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Old 06-28-2013, 07:09 PM   #1
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1 PSI boost to 3.5 PSI back pressure???

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?
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Old 06-28-2013, 07:31 PM   #2
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Hmmmm.... I've been without my car for almost 8 months now. I better not have this problem.

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Old 06-28-2013, 07:43 PM   #3
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Its hard to say if you will or not, I sure hope not.
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Old 06-28-2013, 07:47 PM   #4
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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.
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Old 06-28-2013, 07:53 PM   #5
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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.
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Old 06-28-2013, 08:17 PM   #6
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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.
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Old 06-28-2013, 08:30 PM   #7
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Its 29 PSI at 8.13 PSI of boost. Everything that I have read says this is not a good thing.
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Old 06-28-2013, 09:10 PM   #8
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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....
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Old 06-28-2013, 09:29 PM   #9
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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.
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Old 06-28-2013, 09:35 PM   #10
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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.
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Old 06-28-2013, 11:57 PM   #11
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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.
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Old 06-29-2013, 07:59 AM   #12
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killmode , hit it on the head. im not a turbo man but . he thinking just as i am.
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Old 06-29-2013, 08:57 AM   #13
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Originally Posted by partymn View Post
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.

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Old 06-29-2013, 09:57 AM   #14
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Even with a bigger downpipe the turbine is too small. Sell it to a honda/evo/subaru guy and get a proper setup.
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Old 06-29-2013, 11:14 AM   #15
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You know its funny how no one mentioned or thought this turbo was to small over a year ago when Chris introduced this kit. Now everyone is saying it....

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Old 06-29-2013, 11:28 AM   #16
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It has the same turbine wheel size as the turbonetics kit... I think even Chris said the kit was for 550 Rwhp. The kit was supposed to have 76/75 turbos originally. I'm not sure when the 67mm stuff started I still wouldn't have thought back pressure would have been that high.

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Old 06-29-2013, 12:49 PM   #17
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You know I really didn't want this to turn into another HPS bash session. I think that we all agree on what type of shop it was and have had enough fun blaming them for this kit.

I would like options to correct the problem with the kit set up the way it is. I cant afford to redesign the kit right now nor can I afford to buy a larger turbo. There has got to be a cheaper way to lower the pressure that doesn't require me to change the whole design of the kit. I need to get the backpressure down to a reasonable level to keep my engine alive.

I have a set of exhaust cutouts that will be going on when I get the car back, will that help while they are open? Will it need retuned afterword? I know that it normally wouldn't but I am not sure if it will in this situation.

Could the stock cans that I still have on the car exaggerate this issue? Could they be damaged internally and cause this high pressure? If so those can go away for some flowmasters.

If I get the backpressure down to, lets say, a 1:2:1 ratio will the car need to be retuned? I probably already know the answer to that but you never know.

Could my lack of a catch can also exaggerate this issue?
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Old 06-29-2013, 12:53 PM   #18
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Quote:
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It has the same turbine wheel size as the turbonetics kit... I think even Chris said the kit was for 550 Rwhp. The kit was supposed to have 76/75 turbos originally. I'm not sure when the 67mm stuff started I still wouldn't have thought back pressure would have been that high.
That would be fine if the backpressure wasn't so high. The way it is now the boost is going to have to be turned down to get the pressure to drop. I am guessing this will lead to about 500 RWHP, if I am lucky.
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Old 06-29-2013, 01:32 PM   #19
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Quote:
Originally Posted by partymn View Post
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?
I'm having the same problem with my HPS kit, I payed for an upgraded 80mm turbo for my 418 from Chris & come to find out I might have a 72mm or even a 67mm on there. Either way the turbo is to small even if you could put a bigger down pipe on there which is already about to touch the oil cooler as it is now that would be just half the problem. PCM has my car now & have been awesome to deal with, we are trying to figure out the best way to solve this problem. I have been talking to a local fab guy that works with PCM for turbo builds & we have come up with a few good ideas on how to fix this. Our goal is to find a location that is big enough for at least a 76mm turbo with no less than a 4 inch down pipe ether by moving the turbo like some have mentioned to another spot like behind the head light or even making a front bumper support & moving the intercooler & radiator out a few inches for a bigger turbo.
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Old 06-29-2013, 01:38 PM   #20
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I'm having the same problem with my HPS kit, I payed for an upgraded 80mm turbo for my 418 from Chris & come to find out I might have a 72mm or even a 67mm on there. Either way the turbo is to small even if you could put a bigger down pipe on there which is already about to touch the oil cooler as it is now that would be just half the problem. PCM has my car now & have been awesome to deal with, we are trying to figure out the best way to solve this problem. I have been talking to a local fab guy that works with PCM for turbo builds & we have come up with a few good ideas on how to fix this. Our goal is to find a location that is big enough for at least a 76mm turbo with no less than a 4 inch down pipe ether by moving the turbo like some have mentioned to another spot like behind the head light or even making a front bumper support & moving the intercooler & radiator out a few inches for a bigger turbo.
So that's it? Larger turbo redoing the kit larger pipes. Great I've spent over 20 grand trying to get this car running and now folks are having these issues...

