That added another dimension to the myth of pre-T injection.

It appeared people is getting mix results.

OMG, I made it through all 24 pages... it took me a week at work - seriously, not a full time week, but 'when i have time week'.
some really good info here, but then again, there's some misrepresentation going on. Mind you might might be slightly off topic.

Particulary I want to comment on turbo sizing.

Everybody here seems to be talking about the compressor, and compressor maps, etc. Turbo is made of two parts compressor and turbine. they are conected by a common shaft therefore turbine is as important in making power as compressor being drive by that turbine. Nobody mentioned manifold design/type...

Exhaust housing size is mentioned in only 2 posts in the whle thread, while it is a very important factor.
Exhaust housing size, along with manifold sizing/design and exhaust system greatly affect power and responsiveness of the engin.
Assume good manifold deskign (tulbural, no sharp turns, equal length, full split pulse separation, with 2 wastegates) and ample exhaust system used.
The bigger the exhaust housing the less restrictive the exhaust gasses path, therefore greater power putput. That is aswell compounded by the fact that less restriction lowers EGT's therefore raises knock treshold.

it is common that oem turbo setups usually use smaller exhaust housing as that produces a quick throttle response making car feel more powerfull than it actually is...

ok, ok, where i'm getting at, with regards to pre turbo WI.
I'm saying that all thought I agree with the fact that preT injection will incerase flow of the compressor, i think the because air is dense, compressor is harder to turn therefore is turbine and that is more resistance to the engine.

And if your turbo is outside of efficency range, wi might incerase air flow, but chances are that your exhaust housing is maxed out in terms of flow therefore more air will not make much more power.

Many people here seem to confuse boost with power. power is a function of much much power is made in cylinders and how much is lost for running rngine (resistance of bearings, inertial losses on pistons which are constantly accelerating up and down, resistance of the exhaust gas flow. Generally speaking in a healty setup should produce nearly 200% of it's NA power at 1 bar of boost (i.e. 2 bat absolute pressure). and it's not exacly 100% per 1 bar, but as you incerase the boost you should see incerase in power. keep incerasing boost further and you will eventually get to the point of diminshing returns, where more boost doe not produce as much more power as at lower levels. so you work out a happy safe spot for you or look what can be changed to make that boost range more efficient... bigger exhaust housing, more efficient compressor, etc...

I guess what I'm saying is that with small oem setup type turbo your tuning abilities are limited because of the size of the turbo. and normally stock manifolds are cast and generally pretty bad design (see twin turbo supra stock manifold).

but with building efficient systems (low exhaust restrictions) great efficiency can be obtained. taking that idea to new level, there are some great benefits when we reac the point when boost pressure is higher than exhaust backpressure... then you can use wild cams on turbo motors, and that allows you to spool large turbos with small engine with great efficiency.... a example of bad way to do it is the 800hp skyline mentioned earlier in this thread which at 3 bar makes less power than at 2 bar. too small compressors ? possily. exhaust restrictions must be huge. pumping more air will not solve the problem. get exhaust housings 2-4 sizes larger and it will make 900 on the same boost... they will spool a bit later tho...

I think water (and other pre turbo injection) has it's place and should be further researched. But results may vary in every case. It seems like ideal candidate would be turbos with smallish compressor but large turbine... where compressor is limiting factor of the system... cooling charge air by convection (evaporatino of water or other fluid) is a way to go i think, but needs more experimentation...

I was thinking... maybe along with spraying large quantities of methanol, inject pure oxygen to the intake tract... yes, it might be expensive but power gains might be great too.... would work good on drag cars...

Just getting familiar with this topic again, after being away for a year.

I am seeing some questions and observations that don't have answers, and I thought I would get involved. I have spent much of the last year working through a problem with coolant overheating on GM diesel work vehicles. Since some of my findings are applicable to this effort, I will elaborate.

What I found was that the smallish compressor was working in the northeast part of the map, and in some thermal conditions, "off the page". On further investigation, the temperature of the compressure discharge emerged at near 600 F. I calculated efficiency around the 50% mark. Needless to say, this is in a word, ridiculous! Further investigation led me to question what the effect of this heatup (and expansion) is on the downstream plumbing. Something told me that I was seeing extaordinary head losses with this huge heatup. In other words, the velocity in the IC/CAC plumbing would be increasing dramatically, leading to higher frictional losses. It turned out, the difference between the compressor discharge pressure (work) and the intake plenum pressure (downstream) was nearly 6 psi! This at a plenum requirement of 32 psi. On the diesel this is around 60-65 lb/min of airflow.

