Turbo minivan (planning 3.8L ford windstar project)

[serialk11r]

Originally Posted by js335

I'm still researching and considering the asymmetric turbo setup, the single turbo would be pressurizing both banks intake valves, only difference would be one bank would have slightly higher back pressure due to the turbo, from what I have read so far, this is not a problem.

The ECU doesn't know that half the cylinders are getting more air than the other half most likely, and if it injects not enough fuel into half the cylinders and too much into the other half, something will break pretty fast. If you have 2 O2 sensors, one per bank, you might be in slightly better shape in terms of fueling, but there are still a million other things that could go wrong.

EDIT: oh you want to hook the exhaust to one bank only. That's bad too, because the backpressure will cause less air to go into those cylinders and the same problems will occur. High likelihood of detonation.

[js335]

Originally Posted by serialk11r

The ECU doesn't know that half the cylinders are getting more air than the other half most likely, and if it injects not enough fuel into half the cylinders and too much into the other half, something will break pretty fast. If you have 2 O2 sensors, one per bank, you might be in slightly better shape in terms of fueling, but there are still a million other things that could go wrong.

EDIT: oh you want to hook the exhaust to one bank only. That's bad too, because the back pressure will cause less air to go into those cylinders and the same problems will occur. High likelihood of detonation.

I appreciate the input but I am going to have respectfully disagree with you. The slightly higher back pressure will slightly hurt exhaust scavenging I agree, so a little less air will mean a little richer AFR on that bank. Most modern EFI systems have no problem correcting up to +/- 20% fueling adjustment before a lean or rich code is triggered, and we are talking about single digit % changes to AFR here. It may run slightly rich when forced into open loop during high throttle situations, but running a little rich will help with detonation, not hurt, and who knows maybe a little extra exhaust in the chamber will have an erg like effect to bring down combustion temps, further hindering detonation. All in theory of course.

That being said I believe the keyword in that last paragraph is slight because I think the effect of turbo backpressure on one bank is so small at the boost levels I'm looking at(5-6psi.) its not going to matter at all.

As for detonation, if it were going to occur at that boost level, it will not because I am going to use water injection. I have used it extensively over several years and it does amazing things, I have used it in the past several years and have ran over twice as much boost on an engine with a little higher compression, stock timing, no intercooler, pump gas and properly setup WI system. key is to get a large reservoir.

[RobertISaar]

Originally Posted by js335

who knows maybe a little extra exhaust in the chamber will have an erg like effect to bring down combustion temps, further hindering detonation. All in theory of course.

and here's where theory meets pavement: the backpressure will impede the flow of exhaust gasses out of the exhaust port, rather hot exhaust gasses at that, there's a reason EGR is taken from a much cooler place in the exhaust stream. i would predict a weaker, significantly hotter air mass without water/methanol injection.

[js335]

Originally Posted by RobertISaar

and here's where theory meets pavement: the backpressure will impede the flow of exhaust gasses out of the exhaust port, rather hot exhaust gasses at that, there's a reason EGR is taken from a much cooler place in the exhaust stream. i would predict a weaker, significantly hotter air mass without water/methanol injection.

Not at these power/boost levels. and I was half joking about the EGR statement. Using a very small turbine and high boost levels can cause a condition called "reversion" where the high back pressure from the small turbo can backflow exhaust gas during valve overlap. This is very bad and can result in severe detonation/engine damage. This usually happens when for example a kid with his stock small t25 equipped eclipse turbo puts a boost controller on and puts it through the roof with 30 psi. doesnt last long,ask me how I know. Btw, EGR gas on most gas engines is taken from one of the hottest part of the engines, the exhaust port or manifold.

But I'm not trying to start any arguments here, we don't have millions of dollars of test equipment like the big guys so no one's theories are hitting any pavement until we just try it. I'm hoping to gain some insight from the great minds on this site and share my results so it can be duplicated if successful.

One thing I was hoping to figure out and is usually the hardest part is the turbo sizing. I think I have a plan. T25 is on a stock dsm and runs 11ish psi boost with fast spool on a 2 liter. These are practically thrown away by the dsm guys due to being to small to make big hp numbers. Cheap on ebay all day, flanges and downpipes too. I might be able to squeeze one on the front bank of the van, if not I'll midship mount it underneath(connected to only one exhaust bank). Hook it up, set it at 5 psi and see what happens, if I don't like the results or not enough boost, add another.

