[SOCAL.M6.ZLE]

Originally Posted by KingLT1

Anytime you increase flow on the outlet side of the compressor you will see a drop in boost psi. And anytime you increase flow on the inlet side of the compressor you will increase boost psi. How much gain/loss in psi varies on how much restriction was prior and how much flow was increased.

Exactly...

[2023_ZL1-AUTO]

I should have further asked then: How, do you get an LT4 (ZL1) that you put a CAM in to increase the inlet side? Pulleys, a 2650? The reason I'm asking, when I was looking at a CAM when I first got my ZL1. A buddy showed me his data logs of before and after and I was surprised to see the boost drop after he put a CAM in. He gave me some kind of BS reason why, but I could tell he didn't really know. This is one reason I'm still on the fence about a CAM myself. I think the original poster might not realize a CAM will lower boost, unless they do other mods?

[Joshinator99]

Originally Posted by 2023_ZL1-AUTO

I should have further asked then: How, do you get an LT4 (ZL1) that you put a CAM in to increase the inlet side? Pulleys, a 2650? The reason I'm asking, when I was looking at a CAM when I first got my ZL1. A buddy showed me his data logs of before and after and I was surprised to see the boost drop after he put a CAM in. He gave me some kind of BS reason why, but I could tell he didn't really know. This is one reason I'm still on the fence about a CAM myself. I think the original poster might not realize a CAM will lower boost, unless they do other mods?

A cam helps the engine become more efficient at moving air. So, per Kings post, moving more air after the compressor lowers your boost number. It’s a good thing!

[KingLT1]

Originally Posted by 2023_ZL1-AUTO

I should have further asked then: How, do you get an LT4 (ZL1) that you put a CAM in to increase the inlet side? Pulleys, a 2650? The reason I'm asking, when I was looking at a CAM when I first got my ZL1. A buddy showed me his data logs of before and after and I was surprised to see the boost drop after he put a CAM in. He gave me some kind of BS reason why, but I could tell he didn't really know. This is one reason I'm still on the fence about a CAM myself. I think the original poster might not realize a CAM will lower boost, unless they do other mods?

In agreement with Josh, The cam is post compressor. The boost drops because the valve events created by the larger cam can efficiently move more air. It doesn't mean you lose power. Boost is just a measure of restriction.

[RobZL1]

Originally Posted by Joshinator99

A cam helps the engine become more efficient at moving air. So, per Kings post, moving more air after the compressor lowers your boost number. It’s a good thing!

Bingo bango to these guys, of course. Another way to look at it / more detail:

A belt-driven root-style FI device is spinning at a fixed RPM at a ratio to engine RPM. It's trying to push air at a fixed volume per revolution into and through the engine. A cam and ported heads and better flowing exhaust allow the engine to move that air through the engine without it getting backed up. When the engine is less backed up, it has less "boost."

On the other side, as you increase intake diameters, filter sizes, TB sizes, and blower ratio (through pullies), you can push more air into the heads against the intake valve. If it's more than the engine can ingest by itself based on RPM, valve lift and valve open duration, then you get a backup, measured as "boost."

As you feed an engine more boost, it has more pressure pushing against the intake valve waiting to get let in, and then it can fill the cylinder with more air under boost pressure in the time that's available while the valve is open. Then it's just a matter of balancing cylinder pressure with how much octane you have available.

So, as you get the engine flowing better on the downstream side (heads/cam/exhaust) you likely want to get it flowing more on the upstream side (pullies, blower upgrades, intake stuff) to achieve an acceptable amount of boost to fill the cylinder to max capacity again, while balancing cylinder pressures against available octane.

[Joshinator99]

Originally Posted by KingLT1

In agreement with Josh, The cam is post compressor. The boost drops because the valve events created by the larger cam can efficiently move more air. It doesn't mean you lose power. Boost is just a measure of restriction.

Originally Posted by RobZL1

Bingo bango to these guys, of course. Another way to look at it / more detail:

A belt-driven root-style FI device is spinning at a fixed RPM at a ratio to engine RPM. It's trying to push air at a fixed volume per revolution into and through the engine. A cam and ported heads and better flowing exhaust allow the engine to move that air through the engine without it getting backed up. When the engine is less backed up, it has less "boost."

On the other side, as you increase intake diameters, filter sizes, TB sizes, and blower ratio (through pullies), you can push more air into the heads against the intake valve. If it's more than the engine can ingest by itself based on RPM, valve lift and valve open duration, then you get a backup, measured as "boost."

As you feed an engine more boost, it has more pressure pushing against the intake valve waiting to get let in, and then it can fill the cylinder with more air under boost pressure in the time that's available while the valve is open. Then it's just a matter of balancing cylinder pressure with how much octane you have available.

So, as you get the engine flowing better on the downstream side (heads/cam/exhaust) you likely want to get it flowing more on the upstream side (pullies, blower upgrades, intake stuff) to achieve an acceptable amount of boost to fill the cylinder to max capacity again, while balancing cylinder pressures against available octane.

Great stuff, fellas.

[Smokin19]

No better classroom on engine mechanics than right here on this forum.

[tortilla-flats]

Originally Posted by KingLT1

... Boost is just a measure of restriction.

I never heard it put that way. Makes it much easier to grok.

[SOCAL.M6.ZLE]

Originally Posted by Smokin19

No better classroom on engine mechanics than right here on this forum.

I second that Smokin19...