#ChelseaTheCivic, Part 6-- Race Car Fuel Injector Cleaning Benefits

"Modern" Fuel Injectors

Fuel injectors are tiny valves that feed gasoline into the intake runners or directly into the cylinder of an internal combustion engine.  On some cars, injectors can open and close (one cycle) 50 times per second at engine speeds in excess of 6,000 RPMs.

As wisely stated by Super Street Magazine, fuel injectors are the analogous equivalent to the beating heart in the human body.  These devices can cycle as much as 562,500,000 times in a a typical 200,000-mile Japanese car, and as a result are subject to significant abuse and damage over time.  Needless to say, these components are very important.

An extreme example of a plugged injector.

Use and Abuse

Due to their location, injectors are exposed to unburned hydrocarbons such as gasoline and engine oil, byproducts of hydrocarbon combustion such as soot, and other contaminants.  Heat, vibration, and constant cycling between open and closed states exacerbate the negative affect these contaminants have on injector health.

Another extreme example of a plugged injector

Poor injector health can have a plethora of negative side-effects.  On commuter cars, most people don't get concerned until their car doesn't idle properly or hesitates under load.  These can be side effects of fouled injectors causing inadequate fuel delivery to one or more cylinders.

Stealerships

However, most of our race cars are running in good enough condition that they do not stutter under load or hesitate at idle (at least as a result of poor injector health).  Injectors are important in this context because in racing, the concern is always, "how do we get MORE SPEED!?"

Spencer, Kallie, Dame, and Ken saying "MUST GO FASTER!!!"

But why would clean fuel injectors give us more speed?  Let's cover the basics first...

The Basics of Fuel Delivery in Modern Cars

Fuel delivery to the engine is controlled in a negative feedback loop where the air-to-fuel ratio (AFR) is first measured in the exhaust stream.  The car's computer (ECU) reads the air-to-fuel ratio, and it knows whether there is too much (rich) or too little (lean) fuel going into the engine based on the reading.  Knowing the AFR, the ECU can alter the amount of fuel going to the engine by increasing or decreasing "fuel trim" as detailed below:

When the AFR number is too high, there is a larger portion of air in the exhaust stream, suggesting that fuel delivery is inadequate-- the computer will then tell the injectors to let more fuel into the engine (increasing trim).

When the AFR number is too low, there is less air and more fuel in the exhaust stream, suggesting that fuel delivery is in excess-- the computer will then tell the injectors to let less fuel into the engine (decreasing trim).

Diagram of closed-loop engine operation.

In a naturally aspirated car, an air to fuel ratio of 14.7 is optimal at idle, but under heavy load the optimal ratio varies from ~12-13 depending on application. 

Consequences of high or low AFRs

An engine that runs on the lean side may make more power than an engine that runs a little rich under load.  As a result, some tuners will install adjustable fuel pressure regulators (FPRs) to lower the pressure upstream of the injectors, which will lower the volume of fuel delivered to the cylinders.  For example, on my stock Integra LS motor, AFR at wide open throttle (WOT) was about 12.1:1.  To get more power out of the car, I tuned this to somewhere near 13.3:1.

AEM AFR gauge

So, why not starve even more fuel if leaning out a car will increase power?  Adding more fuel than is needed for optimal power levels means there is more cooling provided to the cylinder in the form of unburned gasoline.  Manufacturers typically want to make their engines last a very long time, so to improve reliability, stock engines typically run a little rich under load.

When a car is leaned out, the cylinder temperatures will be higher, increasing the risk of pre-detonation (fuel combusts too soon before top-dead-center) and damage to the engine.

Diagram of effects of lean engine operation from Laskey Racing

An engine that runs too rich is no good either, as excessive fuel (a solvent) can wash away oil which lubricates the piston-to-cylinder interface and prevents damage and scoring.

The spark plugs can sometimes indicate whether your motor is too rich or too lean

Bad Injectors Are Bad Mkay?

Most engines in sports cars have more than one cylinder.  Ideally, AFR would be measured at each individual cylinder and fuel trim would be changed at each individual injector accordingly.  However, this would increase complexity and cost-- so manufacturers choose to measure AFR in a point downstream of all four cylinders.

Most cars made after 1996 have a two O2 sensors at the catalytic converter.

