Turbine size matters

[jgkurz]

Hi all, I had an interesting result on the dyno recently. Years ago I made 455 rwhp @ 27psi boost with my old non-ball bearing customized T4/T3 hybrid. It had a small .50 compressor housing with a 3" inlet and what Innovative called a GT58 wheel. The hot side was a T350 stage V wheel with a .63 housing. I recently upgraded to a very expensive dual ball bearing  GTX3576R with a 4" inlet and a Tial vband .63 housing. Nothing else changed on the engine.  I like the quick spool so I stuck with a .63 turbine housing. The new turbo made 366rwhp and was done at ~22psi. Adding more boost did not raise HP.  That is a 89hp difference. On a modern engine like in an EVO or STI, my GTX3576R turbo could support close to 600HP. Obviously my old L6 can't flow enough air. What I learned is that the old turbine wheel has a 71mm Inducer/62mm Exducer @ 76 trim. The GTX3576R turbine wheel has a 68mm Inducer/62.3 Exducer @ 84 trim so a bit smaller. Another interesting point is that the new ball bearing turbo had a mirror image dyno curve to my new turbo up to 4500rpm or so. The myth that a ball bearing turbo spools sooner is not true, at least with my engine. 

 

I am amazed that the slightly smaller turbine wheel caused the 73HP drop. I may try a .82 housing and see if that helps although I am confident it will add turbo lag. 

 

-John 

 

 

 

 

Edited August 23, 2018 by jgkurz

[seattlejester]

A couple tweaks and changes makes a pretty big difference, the SX-E model of the SX turbo which in theory has the same 7670 profile with a 1 mm bigger compressor inducer and a billet wheel can flow almost 10 more CFM.

 

I'd have to run the numbers to really get a good visual of the change, but a mm or two makes a huge difference when you add it to the outer diameter.

[malibud]

curious what kind of of set up you have to run 22 psi . I assuming race gas ?

[jgkurz]

On 8/15/2018 at 5:54 PM, malibud said:

curious what kind of of set up you have to run 22 psi . I assuming race gas ?

 

Yes, on the dyno I always like to use race gas for the safety factor. Cheap insurance. 

 

I can safely run 15psi on 92 octane. My recent coolant bypass on cyl 4,5,&6 seems to have helped keep the head much cooler. 

Edited August 23, 2018 by jgkurz

[jgkurz]

Circling back to this thread. I've been working with some people a lot smarter than me and have learned a few things. My GTX3576R is larger than my old turbo in all respects. Garrett claims it will support 600RWHP. Even if that's optimistic, 500RWHP should be possible on a well built/tuned engine. 

 

Notice in the below dyno comparison that the GTX3576R (red lines) fell off significantly starting at 4000rpm and was negative at 3000rpm. The old turbo is represented by the blue lines. I have been focused on exhaust pressure and the turbine housing size. Based on the dyno chart, the experts I mentioned above believe the issue is on the intake side air flow. I'm surprised by this since everything is the same as the old turbo, but with a MUCH larger turbo inlet and K&N air cleaner. 

 

The investigation continues. 

 

 

Edited August 23, 2018 by jgkurz

[Gollum]

My thoughts is that you're not even getting into the main island of efficiency of the compressor map. You're likely ridding the surge line, and the anti-surge ports of the compressor are making that fact hard to tell. This would correlate with max power being 22psi and more boost not adding power. Generally that's because you're on the OTHER end of the map with an undersized turbo, but in your case, adding pressure ratio is just pushing you further into the left side of the map. If you look at the map for the GTX3576r and the pressure ratio you're around (likely about 2.4-2.7) and follow the estimated airflow to make the above dyno'ed HP, you can't put the flow anywhere near the center of the map, if anything it's hard to even get it into the map at all! To make that HP at that PSI, unless the charge temp is insanely high (which I doubt considering your previous dyno with previous turbo) the calculated VE would have to be in the 60's... It's unlikely the engine is that low on VE, which means the only other variable that we can move is compressor efficiency, which must not even be reaching the 70's to explain the low power. Since we know this is a 600+hp monster compressor in the right application, we can only be left to assume you're not even waking the turbo up.

 

What's the specs on the motor? Seems like the easiest way to test this theory that it's the engine not swallowing enough air on the cold side (versus a turbine pressure issue as you'd been looking for) is to get a hold of some more aggressive cams to see if opening up the airflow a bit gets the turbo flowing more air.

 

This is also where talking to someone familiar with many turbos and various known applications comes in handy. Turbos don't just have a PSI they're designed around, but a Flow as well, and the right combination of both is required for a good fit for an engine. I can't say I'm anywhere near that level of an expert for any common engine, but I've read enough stories like this to know that it's never a "go bigger or smaller" conversation. It's always about the system approach and knowing how the turbo fits into the system.

