What is the difference ? Could I use a boost referenced regulator on an EFI setup like mine ? It sounds like a lot less hassles than getting into electronics related in the FMU ? What are the benifits of each ? Anyone?

ttt


I just read that a guy was useing the boodt referenced regulator and he said it wasn;t an FMU . I didn't want to hyjack his thread so I started this one

boost referenced regulator=gos in the path of the fuel return line
fmu=fuel mangment unit, it could be a boost referenced regulator, ecu tuning or anything

Both a boost referenced regualtor and an FMU/RRFPR are installed on the fuel return line of the EFI system.

The difference is that the boost referenced regulator only raises the fuel pressure 1:1 with boost. In other words, for each pound of boost, the fuel pressure will increase 1psi. This is to keep the pressure differential between the injector nozzle and the fuel rail the same. Obviousely fuel flow would be seriousely compromised if the rail pressure stayed at 40psi while the intake pressure/boost climbed to 10psi or more. This is the exact principle of the vacuum regulator used on most stock EFI systems. Vacuum is just pressure below atmosphereic. Most factory EFI regulators will raise the fuel pressure 1:1 with boost (when connected to the intake manifold), so there is no need to buy a seperate 'boost referenced' regulator.

An FMU is a RRFPR (rising rate fuel pressure regulator). There are no electronics involved in a RRFPR. It increases the fuel pressure more than 1:1. Many are 8:1 or higher, and the best RRFPRs have an adjustable rate (such as the Cartech/BEGI units and the Vortech Super FMU). An 8:1RRFPR will increase the fuel pressure 8psi for each 1psi of boost. These are what you want to run if you want to go forced induction without messing with the ECM tune or injectors. They are really only effective to around 9psi of boost (because at this point the stock injectors will probably require well over 100psi of fuel pressure to keep the AFR safe; you are at the point of deminishing returns).

Many people consider the FMU/RRFPR as a band-aid approach, but they can and do work. Both my turbochargeed chevy's are deep into the 12's using them. But custom ECM tuning will open the doors to go a lot faster (and do so reliably).

89JYturbo said it already, but in a nutshell:

regulator: just holds the fuel pressure constant in relation to manifold pressure.

FMU: adds fuel as boost comes in by jacking up the fuel pressure.

While on the topic i've got a question. So ideally we should run the $58 code with bigger injectors and lose the fmu's and regulators. How does fuel pressure relate to this method of tuning? Or in other words should you take the bigger injectors and an afpr and jack up the pressure? I ran an FMU for years but am going to run the $58 code and just wasn't sure what psi we should aim for?

You should match your injectors to provide enough fuel to achieve your power goal at the injector's design pressure, which is usually around 45psi base fuel pressure. The only reason you run a higher base fuel pressure than that is if your injectors are too small. I'm refering to base fuel pressure as the fuel pressure with the engine idling and the FPR signal hose disconnected. You don't want higher than necessary fuel pressure because it will work the fuel pump harder (with regard to fuel pumps, or any pump for that matter, higher pressure output = less flow volume).

Exactly what I was looking for. Thanks.

Just wondering . I do plan on the 749 swap down the road . I just figured I could get away with the Boost referenced regulator and prom tuening? I just hate to go and get an FMU then swap to the 749 a couple years later.

My current setup will be stock 22 lb injectors ( I don';t mind buying bigger ones if needed( easy swap ) 165 ECM with a Prominator pro tuneing chip ( awesome !!!!) . I figured I could just do all the tuening in there . But the fuel was makeing me concerened . So I am just looknig for asimple sollution , without haveign to brake the wallet untill I swap to the 749/$58

BTW thanx all !!!!!

Since you already have a Prominator Pro for the 165 ECM and probably have experience tuning the 165 ECM then I would stick with it for a while. Doing the 749 requires re-wiring, new ALDL files to learn, possible new ALDL log tool to learn, all new BIN data to learn.

Just having a turbo on the engine and tuning with the 165 and an FMU is probably the best route to take. You can tune the 165 to pull timing at various rpm and MAF gm/sec (when under boost). You can do the same with the fuel. With the fuel you will probably max. out the MAF so just run it richer at the top end of the MAF.

My 165 ECM to 749 ECM swap I just did took about 4hrs on the new twin turbo rig. Yeah, why so long? I cut & re-connected the 165 ECM grounds so that they are like the 749 ECM grounds. The Mike Davis list doesn't take that difference into account. I added a DIY-WBO2 harness, ran some oil temp. sensor wiring to the ECM, etc. I hade to make new ECM mounting brackets because of the connector difference from the 165 to 730 ECM. That took about an hour.
The swap took about 5hrs total. Once I get this thing running I then need to fix bugs in the Tunerpro 4.13 ADS file. That will probably take about 10 hours of figuring out. Time spent learning the $58 code parameters is going to be long.

Overall, using the 165 ECM with FMU is a good idea. You won't have to deal with the possible idle & big injector problem or possible wiring mistakes. Tuning will be faster since you know the 165 bettter. Going the 165 ECM only requires buying the FMU which you can sell later on.
The 749 swap will cost you new injectors ($100 to $500), new ECM ($20-$75), new tuning & ALDL ($0-$200).

Being your first boost setup, I would go with what makes the most sense..... 165 and FMU. Learn about tuning a turbo setup using that and at the same time read up on the 749 ECM so that it isn't a major hassle if/when you convert later on. You can even keep the FMU with the 749 if you choose.
FMUs are just as good as big injectors as long as you keep the fuel pressure within reason. A quick calc shows the 22 lb/hr can do about 375-425HP at 80PSI.