This means that if one cylinder is burning lean due to a fouled injector while the rest of the cylinders are burning optimally, the computer may not know that there is a significant issue present and may only slightly increase fuel delivery.  Additionally, fuel delivery will be increased to ALL of the injectors which will make the cylinders with healthy AFRs now run rich and the cylinder with a lean AFR run closer to optimal.

What This Means for Racers

So why not install an aftermarket ECU that can measure AFR at all four cylinders in this example and tune it to deliver the optimal fuel volume?  Well, in some club racing classes such as Honda Challenge H4 (HC4) and Spec Miata (SM), it is illegal to run an aftermarket ECU (as of 2020).

Fancy AEM bling

So, these racers must find other means to insure the health of their engine and increase their horsepower.  As mentioned above, fuel pressure regulator tuning is a popular technique used to increase horsepower without ECU tuning.  Remember that to make more horsepower using this technique, one must lean out fuel delivery as much as safely possible while the car is operating at WOT.

But how much is "safe?"  In a thread on the MazdaRacers.com Forum, members discussed the benefits of fuel injector cleaning.  One member states that a customer of theirs blew up their motor while on the dyno due to leaning out the car too much.  They sent the injectors out to be serviced and they discovered that one of the injectors was bad.

So, as detailed above, it's very important to know the health of your injectors and to ensure they're as clean as possible before extracting the most power you can out of your engine via FPR tuning.

Decisions, Decisions...

So, you now know how important it is to have clean fuel injectors.  But what should you do?  If you're racing, there are five options that come to mind:

1.) If your car runs, you can send it

2.) You can buy aftermarket OEM replacements
3.) You can do "parts bin tuning"

4.) You can try and clean your OEM injectors on your own

5.) Or, you can have your OEM cores cleaned by a professional shop

Cheap, "OEM" re-manufactured injectors from eBay

Here's why you may want to or not want to choose one of those options above:

Option #1: Send it

Full sned with NoMoneyMotorsports Blog

Aside from being a funny thing to say, and something people say to appear cool and laid back/chill, "sending it" could be what's right for you.  The other options I mentioned above are not free and do require time and effort-- whether you're researching the best aftermarket replacement to buy, service shop to choose, or DIY method for cleaning.

Additionally, as I mentioned above, most race cars I've seen in lower power classes such as HC4 and SM run perfectly fine with their stock AFRs, offering reliable, fun track time.

When building a race car or tuning one, it's important to attack the low hanging fruit first.  If your suspension or brakes are not up to par and you're on a budget-- save your money and tackle those items first.

Option #2: Aftermarket or OEM Replacements

The beauty of running an older track car like a Honda or a Miata is that there are usually huge, supportive communities and a vast supply of aftermarket parts-- fuel injectors included.

If you go on eBay and look for a set of stock Integra LS injectors, a set of aftermarket re-mans usually go for about $40 with free shipping.  This is an extremely low cost and as a result it is an attractive option.  Amazon even sells cheap, aftermarket replacements for about $45 with one-day shipping!

Cheap "Catinbow" Injectors

The downside of cheap, aftermarket injectors, however, is a lack of specs regarding flow pattern, flow volume, or how closely they adhere to OEM requirements.  Sure, your Catinbow injectors might be 45 dollars shipped in a day with Jeff Bezos' extremely convenient Amazon service, but do you know how well they're made?

As documented on Motor.com, not only is the proper flow rate or pressure important, but so is the spray pattern of an injector.  OEMs pay PhDs a lot of money to determine optimal intake runner design and cylinder head geometry to ensure the best cooling, atomization, and combustion efficiency.  In fact, my rule-of-thumb for most mods on my own race car is to keep as much as I can OEM while still building a competitive car per the rules.

Fuel injector spray patterns

But what about OEM replacements?  They have the right specs and you can be sure that they're going to give you the best performance.

Except, you forgot to consider the drawbacks of owning an old track car-- such as dealing with OEM-discontinued parts.  Even if you can find a set of new injectors for a 20-year-old car, they will likely be costly.  For example, a set of injectors for a 1998 Acura Integra LS (06164-P72-010) goes for about $170.