 

That said, I'd love to be unhappy about 382whp  

Edited August 23, 2018 by Gollum

[Gollum]

Just another quick thought, is than an even cheaper way to test is to create a boost leak. Install a one way valve (so you don't alter vacuum areas of performance) post turbo and see what happens. This should force the turbo further right into it's map and give you an idea of what's going on. Obviously this isn't a forever solution, just a test method. Though people have created intake bypass systems before, in order to fit large compressors and prevent surging...

[jgkurz]

Gollum, Thanks for putting thought into this. Here are the specs to my car: http://fstrnu.net/z/specs.htm

 

I went with the GTX3576R because I thought the GT35R (or the newest version GTX3582R) would be too big. Several Turbo L28 folks run the GT35R with great success. I went smaller than the GT35R, but larger than my old turbo for the exact reasons you mentioned. I wanted to be well inside the surge line. I did the math a while back to plot my compressor map. I will do it again now that I have real world dyno info. I sure hope you are wrong. Other than low compression, the biggest issue with my setup is the intake, head, and exhaust manifold. It would take big $$$ to fix all that properly. The goal of the project was not more peak power, but a more efficient turbo so I could run more power under curve on pump gas. I didn't think for one second I would be going backwards since my old turbo was a such a terrible design, at least on paper.

Edited August 23, 2018 by jgkurz

[seattlejester]

Hmm I'm not sure, according to this one it seems you would be pretty near the center efficiency island at 2.5ish and about 40CAF, pretty decent 76% or so. The GTX3076R has made over 500whp, so it seems like you are definitely stuck on the left side if you can't make that with the GTX3576R and increasing psi. Gollum may be on point though you may be overfeeding the engine and causing it to surge, but the surge is hidden by the anti-surge ports. 

 

I would venture that in addition to having intake restrictions whether that is intercooler pipe sizing (2.5 inch can support I think like 450hp or so before it runs into aero drag), or intake flow (these heads really don't flow all that much), the hotside may be choking you out if you kept it that small. It does become a restriction at a certain point.

[jgkurz]

I really debated between the GTX3076R and the GTX3576R. I thought my engine could support the GTX3576R based on some basic compressor map plotting and my previous dyno results. My intercooler outlet pipes are all 3". The inlet pipes are 2.5" which match the turbo outlet. The intercooler itself is large and seems to be working well based on inlet/outlet heat tests and previous power levels. I've never done a pressure differential test. I will be verifying some basic things like, throttle opening, turbo damage, air cleaner flow and such before I do anything too radical. 

[seattlejester]

I looked up your previous setup looks like a 76.4/68 setup. This seems really in line with your new turbo proportion and size wise, one would presume a faster spool and more area under the curve. There is literature that says the GT58 wheel will support over 700hp though compare to the gt35 which is stated for up to 600hp, so something there may account for it, although that seems odd. Granted as mentioned the s257 vs the s257sx-e is 1mm and a billet wheel that apparently allows for a 100hp difference as well.

 

Since the exhaust turbine wheel is the same size and you kept your exhaust AR the same it seems like that should support your previous hp. Makes it definitely lean towards the intake side of the equation. Did you have surge with your previous setup? Maybe it was present, but without the anti-surge ports you were basically just holding excess pressure in the pipes while putting premature wear on the turbo. At least that would be one explanation. 

 

 

[jgkurz]

29 minutes ago, seattlejester said:

I looked up your previous setup looks like a 76.4/68 setup. This seems really in line with your new turbo proportion and size wise, one would presume a faster spool and more area under the curve. There is literature that says the GT58 wheel will support over 700hp though compare to the gt35 which is stated for up to 600hp, so something there may account for it, although that seems odd. Granted as mentioned the s257 vs the s257sx-e is 1mm and a billet wheel that apparently allows for a 100hp difference as well.

 

Since the exhaust turbine wheel is the same size and you kept your exhaust AR the same it seems like that should support your previous hp. Makes it definitely lean towards the intake side of the equation. Did you have surge with your previous setup? Maybe it was present, but without the anti-surge ports you were basically just holding excess pressure in the pipes while putting premature wear on the turbo. At least that would be one explanation. 

 

 

 

 

Awesome stuff seattlejester. Thank you for thinking about this with me. My old turbo did not have any anti-surge ports or any surge issues that I could notice. It would jump up to 27psi without too much issue. 27psi was the limit as I was clearly going outside the map on the right at that point. The new turbo does have anti-surge so if I am surging I am not hearing it. 

Edited August 23, 2018 by jgkurz

[Gollum]

IF you can validate that you are in the surge area of the map, and having a hard time finding the sweet spot of the turbo, the "easy" fix is to go up a size on the turbine AR housing. Means less response, but it'll get the compressor flow further right and closer to the sweet spot as it comes on boost and (hopefully) supplying plenty of air as you move through the power band. But I think we all here agree, that turbo should make A LOT more power, indicating something is wrong with the setup.

 

But yeah, start with the easy stuff before going to extreme. Pressure sensors are cheap and loggable, which would allow you to pinpoint exactly where you're operating on the compressor map.

