Please DO NOT Post In The General Section

From this point on until otherwise briefed, posting in the general section of Performance Tech is prohibited. The only thing to remain here will be the stickies. We would just delete this section, but that would cause unintended results.

The majority of the threads created can appropriately be placed in one of the Performance Tech sub-forums or Technical; and the posting of them here is detrimental to the activity of said forums. If you have any questions about where you need to place your thread PM me or one of the other mods.

For the most part you all have caught on without this post, but there have been a few habitual offenders that forced me to say this.

Everyone will get a couple of warnings from here on out, after that I just start deleting threads.

Again if you have any questions, PM me or one of the other mods.
See more
See less

Fuel 101

  • Filter
  • Time
  • Show
Clear All
new posts

    Fuel 101


    One of the most over looked things when building an engine be it N/A or force inducted is the fuel setup. After many hours of researching and asking questions i'm still willing to learn more about fuel. So i'll start with everything i do know and you guys can add and ask questions at will. There will be a test on friday so be prepared!

    The basis of making power in an engine is the combination of multiple areas. The bulk of horsepower comes from flowing as much air in at a cold temperature as fast in and out as possible, combining that intake charge with the proper amount of fuel, ignition strength and timing control. One of the main reasons an engine blows up or performs poorly is because of bad fuel management. Not getting enough fuel causes a lean condition and getting too much causes a rich condition.

    Stoichiometry is the perfect balance of air/fuel but isn't the best mix for an engine at WOT. The air/fuel ratio of stoichiometry is theoritically 14.7:1 meaning at a given point in time inside the combustion chamber there are 14.7 pounds of air molecules per 1 pound of fuel.

    Running lean tends to yield the most power out of an engine but it also increases the temperature, makes the engine expel alot of heat, and is also generally not good for the longevity of the engine. The air/fuel ratio determines whether you are running lean or not. Typical lean ratios are anything above a 13.3:1 ratio. Since running too lean produces alot of heat the sleeves can warp, valves can burn, piston rings can fail (the most likely), and pistons can melt among countless other scenarios. The safest ratio that seems to yeild the most power is between 12.2:1 - 12.5:1. To calculate the a/f ratio you will need to have access to a wide band o2 sensor. These devices are usually found at dyno shops but can be had in guage and electronic device forms for around $290-375. The a/f ratio guages that are commonly in cars from autometer and ect. can only show what they think is the a/f ratio. They tend to only tell you if you are running lean, stoich, or rich. These devices are very limited in tuning and should only be used to monitor not to tune since you never truly know what the meters definition of lean is. Its definition could very well be a 14:1 ratio and by then your motor is already eating itself alive.

    If you run your engine rich you'll probably never blow it. However you will be sacrificing your combustion chamber's integrity. Running rich is usually characterized by the black smoke you see when someone goes WOT. When you see a car that has black soot on the bumper and that soot came from the muffler they are running rich. This condition is once again safe but can foul out the spark plugs meaning there is so much fuel being injected that the spark plugs are covered in fuel, wet, and therefore not able to spark.

    A/F ratios can be controlled easily by the various devices known as AFC's or air fuel controllers. They come disguised in various confusing acronyms but achieve the same goal. It is best to tune these devices on a dyno (for beginners i don't wanna hear anything about egt's from the experts please).

    Now even tho you've got enough fuel coming in what about its delivery. Having a strong beefy delivery system is very important when doing a build up. Starting from the back we have the fuel pump. This pump is needed to provide the rest of the delivery system with the proper psi and amount of fuel. Having an aftermarket fuel pump (walbro 255 lph) will cause the rest of the system to work very hard and can eventually cause other components to fail.

