i need a little more vacume so I was thinking about ditching teh pass valve cover to TB and running a breather and blocking off the TB which will mean more air coming in and increasing the vac. Is this ok or i am backwords here?

 

Mkos,

There are two problems with that theory. The air going through the TB to the PCV system has no more restriction than a breather would, and any exrta incoming air won't change the intake vacuum at all. Allowing more air would tend to reduce vacuum, just like a leak would.

The other problem is that the incoming air ends up in the intake after travelling through the PCV system, and has to be measured by the MAF, or the mixture will tend to get lean. That is why the source hose is connected to the throttle body in the first place. You can expect a code '34' if you use a breather, and no better vacuum.

Instead of changing the PCV source, try replacing the PCV valve. It regulates the amount of ait entering the intake through the system, and therefore regulates vacuum to some extent.

What is the idle vacuum, anyway?

 

Hers the problem. Its showing 14hg's with the new 112LSA Cam and now the idle FP is at 42 where as with the stock L98 cam it was at 38 PSI because of 18HG's. I need a little more vacume so the FP regulator works good.

 

mkos, you're trying to solve a problem that only exists in your mind.
- a 4" change in vacuum shouldn't change your idling FP by 4psi, are you sure it's set at the same pressure (vacuum off) as it was before?

- What do you mean make the FP work better. Do you have a specific driveability or tuneability problem at high vacuum part throttle operation? If not, then everything is just fine, period.

- What are the specs on your cam, LSA doens't mean anything w/o the rest of teh duration/lift numbers. If we knew your engine/cam (and idle RPM) we could tell you if your vacuum was normal for the combo or not. If your vacuum seems low for the combo, it could easily be a tuning issue. Timing , fuel trim , and even min air / IAC setting all play into your idle vacuum. Playing with the PCV does not (excet for making sure the valve is good)

 

sorry guys. Its a L98 base TF Heads 218/224 .496/.503 with 112 LSA I am also running 1.6 rockers. I also replased my FP this winter with a walbro 255 unit. Last year with stock pump its idle was at around 38 with new combo and pump idle is 42. unplugged old pumpwas 45 new pump 48. I was just wondering. A little hesitation at idle withthe new combo. Stock chip though. O2 is .090-.750 at idle Blms after idleing for 5 minutes are 127/128 If i give it gas and let off blms go to 115/143 then come back to the 128/128 mark. thanks guys.

 

oh vacume was 18hg last year. 14ish hg this year. PB work perfect still.

 

An Adjustable Fuel Pressure Regulator is the solution to your problem.

And here is my take on the deal with running an open element breather on a MAF car (much changed from my original views on this) :

The deal is that the PROM calibrations on an MAF system are expecting to get a certain amount of air through that breather pipe that is connected to the TB. The system also is banking on the MAF signal being accurately calibrated to give a certain signal per the amount of air passing through it in grams/sec. Now, the breather pipe goes into a port on the TB on the right hand side (the upper one) and is fed into the engine across the TB plates from the lower part of the center area of the TB. The breather airflow is fed onto the incoming air side of the TB plates so the engine will normally be getting this steady stream of incoming air that is actually not directly measured by the MAF. The PROM knows this (or at least its programmers do ) and adjusts the settings accordingly.

If you block off that port on the TB and install a breather, you will do three things: 1.) Allow the crankcase to breath into the atmosphere which is a good thing for the engine as it will have full venting of the crankcase and will have no chance build up pressure in the crankcase that causes problems with blow-by and gasket sealing. 2.) By not having the breather gasses coming into the engine you will be removing Hydro Carbons that the engine would normally see. This will keep the intake system a bit cleaner since that 'dirty' air will be kept out but will also skew the mixture slightly as the PROM is expecting those HCs and is programmed to take them into account. 3.) While technically not changing the amount of incoming air for the engine, you will actually raise the amount of incoming air to the engine as far as the PROM calibrations are concerned. So the net affect will be a slightly lean running condition as the same amount of fuel is going into the engine per g/sec of air the MAF measures, but in actuality the engine is having more air pass through the MAF sensor than it normally would since you have blocked off that breather port and now forced that air to be brought into the engine through the MAF sensor.

So the bottom line is that you really shouldn't do it. But I can tell you that I have put one on MAF systems before and blocked off the port on the TB and have been none the worse for doing so. I have done this to my GTA.... but I also have been constantly tweaking the PROM for its setup...... It is up to you what you want to do but those are the consequences.

Laterzzzz,
Matt

 

Your idle vacuum isn't too bad at all for the cam, especially considering the stock chip (i.e. idling at what like 600rpms)

Spend your time/energy chasing real problems, there is nothing abnormal with your combo except that you should need to burn some chips for it.