I had a dyno done after installing a 78 FAST intake and a set of L/T headers and my numbers were lower than a previous dyno.
The dyno operator told me one of the reason for a lower number is because I had a vented oil cap and a catch can and this could be causing a vacuum leak.
Can anyone tell me if this can cause a vacuum leak?
Here is a picture of the setup.
Thanks,
SLPRC5

 

ttt

 

Looks fine to me. You dont want gases inside you block, th emore they get out the better.

 

Thanks for your input oh4GTO.
Exactly what I thought. Another forum member is running this setup without any adverse effects. There are earlier modles that run a vented oil cap without losing vacuum. So with the catch can sealed and lines going into it and out to the TB so it's sealed.
SO I'll see what others chime in with.
SLPRC5

 

The PCV and breather are not even part of the vacuum loop.
The FAST intake may be leaking however and that may be an issue.

 

Never heard of such thing. must be a new rule that was declared.

I got my breather cap from ECS. I doubt they would sell me a vaccum leak.

I now only consume 1/2 qt oil between oil changes.

 

I would think it could be a couple of things

1) If you installed a fast intake AND LT headers, then you will most definately need to tune the car accordingly.

2) A breather cap on a N/A motor is absolutly pointless. The whole purpose of the PCV system is to pull the gasses out of the crankcase. This also helps seal the rings. If you run the breather on a N/A setup the PCV becomes obsolete.
The only reason us F/I guys run breathers is because we are unable to run a complete PCV due to pressurizing the manifold.

Not only are you defeting the purpose of the PCV system, but your doing more harm than good. Sometimes more isn't always better.

If it were me, I would check for vaccum leaks, (FAST intakes are known to be warped) verify that your LT's didn't fry an O2 sensor wire, have some adjustments done to the tune, and eliminate that oil cap breather.

 

Thanks for your input.
I have removed the breather oil cap and replaced it with the sealed oil cap. As you see this is a controversial subject, others believe there is no harm or degrading the performance with a breather oil cap and a catch can.
The car had a street tune after the headers and the FAST intake were installed.
O2 sensors have been deleted because I was getting the CEL and the code for the passenger side rear O2 sensor. The wires look fine.
No vacuum leaks were reported by the tuner or installer, but there is a whistle from the FAST and I was told "they" all do that.
The dyno tuner told me that I don't have large enough cam to run the FAST, not enough duration on the stock 02 ZO6 cam. I'll be taking the FAST off and putting back my LS6 intake along with 1.8 rockers, longer hardened push rods and 918 springs before taking it back for another dyno and tune.
My dyno numbers went from 349 rwhp to 339 rwhp. the rwtq went from 351 to 350 rwtq. Both were done on a DynoJet and the first was done in 20 degree warmer weather.
I'm sure other will still chime in with their thoughts.
Very nice Corvette you have.
BTW, how does 801 rwhp feel?
SLPRC5

 

bump

 

As far as I know, the crankcase gasses are vented through the PCV system, but the tube that routes into the passenger side valve cover is actually a fresh air intake to allow the vacuum a supply of air to vent. In other words, the valve cover vent/breather/hose to TB is intake only.

 

Thanks.
This sounds logical, because there is NO suction around the oil cap vent. So with the oil cap vent on that valve cover there are two inlets, correct?

 

I doubt that a vented oil cap is doing a stock(unblown or no nitrous) engine any good. How do you pass visual smog with it in good ol Kalifornia?

 

I was using it to help with the oil usage after installing 02 LS6 heads on my LS1 engine. It is said to lessen the oil consumption.
Haven't had it smogged, not due until next ear. But that is a good point for a visual along with my L/T headers...

 

There is no adverse effects from a breather. If you delete the pcv system(plug the holes) you need a way to get rid of gases in the crankcase. You don't need BOTH the valve cover breather and the pcv catch can though, you would be getting a vacuum leak. On my car the system went from the intake to a neck in on the front of the pass. valve cover to the back of the pass valve cover around the back of the intake to the back of the drivers side valve cover then to the front of the driver's side valve cover. This will allow gases to escape from your crankcase back into your intake to burn off the gases (hense emmissions) and if gasses are trying to escape into the intake while oil passes by the outlet from the valve cover you will get oil in the intake, thus the reason most people run catch cans. If you delete this and plug all the ways the gases can escape from the valvecovers you need a valve cover breather to let them escape, if you run a catch can you don't need a breather since the gases will be running back into the intake to be burnt off but the oil that goes with it is caught in the catch can. It's not rocket science.

In other words the catch can is good for NA where the manifold is not pressurized but not along with a breather, but if you have FI you need to block off the pressurized air from getting back into the crankcase and blowing your dipstick through your hood so you would need a breather to let the gasses escape. If you have a catchcan and breather you can get unmetered air from the breather through the pcv system. Learn how your car works before ya go modding it.

 

This the place to learn and thanks for the lesson along with the other information.

 

Ideal system draws vacuum in crank case to seal rings. This usually requires a separate pump....A&A makes one.

Worst thing is excess pressure. Breathers prevent this.

PCV system is an emissions device/line to pull vapors out of the crank and try to burn them in the combustion chamber insead of releasing to the atmosphere.


DH

 

Good Catch....
I didnt even notice that in the picture. That could be a good reason as to why the #'s are low.
When that car goes WOT, its pulling a TON of air "Around" the MAF sensor.. oooooh, not a good thing.. Plug her up and get it re-tuned..

 

But at over 1,000 bucks, its not in line with other remedies on the market.

The only thing breathers do on a N/A car, is make it smell like ****, pollute the air, cause decreased oil life, and add excess water vapor in the oil..

 

Your setup as pictured is fine. As long as you still have the PCV valve (I can't tell from the picture) there will be nothing wrong with the metering. It's the PCV valve that controls the metering, not the valve cover breather.
As pictured, you have two sources of air to the crankcase. One is the breather, the other is the normal supply fitting at the throttle body. If you want, you could cap the throttle body fitting and remove the small filter and hoses, and also cap the valve cover fitting on the other end just to clean up the engine compartment, if you put the breather back on.

The only time crankcase fumes might come out the breather is at full throttle. As long as there's manifold vacuum and you don't have excessive blowby, air flow will always be in the other direction.

 

I replaced the breather cap with the stock oil cap...will see how it does at the next dyno.
Thanks,
SLPRC5