Turbo Efficiency Discussion

[TGP37]

. Don't let your USB plug touch a positive power source.

Ouch, now that's a good mood killer there.

730

[NateD4]

Which ECM are you running?

I had been looking at a newer E42 or E67.

The emulator is about as good as it gets except for a dyno when it comes to tuning considering it allows you to change values while the engine is running for immediate review of results. It's even more beneficial when you're trying to sort out closed loop idle after a significant injector size change. You would end up burning hundreds of chips otherwise.

[NateD4]

I'm thinking with water injection I might be able to get into the high 30's mpg wise by leaning....



As far as your emulator is concerned what are you using it for?

I'm looking at an aftermarket ECU because the software is going to need heavy mods outside of tuning.

Maybe an emulator would help.

water injection to reduce EGTs and control piston temperatures.

You have oil squirters to control piston temps, just use a good oil cooler to keep oil temps close to 180 deg. Regardless they run cooler than pistons without the squirters.
I plan to take my car to the dyno or to the track after more tuning which has been delayed due to a freak accident that fried my ecm and my emulator. Don't let your USB plug touch a positive power source.

[NateD4]

Water injection is actually better than methanol for cooling as it can absorb more energy and doesn't mess with A/F ratio. However methanol has some other benefits.

I might suggest trying a water/denatured alcohol mix (as denatured is ethanol with some methanol in it). Most hardware stores have it, however I'm not convinced the price is really worth it for mileage.... on the other hand distilled water is really cheap.

My build is a bit different, I'm going to end up at 3.3L with a totally forged bottom end. I plan on running a lot of water injection and up to 10 PSI boost maybe even 12 PSI (eventually). However I'm going to have a long road ahead of me to get all the electronics set up...

I might even try leaning on cruise to a 15 or 16:1 and use water injection to reduce EGTs and control piston temperatures.

Cam wise, I'm sticking to VVT, the torque band benefits seem to worth while to abandon it. I may even get a custom VVT cam made as well, though we'll see. I suspect the stock cam is plenty.


Any chance you can dyno your car and let us know what kind of numbers you have?

[TGP37]

The methanol also provides an anti-freeze effect. Where I live, it gets cold 1/3 the year.

8 psi is great. More then a factory turbo while still reasonable on a stock PCM.

These motors do respond well to boost. First time I did a full throttle run at 5 psi, I was impressed. 8 psi just feels wicked strong. I ran 12 psi for 3 wot runs and it was too much for the 4t60e. Plus 12 psi just felt too stressing on the motor and needed timing pulled a little too far to prevent knock. 8 psi is a good line for me....just enough, not too much. Even at 8psi w/ a bov, I was blowing the intake off the throttle body when coming out of boost. I had to carve grooves for the silicon to bite into, worked great.

You raised a point about richer AFR during decel.....what is the ideal AFR for decel after boost? On one hand, more fuel would cool the pistons, valves, etc. On the other hand, mpg goes down slightly.


The electric cut out, I think is a great idea. Could have it open automatically by a pressure switch similar to meth injection. And have a master override relay to turn the system on/off. She will idle and cruise nice n' quiet, but opens up in boost. Effectively increasing the pressure ratio across the turbine.

Maybe design a circuit that opens the cutout when the pressure ratio across the turbine (downpipe back pressure increase) gets to a specific point. Functioning similar to a wastegate, it could keep turbo efficiency up by relieving excessive pressure in the DP when needed. That "should" help maintain a higher efficiency. While still having a muffled exhaust, it would just bleed out exhaust when needed.

The amount of fuel on decel for me according to the datalog appears to be in the range of about 16-17:1 with a few areas near 14. I just know the popping is gone. My fuel economy still appears great and I've been beating on the throttle a little more.

I have a snow performance kit installed but I only run water through it now because methanol is infrequently available and an unnecessary expense if water is all it will take to get the job done for my boost level. I'm still looking forward to getting a liquid to air intercooler installed. Right now my air temps are running about 70 deg above ambient at 4 psi, which is about 135 deg.

I'm still amazed at how fast the car is now on 4 psi, a full 7 to 8 should really put it over the top as it covers asphalt really quick.

[TGP37]

These motors do respond well to boost. First time I did a full throttle run at 5 psi, I was impressed. 8 psi just feels wicked strong. I ran 12 psi for 3 wot runs and it was too much for the 4t60e. Plus 12 psi just felt too stressing on the motor and needed timing pulled a little too far to prevent knock. 8 psi is a good line for me....just enough, not too much. Even at 8psi w/ a bov, I was blowing the intake off the throttle body when coming out of boost. I had to carve grooves for the silicon to bite into, worked great.

You raised a point about richer AFR during decel.....what is the ideal AFR for decel after boost? On one hand, more fuel would cool the pistons, valves, etc. On the other hand, mpg goes down slightly.


The electric cut out, I think is a great idea. Could have it open automatically by a pressure switch similar to meth injection. And have a master override relay to turn the system on/off. She will idle and cruise nice n' quiet, but opens up in boost. Effectively increasing the pressure ratio across the turbine.

Maybe design a circuit that opens the cutout when the pressure ratio across the turbine (downpipe back pressure increase) gets to a specific point. Functioning similar to a wastegate, it could keep turbo efficiency up by relieving excessive pressure in the DP when needed. That "should" help maintain a higher efficiency. While still having a muffled exhaust, it would just bleed out exhaust when needed.

