Ls7 Compression test

[LS ROB]

Still getting more oil in the catch can than I feel should be in there, so, I decided to compression test the engine. Swap vehicle with Ls7 NA with cam, long tubes, MSD Intake. Performed the test on a cold engine. Cranked the engine 5 cranks, got out and recorded the number on the guage. I did note that all cylinders seemed to hold the reading quiet well. As in, I viewed the reading for roughly 3-5 seconds to see how quickly the readings would fall, if any. My approach may be flawed, so, I am open to any pointers you may have. I also, do not know what psi is supposed to be for a healthy engine. Internet searches show a large variance. I have attached pictures of the spark plugs as well. I should note: the plugs do not have oil on the threads, that is anti-sieze.

Thanks.

Cylinder PSI

1.) 165
2.) 170
3.) 165
4.) 170
5.) 165
6.) 165
7.) 169
8.) 165

#1.jpg#5.jpg#7.jpg#2.jpg#4.jpg#6.jpg#8.jpg#3..jpg

[blindsquirrel]

Whether the gauge drops after you stop cranking is purely down to the check valve in the gauge, there's no pressure remaining in the cylinder after engine stops turning and everything goes static. A leakdown test would be more useful, but still not definitive (there can still be leakage issues while running that neither compression nor leakdown tests can find).

[blindsquirrel]

Oil is fresh, and correct viscosity (no fuel dilution)?

90% or more catch can installs are plumbed wrong, FYI. Usually create more problems than they solve.

[LS ROB]

Oil is fresh, and correct viscosity (no fuel dilution)?

90% or more catch can installs are plumbed wrong, FYI. Usually create more problems than they solve.

I see. The check valve thing makes total sense. I guess I have never really thought of how those things work. I change the oil every 3k. Still haven't bought into Mobil1's 10k miles guarantee. The engine has a little over 6k miles on it and i have changed the oil a handful of times thus far with new Mobil1 oil filter every time. I started out running 5w30 and experienced lower oil pressure than i thought it should have. It would get down to around 15psi at idle but always come back up with any sort of throttle. Cruise shows 28ish psi and over 3krpm shows 38ish. It tracks with what i have found online from GM Performance pdf on the ls7. So, I increased to 10w40 on the most recent change and it pulled the idle numbers up some but still under 20psi. Basically, What I have found is that I had a good bit of oil going into the catch can and through the engine (plumbed wrong as you have said) so i would be low on oil/pressure. Corrected that, and it is alot better, but I'm starting to think that my parts selection is playing into this somehow and that i need to use factory valve covers/pcv system. I did happen to come across some information that states GM now recommends 15w40 for the ls7 but i'm not sure if thats daily use or track use. **Note: I do have a pickup tube hold down to hold the tube and pump together.

[blindsquirrel]

Sometimes (ok, all the time) I think GM's oil pressure specs are written by the warranty department who never want to have to replace anything ever for any reason, and not by the engineering department who I imagine spend the majority of their working day doing this:

picard-facepalm.jpg

[Alvin]

I see. The check valve thing makes total sense. I guess I have never really thought of how those things work. I change the oil every 3k. Still haven't bought into Mobil1's 10k miles guarantee. The engine has a little over 6k miles on it and i have changed the oil a handful of times thus far with new Mobil1 oil filter every time. I started out running 5w30 and experienced lower oil pressure than i thought it should have. It would get down to around 15psi at idle but always come back up with any sort of throttle. Cruise shows 28ish psi and over 3krpm shows 38ish. It tracks with what i have found online from GM Performance pdf on the ls7. So, I increased to 10w40 on the most recent change and it pulled the idle numbers up some but still under 20psi. Basically, What I have found is that I had a good bit of oil going into the catch can and through the engine (plumbed wrong as you have said) so i would be low on oil/pressure. Corrected that, and it is alot better, but I'm starting to think that my parts selection is playing into this somehow and that i need to use factory valve covers/pcv system. I did happen to come across some information that states GM now recommends 15w40 for the ls7 but i'm not sure if thats daily use or track use. **Note: I do have a pickup tube hold down to hold the tube and pump together.

Have you checked oil temps? Anything with a 4 inch plus stroke will start to run up oil temps and that will cause the pressure to drop. This is super obvious when you swap a LS7 into a C5 or something with a oil temp gauge but no oil cooler. I've seen 280F oil temps with 215 water temps.

And I agree. Post a good picture with how your catch can is installed and plumbed. It could be as simple as needing a baffle or a restrictor. Most GEN 4 OEM stuff has a restrictor on the correct PCV port. GEN 3's often do not. Aftermarket likely not.

