Over the course of this off-season (at least in the Northeast), you can expect EJ2 Track Rat to be doing some new and innovative things. For example, EJ2 Track Rat was recently featured on Garage Heroes in Trainings' Podcast.
The Garage Heroes in Training Being Garage Heroes
Well, EJ2 Track Rat has created its own YouTube channel with its first video. The video is already gaining traction as a popular video among the high performance driving and racing community.
It is entitled "5 Things You're Doing Wrong in HPDE and Track Days"
EJ2 Track Rat's First YouTube Video
When you get a chance, take a look. There's some great information on common mistakes made by drivers at all levels in the sport. Feel free to like, subscribe, and comment on the video, or leave your opinions on this blog post!
Racing puts a lot of stress on a car. In addition to the lateral and longitudinal Gs subjecting the chassis, structural suspension components, and bushings to stress, cars get crashed, transmissions break, driveline components break, and shocks wear out. Oh yeah, and engines get abused too, I guess.
Ant working on Alex's #TrashTeg
For example:
After living in a 1998 Acura Integra for 170,000 miles, my B18B1 was transplanted into a 1993 Honda Civic DX for racing duty.
Denise the D Series Integra, Donor to Chelsea the Civic
While in the Civic, it experienced a couple of money shifts, I found some metal shavings in the oil a couple of times (not sure from where), I lost a radiator cap and pegged my coolant temperature in a qualifying session, and toward the end of this season, it began smoking more than usual, and halfway through the season, I also did a fuel pressure regulator tune which doesn't increase longevity.
The motor did still run great, getting me a podium at The 2019 NASA Champs and a win for my last race of the season. However, with all of that abuse, I figured it would be a good idea to get an overall idea of the motor's health.
Engine Bay of Chelsea the Civic
Compression Test
The first test I wanted to do on the Civic was a compression test. So, I borrowed a compression tester, and some other tools-- including a leakdown tester and an air compressor from my friend Anthony, an H2 racer, and went to town.
Ant's Car
A compression test is used to read the max pressure each cylinder can produce when the engine is cranked over. Compression tests are useful for determining the general health of the motor. Max pressures are recorded for each cylinder and then they are compared. If one cylinder is down on compression relative to the other cylinders, you know that there is a problem at this cylinder.
If you do find a cylinder low on compression relative to its siblings, it could be caused by a variety of factors. There could be a burned valve, bad ring, scored cylinder, cracked piston, cracked or warped cylinder head, or more. To figure out where to begin troubleshooting a cylinder low on compression, we do a leakdown test-- this will be discussed later in this post.
I decided to do the test on a cold motor with the cylinder "dry" and with the cylinder "wet." The definitions of a dry and wet test are shown below:
A dry compression test is done with the engine in its normal operating condition. It can be done with the engine cold or hot. I chose to do it cold due to time constraints and because I ran into some issues when trying to do it hot (the pressure gauge broke).
A wet compression test is done to see how well the oil ring is sealing between the piston and the piston wall. It is called a wet compression test because a small amount of oil is added to the cylinder and the compression test is then conducted.
While performing the dry compression test, I made a mistake while taking compression readings on cylinder #1. The connector for the pressure gauge was slightly loose and this likely threw off the reading. During analysis, I will treat this reading as an outlier and assume that the average compression for cylinder 1 is actually 155.
With this being said, two things became apparent after reviewing the data:
1.) Cylinders 2 and 3 were lower on compression than cylinders 1 and 4. Since I overheated my engine halfway through the season, it's possible that the head gasket partially failed in between cylinders, allowing for cylinder-to-cylinder leakage.
2.) Cylinder 3 was the lowest on compression of the three. While performing further diagnostics, this cylinder will receive more attention than its sibling cylinders.
The table below shows the data from this test:
Dry Compression Test on an Acura Integra B18B1 Motor with Two Race Seasons and 170k Street Miles
Wet Compression Test
Next, I performed a wet compression test. I added two caps of 5w-30 Pennzoil Platinum Synthetic Oil to cylinder one to start. After attaching my pressure gauge for the first test and cranking the motor over, it became immediately apparent that two caps of oil was too much. Wet compression at cylinder 1 came back at >300 PSI....
