I have a base setup that I always start with. This base setup includes, the fully adjustable differential, the sport transmission that has the adjustable final drive ratio, and the suspension upgrade that allows for all tire, spring, and dampening adjustments. I have a baseline group of settings also. When I’m through testing an upgrade, I remove the upgrade and reset the settings to the baseline. I then add the next upgrade to test. I test it with the baseline settings. Based on how the car drives, I make adjustments to the settings. I’ve gotten to the point that I can feel where the car needs adjustments and how to make them. The adjustments I make usually improve the lap time. Sometimes I get it wrong and a different adjustment is needed. I’ve gotten much quicker at figuring this out.
I understand the issue with the controller control. That is part of the reason I do 10 laps. However, if I can get the car tuned well, I have found I can take laps much more consistently. The top 3 laps of the 10 are usually within 0.03 seconds of each other. If I feel I haven’t driven the car well, I repeat the 10 laps.
I have noticed my experience has improved my lap time slightly. I was concerned about this and I went back and tested one of the old settings. I did improve on my old lap time. The original time was 1:13.966, the new time was 1:13.898. These are the times using the base setup I mentioned earlier.
Thanks for sharing the process flow…makes sense. At times, depending on the car, the transmission can go one way (or the other) for PI, thus, my post on the sequence. Anyway, your process is very sound, keep at it!
On the driving learning curve (very important to understand as part of this process), this being the Indy Oval and as you’ve learned you’ll gain some time (in your case .068) in a short period of time. This will be different per car and especially per track. After you get rolling you’ll see what I mean. Lately (even though I am still doing pretty bad at the driving), in some tracks I have been able to improve 6-9secs, and more for long tracks.
Keep at it! Good luck [with the builds (#1), driving (#2), and tunes (#3)]!
I’ve finished the first round of testing engine upgrades. I’m not going to report all the times because they are hard to compare since the PI increases are not the same for each upgrade. Instead I’m using the following formula.
Score = (log(BT) - log(UT))/PI
BT is the lap time with no upgrade added. UT is the lap time with the upgrade added. PI is the performance index increase for the upgrade. I won’t explain the formula but I will say it takes into account both the improvement in lap time weighted by the increase in performance index. Higher numbers are better.
Here is how the street level engine upgrades compared.
4.6764, Flywheel
6.2350, Exhaust
6.3460, Fuel System
6.4549, Displacement
6.4702, Oil and Cooling
6.4847, Air Filter
6.5834, Valves
6.6088, Intake
6.9133, Pistons
7.2500, Camshaft
7.6670, Ignition
The top three don’t surprise me at all. With any of those upgrades, the car handled beautifully after tuning. The flywheel upgrade estimate is very unstable because of the equation I used. The score reported for the flywheel should be considered the minimum the score could be. All the other upgrades improved the performance of the car but I could never tune the car to drive as nicely as with the top three upgrades.
I am now going to add the street ignition to the baseline setup and test additional upgrades to see what improves the car the most.
I’ve heard the camshaft is one of the worst possible upgrades. I’ve double checked my numbers and redid the laps in the car. It works well for this car.
I decided to check the other upgrades to the car before adding the street ignition system. Here are the scores for the two items I tested.
5.2809, Roll cage
1.5659, Weight reduction
I was a bit surprised by how little weight reduction helped the car. I may have to try some more tuning on it. The car wasn’t driving smoothly. I haven’t figured out what adjustments are needed.
Interpreting the roll cage score is a bit more interesting. Since adding the roll cage reduces the PI, the score represents changing from the street roll cage to the stock roll cage. Since this has a score lower than most of the other upgrades, it means I should install the street roll cage and use the reduction in PI to buy something that will improve the car’s lap time more than the roll cage reduced the lap time.
For example, I could add the street roll cage which reduces the PI and add the street flywheel which increases the PI. The result is no PI is added to the car but the car goes around the course 0.02 seconds faster. Every little bit helps.
If a car has gobs of torque, then this upgrade is not is not significant. In a low class car, I personally find extra torque + higher rpm do help.
Since Indy oval will be continuous high speed track with no braking, weight reduction will not have much impact on time since top speed will be likely limited by aero drag. I would assume the car will be little more skittish since the suspension would be stiffer for the car.
Some roll cages reduce the PI (or same) but some roll cages increase the PI. Roll cages are a trade-off between chassis stiffness (handling) vs. added weight. If the chassis is decently stiff, then roll cage is not needed. Miata is a relatively modern small car so I’ve found the car to be adequate without one. 100+lbs of added weight will hurt the car’s acceleration/braking on a road track but not so much on Indy Oval.
Thanks for continuing to share your findings Jim. Yeah this whole issue of PI, and how much it really is per part and by sequence of upgrade, I believe will have an impact as how you are calculating the performance improvements per PI. For many years it’s been posted not to upgrade the cam, and also, depending on the class, weight being more critical than cage. Yet, again, these are all car and track dependent. So, you might keep these in mind!
Continue the good work you are doing. Though one can discuss the equation and it’s “generic” value, your methodology and consistency of approach is sound. Good luck!
I thought lower class cars saw a bigger increase with the camshaft update. Now I know why.
