High-Tech Nitrous

Note: this is a draft and some sections need to be clarified and rearanged, but you should still get the idea.

On a recent thread, we were talking about the oil ingestion issue with the LSx. I had stated that the vacuum pump offers upto like a 40hp gain, and was question why; hopefully this will help explain why. Most are aware by now that our motors will ingest oil. If your still in doubt, take your TB off and stick your fingers in for oil, and/or look with a flashlight. It seems to puddle right behind the TB on the bottom of the intake plenum. The LS1 is worse than the LS6 and later LSx motors. If you have an early LS1 change over to the LS6 style PCV system at the minimum, for a slightly better result, though not a complete fix. However, the LS6 has a problematic oil ingestion issue itself, though due to another design matter not as bad, which we will cover later.

Many have tried various fixes for this issue, but to no avail. These fixes included, single catch cans, dual catch cans, larger valve cover breathers, eliminating the PCV (not rec. unless with a vacuum pump), and hybrid designs. Some of these fixes actually help with the oil ingestion problems on N/A applications, however, none eliminate it totally. The real issue in this article is concerning a nitrous motor, which can cause this issue to become worse .

We do not want this puddle oil introduced into the combustion chamber when we are spraying the motor as it can and often does invoke the dreaded detonation. Detonation can be the end of a sprayed motor quickly under certain conditions and at certain times. Just watch a LSx nitrous car, boosted car or even a N/A car do a pull on the dyno and you will see the oil being burned and spent out the exhaust. In addition, for those with a dedicated, and sometimes stock, N2O motor, looking at the oil-fouled plugs will indicate oil present. Mechanical issues should be eliminated as a source of this oil by doing a cylinder leakage test if you think this is needed (look in your intake manifold 1st).

For longevity sake and to have the safest nitrous motor, eliminating this oil in the intake must be considered. Some of the fixes mentioned can minimize this oil collection, and some claim the dual catch can be the best fix outside of the vacuum pump. Therefore, that is one great reason to run a vacuum pump, the oil ingestion issue, however that is not the only reason to consider the vacuum pump.

This next section refers in large part to a loose dedicated nitrous motor. The heavier we spray our motors the higher the cylinder pressure becomes and the higher the force pushing past the rings, and thus more contaminates getting into the lower block (not to be confused with blow-by coming past the rings and getting into the intake, which is covered later). You will see the results of  blow-by coming out your breathers (if you have installed a nice large valve cover breather). If you haven't added breathers to your nitrous motor, you should. The stock PCV system normally gets its "IN" air via a small line at the TB. This will be filtered air supplied by the air cleaner or CAI. This is a closed system like the government wants for pollution control; however, it is not enough breathing capacity for a nitrous motor. Therefore, what happens is this internal pressure is trying to be relieved and will find compromised gaskets as an escape route and result in oil leaks dripping here and there. A nitrous motor needs to breath, so even if not modifying the PCV system a nice large valve cover breather is needed (see picture). Some add one to each valve cover.

So now we know the two reasons for adding a vacuum pump, one is to stop the oil ingestion issue, and the second is to allow a nitrous motor to breath properly. It is the second reason that will allow us to pick up some additional HP compared to a non-vacuumed pumped motor when spraying, and even a slight increase N/A. One recent magazine article showed a 40rwhp dyno proven increase by just adding a vacuum pump (I will try and find the magazine and ink). So now we can talk about why and how the vacuum pump can increase performance, but will need to cover some basic short-block engineering first.

Remember when it was stated that the improved LS6 PCV system was a good choice over the LS1, but still did not help the LS6 motor more than the LS1. Here's why. As the pistons move up and down, they force air in and out of the bays beneath the pistons. At high RPMs this airflow becomes quite violent and really whips the oil up (more oil to get to the intake tract). It also results in parasitic HP lose trying to fight this turbulent mix of air/oil and internal combustion contaminants. Due to a deep skirt design (block structure extends past crank centerline) the LS1 has machined windows between the bays. Now the LS6 was going to be spinning higher (think of your built motor going even higher and n2o motors allowing more combustion contaminants past the rings into the intake) and needed even bigger windows, But couldn't tolerate the strength lose with bigger windows. What they did was to engineer valley mounted oil separators which uses internal baffling to force the crankcase vapors in a circuitous (think roundabout) flow. This in turn causes the oil to separate and drain back into the engine. Does it work? Well it may work, but because of the higher output of the LS6, it doesn't seem much better than a LS1, or it may be much worse with out this extra system. The real fix is a vacuum pump and especially for a sprayed motor and high-performance high RPM N/A motors.

In closing, the LSx series engines are well known for a lot of blow by and resultant contamination of the intake charge with oil forced past the rings into the combustion chamber. The vacuum pump eliminates the PCV valve, allows the rings to seal more effectively, and reduces oil contamination of the intake charge, which results in added horsepower. A side benefit of the negative crankcase pressure the vacuum pump creates is that it also helps to eliminate unsightly oil leaks.

This is just a rough draft, and it will be fine-tuned later. The above info is off the top of ones head...

Robert