L28et Fuel Pressure

[24OZ]

Hi GuyZ,

 

I am running a 240Z with stock L28ET running 7psi of boost and im using the N/A Loom and N/A ECU and Dizzy from a 280ZX - (A BAND AID for now)

 

I am looking into getting a Rising Rate FPR but need some advice as I'm finding it confusing as to which one I need to purchase.

 

When looking at my Turbo FSM it states that idle fuel pressure should be 30 psi and at WOT it should be 37psi.

 

When looking on ebay for an FPR most state they have a 12:1 Ratio. From my understanding, this means that if I set idle fuel pressure to 30psi then with 7 psi of boost, fuel pressure will be 12x7psi = 84psi plus the idle which is 30psi so that makes 114psi fuel pressure when boosting at 7psi. Is that correct? If so why would anyone use one of those?

 

I have noticed some units have a 1:1 ratio which sound as if they are the ones i need to go for, please confirm.

 

Thank you all.

[Drax240z]

The stock unit is a 1:1 ratio.

[Pyro]

A Bell Engineering FMU will work with your setup. It goes in the return line after the stock regulator. It is adjustable to any boost:fuel pressure ratio you need. (1:1, 2:1, 3:1, 4:1,......)

 

The stock regulator handles all the off boost pressures then the FMU ups the fuel pressure during boost.

 

7 psi of boost with stock injectors should need about 50 psi of fuel pressure.

 

I found the boost comes on stronger and quicker if the afm spring is tightened up 5 to 10 teeth.

 

A 1:1 regulator works great with an aftermarket efi system. The fuel enrichment can be made with the computer. The FMU can enrich the mixture by turning up the pressure since the stock computer is not programmable.

 

If you add more boost then you will need two fuel pumps in parallel to make up to 75 psi which is good from around 10 psi with stock injectors.

 

With out 7 psi of boost your engine should be able to handle 30 degrees of total ignition timing which is about 12 degrees initial timing with 18 degrees in the distributor. However, if you turn the boost up, then the timing should be lowered.

 

Turbo engines like a lot of initial timing due to the low compression. So it is a good idea to limit the amount of advance and run 20 degrees of inital timing. I reduced the slot lenght in my distributors mechanical advance with a small weld. So now it has 8 to 10 degree advance with 17 initial timing and 14 psi of boost.

 

Or you can just lock out the distributor advance and set it to 24 or 25 degrees when you set up to 12 psi of boost.

[24OZ]

Thanks for the responses guys.

 

From what you both have said I understand that a 1:1 ratio FPR is what i need.

 

Pyros I am using the turbo injectors so i think 37psi of boost will be fine at my max of 7psi of boost, since 7psi is the stock boost and the FSM states 37psi at WOT. Please can someone confirm I've got this right.

 

With regards to the NA Dizzy, I will be keeping the vacuum advance but blocking off the mechanical advance, I've been told to set initial timing to 10degrees BTDC.

 

Appreciate all your comments.

[Drax240z]

Thanks for the responses guys.

 

From what you both have said I understand that a 1:1 ratio FPR is what i need.

 

Pyros I am using the turbo injectors so i think 37psi of boost will be fine at my max of 7psi of boost' date=' since 7psi is the stock boost and the FSM states 37psi at WOT. Please can someone confirm I've got this right.[/quote']

 

That is correct.

[24OZ]

Thank you Drax.

[Clifton]

Are you using N/A injectors too? What's wrong with the stock FPR? Stock is 1:1. If you are on stock n/a everything you will need more fuel and a 1:1 will only compensate for boost not extra enrichment which it sounds like you are looking for. You'll need a rising rate regulator (greater than 1:1). Or addtional injectors.

[24OZ]

Clifton I am using something similar to this http://cgi.ebay.com/ebaymotors/Rising-Rate-Fuel-Pressure-Regulator-FPR-30-70-psi-Adjs_W0QQcmdZViewItemQQcategoryZ33742QQitemZ8019650720QQrdZ1QQsspagenameZWD1V#ebayphotohosting

, I am using stock 280ZX turbo injectors, i thought i would need this product so as to add more fuel when boosting, are you saying the stock FPR is all i needed? Dang, if that is the case I wish i new it before I bought it.

