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nixit79 wrote:

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Say Positive, tell us more about the turbo 900 layout...again. I have a 900 block, cylinders, pistons, rods, and crankshaft. Ive got a complete donor 650 Turbo engine. I still need an extra set of 650 turbo (all steel) cylinder, and head gsakets to get the compression low, or have them custom made in double thickness (or any thickness for that matter) copper.

Am I missing anything?

Do I really need the 700N exhaust (or was that intake) camshaft?

You were going to use your modded turbo on a 900 engine setup, do you think a non modded turbo would still be an acceptable match?

On water/meth injection.... If you were going to run this on the stock ignition setup, is there anyway to have it supplement the system by using the exisiting retard timing on knock as a back up?

Hello! (BTW - Have front pieces for you, just need to toss them in the polisher over the weekend).

I'll start a new thread on the 900.

I don't know why he would make the statement. The T25 will boost at 3500 when driven by the exhaust volume of a 2.0l engine. So how fast would a 650cc engine need to turn in order to spool the turbo?

Theoretical air flow for an engine is calculated by:

TAF= (displacement x rpm x efficiency) / (cycles)

Assuming a VE of 80%, engine diplacement of 2000cc, an RPM of 3500:

(2000 x 3500 x .80)/4 = 1400000cc/min

1400000cc/min ~49.4CFM.

Solving for the 650cc engine:

(650 x RPM x .80)/4 = 1400000
(650 x RPM x .80) = 5600000
(650 x RPM) = 7000000
RPM = 10769

So the 650cc engine with an estimated VE (volumetric efficiency) of 80% would have to turn 10700 RPM to move as much volume as a 2000cc engine with an equal VE at 3500 RPM.

So I apologize if my comments came across too strong. This is the basic calculation used to size a turbo. Once you know the volume you can size the turbo for your application and HP range, and determine if the T25 can be made to work. The specs on the T25 is what will really tell the tale. The table I looked at places the current GT25 sized for a 1.4l to 2.2l engine in a range of 170HP - 220HP.

Here is one that would work great: ebay item 160295890588 Garrett GT1241.

As to the alternator: The wiring is identical.

maximturbo wrote:

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also.... you state that :

"So the 650cc engine with an estimated VE (volumetric efficiency) of 80% would have to turn 10700 RPM to move as much volume as a 2000cc engine with an equal VE at 3500 RPM. "

While this statement is true, what about the fact that at 3500rpm the 2.0 needs X amount of airflow from the compressor to start making boost.
However, the 650 will need alot less airflow from the compressor to start making boost. As boost is merely a restriction, the restriction will definitely happen sooner in the rpm range on the 650 than the 2.0.

Please explain this one.

Is the gt12 larger than the stock yamaha turbo.

Well, it is all about air flow. In this case the T25:



This table shows the behavior of the T25. The island in the middle is the ideal range. The line furthest to the left of maximum is the surge line (inlet stalling). The line furthest to the right is the choke line (inadequate inlet cross section). The curves cutting across the map are the compressor wheel speeds in RPM.

Without making any temperature correction; converting the 49.4CFM to lbs/min of airflow yields 3.98 lbs/min. Using the x-axis you can see that ~4lbs/min the turbo is barely producing pressure. Keep in mind this value (4lbs/min) happens at 10k RPM on a 650cc engine (which is past the peak HP and torque on this engine). This map indicates that with this flow rate will produce a maximum pressure ratio of 1.3 but is on the surge line (stalling inlet means no pressure). even with a goal of 80HP (~10lbs/min) the operation is still well below peak and falling toward the surge line.

So the issue is not so much the intake volume but that the turbo is not spinning fast enough to compress air. The compressor stage is not positive displacement pump.

Here is the GT12:

As you can see the 4lbs/min will turn this unit. And if the target is 80HP (~10lbs/min) the result will fall into the highest efficiency and highest pressure ratio.

Comparing the two tables shows that the GT12 operates below 12lbs/min and the T25 is just hitting its peak in that range.