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Topic Review (Newest First)
04-22-2009 06:36 PM
1968ccaammaarroo Venting to the Air cleaner is a pretty good way to do it. You might want to check around at the auto parts stores and look at the different "breather" filters out there.

One thing that you might consider is the "breather" filter from a mid 90's VW 2.0L 4 cylinder. It has 2 approximately 18MM barbs on it and a barb on the bottom that would go into one rocker cover.

If your rocker covers have the "grommets" in 2 places on each cover the best way would be to put a breather filter in 1 corner, then run a hose from the same side other hole across to the VW "breather" in that grommet. Then the second barb run a hose to the air cleaner.

This has a couple advantages, you get fresh filtered air into the crankcase to replace the fumes, the VW breather separates a lot of oil and it drains right back into the rocker area and most of all its CHEAP!
04-22-2009 02:50 PM
neverending This is a street car apart from 2 or 3 'run wot you brung' days a year. Having said that, I do tend to 'drive' it unlike most of the rodders I've met in the UK who swan around seldom over 3000rpm. My motor pulls incredibly well between 4 & 5K considering the 8.5:1 compression and there lies part of the problem along with a naf cam. However, I dont have money for cam - heads - etc so I must enjoy what I have. The motor was new 2 years ago. At 10K miles most if not all the valve stem seals destroyed themselves! The dealer was very good about it although had never seen anything like it before. I am considering modifying the Lid of the K&N air filter so the breather pipes run in through the top and are directional towards the centre of the holley.
04-22-2009 02:19 PM
oldbogie
Quote:
Originally Posted by neverending
I know there's been countless posts and I've read most. However it seems crazy to me, I have what amounts to one of the most common set ups in rodding. TH350 /350 290HP /600 holley. Your entry level basic motor albeit a wheezy low compression duff cam motor. I have managed to make it almost fly considering what it is,but I have one or two unanswered problems. Everyone has an opinion and I'm looking for the definative answer to this question. Currently running open breathers on both rocker covers, venting to atmosphere. Introduce PCV and the carb is naf. Cant use exhaust evacuation , too much back pressure. Yesterday the guy I bought the engine from said run pipe from both sides and T into the air filter. Does this sound ok?
Are you driving on the street or racing this?

Basically a new 290 horse 350 should not have so much blow by that crankcase venting is a problem, at least for the street. If this is pressurizing the crankcase to a point a force can be felt when the vents are covered with your hands or to where oil smoke is issuing, then one needs to consider an internal failure.

For the street PCV is the way to go, it insures that combustible gases present int he crankcase are cycled into the combustion chambers and burnt. Venting one side back to the air filter insures both that the crankcase gets clean filtered air to replace the fumes draw out by the PCV and that for a street engine that occasionally sees WOT, where the PCV doesn't function, that there is an alternative path to eliminate crankcase vapors via being sucked into the carb's air horn.

Street engines with Positive Crankcase Ventallation systems far outlast those without. PCV systems are extremely good at getting rid of vapors that left to condense in the crankcase cause considerable corrosion damage to intenral engine structures, and develop sludge and varnishes in the lubricating oil.

A vacuum exhaust system is only required on a competition engine or a super charged engine where the crankcase is under so much blow by pressure that there is not other way to provide sufficient amounts of venting without also putting a pump on the crankcase. Such systems require an oil separator to trap liquid coming out with the vented gases.

Bogie
04-22-2009 09:20 AM
DoubleVision It upsets things likely because you have low vacuum. Causes of low vacuum can be many things such as a vacuum leak, low initial spark timing, low compression, camshaft too large, leaking valves and rockers out of adjustment to name a few.
04-22-2009 05:41 AM
neverending
Quote:
Originally Posted by DoubleVision
Yes, you could do so but you would only want 1 side run into the breather, the other side will act as a vent. However keep in mind this will cause the air filter to ruin alot faster than normal, and they`ll be a mess in the air cleaner.
I don`t understand exactly why you can`t run a PCV as this has the benefit of keeping the oil cleaner so it lasts longer. If you simply don`t have a vacuum port due to the 1 large port on the holley carb you can do it 2 ways. You can get a screw in vacuum port that screws in the intake runner right behind the carb to run the vacuum from the brake booster or you can T the line and have it run both the brake booster and PCV. This last method is what I did once. You can also order 4 hole carb spacers with a built in rear vacuum port. And last but not least, you could always stick a Quadrajet on it.
I dont mind if I run a PCV or not. Does it make any difference if you hook up to the large port on the holley or the intake behind the carb ? Reason I ask is when I hook up to the Holley it upsets things. I also have low vacuum at idle.
04-22-2009 05:21 AM
Fergusonic
Quote:
Originally Posted by DoubleVision
I don`t understand exactly why you can`t run a PCV as this has the benefit of keeping the oil cleaner so it lasts longer.
What other advantages does running a PVC have?
04-22-2009 02:30 AM
DoubleVision Yes, you could do so but you would only want 1 side run into the breather, the other side will act as a vent. However keep in mind this will cause the air filter to ruin alot faster than normal, and they`ll be a mess in the air cleaner.
I don`t understand exactly why you can`t run a PCV as this has the benefit of keeping the oil cleaner so it lasts longer. If you simply don`t have a vacuum port due to the 1 large port on the holley carb you can do it 2 ways. You can get a screw in vacuum port that screws in the intake runner right behind the carb to run the vacuum from the brake booster or you can T the line and have it run both the brake booster and PCV. This last method is what I did once. You can also order 4 hole carb spacers with a built in rear vacuum port. And last but not least, you could always stick a Quadrajet on it.
04-21-2009 11:39 PM
neverending
SBC breathing set up

I know there's been countless posts and I've read most. However it seems crazy to me, I have what amounts to one of the most common set ups in rodding. TH350 /350 290HP /600 holley. Your entry level basic motor albeit a wheezy low compression duff cam motor. I have managed to make it almost fly considering what it is,but I have one or two unanswered problems. Everyone has an opinion and I'm looking for the definative answer to this question. Currently running open breathers on both rocker covers, venting to atmosphere. Introduce PCV and the carb is naf. Cant use exhaust evacuation , too much back pressure. Yesterday the guy I bought the engine from said run pipe from both sides and T into the air filter. Does this sound ok?

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