    In combinations an upgraded fuel pump is very well justified. The minimum i would recommend with an upgraded fuel pump would be a fuel pressure regulator (FPR's). The fuel pressure regulator could also cause problems if that is the only fuel upgrade because if you may ask for too much pressure from a fuel pump that can't perform to its expectations (It can't get it up...the psi i mean ) Atomized fuel is a great way to make power. The better the fuel molecules mix with the air the more smooth the power and burn rate will be. This is very important. Raising the pressure of the incoming fuel makes it so that when it comes out the injectors its traveling at a higher speed and is not clumped together. A fine mist is what your after. 28 psi is at idle and 48 psi is seen at WOT i believe. (Could somebody give me stock fuel pressures if these are incorrect?) Its my personal belief that the fourth mod done to an engine should be a fpr. After I/H/E (substitute cams, pulleys, etc at will) your engine needs more fuel and should be tuned for maximum hp and efficiency.

    The fuel rail is for the big boys in most cases. The stock fuel rail will hold up to 350+ hp i believe but getting an aftermarket fuel rail will not hurt anything. The inner volumes just hold more fuel and can take more fuel pressure

    last but not least on my list is the fuel injectors. Your application is only as strong as the weakest link. So if your injectors are clogged but you have aftermarket everything then your fuel setup is still poor and it may even cause you to run too lean and blow the motor. Running to small injectors will obviously cause a lean condition because the injectors will not be able to flow quite as well. Injectors are measured in cc's. The typical honda SOHC has 230cc injectors and DOHC's have about 290cc injectors (if someone has different figures then please state them, this is off the top of my head). After mild engine work is performed and you have a collection of bolt-ons under the hood you will find the stock injectors to be running a high du\ty cycle. The duty cycle is the time that the injectors are open for. Once the duty cycle becomes to high( its measured in percentage), say 90% duty cycle. Your injectors are pretty much open at ALL times. That is not good. Your injectors are made to pulse not flow continously. At this time using injectors with higher cc's is appropriate. Changing to 370cc injectors or above is a good investment at this point. Most low boost applications can get away with that low of an injector size. Another way is to even use the injectors from other cars such as the mitsubishi/eagle/plymouth turbo dsm's. These injectors are rated at 450cc's and are commonly used in turbo homemade kits. That size injector will be laughing at your low-mid boost application so turning up the fuel pressure should be done but its not absolutely needed. N/A ppl should concentrate on between 330-440cc's in most mild applications.
    Remember that you get what you pay for. RC injectors have been known to hesitate and if your at WOT and they hesitate to perform bye bye engine.

    The last fuel mod i can think of thats currently on shelves for our engines is the fuel management unit or fmu. This is a rising rate fuel pressure regulator and can only be used on turbo or supercharged engines. Its function is exactly what it sounds like, as boost increases this device increases the fuel pressures in ratios. A FMU with a 12:1 ratio means for every pound of boost the unit adds 12 psi to the stock fuel pressure. This is one of the reasons why shelf bought turbo kits are limited to 8 psi. Do the math, if your at WOT and boosting 8 psi then the FMU is going to add 96 psi to your stock 48 psi for a whooping 144 psi of fuel pressure!!! Going too much higher with that amount of fuel pressure would cause your fuel lines to fail...and as far as i know you'd have to get those custom made. The FMU does however come with different ratio discs. So lowering the ratio may suffice in using more boost but these are units i've learned to stay away from when boosting more than 8 psi altogether. The units also have a bad reputation of high gas consumption (obviously), stock injectors tend to quit, stick or fail at 60 psi, and poor idle characteristics. Not to bad mouth FMU's but this is what i've learned.

    Well there you have it folks this is all i can remember and its probably all most of you need to know and then some. Feel free to add, correct, or comment as needed. Thanx ladies and gentlemen and happy tuning.
    Last edited by MRX; 03-11-2005, 09:20 AM.
    Knowledge is EVERY sense of the word

    FSAE (F Series Accord Enthusiasts) ..."A dying breed thats taking it to the next level" #12

    am i giving everybody a brain full or somethin lol...hope it doesn't cause any headaches
    Knowledge is EVERY sense of the word

    FSAE (F Series Accord Enthusiasts) ..."A dying breed thats taking it to the next level" #12


      Holy crapola...

      My eyes hurt now... and I only read a little bit...

      It's late... I'll read the rest in the morning...
      RIP Lifsatrip7



        That wasn't too much reading. Pretty informative and put in simple terms. I enjoy learning/reaffirming things ... thanks.


