Down 30 HP on the Dyno,What are your Thoughts?
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From: Shelby Twp. Mich
Down 30 HP on the Dyno,What are your Thoughts? Well my 408 was was retuned today and down 30 hp and 10 Footpounds of torque from last year on the same Dyno and Same tuner,Only the weather was 10 degree's cooler and Baro higher this year.Tuner said timing was on and AFR was dialed right in to 12.6-12.8.He said its running great from what he could see.My engine builder and I feel like its only running on 7 cylinders.My Tuner said it could be possibly a bad injector(Maybe pluged somewhat)maybe Bad Fuel? Who knows.Could it be a bad spark plug?Because my HP Tuners does not show number 8 in current firing cylinder.I know the Coil and wire is good by checking it the old way.That thing shoots a spark about 3 inches long could go farther if I let it.Could a plug be to week in number 8 to show not currently firing?What do you Guys think I should look for? Thanks for the Help
Can you post the dyno graphs? Preferably with both the before curve and after curve.
How much PTV clearance did you have? What are you spinning the motor to? Ever hit the rev limiter at a high RPM?
So many things it could be. Need more info.
How much PTV clearance did you have? What are you spinning the motor to? Ever hit the rev limiter at a high RPM?
So many things it could be. Need more info.
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what was the humidity difference ?
Originally Posted by Pro Mouse
Well my 408 was was retuned today and down 30 hp and 10 Footpounds of torque from last year on the same Dyno and Same tuner,Only the weather was 10 degree's cooler and Baro higher this year.Tuner said timing was on and AFR was dialed right in to 12.6-12.8.He said its running great from what he could see.My engine builder and I feel like its only running on 7 cylinders.My Tuner said it could be possibly a bad injector(Maybe pluged somewhat)maybe Bad Fuel? Who knows.Could it be a bad spark plug?Because my HP Tuners does not show number 8 in current firing cylinder.I know the Coil and wire is good by checking it the old way.That thing shoots a spark about 3 inches long could go farther if I let it.Could a plug be to week in number 8 to show not currently firing?What do you Guys think I should look for? Thanks for the Help
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Oh yes it can. Especially if the dyno is above sea level by any meaningful amount.30-50% swings in humidity can move HP and TQ buy as much as 10-15%.
Originally Posted by PewterZ28
Humidity is not going to make a 30 rwhp difference! 
Originally Posted by LS1curious
Oh yes it can. Especially if the dyno is above sea level by any meaningful amount.30-50% swings in humidity can move HP and TQ buy as much as 10-15%.
by my math the difference between 0 and 100% humidity while keeping everything else constant causes only about 0.9% airmass difference. so 30hp sway is only only doable if he's got about 3000hp to boot
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No math to post.
Your humidty correction factors need larger corrections with altitude. As humidity goes up timing requirements for the same output also go up.
Ie at 2000ft above mean at 40% humidity a car might want ot need 29 total. the same car at the same altitude might need 32total at 60% humidity.
Do a bit of reading on the GM Ion sensing Ignition for some enlightenment on the subject manner before you tout off about how correct you are.
So if the car was above sea level and the humidity swing was large enough the timing and fuel tune up would need to change to compensate for that.
there are other factors such as ignition pickup accuracy and converter slip that could have a fairly dramatic impact on the output as well.
If the trans fluid temp shoots up from 160f to 210f the converter will allow for more slip with lower fluid viscosity.
this is why good controls are the hall mark of good dynomometer readings. Consistency is the key here.
Your humidty correction factors need larger corrections with altitude. As humidity goes up timing requirements for the same output also go up.
Ie at 2000ft above mean at 40% humidity a car might want ot need 29 total. the same car at the same altitude might need 32total at 60% humidity.
Do a bit of reading on the GM Ion sensing Ignition for some enlightenment on the subject manner before you tout off about how correct you are.
So if the car was above sea level and the humidity swing was large enough the timing and fuel tune up would need to change to compensate for that.
there are other factors such as ignition pickup accuracy and converter slip that could have a fairly dramatic impact on the output as well.
If the trans fluid temp shoots up from 160f to 210f the converter will allow for more slip with lower fluid viscosity.
this is why good controls are the hall mark of good dynomometer readings. Consistency is the key here.
Originally Posted by RedHardSupra
care to post your math?
by my math the difference between 0 and 100% humidity while keeping everything else constant causes only about 0.9% airmass difference. so 30hp sway is only only doable if he's got about 3000hp to boot
by my math the difference between 0 and 100% humidity while keeping everything else constant causes only about 0.9% airmass difference. so 30hp sway is only only doable if he's got about 3000hp to boot
