Greg88

Hi Guys,

I just installed an D1SC on my LT1. I installed a vacuum/boost gauge and the car is reading 7 inches of vacuum at about 900-1,000rpm idle. The problem is I don't know what the car was running prior to the install of the D1SC. I checked all my vacuum lines zip tied them up. I don't believe I have a vacuum leak. I did install a Might Mouse catch can as well not sure if this messed with the system or not. I did try a friends mechanical boost gauge and it showed the same number (7).

Here is some info on the engine:

Short Block
Bored .030 over = 355ci
Mahle Forged 5CC Dished Pistons
Eagle 6” H Beam Rods with ARP Bolts
Stock Crank cut and polished
Melling High Volume Oil Pump

Heads/Cam/Intake
Lloyd Elliot Custom Grind Cam
223/230 .565 Lift 112LSA
LS7 Lifters
Cloyes Timing Set
Comp Pushrods
AFR 190cc (Ported Flow 294/208 CFM)
60cc was 65cc – 2.05/1.60 @.600
Crane 99893 Double Valve Springs
ARP 7/16” Rocker Studs
ISKU Adjustable Guide Plates
Comp 1.6rr NSA 7/16”
Ported Intake
58mm Throttle Body
60LB Siemens Deka Injectors
Aeromotive Adjustable fuel pressure regulator
ATI Super damper Balancer and Hub
Pace Setter Long Tube Headers
Off-Road 3” y-pipe
Procharger D1SC with 7.65” Crank Pulley and 4.00” blower pulley
Aluminum 3” Piping with Ebay FMIC and Red Race Bypass Valve
AEM- 30-3300 Methanyl Kit with 1000mm nozzle
Racetronic 300lph fuel pump and upgraded wiring harness
Mcleod Racing Twin Street Clutch
Tuned for 91 Octane – PCM tuned as 2000 Trans am (LS1 PCM)
10.3:1 Static Compression

I also added a picture for reference on how I was told to install my catch can directly from Might Mouse. Basically a hose comes from my passenger side valve cover to the inlet of the can. A hose from the exit of the can (PCV valve inside can) to the barb beside the old PCV valve exit. The PCV valve exit now has an orifice that allows fresh air from the inlet of the supercharger into the intake for fresh air into crankcase.

I also do not have the factory air pump installed on the car anymore, not sure if this would cause an issue or not?

Any information or guidance is appreciated. The car seems to be running good that's the weird thing.

Injuneer

Do you have a scanner, or scanning software? You can check the accuracy of the boost gauge by subtracting barometric pressure (BAR) from manifold absolute pressure (MAP). That holds for either vacuum or boost. Both BAR and MAP are available from the PCM.

No real experience with a blower application, but wouldn’t it seem possible that even a centrifugal compressor might develop a small amount of boost at low RPM, which would raise the manifold pressure (reduce vacuum) slightly?

Probably a question best asked on the “Forced Induction” forum. But unfortunately it seems to take forever to get an answer due to disappearing participation by the long time members.

Greg88

I can get access to a snap on scanner. I’ll try that out forsure. Both my mechanical and electronic gauges were both showing exactly 7.5 inches. I understand exactly what you mean with the blower providing a small amount of boost. I’m going to do a little more research. I have an oil leak as well, which I am sure doesn’t help with this. Is it common that the EGR valve leaks as well?

Injuneer

Your probably OK with the gauge reading.

When/where does the EGR leak?

I may be showing some ignorance with my questions, but maybe it will stimulate some discussions . And never too old to learn something new.

What MAP sensor are you running - stock 1bar, 2 bar? That will affect the ability of the PCM to report boost above atmospheric pressure.

Continuing thought process - doesn't the bypass valve open (by vacuum) at idle to relieve any boost?

Greg88

Just searching on goggle and people are suggesting possibly EGR leak. Not sure exactly where or why.

I believe the MAP sensor that is hooked into the engine is the stock sensor. Not sure how many bars. My electronic gauge has a MAP sensor which has 3 wires coming from it to the gauge.

The bypass valve does operate off vacuum. So it’s open when it’s positive on vacuum then closes once the boost kicks in.

My PCM isn’t tuned to the final settings ... basically has a start up tune until I get it dynoed.

Greg88

Wow, making my head spin!! The exit side of the catch can apparently has a PCV valve inside the can to prevent air flowing backwards if this makes sense. Is that what you are saying?

If not maybe you can explain/draw what you think needs to be done? Also the can has a filter on the top, not sure if this makes a boost/vacuum leak at all?

Injuneer

I'm assuming you bought the MightyMouse LT1 “wild” kit with the PCV valve in the can fitting. Contact Dave at MightyMouse - contact form on website. The instructions on his website for this specific kit are not “crystal” clear. He shows the LT1 kit installed, using the filter top unit. Then indicates the 5th Gen filter must be pushed down, which appears to block it off. But the connections are not clear.

https://docs.google.com/document/d/1...HM/mobilebasic

https://www.mightymousesolutions.com/contact

Did you put a vacuum cap, with a strong hose clamp on the throttle body port where the line to the valve cover was removed?

Greg88

I did contact him via email regarding the filter! I just assumed with pushing the filter down was to "lock" it into place. Just curious why you think that blocks it off? Not being a dick just curious as I want to learn!

I did cap that barb off on the side of my throttle body with a tight rubber cap.

I'm going to check some connections tonight with the vacuum gauge.

Does the little plastic connector that goes into the passenger side valve cover have a check valve in it at all?