Now hopefully I have not lost you. The plumbing restrictions when considering the 2.5" IC plumbing and the IC itself, totalled 6 psi. (2.5" is way too small)

After working through the compressible flow equations in a 2.5" conduit, it turns out the increased discharge temp was creating much of this loss, via increased air flow velocity. With fluid flow, there is apoint where the force required to push the fluid (air) through the straw (or IC pipe) becomes exponential, the curve quickly rising vertically at some flow rate. When this happens it is time for a diameter increase from the engineers. (what in fact happened, is that GM reduced the diameter from 3.0" in previous models, and to this day there is no known explanation why)

Adding insult to injury, that high temp product was leading to dramatic ambient temp increases behind the grill. The IC sits in front of the radiator, and measured ambient in front of the radiator, on the hot side of the IC, was 240 degrees! So the CAC was acting like a torch to heat coolant. I calculated something like 290,000 BTU/hr of heat exchange with the IC. Nuts!

But back to hot discharge product. The predictions for this non-adiabatic behavior, show that velocity increases dramatically, and adds a lot of added restriction in the plumbing. Clearly cooling the charge increases density, reduces velocity, and hence pressure losses. This means that, for a given desired intake plenum boost pressure, less work (discharge pressure) is required. This compressor now works less, which means higher efficiency. The improvement is cyclical in nature.

it appears that pre-compressor WI, PCWI, can be a performer or a deterent to performance. If you already operate in the efficient islands, on a humid day, then cooling charge can move you to lower efficiency on the left. It also leads to huge condensation effect in the IC. So PCWI would have limited usefulness on a properly designed forced induction platform with large stock amounts of charge cooling. But the undersized compressor, operating on a dry day, with excessive air box temps, should benefit big.

From my point of view, I do not share the idealized concept that WI provides quasi-isothermal compression. I believe that all the inefficiencies of non-adiabatic compression are in place even with WI. But naturally the beneficial impact of cooler charge can be seen in my explanation. But I don't believe that WI improves the efficiency of the compressor, from a purist sense. This assumes that there is no appreciable evaporation prior to compressor, as is the case in an axial mount nozzle in front of the nut.

Richard, I have tried PM'ing you and email. What am I doing wrong?

What happened? Did everyone die? Or is it just cold everywhere but here?

I think theys did :D

Still trying pre-compressor injection... but nothing conclusive yet. BY lowering the onset pressure from 10 to 8psi on my 1.9TD diesel, I was fairly sure that a small effect was noticeable (0.3mm jet, not a lot of water) but then other things conspired against my tests

Have bought some temperature instrumentation to see if I can detect a reduction in charge temp after the compressor, or rather, how significant it is

Harry, I am interested in your results. I have done some post compressor temp and pressure monitoring, but not with WI yet. I did it in conjunction with evaluating larger boost tubes. Used a nifty 4-channel temp datalogger.

If you have a VGT, and if it is like others I have seen, the WI should lower discharge pressure, while maintaining equal plenum pressure. Curious if you find this to be true. The effect should be magnified in systems with a lot of pressure drop, high IAT, and high boost/low efficiency/off map operation.

Anyway, all this means that for a given boost, is less wok that turbo must perform, and lower final charge temps, better charge density, hence better economy. For those that tow, and have a thermo-viscous fan, the fan can be kept off with lower CAC heat rejection, and this can be a huge benefit.

That's the theory anyway.

VGT?

That's me running a small A/R turbo that starts spinning early but soon reaches the turbine limit and probably chokes the compressor too.. hence high EGTs, and haven't been able to see any definite EGt eduction yet, but no doubt there must be some...

Going to look at my compressor vanes today, pretty well requires removing turbo... alos have had turbine/CHRA gas leaks (kKK's are bad for sealing that joint)

Where did the EGT reductions come into play?
I've yet to find a documented case of EGT reduction anywhere in the (sparse) literature.

EGTs not increasing at even higher boost -- yes
EGTs decreasing ---> haven't seen that yet.

Well, true, I had been told not to expect EGT reductions of signifance, however, on a digital EGT a friend with same engine is seeing at least 30C reduction with post turbo Water Injection.

Mine are so high, that I thought I might see something of benefit in that area...

Non-intercooled 1.9 TD diesel, 12~15 psi boost