Fancy but Expensive Injectors

Option #3: Parts Bin Racing

In spec classes, especially, parts bin tuning is a very popular way to make your car incrementally faster.  Parts bin tuning consists of buying multiple used components that you'd like to test and installing them one by one and recording the results.

There are tales of some dedicated SM race shops, for example, buying about 10 old Miata ECUs and trying each one on the dyno to see which one makes the most power.  Another tale is of SE30 racers that buy multiple used MAFs and test each one for the most power on a dyno.

SE30 on the dyno

In this instance, we're talking about parts bin tuning with fuel injectors, which was outlined in an article by another fellow H4 racer, Rob Krider of Double Nickel Nine (DNN) Racing.  In Rob's article, he was provided access to an injector flow tester and cleaner.  He then tested multiple injectors that he found at a local scrap yard and picked the most evenly matched and highest flowing ones to use on his race car.  Results proved successful as he made more power on the dyno.

Rob Krider of DNN on the dyno

This technique is probably the most optimal for a class such as mine, HC4.  However, it requires access to a plentiful amount of spares, it requires money for testing the spares on an injector cleaner/flow tester, and it requires dyno time.

As a result, parts bin tuning is usually very expensive.  Therefore, I did not choose this method.

Option #4: Do it Yourself!!!

To my readers' surprise, I actually didn't choose to tackle a project as a DIY for once.  Yes, it's likely the cheapest route, but it takes the most time and results can vary distinctly.

For example, Super Street tested fuel system cleaners on a 210-k mile Acura Integra (DC4) and 190-k mile Mazda RX7 (FC3S).  The results were disappointing.  The injectors on the Integra didn't clean up at all after using Pro-Gard Fuel System Cleaner and not much improvement was noted in the RX7 either.

Pro-Gard

Sure, there are probably better, more thorough ways to clean injectors on your own-- and I have done these in the past.  But they take a lot of time and can be unsafe in some instances.

For example, I once attached a vacuum tube to the inlet of an injector needing cleaning, filled the tube with acetone, hooked up a tire air compressor to the vacuum tube, and then created a power supply using an old wall outlet adapter (AC-to-DC) and some wire crimpers.  Exposed electrical leads and a volatile solvent?  Yeah, I think not...

Option #5: Make Someone Else Do it!!!

Ahh yes, Capitalist America's favorite solution to most problems people face-- if you can't do something, just give someone money to do it for you.  Always works right?

Stupid stock photo because pictures

For this option, you'll need to research the company that is the best for you.  Make sure whoever cleans your injectors provides you with a flow sheet of before and after cleaning results, make sure they provide some assessment of flow pattern quality, and make sure their turnaround time meets your needs.  This all takes time and is a drawback for this option.

Prices for these services are also somewhat high and can range from ~$75 to $100 not including shipping, but when all is said and done, it's cheaper than a new set of OEM injectors, a little more expensive than a set of knock-offs, and the results are more promising than a DIY project.

In case you were wondering-- yes, this is the route I chose for my Civic.

Mr. Injector

The OEM Keihin fuel injectors on my race car were in service for over 170,000 miles and were over 20-years-old.  They weren't leaking and the car was running well.  I also had tuned the car with a fuel pressure regulator on a dyno earlier in the season and it made some extra horsepower.  Yet, I still figured now was a good time to finally have them serviced.

Crusty and Old Injectors

I chose a shop out of Illinois called Mr. Injector after being referred to them by my good friend Alex who is the owner of #TrashTeg and also has been building cars for a long time now.

The Mr. Injector Logo

Bill has been operating his business for over 25 years and it shows.  Turnaround time was less than a week in total, communication was timely, and the finished product looked and performed extremely well.

Can't believe these are the same injectors I sent out!

More pics

More pics again...

A Picture of my son, Pidgey, standing next to a Jolly Rancher and  serviced injector

Along with my new injectors, I received installation instructions to prevent damage to the seals and I received the flow test results from before and after cleaning.  While all of the injectors were (apparently) out-performing the manufacturer-specified 244 cc/min, the flow they were delivering was highly varied.  After cleaning, they all flowed at 260 cc/min.  The biggest improvement in flow was 6% at one injector.

