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J. Mills Tuning


** If You would like to make an appointment for a dyno tuning session please read and make sure your vehicle is in compliance with the checklist below. Once you have went over the checklist and your vehicle please call (919)494-2711 to schedule your dyno tuning appointment. **

Dyno Tuning Checklist

We have created this Dyno Tuning Checklist as a guide for you to follow to ensure your engine and vehicle are in proper condition prior to your tuning session. The most common cause of unsatisfactory tuning results come from mechanical issues that could have easily been found and corrected prior to the tuning session. You can go through each of the steps in this Dyno Tuning Checklist to identify and resolve common problem areas that can effect the tuning of your car. If you are unable to do any of these things yourself please let us know ahead of time. We can help you if you are near us as we do regular automotive work too. If you are not near us there is a good chance that there is a shop near you that can assist you for a small fee. This list needs to be gone through. We do NOT always have the time to help you fix issues on the day of your tuning appointment. We are willing to help when we can, BUT take note that any time spent fixing mechanical issues on your car so the tune can take place or be completed will cost you our hourly shop rate. That is why we stress that you take the time to read this and look over your vehicle. It CAN save YOU time and money. Say your tune can not be completed due to a mechanical issue that already existed before you showed up to our facility, or say a issue is found on the dyno, we will stop the tuning appointment when we see issues. Before or during the tune! Again any time spent diagnosing or fixing issues on your car or engine so we can complete your tuning session will be charged for.   

Section 1: Mechanical Engine Health

You need to make sure you are tuning a healthy engine. We suggest you complete a compression test prior to your tuning appointment (and a Cylinder Leakdown Test if possible). Typical compression test results should be as followed: 

  • 8:1 - 8.5:1 compression: 150-170 psi per cylinder
  • 8.5:1 - 9.5:1 compression: 170-210 psi per cylinder
  • 9.5:1 - 11.1 compression: 210-275 psi per cylinder
  • 11:1+ compression: 250+ per cylinder (highly depends on cams being used)

Compression Tests should be performed on a warm engine, with the fuel injectors unplugged, and the throttle should be held fully open while testing. These pressure valves will be less at higher elevations, and can be lower on engines with more mileage. YOU SHOULD NOT have more than 20psi variance between cylinders. If you have one cylinder that is showing a greater variance than 20psi then you will need to repair that mechanical problem prior to your dyno tuning appointment. The additional cylinder pressure realized after a custom tune will only exploit the existing mechanical problem causing further, and usually more severe engine failure.

A Cylinder Leakdown Test can also be performed on a warm engine. YOU SHOULD NOT have a cylinder leakage of more than 18-20% in any cylinder. If you do, then you will need to further test to see where the air is leaking from and to; intake valve seat, exhaust valve seat, head gasket, piston rings, etc. Please know that even if either of these test results look good, you can still have an engine that has some mechanical damage and we will be able to recognize any negative symptoms and tell you about the consequences of further tuning your engine if we find issues the day of your appointment.

Check for any engine oil, other lubrication, or fluid leaks. Be sure to use the proper turbo oil feed and return lines and that they are installed properly. Any oil/fluid leak will likely only get worse once the engine/drivetrain is warmed up while on the dyno. An engine's oil lubrication system must be properly sealed in order for dyno tuning to safely continue.

Section 2: Intake, Charge Pipe/Intercooler System, Turbo and Vacuum Line Integrity

Make sure your intake filter has been properly cleaned. Cleaning your intake filter at regular intervals is always a good idea. Its also a good idea before a dyno tuning session. You don't want something as small as a clogged intake filter hurting power production.

Vacuum, pressure, or smoke check all intake, charge pipe/intercooler, turbo, and vacuum lines. Make sure that your intake, vacuum lines, and intercooler piping are sealed when pressurized like when running full boost. Pressure/smoke testing the system to as much pressure as the car is going to run is ideal. Make sure all vacuum lines and intercooler piping is secure so they do not blow off at the tuning appointment.

Check the full exhaust system from leaks from the exhaust ports on the head to the tailpipe exit. Make sure all of the bolts are tightened, in particular, the exhaust system bolts/nuts. An exhaust leak prior to the turbo will lose power and make part throttle tuning almost impossible. Any exhaust leak in the exhaust stream prior to the WBO2 sensor can also throw off sensor accuracy.

Check the BOV to make sure it is seating and sealing properly. Make sure the blow off valve is properly lubricated, seals tight, and is functioning properly.

Test for excessive turbo shaft play. Ensure that the turbo wheels are not spinning. Reach your fingers into the inlet side of the compressor and grasp the shaft. Attempt to move the shaft left and right, up and down. If the shaft moves appreciably in these directions, your turbo has excessive shaft play. You cannot expect a turbo to operate properly if it has worn excessively. Have the turbo rebuilt or buy a new one.

