How to make a progressive work properly on a VW engine.

[busman78]

John, filtered fresh air is being sucked into both valve covers through 1/2" tube/hose, trust me there is a lot of fresh air being sucked in and through the engine, and out the tower and into the intake manifold at center. This is probably 95% or better fresh air with a little oil vapor mixed in, although the oil is baffled through a series of copper scrubbers. A crankcase can have pressure without much blowby, therfore the negative effect I have on the case keep pressure down, evacuates any, if any fumes and keeps the inside of the engine sparkling clean.

Aftermarket air cleaners are literaly worthless for sucking crankcase fumes, they are too large and have no restrictiveness (is that a real word) to them. Great for getting large amounts of air to the carb, worthless for evacuating the crankcase. If you doubt that put a vac gauge on the dip stick tube.

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hey it's your engine, I don't care. But don't kid yourself that it's ok.

The engine should be SEALED. If there's fresh air in there, you have dirt coming in with it too.

Normally you install a PCV valve to prevent back-flow of air into the crankcase, you don't just have an open hose. This way vapor only flows outwards.
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[busman78]

You missed the word FILTERED, the 1/2" hoses to the valve covers have there own filter, that means each one has a filter, therefore it is clean air entering the engine at the valve covers, as VW originally did on the the T4's. The intake sucks it all out, what a concept. The .120 orifice acts as a PCV valve but is a constant since I have a carb and not FI which has AFM and can automatically adjust.

If you would like to learn about this do a search for PCV and Ray Greenwood on this forum and the STF. In fact right now on the Bay Bus Forum the third or fouth thread down is "Type 4 Breather Box Valve Question", it delves a little into this.

[modok]

John, my questions were:

Some type 1 manifolds have separate riser passages from the butterflies to the lower tube, others have an open plenum. Which is better?

And, to go with your baseline jetting, what are the correct specs on the power valve? I'm sure there are different size jets floating around out there.

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but why would you create a vacuum leak on purpose, when you can vent the crankcase without it? "what a concept" - You don't have to get snarky!

Why use something to act as a PCV valve when you can use a PCV Valve.

But this brings up an interesting experiment I have not tried. Put a Wideband on the blowby, to see if you are correct. I contend there is almost no O2 in there.

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Plenum probably doesn't matter much, since they join anyways at the X-tube. There might be a slight difference, I don't know. The heat, jetting, and setup are what's important, since they are almost never done.

I have not played with the power valve. I have not had a need to once the jetting and other setup was correct. Usually the basics are so jacked up, they should be addressed first. A Power Valve just increases the size of the main jet below a threshold MAP setting.

The rampant use of bigger primary/smaller secondary (backwards) and square jetting on the mains, is a HUGE problem. And there is a TON of resistance to try another way. But square jetting leans out bad at WOT, or is stupid rich on the primary.

[Jimmy111]

[millerje78]

informative thread, but why in god's name would anyone pick a center-mounted progressive over dual carbs? shoot, if one goes to the trouble of losing the stock center-mount, why opt for another center-mount in its place? just stating the obvious I guess. seems like the progressive carb was obsolete the day of its inception, but thats only my opinion.
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centermounts have several advantages over duals.

You don't have to take them on/off for engine removal/installation

They are more durable in "rough" applications, the intakes don't come loose like duals do.

No sync issues.

Cost Less.

The main problem with the stock carb is it's too small, and limits power as a result. Centermounts on upright engines work VERY well when they are properly setup. Most are not.
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[millerje78]

[miniman82]

[modok]

Centermount advantages?

One float bowl in the middle is going to be much less trouble than two over the heads.
Also one big air filter in the middle is WAY better than two little ones by the wheels!
For performance though, I don't know why anyone would use a proggy rather than a Drla or Idf; these carbs are made for racing.
The progressive is made for conservatives.
The idea is the progressive carb, with it's progressive action, should have better drivability with better fuel economy, running on it's small primary barrel and venturi.
But it seldom works out. Because they forgot to make the primary small!

The carburetor for conservatives is not conservitive enough to conserve!

To answer your Ceiling Question, Holley rates the proggy at 280CFM!

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Centermounts have a huge advantage off road (no delicate linkage to break or go out of sync), and the air is cleaner in the middle than out by a dusty wheel. Intakes don't go loose either.
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[busman78]

Oh so true, duals really do not like being bounced around.

[vwracerdave]

A tip I'll share. I believe using the stock metal intake gaskets on any centermount carb is important to help heat transfer from the heads to the end castings. I do not use the paper fiber gaskets on any centermount carb. I feel they help insulate the needed heat.
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[vwtrey]

I wish I would have seen this thread earlier. I have a progressive that ran great at sea level, but now its at 6k ft, and I need to rejet it. I dont know what size jets/airs are in it now. Ill have to pull them out and see.

[joescoolcustoms]

[vwguy2]

I have a center mount Weber FEV in a 73 Baja. It gets down to the teens on some nights and the car doesn't want to accelerate from stop for the first 20 minutes or so.

I warm it up for a good while, enough time to scrape all the ice off all the windows and to allow the hazard light switch to thaw.

After I get on the highway, it seems to drive fine. Once I get off the highway, it also drive fine - so it seems to do well once warm.

I tried putting a magnetic block heater on intake manifold, but couldn't get it fit well. I currently have one on the passenger side heat tube which gets at least the tube very hot.

Questions:
1. Will a properly setup intake manifold work down to 10 degree F?

2. Does it make sense to route air from the heat exchanger to the carb instead of the passenger compartment? (I'd rather be cold than fight going up hills from a stop with idiot drivers behind me)

3. the driver's side of the intake manifold says SCAT. Is that "a good intake"?

4. If I give up and switch to duals - will the air filters get soaked on a baja while driving on really wet and poorly drained roads?

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1. Will a properly setup intake manifold work down to 10 degree F?

Yes. But you have to have a good intake AND EXHAUST. A good intake with a bad exhaust will also not work right. You HAVE to have both.

2. Does it make sense to route air from the heat exchanger to the carb instead of the passenger compartment? (I'd rather be cold than fight going up hills from a stop with idiot drivers behind me)

Just use the elbow to draw heated air off the 1/2 head, and route that to the filter. That's what the factory did.

3. the driver's side of the intake manifold says SCAT. Is that "a good intake"?

I have not seen their intake in >5 years. You need one that routes exhaust to the carb base, NOT just along the bottom tube. When I found the one that was designed the best, that's the one I recommend.
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[busman78]

Joecool, I am doing nothing more than what all modern cars do today, clean air in and crankcase fumes out. I am not deliberately trying to create a vacuum on the case, just negative pressure so that pressure does not build and try to find a another way out, like through seals and gaskets.

I am beginning the second transition to this concept, will soon have the filtered air that is drawn into the case getting sucked out into the exhaust, that will eliminate the line to the intake.

If you build race engines then how do you scavenge the case? One way or another crankcase pressure needs to be eliminated. Some like breather boxes, I find them worthless, some do a blow through concept which is very efficient and is an idea I have played with. Now matter how tight an engine is, even with zero leak down an engine will generate internal pressure, why fight it, best to eliminate it, and sucking (or blowing) it out is, in my opinion the best way.