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Whats the deal with the dyno?
Torque is a function of boost and temperature. The ECU will take care of the fuel. The energy released is mostly determined by the oxygen in the charge air.
He has the Viggen ICC, that will help, but on a dyno, tethered to the floor, the vehicle is really not moving very fast. The fans set up infront of the vehicle don't do very much. When you are in the high RPMs and the speedo says you are going real fast, the IC does not see the air blast from that speed. The IC is not working well at all! So the charge air is getting quite hot. So dyno runs have heat soaked IC's.
When you increase your boost, you are simply asking the IC to do more, so on a dyno run it gets heat soaked earlier.
Most often, the dyno runs are done in 3rd gear which avoids the reduced boost in the lower gears. It takes a surprising amount of time to get up to the red line fuel cut on the DynoJets in 3rd gear, so the IC gets very heat soaked by the time you get there and I wonder why the torque is falling off? In the real world, in third gear, you would get up to the red line much faster and thermal load on the IC would be shorter and the IC would be getting lots of air flow from the vehicle speed. So the dyno will produce numbers that underestimate the system.
Removing the grill during a dyno run will help a bit.
Dyno runs cannot be properly temperature correctd either as the effects on the IC cannot be quantified. They can be used for comparisons, if the abmbient conditions are similar. I think that a better measure of the system is watching what a boost guage does on a road run. If the system has had the sources of flow restrictions worked on, then the boost at the high rpm's is the measure of success for any given IC. So vehicles would be divided into two groups, Vigen IC or other, as these would dictate the temperature realms that are being achieved at the manfold.
The eagerness and responsiveness of an engine on the street is also quite independent of horse power. Horse power is the maximum of the curve of torque and rpm's. As the torque starts dropping off at some point the peak HP occurs before the maximun PRMs, that is pretty basic. But does HP indicate how responsive and powerful the vehicle is on the street... NO.
With a MBC and a stock IC, plus the other basic mods, the turbo will spool up faster than most modified ECU setups and the 1st two gears are not torque limited. So in typical street driving this setup can be quite fast. I am not tearing down the value of modified ECU's but simply pointing out that streetability is something quite distict from dyno measured HP. As an extreme example, I could fit a large turbo on a NH900 that would reach peak compressor map efficiency at 5000 or 5500 RPMs. That would produce more HP. But the boost lag would make such a vehicle rather un-spirited on the street. Yet, if you took that vehicle to the track and dumped the clutch at 5000 rpm at launch, you would get some very good 1/4 mile time slips. But you would be getting left behind at every intersection by just about anything.
Now, want to prove that something will produce more power on a dyno! Install a IC water spray or install the Aquamist system. The results will be very convicing as they will dramatically reduce the charge air temperatures for a vehicle tethered to the ground. In the real world, on a street race or track where significant relative air velocities are being generated, the advantage of these measures will be reduced, as the IC will be able to work as it should.
Any changes that reduce flow restrictions will produce more power and increase responsiveness. You do not need to go to a dyno to know that. Anything that increases boost will make more power. This is true for the T5 which works magic and fuel delivery does not come into the equation. So if I can increase my red line boost, I know that my HP has improved.
posted by 207.43.19...
, Mon, 18 Feb 2002 21:48:02
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