I hadn’t thought about the weight reduction not being a big issue because of the course. You described how the car reacted very well. It is more skittish. I blamed that for the car not improving very much. I just couldn’t get a good feeling for the car no matter how I tuned it.
The same appears to apply to the roll cage also. It added weight to the car with little change on how the car reacted. I was suppose to improve handling. The car only lost 0.03 seconds on the lap time. This is the minimum I will consider for a difference.
After getting the tire pressure set, springs should be your next stop. By default the cars are way, way too stiff. I’m no tuning expert, but I find that softer setups work much better. Worm’s guide says to take the tuning pages in order and that seems like the way to go. You get your tires, springs and dampers set, you will be a long way there. (Differential too on RWD cars so they aren’t loose when you hit the gas).
Great post by the way. I wish I had your patience with upgrades. I usually just wing it with the build and my results are all over the place. Sometimes I get lucky, other times I build a snowplow.
If you continue with reduced weight, then I think softer suspension would bring the car’s handling to norm. But this will not likely result in faster lap time, since acceleration is not focus here.
If you are looking for pure speed, then weight reduction will not help much UNTIL the car moves into higher classes where tire grip approaches/exceeds 100%. In D class, I think the tires were at 30~40% through the corners so no worries.
I wouldn’t add the flywheel. I did it for testing purposes. The reason I tested it is because it increases the PI about the same amount the chassis reinforcement/roll cage upgrade reduces the PI. In other words, when I add the street chassis reinforcement/roll cage upgrade and the street flywheel upgrade, the PI doesn’t change. However, the lap time improved slightly.
I appreciate your comment. I should have explained why I did what I did. I am trying to chronicle my experiences so other racers may learn from it. I need to be clear why I am doing what I am doing. Thanks for reminding me of this.
kind of what i figured you were doing, but in all reality to show how worth the upgrade was you probably should have also compared it to putting the most valuable upgrade that keeps you within the pi limits there also…
Sure it made you .0* faster with the flywheel, but the flywheel is basically considered a negative upgrade according to your formula… you should also compare that with ignition stage if it stays within the pi limit or difference also, something that actually increases horsepower instead of reducing 3 lbs for the flywheel (with a heavy pi hit) with no power increase. can probably use the first intake option and stay at the same pi as flywheel. and then test the time difference.
I’ve taken a few days off from doing this. I am trying to figure out what the anti-roll bars do. When I add some of the updates, I get some very slight oversteer coming out of the corners 2 and 4. I tried adding the antiroll bars to see if I could fix the problem. What I consider reasonable adjustments don’t seem to have an effect on the car. I think I might go to extreme settings to see what does happen. However, I’ve learned a lot more about springs and might revisit adjusting them. Another adjustment I might consider is the differential. Adjusting the differential cleared the same problem when the car had no upgrades.
Roll bars stiffen the car laterally. They are litterally a bar that runs across the bottom of the car tieing the left wheel to the right in either front or rear or both. It stiffens the car and prevents roll, hence the name. Stiffening the car is going to make the car react quicker yet without fine tuning may cause the car to plow or oversteer as it is now much stiffer.
As well as stiffening the car laterally, ARBs perform a useful function of transferring weight from one axle to the other. Stiffening the front ARB shifts weight to the rear axle which has the effect of increasing grip at the rear. Similarly softening the rear ARB reduces the weight being transferred to the front axle. This is useful with RWD cars. Reversing this procedure would be beneficial for FWD cars i.e. stiffening the rear ARB and softening the front ARB. Achieving the correct balance is trial and error I’m afraid but you seem to have lots of patience lol. Keep up the good work, a very interesting thread.
To solve the oversteer problem on corner exit try softening the rear ARB.
A couple of interesting insights from your post Moss…thanks!
I usually have the lower ARB values opposite to the highest % weight, from a Front-to-Rear standpoint, which sort of matches to your insights the majority of the times. Then, there are the famous mid-engine cars which at times end up opposite to my initial base prediction. In addition, there are some weird cars that require a lot of messing with of the ARBs.
Any thoughts around muscle cars…they are one of my nightmares to tune ARB’s, both on entry and exit oversteer, and at times, some mid-turn. I run into this issue a lot of times, especially mid-range classes (B-A-S). I usually don’t use above that, just a couple of cars.
Most muscle cars have a lighter rear and are RWD. I usually start off with the front ARB stiffened to around 30 and the rear softened to 10 and take it from there. Grip on the rear usually needs to be improved to avoid oversteer on exit. For oversteer on entry problems I would try raising the decel value on the diff.
Thanks for the tip Moss, it’s appreciated! For some reason, I have been using a base tune with the ARBs setting much closer (ex. 19/13, based on weight dist plus adjustment) than your suggested range, and then, I start going crazy tweaking away and get somewhat confused as to where to focus my “sweat” zone. On the Diff, I have been getting a little better at (first) identifying and then addressing this issue, though still learning a lot. Seems Diff one can actually find several acceptable zones.
I forgot about this. Thank you for bringing it up.
To me personally, ARB is the most difficult parameter to tune because I find it difficult to feel. Reading this post, maybe my front/rear ARB settings are too close together.