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Discussion Starter · #1 ·
I'm in the process of sprucing up my 4th gen 3sgte to drop into my '91 turbo. From everything I've seen around the internet, the ct15 is a really fun turbo but it tends to have a harder time keeping up higher in the rev range. I know that this issue has been discussed at length on the interwebs but a lot of the threads that I am finding are a little bit outdated. From the places where i've seen real dyno numbers thrown out, it looks like the prime modified ct15's have the best output, however they do not provide that service any longer. It sort of appears to me that the prime guys would actually modify the exhaust side of the turbo as well as the compressor side. Does anyone else do that or am I mistaken? I have also seen some mentions on various threads about these modified ct's not always lasting very long. Does anyone have any experience with this? Anyone have any experiences that would be helpful in deciding which shop would be best to go through?
 

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Discussion Starter · #2 ·
I am also just finding really mixed information on how easy it is to break 300whp reliably with a 4th gen. lots of places I see people say that all you need to do is have a billet wheel/ wastegate actuator installed as long as you have a good intercooler and your engine can breath well. However in other places i'm seeing people saying that those things wont get you much above 280.
 

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I don't know who still does these anymore. I do have an upgraded ct-26 style turbo if your interested. It should make 300whp. Unless you find someone to upgrade your ct15 you will need to source a Gen3 exhaust manifold to use any CT based turbo setup.
 

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I personally wouldn’t rebuild the turbo, as most rebuild kits are using Chinese internals and people’s experience has been that they tend to not be reliable.

Id personally chop the stock manifold and weld a v-band on it and runn EFR 6758 or 7163. Maybe G25-550, although the flow capability of those at lower pressure ratios doesn’t appear great. Seem like they really favor very high PR applications.

Some mild cams would really help things too, especially at pump gas boost levels.

C15B can maybe do 300 rwhp, but it’ll be completely maxed there on pump gas and isn’t what I’d call a really robust/safe setup on a stock ECU. Lots of people do it, but it’s threading the needle pretty tight on pump.
 

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Discussion Starter · #5 ·
It appears that ATS racing still builds their "sweet 16" which is kind of what I had planned. They use cheap chinese parts for their billet wheels? they use kanagawa wastegate actuators, not sure where those are made but people seem to like them?

with everything I'm doing for this swap right now, i dont really have it in the budget to buy another manifold and turbo and sort all of that out. I'm also rebuilding the e153 while its out and i have already bought a quaife LSD that's going in. So considering how much I'm spending all at once, that's not an option at the money. But I do really appreciate the thorough answer for down the road.

Some cams could potentially be in the budget though. I might have to pull my head anyways as i just realized that my compression tester is reading 30psi in every cylinder and i hear lots of hissing when i turn the crank pulley on the stand. I just put a new timing belt on so i'm thinking maybe my timing is off...

literally just found that problem 5 min ago so now that's playing into my mental budget haha
 

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Discussion Starter · #6 ·
defsport, among normal people I generally am considered pretty mechanically savvy but in the world of people who really tune their cars, I have soooo much more to learn. this isn't my first engine swap but as far as truly understanding how everything works and how every little minor change effects things, I am really just starting out haha.

so with that preface, I would really love to know more about what you mean by unsafe. Do you mean that running enough boost to produce 300whp on stock ct15 or a ct15 with upgraded wheel/ wg actuator would be potentially risky for my motor? or risky for the turbo itself? And would mildly more agressive cams make running that same setup more safe? or do I need to upgrade the turbo to really get much benefit from the cams?

Thanks a ton for the help, really trying to soak up as much as i can. I really like to have a full and rounded understanding of what I'm doing and why I'm doing it if at all possible.
 

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I won’t say for sure what parts ATS uses, but 99% of “billet compressor wheels” and “turbo rebuild kits” are Chinese and usually of pretty low quality. Given how many people blow these “upgraded turbos” at fairly low mileage, I’d be very wary.

Engines are air pumps, flow more air with more fuel to meet it and you make more power. Bigger Cams flow more power high RPM, so less boost for the same power. Less heat, lower combustion pressure/temps.

You seem pretty set on the ATS turbo. I would say there are probably worst ways to go, but I’ve seen them deny warranty due to some stretches for rebuilt turbo failures IMO. Your call on if you feel the same based on your research.
 

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You seem pretty set on the ATS turbo. I would say there are probably worst ways to go, but I’ve seen them deny warranty due to some stretches for rebuilt turbo failures IMO. Your call on if you feel the same based on your research.
When I was researching the CT27 that was claimed to be on my car, I looked it up on ATS and noticed their high zinc content oil requirements for warranty work. My first thought was "Wow, that would give them a lot of room to deny a claim."

