only90s

Been having lots of problems with the PCV/breathers/crankcase pressure on my new build...Lately I have been venting PCV to atmosphere and running open breathers on each valve cover.

I have seen numerous blown/turbo cars in magazines all running the PCV to vacuum and valve cover breathers.

Car is getting tuned this Friday...talked to my tuner about it last Friday. He told me the PCV should be hooked to vacuum and OK to run the breathers. He will tune out any vacuum leak created by the breathers. He has lots of experience with blown Mustangs and says this the best system for a built 5.0 that is blown.

Car does seem to run better with the PCV hooked up..now running to vacuum via an oil seperator...of course there is an occasional idle surge, but all my oil seepage has stopped.

I will let you all know Friday how it works out.

samseed101

He's going to create a vacuum leak and then try to tune around it? Not so sure that's something I'd want to do. That's going to require a fair amount of time to adjust all the necessary functions, tables, and scalars. I'm not so sure that it's worth it. There's no real reason you shouldn't be able to run a simple breather setup. Quite a few of us run that sustem with fair amounts of boost and there isn't an oil or pressure issue. If there is a problem with oiul loss, then there's a larger underlying problem that needs to be addressed. Tuning around a problem is never a good idea.

only90s

I hear all your points loud and clear and thanks for all the help by the way.

In any event I have been doing ridiculous research on this matter..and the following arguement is often made: Under vacuum the PCV eliminates the crankcase pressure, but under boost it is not effective. The breathers can eliminate the crankcase pressure while under boost.

This guy has built and tuned numerous blown mustangs from the 60s to the present so I will see what happens.

only90s

Also in the last two months I have seen a 600 plusrear wheel horse 5.0 and a 700 rear wheel horse 383 both blown running the PCV and a valve cover breather.

So if they can do it my mere mortal 400 plus at the wheels(I hope) can do it.

samseed101

That part is 100% true, but that's not where the problem would lie. Under boost, there would be no vacuum anyway so there's no way to have a vacuum leak under boost. The problem would lie in the DD part... when driving under normal situations (N/A.) That is when you would have unmetered air coming into the system.

And the amount of unmetered air coming into the system is going to change as well. It's going to depend on air density, air temp, humitidy, altitude, etc... All of those have to be acocuinted for. And then as the filters get dirty (especialyl from oil mist that will spray through it at when under boost) and that will restrict the amount of unmetered air that is coming into the system. That, in turn, could cause you to run rich because he tuned around a vacuum leak by adding fuel and adjusting the MAF transfer (after assuming a certain amount of unmetered air was slipping by.) I don't see how that could be accounted for.

As far as building blown cars from as far back as the 60s. I don't doubt that he knows his **** inside out and knows a hwell o a lot more than me. But keep in mind that when you're talking from the 60s until at least the early 80s, were talking all carb and no EFI. So there's no MAF metering air to worry about. Also, if he were tuning it for a strip car, then I imagine that would be easy to work around. It would be similar to my "nitrous" tune. But that's something I only select when i know I am about to run WOT and spray. Because it would run like **** if I did it on a regular basis.

Again, I don't doubt that the guy knows a ****load more than I do about it. But I am curious how he will deal with all of those factors. Tuning takes a LONG time unless they take shortcuts. You have to work on getting it to idle and drive right forst. Then when you got the numberse set, you can work on tuning your OL WOT runs. It takes a decent amount of trial and error and some adjusting. Most tuners I know take several shortcuts just to get teh car in and out of the door (due to teh sheer volume of cars they have to work on.) I just can't imagine someone would spend the extra time with a dyno and a WB sensor trying to nail the tune...not without getting paid a LOT of money anyway.

luckythirteen13

why would anyone created a vacuum leak and then tune around it?? that just sounds retarded to me. if your so worried, by a vacuum pump

Joel5.0

As Sam says.....IMHO, that's a band-aid tune.....not questioning the guys experience and know-how, but those tunes fall under the GIGO category for the part-throttle and idle conditions....why?.....it leaves an "unknown", a variable that is not measured and accounted for, so the system can determine A/F and timing before tha fact.......the system will compensate, but based on the "after the fact" information from the O2's, and when the fuel trimming takes place, the conditions will have changed all over again. It's tuning EFI, but carburetor style. Alternatives?.....no PCV, just breathers, Pan-Evac or a vacuum pump....

samseed101

I'm assuming that the tuner is willing to spend a LOT of time on this and knows what he is doing. It can be done, but it's not easy. Mostly because the amount of air that is being leaked in will change on a regular basis and there's no way to tune around that. You can get it close, but it will never be as good as it should be.

It doesn't seem worth it when you weigh the pros vs the cons. If it is being done because of a problem with oil spraying out of the valve cover breathers, then it's not going to help. It would actually make it even worse. With an open system, pressure can escape through the 2 valve covers and through the PCV valve that's vented to the atmosphere. But if you plug off the PCV valce (which is exactly what will happen under boost if it's connected to the intake) then you are eliminating one of the three places that pressure can be released. So that will increase the amount of oil mist that sprays out of the breathers.

It would only really offer a benefit when driving under normal conditions but that would still leave you with the vacuum leak problem. And again, the only benefit is that it will be pulling air through the crankcase to save your oil and get fresh air in there. Nothing that can't be done with a simple evac system.

But maybe the tuner knows something I don't know. It just seems like a tall order to me. I am also curious how he will account for the ever-changing amount of air that is being "leaked."

only90s

I have basically confused the hell out of myself with this issue...I understand everything you guys are saying and it makes sense....

However, the car is running pretty decent right now on the stock computer...I ripped out my SCT Chip because there was something wrong with it and the carwas running way to lean. Now with the PCV hooked to vacuum and the breathers the car runs really strong...no more seeping oil from unknown places...breathers are dry..only problem is an occasionaly 200 rpm surge at idle...which I assume is the alleged vacuum leak...

The tuner laughed when I brought this exact issue up to him about the vacuum leak...so he is either Really Good or an idiot.(He told me to say off the internet...now why would I do that)

I will let you all know on Friday the verdict.

jasonvri

LOL
I'll question this tuners abiltiy...
I've seen too many posts from guys going to 'professional' tuners, just to get a hack job done on their car.
[:@]

From the tuners point of view...
I would suspect it would be more cost effective to tune around the problem, than to purchase and install the hardware to fix the problem correctly?
Dyno time is nearly all profit?


random thoughts,
jason