Flow test results from Mr. Injector

A nice bar graph of before and after results

Concluding Remarks

Would I go to Mr. Injector again?  Yes.  I've seen his work put to the test in my buddy's builds and his work was fast and of high quality.  I'm looking forward to installing these on my car and I'm glad I haven't ran into any issues at the lean AFR I'm currently running on my Honda Challenge H4 car.  Maybe I can lean it out even more now!

Thanks for nerding out over injectors with me, readers.  Until next time, have fun and take it easy.

Budget Transmission Part 2: How I Chose a Road Racing Final Drive

Introduction

In my last post, I discussed the first upgrade for my budget transmission-- moving from a helical limited slip differential to a clutch-type differential.  If you didn't read that yet, I suggest you go back and take a look.

A pic from my Instagram of Damien and I at New Jersey Motorsports Park (Photo by Windshadow)

The second of two transmission modifications allowed in the National Auto Sport Association's (NASA) Honda Challenge H4 class is a final drive gear with a different gear ratio from stock.  

So, what does a final drive do?  In this post, we'll delve a little into that and we'll discuss how you should choose one for the road course.

What is a Final Drive?

The final drive is basically the last gear between the transmission and the drive axles.  By altering the final drive gear ratio, you alter the amount of wheel rotations per rotation of the selected gear.

So, a 4.2:1 final drive will rotate the driven wheels 4.2 times for each rotation from the transmission and a 4.7:1 final drive will rotate the driven wheels 4.7 times for each rotation from the transmission.

Understanding a Final Drive

If we select a "shorter" final drive, we are saying we want a final drive with more rotations at the wheels per rotation at the gear.  This gives us more torque at the wheels and more acceleration, which we gain in return for a loss in top speed.  We call this a "shorter" final drive because the amount of time between gear shifts is now not as long as it once was.


2 Fast...

On the flip side, if we choose a "longer" final drive, we are trading straight line torque and acceleration for top speed and a potential gain in fuel economy.  The longer final drive gives less rotations at the wheel per rotation in the selected gear.  It takes more time between shifts, so we call it "long."

Why Should I Change My Final Drive?

In a drag racing car, we can go faster by turbocharging our cars or modifying the engines to generate more torque and horsepower.

However, if the stock final drive is too short, one disadvantage is a loss of top speed.

If the stock final drive is too long, one disadvantage is a loss of torque at the wheels.

So, drag racers must find the proper balance between torque to the wheels and top speed by selecting the correct final drive.  Many other factors play a role in this phenomenon, but they're beyond the scope of this article.


A Camaro at the strip

In road racing cars, the sessions are typically longer, the tracks have corners and elevation changes, and horsepower isn't as important as cornering speed in most amateur classes.

So, to go faster we can't rely on adding power at the cost of reliability, choose a final drive that will give us the best straight line speed, or choose the final drive with the best acceleration.  We must consider other factors.


Ken, Kallie, and Brian at New Jersey (Photo by Windshadow)

How to Choose a Final Drive

There are five steps outlined in this article for choosing a final drive.

Step 1: Find the Powerband

Step 2: Find your Corner Speeds

Step 3: Compare Final Drives for Each Corner for Each Track

Step 4: Repeat Step 3

Step 5: Test

Step 1: Find the Powerband

Let's take a look at the stock, 94-01 Acura Integra LS/RS/GS-- a popular Honda for road racing due to its suspension geometry and operating costs.

The stock Integra that loaned its motor to my race car

The powerband for a car is a colloquial term which refers to the engine's RPM range at which it operates most efficiently.  If you're low on money and have a relatively stock motor and no dyno sheet, a great way to find your car's powerband is through the internet.

Wikipedia states that the stock 1998 Acura Integra generates peak torque at 5,200 RPM and peak power at 6,300 RPM.  So, we will conservatively assume that the powerband is from ~5,000 to ~6,500 RPM, allowing for shifting inaccuracy and any changes in engine efficiency due to age and use.

Pulling a stock Integra motor from #TrashTeg

So, we know where the car's RPMs need to be to remain happy, but how do we apply this to the track?  You may be racing Summit Motorsports Park Main with a 0.55-mile-long straight or Lime Rock Park which is a Miata track.  You may be racing somewhere with anywhere from ten to twenty-five corners, all with different average speeds and elevations.

