<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Almighty-Si:
The volumetric efficiency of an engine plays a huge roll in properly sizing a turbo for a motor. Though only being 1.6 liters the B16's volumetric efficiency is much greater to that of the 2.0 liter Mitsu motor.
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You're right, the volumetric efficiency does have a big effect on selecting a turbo. But so does many other factors.
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Almighty-Si:
Being I am an idiot and you are smarter than I, maybe you can work the equations and explain them to everyone so it makes sense.
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I never said you were an idiot, but ok, i'll do as you wish <img src="http://www.clubhonda.com/infopop/emoticons/icon_wink.gif" alt="Wink" width="15" height="15"><!--graemlin:;)-->
When picking a turbo, you must consider many things: volumetric efficiency, engine displacement, boost pressure, intercooler efficiency, etc. They all play a major role in the performance of a turbo.
Each turbo has a compressor map which plots an engine's RPM range across a graph, which takes into account the amount of boost being ran and the air being flowed. There is a certain range that the turbo will work at its peak efficiency, which is where you want your car's power band to fall close to.
A turbo will not use its full potential if it is not operating near its peak efficiency range. If a turbo is operating well under its efficiency range, then the motor will not spool the turbo enough, and it will lag badly and not produce as much horsepower as it should. If it is operating well over its efficiency range, then it will spin the turbo too fast, shortening the life of the turbo, creating a LOT of heat, and it will spool up very quickly then top off. When the turbo is working too hard, it will start to blow very hot air; it gets so hot that it no longer produces more horsepower w/ the boost that it builds. This is when the turbo is operating outside of its thermal efficiency range. It may be blowing more boost, but the air is not producing any additional horsepower.
Most car manufacturers mate a turbo to a motor so that it produces good low and midrange power, and so it spools up very quickly. This is because most people buy a car for driving around town, and do not want to have to wind it out every time they pull out of a parking lot just to get somewhere. People want low-end torque. This is not the best way to go fast, though. You want the turbo's efficiency range to fall on your motor's powerband, w/o becoming inefficient.
The T25 does not really have a compressor map floating around anywhere. After some research, I found that apparently the T28 is something of hydrid between a smallish (~45 trim) T3 and a T25's wheel. So w/ my thinking, The T3 should produce more topend power w/ a slightly longer lag time. To roughly simulate the T25, I would just take the T3's results and lower them a bit.
I put the B16 against a 45-trim T3 to see roughly how it would fare. I used a VE of 90%, which should be about right. I used a base of 6psi, since that's about what you would have the stock wastegate spring set to. Everything else I just used average figures.
Here is the 45-trim T3 map:
http://www.turbofast.com.au/img/t3-45.JPG
At 6psi, the boost would be right at 1.48 bar on the right hand side. The B16 would start its RPM's at the far left, and would hit 8k at about 19 lb's/min on the bottom. So just imagine a line being drawn at the 1.48 mark all the way across straight to 19. You will see that on the B16, it is very near the turbo's efficiency range between about 2k and 6k, therefore producing very nice driving characteristics. Spool time will be very short.
Also notice that past 6k, it starts to fall out of the efficiency range, but it's not too far out. It will begin to fall off on the top end, but it should still produce some nice top-end gains w/o any negative effects. It will still produce some good power, just not as efficiently. It is still pretty thermally efficient. Notice that raising the boost level will bring the efficiency range almost perfectly into the middle of the B16's powerband.
After looking at the B16 plotted on the compressor map, I maintain my opinion that the T25 would be a very good turbo for the B16. It is cheap and easy to find, and produces a fast car that does not have to be at 4k before it starts to boost. If you want to spend the extra cash and have better top end, go ahead and spend 400-650 on a new T3/T4 hybrid or the such. IMO, using a pretty good intercooler on this setup would yield some very pleasing results.
Class dismissed! <img src="http://www.clubhonda.com/infopop/emoticons/icon_razz.gif" alt="Razz" width="15" height="15"><!--graemlin::p-->
Who needs VTEC when you got torque?!