[oil pan 4]

Originally Posted by js335

I live in hampton roads, VA.

I lived there for 5 years right off the the new and improved King street, moved out to NM in the first part of 2011.
When I was living in hampton I never thought I would want/need a turbo on my diesel. Loosing 10% of the avaible air mass will change your mind real fast.

[mechman600]

Adding a turbocharger is not going to help FE unless you [at least] change final drive ratio, transmission shift points & lock up strategy, etc. - all things that be beneficial without a turbo anyway. Like already mentioned, a turbo only helps FE when the engine is downsized.

Why not do something ridiculous: disable half your engine (remove one bank's pistons and valve train), as this has been proven to increase FE, and turbocharge your remaining 1.9L 3-cylinder to gain some of the power back.

[serialk11r]

You're missing the point. When there's uneven scavenging and backpressure, the injectors can't inject more fuel into some cylinders and less into others. Thus you will have the wrong amount of fuel in ALL the cylinders.

This is why unequal length headers are bad for performance, the screwed up scavenging makes it hard to deliver the correct amount of fuel to any cylinder, so you have to just squirt more fuel altogether, which is not good.

[RobertISaar]

Originally Posted by serialk11r

You're missing the point. When there's uneven scavenging and backpressure, the injectors can't inject more fuel into some cylinders and less into others. Thus you will have the wrong amount of fuel in ALL the cylinders.

to split hairs: you can.....

but only if your PCM is capable of doing so. starting in ~1994 or so, certain GM PCMs started supporting "individual cylinder trims" that allows you to skew the delivered fuel to each cylinder. certain V8s suffered from one cylinder basically "stealing" the air charge from another cylinder, causing it to have noticably more air in that cylinder compared to another cylinder. so without it, a couple cylinders would always run rich and a couple would always run lean.

i don't think any of the V6 engines had that issue, but the capability still existed IIRC.



but, this is ford we're talking about, so i have no idea if any of it applies, or if it's even possible for a tuner to access it.

[serialk11r]

Originally Posted by RobertISaar

to split hairs: you can.....

but only if your PCM is capable of doing so. starting in ~1994 or so, certain GM PCMs started supporting "individual cylinder trims" that allows you to skew the delivered fuel to each cylinder. certain V8s suffered from one cylinder basically "stealing" the air charge from another cylinder, causing it to have noticably more air in that cylinder compared to another cylinder. so without it, a couple cylinders would always run rich and a couple would always run lean.

i don't think any of the V6 engines had that issue, but the capability still existed IIRC.



but, this is ford we're talking about, so i have no idea if any of it applies, or if it's even possible for a tuner to access it.

Right, technically it's possible, but I think you'd be hard pressed to find an MAF count greater than 2 (I've only seen this on V8/V10 and above) and an O2 sensor count greater than...2? I'm not sure about V8s, my 1ZZ has 1 O2 sensor per bank. I don't know how many O2 sensors are fitted to his engine.

At any rate, there's the issue of the opposite cylinder bank "stealing" quite a bit of charge from the 3 with the added backpressure.

[js335]

Originally Posted by oil pan 4

I lived there for 5 years right off the the new and improved King street, moved out to NM in the first part of 2011.
When I was living in hampton I never thought I would want/need a turbo on my diesel. Loosing 10% of the avaible air mass will change your mind real fast.

Im not too far from there, other side of the water, I always want to put a turbo on everything

Originally Posted by mechman600

Adding a turbocharger is not going to help FE unless you [at least] change final drive ratio, transmission shift points & lock up strategy, etc. - all things that be beneficial without a turbo anyway. Like already mentioned, a turbo only helps FE when the engine is downsized.

We shall see, I read otherwise

Originally Posted by mechman600

Why not do something ridiculous: disable half your engine (remove one bank's pistons and valve train), as this has been proven to increase FE, and turbocharge your remaining 1.9L 3-cylinder to gain some of the power back.

because that does sound ridiculous. and complicated to make work right.

Originally Posted by RobertISaar

to split hairs: you can.....

but only if your PCM is capable of doing so.

you are correct, this van is a 99, single bank o2 sensor fuel control for V6/V8 engines went away in the early 90's with OBD1, this OB2 engine is more than capable of making individual bank fuel trim adjustments.

Even so, I've turbocharged many cars before, and the issues you guys are talking about would certainly come into play at high boost/power situations, but not this.