Whats the difference between an F7 & F3?

From Wikepedia

The F3 (1946) had a different roof arrangement, and slightly different dimensions, than the FT. The 567B engine was uprated to 1,500 hp (1.1 MW). F3s were often nicknamed “chickenwire” for the vents along the top of the sides.

The F7 (1949) and F9 (1954) were evolutionary, the F7 had improved traction motors, the F9 a 1,750 hp (1.30 MW) 567C engine. A louver arrangement over the vents changed their appearance from the F3.

Many of the F3s had the small number boards.  

The wiring and the traction motors were less robust than the F7 and tended to cause problems at low lugging speeds.

Perhaps the best spotting feature is the dynamic brake fan/grid opening.   The F3 had 2 longitudinal screened panels on the roof behind the cab for the dynamic brake cooling.    The F7s had a 36 inch fan housing the same as the ones in the back for the radiator.   

Screening was not universal on the F3s.   It evolved also.    At first it came down between the portholes and covered the area where the louvres are located.   There were no louvres, just square openings in the side covered by the screening.   This is the early "chicken wire" units.    Later  production units had the louvres and the screen was reduced to running along the top where the vents are in line with the cab windows.   I am not sure but I think the final ones actually without any screening, they had the vents like the F7s.    the F9s had a different type of vent than the F7s and the front porthole on the F9 was about 3-4 feet toward the rear compared to the F7.   Finally the F9 had 5 square vents along the side while the F7 had 4.    Most of the differences between the F7 and F9 are almost not noticable from any distance.    The F3s do look different.

Pictures from Steamtown.  F3 Lackawanna, F7 Reading.

The difference is small enough I run F3s and F7s together: I have a bunch of Santa Fe Warbonnets and frankly they look close enough no one ever comments on it.  The slight actual appearance differences between the two in the real world aren't any more than the variations you see between WBB, Atlas, Lionel and MTH when they try to model the same loco, but get the details slightly different. 

Agree with all the statements here..........  additionally,  many RR had there own specific variations so no one is correct.  My home RR the Florida East Coast ran there F3 looking more like F7 with the shorter almost flush roof fans.

Run them all together would be correct for most RR.  They mixed and matched as power was available.

Mark

The Reading units are FP7's.  They're 4 feet longer than the F3 or F7 to accommodate additional water capacity for the steam generators.

Rusty

Basically, for most modelling purposes:

F3 Phase II carbody, (Phase I had 3 portholes on the A unit) :

F7 Phase I carbody:

Rusty

I forgot about the high fans and low fans.   PRR had a bunch of the first F3s with the high fans.    They do make the units look different also.

Learning the differences between the various units on your favorite RR and then modeling them correctly is what makes it fun.    They are not all alike even on the same RR.   

Got that right.

All from Santa Fe's 16 class F3's: (16LABC-36LABC)

Factory fresh:

After shopping:

An F3 in F7 clothing.  Note the rectangular dynamic brake intakes on the roof and low fans:

F3 in F9 clothing.  Note the 48" dynamic brake fan:

Rusty

In 1951, Santa Fe covered all the chicken wire radiator panels on its passenger F3's, using Farr stainless steel vertical-slit panels removed from freight F7's 259 through 268.

Attached is a chart showing the differences over time for the as delivered F2 through F5, F5 being an unofficial designation for the final F3 iteration.  It does not include the F7, but the F7 and F5 had very little external differences.  The big difference with the F7 was the improved traction motors and increased tractive effort rating.  Maybe someone can add another column for the F7.  As mentioned above, the railroads modified/upgraded their engines over time with many F3s looking like F7s by the end of its career. 

To a modeler, it was the carbody versions.

To a railroad, though, the difference was primarily electrical.  There were some unanticipated weaknesses in early F3's, which EMD continually addressed and improved throughout F3 production, so that late F3's (F5's) were much more robust than 3-portnole F3's.  The F7 had even better and higher capacity electrical gear, as well as automatic transition.

The F3 would properly get the "Most Improved" EMD locomotive award.

I appreciate the explanations form all of you and thanks for taking the time to respond to the OP question.

It is a interesting read to some of us that have a limited knowledge in reference to trains.

Larry

Without a doubt my favorite front end of a train.  Known as Bulldog Nose. Great informative thread.

Yes - certainly informative, and interesting. Good point made about what is important to modelers and rail fans and what is important to those who actually use the machines. Some of the things that we notice, the real railroaders don't even "know".

=======

Laidoffsick - F7 - F3 = 4. You beat me to it.

==========

Hardware -

"...favorite front end of a train". Ah, no. That would be this: