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Very Important Ls7 Info


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This was posted on Z06Vette.com. Just passing it on...



If you don't want to risk damaging your LS7, read this very carefully. If you're one who insists on using the engine to slow the car rather than the brakes, especially on the track, pay special attention.

Some of you may have noticed, read or heard about oil pooling in the intake tract to the point it was pouring out through the air filter. This has also resulted in the hydrocarbon collection pads becoming unglued. Here's why...

The LS7 does not utilize a typical PCV system. Instead, the dry sump system performs this function. If you look at the top of the oil reservoir, you will see some small black hoses. These hoses carry oil vapor scavenged from the engine crankcase to the intake tract whereby it is burned by the engine. Under certain conditions, this vapor contains not only vapor but also engine oil. This is by design, is normal, and can be cleaned during routine service, per GM. The hydrocarbon absorption pads in the intake absorb unburned hydrocarbons and further help reduce emissions. If they become oil soaked, they can become unglued resulting in a loss of power and possibly engine damage.

During sustained high RPM use, such as that typically seen on the track, more oil laden vapor than normal is drawn into the engine through the intake. However, a potentially serious problem such as hydro lock can possibly occur if the driver uses the engine to brake by downshifting instead of using the brakes.

Downshifting is for rev matching in order to balance the car and hence aid corner exit speed by being in the proper gear for acceleration, NOT TO SLOW THE CAR!

You are not driving a semi with a "Jake brake". If you do this with the LS7 dry sump system out of habit you may very well damage the engine.

By downshifting to slow the car while at a high RPM, such as at the end of a straight for example, an abnormally high vacuum is created in the engine crankcase due to the throttle plate being closed. This in turn can result in an excessive amount of oil being drawn into the intake tract when the reservoir is filled to the prescribed 8-quart capacity.

In this regard, you may have read or heard not to fill the oil reservoir above the middle dimple on the dipstick and this is why.

In summary: again, do not downshift to slow the car. Use the brakes, as that is what they’re for. This is mentioned in the manual and/or on the CD. We have had this discussion here on the forum several times and I have always cautioned against doing so. With a normal PCV system it isn't as much of an issue but bad habits will usually come back to bite you and this is one such example.

Edit: remember, this is a production street car and as a such must comply with emissions regulations. Race cars do not. Race car dry sump oiling systems therefore do not have vapor recovery systems plumbed into the intake. In addition, they don't have hydrocarbon absorption pads in the intake tract to come unglued.

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Robert and Elizabeth

Wow, I did not know that. Robert and I downshift quite often. I will review my owner's manual and also talk to Mike about it too. Thanks Steve for the heads up! :thumbs

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