1 PSI boost to 3.5 PSI back pressure???

[partymn]

So my car is having some issues with post turbo back pressure as it climbs higher in the boost. My tuner is saying that my down pipe and possibly the turbo are to small for my LS3, 67/67 turbo and 3 inch down pipe with 2 1/2 inch pipes all the way back with no cats. I really wish that I would have realized this when I first installed the turbo but I was so excited to finally get it that I over looked this detail. On the bright side its nice to have my car in the hands of a shop that knows what they are doing. The initial shop that tuned the car missed this.

So maybe its time for us all to get better educated on this topic. Any of our experts want to throw out some information on this?
Am I heading down the same road as GbrilliantQ with bent rods and blown out engine blocks?

[GbrilliantQ]

Hmmmm.... I've been without my car for almost 8 months now. I better not have this problem.

From my Note

[partymn]

Its hard to say if you will or not, I sure hope not.

[killmode_on]

Holy crap, that's really not good.
You have a single 67/67 with a single 2.5" down pipe? That is totally unacceptable. A single 2.5" pipe is good for less than stock HP.

[partymn]

Sorry for the mistake but the down pipe is 3 inches and the merge pipe is 2 1/2 inches, I will change the original post. However, its still not good.

[JLE58]

The turbo would be fine for 7-8 psi. Anything more than that is to much. I've said it more times than I can count a 67mm turbine wheel is to small for a ls3. That kit was never supposed to have a 67mm turbo of course it also wasn't supposed to be crammed between the motor and radiator either. Either way I wouldnt think backpressure would be a big problem at your boost level.

[partymn]

Its 29 PSI at 8.13 PSI of boost. Everything that I have read says this is not a good thing.

[JLE58]

I wouldn't think it would be that high. All of the turbonetics kits have a 67mm turbine turbo I believe. I'd see what some of those guys are doing to keep backpressure down. I'm sure most of them have never tested it. A larger down pipe would be the first step. That turbo does have a t4 .96 ar exhaust housing correct? You don't have much room for a larger turbo....

[partymn]

Yes it does and no I don't have much room left. I think SSDIAZ is running a 72mm but I am not sure. All I know is that the back pressure is high as hell and it is limiting me to 546 HP and 600 on torque at 8.13 PSI.

[partymn]

Are there other ways to help this problem that don't require me to have a down pipe made and a new tune after that.

[killmode_on]

You need a bigger turbine wheel #1.
And a bigger down pipe or at least expansion chamber right out of the turbo #2.

Single on a 6.2L motor should be a minimum of a 75mm turbine wheel if you want everything to work HAPPY HAPPY HAPPY.

[dekan513]

killmode , hit it on the head. im not a turbo man but . he thinking just as i am.

[JLE58]

Originally Posted by partymn

Yes it does and no I don't have much room left. I think SSDIAZ is running a 72mm but I am not sure. All I know is that the back pressure is high as hell and it is limiting me to 546 HP and 600 on torque at 8.13 PSI.

Your not going to make much more than that even with a bigger down pipe on that turbo. If it was mine I would move the turbo over to the driver side bring it up and point it towards the head light. Build a bigger cross over and down pipe and put a bigger turbo on it... That would be the way to make it right would also help with the drain issues. What turbo is on it Comp? I'm not sure how Diaz got the turbonetics turbo but my guess would be Chris pulled it off another car and charged Diaz full price for it. Either way I would bet money he never bought that turbo new from turbonetics.

[Unreal]

Even with a bigger downpipe the turbine is too small. Sell it to a honda/evo/subaru guy and get a proper setup.