#1. Air Flow through the head
#2. Pressure to maintain proper combustion
#3. 14.7:1 Air to Fuel Ratio
As the modification list grows with your Prelude, you need to keep all three of these in mind and remember them at all times. For this article however, we're going to look at #3 as it's the main focus of the aritcle.
It should be known that the more air you put into an engine, the more hp your going to net from it (in most cases, not all). In all actuality, you need to maintain the proper balance of a 14.7:1 Air/Fuel ratio. As is read, that is 14.7 parts air to 1 part of fuel; an engine is nothing more than an air pump. For this matter, pressure is a big deal when looking towards performance. A setup such as a Turbo or Supercharger will do no more than force more air into the engine at faster rates causing it to work faster and net more power. 1Thus we get the bi-product name of "forced induction" setups.
The fact is however, the more air you put in, the more fuel your going to have to supply to the engine in order to maintain a proper Air/Fuel Ratio. With turbo's on our 3G's, it's acting as a forced induction system which is suplying radical amounts of air for the head to breathe. If your air increases and your fuel stays the same, you've got a problem on your hands that goes by the technical name of "running lean". This simply means as stated, too much air and not enough fuel. Running lean will actuall blow an engine if the pressure is too high so you have to watch it real close. However, if your supplying more fuel than you are air to the system, then your going to "run rich". Unlike running lean though, it's not as serious of a problem when your running rich. By running lean, you actually up the compression in an engine which is why it can cause damage (ie. bend vlaves). If there's one lesson you haven't learned already, it should be this, "you can't get something for nothing."
Everything should be monitored with an Air/Fuel ratio guage. These come in all sorts of sizes/brands, and can be mounted virtually anywhere. If your one of those people that aren't into guages as they seem to look like "rice" (I'm probably one of the most "non rice" people you'll ever meet), then you've been properly warned. When do you need an A/F guage? I'd say when you start getting into playing with things that a normal moder might not. Such items include turbo's, NOS, or if you're one of the select few that have an H22A(4) engine conversion, VTEC controllers. These items are air/fuel dependant as to how well they are going to work for you. Now that you understand the importaince of air/fuel guages and some of the terminology that is derived from them, let us now look at a few ways to remedy these issues from ever becoming a concern.
First and foremost, I firmly believe that you should start by tackeling the stock fuel pump. If you do not already know know how a fuel system works, I'm going to take a brief moment to explain it in terms for your 3G. Our tanks have two lines inside; the fuel outlet line and the return line. These lines meet in two places, the tank for one and they meet at the other end at the location of the stock Fuel Pressure Regulator(FPR). Thanks to Honda, our systems are equipted with an FPR that actually works fairly well. The max pressure allowed through the FPR (stock that is) comes to about 46 PSI which only really happens at Wide Open Throttle (WOT). The beauty of the stock FPR is that it'll ONLY use the amount of fuel that it needs for the amount of RPM's your turning over. So, let's say we have a brand new Walbro 255 L/PH fuel pump installed and we're pushing upwards of 6K on the tach.; what about the other enormous amount of fuel flow past 46psi? This is where your return line comes in. Whatever the OEM FPR doesn't want, it'll send back to the tank via the return line. Seems how this happens so fast due to the increased fuel pressue from the pump, your fuel is staying cooler through this process and is also ensuring for a better combustion in the chamber(s). The only thing that makes this fuel pump even installable is the fact that there's an FPR.
Now for a quick look at FPR's. In order to compensate for the needed fuel to add to the Air/Fuel ratio (under boost), you have got to have an FPR that'll allow for more flow. With a turbo setup on our 3G's, the stock FPR won't work. For this reason, Tom Coleman has included a special rising rate FPR from Vortec. I'm not 100% sure on all of the details, but they'll allow for more fuel flow over stock, and I gussing in the range of up to around 85 - possibly 90 PSI. I can hear the question coming now, "Why can't I just upgrade the FPR and forget about the Fuel Pump?" Look at it this way. If you have a higher pressure FPR and your running a turbo application at say 5 PSI of boost, you'll probably be putting out about 60-65 PSI of fuel into the fuel rail via the FPR. Up above I mentioned something you need to keep in mind, "the stock fuel pump will handle about 45 to 50 PSI MAX". What happens if you try and use more fuel than your supplying? You'll run the system dry, the car's going to lean it self out due to lack of fuel, and your pump could possibly burn up. Now look at it the safe way. You upgrade the pump first and nothing is changed as your system will only accept so much at a time. Everything else is being sent back via the return line. You maintain proper pressure, and have no problems with the FPR. When your under 5 PSI (5 could be any number) of boost, it'll supply the needed amount of fuel to maintain what the system wants/needs, and still be able to keep the fuel moving. Best of all, your not going to burn anymore fuel than you would have with your stock pump. Why? The excess is being recycled; how could you burn more?
A few added bennifits to moding the pump first include; you'll notice an increase in power production while also running with a non turbo application. Maybe not at all times, but you will in the upper RPM's. Why? Again, let's paint a picture. If your Pump is about maxed at around 45 PSI, and your FPR is maxed at 45 PSI (45 is pretty much the stock MAX on any vehicle), then your having little to no amount of flow through the lines. If you can provide the gas fast enough, then your system will respond faster and with an added "touch". If you know what air being sucked in thorugh an air filter sounds like, you'll notice a big time increase in that noise as well. Why? B/c your gas is flowing through your fuel rail and your other lines at such insane speeds, your new sound is nothing more than that increased fuel flow. Believe me, your Prelude will sound like a jet engine. Another interesting addition is the "prime" sound you'll hear from the driver side rear area. This 3 - 5 second "prime" sound is your new fuel pump which is getting ready to supply the needed fuel to run the car.
In part 2 of "Fuel Pump Upgrade/Install" we'll look at how to properly select a fuel pump for your application, and actually get into the install process. I'll post a quick link here when I get part 2 writen which should be in the next few days depending on how long it takes me to tear my friends Turbo 3G engine apart.