Gymkata

Thoughts? I didn't even know about M235I until I saw this thread over at clublexus.

Is altitude really that big of a factor?

http://www.clublexus.com/forums/is-f...i-vs-is-f.html

berny2435

yes, Altitude can be a large factor in performance of a NA car. Google Atmospheric pressure. You basically loose compression ratio at higher elevations. Loss of compression ratio = loss of power. Boosted cars can often make up for that if they can automatically adjust boost pressure on the fly via ECU or whatever your wallet can afford for aftermarket mods. MAP pressure sensors and electronic solenoids for waste gate control are great things! Boost by gear, boost by rpm, min or max boost whenever are a simple reality now.

suprmonky73

lol brand fanboys. lots of butthurt

tnE30fan

It's probably more correct to say that the intake charge is less dense in higher altitudes ("thinner" air) rather than saying it's akin to "losing compression ratio". Less oxygen in the intake charge = less fuel you can burn = less power. Compression ratio is a direct function of stroke in a piston engine, on the other hand. (Or more specifically, combustion chamber volumes at BDC and TDC.)

berny2435

yeah, I didn't word that well. I meant to say there is a correlation there but not a physical change in the motor obviously.

I agree with you. The Naturally aspirated car, only has atmospheric pressure (and the amount of o2 in it) to work with while the boosted car can make up for a loss of atmospheric pressure. loosing 1psi of atmospheric pressure b/c you are XXXX feet above see level puts less dense air in the chamber. NA motor is essentially compressing less air/o2. Loosing it's ratio of compressed air at higher altitudes. The boosted car will typically shoot for it's PSI numbers regardless of where it's at.

NuncoStr8

That was pretty funny. Bunch of pots calling the kettle black on the Lexus forum, but yeah, most definitely a lot of BMW fanboys on their forum. Surprising, really. You wouldn't expect to see fanboys on a site called ClubLexux.com, nor on 2Addicts.com

And yes, altitude does make that much difference.

deepbluejh

So yes... altitude does play a factor, but don't ignore the fact that BMW turbo 6s are hilariously underrated these days as well.

berny2435

Not sure how many times they tested it either, but the other thing that these car reviewers grossly underestimate and don't talk about is tires. 4 year old Bstone RE050A Runflat crusties vs brand new michelin super sports(non-runflats) is going to make difference. More so on a track, but can make a difference in a drag race as well.

deepbluejh

To be fair, it looks like they just rolled onto the throttle instead of launching the cars - which is going to reduce the impact of the tires off the line.

yamahaSHO

Boosted cars lose power too (SC on par with NA, Turbo not quite as much loss); they deal with the same lack of atmosphere, so for them to compress it, a turbo works harder and gets hotter.