Is too much boost for a given fuel bad?

[8v-of-fury]

Oh, and you shouldn't take the boost pressure from the turbo outlet, only the wastegate control. The pressure you should measure is the  plenum pressure. Temperature drop from the intercooler and restrictions in intake stream will affect your readings otherwise.

Nice test. So you found that with fueling unchanged you had more power at a higher boost level. However if the turbo is stock on the AAZ, 23psi is way too much for it :O. I think the gt15 is really only good to 18 max tops. If you were to set the waste gate to 18psi, you would probably see even better performance at this fueling than at 23+. 

[R.O.R-2.0]

Ok, so I was playing again today. I disconnected my LDA, and set my fuel screw so it could smoke off boost, but not on. Kept my waste-gate disabled, and did a 60-90km/h pull in 4th gear up a bit of a hill. Set the wastegate to open at the stock 9psi, then did another 60-90 pull up the same stretch of road.
No LDA, no wastegate 5.9 seconds maxed out around 24 psi boost (hard to tell exactly because I was paying more attention to the speedometer and the road).
No LDA, waste-gated  6.0 seconds maxed out at 9 psi.
With LDA, no waste gate, I backed off the throttle when the needle headed towards 30psi.

That doesn't actually mean that 24psi is good for that fueling, just that the most efficient would be closer to 24 than 9. I would conclude that I have a well matched turbo for my setup, and have a hard time attaining too much boost for a given fuel, but if I could reach too much boost for this fueling, it would be a bad thing. If I turn the fuel down, 24psi would be too much, but I likely wouldn't be able to make that much with my setup.

Oh, and you shouldn't take the boost pressure from the turbo outlet, only the wastegate control. The pressure you should measure is the  plenum pressure. Temperature drop from the intercooler and restrictions in intake stream will affect your readings otherwise.

when the intake plenum, and turbo inlet are 6" apart, i dont see it being a BIG issue..

im running sans intercooler right now..

[dh13]

I read most of what was going on in this thread but not everything in detail.

One thing to consider is the fact that the turbo on a 4bt does not have a wastegate or vanes (at least on the rotary pump engines), the engineers at Cummins did this on purpose. They sized the turbo to the engine. This allows the the boost levels to be driven by engine RPM and fueling. This also allows for optimal AFRs whenever possible (although, being mechanically driven there are times at intermediate load levels the AFRs are not so optimal). So in this case if we look at boost relative to fueling, one can say that boost is at least partially driven by fueling levels (you also must account for a properly sized turbo).

Also, belchfire, mentioned Cummins running 70-90 psi. That is not the upper limit on boost levels, competition tractor pullers using the International DT466 or the alike are ranging anywhere from 100 to 300 psi. (quoting this from this article: http://www.enginebuildermag.com/Article/2192/tractor_pulling_its_not_your_granddads_john_deere_anymore.aspx)
And you may say that those are excessive and they could make more power with lower numbers. But one thing you have to take into consideration is that fact that these engines are tuned extensively. When the average build cost for these engines are $50,000, there is no guessing on stuff like boost levels and fueling.

So in the case above high levels of boost and fueling can make high power numbers.

Also there is one thing to consider about fueling and that is the concept of over fueling. Over fueling to a point where the amount of excess fuel being injected into the a cylinder, cools the combustion process can be useful. Excessive over fueling can lower the temperature of the cycle because the unburnt fuel is able to carry heat out of the cylinder much faster than air alone. This allows for increased boost levels and increased power values from a given engine.


I'm not trying to make a point here, I am merely adding information to the thread.

[carrizog60]

if too much fuel gives high egt how can we over fuel to cool it down?

[dh13]

if too much fuel gives high egt how can we over fuel to cool it down?

I am no expert on this but I would assume a set of extrudehoned injectors would be in order; also, the addition of a a "P-Pump" or larger head on a rotary pump would be needed. 

