White_Shadows

Good post. Out of curiosity, does that factor in that you are having combustion on every "stroke"?

MazdaManiac

iTrader: (3)

Thanks!

I wasn't directing my post at you particularly, but I can if you like.

To me, its interesting that the people that are re-inventing the wheel are primarily spending so much energy trying to convince everyone that they understand that a circle has four corners.

Who are you trying to sell this concept to? Yourself or everybody else?

Just build it. You will get the "ah-ha" along the way.

bhop

^ Happens to me everytime I look under the hood....

I'm no professional.

White_Shadows

Up to you. I have strong shoulders, have at it. lol
Probably only reason I had at it was just to see if I did learn anything along the way that was FREE (well cost of the internet)
As I said in red all I ever asked for was a good turbo at a tiny size. If for my application someone has a better idea for two turbo's to fit under the hood close to the exhaust ports, by all means.

maxxdamigz

iTrader: (1)

Hmm - maybe I need to reread this thread, but what is your model for an engine that gets good fuel economy with a turbo? Then, take that engine and flat out steal its characteristics - well not the components and design, but the concept. Then look at those concepts and see if the renny is at all compatible. From what I hear, the smart cars getty shitty MPG for their overall designs. The hybrids are out and I don't think they're turbo. A mid 90s civic hatch gets good gas mileage but that isn't turboed. Anything with variable valve timing is out unless you are going to develop sliding port technology (which would be pretty sweet).

Edit: Ok, so the test case was a prius hybrid. The net design was to increase low end torque and reduce the need to high rpm use to meet fixed power output requirements. My suggestion, then, would be to take the 6 port out and put in a 4 port from an auto. Redesign the airflow pathways for a lower end torque peak. Then select a turbo/turboes designed to push your torque peak even lower. When all is said and done, you'll have the first 110 whp manual renny but maybe it'll crack 25 mpg. There are tons of other gains to be had. Remove the A/C, thin up the wheels, weight reduce everything. I'm sure on a skinned sandrail chasis on street tires, you might be able to stretch out 30 mpg. Basically, what you want to do is reduce the HP of the engine to the point that it is an utter dog. Then take a MPG reading where the lack of power is killing you. Then turbo it and compare.

thewird

What I've been trying to say is you cannot increase the efficiency of the motor without redesigning the motor itself (assuming ideal tuning). Increasing torque by adding more air and fuel per combustion will LOWER your MPG. If you cannot understand that, then I give up.

You can come back in a few months so we can tell you, we told you so.

thewird

Loki

iTrader: (1)

Ok look, I think we can all respect that fact that you're trying to build a more efficient Renesis, and after thinking about it a little more, I think there might be something there. The key, however, is to run no boost at all. Every conventional turbo is built to provide a positive pressure to the engine at some point, whereas you need a setup that will max out at 0psi (or you feather the throttle to keep it that way). 1-5psi at all times will definitely add fuel consumption, look at supercharged cars. (And we can continue the cfm vs. psi thing at some point later, but read that book and/or some other resource on internal combustion thermodynamics, you need to understand it if you're going to R&D).

However, I like your idea of recapturing exhaust energy to push air in... but only to the point of atmospheric balance, anything beyond that you're doing work to compress the air and burn more fuel for no reason. The turbo will help the engine get to 0psi manifold pressure, where it is most efficient, quicker. The problem though, is that at 0psi it's as if you're at full throttle, so you'll be burning a corresponding amount of fuel. We can estimate quickly how much energy you would be saving under ideal conditions if we had the airflow graph of the engine from idle to redline, but realize that the savings in energy is relative, as you're still burning more fuel at that point than a standard Renesis... you're just burning it more efficiently.

So.. we're kinda back to needing a smaller engine to start with, and using a turbo to bring it up to the power level of the Renesis. What you can do to effectively recapture exhaust energy is pipe the turbo's outlet not into the engine, but into a compressed air tank as energy storage. What you do with that compressed air after that is entirely up to you, but you can, for example, replace your alternator with a compressed air turbine that would generate electricity for everything you need, and convert to an electric water pump, a/c, power steering pump etc.. OR if you wanted to get fancier you could pipe the compressed air tank into the engine's intake on a cut-off, but disable ignition and fuel when air is pumping into the engine, which will turn it quite nicely on its own for cruise... and you'd need to bypass the turbine when running on air only. In this case the choice of turbo almost doesn't matter, since you're not compressing directly into the engine, so pick something that won't create an exhaust restriction, which means a large turbo... spool is irrelevant on this kind of setup.

So yeah, I think the key to your idea is not to try to use energy recovered from the exhaust right away, but store it so you can use it when you need it.

JinDesu

iTrader: (2)

Just to ask a quick question here...

OP (and I think Bret touched on this), you are looking at using a small turbo to provide additional power so when you lengthen the gear ratios, you can run the car at say normal highway cruising speed (60-80mph) at a much lower RPM than the stock RX-8, correct? And that is where you are hoping to save the fuel, correct?

I'm seeing so many different arguments in this thread, I've sort of lost track of what the point of the thread was.

White_Shadows

And I see you don't understand and I see Loki now does. I never said add more fuel. I most certainly said use the fuel already supplied more effiecently.

Loki that is exactly what I was refering to. It may be "0 psi", but to me seeing that visually I don't know if that is enough positive pressure in the intake and manifold. I guess I can change it to 0-5 psi because I won't know till tested. I have been tracking my exact gas mileage for the past year so I will have a good comparison.
Almost done with this class soon as I am second job will come in and I should be able to fund the project.

White_Shadows

Naw that was just my argument to being told it will make to much power. The idea is to use the fuel already being supplied to the motor more efficiently. Currently far to much fuel is being sent into the motor and not being used.

EMart11b

iTrader: (5)

I'm not an expert or anything but wouldn't leaning out the tune accomplish this...? :

thewird

Yes, I've given up on trying to explain it.

thewird

ferg

can you put that on a go-ped?