Not faulting ATS for trying to cover their bases, and they seem like they offer some nice products, but it did make me start planning for another option if the CT27 turns out to have been thrashed.

"Rebuilt upgraded" OEM turbos always carry a bit more risk than the name brand off-the-shelf stuff though IMO. Just like modifying a car, you are introducing a higher risk of issues the more you tinker with something.
 

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You can spend as much on a turbo setup as you did for the engine if you want reliable. You could just enjoy it stock. I always see this happen to people, they hear something bad about an engine or car and decide it must be upgraded when they have not even experienced it to even see if its worth the trouble to upgrade. Many go down this rabbit hole and never even end up driving the project. Just put it in stock and enjoy it then decide if you want to change the turbo. Its not that bad to get it off in the car.
 

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Also a little bit about the re-built turbos. I think the main problem with this is part of why they require the special oil for turbo warranty. If your upgrading your turbo, you are probably looking to make max power, so you throw that bad boy on and crank it all the way up to what your fuel can handle. It just runs the turbo at the end of its capability and if you get a small boost leak it will be spinning even faster to keep up and burn out fast. You may never even have known there was a boost leak causing the turbo to overspin. That with being maxed out to begin with makes these turbos give up fast. If you re-built and or upgraded the turbo and just ran stock boost it would probably be just as reliable as a stock turbo.
 

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Good point on people introducing failures and journal bearing turbos maybe not being the most tolerant of super high shaft speeds.

But I think it’s something to be knowledge before making the plunge, as they do seem to have a very high failure rate compared to more modern, brand new turbos.
 

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Discussion Starter · #12 ·
I won’t say for sure what parts ATS uses, but 99% of “billet compressor wheels” and “turbo rebuild kits” are Chinese and usually of pretty low quality. Given how many people blow these “upgraded turbos” at fairly low mileage, I’d be very wary.

Engines are air pumps, flow more air with more fuel to meet it and you make more power. Bigger Cams flow more power high RPM, so less boost for the same power. Less heat, lower combustion pressure/temps.

You seem pretty set on the ATS turbo. I would say there are probably worst ways to go, but I’ve seen them deny warranty due to some stretches for rebuilt turbo failures IMO. Your call on if you feel the same based on your research.
yeah, I'm not set on the ATS turbo at all. Prior to this discussion it seemed like the best option so it was kind of my plan, but if it doesn't seem like a good idea then I wont go that route.
 

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Discussion Starter · #13 ·
You can spend as much on a turbo setup as you did for the engine if you want reliable. You could just enjoy it stock. I always see this happen to people, they hear something bad about an engine or car and decide it must be upgraded when they have not even experienced it to even see if its worth the trouble to upgrade. Many go down this rabbit hole and never even end up driving the project. Just put it in stock and enjoy it then decide if you want to change the turbo. Its not that bad to get it off in the car.
Yeah, that has been my plan all along if the "billet wheel" rebuild didn't seem like a good call. As far as things to replace while the engine is in the car, the turbo is a pretty easy one. I think even with everything stock, the gen4 motor is going to feel a lot livelier than the tired old gen2 that is currently in my car.
 

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For a time I have been under the impression that a Gen4 with a good intercooler and free flowing exhaust could net you about 300hp. Don't know where I read it but I think it was an older thread on this site.
I honestly have no idea on HP/Torque ratings with my setup (Stock other than, Intake,Trust intercooler+Blitz exhaust) but I can say the car is FAST. Within my experience.... REALLY FAST. I know I am just over 4 seconds 0-100kph and have taken it to 278km/h and it still had more to give, if I wanted to take it. I may be only hitting 260-280hp but had always figured I was at that 300mark.. at least "on paper". Really hoping one of the tuner shops close to me does a "dyno day" this summer and I can get in for a cheap baseline.
Before I got my boost controller installed and functional I did think about upgrading the turbo but now..... after driving it for the last few weeks..... the factory turbo setup is just dandy IMO.

It is my intent, rather than too look into turbo options, to take the money I would use for a turbo/manifold/plumbing and build up a nice strong short block that can handle more revs and more boost. GEN4 internals seem to be the weakness that gets pushed, I have no interest in testing those limits but I will build something to set new limits. After that if I find the turbo running out of puff or not performing to my liking, I will get back on the turbo upgrade train.
 
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