shaved intake 280zx, now won't start

[JSM]

Not Paul, but on EFI if you are using an AFM ( flappy doodle ) or MAF ( Mass Air Flow ), ALL of the air that is ingested by the engine has to be maesured by the AFM or MAF.

I am curious though, from a pure air to gas ratio burning in the cylinders, how does the air entering into the block have anything to do with the calculation needed by the EFI for normal operation? Is the amount of air (pressure from combustion) somehow entering the combustion chambers and the ECU has to compensate for this during the normal cycle of the engine?

 

I know from Paul's post on page one he had to adjust for this because he vented the valve cover so it has to, But if both the block and valve cover were vented outside of entering the intake, an adjustment to the EFI would still be needed?

Edited January 28, 2017 by JSM

[ZHoob2004]

Fuel charge is calculated based on the amount of air going into the cylinder. If the air is not all drawn through the metering device, then the mixture will be calculated based on incorrect information and will be lean due to the additional air.

 

The air entering the block through the valve cover matters because that air is eventually drawn into the intake through the pcv valve on the bottom of the intake.

Edited February 3, 2017 by ZHoob2004

[JSM]

So with that logic removing both PCV and valve cover inlet from the EFI intake would eliminate any AF ratio issues from normal combustion?

[Chickenman]

So with that logic removing both PCV and valve cover inlet from the EFI intake would eliminate any AF ratio issues from normal combustion?

 

Yes, but you don't want to ever do that ( remove PCV system and replace with VTA )  on Daily Driver car. You will get much quicker contamination of the oil. Carbon particle contamination, water vapor and acid buildup. As wee the piston ring seal will be affected, negative crankcase pressure aids ring seal. The crank seal and rear main  seal will all be less  effective as the sealing lips are designed to operate at negative crankcase pressures. Note: the odd WOT pass is usally only for a short time, and any pressure buildup in the crankcase will be relived once the throttle is lifted.

 

Oil contamination is the main effect though. Carbon particles and acid buildup are nasty. Rod and main bearing life will be shortened.

 

The following article explains the benefits of a Positive Crankcase system:

 

http://www.agcoauto.com/content/news/p2_articleid/197 

 

 

In addition; 

 

Quote from Engine Labs article

 

PCV and It’s Importance

All internal combustion engines generate some type of crankcase pressure in the form of blow-by. Blow-by is combustion gasses that escape past the piston rings. In the early 1960s, General Motors identified crankcase gasses as a source of hydrocarbon emissions. They developed the PCV valve in an effort to help curb these emissions. This was the first real emissions control device placed on a vehicle. While most of us who are performance enthusiasts will roll our eyes when emissions controls are even mentioned, GM actually did the performance world a favor here. Not only does a properly operating PCV system reduce the overall emissions output of a vehicle while at the same time not sacrificing horsepower, it also has other benefits. It improves gasket seal, and prolongs gasket life by reducing the blow-by effect. Further, it also helps reduce the amount of oil an engine consumes through the combustion cycle, or loses due to leaking seals. 

 

 

 

 

With race cars it is not such a big issue ( using Vent to Atmosphere of Cranccase and Valve cover ):

 

1: Race cars change oil frequently. Usually after one race. 

 

2: Real race cars have Dry sumps or Vacuum pumps for the sump. The scavenge stage in a Dry Sump creates a strong negative pressure in the sump. This helps with ring seal immensely. Some NASCAR engines are pulling well over 14 inches of vacuum in the sump. HP gains  of 20 to 23 HP on a 600 HP engine with 12 to 14 inches of vacuum are common. Better ring seal, enabling the use of low tension rings  and reduced windage in the sump are the reasons for the HP gain. 

 

The following article explains the importance of maintaining a negative pressure in the cranckcase.

 

http://www.enginelabs.com/engine-tech/engine/tech-crankcase-pressure-control-oil-and-air-control/

 

Edited February 3, 2017 by Chickenman

[Chickenman]

From engine labs article:

 

Ring Seal and Pistons

Ring seal plays a vital part in how your engine uses oil and performs as well. Proper ring seal reduces blow-by, thus decreasing pressure inside the crankcase. Running a vacuum pump in a racing engine, you can actually change to a lower tension ring package, using back cut rings instead of the older style high-tension D-rings. This allows for lower internal friction and an improvement in overall engine performance. 

We talked with Gary Meier of JE Pistons about this. Meier tells us “Ideally you want a back cut ring with gas port pistons, the system seals better and is more efficient. If you run with a D-wall ring you are only going to gain a minimum amount of power.”

Meier points out that using gas ported pistons with lateral ports is the best choice. “In the old days, guys would argue that the gas ports would get clogged up and then they weren’t doing any good. These days the fuel is so much better that it has eliminated that argument unless you are running extremely rich or something else is wrong,” says Meier.

Since running a vacuum pump pulls oil away from rotating components and back to the pan, windage is reduced. The more is better approach does not apply to engine vacuum however. Running a high level of vacuum can have an adverse effect on engine life.

While Meier was able to tell us “On a standard 600 hp engine, 22-23 hp is not out of the question with vacuum at around 14-15 inches of mercury.” While some high-end race cars will push beyond those numbers to run over twenty inches of vacuum, these are cars that are generally towed and pushed through the staging lanes and their engines live the majority of their lives either warming up for a race or making a pass at the track. 

 

“Above 14-15 inches of vacuum, you pull too much oil away from the wristpins and cylinder walls,” said Meier. In these cases, the higher end engines will employ measures such as oil squirters to spray the wrist pins, as well as special camshaft squirters, and even other provisions to oil the rocker arms and valvetrain. All of this must be taken into account when running higher levels of vacuum. 

While vacuum pumps in the past have been thought of as something for high-end dry sump race engines only, they can also increase the power in a wet sump system as well. Meier recommended this for drag race engines only however. He also stated that the horsepower gains would not be nearly as significant as it would be with a dry sump system. In wet sump systems the expected horsepower gains would be in the neighborhood of 6-12 horsepower.

The same rules apply with regard to running too much vacuum. Peterson Fluid System’s, Wade Moon, pointed out that his company offers a single-stage wet sump external pump with a section on it just for pulling vacuum. 

Edited February 3, 2017 by Chickenman

[JSM]

Yes, but you don't want to ever do that ( remove PCV system and replace with VTA )  on Daily Driver car. You will get much quicker contamination of the oil. Carbon particle contamination, water vapor and acid buildup. As wee the piston ring seal will be affected, negative crankcase pressure aids ring seal. The crank seal and rear main  seal will all be less  effective as the sealing lips are designed to operate at negative crankcase pressures. Note: the odd WOT pass is usally only for a short time, and any pressure buildup in the crankcase will be relived once the throttle is lifted.

 

Understood.  My thought was to run the PCV, before the AFM so it could be metered and vent the valve cover , but with the oil vapor aspect of it it probably wouldn't be good for the AFM!

[Chickenman]

^ The factory Nissan PCV system is very good. It's very well designed with lots of internal baffling, both in VC and engine block. . Just maintain it and keep it stock. Including all routing