RDX vs CX-7

[BaconNeggs]

This guys impression sounds pretty similar to what I felt when testing both out except for a few points. Its a fair review considering its from a honda biased site.

http://www.vtec.net/articles/view-article?page_number=1&article_id=635820


"...When we tested the RDX the temps were in the upper 80s to low 90s and humidity was quite high.
For the CX-7, the conditions were far more favorable - a sunny, clear day in the low 40s and very low humidity."

From my experience cars feel like they perform best around 65 degrees medium humidity, and from what people have said on the board it does better in the warmer climates. And at highway speeds it always feels eager to go faster so i don't get it when he says it lacks power.

[Alpha Wolf]

I have seen that before.

Not too bad for a Pro Honda review.

One has to wonder if the car tested had the required ecu and tcu updates reflashed into it.

Also as mazda has both a Ipod jack option and one version of the CD changer than will play MP3 disks those gripes of his saying they were not available are a bit off.

Not sure why he wants a hotter more humid day Mine seems to run better the colder and drier it is.

[fat tony]

From my experience cars feel like they perform best around 65 degrees medium humidity, and from what people have said on the board it does better in the warmer climates. And at highway speeds it always feels eager to go faster so i don't get it when he says it lacks power.



This doesn’t make sense. The cooler the air the better hence the intercooler to bring down the temperature of the air. Also the colder the air the more dense and that means there is more O2 in there so better combustion. I haven’t had the chance to drive the 7 in the winter but my last car that was forced induction it was always faster in the cold (it had an intercooler also). I had it on the rollers a few times the club used to meet every year the car would always knock out more ponies if it was colder.

[HeavyH20]

I think if Mazda simply tuned the CX-7 a little tigher, it would come close to matching the 6.5 0-60 number the Acura pulls off. There is better than a second plus improvement in the CX-7 with a simple transmission tune from the embarrassingly slow 7.9 seconds it currently takes to reach 60 mph in drive.

[BaconNeggs]

Everything has an ideal operating temperature range. Take simple physics, electricity flows better through a wire when its cooler, but when its too cold electricity doesn't flow at all. Another analogy might be why they don't run marathons in the middle of winter. Runners will expend energy raising their body temperature. People still go out to jog in the cold, but its less than ideal.

When it comes to cars, thre's also the heat transfer of combustion. Lower air temperature means bigger difference of temperature change to combustion in the milliseconds that is one engine stroke. That means lowered efficiency.
Think about it, if cold air meant better performance why wouldn't race car engineers put refrigerant somewhere along the air intake process? It wouldn't be a hard thing to do.

[Alpha Wolf]

I have raced my Drag cars all over and the same car runs 10.30's on a cool 60 deg day with low humidity at Baylands runs 10.99 in Sacramento on a 104 deg day. By your logic of heat transfer and thus loss of efficiency it should run faster at Sacramento.

My FZ1 liter bike makes noticibly more power at sea level on a cold day than at the same level on a hot one.

Yes if the air and block are nearer in temp you loose less thermal energy to the air. The power loss here is trivial when compared with the other factors which affect engine power output. Air density, etc...

But your radiators and intercoolers loose efficency. Both of these work better when the difference between their core temp and ambient air temps are farther apart.

The temp and altitude also affect air density so you will be starting with less atmospheric pressure to compress on a hot day vs on a cold one

Cold Day = More Power
Hot Day = Less Power

Higher Altitude = Less Power
Lower Altitude = More Power


Yes they do that is what the cold spray units are for. They spray cold gas or water onto the intercooler to increase its effectiveness. Also I used to place iced damp cloths between the intake runners of my car to cool the charge.

The factorys do not do this because it is too complex and too expensive and is not necessary to reach normal power levels of normal cars.

[BaconNeggs]

You're missing the whole point about temperature range. A cold day in california is 60 degrees, which I originally said is ideal for running a car. The article was running the car at 40 degrees, thats not far from freezing. What I'm saying is that running a car at low temperature is detrimental as high temperatures. I would say cars are calibrated to run best around 60-80 degrees.

Even with water sprays, do you think the intake air ever got below say 55 degrees? no becuase they're used when the temp is extremely high.

I was talking about refrigerant being used on 10 million dollar race cars, if it was an advantage to have super cold air, they would use it.