Can a mod sticky this?
Eh...... Anything you do isnt going to be good on the tranny. I would say 1500 rpm's as a safe bet. Some people might tell you 1.6-2k. I would try to keep it on the lower end... rather safe than sorry and ANY powerbreaking, even if its mild, should help your start and your time.Originally posted by smokeU6s@Jul 12 2005, 03:42 PM
Im going to be racing my friend at Atco later in the summer most likely and I have a question about power braking. What would be a good launch rpm for the 5sp atx? While not being too tough on the tranny?
to power brake properly apply brake and apply as much gas as possible without the engine lugging or over powering the brakes.let it shift at 6.5 or around there. shifting earlier your gonna be slower. redline is where to shift. you wont hurt anything bringing the duratec to 6.5 it can handle alot more.so if i do power braking, do i rev it up to around exact 3k then let go of the brake right there... or if i rev it up a little higher and then when it drops down to 3k i let go of the brake?? and if i use the "M" at whens a good time to shift? i usually do around 5.5k to 6k no higher than that b/c 6.5k is the redline.....[/b]
You just need some practice, plus altitude doesn't help. Is yours stock? What fuel were you running? How many miles on the car? How many miles since last oil change? Track temps?Dang, I must be really horrible it seems. 16.49 @ 83+ mph at Bandimere Speedway in Denver. RT .574, 60' @ 2.2. Launched at 5k rpm, dumped the clutch (cringed as my rear diff slammed), and the whole drivetrain just bogged down (prob from too much gas). It was my first time, I guess I should take it out and practice.[/b]
Here is a link to the current SAE standard http://www.mazda6tech.com/images/dyno/sae.pdfAltitude does have an effect, especially since you are in the mile high region. But since you have a turbo it shouldn't effect you as much as the NA cars, aka Charger R/T and Impala SS. I think the rule goes for every 1,000 ft above sea level expect about 3-4%% loss in HP on NA models (Technically it's not altitude but air pressure, but they tend to go hand in hand in our world). Below is the SAE correction factor for Horsepower dependent upon intake temperature and air pressure.
The SAE correction factor can be approximated using this equation:
CF = 1.18 * (29.235 / Bdo) * ((square root (To + 460) / 537) - 0.153)
where CF = the correction factor, Bdo = the dry ambient barometric pressure in inches of mercury (in/Hg), and To = the intake air temperature in degrees Fahrenheit
Sea Level barometric pressure is about 29.235 in/Hg. So if a engine makes 100HP at sea level on a 77 degree day, it would make 95.96HP at a 1000ft elevation (1 in/Hg drop in barometric pressure), or a 4.04% loss in power just for 1000 ft.
Other factors that will cause power loss are high temps and high humidity. Now although a turbo shouldn't be as effected by elevation/air pressure as NA cars, it can still lose power (close to the amount a NA car can too!) if the turbos efficiency for boost is already tapped at sea level. In other words if the turbo is making 16PSI of boost at sea level and the turbo and controller are only capable of doing 18PSI consistently and under control then at high altitudes you will probably be losing almost as much power as an NA car since the turbo is unable to overcompensate enough for the lower air pressure (of course I may have read that wrong).
Below is a website to do power conversions based on altitude, humidity, ambient temp, abient barometric pressure, etc. :
Horsepower Altitude Conversion
Based on your info, I did two calculations on the site (one at 24 in/Hg based on altitude, one at 29 in/Hg based on weather channel reading). Since you said it was raining I set the humidity high at about 90% and temp at 90 degrees. Based on those numbers, HP loss on a NA car would range anywhere from 28.2% to 43.2%. So a 345HP Hemi would have been running at the equivalent of a 196HP to 247HP car. That's quite a loss! And judging by the times they ran and the heavy weight of their car, that sounds about right. Also their runs should be fairly consistent being automatics.
Sorry about the incorrect calculation. That was a cut and paste directly from Neuspeed's site that was explaining SAE adjustments and formulas. So if there is an error, it's on Neuspeed's part.Here is a link to the current SAE standard http://www.mazda6tech.com/images/dyno/sae.pdf
Your formula is not quite right, corrected:
CF = 1.18 * (29.235 / Bdo) * square root [(To + 460) / 537)] - 0.18
You can't broad brush a turbo like that, assuming all turbo's are at limits of back pressure and efficiency at sea level. Best to just add boost pressure to top and bottom of the dry pressure ratio ... close enough.
When I use that calculator (by Whadil?), I get about 22-25% power loss in this case. You can't enter a low ambient (24") and a high elevation. If you enter 5700 ft, you then enter the local station barometric pressure from weatherchanel, which is an adjusted equivelant sea level pressure.[/b]