How much, if at all does high density altitude numbers affect a blower or nitrous or a combo of both setup? I know NA, it will hurt your HP the higher the DA goes, but was just wondering about a boost and or nitrous setup. Thanks.

Ken R.

 

You'll still lose hp but not as much. There's less air to compress so to get the same level of performance, you would need to increase the amount of boost the engine receives to force more air into it. Trying to increase boost especially with a blower also builds more heat plus causes other problems.

NOS is a little different since it contains the same amount of oxygen for the engine to burn with the fuel no matter what altitude it's at. If a NA engine makes 500 hp at sea level but only 400 hp at altitude, a 200 HP NOS shot will still only give it 200 more HP. The engine will still be down 100 hp because of the altitude.

 

I can't tell you how much, but I can tell you DA does effect any motor, even
boost.

Just look at how much slower the top fuelers run way up in the hills.

 

Yeah Tony Schumacher ran a 331 or something nuts at Mile High with a 8400 DA... the track conditions slowed those boys down more than normal... BUT they get 90% Nitro vs. 85%, unlimited blower speed vs. a limited blower speed of 150% of RPM but they also get less GPM of fuel 66 at altitude and 70 normally.

There is a index for correcting forced induction cars with high DA's that NHRA uses compared to NA cars, it has a much smaller factor.

Compare a 207mph Pro Stock Car in good air to a 193.7mph Pro Stock car at a 8400 DA, then again they build motors especially for the high DA races like that...

Bret

 

Nitrous motors still slow down in bad air. Only a PORTION of the total intake charge going into the cylinder is supplied by the bottle, the rest is still from mother nature.

 

Little calculator

 

Thanks for the info guys.

Ken R.

 

The rule of thumb I've always seen used is a 3% power loss for every 1,000 feet of elevation for naturally aspirated engines.

Supercharged engines suffer as well, and almost as much as naturally aspirated engines. Since a supercharger's speed is linear in relation to engine rpm, boost is going to drop over the entire rpm range as the air gets thinner. In other words, you can't maintain sea level boost levels at higher altitude without changing pulleys to compensate. However, if you do, you should be able to maintain the same boost response you had at sea level, relative to engine rpm.

Turbochargers, on the other hand, can often automatically adjust to changes in altitude because their speed is independent of engine rpm and limited by the amount of exhaust energy bled off by the wastegate. In other words, they can just spin faster to make the same amount of boost.

For example, if your wastegate is set to open at 10 psi at sea level, you'll probably still be able to make 10 psi without changing a thing, even at 6,000 feet, because the wastegate simply won't open until you hit 10 psi or redline, whichever comes first.

Boost response will certainly suffer somewhat, because it will take more engine rpm (exhaust energy) to produce the same boost levels, but you should be able to maintain your maximum boost level no matter what the elevation, assuming your turbocharger is sized properly and isn't being run out of its efficiency zone at the higher speed it will be turning, and assuming you don't run out of engine rpm.

 

Just pay attention to pressure and temperature. Standard atmosphere is 29.92 in/Hg and 15C or 59F. Lower pressure and higher temperature will cause a loss in performance. So if it's 59 degrees and the barometer is at 29.92 in/Hg and you are at or below sea level with a relatively low humidity you will see your best performance, more so if the barometer is higher (29.92 in/Hg +) and the temp lower. This condition will simulate that you are at below sea level altitude.

The more air you can induct the more power you will make, as most of us here know already, cold temperatures and high pressure will condense the air for your benefit - the super charger of mother nature.

So to answer the question, it does affect FI cars to an extent, more on blower cars than turbo, as jimlab explained. N20 cars while spraying will not see so much of a loss but there will be a little, I like to think of Nitrous as "weather in a bottle" if it is hot and muggy outside. It cools the air and increases cylinder pressure, just what high pressure and cold air would. But N20 will still have the added benefits of it's purpose.


P

 

On the subject of blowers, do centrifugals fair better at higher altitudes than blowers of the positive displacement variety?

 

For example, I lost 18% of my power to the wheels coming down here to Albuquerque from Tacoma, WA. 7,000 DA sucks.