3.4 Dme

[Topless]

" The dyno say I have 180 hp on the wheels @ 5500 feet altitude asl. (Yes we all live here very near the clouds...lol)
Do you perhaps know if this is more or less what the 996 shows on the dyno. I know the engine is rated at 300hp."

Ouch! Sounds like you have a pretty big tuning window still. My bone stock 2.5L is about 175RWHP at 1400' elevation. Only engine mod is a clean air filter and UD pulley.

... also the fast color: Guards Red.

[insite]

Originally Posted by Topless

Ouch! Sounds like you have a pretty big tuning window still. My bone stock 2.5L is about 175RWHP at 1400' elevation. Only engine mod is a clean air filter and UD pulley.

he's at 5,500 feet above sea level. at one mile, HP for a normally aspirated engine drops by about 20%. he should be around 195 - 205 RWHP with that engine at that altitude.

[Topless]

Originally Posted by insite

he's at 5,500 feet above sea level. at one mile, HP for a normally aspirated engine drops by about 20%. he should be around 195 - 205 RWHP with that engine at that altitude.

Hi Kevin,

I was figuring a well oiled 3.4 at sea level to be about 260rwhp and at 5500' to be around 217rwhp. Here is my altitude calc: 5.5 x .03 x 260= 43hp loss. Lots of tuning room if he is only getting 180 now.

[insite]

topless -

your calculations aren't right. you're just assuming a 3% loss for each 1000'. the pressure drop is NOT linear.

the SAE correction equation is:

cf = 1.176 * ((990/Pd)*(Tk/298)^.5)-.176

one over this cf yields the percent power available at that pressure. Pd is the pressure of dry air at altitude, and Tk is the temperature in degrees kelvin.

i'll use 15 degrees C since that's what my altitude pressure tables are calculated for. at 5,500', the pressure of dry air is about 820mb.

if i plug all this into the equation, i get a cf of 1.22 or an HP yield of 82%.

that means that if your assumption of 260RWHP at sea level were used, the HP available at 5,500' asl is 213.

FYI, Raby says he usually sees about 240RWHP from the 3.4L. this would yield 196RWHP at that altitude.

[Topless]

Originally Posted by insite

topless -

your calculations aren't right. you're just assuming a 3% loss for each 1000'. the pressure drop is NOT linear.

the SAE correction equation is:

cf = 1.176 * ((990/Pd)*(Tk/298)^.5)-.176

one over this cf yields the percent power available at that pressure. Pd is the pressure of dry air at altitude, and Tk is the temperature in degrees kelvin.

i'll use 15 degrees C since that's what my altitude pressure tables are calculated for. at 5,500', the pressure of dry air is about 820mb.

if i plug all this into the equation, i get a cf of 1.22 or an HP yield of 82%.

that means that if your assumption of 260RWHP at sea level were used, the HP available at 5,500' asl is 213.

FYI, Raby says he usually sees about 240RWHP from the 3.4L. this would yield 196RWHP at that altitude.

Of course you are right that the alt./air pressure relationship is not linear. Your pressure figures are good. I have seen several 996 3.4L dynoed in San Diego between 255-260 rwhp so I think those are good numbers for a healthy motor near sea level. Jake's shop is at 1500' or so, which might explain his numbers. Any way you slice it the OP should have some hidden juice somewhere in that motor even at 5500'.

[PleGrange]

Thanks Gentlemen,

I will look into the HP figures.

Regards
Pieter