuel ­Mixture
The best way to read and tune the air/fuel mixture of an engine may be to use the tools together so you can use the advantages each method offers.

There is nothing as accurate or comprehensive as a gas analyzer for reading the air/fuel mixture of an engine, so use it for steady-state tuning and establishing an operational baseline tuning targets.

Then, because there is nothing as fast as a digital air/fuel meter, use it when you are tuning for real world driving conditions.

Starting points when you are setting the air/fuel mixtures of a generic engine are:
Idle: 1% to 3 % CO or a 14.1-13.4 to 1 air/fuel mixture, Cruise RPM: 1% to 3 % CO or a 14.2 –14.0 to 1 air/fuel mixture, Power Mixture and Acceleration: 6.6% CO or a 12.0-1 air/fuel mixture.

Some high performance engines with fast burn cylinder heads may use a slightly leaner power mixture of 4% CO or a 13.0 to 1 air/fuel ratio.
The thing you need to know is that both methods are used to read the average air/fuel mixture of all the cylinders that the units are looking at, more than likely the air/fuel mixture will ­actually vary from cylinder to cylinder.

Advanced Tuning
The next level in performance tuning is to use multiple air/fuel sensors to read the air/fuel mixture of each cylinder and how the g-forces effect each cylinders a/f mixture during actual race conditions.

One of the reasons that the NASCAR and NHRA Pro Stock engines are making so much power is­­ ­because they used the air/fuel mixture data they get while using one a/f ­sensor per cylinder to design the fuel system so each cylinder gets the ideal air/fuel mixture as they are tuning the engine on a dynamometer.
Then they take the car to the track so they can see how the air/fuel mixture readings change and make final tuning changes to attain peak performance under real operating conditions.

One very good example of the competitive advantage available thru advanced tuning is how Wilson Manifolds was able to provide drag race and oval track customers with induction systems offering more power at the track because their manifolds are designed to provide every cylinder with the ideal air/fuel mixture.

Note: NHRA allows the use of A/F sensors in all events, but NASCAR does not allow their use during sanctioned events.

The Results
These “little” fine tuning details can make the difference between a satisfied customer who tells everyone they see what a great engine they got from their engine builder and an unsatisfied customer that tells everyone they talk to how disappointed they are with how their engine performs.

These tuning services can be done by the customer, by your shop or from a list of shops in your area that are experienced in tuning.

The best way to insure the engine you built is performing as well as you built it and insure customer satisfaction is to inform the customer how ­important it is that they pay as close attention to these fine tuning procedures as you did when you built the engine.

If you supply your customer with the information they need to know, they can give their engine the ideal ignition spark timing and air/fuel mixture curves, the engine will be more reliable and it will produce all the power and driveability that you built into the engine.

Make it clear that while you have done the job correct in your shop, they have the obligation to follow up with equally good installation and tuning to get the best reliability and performance from their investment.

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