Some corners are extremely important and can lose races if the car and driver are not fast through them and out of them-- like Turn 1 at Watkins Glen.  Some corners are not important at all and are referred to as "throw-away corners,"

So what do we do?

Turn 1 at Watkins Glen International Raceway

Step 2: Find Your Corner Speed

Disclaimer:  This is where we must analyze our cornering speeds-- it is an art and our conclusions may not always be the same.  However, i'm going to do my best to break it down so you can make your own decisions in the end.  The most important thing is that you trust your gut and supplement that with real-world data.

Using an AiM Solo or an equivalent lap timer, take a look at all of the tracks you race in a typical season in your area.  For each track there will be several key corners where exit speed is critical because momentum is lost.  For example, below you'll find a trace of one of my fast laps at NJMP Thunderbolt last year with a 4.2 final drive:

Data from an AiM Solo

There are three graphs drawn versus track distance in the above figure.  In order from top to bottom they are: lateral G's, longitudinal G's, and speed.  We use the longitudinal G and lateral G graph as a reference point and the speed trace to see what our corner speeds are.

In this figure, I have highlighted several corners where a lot of momentum is lost due to braking which is required to make the tight-radius corners.  Those corners are 1, 2, 5, 7, and the exit of the octopus.  Below you'll find a track map and video for reference:

NJMP Track Map

A lap of Thunderbolt in my old single cam HPDE setup

Looking at the AiM data, we can see the following corner exit speeds for a 4.2:1 stock final drive in an H4 Acura Integra:

Approximate minimum speed per corner at NJMP Thunderbolt

Watching video and using common sense, I can look at these speeds and remember what gear I'm in while on track, which is third gear for every. single. corner!  Why is this useful again?

Step 3: Compare Final Drives

The internet doesn't just have the powerband for a stock B18B1, it also has calculators that allow you to look at the RPM vs Speed trace for a stock Integra transmission.  The calculator I like to use for Hondas is from Zeal Autoworks.  It's been around since forums were hot and it's still in use-- so you know it's good.

You can choose the Honda transmission you're interested in and alter gear ratios as well, comparing two at a time.  Tools for other cars are likely to exist on the internet as well.

Zeal Autoworks Transmission Speed Calculator...Stock 4.266:1 Final Drive in an Integra

The screenshot above shows the max MPH for each gear using a stock 4.266 final drive in an Acura Integra.  Using this calculator, we can also get the values for a transmission with a different final drive.  For our example, we'll look at a comparison between a stock 4.2:1 and an aftermarket 4.7:1 final drive.  Trans 1 uses a 4.2:1 final drive and Trans 2 uses a 4.7:1 final drive:

We can see that the RPM increases much quicker for a given change in speed with the 4.7:1 when compared to the 4.2:1.  However, you'll also note that the top speed in 5th gear is much lower with a 4.7:1 final drive than it is with a 4.2:1.  This reinforces what we stated above, that a longer final drive has less acceleration ability, but a higher top speed, and vise-versa.

Now, we know the corners we want to optimize our car's final drive for, we know the minimum speed through the corners, and we know the power band for our car.  All that's left is to compare graphs of RPM vs. speed for different final drive ratios to find the most optimal for your car.  For the sake of simplicity, we'll analyze the comparison between a 4.2:1 and 4.7:1 transmission further.

Dame and I going at it at Lime Rock Park

Below you'll see the graph we looked at previously, but this time I've overlaid two y-axis lines and several x-axis lines.  The y-axis lines are in red and they represent the powerband and the x-axis lines are the minimum speeds for the corners we deemed most important at NJMP Thunderbolt.

Overlaying pertinent powerband and track corner speed data on the RPM vs speed trace for different transmission gearing

Corner by corner, let's look at what the data tells us...

Step 3a: Compare Final Drives-- Corner by Corner Analysis

In this next sub-step, we will go through each of the corners we deemed most important and select the final drive ratio that benefits us most.

Turns 1 and 2:

Below is a graph of RPM vs speed for a transmission with a 4.2 final drive and a 4.7 final drive.  We can see that when proceeding through Turns 1 and 2 in a 4.7:1 final drive transmission, we have two options for gear choice:

We can stay in fourth gear through turn 1 and keep our feet to the floor as we progress through turn 2, minimizing brake input.  Or, we can keep the car in 3rd, turn into corner #1, and shift into 4th out of turn 2.  Either way, we need to row through the gears to optimize mid-corner to corner exit speed with the 4.7:1 final drive.

