No, 15psi on a 50trim is not like 22psi on a 16G. They will both be about the same at 15psi. Once you get to the point where the efficiency of the 16G starts to drop, that is when you start to see differences between a smaller turbo and a larger one.

And guys, give up the CFM ratings. Cubic feet of air doesn't tell you what the mass of the air is! You could have 1 oxygen molecule in a cubic foot of air, or you could have millions. You want mass airflow, lb/min, grams/second, etc...

 

Thanks Shape.. Couldn't have said that better myself..

All I'm doing in addition to the lowered mass/friction in the turbo (and the umpteen explainations of BB/Ti over a big turbo upgrade) Is looking at each and every point in the intake and exhaust tract, and reducing restrictions.. restrictions are things that cause bottlenecks in the system and force the turbo to work harder and lose efficiency, the better efficiency in the turbo means that the impeller is a lower restriction in the exhaust, etc..

I'm not trying to make big numbers, I'm trying to build a car that makes usable power and is fun to drive. Heck, this may all be a futile waste of time to use a stock turbo, HOWEVER, every modification I've made will only help a big turbo swap if I ever were to try it in the future.

Admittedly I like to go against the grain of most tuners, but I have my own opinions and theories that I'd like to try.. I just can't in my heart bolt on a bunch of parts that I didn't determine for myself was the best way to go. Besides, what I thrive on most is the R&D and learning. Besides how many features articles can be done on the same basic combinations that do the same thing? I carefully selected each part I'm using based on their desirable features, and every other component I've chosen in the system..

Fine, This has taken me a year to do, and I still haven't even finished bolting things on yet.. but 80% of the work is in the research and careful analysis of what is available and how can I use it in a way that exploits the most desirable traits.

Now back to our BB Convo..

 

I know it is $$, but I'm surprised we are not seeing more head work (esp on the exhaust side). porting of the manifold / polishing etc.

Yes, kiss your warrenty goodbuy, but I have driven a few cars before an after, wow, like night and day.

 

Truth is, that is probably due to "down time". Think about it, how much down time is the average owner looking at for a turbo swap vs. head work. A day vs. a week (or weeks), not much of a decision for the one car guy. Now for people wanting to get the most out of OEish turbos, they are going to have to visit this sooner or later.

 

Yep.. I'm already entertaining head work.. However I plan on buying a complete head outright to avoid the long downtime of sending out my head and having it done.

I think ANYONE who is looking to make gains is going to eventually have to do head work.. Not just the OE optimizers..

It just makes sense to optimize what is there, your going to have to address these things eventually for reliability sake on big turbo or OE turbo cars..

 

Of course anyone would do well (next to a must depending on the application) to open up the head... but I thought we were talking about OE conversions and the such.

 

Top! Let's get some more information on here... A local custom turbo fabrication shop wants to do a compressor wheel swap on my car for about $325.00. What specifications should I request in doing this? Ti shaft and exhaust wheel? What seems to be the best combo?

 

First and foremost, find out what reverse wheels they can get their hands on. I'd be willing to bet that their tune will change when they find out what they have to work with. The reverse rotation turbo we have, is not that common... well, at least to upgrade.

 

The truth of the matter is if you want the Titanium exhaust wheel, for $400 you can get an entire OE Ti turbo.. But if he's doing the BB conversion also, then its worthwhile.. There are only two turbos that I'm aware of that use the reverse rotation, and both are basically similar anyway. However, you need to determine your actual needs before you can really spec out anything. If you want any sort of custom compressor wheel it will have to be CNC machined.. wait until you see the design time and costs associated with doing a one-off!

 

Why do people insist on running a larger turbo and lower or the same boost as the stock turbo? Someone please tell be because I can’t get my head around it. I mean if you were running a strocker or had a really good set up that flowed really well and were finding the stock turbo was to small then yes, but pushing 350 bhp from a GT35R is criminal. I now Garrett has produced a series of turbos that do perform very well at lower pressures but they do work a lot better at higher pressures.

And why do people go straight for the biggest turbo they can find? Why stick the HUGE GT35R on the when the GT30R is more than capable of producing 500+bhp? then there are hybrids, honest there are hybrids but I have seen none over here! I mean on a 2.0ltr you would be better putting the turbine from the 30R/32 onto the compressor of the 35R this would give you huge potential but not lag like crazy.

Please tell me if I’m wrong.

MalibuJake, I like your approach to tuning as is similar to what race teams do when building engines. There’s little point in a turbo capable of 500bhp if you have to run a restrictor that only lets you run 300bhp!!!!

Shape…. You knowledge continues to impress.

Thanks Chris.

 

boost pressure is not the same thing as airflow which is what you get more of from a larger turbo. in fact, past a certain point, boost pressure is actually more of a measure of how much air your engine isn't able to breathe.

put another way, 21psi from a stock turbo (~36 lbs. of air/min) is less airflow than 21psi from a gt30 (~55 lbs. of air/min)

 

EZ, that makes perfect sense. Another thing to think about is the temperture increase. But, I think that a Ti shaft with BB conversion should be worth a little more boost out of the same turbo, without a temp increase. Plus it would spool a ton faster than a bigger turbo.

I guess the thing I can't get my mind around is how a bigger turbo is even able to "spool like stock". I mean, it takes a certain amount of air to spin the turbine. Bigger exhaust wheel, bigger amout of exhaust to spin it. Right?

 

I'd say you need to select your turbo based on how you'll drive your car. Probably 99% of guys on this site should stick with the stock turbo, (BB conversion would be nice but not required).
For the other guys, just stepping up to a GT30 should be enough. The GT35Rs (or anything bigger) are really for drag racing, way too much lag. Maybe if you used NO2 to help spool-up it could be considered semi-streetable, but not very practicle.
Everybody wants high boost, low temps and no lag. We'll just have to wait for pnuematic valve springs, variable vane turbo's and "smart" ECUs.

 

I really think the BB 50 Trims are efficient enough to spool just as fast, if not fast (with proper Tuning) as the stock turbo and make 400-450WHP pump gas. Thast what I want.

 

the BB 50 trim is also cheaper