          My eyes started to water lol but yeah Turbo setup is too complex better do all motor then
          Henry R
          1992 Accord LX R.I.P
          1993 Accord EX OG since 'o3
          Legend FSM

          'You see we human beings are not born with prejudices, always they are made for us,
          made by someone who wants something' -1943 US War Department video


            great post dood, learned a lot

            thanks for taking the time to inform us
            MEMBER'S RIDE

            i was driving along today and the check engine light came on.
            i pulled over and looked under the hood.
            the engine was still there...
            ...silly light!


              Good job... Pretty informative, and good for Newbies... There's only one thing, I think you confuse what is a rich and what is a lean mixture (at least as far as what the numbers mean).

              Typical lean ratios are anything below a 11.5:1 ratio.
              Should probably read "Typical lean ratios are anything higher than a 11.5:1 ratio.".

              The lower the first number, the richer the mix... ie: 9:1 is richer than 11:1. The A/F ratio refers to the parts of air to 1 part fuel.

              My life is rated R.




                  Originally posted by 90Accord-R
                  Good job... Pretty informative, and good for Newbies... There's only one thing, I think you confuse what is a rich and what is a lean mixture (at least as far as what the numbers mean).

                  Should probably read "Typical lean ratios are anything higher than a 11.5:1 ratio.".

                  The lower the first number, the richer the mix... ie: 9:1 is richer than 11:1. The A/F ratio refers to the parts of air to 1 part fuel.
                  can somebody confirm this? Because i've only seen it the other way that i'd stated it but i have seen it his way also. Thanx for the replies guys. Theres actually a little more but i may or may not type that because it gets complicated and i haven't read up on the gruesome details of it yet
                  Knowledge is EVERY sense of the word

                  FSAE (F Series Accord Enthusiasts) ..."A dying breed thats taking it to the next level" #12


                    great guide. i plan on getting a walboro fuel pump along with a fpr. i do however have one question though i dont know if the answer will be to my liking. I don't exactly have a dyno in my area. Is it possible to tune fuel pressure without a dyno or would it be running too much of a risk. would going with other people's figures be a good idea?

                    1991 JDM Galant VR-4


                      I've always seen that the higher the ratio is the leaner you are. I heard it was safe so go a little over 12:1 also...


                        i remember looking at a greddy a/f ratio gauge (a mechanical one). Its range was from like 0-20 and they said it was between 12.5 and 13.5 that you wanted to stay between. Any lower than 12.5 was too lean and higher than like 15 or 16 was a little rich. Since i wrote that entire article from what was in my head i may have confused the two. If somebody wants to do a quick search and copy and paste their findings that'd be great

                        growguy: I'm certain with experience its very possible to street tune fuel pressure but it is something i'd leave to a dyno since i've never done such a thing either. But just getting a fpr and raising the pressure like 10-15 psi would not hurt at may even help if you keep experimenting.
                        Knowledge is EVERY sense of the word

                        FSAE (F Series Accord Enthusiasts) ..."A dying breed thats taking it to the next level" #12


                          will any dsm injectors do as long as thay are 450 cc? and do they just plug in or do they have to be modified to fit our cars?

                          Originally posted by fizzbob7
                          first off, don't be a sissy bitch.....that's what you're being
                          Originally posted by ACC0RD22
                          no need to get sand in your vagina over this guys.
                          So. Cal OUTLAWZ


                            how much hp would one be looking to get from a 10-15psi increase? within this safe range what kind of tuning would be a good idea?
                            1991 JDM Galant VR-4


                              The best dsm injectors are the blue top ones I think. Pretty sure they are from the 1st gen manuals. You just have to cut off a little piece of plastic so they will fit in the fuel rail, but it is not big deal.
                              Growguy are you talking about adding 10-15 psi fuel pressure? Why would you want to do that? Adding more fuel doesn't give you anymore power. It would just make you run rich, waste more gas, and LOSE power. You would only want to increase the fuel pressure if your car was running too lean... running a little lean as long as you don't have any detonation will get you more power it is just more dangerous because of the risk of detonation.