Discussion regarding back pressure and boost pressure

[euroford]

I've been monitoring my backpressure (after fixing the sensor!) and am kind of curious about discussing its relationship with boost pressure and how that may be impacting the performance on my truck, and maybe coming up with some ideas to optimize it.

First off... truck is running great, it just leaves me curious if i'm leaving some performance on the table and really just want a better understanding of the finer points on this thing. I'm running Swamps 200/30 injectors and some other mods along with a stock platform turbo; rebuilt last year with a 360 deg. thrust bearing kit, WW2, 1.0 A/R housing and EBPV ****** along with a disconnected and fully cranked down banks wastegate actuator.

obviously i am leaving some performance on the table with that turbo, i'll be doing a 354.5SXE eventually, probably in the spring, but right now, the stoker is what i'm running.

running around in my hot street tune i typically see about 23psi max boost, along with that i can see about 39psi of backpressure. In my race tune i can see a touch over 30psi, not sure about backpressure.

Basically, that sounds like a lot of backpressure for how much boost i'm making, i'm curious to understand why and to get your thoughts on if i should be seeing more.

I was seeing a bit less boost, but i replaced all of my boots and clamps and this helped wake it up a bit more, i also picked up a PSI or two by cleaning my air filter (AFE).

any thoughts from you guys?

Maybe still have some boost leaks somewhere? Maybe the AFE filter is restrictive? Maybe this is just a factor of being here in CO and doing all over my driving at 5000+ feet? maybe i'm beating the crap out of my turbo and its time to rebuild it again? maybe the stock turbo just can't flow well at that point.

I know most guys around here are running much hotter setups, but this has proven to be a very nice street setup. i'm also just a tinkerer so i'm always looking for the little ideas to help optimize it. its also just fun to banter about it here on the forums.

 

[cjfarm111]

When I was live tuned a few years back when I had a 38r I was told by my tuner that at 30psi of boost the back pressure was almost twice that. That's not good

 

[Swaan]

Generally you want close to 1:1 ratio boost to back pressure. But ive found that on a properly setup system you only maintain 1:1 till about 3/4 throttle, then after that back pressure will creep up a bit.
Personally i think anything thats up to1.5:1 ratio is acceptable and not out of the norm

If you can maintain 1:1 all the way to redline at wot i think your leaving drivabillity on the table at lower rpm and power levels.

Contrary to many peoples beliefs a little back pressur is fine.

2:1 is getting unacceptable thou and time to step up to a bigger charger.

 

[Swaan]

I've been monitoring my backpressure (after fixing the sensor!) and am kind of curious about discussing its relationship with boost pressure and how that may be impacting the performance on my truck, and maybe coming up with some ideas to optimize it.

First off... truck is running great, it just leaves me curious if i'm leaving some performance on the table and really just want a better understanding of the finer points on this thing. I'm running Swamps 200/30 injectors and some other mods along with a stock platform turbo; rebuilt last year with a 360 deg. thrust bearing kit, WW2, 1.0 A/R housing and EBPV ****** along with a disconnected and fully cranked down banks wastegate actuator.

obviously i am leaving some performance on the table with that turbo, i'll be doing a 354.5SXE eventually, probably in the spring, but right now, the stoker is what i'm running.

running around in my hot street tune i typically see about 23psi max boost, along with that i can see about 39psi of backpressure. In my race tune i can see a touch over 30psi, not sure about backpressure.

Basically, that sounds like a lot of backpressure for how much boost i'm making, i'm curious to understand why and to get your thoughts on if i should be seeing more.

I was seeing a bit less boost, but i replaced all of my boots and clamps and this helped wake it up a bit more, i also picked up a PSI or two by cleaning my air filter (AFE).

any thoughts from you guys?

Maybe still have some boost leaks somewhere? Maybe the AFE filter is restrictive? Maybe this is just a factor of being here in CO and doing all over my driving at 5000+ feet? maybe i'm beating the crap out of my turbo and its time to rebuild it again? maybe the stock turbo just can't flow well at that point.

I know most guys around here are running much hotter setups, but this has proven to be a very nice street setup. i'm also just a tinkerer so i'm always looking for the little ideas to help optimize it. its also just fun to banter about it here on the forums.

If your seeing 23psi boost and 39 psi back pressure on your hot street then the back pressure is probably well over 2:1 on your race tune. You would see a huge improvement with a 364.5 sxe.

This is what takes out the thrust bearings in turbos also.
The stock turbo dont last long with 30 psi boost levels because of that.

 

[superpsd]

Might just play with the wastegate to reduce back pressure and see how the reduction of back pressure has effect on power and EGT. Other than that you are pretty much maxed out. You could try a 1.15 exhaust housing that will reduce drive pressure but may be way more laggy.

 

[euroford]

Tinkered with it just a little bit this weekend, i tapped new lines for the boost gauge and blow off valve, so now they are running off independent lines and the MAP sensor is on its own dedicated line from the stock tap. Its nice when a little thing makes a nice improvement.

The map sensor is showing much more accurate numbers now (before it would lag way behind the mechanical gauge) and the blow off valve is much more responsive. Most importantly, my boost gauge is giving me a more accurate reading, i'm seeing up to 28psi on my hot street tune. this is much more in line with my expectations and makes the backpressure ratio sound a little more friendly. Haven't ran in the race tune yet.

i'm sure i'm beating the snot out of the stock turbo, i feel a little bit better about it having done a 360deg. thrust bearing upgrade, though i haven't read much about the real effect of this on the longevity of the stock turbo in a performance application. I still have another fresh rebuild kit sitting on my workbench and maybe next month i'll give it another rebuild. have a kitchen remodel to finish first...

right now the wastegate is not hooked up and cranked down tight, I've always felt that my EGT's were under control, i have to be really beating on it to get 1200deg in the hot street tune and that's a rare occurrence, only when driving in full loony mode over top of Berthoud pass. In the race tune i'm barely hitting 1600deg when i fly through the traps at Bandimere.

but... if i'm getting all the boost i can out of this turbo, it would be a good idea to wastegate that excess pressure. I think i might look into a boost controller and get that wastegate working again. I know i could just hook a line to it and adjust the preload, but that sounds like a flawed strategy vs. how the wastegate will operate with a controller.

and yeah... definitely leaving a lot of performance on the table with this turbo. I'd love to do a T4 upgrade, but i'm also considering the KC38r. that thing has a lot going for it. last year (when i had a nice chunk of spare time!) i fabricated a custom set of uppipes (coated, wrapped, ported, polished, stainless TIG'd) so keeping those is a bit of an advantage for me. if i hadn't done that i'd be totally committed to a T4 upgrade.

on another note, since i mentioned it above, I run turbosmart's blow off valve and controller, i hope this help alleviate a little abuse from the turbo, but mostly i run it to improve turbo response when shifting gears. by elevating a little boost reversion into the charger it helps keep turbo RPM's up and helps a lot with turbo responsiveness between shifts. I highly recommend it for the stick shift crowd.