Wicked .Thats exactley what I wanted to hear . I plan on running only aroun6-7 psi with the FMU setup .

If ya'll don't mind.....

I could take a COMPLETELY stock computer system, add a turbo to the engine, buy a "cartech" or similar Boost Ref. Reg., and not have to do anything with the factory ECM if I was to stay at or under 9 psi?

Is the RRFPR better, or about the same? Again, this would be all under 10 psi.
Is this applicable to pretty much any type of fuel injection system? Say a LS1 or 95 and newer Chevy Truck Vortech 5.7? Even a older TBI 350?

Only other thing with a totally stock ECM would be timing controls though right?

Thanks alot guys, learning more everyday

Not sure if you are askng or saying thats pretty much what I was asking in the start of this . I am not sure if the rrfpr will provide enough .....but again this is what I am trying to find out .

Thats a touchy question. There are a lot of variables, but for the most part the idea of the RRFPR is so that you don't need to mess with injectors or the ECM. I would consider the RRFPR to be safe in most applications up to 6psi of boost, and in some cases will work well to 10psi.

However, you need to keep in mind how they work, and that is by driving the fuel pressure sky high as boost comes in to force enough fuel through the stock injectors so that the AFR stays close to coorect (I say close because as you can imagine this method is not exact science). Because of this high fuel pressure demand, you will often see a booster pump run inline to help keep fuel flow volume up even at fuel pressure near (and sometimes over) 100psi.

My Z24 uses the Cartech FMU and it needs 120psi of fuel pressure to keep the AFR safe at 10psi of boost. Most people are surprised that the injectors don't lock and that the Holley 255lph pump can keep up at those pressures, but the system has been working perfectly now for over a year and a half. This extreme fuel pressure is why the FMU/RRFPR is limited to around 9psi of boost. My TT IROC does use slightly larger injectors, but it is probably overkill for the 6psi of boost that I run. I had to lower the base fuel pressure lsightly to keep from setting a rich code in the ECM while idling or running at part throttle.

Like you metnioned, the issue then wil be the ignition. With the TPI, you can at least back off a few degress of base timing to help avoid pinging. That, coupled with premium fuel and colder plugs should keep detonation at bay for mild boost. There is the boost retard boxes as well if you run into trouble. ALky/water injection is another method of eliminating detonation, and has been proven very successful.

IIRC< the TBI systems don't function too well with an FMU. I'm sur ethey can be made to work well, I guess they take some finesse.

So to sum it up, yes the FMU/RRFPR is designed to run a boosted engine without any other fuel system mods (save for maybe a better in-tank pump or add on booster pump). The nice thing is that they are easy to use, quick to tune, and maintian OEM driveability off boost. However, custom ECM tuning, big intjectors, etc. will always be the choice of people who take the tuning seriously. The FMU may just be the best place to start for mild street turbo systems.

Well, I’d strongly disagree with that, they work fine, most people just don’t understand enough about both, the fmu and the tbi setup to get it working right

I was speeking from info on a thread over at TM. Seemed everyone there thought an FMU on a TBI was worthless. Good to know that it can be made to work for budget TBI turbo projects.

yea, if it's the thread that I'm thinking about I had it open in my browser for over a month trying to find time to reply and fix everything that was wrong in that thread and finally got to the point that "I don't have time and this is so screwed up that there is no real saving this mess..."

How could one be used with a TBI then?

Just like with anything else, it's just a matter of getting the ratio low enough and/or bypassing enough of the signal to get it working right with the lower pressures.

I guess a more accurate answer would involve that most people don't seem to manage to get them working right on anything and where 20psi or more too much on a port injected setup makes for a lot fewer problems then on a TBI setup that runs 1/4 the pressure to start with.

I used a 2:1 regulator in series with the stock fuel pressure regulator when I had the supercharger on my stock Cross-Fire engine. I connected the vacuum hose to a vaccum port on the TBI just like you would on any port injection engine. You need a weak spring to get the base pressure right in the FMU, but that is the only differance.

The increase in fuel flow is sqrt(new prerssure/old pressure).

At 6 psi boost the engine will flow about 40% more air.

If you double the fuel pressure you get sqrt(2/1) = 1.41 = 41% more fuel flow.

That is a good start.

On a TBI you start with perhaps 12 psi fuel pressure. To double the fuel pressure you need an extra 12 psi when you have 6 psi boost. With the plenum pressure that is 18 psi increase in absolute fuel pressure. A 3:1 FMU will give you that (18/6 = 3).

0 psi boost = 12 psi fuel pressure.

3 psi boost -> 12 + 3*3 = 21 psi absolute fuel pressure (21-3= 18 psi differential pressure over the injector).

6 psi boost -> 12 + 6*3 = 30 psi absolute fuel pressure (30-6= 24 psi differential pressure over the injector).

On a TBI the fuel pump has to deliver 12 psi without boost. At 6 psi boost the fuel pump has to deliver 30 psi fuel pressure. This requies a 3:1 FMU to get 41% extra fuel

If you start with a higher base fuel pressure like 45 psi normally used on port injection it gets even worse.

At 6 psi boost you still need to double the fuel pressure. That requires an extra 45 psi fuel pressure over the injector. 51 psi extra with the plenum pressure added. You need an 8.5:1 FMU to get that (51/6 = 8.5).

On a MPI the fuel pump has to deliver 45 psi without boost. At 6 psi boost the fuel pump has to deliver 96 psi fuel pressure. This requies a 8.5:1 FMU to get 41% extra fuel

As you see you need much higher ratio on the FMU to get the same gain if you start with a higher fuel pressure.

I should say this is all for a TPI setup