So, for cylinders 2, 3, and 4, I added only ONE cap of oil, using the same oil, and achieved more realistic results. After performing the wet compression test, it was apparent that cylinder 4 had the highest wet compression and cylinder 2 had the lowest wet compression. Perhaps the piston rings at cylinder 4 were in better condition than cylinders 2 and 3.
Wet Compression Test of a B18B1
After some consideration, I'm not sure that the wet compression test provides as much value as the dry compression test because there are too many variables in the test, such as:
1.) The exact amount of oil added to each cylinder (an oil cap is not most accurate way to add)
2.) Where the oil lands on top of the piston when it's injected into the cylinder
3.) When the oil is injected vs. when the compression test is taken (more time allows more oil to seep past rings)
4.) And more...
I think performing a dry test cold and a dry test hot would give a better subjective overview of how the engine is performing.
Leakdown test
As mentioned above, a leakdown test is used to determine WHY a cylinder may be down on compression relative to another cylinder. A good DIY for the beginner on this process is shown in the video below:
To do the leakdown test, I wanted the motor to be at running temperature to ensure the valves and valve seats were fully sealing inside of the cylinder. I also wanted to ensure any residual oil from the wet compression test was out of the engine.
I Ran the Civic for 15 Minutes After it Stopped Smoking
I set the air supply from my air compressor to 60 PSIG and began conducting the leakdown test, recording the leakage pressure to get a percentage leakdown for each cylinder. I did this test twice for each cylinder.
Let's take a look at the leak down percentages below:
Leakdown Percentages for a B18B1 at Running temperature
There are four test results that show nearly 100% leakby and four tests that show realistic leakby values for a motor that doesn't run like a bag of rocks. I treated the high readings as outliers because they didn't make sense for a motor that runs as well as mine does. Additionally, I've seen excessive leakby on engines where the cams were still installed in the past.
With the cams still installed, slack in the timing belt, stiction between residual oil, cams, roller-rockers, pistons, and cylinders becomes a factor in ensuring the valves fully seat when the piston is rotated to TDC. So, I took the best reading for each cylinder and used that to calculate a leakdown percentage.
Interestingly, cylinders 3 and 4 had the worst leakdown percentages of the four cylinders, but only by 2%. Recall that cylinders 1 and 4 had the highest compression readings of the four cylinders and cylinder 3 had the lowest compression reading.
To determine where the leakage is coming from, for each test, I listened to see if I could hear air hissing out of the throttle body (which would imply intake valve leakage), air leaking out of the exhaust (implying exhaust valve leakage), and air leaking out of the valve cover (which would suggest piston-to-cylinder leakby).
Below is a table showing where air leakage was heard for each successful test-- that is, I ignore the tests with erroneously high leakby values:
B18B1 Leakdown Test Observations
In all tests, it is apparent that leakage for each cylinder was due primarily to leakage between the valves and valve seats, which is to be expected from a motor with 170,000 street miles. Additionally, I did hear some air hissing out of adjacent cylinders when conducting leakdown tests on the middle cylinders-- which corroborates suspicions of head gasket failure.
Oil Analysis
Oil is used to lubricate any rotating and reciprocating components in the engine, such as the crankshaft and bearings, connecting rods and bearings, piston-to-cylinder surfaces, camshafts and journals, and roller-rocker surfaces (to name a few). Lubrication for these components is necessary because they are constantly creating friction during normal engine operation.
If adequate lubrication is not present in the engine, affected components will fail and metal bits from them will end up in the oil, in addition to other contaminants.
VTEC Valvetrains See Even More Heat and Friction Than Their Non-VTEC Counterparts
Metal isn't the only thing that shows up in engine oil when the engine is not running optimally, however. A sample may show that an engine is running too hot as evidenced by degradation of additives or carbon chains in the oil. A sample may also show that the engine has excessive blowby or incomplete combustion as evidenced by unburned fuel or sulfates and nitrates which have dissolved into the oil.
So, we sample the oil to get an additional snapshot of engine health from a different perspective.
Oil analysis isn't guaranteed to identify a failing engine. For example, a healthy running engine that experiences a brief transient where a bearing is partially wiped at the crank may have a relatively healthy oil analysis, but a large, insoluble piece of bearing may be present in the oil. This happens frequently in heavy industry with steam turbines, for example.
