Guys,

For the record, I am not opposed to using a catch pan. It’s just that we didn’t have one before, and the builder never mentioned one when we discussed this vacuum tap ProCharger intake extension. We are getting together tomorrow and we will discuss.

Thanks. Brad.

Dan,

You're taking this all wrong. I’m asking questions for a reason. As I said, I’m getting conflicting information from voices I’ve learned to trust.

About vacuum and pressure…. Exactly. You CAN’T have positive crankcase pressure if you’re drawing a vacuum on it. From everything I’ve read, positive crankcase pressure is to be avoided. So a vacuum is applied. Or, at least, it’s vented. This is literally what a PCV is for. You draw on intake vacuum to pull any pressure from the crankcase. Like you said, it ain’t rocket science. It’s not like engines haven’t been set up this way since it was discovered that crankcase pressure was bad

Yup. A 900HP blower motor “ski boat”, that ran for years with nothing more than an oil and plug change in the off seasons. And that was set up exactly as I’ve described; drawing a vacuum on the crankcase from the flame arrestor.

I understand perfectly why there is more cylinder pressure in a boosted engine than NA. We weren’t discussing cylinder pressure. At all.

As I said…. I’m not opposed to a catch can. I will be discussing it with the builder tomorrow. He has two of them on his engine, but he also doesn’t have a full-on chimney where the vacuum will be applied.

Thanks. Brad.

I disagree. A boosted engine will see more pressure get past the rings and pressurize the crank case. What you are doing in not fully pulling a vacuum on it. IMO you will have more pressure on the crank case then your setup can get rid of.

What size line are you running from the valve cover to the air filter?

There was always additional power picked up when I increased the tube inlet size to the blower inlet, free hp. I would make the setup larger in diameter. You will have to get a larger diameter air filter setup though.

There are many benefits of running a vacuum pump. One is better ring seal/more hp.

vacuum in the crank case helps the rings stay seated and stable for a better seal

It helps to seal the piston rings and decreases effort required for the pistons to move. It has been proven over and over to add power. Thats why drag guys spend thousands of dollars for vacuum systems. Many of them have no engine bay to care about, they want power.

Under,

OK.... For context... The 496, in OEM configuration, has no vent to the valve cover. Never did. Not in the truck engine. Not in the Merc engine. GM's solution to crankcase pressure was to build a PCV of sorts into the underside of the intake manifold. It literally draws a vacuum on the crankcase, from the intake. This works great in the absence of a boost condition. In the presence of positive intake manifold pressure, this "PCV" actually induced pressure in the crankcase, in addition to whatever might already be there from ring blowby. This is one of many issues that ProCharger didn't address in their kit(s). In fact, after discovering the issue, by witnessing oil on top of the button at the top of the dipstick tube (that only showed up after I'd run hard enough to get into boost), I called ProCharger to see if they had any sort of fix for it, and they were apparently not even aware of it (at least, that's how it sounded over the phone). We have since eliminated this PVC circuit on the intake, so that issue has been resolved. As we bought the boat, there was also a port fitting in the oil fill cap, with a hose dangling in front of the flame arrestor on the intake snout of the ProCharger, which is down low on the port side of the engine. We did see SOME oil loss over time (a quart or so a season, maybe), but it was minimal, and I can't really be sure whether we were consuming it internally (rings, valve seals, whatever), through the vent hose and through the intake tract, or out the dipstick. I will say I never saw any oil to speak of in the bilge, so, while there was obviously SOME getting out the top of the dipstick, I don't think it was a significant portion of the little loss we saw. I know we hade a FARQ ton of oil in the bilge, front of engine and back of rear seat after the piston let go, so I'm very aware of what REAL crankcase pressure looks like. By the looks of the area of the bilge around where the ProCharger intake is (where the crankcase vent tube was dangling), there was no sign of a significant amount of oil, but there was a thin residue of what appeared to be oil vapor adhered belt dust. Nothing seemed irrational about it, considering the blower belt and vent tube in the area. There was also some of this gunk on the screen of the flame arrestor. This was actually where I initially came up with the idea of the extension that incorporated the port/hose barb in the pics above.