You have to understand that the concept of excessive over fueling should only be used in "race" applications. By no means would a vehicle with the amount of fueling needed to accomplish this concept be streetable.

[belchfire]

dh13's reference artical sheds some interesting light on what is possible. Looks like water injection is probably the best way to drop EGT's but not all that practiable for street use. I've run vehicles on the street with all but full race engines in them and it's no fun in stop & go traffic. While there's no such thing as too much power, driveability has to be considered. Always good to keep in mind the intended purpose of your machine so that driving pleasure doesn't turn into a chore.

[dh13]

dh13's reference artical sheds some interesting light on what is possible. Looks like water injection is probably the best way to drop EGT's but not all that practiable for street use. I've run vehicles on the street with all but full race engines in them and it's no fun in stop & go traffic. While there's no such thing as too much power, driveability has to be considered. Always good to keep in mind the intended purpose of your machine so that driving pleasure doesn't turn into a chore.

I guess the water/meth injection slipped my mind. Mainly because it has been cover so much and has been around for a long time. It was used during WWII in air crafts.

I like your thoughts on driveability and purpose. I feel sometimes people do not understand these concepts.

[belchfire]

When I was a kid every day was race day. A few years and a lot of tickets later I learned that it was every other day.
The water/ meth injection was on gas engines to control detonation. I'm pretty sure that for diesels it's about EGT reduction and charge densification. I would imagine that it's done after the turbo as before would erode the impeller something fierce.

[R.O.R-2.0]

When I was a kid every day was race day. A few years and a lot of tickets later I learned that it was every other day.
The water/ meth injection was on gas engines to control detonation. I'm pretty sure that for diesels it's about EGT reduction and charge densification. I would imagine that it's done after the turbo as before would erode the impeller something fierce.

nope.. they shoot it pre-turbo on the tractor pullers to keep the compressor from melting.. believe it or not, it DOES NOT cause any erosion of the compressor wheel.. idk about long term wear tho.. after 200k miles of water injection, it could cause a LITTLE bit of wear on the compressor..

[dh13]

When I was a kid every day was race day. A few years and a lot of tickets later I learned that it was every other day.
The water/ meth injection was on gas engines to control detonation. I'm pretty sure that for diesels it's about EGT reduction and charge densification. I would imagine that it's done after the turbo as before would erode the impeller something fierce.

nope.. they shoot it pre-turbine on the tractor pullers to keep the compressor from melting.. believe it or not, it DOES NOT cause any erosion of the compressor wheel.. idk about long term wear tho.. after 200k miles of water injection, it could cause a LITTLE bit of wear on the compressor..

According to SAAB, this is not the case. Even particles of water as small at 10 micron will erode the compressor wheel. Of all the water/meth systems that I have seen, never have I seen it injected before the compressor wheel on road applications.

You are correct in the fact that tractor pullers do it. Although, for two different reasons. The first is to cool the air going into the turbo. Second, to actually increase the efficiency of the turbo. It acts as a seal between the compressor wheel and the housing, increasing the amount of air the turbo can actually pull.   

Also injecting water/meth before the compressor will do little to nothing to keep the "turbine" from melting. The compressor is the cold side of the turbo, the turbine is the hot side of the turbo. I would think that lowering EGTs would be the only way to keep the turbine from melting. I am not sure there would be much heat transfer from the turbine to the compressor or vise a versa. I am talking the wheels themselves. I know heat transfers quite a bit from the turbine housing to the compressor housing and what not.

Just some food for thought. Adding to this already overly complex thread. Sorry I had to with it being finals week and all...

[belchfire]

What a dummy. Of course the exhaust is on the other side of the compressor. What was I thinking?  OK how about this. The water cools the combustion as it's being converted to steam. The old latent heat of vaporization thing. That would surely drop EGT's. Inlet injection probably does do some erosion but then we get into race v/s driver application. I've seen a lot of ill advised ideas done for racing but the only thing is winning and it doesn't matter if the engine is a smoldering pile of metal at the end.