The Dyno accuracy
KilrZ06 said:
Would adding higher pressure injectors fix the surging problem since you wouldnt have the leanness, or is this a programming thing?
The problem is in the Closed Loop cell 21 (deceleration)
This is the cell affecting deceleration (foot off the throttle)
Even with our 30# injectors, there is a slight feeling of surging at zero g. The Magic Box addressed this problem on the 2001 Z06s with the Granatelli MAF and the screen out senario, but is not the way we want to go on the 2002.
All other closed loop fuel cells return to stoichiometric (GM likes 14.6:1) within a few miles of driving normally. (usually 50 or so miles, with one cooldown session overnight)
WOT is also Open Loop, but does richen up with bigger injectors during full throttle settings. Too much injector here, is not good. The proper a/f ratio differs with each engine, and is also affected by water temp, oil temp, barometric pressure, altitude, and several other factors. This is why dyno tests done by the consumer will yield numbers which can vary from expectations from one day to the next, one dyno to the next, even on the same dyno, same day, within two minutes of one pull to the next.
Our 310 cc/
[email protected] injectors vs stock of 255cc/
[email protected] make a difference but the primary objective is to provide an injector that is not already too small from the factory and way too small with an intake mod. Our a/f ratio at WOT is just right with the blueprinted RC Injectors, and no more spark knock timing retard. They provide enough headroom for additional airflow to the 485 to 500 HP mark (flywheel).
Katech Engines uses 36# injectors with there LS1 to Z06 conversion packages making 440 to 485 RWHP. They are using bigger valves, head work, and a larger cam in their upgrade package. I asked Russ Collins at RC how the 255 cc/min injectors could make the 405 HP on the 2002, and he stated that the Bosche Injectors have very lightweight components which allows them to run at well above the 80% duty cycle, but suggested that they were dialed in for smog considerations, not performance. Two less cats? Leaner injectors make sense for the stock intake, but that's it.
One very important thing to ask of the dyno numbers posted anywhere is the S (smoothing value) There are 5 difference smoothing views that can be used on the DynoJet Dyno. S-1,2,3,4,and 5. Someone who wants the highest numbers on one pull vs another can hit F4 on the computer and change the peak RWHP and Torque numbers by as much as 5 HP.
S Value Viewing: On our 367/357 pull on the SideWinder, there were S values which would have put our numbers OVER 370 RWHP. Since Darren uses S-3 on all dyno pulls as a standard, we use that same value for stock, Halltech, or whatever we do. Is is tempting to change it? Only if you are trying to fool the public.
Tire pressure: Another area of discrepancy, and one that someone could use to 'play with the numbers' is the rear tire pressure. Our tire pressure was not touched from the factory. They were at 36 psi for all pulls, stock and Halltech. Letting air out of the tires can effectively lower numbers by as much as 15 RWHP according to Darren at R&D, and Steve at Powertrain Dynamics. So if you run stock at say 22 psi and your mod at 36 psi, you've got 15 RWHP without touching the engine.
Ice: Some guys take a bag of ice and put it on the intake manifold to increase dyno numbers. I have heard that it works, but have never tried it.
Fuel: 91 Octane anyone? Sure it works, but the Z06 calls for 93 Octane. The manual states 91, but I gaurantee that if your water temps are up, and the Octane down, spark knock sensors will go into overtime. So heat up the motor real good, do your stock pulls with plenty of spark knock, then add high Octane fuel and do your mod pulls> Result: 6 to 7 RWHP. Halltech dynos with the fuel available at the local pump only. For all pulls.
For instance, the stock pulls on our 2002 have varied from a low of 334 RWHP to 350 RWHP within two minutes on the dyno. This was due to the water temp changing only 15 degrees. This is why our T-1 kit, which addresses this inconsistancy in water temps.
Another problem is the dyno software. It makes assumptions based on barometric pressure, water vapor, ambient temperature, and altitude.
A baseline of 1.00 is what we try to dyno at each time, so that the dyno software trimming is not a factor in these inconsistancies. We also have been dynoing at 198 water temps, which are too high, but without a thermostat, we are stuck. We dyno with a fan blowing into the radiator cavity to keep water temps as cool as possible and to allow ambient airflow to the filter. Oil temps should be 210-degrees or above. 210 is where API rates the oil viscosity, so lower than that will take away power since the oil is not even at operating viscosity.
When dyno testing is done on a very hot day, with less than ideal conditions, the correction factors used by outdated DOS software literally 'guess' at the horsepower numbers.
As you can see, dyno testing is a science and even when done under the very best conditions, by shops that do this for a living every day, numbers should be used as baselines against mods done on that day only, AFTER PCM LEARN drives. Any other dynos are useless and serve only to confuse.
[One last point: None of the dynos will show the effect of ram air, or even cold air. The reason is simple. Dynos are in an enclosed area, which heats up as pulls are done. The engine is getting no outside ambient air to cool the engine, water and intake. Does it matter? What do you think?
Ram air does not exist with our systems, and would not work without extensive PCM trimming. The turbulence of TRUE ram air would make metering airflow extremely difficult, but not impossible. The basic problem would be to have one a/f ratio for vacuum at the manifold and another a/f ratio when the manifold saw some positive pressure. This pressure can be as much as .3 to .7 psi between 100 and 200 mph. Warren Johnson claims to have been able to see 1 psi at 200 mph in his enclosed airbox. Since he uses carburetion with no way to trim the a/f ratio, he must set the jetting at the ideal a/f ratio for this amount of boost, but will suffer some degredation of performance prior to the ram effect.
Jim Hall
