Hello Fubar57,
Thanks for the drawings. Those are pretty nice drawings. What is the source?
I am actually pretty familiar with the differences between the F4U-1 and F4U-4 but am trying to work on a 3D model so I am looking for exact dimensional differences to account for the 4.125 inch length difference.
I have several sets of dimensional drawings for the -1 but nothing except for overall dimensions for the -4.
Also, although the labeled dimensions look accurate, the drawings themselves don't always have the correct shape (such as the set by Paul Matt).
The attached drawing of the F4U-4 looks pretty good but I don't know the source either. If I can find the source, perhaps I can also find the equivalent F4U-1 drawing and do a comparison as you have done. Comparisons between drawings by different artists is generally a waste of time.
Regarding Exhaust Manifolds and Backpressure:
A supercharged engine has the same issues with backpressure as a normally aspirated engine.
The TURBO supercharged engines generally do not have the same issue because by the nature of their exhaust being used to drive a turbine, there must be backpressure caused by the resistance of the turbine.
Another possibility that was not generally seen until after WW2 is the turbo-compound engine. In this kind of engine, the exhaust gas is also used to drive a turbine but instead of the turbine driving a supercharger, it is geared back to the propeller shaft to provide additional power.
In piston powered aircraft, if the exhaust pipes are direct aft, the exhaust gasses exiting at high velocity and pressure adds possibly a few hundred pounds of thrust as a rocket effect. This rocket effect may be worth a couple hundred horsepower at high speed because as speed increases, the propeller efficiency gets much lower and exhaust thrust becomes a significant amount of the total thrust generated.
Regarding Automotive Exhaust Headers (Tubular Exhaust Manifolds):
Each cylinder on its exhaust stroke provides a high pressure blast of gas out the exhaust port.
Note that this blast or pulse is intermittent: Each cylinder only has one pulse per 720 degrees (2 revolutions) of the crankshaft.
Thus if you have a very long pipe attached to the exhaust port(s) (maybe it has more than one exhaust valve), the moving gas does a lot of starts and stops.
The trick here is that if you make one cylinder's exhaust pipe (runner) the proper length and combine it in a collector that is connected to another cylinder's exhaust, it can be timed (tuned) so that as one exhaust valve closes, the next exhaust valve opens, the column of gas provides a suction to help draw (scavenge) the exhaust gas from the next cylinder.
Exhaust scavenging can have a significant effect on the amount of charge air that is moved through an engine and thus add significantly to the power output.
The intake system is very similar in terms of gas flow so on modern cars, one often finds a plenum behind the throttle body and intake runners to each cylinder.
The problem with these designs is that the runner lengths tend to be optimal for a fairly narrow operating range so often one sees perhaps two sets of intake runners: One for high RPM and one for low RPM with a computer determining when to switch between them.
When things work very well, sometimes, the engine's volumetric efficiency in a certain RPM range may be quite a bit higher than 1.
That means that a cylinder may be pumping greater than its own volume of charge air. (This is quite rare but does happen.)
From Shortround6's images:
The first appears to be a typical Formula 1 V-12 engine with Weber carburetors. The intake is on the outside of each bank and the exhaust is between the banks. Note that this makes the exhaust runner design much easier. The typical engine firing order tends to alternate (mostly) between opposing banks of cylinders and for optimal scavenging effect, the exhaust pulses should come at regular intervals at the junction of the pipes.
The second image shows a very atypical set of headers for a V-8 engine. This setup was fairly common among oval track (Think Daytona stock car) racers at one point. Perhaps it is still common. I don't follow the sport any more.
Off the race track, this setup is not nearly as useful because the runners are too long to be useful at the typical engine speeds on the street.
I am sure some of you fellow gear heads already know this stuff, but hopefully this clears things up for some folks.
There is obviously a lot more to this game but no point in putting anyone to sleep.
- Ivan.