Looks great! Wouldn't work for boosted apps, but I bet it works great on the stroker.
...although, with a good high-flow check valve I think I could see this working on a boosted motor. Now you got me thinking!
I just have my PCV system venting to the atmosphere due to the boost, but it would be great to have crankcase vacuum when not under boost.
How are you measuring vacuum?
Forced Induction (FI) engines, be they Turbocharged or Supercharged, share a number of interesting issues. First thing to consider is the TB location. The TB will either be in front of the compressor making is a draw through configuration, or it will be after the compressor making it a blow through configuration. More about that later...
Both have advantages. For this discussion however...
FI engines, large displacement and high compression engines all share common problems. With higher cylinder pressures comes greater blow by. Which is to say the amount of compression that leaks past the compression rings into the crankcase. Also, spark advance becomes an issue with the higher cylinder pressures as the engine will have a tendency to detonate, aka "ping".
ALL ENGINES HAVE BLOW BY. sorry about the yelling but... The purpose of the PCV system is to deal with the blow by by preventing the oil vapours from being discharged into the atmosphere. The problem that the engine has with oil vapour is that is does not burn nearly as well as fuel. This makes timing critical as the oil vapour effectively lowers the octane of the fuel. The more vapour, the lower the effective octane.
So, let's look at ScienceguXJ's issue. He has increased the displacement by 25% and raised the compression ratio from 8.8:1 to 10:1.
If we accept the data that says the compression ratio is 9.1:1, what he has would be an increase of 10%. From the 8.8:1 starting value, the increase is 13%. Either way, this is asking a great deal of the stock PCV system.
His compression test reported a range of 175 psi to 182 psi. Given that a "perfect" 10:1 ratio should reveal 180 psi, his engine (after 3 years) is in very good nick indeed. It has a 3.8% compression spread which for a non-blue printed engine is remarkably good.
We spoke extensively while he was here and he realized that the issue may have been present from the off. I suspect this to be the case and, I am not surprised. Nor do I accept that the engine builder is at fault. IMO, the stock PCV system was overcome by all of the changes made.
We measured the manifold vacuum at the port that used to service the return line from the PCV system. On the 99.5+ manifold, that port is located just aft of the TB, on the top of the manifold. We saw a very solid 15" Hg which, for being at around 6,500' in altitude, is actually rather good.
This became the base line.
We then disconnected the feed line to the front elbow at the air cleaner box and installed the vacuum gauge there as a dead head, not pass by. What we saw was, I believe, 12" Hg. Last time he was here, the same test showed 4" Hg. He has achieved a 300% increase.
I expect his issue will be greatly reduced, if not eliminated.
As for my engine, it's idle vacuum level is 10" Hg owing to the recirculation valve that sits between the compressor intake and the engine intake manifolds. With the TB closed, the "excess" pressure from the compressor is ran back through the compressor. Unlike a Turbo, the compressor is making boost constantly. My TB is draw through in configuration and the vacuum ports are located just under the TB.
Most, if not all, aftermarket Turbocharger setups have the TB in the stock (makes it a blow through) location and utilize a blowoff valve (BOV) or dump valve to relieve the pressure when the throttle is closed. Another approach for Turbo systems is to draw through the TB. Of course, this means it has to be relocated... And a waste gate has to be installed...
For those with a turbo that wish to increase the crankcase vacuum, the return line from the valve cover can be routed to the compressor intake. BUT, and it is a big but, the oil vapors will contaminate the TB. The best bet is to re-plumb the TB to a draw through.
What would be of great service to all would be if we could get some additional data to work with from you folk out there. Let's look at what the typical idle/PCV vacuum is on a stock engine.
Anyone want to help?
Sort of sorry for the book but, it needed done and, you all know how I am...
