[Sillysspeed]

First mods to these cars should be catch can and expansion tank

[Greg83]

Originally Posted by arpad_m

"Negative" pressure is (partial) vacuum, this is normal while the car is running with the supercharger bypassed (for fuel economy), the pistons create a vacuum that then helps suck in air via the intake, this is how all naturally aspirated engines work. Once the supercharger kicks in (when you give it some gas), it will immediately build boost, and on your LT4 you should see 9.7 to 10.2 psi.

Bleeding the intercooler circuit is a no brainer, make sure you get it done, as others already stated above. Unfortunately GM did not add a supercharger coolant tank from the factory, so you're at the mercy of whoever assembled the engine and filled the fluids to have done it properly, the only way you as an owner could check is opening up the S/C coolant loop.

I'd say let the dealer do it under warranty, and you make sure they know what they're doing, don't hesitate to go to a different service department if you see anything suspicious.

I’ll definitely try that after the fresh gas. Thank you!!!

[Greg83]

Originally Posted by FrostZ

arpad_m hit the head on the nail, LT4 blower has a vacuum bypass on the blower that is open at idle and cruising as soon as you lean into the blower creates boost closing the bypass and allowing boost to ramp up. Max boost I see is 9-10 maybe 11 PSI depending how dense the air is but that's based on the rather simple gauge.

Thanks!

[radz28]

I can't confirm this, but I THOUGHT I read the bypass valve was controlled by the ECM on the newer cars. I don't know if that's true (I think there is some merit to it, but I'm getting to that), but I know on my '20, there is a set screw that adjusts the bypass valve in the blower, and by adjusting that to close all the way gave me a little more boost pressure. I believe there are still pressure limits the ECM uses to influence the OEM bypass valve, but all I'm saying is that a lot of people before me made sure their valves were adjusted such that they closed all the way, because they picked up boost/power if they were not.

[WhiteMale]

If you need to with that tank of bad gas or god forbid they filled it with 87 octane, dump in a bottle of booster and top it up with 93.
When I picked up my car my salesman took me right over to the 93 pump at the station.
I checked my bypass and it appeared to be set up correctly but I'd swear I've seen on this fourm a pic of two and you can tell that it's open or not set up correctly.
I had removed that sound plate off the lid and with that opended up you can see the butterfly and easily set that up, if you need to.

[Greg83]

Thanks guys! Lots of good info. I did a little research and it looks like my coolant tank is a little low so I will top that off and bleed the supercharger system. I assume that system is under more pressure the hotter it is? Should I bleed it while the engine/coolant/SC temps are cool (like you would with a regular cooling system) or should I do it when the car is warmed up or even hot to create the pressure to bleed/burp the system?

[Nimair.ZL1]

Doesn't really matter when you bleed it. What matters most is all the air being out of the system. Whenever the intercooler pump sees air it stops. You want to make sure that there is constant coolant flowing to the pump and no air pockets

[RobZL1]

Originally Posted by Greg83

Thanks guys! Lots of good info. I did a little research and it looks like my coolant tank is a little low so I will top that off and bleed the supercharger system. I assume that system is under more pressure the hotter it is? Should I bleed it while the engine/coolant/SC temps are cool (like you would with a regular cooling system) or should I do it when the car is warmed up or even hot to create the pressure to bleed/burp the system?

There is no tank on the S/C loop, the clear dual tank on the left is for the radiator.

[Vigilante375]

Originally Posted by Greg83

Thanks guys! Lots of good info. I did a little research and it looks like my coolant tank is a little low so I will top that off and bleed the supercharger system. I assume that system is under more pressure the hotter it is? Should I bleed it while the engine/coolant/SC temps are cool (like you would with a regular cooling system) or should I do it when the car is warmed up or even hot to create the pressure to bleed/burp the system?

As mentioned, the tank on the passenger side of the engine bay is the coolant for the radiator. The top portion should be nearly full and the bottom portion needs to be about halfway. Both sections have a fill line.

The ZL1 has no factory tank for the supercharger coolant.

There is a method to bleed the supercharger intercooler and if you search YouTube (or on here) for ZL1 supercharger bleeding, you'll find methods that will work. I would recommend buying an actual reservoir from a vendor so that you'll never have to worry about air being in the system as it'll get the air out for you while you drive.

I have an ADM reservoir and have had 0 problems with it. But there are a handful out there to choose from but I think this one is the most simple and not that big while being very easy to install.

[Greg83]

Awesome. Thanks guys!!

[Xelor]

I would go do some 50 to 120 pulls on the freeway. See how it runs. I never followed the 500 mile break in. I ran it hard from the Dealership Day 1.

[DangerZL1]

Display the boost gauge on the instrument cluster jut to see how much boost it’s making if you haven’t already checked

[wakespeak]

150 miles? Dealer filled my car with regular. Might be that simple.

[Rapid_blue_zl1_22]

Originally Posted by Idaho2018GTPremium

Some misinformation in these responses. First, the ZL1 doesn’t limit power below 500 miles. 2nd, the comment about “being in the power band” is inaccurate as well. The LT4 makes peak torque below 4K rpm, and in a given gear, THAT is what you feel. So it should feel strong at 3500 rpm in 3rd gear, for example. In 3rd gear the car pulls harder at 3600-4000 rpm than it does at 6000 rpm. So if it feels like an SS, something isn’t right. I second (or third?) the s/c coolant air bleed. It’s pretty easy to do on your own and can be done at home, and you don’t need a custom tool like some will claim. Or you could risk it at the dealer. Make sure the s/c coolant reservoir is full as well.

3rd: the LT4 runs fine on 91, not ideal, but it still makes a lot of torque. That’s all there is in a huge part of the country.

There isn't a S/C coolant reservoir from the factory.