 

Appreciate everyones help on this.

[Clifton]

Clifton I am using something similar to this http://cgi.ebay.com/ebaymotors/Rising-Rate-Fuel-Pressure-Regulator-FPR-30-70-psi-Adjs_W0QQcmdZViewItemQQcategoryZ33742QQitemZ8019650720QQrdZ1QQsspagenameZWD1V#ebayphotohosting

' date=' I am using stock 280ZX turbo injectors, i thought i would need this product so as to add more fuel when boosting, are you saying the stock FPR is all i needed? Dang, if that is the case I wish i new it before I bought it.

 

Appreciate everyones help on this.[/quote']

 

The fpr you got on ebay is the same as the stock one, 1:1. It just adds 1 psi fuel for 1 psi of boost to compensate for the manifold pressure that the injector is injecting into. Raising rate fpr's add additional fuel. I would probably get a wideband next.

[nienberg.11]

24OZ, I'm with clifton and pyro on this. You need an fmu w/ an adjustable rate of gain like what Pyro was describing. I personally run the BEGI 2025 fmu, and it works great. These are readily available on ebay. Also, in regards to supporting higher fuel pressures, something better than the stock pump will be required. I have to clarify though, that although Pyro is a brave guy and a pioneer for running n/a injectors and 100 psi fuel pressure supported by multiple stock pumps, you will probably find it easier and more reliable to get a single Walbro or other high quality pump that is designed to flow high volumes of fuel and support high fuel pressure if you have the money. There is a safety issue or two to be addressed here as well. I'm not sure how great it is to run 50+ psi through a stock fuel filter. I personally have my pump placed in such a way that my fuel filter is unpressurized. Also, if you have original fuel lines on the motor you might consider replacing them to avoid leaks/fires/death. I run the setup described above on zxt injectors and 7 psi boost and around 50 psi fuel pressure and it works excellently.

[24OZ]

Thanks Neinberg for the advice.

 

One thing I can't seem to understand though is that why would I need 50psi of fuel pressure at 7psi of boost, when the turbo FSM states that fuel pressure should be 30 psi at idle and at WOT it should be 37psi.

 

Now stock turbo pressure is 7psi on the ZX Turbo so I would assume fuel pressure should be 37psi at 7psi of boost and 50psi fuel pressure would be too much..

 

Am i reading this incorrectly..

 

Thanks for trying to help me understand this!

[nienberg.11]

24OZ, you make a good point... there will be a discrepancy between the fuel pressure required for a stock turbo car @ 7psi and what you will need with an n/a ecu. I'm running the '77 ecu so I run about 50 psi for 7 psi boost, whereas if I had the turbo ecu, I would not need the fmu, pump, and increased fuel pressure b/c the injector pulse width would be lengthened to compensate for boost up to the zxt boost level of 7psi.

[24OZ]

That makes total sense, now I understand.

 

To recap:

 

The turbo ECU would have give the injectors an increased duty cycle at 7psi but when using the NA ECU at WOT the Duty Cycle will be a lot shorter, hence the need for more fuel (pressure) to gush into the injectors to compensate

 

I think I learnt something tonight!!

 

One other thing, I am using a stock 280ZX pump, would i definately have to upgrade? I am going standalone next year so duty cycle can be increased and fuel pressure lowered.

[nienberg.11]

For a standalone system I would say the stock pump would be all right, but I can't speak from experience on how well it will hold up under high pressures. I'm sure pyro could tell you, but judging by the multi-pump setup he's running now i'm guessing he didnt have much luck there.

[24OZ]

I forgot to mention yesterday that I am using the NA Air Flow meter, due to it's internal size being smaller (less airflow) maybe I would need less fuel pressure at WOT since I wouldnt be taking in so much air and therefore wouldnt be leaning out so much to warrant 50psi??

 

Just a thought, would be interesting to hear what you think.

[Drax240z]

whereas if I had the turbo ecu, I would not need the fmu, pump, and increased fuel pressure b/c the injector pulse width would be lengthened to compensate for boost up to the zxt boost level of 7psi.

