Toque

Guys:

Just thinking about this lately and thought I would post my thoughts on the subject. Please feel free to add to it or correct me if I'm wrong.

I don't think I have ever read this topic on the forum before.

Given that the dyno helps to dial in your Air/Fuel ratio you want to make sure that when you get a dyno tune you follow the below tips.

For max power most tuners will adjust your air/fuel ratio's to about 12.8-13.0 to 1. Air is 12.8-13.0 where Fuel is 1.

Rich Air/Fuel ratio - Too much fuel, and not enough air for max power.
Lean Air/Fuel ratio - Too much air, and not enough fuel for max power.

Running in a Rich condition is ok, and not going to hurt anything. Running Lean can cause engine issues for sure.


1.) Clean your Air Filter.
The more air you get into your engine, the more power you will make and the tuner will adjust the fuel trims to match the amount of air your getting into the engine. As your air filter gets dirty over time your engine will get "less" air, and start to run a little "Rich". Running your car Rich is totally safe. If you dyno with a dirty air filter and the tuner tunes your car with that amount of air your going to have issues the next time you clean your air filter. Your engine will now see more air and you will be in a "lean" condition with a clean air filter.

2.) Clean your MAF
Since the MAF reads the air velocity running thru it I can only imagine cleaning it would be a good idea.

3.) Make sure that your tire pressures are at the correct PSI
Set your tire pressures to the Manufactures recommended PSI before a Dyno tune. If the tire pressure is too low then your going to cause a drag and dyno less HP.

4.) Make sure that your running the correct octane fuel you normally run.
Your tuner will dial in various aspects of your car's computer tune. One of those aspects is your timing. They will look at your knock sensor and if it does not detect any pre-detonation then they will increase your timing for more power. If you go to a dyno tune and have increased your normal octane level you will make great power. Once you go back to your normal octane fuel your engine will start to knock (pre-detonate) and your knock sensor will detect this and pull timing from your car. This will reduce HP from your motor.

5.) Try to dyno on a cool/cold day.
Its always a good idea to Dyno on a cool day. Not just because your car will make the most power, but because the colder it is... the more dense air will get into your motor. Your tuner will set up your air/fuel ratios to optimum in cold weather. As the outside air temps get warmer your car will see less air because its not getting as much air as it did when it was cold. This will cause you to run slightly rich with is perfectly ok and not hurt anything. If you were to dyno on a very warm day and the tuner dials in your air/fuel ratios then you will likely run into a lean condition when the air temps outside get cold. On a cold day your engine will be getting much more air, and not enough fuel.


Hope this helps !
Toque

Bill Curlee

Some info I thought to add:

Add "ALL" the mods you can at one time and then TUNE.

Make "SURE" that you do NOT have any "CURRENT" PCM DTC's

Make sure your battery and chaging system is 100%

ALWAYS,,,,,, ask the TUNER if he"LOCKS" the PCM after tuning. If he does, your screwed!

BC

Toque

Good tips... thanks Bill !

All_Motor_C5LS6

Running too rich can wash out the rings

vettenuts

One thing I can add that bit me a few years ago. First dyno was with summer blend fuel, made a small change and wanted to see how the motor responde however second trip had winter blend fuel. Lost almost 5% on the entire curve because the winter blend has less BTU than the summer blend. On a later dyno, now with summer blend back in, curve was back to first dyno level.

Bottom line, with small incremental changes to the motor such as an electric water pump, the hp difference may get swallowed up in fuel differences if you are not aware of this.

zeke2u

Toque - I'm kind of new to 'vettes - I've only had my Z (2003) for a year - so forgive me for being so ignorant. But, I find it kind of hard to believe that the engine management system cannot adjust lambda by taking into account varying ambient temperatures or pressures. I do have experience with Saab engine management (Trionic/T5) and as much as 18 years ago Saab (T5) was able to adjust fuel accordingly with input from the MAP and a temperature sensor mounted in front of the throttle body. They changed the system, slightly, and went back to a MAF with the T7, but still had a temperature sensor which the computer used to calculate proper lambda (~14:1 ratio). It is very critical for turbocharged engines, because of the higher pressures involved, to have air/fuel ratios at lambda. Saab was able to do this with an ingeniously simple design using a minimum of external sensors and the spark plugs as the major sensor which gives combustion data. Although they went bankrupt, GM obviously liked their engine management philosophy - otherwise, they wouldn't be so reluctant to let the Chinese have it.

I love my Z and I think, on the whole, that it is one of the best vehicles ever produced in 2003. However, I would have thought GM would have at least integrated the engine management they inherited from the Swedes (Linkoping University) to their higher end vehicles like the 'vette or Cadillac.