Joseph.

What are you trying to figure out exactly?

You are right that the turbo will always have back pressure while spinning. Mainly due to it's radial in flow and the centrifugal effects.

If you are talking A/F ratio... You will probably get some weird ratios on throttle cut.

I would suspect a rich mixture as you cut air with the BOF valve.

One thing to watch is shaft speed on the turbo as a BOF valve without enough back pressure reduces load on the compressor disproportionally with turbine load due to mass flow and energy differences.

I think aftermarket fuel computers have an option to cut fuel on deceleration. I would also open the waste gate to normalize the exhaust and intake pressures during throttle down.

Beyond measuring exhaust back pressure to see if it was practical for me to drop down one turbine housing size, I wasn't trying to figure anything else. Holding the wastegate open off boost was something that originated from Corky Bell and an idea years ago when turbocharging wasn't near as popular as it is now and before I realized how outdated much of the info in his book is since fuel injection was still kind of new. I had given the idea some thought recently because with the boost control solenoids it would be pretty easy to accomplish and I like the technical aspect of mechanics and engine management physics.

I was getting good mileage with a turbo long before this, I got as much as 28 mpg with a low compression 3100 (iron heads on it) and the 4 spd muncie with high hwy rpm.

I have a wastegate for managing boost, the blowoff valve is to avoid compressor surge and shock wave damage and was only a problem during the brief period where a boosted run blew a poorly connected pipe out of the silicone coupler. The AFR on throttle cut depends on programming of decel fuel, I just realized yesterday that I don't have the occasional pop on hard run decel I had on the previous motor because the tune has changed in a manner that richened the exhaust on decel accorging to the history table.
I have a good size turbine housing so at cruise there's no back pressure issue. What I regret is not taking a brief moment to make a simple 3" dump pipe that I could quickly install for open exhaust since my muffler system is held on by a V-band clamp and a support spring at each tail pipe. I plan on installing an electric cutout though. The car is blazing fast on just 3 psi I can't stress it enough in comparison to when the engine was first built and to the stock motor. Degreeing the camshaft in is crucial because that's the difference between falling off at 4000 rpm vs pulling through to who knows what since I back off throttle due to engine sound since my rpm gauge isn't working.

[NateD4]

Joseph.

What are you trying to figure out exactly?

You are right that the turbo will always have back pressure while spinning. Mainly due to it's radial in flow and the centrifugal effects.

If you are talking A/F ratio... You will probably get some weird ratios on throttle cut.

I would suspect a rich mixture as you cut air with the BOF valve.

One thing to watch is shaft speed on the turbo as a BOF valve without enough back pressure reduces load on the compressor disproportionally with turbine load due to mass flow and energy differences.

I think aftermarket fuel computers have an option to cut fuel on deceleration. I would also open the waste gate to normalize the exhaust and intake pressures during throttle down.

[TGP37]

Good mpg, a sign of a well built engine. Some people say, "What do you need a turbo for?" well, it increases the cars fuel efficiency......when my Wife drives it, lol.

Pretty cool Joseph. I too think the pressure spike from a quick tip in is spool related. Possibly flow related as well. As the mass flow ahead isnt up to speed yet.

Do you get any brief exhaust vacuum pre-turbo when closing throttle at higher RPM's? You know, turbo well spooled up but exhaust flow drops. Noting the compressor wheel is happy with the BOV opening up.

At that brief moment, the compressor is moving air that gets removed at the BOV. But the turbine doesn't see that air mass after combustion, obviously. So the compressor is moving more air then the turbine experiences. Making the ratio off...sort of....I think.

Maybe forcing the wastegate open at throttle closing, allowing the turbine to spool down w/o added resistance.

I didn't note any vacuum (scavenge effect) on the gauge if any and doubt it is likely to occur as a result of the turbine because the blade design is not optimized for it considering the turbine blade arrangement is nearly the same as the compressor arrangement with the blades spinning in the opposite direction of what pulls air, except in the turbines arrangement the centrifugal movement of air may have an effect which would favor residual back pressure instead.

Whatever the case there is no sense in leaving the line in the car because first start moisture gets in it and stays unless you allow it to bleed out.

I considered an arragement to open the wastegate off boost by using a stock wastegate solenoid connected to the top port on the wastegate and using it as a switch that moves between open air and manifold pressure arranging it to switch to manifold pressure under vacuum and atmosphere underboost since the solenoids have 3 ports arranged for that function. I considered doing it for fuel economy but with a properly sized turbine housing fuel economy at cruise is not a problem and the motor is already showing signs of better fuel economy than the previous two around town. I haven't measured it but I can tell by how slow the fuel gauge drops even with spirited driving that it's better.

[TGP37]

Pretty cool Joseph. I too think the pressure spike from a quick tip in is spool related. Possibly flow related as well. As the mass flow ahead isnt up to speed yet.

Do you get any brief exhaust vacuum pre-turbo when closing throttle at higher RPM's? You know, turbo well spooled up but exhaust flow drops. Noting the compressor wheel is happy with the BOV opening up.

At that brief moment, the compressor is moving air that gets removed at the BOV. But the turbine doesn't see that air mass after combustion, obviously. So the compressor is moving more air then the turbine experiences. Making the ratio off...sort of....I think.

Maybe forcing the wastegate open at throttle closing, allowing the turbine to spool down w/o added resistance.