ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Car Modding, Car Tuning and the Science of Horsepower - Tuning Out Temperature Effects and Heat Soak

Updated on August 25, 2014

Air temperature happens to be a particularly nasty variable in the world of car performance for 2 reasons. First, it tends to throw off all of the sensors responsible for calculating fuel. Second, hot air induces knock and can cause major mechanical issues and expensive explosions when you start adding boost. While hot air is a major concern, it's more of a concern that the computer isn't aware of it. As long as your car is capable of compensating for temperature changes, at least you can tune some safety into your car to protect your engine from a dangerously lean condition leading to detonation.

Thermodynamics works against us

Every PCM is different but particularly with VE (Speed Density) tunes, there will be tables to provide fuel enrichment as a function of temperature. This is one of the many reasons I like a speed density tune over a MAF tune. Whereas the MAF sensor magically computes everything at the same time, a speed density tune breaks it all down into components, each measured by different sensors and this lets you take control of each variable separately, including temperature. Ever notice how a perfectly tuned MAF table will become bent a month later with almost a perfectly straight slope, trending from negative LTFTs at low frequencies to positive LTFTs at high frequencies? That's because the damn thing is getting fouled up and the layers of gunk are insulating the wire from the effects of temperature that the intake air would normally have on it. MAP and IAT sensors don't suffer from this fouling effect and they make it easy to tune one parameter without touching the other.

Go into your tuning software and look under the Airflow (possibly fuel) category. Around where your VE table is located should also be a table for fuel enrichment vs IAT. In HPTuners the table is called "Charge Temp Mult". Irrespective of anything else, this table will apply a correction factor to whatever the PCM thinks the correct injection pulse width needs to be for a given air flow value. If the computer thinks that based on 30 kPa, 30 degrees C and 600 RPM, the pulse width needs to be 5ms, this table will multiply that by a certain factor to either add or subtract fuel, based solely on temperature. So what we want to do is determine what temperature does to the air mass WHEN EVERYTHING ELSE IS CONSTANT. For this you need to take the car out for a road scan. As I've said countless times, make sure you drive the car long enough that all the fluids reach nominal temperatures. Don't start scanning until all the temperatures stop changing and the car is all warmed up. For this particular road scan go easy on the car too. No need to punch it. We are just trying to establish a temperature baseline. What I recommend is to go for a 5 minute drive on the highway. Watch your IAT on your laptop and you will notice it drop to something fairly close to ambient and then stay there, as long as you're cruising at highway speed. Now, CAREFULLY, find a nice big shoulder on the side of the highway where you can SAFELY stop for a minute, check that there are no cars behind you and pull over with your hazard lights on. Once on the shoulder, stop quickly, put the car in park or neutral, watch carfully for the tachometer to stabilize on your idle RPM and then start scanning immediately. You will notice your IATs start to shoot up as soon as you stop the car and this is what we want. Don't do anything, don't even breathe. Don't touch the gas pedal. Make sure you don't alter the engine in any way by shifting gears. Leave the car alone and let the intake air heat up. After letting it heat soak for a minute or so it should have climbed by at least 10 degrees, perhaps closer to 20. By the time it rises 20 degrees or so, stop scanning. THEN, shift into drive, give the tow truck driver the finger, pull into traffic carefully and go home.

This is the sort of table you will need to adjust, no matter what software you have.

Dump your scan to an excel file and isolate only the lines where the RPM, MAP and ECT were consistent for several CONSECUTIVE lines in your scan. Graph IAT vs STFT and LTFT (your fuel trim). What you should see is temp along the X-axis and fuel trim on the Y-axis. You should notice the fuel trim either rises or falls with a linear slope over the entire range of temperatures. You can add an interpolation line if you like, to make it easier to read. Try to pick a part of the graph where the LTFT did not change and then for that section only look at the STFT line. Say for example, your LTFT didn't change between 30 degrees C and 40 degrees C. Now determine the STFT value at 40 and the STFT value at 30. Subtract them. Say you get 3 - (-1) = 4, so the STFT rose by 4 over a span of 10 degrees. That's the key! That's what you want to know. Go back to your tune and find that Charge Temp Mult (or equivalent) table. Each cell should differ from the others by a certain number of degrees. Mine differs by 10 degrees per cell so in that case, what I'd want to do is declare a cell in the table to be my neutral cell... the cell that I won't touch. You should pick your neutral cell to be the temperature that the IAT is most often at, most of the time while driving. Let's say that's 30 degrees C. Leave that cell alone. It should have a 1.0 in it, meaning no correction. Now if the next cell to the right is 40 degrees C, you'd want to put 1.04 in there, meaning add 4% fuel. You'd want to put 1.08 in the next, 1.12 in the next and so on to create a trend line of constant slope. Do the same thing in the negative direction (0.96, 0.92, 0.88, etc.). Now, every time the PCM has to determine how much fuel to add, it will first look to the VE table. The RPM and MAP values measured will determine which cell it reads. It will then calculate the fuel enrichment based on that VE value it just read but first it will look at your new temperature table and multiply by the factor it finds in there for the current IAT temperature. This applies the precise correction needed to prevent the phenomenon you observed when you were scanning the car and pulled over on the highway. The heat soak caused the fuel trims to change because the VE values were only good for 1 temperature. Now that you've created a "correction table", the VE value will always be good because the temperature effects on it are perfectly negated by this new table.

A word of caution. The scan you did was only at 1 engine operating point. There's no guarantee that temperature effect will be exactly the same at all other operating points. However it's extremely difficult to induce heat soak when the car is moving so the best results you'll ever get are from the method described above and these should be massively helpful for the computer, even at other operating points. You may wish to fine tune the temperature table even more by repeating this exercise a couple of times but in general you will find the temperature table far more stable and easier to dial in than your fuel or spark tables typically are.

Why CAIs actually do work

What is the average ambient daytime temperature where you live, when you would most likely drive your car for pleasure?

See results

Comments

    0 of 8192 characters used
    Post Comment

    • profile image

      Enrique 

      3 years ago

      I appreciate your kind and gerenous advice a lot!. I have been trying it hardly and did not get those amazing results!. It is nice to see that you got my comment in a good way!God bless you!VA:F [1.9.10_1130]please wait VA:F [1.9.10_1130](from 0 votes)

    • profile image

      Victory 

      3 years ago

      Damn, I wish I could think of soeimhtng smart like that!

    • chriscamaro profile imageAUTHOR

      chriscamaro 

      3 years ago from Ontario, Canada

      I'm not sure I understood all of what you said but if you are saying that you can't log all of the variables I mentioned in the hub, the only 2 that are really important are the IAT and the LTFT. If you can manage to log those and if you can get your car to a steady-state condition on the highway before stopping, you should get enough data to make the adjustments to your fuel map.

    • profile image

      Johne390 

      3 years ago

      I need to input, like a bunch at the same time as I hadn't the benefit of examining everything you had to declare, I couldn't rally round on the contrary elude draw your attention before long. The as if you needed an excellent grasp on the subject kdadgkdagbec

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)