 

I thnk you are missing the point here. Turbo injectors are larger than NA injectors, so they flow more fuel for a given pulsewidth. With the NA ECU and the turbo injectors you are going to have too much fuel below atmospheric pressure, (the turbo ECU will have a lower pulsewidth here) and you'll gradually lean out as you build boost, as the NA ECU is going to keep a steady pulsewidth independant of boost level (ie: afm door fully open) but with 44% (or whatever the increase in fueling is from NA to Turbo injectors... 180cc/min -> 260cc/min IIRC) more fuel flowing than it would have with the NA injectors. All things equal, you would achieve the same AFR on your setup as a stock NA engine has at 6.5psi boost, when using turbo injectors and a NA ECU.

 

The AFM being smaller is going to decrease the amount of air flowing for a given fuel setting, therefore leading to a richer mixture throughout the range as well... something that bodes well for a turbo setup, as the stock AFM on an NA 280zx seems to dyno in the 12.5-13.0 range at full throttle in my experience.

 

In summary, I would think an NA ECU, NA AFM, NA FPR and turbo injectors would put you in the right ballpark for fueling below 7psi, though you are going to be too rich at manifold pressures less than atmospheric.

[24OZ]

This is something i have been waiting to hear!

 

So basically I can run stock fuel pressure for a turbo motor, ie..

 

30psi at idle and 36psi at WOT.

 

I did not like the idea of going to 50 or 60psi of fuel pressure, something would have popped!

 

Thanks Drax.

[nienberg.11]

I thnk you are missing the point here. Turbo injectors are larger than NA injectors, so they flow more fuel for a given pulsewidth. With the NA ECU and the turbo injectors you are going to have too much fuel below atmospheric pressure

 

Drax, I see what you are saying, but in my case, I have the afm adjusted so that my turbo injectors are not creating overly-rich conditions below atmospheric pressure. I was working under the assumption that 24OZ had also leaned out the afm, but if he hadn't I see your point about how he could run pig-rich under normal conditions and come out all right for 7 psi w/o additional equipment. It's do-able but it wouldn't perform very well.

24OZ, have you run the car any w/ the turbo? I ask because I tried using my n/a afm and the turbo, and it didnt work out so well. The turbo couldn't draw enough air through it and the car would choke out at 4000 rpm. I had n/a afm electronics swapped into the larger turbo afm housing which fixed the problem.

[Drax240z]

In the end there is only one way to know for sure. Stick it on a dyno, do a baseline, log AFR's... For $75 or so you'll know where you stand and take the guesswork out of it.

[Guest bastaad525]

didn't read the whole thread but thought I'd pitch in.

 

I'm using one of BEGI's RRFPR's as well. Mostly stock L28ET setup in a '72 240, stock T3, stock EFI system, stock turbo injectors. Running 13-14psi of boost. I did upgrade to an MSD high flow fuel pump, though the stock one flowed plenty enough to support 200 whp at 10psi.

 

Tuned on the dyno, I ended up running about 70psi of pressure at WOT/full boost. Off boost and up to about 3psi the fuel pressure is stock, then after 3psi the RRFPR kicks in. I was able to get a nice safe air/fuel ratio all the way to 6000 rpm with this setup. I didn't need to run two pumps, and I've had no issues with running the higher pressure.

 

I'm using all the stock fuel lines though I did run a larger return line, the stock 240 return line is VERY small and caused the fuel pressure to skyrocket when I installed the MSD fuel pump. So I switched over to an unused vent line on the driver side of the engine bay which was about twice as bit, 1/4 inch or so, and fuel pressure returned to stock. I'm using the stock fuel filter as well.

 

I've been running this setup for over a year and have had no problems other than an overly rich midrange. This is not the RRFPR's fault though, it's actually inherent to the stock 280zxt fuel system, as anyone who has dynoed a bone stock 280zxt setup at stock boost will tell you they like to run real rich from about 3000-4000rpm.

 

I'm very happy overall with the BEGI unit, it was easy to install and tune, the only downside is that it's a bit pricey, considering you can pick up a set of 370cc injectors used for less than $100 easy. Though the injectors are harder to install and you have to tweak with your AFM to get the car running decently in around town driving whereas the RRFPR doesn't affect around town driving at all.