Supercharging book is complete, Finally!

[raff_gta]

its definitely a very subjective question isnt it. Still, I wonder if making the engine rev to make the power would be a better idea? Because the graph would be stretched out further (by 1500 revs or so) it'd have about the same area under the power curve, while not having enough torque to break the gearbox right?

releastically though, bang for bucks, supercharger is the clear winner, especially when you take heat into account...

[Greg Gordon]

It's funny you mention that! The higher rev idea is something I have been thinking about a lot. If we could extend the rpm range out to...say 9000, we could keep the motor between 6000 and 9000 all the time where is always makes near peak power.

Greg

[raff_gta]

its just a matter of keeping her in the powerband though... and realistically on the street, when coming off the lights or whatever, you need atleast **some** bottom end to get you up and going...

on the plus side though, you cant discount the noise of a V6 spinning to 9 grand!

[Greg Gordon]

Yup, that's the problem. All engines are a series of compromises, I would have to lose some low end to get it up to 9K.

Greg

[raff_gta]

no joke! do you have any idea what to do with the top end to accommodate for 9k?

[Tifosi]

Keep throwing money at it in exponentially increasing amounts until it doesn't violently blow itself apart anymore?

[raff_gta]

That or...

You could diagnose what fails when they do rev hard and develop a solution to overcome it.

From what I've read, its mainly the pushrods that fail, that and the issue of rotating mass associated with the pistons, rods and crank. Still, Im sure that with some forgies and a balance bottom end, along with some strong, light pushrods, 9 grand isn't too illusive?

[gtv27]

I wouldn't be surprised if works Group A engines saw close to that, albeit briefly and with the benefit of short-lifed parts and regular rebuilds.

[Greg Gordon]

Ultimately Darren's analysis is correct, it takes a lot of money in parts, some of which will have to be custom made. It's a whole lot easier and it makes a lot more sense to build a 7500rpm 2.5. That's just a matter of good rods and normal valve train upgrades.

Greg

[MALDI]

In post #20 of this thread I suggested that water was a "spectator" to the combustion process. I now believe that this is incorrect and I just wanted to correct the record. Although water does not provide any energy it does partcipate in combustion. Different amounts of water will affect combustion in different ways.

See this link for an interesting discussion:

The Mayfield Company Homepage - Automotive Analyses


From that link:

"... under certain conditions ( normally supercharged ) water can replace fuel up to about 50% and develop the same power output, or that the power output can be increased by up to 50% addition of water. These conditions were investigated by NACA and others for piston aircraft engines. It is important to note that these improvements came at the upper end of the power range where sufficient fuel and air was available to have an excess of energy that could not be converted to usable pressure in a timely manner."

[Greg Gordon]

There has been some debate about exactly how water contributes to the combustion process, if at all. It's universally agreed that water is an effective anti-knock agent due to its ability to cool the the fuel air charge in the combustion chamber. Beyond that there is some debate. NACA reported small power gains with water injection, and they were not sure where they came from. They speculated that it was from a small amount of cooling in the intake system before the combustion chamber. I am not a chemist so I really don't know, I was totally lost during high school chemistry.

The quote from that report sounds a lot like what was reported in "Group B" of report 756. This report is in the bibliography of my book and the data from "Group A" is presented in the water injection section of my book. I specifically left the "Group B" data out of my book because it dealt with insanely lean fuel air ratios in an attempt to reduce total liquid consumption (fuel and water) to allow for more payload (bombs). I figured this would create confusion and it wasn't relevant so I left it out.

That quote by itself does NOT mean that the water is contributing to the combustion. In that test they leaned out the mixture A LOT, like down to about 22:1 and dumped in a lot of water, like a water fuel ratio of about 1.5:1! That huge amount of water was so effective at suppressing knock that they were able to get the power back up well above what the engine made with fuel alone by increasing boost and ignition timing. In other words, the power did not come from the water, it came from more boost, more fuel (although at a leaner mixture) and more timing.

I left this data out because while these ultra lean mixtures and ultra high water/fuel ratios worked in the lab, they NEVER worked in the real world. They were too depended upon ideal consistent conditions and they introduced new problems like water collecting in the oil pan.

It's important to keep in mind that we really don't need to know the chemistry of combustion for the purposes of building a car with water injection. It's somewhat analogous to telling time. I can use my watch perfectly well, but I have no idea how it works. What you do need to know, I tried to cover in my book, how much to inject, what to inject, and what sort of results can be expected. Of course I also touch on system design, installation, and various products.

Greg Gordon

[MALDI]

Quote:

Originally Posted by Greg Gordon It's important to keep in mind that we really don't need to know the chemistry of combustion for the purposes of building a car with water injection. It's somewhat analogous to telling time. I can use my watch perfectly well, but I have no idea how it works. What you do need to know, I tried to cover in my book, how much to inject, what to inject, and what sort of results can be expected. Of course I also touch on system design, installation, and various products.

[Greg Gordon]

Taken out of the context of the previous two posts, that quote doesn't quite mean the same thing. Of course it's important to understand how things work, especially if you are building something.

I was talking about this one specific issue that even NACA never fully figured out (as far as my research can tell) which is the event in the combustion chamber with water present. (Maldi:that's what I think you are talking about when you mention water being a "spectator" or a participant in the combustion) Even so, the only mystery is the 1% increase in power they could never really account for. It could be due to some effect the water has on combustion, cooling in the inlet pipe, steam pressure...I don't really know. However we are only talking about 1%.

Sure, it's best to be armed with all the information you can get, and if you can figure this issue out, that's great! You may very well be able to with modern computers and a good knowledge of chemistry. However you certainly don't "need" to figure this out in order to use water injection.

Greg

[Greg Gordon]

For what it's worth, I actually though I spent too much book space on the water injection section and the NACA reports dealing with it. I may have been wrong there, I could have included that "group B" data as well as some other scientific data, but I didn't think anyone would find it interesting.

Greg

[MALDI]

Quote:

Originally Posted by Greg Gordon I could have included that "group B" data as well as some other scientific data, but I didn't think anyone would find it interesting.