Injuneer

Look at the sketch at the bottom of the instruction sheet. At the top of the can is a pink insert that appears to seal to the edges of the can. It has a smaller diameter cylinder, with multiple small holes at the top. The holes appear to be the path that allow air flow to/from the filter. I am GUESSING that when the filter is pushed down, the inside surface of the top of the filter seals off the flow holes. I have never used the MM, but given the design of the stock PCV system, it should probably remain “closed”.

Under boost the cap on the throttle body hose nipple could be blown off. I have a small worm type clamp on the hose, which stayed in place after a nitrous “pop” that bent the bottom of the throttle blades to a 90° angle.

The stock plastic elbow that pushes into the grommet in the valve cover is only an open, 90° elbow - no check valve.

In the stock PCV design, the hose from the throttle body to the valve cover serves two purposes, and needs to be capable of flowing in both directions. The port on the throttle body connects to a hole in front of the throttle blades. There is very little vacuum at that point, just a small negative pressure due to pressure loss through the air filter, ducting and MAF.

N/A operation - With vacuum in the crankcase, the vacuum pulls filtered air that has passed through the MAF sensor through the hose, into the valve cover, and through the crankcase where it picks up the blowby gasses. At WOT where there is no intake manifold vacuum and high blowby, if pressure builds up in the crankcase, it relieves by flowing up to the valve cover and flows from the valve cover to the throttle body. That's why a plugged PCV valve, or excessive ring blowby can cause enough flow toward the throttle body that it entrains oil and dumps it into the airstream entering the intake manifold.

Greg88

Ahh, im picking up what your are saying. I wonder why they even bothered putting a filter on the can then? I guess keep it multi purpose.

Ill keep an eye on that fitting, maybe throw a zip tie on it!

Thanks for all the help!

Injuneer

And just to be sure everyone is on the same page on the stock PCV valve end of the system.

While it appears the end of the PCV valve inserted into the grommet on the driver side of the intake manifold is exposed to the intake plenum, it isn’t. Immediately inside the manifold is a wall that separates the PCV system from the intake plenum. That provides a passageway from slots on the bottom of the intake manifold, to the inserted end of the PCV valve. The PCV valve is pulling air and blowby gasses directly out of the crankcase. The external end of PCV valve connects to the intake manifold plenum via the vacuum port - 93/94 use a C-shaped hose to connect to the vacuum port on the manifold just behind the PCV grommet. 95-97 use the rubber/metal tube to connect to a manifold vacuum port under the throttle body.

If you leave the stock system in place with boost, the line from the throttle body to the valve cover puts the boost pressure fully into the crankcase. And the boost pressure is seen at the manifold vacuum port, putting pressure on the outlet end of the PCV valve. In effect, there is no crankcase ventilation taking place and oil system seals are going to start leaking, the RTV will blow out of the intake manifold/China wall seal. At least until the hose from the throttle body pops off.

Greg88

Which totally makes sense how my catch can is hooked up. Now it has an inlet from the air intake side of my blower to the old PCV exit location which provides fresh air into the crank case. The air vents out of the passenger side valve cover into the catch can. Then oil/air is seperated and then the clean air goes back into the intake on the old “C” shaped hose inlet beside the old PCV exit. Correct?

Injuneer

To me, the air flows out of the system under boost, into the suction side of the blower, not the other way. There is a slight vacuum at the blower suction, caused by pressure being lost through the air filter. When pressure starts to build in the crankcase, the flow has to be into the blower suction side. The catch can has to knock the oil out of the blowby leaving the crankcase and entering the blower suction. Any appreciable amount of oil in the feed to the engine will reduce the effective octane of the gasoline, and result in detonation.

But maybe there is some other way it works as you sketched it. I would clean up your sketch, showing the catch can in a more realistic representation, with the inlet and outlet shown on the sides, labeled clearly, and the filter shown on the top. I believe you show the outlet of the can connected to one of the vacuum ports on the driver side of the intake. If that's the case, label it as such.

Then attach the sketch to an email to MightyMouse and see if it is correct.

Greg88

That is actually the same photo I sent Dave at Mighty Mouse. He said that was correct. Here are some of the comments he made about it all:

"the catch can has a new pcv built into it that goes straight to intake manifold vacuum.

normal pcv cycle is from fresh air into pcv orifice clean

out of valve cover plus blowby dirty to can

remove stock pcv hose passenger side and stock pcv hose and valve drivers side

you will cap off the port at the top of the throttle body

you will run the large hose from the passenger valve cover to the catch can inlet

run the pcv valve exit from the can to the intake manifold vacuum barb drivers side

you will install PCV orifice provided in the pcv grommet and connect this to your main air filter with hose, or mount a small separate filter here for pcv air supply."



can pressure release if necessary, or vacuum through can pcv valve to intake manifold

the old pcv is removed and the supplied orifice put in its place. this is now just another crankcase passage, one that is shielded, restricted, and repurposed for controlled pcv fresh air supply.

the pcv control and boost checking as well as the one way pressure release is all built into the can, as it is of course needed. "


In regards to the hose from the inlet side of the blower to the old PCV area, I don't understand how that hose is "shielded, restricted, and repurposed for controlled pcv fresh air supply"

Injuneer

If he approved your sketch, that should be good enough.

I don't quite understand it. Under boost the pressure in the intake plenum is going to be higher than the pressure in the valve cover. I can't see how anything could flow out of the can into the vacuum port entering the plenum. Maybe there are two differnt operating modes.... one for idle/limited boost and another for high boost.

Here's a foolrpoof system.... a (black) crankcase vacuum pump (right under the intake elbow) connected to the driver side valve cover. But that thing made close to 30 PSI.