Hello there, I've been looking around for quite a while and I'm stumped on why there is a noticeable difference between the sound of an F40 vs it's freight counterpart when NOT in HEP mode. It's probably the only model I can think of with the 645 prime mover that doesn't have the distinct sound that others with the engine type have such as the GP and SDs of the same series. I know that the F40s are supposed to literally be the cowl variant of the GP40 and that while connected to passenger equipment, unless they have a separate HEP generator, are set to a high RPM to supply power to the coaches, but I also know that this setting can be deactivated to conserve fuel when not required to supply the extra power.
Here's an example of an F40PH-2CAT, a rebuild supplied with a separate HEP generator so it doesn't need to be at full throttle on the prime mover constantly:
http://www.youtube.com/watch?v=lROsmMDQjEA&feature=related
Compared to a GP40-2, also in passenger service, there is a noticeable difference with the geep having the typical sound of the 645 prime mover:
http://www.youtube.com/watch?v=3V20p9x6frI
Edit: After drawing more comparisons the only time the two seem to have a similar sound is when both are running at an equivalent RPM of notch 6 or higher. Another thing to note is that according to what I've read, all of the 40 series locos make use of the 16-645E3, all equipped with turbochargers.
It may be something as simple as a different design for the exhaust, perhaps a better muffler or spark arrestor. In 1st generation days, the same model on different railroads would sometimes have a different sound.
John
If that's the case it's more than just the exhaust, on the geeps and SDs one of the things you hear the most is the turbo while on the Fs, the main thing I hear when not at full throttle sounds like a large fan, something I can't really hear on the freight counterparts, it's almost as if the sound of the fans replaced the sound usually made by the turbo.
EMD locomotives either have a blower to force air into the air box of the engine or a turbocharger. A blower is driven through gears by the engines flywheel. A turbocharger is driven by the engines exhaust. The F units and early EMD units were usually all driven by blowers. Any locomotives driven by blowers will have the exhaust go through two single stacks out the top. Any locomotives with turbochargers have all the exhaust flow through a manifold and out through the turbo. The distinct sound of the F units and other units such as the SD9's sound that way because of the two exhaust stacks as they are both blower run and not turbocharged.
The 645 engine (in various cylinders) was the standard in all EMD locomotives until the SD50 (or was it SD60?) when the new 710 engine came into play. Even with the 710 engine and the higher cubic inches it is nearly identical to the 645.
The F40PH and the GP40-2 have the exact same 645 engine. The only difference is the cowl body and probably a higher traction motor gear ratio. Of course the F40PH has a HEP generator but that is not driven by the engine nor does it have any effect on the engine.
The F40PH-2 does have a different sound and is much quieter because a cowl body only has a few access doors on either side. The cowl design also is farther away from the engine which reduces noise especially at idle. The GP40-2 has access doors from the generator room to the rear of the locomotive which doesn't hide noise very well.
The HEP generators are not that loud at all. Even inside the unit they are not nearly as loud as the main engine.
If you were to switch bodies with the GP40-2 and put it on the F40PH you would notice the F40PH being much louder and the GP40-2 much quieter. Another good example is the former CN SD50F which also had a full cowl design. These units were considerably more quiet then the locomotives in front or behind them.
On an as-built F40PH, the HEP alternator is driven by the prime mover, which is why the prime mover runs at full RPM even at station stops. Metra's MP36PH-3S engines have the same arrangement.
All SDP40F, F40C, and F40PH models were originally equipped with exhaust silencers mounted on the turbo and a sound insulated carbody. All F40PH's also were equipped with 48" Q-fans for the cooling system. The carbody side panels were sprayed with a damping material on the inside surface and there was an acoustical foam-barrier-foam insulation behind perforated metal on all of the removal side panels. The GP40-2 never had any carbody insulation and was not equipped with an exhaust silencer and Q-fans until required by EPA/FRA regulation starting in January, 1980. But passenger operators wanted quieter locomotives, so were the first recipients of the sound treatments.
FWIW, the silencers on the 40-2 turbo locomotives and the above passenger models were identical, whereas, the silencer used on the 50 series had a differently shaped exhaust duct to provide more attenuation that was required because of the 950 rpm engine speed on the 50's.
So the answer to the question is due to silencing techniques to make the prime mover quieter? Even with dampened sound I would expect to hear the sound the other 40-2 series locos all share and this seems to be the only major difference. Any F40PH-2 rebuilt with an auxiliary HEP generator (the F40PH-2CAT being the primary example) is able to preform more or less identically to their freight counterparts as far as the RPM of the prime mover without having the burden of supplying head end power. Again, all of the specs I've been able to find on the F40PH states that it has the exact same prime mover as the GP40 and SD40 series locos, with or without the -2 upgrades, a 16 cylinder turbo charged 645 series prime mover.
Using NJ transit as an example again, I'm curious why their F40s are silenced while their geeps received no such sound suppression. Granted, as was said above, being a standard hood unit makes it louder but comparing it to other gp40s by freight railroads, the only difference in sound level I could pick up in the earlier example was due to sound pollution from the lead engine.
Because it costs money to add those parts and they weren't required to do so as the units were grandfathered in.
A good comparison might be to find a 1980s built GP40-2 to compare to.
Sound dampening and exhaust changes will have an absolutely profound effect on the "note" of the exhaust.
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