In warm temps....

[kchummer]

my 2004 h2 w/ 30k on it seems a bit sluggish after approx. 10 mins. of ridin around..?? When leavin it seems normal, but seems to lose power if A/C is on or is around 90 out....Is it normal or could something like ig. switch be doin it...?? also battery light stays on for 5 sec. after shut off which ive read does relate to switch.....my only mods are Magnaflow exhaust and throttle body spacer...I was thinkin maybe to large exhaust when air is so minimal at 90-100 causes a little decrease in performance....

[kchummer]

no pros ayy....Ill look at forums elsewere

[HummerJim]

Yes, the air mass sensor senses the hot less dense air and after the engine gets warm the performance is not quite what it is in 80ish weather because timing is held back and fuel is sprayed in at a lesser rate - there is a technical discussion about this in the search - but it boils down to the air mass sensor and the ECM. Also, a larger diameter exhaust will trick the ECM into thinking the air is even less dense and cut back fuel delivery more - there's two posts on that too. When I drove through Nevada at 110F last year I noticed the same thing.

[kchummer]

Tx Jim!! makes perfect sense...

[IRA51]

I notice it all summer here in hell with a stock exaust and airbox.

[Big.Z.hummin]

mine does that to when in the 90 to 100 degree range. i lose acceleration and when i step on it my stock air intake screams like a biotch. its kinda annoying but we dont have to many days over 90 here in nashville

[PHATBOYPIMP]

I didn't have this problem until I read this post.....lol

[porschett]

We average temps in the mid-90's, with heat indexes averaging 105 to 110. I've never experienced this.

[kchummer]

u may not know wat its capabilities are....lol

[porschett]

Originally Posted by kchummer

u may not know wat its capabilities are....lol

Let's see, 3 Porsche's, a DB9, 18 years racing, think I may have an idea or two about the capabilities of a truck!

[HummerMann]

Being a Northerner I don't notice this much, BUT when I was down in Langtry, TX last month in the middle of nowhere in 95F temperatures, I DEFINITELY noticed this phenomenon. It reminded me of being in the mountains - I agree that it all has to do with air density.
Hot air is less dense, so you produce less horsepower. When I used to drag race we'd place ice on the intake manifold and in a screen by the air cleaner to make the air more dense. If you use the standard Morton/McFaren horsepower/air density chart - 95 degrees gives you 12% less horsepower than on a standard day which is used by Detroit to measure engine horsepower. A standard day is sea level, 59F and a barometer of 29.92. Yep I have a graduate degree in mechanical engineering. SO 12% is a loss of about 36 horsepower.
Then you can complicate it even more using the Military Standard Hot Day which is used in certifying Humvee/H1 engines.
http://www.eng-tips.com/viewthread.c...=231931&page=2

[kchummer]

Originally Posted by porschett

Let's see, 3 Porsche's, a DB9, 18 years racing, think I may have an idea or two about the capabilities of a truck!

I was bein fececious...(? SP ?)....lol.....

[IRA51]

it is a fact that high underhood temps on a vehicle with an IAT sensor will suffer a loss of power and preformance in high heat. last week I had 165 degrees under hood temp (measured next to the air box ) all my vehicles run stronger in the winter here in Phoenix. If I drive up to Flagstaff in August you can feel the differance in power and preformance . and it is not just the altitude all my baro's are working fine.