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Valet mode versus full power mode.

F

Future vetter

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Hi I'm new to the Corvette world and I was wondering if you get better milage in valet mode rather than full power mode?
 

Rob

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13,763
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1990 Corvette ZR-1
Yes.

The Valet key prevents the secondary port throttle system from engaging, therefore the engine is limited to approximately 210 horsepower. Legend has it that the Valet key is to prevent the car from getting in to danger in the hands of the wrong driver, however, anyone who has ever driven a ZR-1 knows well enough, that regardless of what position that key is in, you can get into trouble either way. If I recall correctly the reason for the valet key was actually to help the car pass federal emissions testing.

Contrary to popular belief, the secondaries don't just kick on as soon as you turn the key. A few parameters must be met. I'm probably going to screw this up, because I'm going upon memory, but bear with me: oil temperature must be up to normal operating temperature, engine temperature must be up to normal operating temperature, I believe manifold air pressure must also be at normal operating pressure and the correct amount of throttle must be present.

If all of these paramaters are met, and the secondary port throttle system is "charged" so to speak, the ECM will send a signal for the secondaries to trigger once the gas pedal passes that threshhold. The level is approximately 2,800 rpm. At that point, the secondary fuel injectors kick in, the secondary fuel pump turns on and the secondary port throttle valves open depending upon the amount of throttle fed.

When the engine is only running on its primaries, air enters the system only through the primary throttle blade in the throttle body. Once the secondaries are engaged, the larger throttle blades open.

Now, if one of the parameters described above, is not met, the secondaries will not engage. That's why, when the car is cold, you can turn that key and smash that gas pedal all you want; you're stuck with around 210 hp until all parameters are met and the ECM says, "let's go for it."

The entire secondary port throttle system of the ZR-1 runs off an intricate vacuum system. If you've ever seen an LT5 engine with the plenum taken off, you'll see what I mean. It's a maze of vacuum tubes and hoses under there.

From Graham Behan, one of the original LT5 Engineers now working for Lingenfelter Performance Engineering:
The intent of the "Valet" mode was actually to allow the engine to operate on eight injectors whilst on the emission test cycle. The primary lobe of the LT5 intake cam is 20 deg shorter in duration than the secondary lobe. On a 90 MY car the power key could be left in the full power mode at all times, unfortunately for the 91 MY and above we were forced to adopt a strategy whereby the system would be in "Normal" mode(8 injectors) at every start. Hence the change in the key system for the later cars, this strategy prevented the power key from being considered an emission defeat device.

Hope this answers your question. :D
 

vettl83

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Apr 26, 2002
Messages
175
Location
Casper Wyoming USA
Corvette
91 L98 Quasar Blue, 91 ZR1 Red, 07 AO Coupe
If I remember correctly I believe the owners manual recomends exercising the secondary injectors periodically at an off road location to keep them clean. Myself I keep mine in the full power mode at all times. As for fuel mileage I haven't noticed much difference in either mode if the car isn't being taken out and flogged everytime you climb in it. Good luck future Vetter and if you can swing it buy the Z you will be pleased !
 
F

Future vetter

Guest
I went and test drove a 92 ZR-1, on a trip to Vegas over the week end and let me tell you after listening to that LT-5 torque to me as I rowed through the gears is the best thrill ride I could ever want.:D
You don't even have to drive fast to enjoy the car.
I think when I have the means, I want a ZR-1! the Corvette is :BOW the ZR-1 is *****en!
I love that big monster that lives under the hood the sound is reason enough to get a ZR-1.
I will have more questions in the future and like how helpful everyone is, thanks.
 

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