1 PSI boost to 3.5 PSI back pressure???

[GbrilliantQ]

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....

From my Note

[JLE58]

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.

[partymn]

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?

[partymn]

Originally Posted by JLE58

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.

[pincushin3819]

Originally Posted by 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?

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.

[GbrilliantQ]

Originally Posted by pincushin3819

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

From my Note

[killmode_on]

Originally Posted by partymn

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.

[pincushin3819]

Originally Posted by GbrilliantQ

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

From my Note

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.

[JLE58]

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.

[killmode_on]

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.

[SRT10KLLR]

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?

[partymn]

Comp Turbo

[partymn]

Originally Posted by pincushin3819

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.

PCM has mine as well, they are great to work with. I would do something of that nature but I am just ready to foot the bill for it. Not this close to Camaro Fest anyway.

[partymn]

Originally Posted by killmode_on

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.

Kind of. Its not really as tough of a spot as it could be, I just want to minimize the backpressure and take that strain off my system. I am not changing the whole system and the turbo whine is too addicting to get rid of either.

Go back to stock, why would anyone do that. Its still sitting at 546 HP and 599 Tq, going back to stock would be like driving a Prius.

If the answer is as simple as being out of turbo, then so be it. I will live with what I got until I can financial justify doing further changes. However, there is always something that you can do that will not break the bank and still improve the situation. Throwing money at it is not the answer to every question on C5. I am just trying to figure out what is the correct route to take.