How heat/humidity effects dyno results
 

I just had headers installed on my car and the resulting dyno numbers are - let us say - less than impressive. Bottom line is I LOST about 25 HP. :) I went from 422HP down to 395HP.

However...the first dyno was taken at ECS in New Jersey in probably 50 degree weather. This dyno, however, was taken during monsoon season in Phoenix, so the temperature was between 100 and 105 degrees with 80% humidity, at least.

So, my question is simple...can the environment effect dyno results this much? I can't imagine that installing headers would provide such a significant decrease in horsepower and torque.

Thanks.

I can't speak to you mods in question, but yes, temperature will make a big difference.

It absolutely makes a differance. Temps today in Palm Beach County were in the mid 90's with what feels like 150 humidity. Seat of the pants feel during on-ramp blasts is markedly different at 7am vs. 2pm when it's ungodly hot. The differance is less dramatic in my normally aspirated DD a4 than my blown m6, but I'm sure that I don't get down on the DD like I do the m6! I know it sounds a little silly but I've postponed my dyno-tune till it cools off a little down here. Between the temperature and the fact that my tuner uses a Mustang rather than Dyno-jet, I'm concerned about posting a lower number than I might be expecting! I know that whatever the number is, it's just a tool for the tuner but I'd like to post a higher # if I can. Is that retarded?

I knew that it made some difference, but I wasn't aware that it could take off 25 horsepower or more, though. I guess I need another tune some time this winter to get a more accurate measurement of its improvement after the headers install.

Thanks.

Probably but we forgive you.

Difference - yes.

Too the degree (pun intended) noted - No (but there will be some).

Was one dyno corrected numbers and the other not :confused:

25hp? That's nothing! We've lost more than 70rwhp due to heat soak, 98 degree & 100% humidity Florida sauna. We just finished dynoing a project car at 553rwhp after 2 hours of pulls and retunes in the above weather... the first pig rich 12 degrees of timing pull was 480rwhp... by pull 4 it was 549rwhp, still rich.

Several pulls and retunes later, we sprayed meth, leaned it out and added 5 degrees of timing - it should have been over 600rwhp, but the best we could do at that point was 553rwhp SAE corrected in those unbearable condition.

Nice cold, dry weather and you get big numbers

Stephen :cheers:

Where did you dyno at?

Last time it was cool out a few months ago, Extreme kept saying they were too busy for a dyno run. I called them at least 3 different times and finally gave up.:(

Xtreme Motorsports on S. Smith Rd. in Tempe. Is that the place that you're referring to? They have been pretty busy...my car had been there for a few weeks, so those customers, I'm sure, have priority for tunes after any work that they had done.

6% difference, NBD, definitely weather related. A very basic equation for power is Hot temperature(combustion temperature)-Cold temperature(outside air temp) divided by a constant of some sort will result in your power potential. Get it dynod in January and you will be quite pleased.....:cheers:

Wow. Okay, this actually makes me feel a little better about this situation, as it's true that heat and humidity can not only make a difference, but a significant difference, in dyno numbers.

I'm sure Stephen would know for sure, but I have heard that you lose about 10 Rwhp for every 10 degrees the temp goes up :cheers:

As the humidity goes up I notice a huge SOTP difference in power in my maggie setup. The difference from going to work and coming home from work is at least 25hp if not more. NA I didn't notice a huge difference but FI I do. I can also see it in the boost gauge. I loose about a pound of boost in mid 90 degree humid air.

I bought my Maggie car from a guy and the dyno sheet showed 483rwhp on a 103 deg. day. I bought it in Feb. and took it back to the same shop, 21stCMC and they dyno'd it at 520rwhp on a 65deg day. It showed a bit lean at 12.8:1, so they richened it up to 12.0:1 and it came down to 510hp. Now it is summer again and it is running pig rich because they changed the WOT/VE tables and not the temperature vs. fuel tables. I haven't taken it back, but I will have to because there are black dots all over the back end from it and I know I am losing more power than I should due to the fuel overage. So I would recommend that you make sure they tune the fuel in the temp/fuel table so your fuel ratios stay proper year round.

Temp/Humidity effects
 

Talk to any private airplane pilot and you will find that Temperature and Humidity are one of the most influential effects on a small airplane's ability to take off from an airstrip. I have been told that if at sea level and the temperature is in the triple digits and the humidity is in the single digits, the airplane performance is "de-rated" due to the Temperature and Humidity. So I am sure that a land based motor would be effect exactly the same way. This is also important for you fellas who think their 'vettes can fly! :crazy:

Did you have headers on during the first dyno runs? If not then that is actually a 45 hp difference. You lost 27 hp from the original dyno pull and you lost about another 20 hp that would have been the gain from the headers. So that is about a 10% change. So I guess the question is can dyno numbers vary as much as 10% due to extreme changes in weather?

I did not have the headers installed during the first dyno run, no. Thanks.

You don’t know what you gained or lost unless you did a dyno run on that day before and after the header install. That is basically what a dyno is good for, to measurer changes that you do on the same day and dyno. There is not too much value in comparing dyno numbers on different days with different dynos with all the variability between them and the environment.