Section 3: General Pre-Tuning Maintenance Questions

Do you have all fluid levels where they need to be? Make sure all fluid levels are up to par. This includes engine oil, anti-freeze, transmission fluid, differential/transfer case fluid, brake fluid, clutch hydraulic fluid, etc. If your engine oil and filter have been run for more than 3,000 miles, please replace the filter and your engine oil. Bleed the coolant system before you come for the appointment. If your engine has an overheating problem, DO NOT come for the appointment, because we can NOT tune a car that is overheating. The vehicle must also have at least a half tank of gas for the dyno tuning appointment. If you want calibrations for additional fuel types please be sure to properly prepare to safely evacuate the existing fuel your self (unless you want to pay us) and to provide sufficient quantities of the new fuel for the tuning session (we do NOT sell fuel). If you want a tune for race gas, it may be necessary that you schedule two different tuning sessions because your engine will most likely be heat soaked after the pump gas tune and will need significant time to cool off before a more aggressive race gas tune should take place. Always let us know you are looking to tune on 2 fuels. Never assume we have the time. Time may not allow for it on our end. Just let us know before hand is all I ask.

Do you have any Check Engine Lights (CEL), Codes, or Malfunction Indicator Lamps (MIL) on? Do not schedule a tuning appointment if your check engine light is on due to something that is mechanically wrong with the vehicle. Please have any mechanical problems diagnosed and fixed prior to scheduling your dyno tuning appointment. If your engine light is on and you are uncertain that it will be a issue come tune time please just contact us and we can let you know if your good to go or not. Any time that we spend fixing issues on your vehicle will cost you the same rate as our hourly shop rate. ALSO, issues big or small can not always be fixed on the day of your appointment. Remember we are a business. We have other things planned throughout our work day. We have to stay on schedule too.

When was the last time your fuel injectors were cleaned and checked for a system balance? IF YOUR VEHICLE (OR INJECTORS) ARE OVER 5 YEARS OLD, we highly suggest you remove your fuel injectors and have them cleaned and calibrated by an injector cleaning facility, WHICH WE DO!!!! Since when we tune your motor we will only be metering the Lambda (Air/Fuel Ratio) from one location with the assumption that all fuel injectors are flowing the same rate. If you have one poorly flowing fuel injector, then it is possible to further damage your engine by completing a dyno tune.

How old is your fuel filter? Stock fuel filters usually work well, but when you are flowing much more fuel through them, they can clog much faster. Please inspect and replace your fuel filter (if need be), any blockage in fuel flow to the engine will cause pre-mature fuel pump wear and can lead to engine damage if the fuel filter is clogged, causing a lean burn condition. You should not have installed aftermarket (higher flowing) fuel pump(s) if you see dirt, debris, or rust in the tank. If there is a rust in the tank, replace the fuel tank. You can destroy your new fuel pump if you leave junk in the fuel tank.

How old are your spark plugs? If you are unsure of when they were last changed, please replace them with new ones. Be sure to gap them appropriately and to use a small amount of anti-seize when installing the new spark plugs. Bringing extra spark plugs to your tuning appointment is never a bad idea. Sometimes while tuning it is possible to foul the plugs to a point where they will need to be replaced. New spark plugs are NOT included in the tuning rate. Please be sure to consult with us about the proper temperature range spark plugs that should be run in your vehicle if you are not sure yourself.

Can your vehicle drive straight? Is your vehicle alignment good? Wheels need balancing? The vehicle must be able to drive straight as with us you will be getting tuned on a chassis dyno. Bad alignments and unbalanced wheels can hinder the power output reading when tuning on a chassis dyno.

Can your vehicle drive onto the dyno safely under its own power? The vehicle must be streetable and the driveline and drivetrain systems must be in tact and safe. If you have any clicking CV joints then repair them prior to the tuning appointment. Be sure to inspect your wheel bearings as well. The same stresses that your vehicle sees out on the street are seen on the chassis dyno, although a failure on the chassis dyno puts your vehicle and us in a very unsafe environment until the vehicle and chassis dyno come to a complete stop. Also, with the rise of the "stance" scene we will be turning away any vehicles that have overly stretched tires and excessive camber. We will make the call here as to what is overboard. If we feel it is unsafe, we will turn it away.

How strong is your battery/alternator? Please make sure these items are strong and operating properly as they are required to work in order to tune the car correctly. 

If you are uncertain on sizing your injectors or picking the right plugs for your setup here is some info below that may help lead you in the right direction as to what you will need.

Injector sizing

240cc - 170-180 whp

310cc - 200-240 whp

370cc - 250-275 whp

440cc - 300-325 whp

550cc - 350-375 whp

650cc - 400-425 whp

750cc - 450-475 whp

1000cc - 600 whp

1200cc - 700 whp

1600cc - 850 whp

Spark Plug Heat Range

Resistor Style Plugs

NGK BKR7E good up to 500 hp

NGK BKR8EIX good up to 600 hp

NGK BKR9EIX good up to 700-800 hp

NGK R6601-10 good up to 1000 hp

Non Resistor Style Plugs

NGK BKR7E good up to 500 hp

NGK R567IA good for 600 - 1000 hp

Ok, One more time. We want you as the customer to go through the checklist so you do not waste both your time and ours. We do not always have the time to help the customer trouble shoot issues the day of their tuning appointment. So PLEASE take the time to look over your vehicle. If you are not sure that your vehicle is mechanically sound, it may be best to arrange your vehicle to be dropped off with us for a few days. This way we can go over the vehicle and make sure it is ready for tuning. This would also assure that we have the time to find and fix issues that arise along the way (cost applies).


8 out of 10 cars that we tune seem to need mechanical work and fixes before tuning can be completed 100%.

Please be prepared for such. Again it may be best to drop your vehicle off with us for a few days for your tuning needs.

**If You Wish To Make an Appointment Please Call (919)494-2711**