PVC Blower
The new stroker engine with the aggressive cam does not develop a lot of vacuum. At idle it is about 14” Hg (normal engine would be 18” to 20”). When revved up vacuum goes to roughly zero. On the highway it is perhaps 2” or 3” Hg. This will become much worse someday when the blower is installed.
I have installed a small vacuum tank and check valve to help with brake boost. That worked surprisingly well. But the PVC system does not work well and in spite of the blow by testing showing low numbers I know the blow by is much higher at high rpms under load. I know this because I am getting oil in the intake from the PVC inlet tube. Also, last summer the Mobil 1 oil got pretty dark pretty fast indicating that fumes are not being effectively removed from the crankcase.
Other testing (leak down, compression, etc.) indicates nothing is wrong and that is the nature of this beast.
Catch cans on both ends of the PVC will certainly help catch the oil mist and I have installed them. Tom at Super Six says this is pretty normal and advocates just putting breathers on the rocker covers. Others on various forums say the same. But it is stinky and this is not a drag car that gets used for a few minutes a month. Also, I am not really interested in time traveling back to 1940s technology.
A full on belt driven vacuum pump would solve the problem. But these present additional problems. Seals on the engine need to be turned around and dirt can get pulled in at every leak. I have to admit an additional 20 HP or so would be nice. It is also expensive.
I think I may have an additional problem given that this is an autocrosser with a stroker engine and normal sized oil pan. I think that the crank is getting into the oil on course and seriously throwing it around making a lot of mist. There is a windage tray but it is small.
Exhaust eductors work well but only on open/nearly open pipe drag cars at high throttle. I decided to experiment and go another way.
I made an electric PVC pump to push blow by fumes into the intake manifold. First what this system is not:
It is not a vacuum inducing system designed to make horse power. I just want to effectively remove fumes from the crank case, keep oil out of the intake, and extend oil life.
The pump of choice was an aftermarket design smog pump for several Toyota and Lexus models. The choice was made because this unit can be completely disassembled, modified, & rebuilt. As noted above this is an experiment. I needed to be able to change it if needed.
Test Smog Pump Link
Change was needed very quickly. I am not sure what voltage these pumps run on but 12 is not the number. It ran on the bench for about 10 minutes and then let the smoke out. During that time I determined it moved quite a bit of air but I did not know how fast it was turning.
Several evenings hunting found this replacement motor:
Machifit 895 Motor Link
The version I bought spins at 3000 rpm at 12 VDC and 6000 RPM at 24 VDC.
It fit up perfectly in the pump. However, testing indicated at 3000 rpm it barely kept up with the blow by under light load. A little more research found this 12 VDC to 24VDC converter.
12 VDC to 24 VDC Converter Link
This will allow the motor to spin up to 6000 RPM. Testing with the pump connected through the Mishimoto catch can and some hosing indicated flow rated 50% more than when revving up the engine. Let’s try it…
I made up a bracket to mount the pump where the battery used to be. The location allows easy access and the ability to drain the catch can.
After a test drive I found that once things got hot the rubber housing around the motor started to collapse on to the motor. I made a cage out of some wire mesh to reinforce it. I also found it needed reinforcing on top because the rubber cover would pull down onto the spinning motor shaft stub and burned a hole in it. That is a bottle cap pushed in there to hold the soft rubber away from the shaft. All held in with some RTV it works very well.
I contemplated putting this motor on a vacuum switch but after testing I decided it does not overheat and appears to be able to run indefinitely. I decided to forgo the response time for the motor to spin up and become effective. It runs all the time the ignition is on.
That was immediately a problem as it is whining away even if the engine is not actually running. I added a switch to turn off the entire aux power circuit I added with the power steering pump (it has a temperature switch so it does not run all the time).
I cut up the additional dummy button on the console that is intended for fog lights and fit the switch inside.
It took a bit of fiddling and trimming but it fits (barely).
So – How does this work? Jury is still out. First event was last weekend. Came in 13th and 9th in PAX on the two days. Mistress performed very well:
- New rear coil overs are very nice. At the test and tune on Friday I was able to get the car very balanced in long sweepers and get tire pressures set up.
- No leak at the front main seal area.
- The power steering cooler worked very well. Fan came on sometime during a run and shut off a minute or two after words. It did not heat up the tire (although I was spraying both front tires each run (very hot weekend)).
- Race Louvers dumped heat and allowed the engine to cool back down quickly even without the hood up (and they look cool).
- The brand new O’Reilly replacement power steering rack blew out a seal on Sunday with two runs left. It was packed up and sent off to Turn 1 Steering for a proper rebuild Monday night before I even unpacked the truck. I checked temperatures on the pump and rack and never saw them more than about 165 degF. Just not up to this kind of abuse.
The PVC pump worked – but not well enough. Oil still looks like new. However, I still got oil in both catch cans (PVC inlet and outlet). In fact, the inlet can collected more oil than the outlet can at the pump. Interesting - All the motive forces (engine vacuum and pump) are pushing towards the intake manifold. Yet the upstream can collected more oil.
This makes me wonder if there is not another dynamic involved (dynamic being the key word). The inlet PVC tube connecting the air intake to the rocker (through the catch can) is near the back of the engine. Is it possible that, under acceleration and WOT, with blow by at max, there is oil collecting at the back of the rocker cover and finding its way out? The other PVC tube would see the same pressures but it is at the front of the engine.
Either way, oil should not find its way out that tube if the crankcase is under even the slightest vacuum. Need more/better pump. The same people above supply a 6000 rpm 12VDC to 12000 rpm 24VDC motor in the same housing. It should arrive in another week. Even if it is not 100% effective it appears to be helping. We will see...
Below is a video to my best run on Sunday. This is at Chippewa County Airport (formally Kinross AFB in Michigan’s eastern Upper Peninsula. A very good venue for autocross.
Run 5 Sunday - Kinross