 

Another potential thing to consider: A larger compressor needs more turbine power to get the airflow out of it. It's potentially possible that your small turbine AR can't keep it flowing at the top. The problem I have with that theory here is that you're able to reach much higher boost targets when you want to. If you were choking the compressor because of lack of turbine energy available, you'd see boost drop off when setting pressure targets as high as 27.

[jgkurz]

1 hour ago, Gollum said:

Another potential thing to consider: A larger compressor needs more turbine power to get the airflow out of it. It's potentially possible that your small turbine AR can't keep it flowing at the top. The problem I have with that theory here is that you're able to reach much higher boost targets when you want to. If you were choking the compressor because of lack of turbine energy available, you'd see boost drop off when setting pressure targets as high as 27.

 

The 27psi was with my old turbo. The new turbo hit a wall after 22psi. I tried higher than 22psi but it made no more more and boost would drop back top 22psi again. 

 

Changing the Tial v-band turbine housing from a .63 to a .82 might be worth a try but it will cost me ~450.00. That's a lot better than a new turbo I guess. I could sell my .63 for 150-200.00 or so which would help.  

[seattlejester]

Hmm I don't think that turbo should really hit a wall like that if you were force feeding 27 with your old turbo at least. Have you checked for pressure leaks? I've had some real tricky ones, like a clamp that had partially blown off but was still covering up the gap, or a clamp a coupler that would only leak when you let off throttle and increased the pressure in the boost pipe. I might also suggest finding a manual boost controller to eliminate a faulty solenoid or controller feed setting.

 

If power is your goal, a bigger hotside would definitely push you towards it. My turbo which has similar specs is designed around a 1.0+ turbine AR to hit the max numbers so a 0.63 is choking it a good deal by comparison, but I still feel like you should be solidly in the 450-500ish area. 

[Gollum]

On 8/14/2018 at 6:36 PM, jgkurz said:

Adding more boost did not raise HP

Ah ha! My fault for assuming what this meant. I was assuming you meant that raising PSI lead to increased boost without more power, like an out of breath turbo on the right side of it's map.

 

If you were indeed inlet restricted (meaning the engine can't flow enough to push you right in the map, instead walking up a straight line not moving right) you'd still likely be able to target higher and higher boost levels, it'd just surge worse and worse. But as pointed out, you're pushing 400+ crank hp, which means you're AT LEAST around 35lb/min in flow, which isn't THAT close to the surge line...

This leads me to two potential culprits:

 

1) You have a pretty healthy boost leak.

 

2) Your turbine's max flow can't spool the compressor any more

 

I'd see if you can find someone nearby that might let you borrow their turbine housing for a session. And also maybe try to find someone with a smoke test machine for tracking down any leaks.

[Gollum]

Worth reading for the technical gems that are easy to pick up, even if it's not your engine platform:

 

https://www.perrin.com/blog/post/garrett-gtx-turbo-comparo-part-2

 

A great piece of it:

 

Quote

23lbs/min under those conditions and as the turbine pressure raises it hit a wall. Basically adding more exhaust pressure will not do anything for the ultimate flow of the engine. On the 35R turbine map the .63AR housing hits a similar wall at 23lbs/min. This is why at the same boost levels as the 30R the engine wasn't flowing more air making more HP. But if we step up to the .82 there is an instant 5lbw/min of air flow gained from the turbine wheel. 5lbs/min is 50 engine HP worth of airflow so this should net close to 50 more Wheel HP. But of course at the expense of lag. In past tests .82 GT3582R would spool around 4500 RPM and with the GTX i think it will be the same. In the past we would say that when pushed the GT30R w/.63 made about, 400WHP, then .82 added 50WHP to that number, then a GT35R w/.63 added another 50 ish and then the .82 added even more.

 

[jgkurz]

24 minutes ago, Gollum said:

Worth reading for the technical gems that are easy to pick up, even if it's not your engine platform:

 

https://www.perrin.com/blog/post/garrett-gtx-turbo-comparo-part-2

 

A great piece of it:

 

 

 

 

I have read parts of that article in the past. It is an excellent piece. It's amazing that a street 4-cyl can support a GTX3582R. 

[rossman]

Your issue sounds similar what big-phil experienced back in 2009 except you aren't hearing the turbo flutter as he was. The solution, as recommended by Tony D was to go with a .82 turbine.

 

 

[Bernardd]

Call Jeffp about a .82 turbine housing.  He might have one for you.  Have you verified that your blowoff and wg are not opening?  While I didn't do testing on the dyno with my old setup I went through a similar issue with a stage 3 .63 vs a .82 exhaust housing.  The .82 took about 300 more rpm to achieve max boost but the power difference was very noticeable.  I can't remember my trap speeds but it was obvious that the spool vs power wasn't significant enough to keep the smaller housing installed.  The smaller housing also made the engine more sensitive to detonation.  That was my experience.