Low boost turbo for Mazda5

[viktor_k]

Ok, now I'm going to be called the "BIGGEST" troll, but seriously though, not trolling, I've had this idea for a while, but my previous car trembled from even a thought of doing this so wanted to get some feedback about this.

So, the idea is to build an electric driven turbo (no don't think those duct fans or anything like that), an actual compressor housing that is driven by a high speed dc motor. I've done my share of research and tried to swim through all the "e-turbo" junk out there, its pretty thick, but there were a couple of companies that actually built a very similar concepts to what I'm envisioning. Unfortunately they only deal directly with car manufacturers and don't sell their products to the public.

The point is not to gain HP but to increase lower end torque. To increase HP you need too much air up top, and thats when you need more fuel and so on. I'm about fuel efficiency and getting more torque down low would keep me from going into higher rpms, staying in the lower rpms has other benefits but i do understand that it will still need to be compensated with more fuel.

Anyway, so here are my questions:

1. If my total air volume is not going to increase over what the engine requires at 6k rpms, will the stock AF meter be able to handle it? I need to understand this a little more, since you could have 3-5 psi of pressure, is the AF meter able to understand that?
2. If my total air volume is not more than at max rpm, we should be ok with stock injectors too, right? We're not talking about increasing overall HP/Energy, but raising the torque down low.
3. If we're talking about increasing 30-50lbs of torque, anything else we need to worry about? How's ecu going to react when I jam more air at partial throttle?

Again, this is not for WOT, but for partial throttle, so closed loop operation only.

I do have a turbo and electronics laying around waiting to be tested with, probably not the best case but good enough for test. I can pick up a brushless motor that can spin up to almost 80k rpm, or use a small belt/pulley setup with a 40k motor. (although i'm not certain that the motor will handle that much load at 80k rpm, something i'm still looking into).

This is also for "once in a while use", not all the time.

 

[rodslinger]

1. If my total air volume is not going to increase over what the engine requires at (WOT) 6k rpms, will the stock AF meter be able to handle it?

- Yes. My MAF is accurately measuring airflow up to about 8.0lbs of boost at 6400rpms. No voltage clamp or signal alteration on my setup. However the stock injectors may or may not support the fuel flow up to the 4 or 5psi you are looking for. If you end up needing larger injectors you'll need to alter the injector timing to compensate or go ghetto and alter the MAF signal instead to match the needed injector load. The 2nd option will guarantee a P0101 MAF out of range error when you scale it down.


2. If my total air volume is not more than at max rpm, we should be ok with stock injectors too, right? We're not talking about increasing overall HP/Energy, but raising the torque down low.

- Sounds like under that scenario you would be OK on the stock injectors.


3. If we're talking about increasing 30-50lbs of torque, anything else we need to worry about? How's ecu going to react when I jam more air at partial throttle.

- I'm finding the ECU is pretty tolerant to boost. If you are driving an automatic the transmission computer is a different story. You'll be placing a lot more torque into the transmission at what are probably going to be light throttle loads. The TCM is calculating slow and easy shifts with low modulated line pressure. That extra 40lbs or torque are going to show with a little flare on upshifts and you may find the trans not completing the gear change until you back off the gas. You'll need to change your driving habits a little. Either go easy on the gas on upshifts or let off on the gas during the upshift.

If you have a manual then this isn't an issue.

 

[viktor_k]

Yea, manual it is, well I may just have to roll up my sleeves and give this a shot. So just to be clear, the ecu should adjust the amount of fuel its putting in based on the MAF readings? I'm a little worried leaning it out and going kaboom, obviously this isn't going to be over 5psi and we're talking 2-4krpm only. What worries me is the electronic throttle, I'm guessing that the ECU is going to monitor throttle position as well, would it not freak out when it sees a bunch more air coming in at X position and X rpm? or does it not care?

Sounds like from your experiment it seems to work though.

 

[rodslinger]

Yes it will add fuel with increased MAF flow but don't rely on that alone. The car is also taking data from the upstream air fuel sensor to add or delete fuel to keep the desired air fuel ratio. You'll want a richer mixture when in boost so you'll need to alter the air fuel sensor data. Essentially you'll need to make the signal from the air fuel sensor show lean at the same time add more fuel to compensate. This lets the ECU see what it thinks is a normal air fuel signal but you are really getting the rich blend you'll need when in boost.

An AEM F/IC 6 will take care of the injector timing changes and the air fuel sensor adjustments. You have to use something to alter the injector timing and air fuel sensor. If you just try to add fuel the air fuel sensor will see it and the ECU will pull injector timing to compensate.

 

[viktor_k]

Hmmm, that's what I was trying to avoid, modifying anything with ecu, so are there "safe limits" of boost that you'd be ok with without needing to fool the ecu?

 

[rodslinger]

I'm not around where I can look at my fuel tables but I'm already adding about 3% more fuel at only 1psi of boost to start getting the system over on the rich side. This is with air fuel sensor adjustments. Depending on load and rpms I can be adding about 10% or more at 3psi and above.

I'm not calling any safe level to be trying to run boost under normally aspirated air fuel mixtures. You'll be asking for trouble. I'm at about 13.6:1 at just 1psi of boost. Down to 13.0:1 by 3psi and at about 12.5:1 air fuel ratio above that.

 

[cburrell]

Honestly, if you want tons of low end torque, why don't you just wait until the summer when the Skyactiv D turbo diesel 6 comes out, it has 310 ft-lb of torque at 2000 rpm's and it is estimated to get mid to high 40's mpg's on the highway. There you go, great low end torque and great fuel economy.

 

[viktor_k]

Honestly, if you want tons of low end torque, why don't you just wait until the summer when the Skyactiv D turbo diesel 6 comes out, it has 310 ft-lb of torque at 2000 rpm's and it is estimated to get mid to high 40's mpg's on the highway. There you go, great low end torque and great fuel economy.

Well, i would, but unfortunately it only has 2 row seating. There's no 3 row seater that is as fun and economic as the 5. I hope the skyactive-d makes it to the 5, with a revised rear-end styling as well.

 

[viktor_k]

I'm not around where I can look at my fuel tables but I'm already adding about 3% more fuel at only 1psi of boost to start getting the system over on the rich side. This is with air fuel sensor adjustments. Depending on load and rpms I can be adding about 10% or more at 3psi and above.

I'm not calling any safe level to be trying to run boost under normally aspirated air fuel mixtures. You'll be asking for trouble. I'm at about 13.6:1 at just 1psi of boost. Down to 13.0:1 by 3psi and at about 12.5:1 air fuel ratio above that.

Stupid question, but wouldn't be better/more efficient to have a knock sensor installed to detect pinging and push the car as lean as possible? Doesn't the 5 has a knock sensor by default?