Graph of RPM vs. speed for a transmission with a 4.2:1 final and a 4.7:1 final

Yet if you look at the green line in the above graph, you'll see that through turn 1, you can maintain 3rd gear, through turn 2 you can maintain 3rd gear, and once through turn 2, onto the back straight, you can shift into 4th all while staying in the powerband.

This implies that a 4.2:1 final drive is most advantageous for turns 1 and 2.

Turn 5:

The next corner we'll analyze is the slow left-hander out of the high-speed, sweeping right-hander at NJMP Thundebrolt-- also known as Turn 5.

Photo of Condor Speed Shop's Bimmer through what looks like Turn 5

The graph shown below is similar to those above, but the x-axis line in this graph is for Turn 5.

Turn 5 min speed, stock Integra powerband RPM range, and RPM vs speed plots on one graph

Driving a 4.2:1 transmission, we have two options for gear choice-- 2nd or 3rd.  In either gear, we're significantly far from the powerband while close to the minimum speed for this corner.  4.2:1 is far from optimal for this corner.

However, a 4.7:1 final drive puts us at the intersection of the powerband for our motor and the minimum speed for Turn 5 when in 3rd gear.

From this, we can conclude a 4.7:1 final drive is better for Turn 5.

Turn 7:

The second-to-last corner we'll analyze is Turn 7 at NJMP Thunderbolt.  This corner is a lot of fun because it requires a lot of braking, but if you choose the proper line and throttle/brake inputs through here, passing can be completed against a fierce competitor.

Looking at the graph below, it appears that a 4.2:1 final drive would be the best from the middle to the end of turn 7 as it requires less shifting and starts at the bottom of the powerband.

Keep in mind, however, that exiting turn 7 is not a straight, but a decreasing radius right-hander that requires grip.  Not all speed through this section is due to final drive selection.  It could be due to other factors not covered in the scope of this article, such as driving style or differential setup.

With situations like this, it's best to rely on your experience driving the track.  Feel the corner and use your intuition to gauge what would be most advantageous in the big picture.  I may think this is an important corner for final drive selection, but maybe it's not!  Remember what I said in the beginning disclaimer-- this is an art.

Take a look at the graph and map below:

Graph of turn 7's min speed on an RPM vs speed graph for a stock Integra with different final drives

Diagram of T7 at Thunderbolt

The Exit of the Octopus

 If we zoom out on Turn 7 and The Octopus together we can better put things into perspective.

The "back half" of NJMP Thunderbolt

From the exit of The Octopus, it's easy to see that the 4.7 final drive is better positioned to exit the corner than the 4.2 final drive is.  The 4.7 AND the 4.2 final drive are both in 3rd gear which means they still have a 4th gear to shift through before they reach the abysmal, long fifth gear in these cars.

Engine speed vs car speed chart for the exit of The Octopus

However, a car must be tuned within the context of the track and therefore it is an art as mentioned above.  Keep in mind that after the exit of The Octopus, racers in a low-powered car will never lift until they get all the way back to Turn 1 at NJMP Thunderbolt.

This reinforces the point that tuning a car cannot focus on only one aspect-- road racing or for the drag strip...

Photo by Viken Photography

Step 4: Repeat 3A

Using different ratios, now it's time to experiment with which one works best for your driving style for a given track.  Additionally, remember to consider corner speeds for other tracks you regularly drive.  Lime Rock Park and Watkins Glen may deserve two totally different final drives for example.

Step 5: Test

Lastly, get your car on the track and see if it works.  Compare data using your on-track lap timer.  This is an essential tool.

Conclusion

As stated above, a final drive can have a large influence in corner exit speed for a track car.  While it also factors into the top speed of a track car, there are other factors to consider such as gear ratios for each individual gear and overall horsepower/torque for the car.  Additionally, there are factors that will make the car corner faster, thus potentially affecting final drive choice.

Photo by Viken Photography

I'm glad you guys had a chance to stop by.  Please recommend my blog and share my posts if they help you at all.  See you guys next time!