Can you explain the physics behind it?

 

From my understanding the srt4s computer shoots for torque targets. It's common for srt4 owners at higher altitudes to see more boost as the computer attempts to compensate for the thin air. Apparently this caused quite a stir when the car was released, owners at sea level were wondering how come their cars weren't making as much boost as ones at high altitudes.The computer shoots for an absolute pressure (atmospheric+manifold boost) and adjusts the wastegate accordingly, as opposed to a merely running say 15 pounds into the manifold regardless of what the density of the air is at that altitude.

 

Turbo at altitude: Exhaust gases spin the turbo. Since there's less atmospheric pressure, there's less pressure at the outlet of the turbo. This leads to a higher differential pressure across the turbo blades, so the turbo spins faster, which leads to boost that tends to compensate for altitude.

In simpler terms, we know the air is "thinner" at altitude. This leads to the turbo spinning faster, since the air that the turbo is pushing against is "thinner" so for a given rpm, the turbo spins faster than it would when at sea level. This leads to more compensatory boost, even though the air is thinner. Turbos, rather than superchargers, are used in airplane motors for this very reason - inherent altitude compensating boost.

The same principle applies to the centrifugal blower, but since it's tied to motor rpm, it doesn't benefit as much. A roots style blower doesn't benefit much at all, unless it's oversized and tends to use the blowoff valve a lot at sea level.

 

An old modified turbo Subaru can beat LT1 Camaros through certain mountain passes in CO. Good times when all NA cars are down 1/3 in horsepower.

-B

 

But at altitude there is less pressure at the inlet of the turbo also, making the turbo spin slower. How does this affect things?

What do you think of the new Z06? 500 horses from a 7.0 liter V8 and 3160 lbs. Should be a screamer! Are you going to trade up?

 

Yes, n/a cars suck at altitude. I've learned this first hand against turbo cars many times. I race at 4000-5500' above sea level.

 

But at altitude there is less pressure at the inlet of the turbo also, making the turbo spin slower. How does this affect things?

I think that the turbo would take longer to spool, since less initial power means less initial flow.

What do you think of the new Z06? 500 horses from a 7.0 liter V8 and 3160 lbs. Should be a screamer!

Yes, wonderful stuff. The rumor is it will have Ti rods, and as you've mentioned, a 427, with a near 7K redline.

Are you going to trade up?

Not anytime soon. I still have to pay off my Z06, and even if I did it early, I won't buy the 1st year of any vehicle. My wife's '98 is 1 year after the C5 intro, and my Z06 is 1 year after the Z06 intro. On top of all that, I'm somewhat torn by the new styling. I immediately *loved* the C5 styling compared to the C4 stying, but I don't have the same sense of "WOW!!" when I see the C6.

My guess is that the 2nd or 3rd year of the new Z06 will bring another 15-20 horse gain, just like it did from '01 to '02.

 

Finally got a race in with this kid. We went from a stop once and Two 20mph rolls. My traction was terrible to say the least with balding all seasons. This was a while ago, and I forgot to post it.

Race one from a stop: Went on the third horn, this kid being honest as usual went just after the 2nd horn, I sat and spun, and couldnt make up the difference.

Race two 20 mph roll: Third honk again, again he went just after the 2nd, I spun but began gaining, but decided just to shut it down.

Race three 20 mph roll: This time we went on ready-set-go since counting was too difficult for him. Both hit it at the same time, minimal spunning, I pulled hard on him in 1st, the 1-2 shift I gained a few more cars, he was 4-5 cars back before he completely gave up.

In my book he redlighted the first two, but some call it a loss. Either way I dont care, the only one that mattered to me was the third race that showed the cars ability equally. BTW on the third race he claimed to "didnt know we were racing" True Character this kid. I've vowed to never race him again for his ethic problems.

SRT-4 has certain things done which I cant really remember, but I know it had higher boost, etc, etc. Claims to beat everything, LS1's, etc, but doesnt every SRT-4?

-Dustin-

 

Get some nittos drags on the back for playing around if not everyday driving.
Those goodyear are huge money you have them all around now..?
I woudl burn them off in a season better to use nittos .And then get a stall , nice stall and your gears woudl be ok..I like my 3.42 but some guys like 3.73 and even 4.10.I think my 3.42 and 2800 vig will be about perfect combo for me.And plenty since the wife drives this car too.Or just do what I did and slap on a nice nitrous system and say goodbye with your now estimated 500 hp with a 150 shot as figure you should have around 350 engine hp.No stock turbo srt 4 or dsm can stand up to that hp level if you had that in your car.
Of course a 75 shot or so of spray in an srt 4 or dsm can do wonders too .