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  1. #1

    Altitude and Horsepower

    After cruising around with Randy(TNrxp) we got to talking about speed and alititude. He said his stage 1 RXP was turning +2mph down in New Orleans which is pretty much 0ft elevation. He said water/air was about the same. Nashville is usually 95 air/85 water and 60% humidity during the hot months.

    I found this site.
    http://www.wallaceracing.com/braking-hp.php

    Nashville is about 500ft elevation. So this site says with 2229.3 horsepower (stage 2) and 500feet is a 3.44 HP loss.

    Riva shows the stock to be 208.9 HP at 8100 and the stage 2 to be 229.3HP at 8100.

    Being the stage 1 goes to 210.6 with a 1.7HP increase from stock and giving about 4mph. I would think 3.44HP drop is pretty considerable and probably could be a safe bet to say going 500ft you loose about 2-3mph.

    I was able to pull 69.7 this weekend crusing with Randy's (TNrxp). It was 95air, 85water and 60%humidity. Water got to high 70's in some spots but would change back, not enough to change the cooling.

    Anyone else have some numbers for higher altitudes ?


  2. #2

    Join Date
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    It def has an effect because I live at 3600 feet and can only turn 7500 rpms at 63mph on the gps.(stock 05 rxp)

  3. #3
    Quote Originally Posted by Ty
    It def has an effect because I live at 3600 feet and can only turn 7500 rpms at 63mph on the gps.(stock 05 rxp)
    Says 208hp (stock rxp) 3600 feet = 22.46 HP LOSS

  4. #4

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    yep it blows, the only advantage is cooler temps.

  5. #5
    captain obvious Lurker's Avatar
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    I remember seeing NHRA tables for altitude correction. The higher up you go the less dense the air becomes thus decreasing horsepower. This is the same reason the military started boosting plane engines like the p51 mustang. I remember reading something about there being a altitude controlled wastegate or something of that effect so that the boost would only come on when it was really needed in the high elevation

  6. #6
    JFizzleJR's Avatar
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    my altitude is 1300 ft above sea level and my stock 05 rxp averaged 67.4-67.6 mph with a best of 68.1 then averaged 68.2 with a best of 68.6 with rideplate holes filled. this was with 70ish° temps for water and air. by that calculator its an 8 hp loss for me. i still hit 8100 rpms in 60-70° weather tho. lately its been 7900-8000 in 80°. about how much speed do you think would be lost between being 200 hp or 206-208?
    Last edited by JFizzleJR; 08-07-2006 at 02:45 PM.

  7. #7
    Quote Originally Posted by Schlonky1
    my altitude is 1300 ft above sea level and my stock 05 rxp averaged 67.4-67.6 mph with a best of 68.1 then averaged 68.2 with a best of 68.6 with rideplate holes filled. this was with 70ish° temps for water and air. by that calculator its an 8 hp loss for me. i still hit 8100 rpms in 60-70° weather tho. lately its been 7900-8000 in 80°. about how much speed do you think would be lost between being 200 hp or 206-208?
    I bet if you saw 90degree air temps and warmer water you would be at 7700-7800 which is a good 2-3mph short. If thats as hot as it gets there I think your in good shape with your pitch etc.

  8. #8
    JFizzleJR's Avatar
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    Quote Originally Posted by Kinchyle
    I bet if you saw 90degree air temps and warmer water you would be at 7700-7800 which is a good 2-3mph short. If thats as hot as it gets there I think your in good shape with your pitch etc.
    i saw 7900-7950 in 95 air 80 water but didnt get any speed readings

  9. #9
    I live at 6000ft above sea level so i loose a sh1t load of power.

  10. #10
    Will work on YOUR ski for FREE! GeoRXT's Avatar
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    Im lucky I guess Im right at sea level!

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