timing vs altitude
06-19-2011, 11:15 AM
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timing vs altitude Does anyone live in the 4000-6000 ft range and have any advice as far as timing advance and other tune parameters are concerned? I own an 08' GXP LS4 basically stock minus a k&n intake and a mail order tune from Overkill motorsports. The base tune I'm certain is for a stock intake and sea level conditions and I'm wondering what tables should be tweaked to compensate for the changing altitude. Right now the max MAP kpa is like 101 which isn't seen here, max hovers around 86 kpa. Also the MAF data I'm pretty sure is reflective of the stock intake so I'm not sure the tune is, or needs to, take into account the higher (lb/min) flow from the aftermarket intake.
Last question is about timing, since the air is significantly thinner at this altitude, I've heard timing can and should be advanced anywhere from 4 to 10 degrees in some circumstances. This was coming from a local high performance shop with a respected tuner. Issue I have now is do I make this easy on myself and dyno tune it to tweak, or do I keep resending the ECM, TCM back to Overkill for adjustments. Cost to ship is 18 bucks, 50 for lifetime tuning. Dyno is at least 150 up front to unlock the car with HP tuners and then dyno time, not including tune rates. Not wanting to drop a ton of money here.
Thoughts?
Last question is about timing, since the air is significantly thinner at this altitude, I've heard timing can and should be advanced anywhere from 4 to 10 degrees in some circumstances. This was coming from a local high performance shop with a respected tuner. Issue I have now is do I make this easy on myself and dyno tune it to tweak, or do I keep resending the ECM, TCM back to Overkill for adjustments. Cost to ship is 18 bucks, 50 for lifetime tuning. Dyno is at least 150 up front to unlock the car with HP tuners and then dyno time, not including tune rates. Not wanting to drop a ton of money here.
Thoughts?
06-19-2011, 01:04 PM
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No issue with timing and altitude. At alt the engine will not be able to ingest as much air as down low. The PCM will be all over this and not hit as higher airmass cells in the timing tables. The PCM does calculate the air flow model taking into account the barometric pressure too.
