A constant boost compressor will give you more low end torque and less high end torque (or in other words less power) assuming both compressors deliver the same amount of pressure at maximum power (well, if the constant boost compressor is indeed less efficient.)

An ideal engine has a constant torque level over a very large speed band. I guess you could call that in general most user friendly, however it might also be a matter of taste, some poeple might prefer peaky engines because it gives them more satisfaction for whatever reason. A compressor with a constant boost is more likely to deliver constant torque.

I didn't know BP was a "very small" company. Or were you kiding?
What I had said was the lower the grade fuel you can run without getting into detonation the more power you will make. The more MPG also. The reason is that "octane" is a messure of resistance to detonation. This will slow the burn down. The additive takes space away from real energy producing fuel. I doubt you can get anything running 101 fuel. For that matter you could try NASCAR fuel at 104 and make less power yet.
So a detonation resistant design chamber can run cheaper gasoline. Or it can have higher compression ratio or more boost. This is the condition we have with a good four valve head. IE: Cosworth. Which is the grandaddy of all the chambers we have out there now. They are all evolutions if not direct copys of the Cosy.

How the rotary relates to this I have yet to learn. Maybe RG can comment on that.


Now porting will help with a blower possably more then without. That assumes it was done properly. Next we should understand that manifold pressure is resistance to flow. Therefore a ported engine may show lower man press but will make more power. That is your goal, more flow throgh the engine. NOT more pressure.

The AFS will start making pressure at off idle if the throttle is open. Thing is it shouldn't be. In the Rx 8 case it will not be because it is fly by wire and you can have your foot to the wood and it will only open the amount programed into it.

If it were a perfect world the torque curve would be like an electric motor, full torque it idle. I don't think you could use a powerplant like that with the sort of chassis we use. At least with the sort of driving style we are used to.

Yes the supercharger will have excess capacity. I would be the best engineer in town if I could design a blower to be just perfectly matched to peak at the same time as the engine. THe only insurance you have of not running out is to design it over. Remember what I just said, if you get more flow the pressure will go down. Don't equate this with a lack of capacity.

Hope that helps, Richard

Is the Pope a Catholic?

Yes, But is he Polish? :confused:

RP,

I did reply to your post about the Materials Prof. I don't know him. Nor, have I heard of him. However, this is a bit out of my experience level. My focus has been in the performance world not so much in the materials world. Although I have run across some interesting tid bits from time to time.


Wildcard,
You are absolutely correct about the turbofans. The F111 was the first turbofan engine placed in a fighter application. In fact, there was tremendous discussion about not letting this airplane fly in Vietnam because they didn't want the potential for the technology to fall into others hands. All US fighter engines since have been turbofans (albeit some have been called leaky turbojets because of their low bypass ratios 0.1 - 0.4). Most commerical gas turbine engines used low bypass ratio turbofans prior to the TF39 used on the C5A. They had bypass ratios in the 1.5 to 2.5 range. The TF-39 had a bypass ratio of approx 8 but today most of the high bypass ratio engines have ratios in the 5-6 range.

Hymee,
As to the question about the thrust production of high bypass versus low bypass ratio engines. Here's one way to think about this. Both engines could be considered to have a fan exhaust stream and a core exhaust stream. These may exhaust through one nozzle or they may exhaust through seperate nozzles.

In general:
The high bypass turbofan with a bypass ratio of 5-6 has 5-6 times as much air going through the fan exhaust stream as through the core exhaust stream. The exit velocities are not the same because the core exhaust is much hotter than the fan exhaust. However, the fan stream generates the predominate thrust because of the fact that it has 5-6 times the flow as the core stream. Gas velocity differences do not come close to making up the difference.

As the bypass ratio comes down, in general, the averaged exit velocity increases (core and fan stream) so the specific thrust increases (thrust/lb of airflow). However, this happens at the expense of more fuel consumption. In this case, more of the thrust comes from the core stream and less comes from the bypass stream. I think this is what you were trying to say earlier.


globi
We've played in the silicon nitride world for some time now. These would be great materials if they weren't so brittle. They have very little fracture toughness so when you hit them with even small impulse loads they fracture. The key will be finding proper matrix materials to act has binders to allow these materials to work. This is going to happen in our lifetime. I'm just not sure when. When it does, there are going to be performance improvements for everyone. It's may provide some revolutionary changes.

Jon, how do you know I was speculating? ;)

And It's been a few days and I'm still here. :p

Thank you turbine_pwr, your answers are as always very informative and authoritive. :cool:

For those interested. The A160 is an unmaned helo. Still in development I have the website, I'll get it up later. (Did I just say that?) I'll post it later. That's better.

A Boeing project.

More efficient and 'simpler' jet propulsion?
http://www.crd.ge.com/01_coretech/pu...opulsion.shtml
http://www.grc.nasa.gov/WWW/AERO/base/pdet.htm

Apparently Richard is having a problem getting it up. :eek:

A160 link from Google:

http://www.globalsecurity.org/intell/systems/a160.htm

I don't think Richard will appreciate that comment too much :p

Silly question.. Is it possible to start out with like 20 psi and gradually drop the boost up til redline?

High boost at lower rpms needs less fuel and generate less heat than the same boost at higher rpm. Hence you could get some insane lowend gains without compromising the engine at higher rpms..

Theoretically that is possible. The hard part is going to be finding a turbo that has it's efficiency range based on this and also finding one that will spool up to these numbers at a low rpm but still not be a restriction to power at high rpms. The idea is sound but the actual ability to pull it off in practice may be limited.

I was more thinking about SC. Not that I know a lot about sc, but from what I gather you should be able to have full boost at a lower rpm.

These SC's will do exactly that:
http://www.boosthead.com/home.php
:)

For 15 seconds.. hehe

Well to be fair: 15 seconds every 10 minutes. (Still better than driving around with an empty N2O bottle in the trunk).
Here's the diagram you've been looking for:
http://www.boosthead.com/installation_docs/doc20.gif

Wouldn’t it be possible to make some sort of reverse gearing where the higher the rpm the slower the sc spins? It will of course have more parasitic loss at lower rpms, but the characteristics of such a sc would rock insanely. Wonder if the drive chain would be able to handle the “abuse” of massive boost at low rpm, but that is another story.

Anyone have a compression map for the axial flow sc? At what rpm is it possible to gain 20+ lbs/min?

You might want to be looking for a Twin Screw SC if you are going to try this. They can produce max boost at idle and then you could just tune it down as the revs increase. A Roots SC can do that too, but I doubt you would be in the efficiency range of a Roots if you were going to try this.

This hps curve would give me wet dreams. In fact, it allready does.

(red = new, black = stock rx8)

How can you "tune it" down?

twospoons, doesn't a Ford Mustang or a VW Golf TDI have sort of that red curve?

Mustang is somewhat similar, but it doesn't go as fast up and stops at 5.5k :)
VW tdi looks like a heart beat. Very narrow powerband and dies horribly.

Somebody might want to double check this.

Horsepower needs to rise as rpm's rise in order to keep acceleration linear. The goal should be a flat torque curve.

Yeah but a chip (such as Upsolute) can really help that engine out.

My guess would be to possibly get a sort of boost controller or get a weird gearing setting. It just seems that the best solution for something you want to produce max boost at low rpm is that you would be least overspending if the boost level didn't naturally increase.