Optimum piston speed?

[TheEnemy]

Is Z supposed to be the port velociy, or the valve opening velocity?
I ask because the equation takes into account valve diameter, but not valve opening.

I noticed that there is no parameter for manifold pressure, wouldn't that affect the actual mach number? Or does it mean that at lower throttle (lower manifold pressure) that a lower velocity/rpm is desireable?

[Christ]

You can scan them and upload them to your ecomodder album.

[gone-ot]

Originally Posted by Christ

You can scan them and upload them to your ecomodder album.

...page 245 - FIG. 10-6:



...page 247 - FIG. 10-7:



...page 248 - FIG. 10-8:


...page 250 - TABLE 10-1:

[Christ]

Top right of the screen, click "user cp", then on the new screen, on the left, under the "networking"heading, find "pictures and albums".

Click that, then follow the directions per uploading images.

[gone-ot]

...here's more info about Mach index (Z <= 0.6 )

2-Valve vs

http://teacher.buet.ac.bd/zahurul/ME...efficiency.pdf

http://www.not2fast.com/gasflow/Lecture08.ppt

http://books.google.com/books?id=WLd...0valve&f=false

http://books.google.com/books?id=Utx...0valve&f=false

[TheEnemy]

After looking closer at the equations, I did notice a correction for intake manifold pressure.

a = inlet sonic velocity, which is dependant on pressure. Which means at lower throttles will yield better VE at lower RPM.

Larger/more open valves lower Z raising the RPM of best VE.

So would what would altering the intake runners do? such as smooting out the sides to get higher flow velocity (not increasing the runner volume by much I hope)?

All of this is fine but how does it relate to the real world? Does best VE correspond to the torque peak?

How does this relate to engine efficiency?

[Frank Lee]

VE is nice and all, but I was after the bsfc peak... the reason for an optimal piston speed has been mentioned earlier in the thread (thanks guys ) but I resurrected it just cuz I found this:

Sfc measures how efficiently an engine is converting fuel into work. The graph of an engine's sfc plotted against engine RPM will be "U" shaped. At high speeds the sfc increases due to increased friction, while at lower speeds the sfc also increases due to higher heat losses from the combusted gas to the cylinder and piston wall because of the increased time the hot gases remain in the cylinder. This is also the reason why air cooled engines are usually less fuel efficient than water cooled engines.

And also why there are differences in optimal piston speed between 2 and 4 strokers, and gas and diesel.

It seems in the case of my slow-turning F150 that too much of my gasoline's heat energy is going into the coolant. This also offers a partial explanation for why my fe DROPPED when I "geared" it down with taller tires- the other part being the effects of the tires themselves on aero and whatnot- but it tells me that were I to keep the original sized tires and gear higher with gears, chances are that would fail to improve fe as well.

[8307c4]

Originally Posted by Frank Lee

This also offers a partial explanation for why my fe DROPPED when I "geared" it down with taller tires- the other part being the effects of the tires themselves on aero and whatnot- but it tells me that were I to keep the original sized tires and gear higher with gears, chances are that would fail to improve fe as well.

No, chances are what caused your truck's fuel economy to drop was that you raised the truck into the air by installing larger tires, the height of a vehicle from the ground has a big effect on fuel economy, engine rpm's in and of itself not as much, smaller tires would likely get you better fuel economy but it would be because it brings your truck closer to the ground, now...

You really shouldn't be running off-size tires, it affects your speedometer in ways which a part of me suspects that you know this and were using the bigger tires as much for this reason and to your advantage, but maybe I'm mistaken, either way you should only run OEM-specific tires.

You want better fuel economy you'll need to lower your truck about an inch, but do it via the suspension, not the tires, if you want to gear it up or down you'll need to address this via either the transmission or the transfer case / differential gear ratio(s).

I'll grant you that bigger tires are much like a different gear ratio, but not really... Bigger tires have effects beyond what meets the eye and the gear ratio is but a side effect, one which again shouldn't be addressed via the tires.

We modify a vehicle 14 different kind of ways, next thing you know there comes a mechanical failure of some kind, ain't going to find a mechanic that wants to work on it when it's been figgerfied that many ways can't anyone figure out what's wrong because nothing works the way it should, see?

Lets do things a proper way, that way when it comes time to troubleshoot, we know where to start.

Peace out

[TheEnemy]

837c4:

Most of the people here are very DIY, so for the most part any repairs are done at home. Most mechanics wouldn't care if it takes an extra hour to remove an aftermarket panel, at $80 an hour which is a very typical rate. Mechanics are used to working on modified, or even messed up vehicles. As far as modifications go, all of the mechanics I know modify at least one as a hobby. There are many shops that even specialize in modifying vehicles.

We know how gearing changes/tire size affects and that gets corrected for.

Personally I prefer a little extra clearance on my vehicles, due to the terain I often drive in. My wifes Accord has a few scratches and dings in the undercariage.

[8307c4]

You folks with your hypermiling addiction compromising safety and making modifications to the point of ridicule, it is a total turn-off.

Now I'm going into my cp to turn off reply notification.