Size of the tank is fine, but its really about the horsepower of the motor and amount of air motor can put out so that you don't have long period of motor running in order to build a pressure in the tank. This 3hp engine is much better than large size tank with 2hp engine.
This Portable Compressor is Rugged and Well Built ! - Surprised and impressed! I looked at Home Depot and Lowes and decided to order this air compressor to save the Tax and the trouble of bring it home. )

Pluged it in, It filled the 4 Gallon tank in 44 Seconds. Thats starting with the tank completely empty.

Looking at the other brands of portable compressors I really like how well this one is built.
Great little air compressor - This air compressor is great! This unit is fairly quiet, compact, light enough to be toted around if needed, no oil needed and very powerful. This unit replaced a 12 year old 15 gallons, 2 hp, craftsman rolling air compressor and all I can say is that I wish I purchased this unit sooner. When comparing the 2 units the Porter Cable is definitely stronger, the only difference being that when you are running any tools the compressor is running almost non stop compared to a unit with a larger tank that does not have to refill as fast. I consider this a plus though, because I always drain the tank after each use and it does not take as long to release all the air. At this price range there are many choices out there for anyone looking for a compact air compressor but when you start to compare CFM ratings @ 90 PSI this one has the highest ratings.
Frustrated with the technical assistance - When I bought my CPF23400S, I did it because I saw some good comments about Porter Cable equipments, and most important, they have a lot of places for technical assistance.
I received my compressor and unpack it. When I turn it on, the tank pressure gauge wasn't working. I went there with the compressor and they took it and said to leave it there for one day, and on the next day they should call me to pick it up. But, after 3 days, they still didn't have changed the little tank pressure gauge, and they said "we are waiting for Porter Cable to send this piece to us, you have to wait until next week". Ohhh! Come on!!!
I can't believe that! The most common and cheap part of a compressor they don't have in stock!?
Is that kind of technical assistance we have from Porter Cable when we just buy a brand new compressor and need it working???
I think I should send it back and bought another from another company, because, now, I'm just waiting and I can't do my job.
Great General Purpose Portable Compressor - I bought this compressor to run nail guns, air sand and spray paint.) The tank pressure gauge is just behind it. This regulates the pressure that reaches the hoses, not the tank pressure. It is also handy to limit the pressure to safe levels for your various air tools.

You do have to "break it in" before working with it; just open the drain valve and let it run for 15 minutes. I can easily carry it with one hand from the tank side. I wired my shop area with 12/3 to carry enough current for power tools. It is not as loud as large upright compressors, but it does make a fair amount of noise, although not as much as I expected. I use it with a Souix air sander and it does run longer when I am working. If you take on a tractor trailer, get a bigger compressor.
Plenty of Power to Offer...but it needs plenty, too. - I tried the compressor on an
undedicated 15 amp circuit, and it immediately blew the switch every
time. I called Porter Cable and they admitted this 3HP motor NEEDS A
DICATED 15AMP CIRCUIT (with nothing else on the circuit to compete).
I also learned (the hard way, of course) that if you are using the
compressor with a 50' extension chord (with too high a guage) on a 20
amp circuit, the pump will not get enough electricity to pump air
after cutting-in when the tank pressure drops to 110 psi (the
specified cut-in pressure) - the pump will start pumping, but quickly
stop and you'll hear the motor straining until it blows the 20 amp
circuit, too. Porter Cable told me that if I plan to use even a 20
amp circuit with an extension chord, I need to use a 12 (preferable
10) gauge extention chord (ideally 25' rather than 50'), or the pump
won't get enough juice to cut-in properly and refill the tanks. It's
cheaper, my new Porter Cable friends say, to buy more air hose than
the right gauge extention chord - Ah, such knowledge I'm gaining.
Sadly, the compressor arrived with an air intake filter housing badly
bent downward (done apparently at the factory, as the box from Amazon
wasn't damaged), so I couldn't remove the air filter. AND, the drain
valve (to drain water from the bottom of the tank) would not
completely close allowing lots of air to excape from the tank. In my
chats with an Amazon tool sales rep, and later with a Porter Cable
tech rep (to help me unravel the compressor's electrical-needs
mysteries), both Companies quickly and nicely insisted on sending me a
new air intake filter housing and a new drain valve (I guess I'm
getting two of each?) - no questions asked. The machine is fairly
loud, but it only takes my pump about 6 seconds to refill the tanks
from the 110 psi cut-in pressure to the specified 135 psi cut-out
pressure. I figure the noise level goes hand-in-hand with the added
power this compressor offers - power I think I need.
This is a SERIOUS compressor - Desipite its small size and minimal air tank capacity, this is a very serious commercial duty air compressor. AC induction motors like the ones found in this compressor are far superior to brushed AC motors found in most "consumer" air compressors. Because of this motor, the compressor is able to deliver air flows similar to larger 15 gallon compressors. Quite frankly, I'm amazed that anyone can sell this compressor for such a low cost. Aside from air sanding or heavy duty HVLP paint spraying, there is nothing that I cannot do with this compressor.
First Impressions... - It only took 3-days for my new compressor to arrive at my doorstep! And best of all, the shipping was free! I immediately unpacked the unit and checked it over. I followed the manufacturer's advice and went through the 15-minute break-in period leaving the tank drain valve open while the motor was running. When I shut the valve after 15-minutes of run time, it only took a few seconds to fill the twin tanks to 130 p. Although I haven't used my compressor yet, first impressions are everything. This unit is compact, relatively light weight, fairly quiet, and fills up extremely quick! I can't wait to attach my air nailer and get to work!!!.
Darn Good Little Compressor - Short and sweet - this compressor delivers on its promises - it is easy to use, easy to break-in, easy to maintain, and you can't beat the duel air hose inlets. I have found both of the built in pressure gauges to be accurate, and the oil-free motor is quieter than other compressors I have used (although it still makes a good bit of noise). To me, that's portable - I can understand how that would not be the case with everyone, but my experience leads me to believe that this compressor has a very good weight-to-horsepower-to-air storage capacity ratio. Also, this thing is built like a tank - strong welds, a great 'roll-cage' and tough rubber feet.
Excellent compressor - quietest I've used in its category - I am never able to live without a good air compressor. I use them for a variety of tasks from simple blowing to nailers and air hammers. As smaller air compressors go, this one really delivers a nice, steady pressure for quite a long time.

Normally I like to blow through my air gun at about 50psi to clear sawdust. Blowing air at that pressure really drains a small compressor fast, but this one really handles it well and gives me quite a bit of extra time due to the fact that the motor really kicks in quickly and efficiently to keep the pressure up. In fact, from empty it only takes about a minute to fill the tank, which is nice.

I couldn't outpace the compressor with a single nailer.

The two air ports is really nice in one this size because I can put the compressor underneath my workbench and mount a static line on my workbench for easy access anytime while leaving the other open for longer hoses. These size compressors can make an INCREDIBLE amount of noise, but the Porter-Cable 3hp 4 gallon side stack really keeps the noise level at a minimum.

This compressor by far exceeds what I expected it to do.