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Discussion Starter · #1 ·
Things to show in your dyno results posted:

One very important thing to ask of the dyno numbers posted anywhere is the S (smoothing value) There are 5 different 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. We have also determined that the difference between Windows Software and DOS software is not worth discussing. We saw virtually no difference in our stock pulls from a dyno using WINPEP and one using the DOS version. None.

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
 

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Jim,

Thanks for the great update, we have lotsa members looking for dyno #'s and a general understanding of how it works..........................

:cool: :cheers:
 

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Hmmm, the tire pressures used at 36 lbs is interesting. I am assuming that those are hot pressures, since I was told during my Museum Delivery to set cold pressures at 30 psi. My car sat for a while this morning before putting on the rollers - we did check tire pressure to ensure both sides were equal and not BELOW 30 psi, and the pressure was 32 lbs. Looks like we should have put 4 more lbs in each side - maybe we would have gained a few more horsies....
 
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Discussion Starter · #4 ·
I don't have all the answers

but this information is what we have learned over the past 3 years of dyno testing and over 100 pulls on four C5s. Dyno days are the best training of all, where there are 30+ C5s with all kinds of mods. After awhile, you can practically predict the results of certain mods.

The tire pressure thing, was information given to us intially by Steve at Powertrain Dynamics when we started dyno testing our 2002; he even checked our tires for the stock pulls to make sure we were not sandbagging. That same day this info. was verified by Darren @ R& D Dyno. Darren says that the "Ricers" inflate their front tires to 40 psi or more just to squeeze the most out of the pull.:-?

Jim
 

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Re: I don't have all the answers

cold tire pressure is rated at 30 pounds. it even states that on the drivers door unless the 2002 have different ratings for some reason. was your tire pressure at 36 pounds cold? if not, at what point was the tire pressure measured at? I didnt know that pressure increased that much when warm.

Thanks,
don

Halltech said:
but this information is what we have learned over the past 3 years of dyno testing and over 100 pulls on four C5s. Dyno days are the best training of all, where there are 30+ C5s with all kinds of mods. After awhile, you can practically predict the results of certain mods.

The tire pressure thing, was information given to us intially by Steve at Powertrain Dynamics when we started dyno testing our 2002; he even checked our tires for the stock pulls to make sure we were not sandbagging. That same day this info. was verified by Darren @ R& D Dyno. Darren says that the "Ricers" inflate their front tires to 40 psi or more just to squeeze the most out of the pull.:-?

Jim
 

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Interesting post jim. I agree compleatly that comparing different dyno's on diferent days is an excercize in futility. The proof of the pudding is how "your" car "goes" in the real world. Dyno's are just a more convenent way of tuneing than at the track. Ric
 
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Discussion Starter · #7 ·
PowerShifter said:
Interesting post jim. I agree compleatly that comparing different dyno's on diferent days is an excercize in futility. The proof of the pudding is how "your" car "goes" in the real world. Dyno's are just a more convenent way of tuneing than at the track. Ric
I agree 100%.

The tire pressures were hot. I had about 1 hour of driving. My point here is very simple. Some companies could start with low pressure to dial in stock numbers, then bump the pressure for their mod pulls. Just wanted to reveal as much as possible about different techniques for making numbers whatever you want them to be.

Our dyno numbers are as pure as we can make them, since we are in this business for the long haul..we know our customers will attempt to duplicate our findings.

Jim
 

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Dyno CF Software

Humm .... I don't know why older versions of the SAE Air Correction Factor wouldnt' give you the correct CF, unless they are based on an older version of the correction formula. AFAIK, the latest SAE correction formula is based on SAE Paper #J1349 (Rev June 1990), and is the formula used by Dynojet.

I can calculate the correction formula with a hand held $2 calculator -- so I doubt if even the most basic computer would have a problem with it :D.

Comment on the ram-air issue. I agree with the manifold pressure vs. speed numbers you posted (these are from the stagnation air pressure fomula -- I crunched them before :D). I'm surprised that the manifold pressure sensor in the C5 does not read above atmospheric pressure -- in this case, it would have to be able to sense around 15.7 psi (absolute) max. If GM designed the FI system to not recognize any manifold pressure above this, then yes, the FI would not compensate correctly for a ram-air system at high speeds, and the A/F would be running too lean.
 
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Discussion Starter · #9 ·
Dyno numbers today were disappointing

This car is the hardest C5 we have ever tried to dyno.

Our best numbers today 369.1 RWHP/357.4 RWT with the T-1.

A/F ratios appear to be dead nuts on during the pull, so I'm going back to the Donaldson design filter and have S&B make them.

Hopefully we can get these made in the next two weeks. They will be free to anyone who has purchased our SideWinder for their 2002 or 2001.

We should be at 375 RWHP with our T-1 package, but we are not.

It was hot today, and we started at 364.1/352.6 on our 1st pull. Down from the 367/357 10 days ago.


We did not use the fan switch, since we sold our unit earlier to an anxious customer. This may have helped, since our best dyno was with the water temp at 198.

More homework.

Jim
 
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