What we've done here is to move that PVC circuit from the intake manifold to the intake of the ProCharger. Whether there is any oil or oil vapor making it to the cylinders has not changed, outside the fact that it is less likely oil will make it to the port in the oil fill cap than there was it would get sucked into the PCV under the intake manifold (or, at least, logic would dictate). I have no doubt the current sitch is not drawing nearly as much vacuum as the OEM intake circuit was, but it's also never going to induce pressure of any kind. Essentially, what we have is a passive crankcase vent with some attempt to induce vacuum. Additionally, the OEM should have drawn less and less vacuum as the throttle body opened up, even without the ProCharger, as an engine at WOT is at zero manifold pressure; neither pressure nor vacuum, as I understand it. The current sitch should induce more and more vacuum as the RPM increases, to coincide with the potential for increased ring blowby due to increased cylinder pressures from boost. We have improved the overall setup by orders of magnitude, as-is, from my observation.

I just don't see the potential of a vacuum pump fitting into the current configuration. Not a belt driven one, anyhow. I suppose an electric one could be implemented, but I'm sure that opens up a whole new can of worms. FWIW... You'd be surprised how much vacuum can be drawn by venturi. Something very similar is used to empty waterbeds in a matter of minutes, even drawing the water uphill, and carburetors draw fuel by venturi principle. Once we get the engine running, I will check the draw on the vent tube. I'm betting it will hold itself to your thumb quite well. We'll see.

As it turns out, the builder has a couple catch cans he is willing to let me select from. We will be discussing the matter later on today (assuming we're still on). As I stated earlier, I am not opposed to the idea. We, the builder and I, just hadn't discussed it to this point. Someone asked if I was intending to implement one, I answered no, and the flame-on commenced. I think we had a fair bit of talking past one another. It happens on these forums. Meh....

I still can't wrap my head around the increase in HP from drawing a vacuum on the crankcase. But I'm certainly not going to argue against it, as I have no clue on the matter. My question on it earlier was a genuine one. That said, HP was never my interest in this specific venture. I was simply trying to do something with the crankcase vent and replace the crankcase vacuum draw lost with the intake manifold modifications.

To answer your question... It is a Ø1/2" ID hose, but there are ~Ø3/8" passages through the fittings on either end.

Thanks. Brad.

Technical Minute: Vacuum Pumps and Power - Automotive Tech Info

If you end up using the catch can, I would look at the Motion Raceworks one. I put them in my black thunder laster year and have been very pleased with them. There is a big difference between the cheap ones a good ones.

Brad everything you typed out about the stock 496 truck engine has nothing to do with a boosted 496 marine engine. It isn't even apples to oranges.

I'm curious how much "vacuum" do you think your new setup will put on the hose mounted between the tb and air filter?

UnderPSI,

No? The only differences between the truck engine and the Merc engine are the cam, a deleted fuel return line, the cooling plumbing, exhaust and ECM. That's it. Same rods, pistons, rings, intake... Literally ALL the components related to the topic immediately on hand are the same. Since my engine actually has the good crank, I suppose Merc might have had the presence of mind to actually address the main and rod bearing clearances while they were at it. I'm not holding my breath, because they chose not to address the valve springs while they were changing the cam (all this assuming Merc actually did these things rather than specing these changes from GM). Otherwise, ProCharger and their significant shortcomings with the kits they provide aside, not only is it, in fact, apples to apples, it's granny smiths to granny smiths. I was simply laying out what I had prior to the piston failure. Keep in mind, the ProCharger has been on the engine since LONG before I bought the boat. Prior to the piston failure, whenever in boost condition, we were actively pressurizing the crankcase, despite an open vent in the oil fill cap, enough to force oil up and out of the top of the dipstick tube. I'm guessing it's been running like this for 300+ successful hours. In the rebuild, we have converted from that condition of actually inducing positive pressure into the crankcase under boost condition to, at the very least, NOT. That alone is a MASSIVE improvement. With the hose connected on the intake side of the ProCharger, that port will always be in a state of vacuum until whatever blowby we have induces more pressure than that vacuum can overcome. Since that vacuum will be relative to RPM, I'm betting that condition is never reached. We'll see.

As for the level of vacuum that will be pulled at the intake port, I'm betting it will be enough at WOT to pull a blood blister on whatever you're dumb enough to stick the other end of the hose to. Are you familiar with Bernoulli's principle and Venturi effect? Your carburetors are.

At the end of the day, I'm working with what I have. I HAVE to draw a vacuum on the crankcase somehow (right?), and I CAN'T do it with the OEM intake PCV circuit. So, I'm relying on the success of the dozens (of dozens...?) of 496 Whipple setups out there that DON'T have catch cans, but, rather, a blower intake ported PCV circuit and a filter on the end of a passive vent hose that NEVER has any oil in it. I am simply combining the two into one circuit. If, by some happenstance, I see oil or oil residue in this vent line after initial run in, I'll address this topic accordingly.

Thanks. Brad.