Wtf

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Old 06-29-2013, 02:02 PM   #21
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You know I really didn't want this to turn into another HPS bash session. I think that we all agree on what type of shop it was and have had enough fun blaming them for this kit.

I would like options to correct the problem with the kit set up the way it is. I cant afford to redesign the kit right now nor can I afford to buy a larger turbo. There has got to be a cheaper way to lower the pressure that doesn't require me to change the whole design of the kit. I need to get the backpressure down to a reasonable level to keep my engine alive.

I have a set of exhaust cutouts that will be going on when I get the car back, will that help while they are open? Will it need retuned afterword? I know that it normally wouldn't but I am not sure if it will in this situation.

Could the stock cans that I still have on the car exaggerate this issue? Could they be damaged internally and cause this high pressure? If so those can go away for some flowmasters.

If I get the backpressure down to, lets say, a 1:2:1 ratio will the car need to be retuned? I probably already know the answer to that but you never know.

Could my lack of a catch can also exaggerate this issue?

You are in a tough spot and really can't afford to get yourself out of correctly. You should probably take this mess off your car and put it back to n/a.
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Old 06-29-2013, 02:03 PM   #22
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Originally Posted by GbrilliantQ View Post
So that's it? Larger turbo redoing the kit larger pipes. Great I've spent over 20 grand trying to get this car running and now folks are having these issues...

Wtf

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Yes, if your wanting to make over 500-550rwhp safely you will need a bigger turbo & down pipe set up. I'm not sure on pricing to relocate the turbo just yet but I will update.

As far as cats, exhaust & cut outs for back pressure I have ran open down pipe which did help the back pressure a little bit but it still was to high to run over 550rwhp my boost went up to 9lbs then fell on it's face in the upper rpms which is clear to see the turbo is well out of it's rang.

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Old 06-29-2013, 02:06 PM   #23
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It's not going to go away without larger turbo. I asked what size exhaust housing is on that turbo also like I said I wouldnt think it would be that high... The more free flowing the exhaust is the lower the backpressure will be but I don't think your going to free it up to much more than you have. You can try aftermarket mufflers and 3 inch exhaust may help a little.
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Old 06-29-2013, 02:10 PM   #24
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Why do you guys keep trying so hard to do a front mounted single in these cars? They don't take to it well. If the engine bay was laid out differently, then sure put a T6 based turbo up there and run a 4" down pipe. But you'd have to hack the hell out of the car to fit all that.
A pair of 65mm turbine wheels with a pair of 3" exhaust pipes and the turbos mounted where the catalytic converters use to be. It works so well, I honestly think GM designed the car thinking they might TT it some day.
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Old 06-29-2013, 02:16 PM   #25
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If you have a Comp Turbo you may be ok as they use straight cut wheels. Other companies use the larger size(inducer/exducer) for advertising purposes so a 67 wheel will be 67 on the large end but only 62 on the small end. Whereas Comp's are 67 all the way still small but a little more forgiving. Also, they can fit a bigger wheel using that same turbo. I have one of their CT43-8079 turbos on the Hemi Ram.

Which turbo do you have exactly?
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