However, health assessments are broad and take into account many factors...we want to analyze the "big picture" and avoid relying on only one test to determine if our engine is healthy or not.
The Big Picture (A Cool and Good Stock Photo)
So, after performing my compression and leakdown test, I decided I'd send the oil to Blackstone Laboratories for analysis. Blackstone laboratories is based out of the Midwest. They will send you a sampling kit for free and all you have to do is pull a sample of oil and send it back to them.
A Blackstone Laboratories Oil Sample Kit
In the sample kit, they have a questionnaire that asks about the car's use, any important info like engine swaps or mods, and the age/mileage on the oil. They have experience analyzing many types of cars from daily drivers to race cars. They even have experience in analyzing hydraulic fluid or fluid from industrial machinery.
Within two weeks, I had my oil drained, collected, mailed, and sampled by Blackstone. Their analysis stated that my motor was in healthy condition with wear parameters below or in-line with expected values for most motors similar to mine. Take a look at the results below:
Blackstone-Provided Comments on Engine Health
They provide an extensive data sheet showing wear particles found in the oil with average values for comparison purposes. The table below shows this:
Elements Found in Oil
Lastly, they provide a table on values such as percentage anti-freeze and viscosity of the oil:
Additional Oil Information
Conclusion
After discussing results from the tests above with champion level racing drivers and builders in the amateur motorsports community and after analyzing the results on my own accord, it became apparent that the motor was in good health.
Wear material in the oil was low, suggesting the engine did not have significant degradation due to a lack of lubrication anywhere in the rotating/reciprocating assembly. Leakdown wasn't exceptionally high, and any leakdown present in the engine was most likely due to valve-to-seat leakage, and not bottom end leakage which would require an extensive rebuild.
The head gasket was a likely contributor for high leakdown % on cylinder 3 and also for lower compression numbers on cylinders 2 and 3. This was likely the result of damage from pegging my coolant gauge high during a qualifying session at the beginning of the season in 2019 at NJMP Thunderbolt.
Overall my B18B1 is in good condition. I know that I can likely run this motor for another season with no issues. This knowledge will allow me to focus my efforts on other upgrades to improve the car's speed, such as suspension and brakes.
Thanks all for reading. I hope this post was informative and interesting.
The Integra
and Civic chassis that Honda produced from the late eighties to the early 2000s
were set apart from average FWD cars because they could handle well out of the
box. With modification, they could handle even better.
One common
problem with FWD cars is understeer. Because the front wheels are doing
the accelerating, turning, and the majority of stopping, the tires tend to
"fall off" sooner than their RWD counterparts. To combat this,
FWD race car builders increase the chassis frequency, or "stiffness,"
of the rear of the car using sway bars or stiffer springs.
In this
post, readers will see how EJ2 Track Rat was able to create a low-budget
solution for drivers looking to increase rear roll stiffness via use of a stiffer
sway bar in the rear of the car.
Background
Alex's
TrashTeg was driving fairly well. He was able to pass competition school
with NASA Northeast in it and he learned a fair amount about racecraft during
the course of the season. He was also having a ton of fun. However,
Alex was beginning to realize the limits of his budget-built car-- Partially
because his car had too much dive, squat, and roll under braking, acceleration,
and cornering, respectively.
When
TrashTeg was first built, it had the following setup:
205 Toyo RRs
At a ride height of ~5.5-6 inches
With a front spring rate of 650 pounds/inch,
Rear spring rate of 750 pounds/inch,
No front sway bar,
A 25 mm GodSpeed (eBay) rear sway bar,
And some Koni Sports he got for free from our friend
Anthony
Our goal was
to increase the roll stiffness of the car while still keeping the car
controllable at the limits with a healthy amount of rotation in corners.
We had two options: increase front and rear spring rate, with a stiffer rear
spring rate than front, or increase front spring rate and throw a big rear bar
on.