[LS ROB]

I have increased most of the lines to 1/2" to see if that helps. May be a bit tough to see but here is the layout: I have a 3/8 line After MAF but before TB to PS valve cover. Driver side valve cover comes around the back of the engine and goes into a tee which goes into the catch can. The line from the valley cover also goes to the tee which goes into the catch can. From the can, the line goes the intake just behind the throttle body. Hope you can make out some of this with these pictures.

I have never checked the oil temp, but sounds like I may need to look into getting a cooler.

after maf b4 tb to pass vc.jpgcan.jpgdriver vc t into valley plate to can.jpgoverall.jpgto intake from can.jpg

[blindsquirrel]

Why is it I see both a MAF sensor, AND an open-element filter thing on top of the catch can? Those two do not go together.

[edcmat-l1]

Yeah not a fan of those Mighty Mouse catch cans. If your LS motor needs that much crankcase ventilation you need to pull your motor.

Catch can routing should be valley cover to catch can, catch can to intake port. The valve cover vents should be your crankcase "in".

[LS ROB]

Why is it I see both a MAF sensor, AND an open-element filter thing on top of the catch can? Those two do not go together.

Per Mighty Mouse, the open-element is sealed when normal driving and vents to atmosphere at WOT. It looks like I can order a sealed lid from MM for $30 bucks and is probably what I will do since I have questioned this since day I ordered it.

[LS ROB]

Yeah not a fan of those Mighty Mouse catch cans. If your LS motor needs that much crankcase ventilation you need to pull your motor.

Catch can routing should be valley cover to catch can, catch can to intake port. The valve cover vents should be your crankcase "in".

I can understand that. At this point, im just doing what i can with what i got. I appreciate your instruction!

[blindsquirrel]

Why does it need a catch can? What does that do that a properly set up closed PCV system doesn't? Is it just car jewelry or has someone convinced you it does something useful?

[Alvin]

Per Mighty Mouse, the open-element is sealed when normal driving and vents to atmosphere at WOT. It looks like I can order a sealed lid from MM for $30 bucks and is probably what I will do since I have questioned this since day I ordered it.

They really don't vent much. Found that out the hard way. You could put shop air to one side of it and the amount of air that makes it thought the filter element and small orifice they have will barely make a dollar flap.

[GHuggins]

They really don't vent much. Found that out the hard way. You could put shop air to one side of it and the amount of air that makes it thought the filter element and small orifice they have will barely make a dollar flap.

Agree 110% with this. Had a badly machined block that wound up puking coolant on 7lbs of boost. Not sure how much air wound up in the crankcase, but would think if the catch can breather was working any at all much it wouldn't have blown the front and rear mains out Unfortunately found out all 3 at the same time................

[LS ROB]

Why does it need a catch can? What does that do that a properly set up closed PCV system doesn't? Is it just car jewelry or has someone convinced you it does something useful?

Never had any experience with pcv systems until now. When I first built this engine, I would hear hissing coming from the engine compartment when I would turn the car off. It was building pressure, so i researched it and seen that most folks add a catch can to handle those issues. It's more ignorance than car jewelry, really. I'd love to have a bit more space in the engine bay.

[LS ROB]

It appears that I have the option of purchasing the "sealed" lid for this catch can. If you all have any other suggestions; i'm open to try them. Just be aware that this isn't a strong-suite of mine so please, dumb it down for me lol

[92rsz]

Why does it need a catch can? What does that do that a properly set up closed PCV system doesn't? Is it just car jewelry or has someone convinced you it does something useful?

Go to the mightymouse website and check it out. His catch catch cans are not a gimmick. Most, if not all, of the factory pcv systems allow oil to get sucked into the intake. Fine for a stock vehicle I guess. If you're driving hard at high rpms, enough oil can get sucked into the cylinders to start causing knock because it lowers octane when you burn it. My ls7 intake was caked with oil. Put in a catch can and not a drop now

[LS ROB]

Go to the mightymouse website and check it out. His catch catch cans are not a gimmick. Most, if not all, of the factory pcv systems allow oil to get sucked into the intake. Fine for a stock vehicle I guess. If you're driving hard at high rpms, enough oil can get sucked into the cylinders to start causing knock because it lowers octane when you burn it. My ls7 intake was caked with oil. Put in a catch can and not a drop now

Curious; How much oil are you catching in your can?

[92rsz]

It traps a few ounces every thousand miles or so. Never measured exactly. I use a spray paint can cap to drain it and it usually fills it about 1/3rd

[blindsquirrel]

Baffled valve covers and an old-style clickety-clack PCV valve will give the same result. The stock fixed-orifice PCV 'valve' used on the LS is beancounter garbage. No catch can needed.