ok i'm really confused someone help me out... Do i need to use the vortech fmu with an afpr if i am going with bigger injectors a fuel pump and running 11 psi?? I can't seem to figure it out. Or are there boost dependent rising rate afpr. Can someone clear it up for me thanx

 

also when i get the jwt ecu w/ sc, 370cc, z32 maf programs would i need a rising rate afpr or the fmu at all? clear it up plz

 

First you need to clearly understand what each of these fuel delievery components do.

AFPR adjust base fuel pressure. Base fuel pressure will impact both the amount of fuel delivered at idle and throughout the rpm range. A AFPR is need/used for a few different reasons and for a few different fuel delivery set ups. If your going to be using larger injectors without the aid of something like e-manage or a JWT ECU then you will have to have an AFPR, the reason being is that your computer does not know that the larger injectors are present. The ECU will tell the injectors to pulse assuming you have the stock 260cc injectors. But if you had 370cc injectors installed then every pulse would contain about 40% more fuel. At idle this could cause flooding and idle problems. So you use a AFPR to turn down base fuel pressure so that the 370's are maybe supplying 20% more fuel instead of 40%, thus avoiding too much fuel being dumped at idle.

Changing the fuel pressue is almost like changing the size of injectors. In another application, an AFPR can be helpful with an ROM tune like a JWT ECU. When a walbro 255 fuel pump is installed base fuel pressure will increase from about 34 psi at idle to about 42 psi at idle. This is because the stock FPR cannot control the more powerful fuel pump correctly. A jump from 34psi base fuel pressure to 42psi base fuel pressure is not a big deal and will not cause driveability issues but it still might help to bring it back down to 34psi when using a ROM tune.

Ok, so lets say you have a JWT ECU programmed for 370's. The AF ratio set by JWT is all dependant on the injectors being 370's. If the injectors are a little larger or a little smaller the AF will be a little higher or a little lower. And, like I stated before changing fuel pressure is like changing the size of the injectors. JWT assumes your base fuel pressue is the stock 34psi, but if it is 42psi because of the walbro then your actually running a little bit larger than 370 injectors and the target AF set by JWT might be a bit lower. Conversly, if you had a base fuel pressure of 30psi then your 370's would flow a bit less and your target AF ratio set by JWT would be a bit higher. But in reality, a 4-5 psi change in fuel pressure will not change AF drastically. 370cc injectors don't flow exactly 370 anyhow.

Adjusting base fuel pressue can also be looked at as a way to tune AF a bit as well. Let's say you have a JWT ECU programmed for 370's, a walbro fuel pump, and the stock FPR. You go dyno your car and your AF ratio is 12:1 accross the board. If you were to install an AFPR and turn up the base fuel pressure you migh be able to bring that AF ratio down to 11.8. Large adjustments cannot be done this way but small ones can. The same thing can be done with an S-AFC as well

So now we know that AFPR is essential to have if your trying to run larger injectors without the computer knowing you have larger injectors because too much fuel will be dumped. So turning down base fuel pressure will help elivate that problem. But what about when your driving around. Your not going to just have your car idling all the time.

If your going to run larger injectors without the computer knowing it, (ie; JWT ECU or emangae) then you also need something to control them during driving conditions. The easiest way to do this is with a S-AFC. You can increase of decrease the amount of fuel delivered at selected rpm points, but not at idle.

So you put the 370's in. Turn down the base fuel pressure so your car will idle right. Then go dyno and use an S-AFC to either subtract or add fuel at different rpm points to get your desired AF ratio.




Now the FMU. All the FMU does is increase fuel pressure base on the amout of boost is sees. And we know that increasing fuel pressure is kinda like increasing injector size. An FMU is nice because it will not change fuel pressure (injector size) until boost comes on. So your not adding more fuel until you see boost, so it does not cause too much fuel to be dumped at idle like installing larger injectors will. As boost increases so your AF raito will drop.

When JWT reprograms your computer there should be no need for an FMU. Your computer will be programed to supply enough fuel at given rpm, load, and TPS points to maintain their targeted AF raito. No need to make the injectors flow more fuel via fuel pressue if the computer is taking car of it.

 

Im trying to pick a fuel setup right now for my turbo setup. I can get a S-AFC 2 for cheap so I will be using that until I get a eManage Ultimate. Im going to go with a Walbro 255 fuel pump, FPR and maybe 380-510cc injectors. Im still trying to decide on injectors since I have a DE-K motor with top feeds. I have a few injector choices but they seem to be very expensive. If anyone has any suggestions that would be great.

I have done some research but I dont think I fully understand everything. I will be running bigger injectors so to prevent flooding on starts I will need to lower base fuel pressure. If I do that and adjust fuel with the S-AFC 2, will all be okay? I have the idea that since the base fuel pressure is lower, I will not be to provide enough fuel up top if I am running more boost. Going with the e-Manage should fix this problem or going with a FMU...but I would rather wait it out on until the e-Manage. I plan to run around 6psi at the start and eventually run 12-14psi.

 

Mike-That was a mouthful.

An fmu is a coarse way to tune. It helps you deliver the proper amount of fuel but needs to be fine tuned with a fuel controller.


JeEve-Are you going S/C or Turbo? The way you tune them is slightly different. For example, Mike needed to run a 10:1 fmu disc for 6 psi on stock injectors, while I used an 8:1 disc. It has to deal with the power and torque curves.

As for the larger injectors for the 5th gen, DSM injectors should fit and you have many inexpensive options with those.

 

I am going with a turbo. As for injectors, if the DSM injectors work that would be great since the are very cheap. I put some DSM injectors in a turbo Honda with slight modification, hopfully they will be close enough to work.