Lower PSI after cams/turbo upgrade...normal?

[GSX26]

Well, I had a agp t3/t4 50 trim. I ran 21-22 psi daily without seeing any knock. I replaced it with a garrett t3/t4 57 trim (thought 50 was broke, but it wasn't, explained in other threads). I also put in a set of fp2's and arp headstuds. Now, I am running 16-18 psi, any higher, and I knock at the top of the gears. I am also untuned right now though. I tested boost gauges just to make sure mines accurate, which it is. I also have a vac of -13 or so at idle (is this normal with cams?) So, my question is: Am I flowing the same amount on less boost because my cams are flowing more air? Thanks in advance!

 

[92awddsm]

Well, I had a agp t3/t4 50 trim. I ran 21-22 psi daily without seeing any knock. I replaced it with a garrett t3/t4 57 trim (thought 50 was broke, but it wasn't, explained in other threads). I also put in a set of fp2's and arp headstuds. Now, I am running 16-18 psi, any higher, and I knock at the top of the gears. I am also untuned right now though. I tested boost gauges just to make sure mines accurate, which it is. I also have a vac of -13 or so at idle (is this normal with cams?) So, my question is: Am I flowing the same amount on less boost because my cams are flowing more air? Thanks in advance!

The 57 trim isnt as efficient as the 50 trim is on pump gas. The 57 heats up the charge more than the 50 which will cause knock. The 50trim isnt called the "pump gas king" for nothing.

 

[boostedinaz]

Well, I had a agp t3/t4 50 trim. I ran 21-22 psi daily without seeing any knock. I replaced it with a garrett t3/t4 57 trim (thought 50 was broke, but it wasn't, explained in other threads). I also put in a set of fp2's and arp headstuds. Now, I am running 16-18 psi, any higher, and I knock at the top of the gears. I am also untuned right now though. I tested boost gauges just to make sure mines accurate, which it is. I also have a vac of -13 or so at idle (is this normal with cams?) So, my question is: Am I flowing the same amount on less boost because my cams are flowing more air? Thanks in advance!

First off get a tune. You can not say, "I knock at 17 psi but I could run 20 on my old turbo", if you are not tuned. You may be able to run 22 on the new turbo or only 15 only a good tune will tell you that. Basically your question is impossible to answer if your car isn't tuned correctly.

In theory you should be able to make more power with less PSI for two reasons. One you have a larger turbo so you shoud flow more air at the same PSI, on top of that you have larger cams so they should improve the efficiency of you motor making for more power as well.

Get it tuned and see what happens.

 

[PSI NRG]

Yes, you cant expect to just slap a bigger turbo on and expect it to run the same as the old set up anytime you change the flow characteristics requires a different tune, for example in your case running a larger turbo which will flow more air and require more fuel.

 

[Gamble97]

The 57 trim isnt as efficient as the 50 trim is on pump gas. The 57 heats up the charge more than the 50 which will cause knock. The 50trim isnt called the "pump gas king" for nothing.

really? I never heard that before.
Not to get off topic, can you run pump gas on bigger turbos, just not as much boost?
pm me if anything and I'll tell what I'm getting and to get some more input from you guys.


back on topic

 

[GSX26]

Yeah, I know about the whole tuning thing, but I haven't got the chance yet...hopefully this weekend. Thanks for the responses, I was just trying to see if it was normal or not, I'll know for sure after my tune!