A good, low cost pump upgrade for DSMs heavily into racing is a Walbro pump kit, which allows you to fit a much higher flowing pump into DSMs. It is cheaper than the other Denso upgrade pumps, and is a much easier install on 2Gs because it is the same physical size as the 2G pump, while the Densos are much larger. If you wish to reinstall the stock pump later, it is possible to put it back in with just a quick wire modification on 1Gs, and no modification at all on 2Gs.
Warning: these pumps are quite a bit louder than stock. They have a low-pitched whine/roar to them, unlike the high-pitched whine of the stock and ND pump. If you want a very quiet pump, this is NOT the pump for you.
Walbro pumps are available as 190lph , 255lph , and 255lph High Pressure. The 190lph is good for DSMs with mild mods, the 255 is for more heavily modded cars, and the 255HP is for people with extreme mods running high boost (though it will work just as well as the standard 255 for street cars, it only develops more flow at very high boost levels, at lower boost levels, it is the same as the standard 255 pump).
Note, however, that using a 255 or 255HP pump on a DSM will probably require an adjustable aftermarket Fuel Pressure Regulator, especially if using larger injectors, in order to get the fuel pressure curve more linear. Any very high flow pump can overrun the tiny stock FPR, causing the base fuel pressure to be higher, and making the fuel curve nonlinear, making the ECU's control of the fuel more difficult. When coupled with larger injectors, you can basically flood the engine with fuel, causing your car to run super-rich (black smoke out the tailpipe almost all the time), lowering mpg and power. Installing an adj FPR allows you to dial the base fuel pressure back to stock, maintain a linear fuel pressure curve, and gain back mpg and power.
Here is a flow graph of the stock DSM pump vs. the Walbro pumps. The GSS278 is the 1G 190lph pump, the GSS250 is the 2G 190lph pump, the GSS315 is the 1G 255lph pump, the GSS317 is the 2G 255lph pump, the GSS341 is the 1G 255lph High Pressure pump, and the GSS342 is the 2G 255lph High Pressure pump. Note that 1Gs have a base fuel pressure of 37.6 at 0psi, and 2Gs run 43.6 at 0psi. So at 25psi boost (which is only to be run on race gas), you'll only need 62.6 and 68.6psi of fuel pressure respectively. Note the light blue shaded areas, this is where you will need the fuel the most when at the track. Note how much higher flow the Walbros have over the stock pumps at this critical point.
Here are the numbers for the above pumps.
http://www.roadraceengineering.com/fuelpumpflowrates.htm is RRE's page comparing DSM Walbro pumps to the stock DSM pumps, the "standard" ND upgrade pump, and the Supra Denso pump. As you can see, the Walbros do pretty well, the 190 is slightly better than the "standard" ND upgrade pump, and the Walbro 255HP pump is close enough to the Supra pump to not matter for most people (and the install of the Walbro is much simpler on a 2G than the Supra pump). This page also shows how bad the 1G pump is at higher pressures, and how much simply rewiring the stock pump helps fuel flow. Note that the most useful pressure to look at is the 58psi readings, as that corresponds to about 15psi boost on a 2G and 21psi boost on a 1G.
I am selling any of these pumps, with installation kit, for $150 plus shipping. If you use PayPal balance/EFT payment, cash, MO, or cashier's check, there is a $10 discount. In other words, you only pay the above full price if you use PayPal creditcard funded payments. I only sell the 190 and 255HP, since the 255HP has the same basic flow characteristics as the 255 at lower pressures and higher flow at higher pressures, so there really isn't much need for a 255.
I can now take credit cards via PayPal.com - see those sites for info on paying via credit card. (NOTE that if you pay via PayPal, let me know if you are funding the payment by EFT/PayPal balance or CC, I have different accounts for each type of payment. Do not use my email address as the PayPal ID, it is not used for either of my PayPal accounts!). If you send a personal check, expect a 2-3 week delay on shipment. USPS Money Orders preferred as payment from the US, and I am now only taking Canadian Postal Money Orders or PayPal as payment for Canadian orders. When you send payment, be sure to include your email address and note in the letter what year/model your car is, as I also sell pumps for Miatas/RX-7s. Please do not send payment without checking with me first for the correct account info.
DSM Pump info
I also have the Walbro intank pumps for Mazda RX-7s and Miatas, info is here. I can also now get pumps for 92-00 Civics and 94-98 Integras, if you have any Honda buddies that have turbocharged their cars. I can also get them for Mustangs, 84-90 FWD Mopars, 84-86 Buick Grand Nationals, 85-92 GMs, and many other cars. Walbro is now selling inline pumps for installing outside the gas tank, if you want one, email me for info so I can check into them for you.
Please note I only sell intank Walbro pumps, I do not sell inline pumps or any other fuel related parts.