Hey guys...

turbochargers.com says thaT:

a T25 to a T28 upgrade is done internally in the housings
clipping is done on the turbine wheel and is also done internally so it directly bolts on
thanks


So my questions are:
1. you can make a T25 a T28????? AND it will but the stock blue bird manifold?

2. What the heck is clipping?


And finally correct me - but to start off what would I need to run this turbo?

I'm thinking bigger injectors, cobra maf - anything else?

Thanks
Chris

I'd like to know the answer to these questions too. What can be done to a stock T25 and still fit on the BB manifold?

Hit this link, then click on the "T25 to T3 conversion" link on the left-hand side. I asked the owner of this shop the very same question...

http://www.jgstools.com/turbo/

His reply:
"If you can measure your T25 compressor housing, I can tell you if its going
to fit.
If it will fit, I have a .60trim T3 upgrade for 399.99, for one with a .46
T04E compressor wheel its 599.99 (good for upto 400HP)."

So, somebody needs to measure a T25 housing and then we can email those measurements to him. If this could be pulled off without hitting the block...... :)

The T-28 comes with a bigger compressor wheel (60 trim 60mm vs. 60 trim 56mm) in a T3 compressor housing and also a bigger turbine wheel (79 trim 53.8mm vs. 62 trim 53.8mm) in a bigger housing (.86 vs. .64). So, it's more than just "internal changes." Both use a T-25 exhaust housing so both will bolt up to a BB manifold. BUT, you will have to grind down the block to use the T-28 on the BB manifold because of the larger compressor housing.

Clipping: basically when you cut the "fins" away at a small angle.

T-28 = Hybrid turbo.

A T-28 is a T-25 turbine (53.xmm inlet diameter) mated with a T-3 (60 mm OD) compressor. The wheels can be any trim, and the housings can be any A/R.

To convert a bluebird T-25 to a T-28, all you would have to do is swap the compressor wheel out for a T3 wheel, and rebalance the turbo. You could either fit a new compressor housing that is machined for the bigger wheel (you would probably have to fit a new backplate, too), or you could just re-machine the T-25 housing so that it would accept the bigger T-3 compressor wheel.

Now you have a compressor that will flow more, but you are still stuck with the stock 62 trim turbine in a 0.64 A/R housing. To get the turbine flow up, you can either fit a bigger trim turbine wheel, and carve out the stock 0.64 A/R housing to fit the bigger wheel, or you can can put a bigger A/R turbine housing on, or you can fit a bigger turbine wheel and a bigger A/R turbine housing. Or, you can clip the turbine wheel. Clipping means that you cut back the blades at the exit of the wheel in order to increase the throat area at the exit of the wheel.

A lot of shops will give you the following 'upgrade' on your stock T-25: take out the stock 56mm T-25 compressor wheel. Re-carve the stock compressor housing, and put in a 60 trim (or better yet, 'Super' 60) T-3 compressor wheel. Then, they will give you a 15-20 degree clip on the turbine wheel. You end up with a turbo that is completely outline interchangable with your stock turbo (since it uses all the same housings), but will flow more on the compressor and turbine side.

The problems with this 'upgraded' turbo are as follows:

Putting a larger diameter compressor wheel in the stock T-25 housing eats up all the diffuser diameter. The diffuser is the place where all the high-velocity air coming out of the compressor wheel gets slowed down and converted to static (boost) pressure. Without a good diffuser of appropriate diameter, the high velocity of the flow coming out of the wheel doesn't get converted to static pressure, and the energy contained in the flow is lost in the compressor volute. This causes a sizable loss in compressor efficiency. The stock BB compressor struggles to break 70% compressor efficiency (peak), so losing 4-5 points from a poor diffuser design is very bad. I know people who have run turbos like this, and seen their compressor outlet temperatures increase by 100 degrees F or more after the 'upgrade'.

Clipping a turbine wheel exducer results in an underturning of the flow exiting the turbine wheel, so that the flow leaves the wheel with appreciable amounts of exit swirl. Although moving the throat upstream increases turbine flow a little, the loss in efficiency more than offsets this. Considering that a stock BB turbine struggles to break 60% turbine efficiency, the loss of 5-6 points in turbine efficiency caused by a 15 degree clip will cause a noticable drop in performance.

Such an 'upgraded' turbo will set you back about $400, will lag worse than your stock turbo, and will maybe make just a few more horsepower over the last 1000 RPM or so of the engine's operating range (losing power everywhere else).

If you have a stock BB turbo on your car, here is my advice to you: LEAVE IT ALONE. If you want more power, I suggest you do the following: 3" exhaust, front mount intercooler, free-flowing cold air intake, 3" downpipe, go to about 10 psi of boost. Once you have gotten to this point, if you want a little more power, go with a set of S3 cams, and *maybe* if you feel like it Extrude Hone and Swain coat the turbine housing and the exhaust manifold. Any other 'upgrade' to the stock turbo is a waste of time and money. Save your money until you have enough to buy a decent upgrade.

Wow, thanks for the info. It's good to know these kind of things.

Ditto - thanks much!

Looks like Pullies for me!

Chris

Now, how did I know that would elicit a response from Rob Cadle?

GREAT info, Rob. Thank you for sharing it with those of us who are still somewhat-new to turbocharging. :D

'*** boy there knows his stuffingz. I think I can summarize for him. If you have a T-25 and want more power, buy a T-28 don't try to upgrade the T-25. If you have a T-28 and want more power you must not like 3rd gear, buy a T3/T4. If you have a T3/T4 and want more power you must hate your transmission, buy a spare. :D

So... If I want to upgrade to a T28 from a BB. I need the GTiR manifold and T28 turbo assembly with the appropriate gaskets and new downpipe. Anything else I'm missing?