Since I only had a pair of 800 pound/inch springs in my garage, we figured we'd
throw the 800 pound/inch springs up front, and increase rear roll
stiffness without springs. The easiest way to do this is with a bigger sway bar, which
A-Spec Racing (ASR) makes. Their 32 mm hollow bars come in different
thicknesses and since they're hollow, they have the advantage of less weight
vs. their solid counterparts for the same amount of torsional resistance.
ASR Hollow Rear Sway Bar Kit
However, ASR
bars are not cheap at ~$500 for a full kit and Alex had already purchased a
$300 eBay sway bar kit. He wasn't about to spend $500 more for the ASR
product as a result. But, he and I were both interested in doing
something creative.
Much debate
was had on this thread-- specifically whether one can weld to a sway bar and
expect it to work because sway bars go through a forging process that allows
them to become "spring steel." Spring steel is highly
malleable, but returns to the shape it was bent from fairly easily.
Welding to spring steel changes that property and increases brittleness.
Example of a Cracked Sway Bar (Not Ours)
Doing the Deed
Since we don't care about armchair engineers and we buy parts for our
destined-for-doom race cars on eBay, we decided it'd be worth a go to attempt
something similar. The new setup would have the following changes:
Ride height lowered to 5" at pinch welds
Front spring increased to 800 pounds per inch
A "custom" xxx mm solid rear sway bar, courtesy of
the plumbing aisle at Home Depot
We started by purchasing some steel black tubing with an inner diameter of 1" and a wall thickness of 0.133" for about $20. A 1" inner diameter equates to 25.4 mm which is only slightly larger than the OD of our eBay sway bar. Our plan was to cut this bar to length so that it would fit between the pillowblocks that mount the sway bar to the subframe. Then, we would cut the bar in half, length-wise, and weld half of the Home Depot pipe to the sway bar. This would result in a solid sway bar with a diameter of ~28 mm.
Sway Bar Diagram from ASR
Our Plan from EJ2 Track Rat
We laid out the eBay sway bar after purchasing the pipe from Home Depot and we started by measuring where our addition would be and how short we'd need it cut.
Laying Out the Sway Bar
Next, we cut our Home Depot pipe to length using a cut-off wheel. Ideally this would be done with a band saw, but with a pipe-vise it's easy to do with a $30 Harbor Freight cut-off wheel. The cut just isn't as clean.
Alex Cutting Home Depot Pipe to Length
Next we cut the pipe in half, lengthwise using our cut-off wheel and our old school bench vise from eBay.
Cutting the Home Depot Pipe in Half Length-Wise
To weld our cut-off half of the Home Depot pipe to our eBay sway bar, we would need to first clamp the OD of the Home Depot bar to the sway bar. After grinding the surface of the Home Depot pipe and the sway bar clean, we clamped the Home Depot bar to the sway bar using a set of Milwaukee vise grips.
Half of a Home Depot Pipe Clamped to an eBay Sway Bar
I ran a bead across a section to the left and right of the vise grip, then moved the vise grip down the length of the sway bar and repeated the process...the entire thing was done with flux wire.
Close-up of Beads Ran Next to Vise Grip
The entire bar welded up looked amusing, to say the least. It really was also great practice for welding. I needed some, so this was of benefit to me.
Picture 1 of Welded Sway
And Picture 2...
Finally, we sprayed the bar gloss black and mounted it onto the car. Once on the car, we checked to ensure clearance between our modified bar and the subframe brace was satisfactory.
The Bar Mounted to the Subframe
Checking Fit with Bar at Full Droop
Checking Fit with Bar at Full Compression
And after installing the rear bar, we installed my front springs and manually set ride height as we always do-- the LoBuk way.
Alex Setting Ride Height to Clock Bushings
Another View of Alex Setting Ride Height to Clock Bushings
Impressions
Alex tested TrashTeg at Watkins Glen in October of 2019 with NASA NE to see how the changes improved the car.
Alex Suiting up for a Race at The Glen
On Track, he noticed sharper turn-in due to the stiffer front springs, but the larger rear sway also allowed the car to have less mid-corner push. The new sway bar we created held up for a full weekend of abuse at one of the best and most demanding tracks in the Northeast.
After our racing shenanigans on Saturday we attended a NASA Northeast BBQ and had a good time. The car held up, the mods made it faster, and we had a great time.
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.
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.
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,"
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.
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.
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...
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.
