Fuel pressure regulator, simple mod idea?

[qsiguy]

Now that is some awesome information Steve, thank you. I hadn't considered the pressure differential caused by the boost pressure on the outlet of the injectors. This makes much more sense.

Any chance anyone knows a formula to determine the theoretical new injector size when you increase the fuel pressure?

[npez]

Any chance anyone knows a formula to determine the theoretical new injector size when you increase the fuel pressure?

Shane,

Don't know the specific formula, but I found this calculator - seems correct from just eyebaling it. http://www.csgnetwork.com/fiflowcalc.html

Thanks,Nick.

P.S. If you really want to know the formula I can go through the Javascript and find out

[qsiguy]

That's a cool calculator Nick, thanks for the link. According to that calculator the stock 370cc (or ~35.21lb) injectors will act like 384 cc / 36.59 lb injectors if I increase from 43.5 psi to 47 psi of fuel pressure. I wonder what the max is for the injector if you keep increasing the fuel pressure? If the fuel pump relief valve opens at 65 can we keep increasing fuel pressure to say 60 psi? According to the calculator going to 60 psi of fuel pressure would increase the 370cc injectors to that of a 434.61 cc injector. Hmm. This gets the old gears turning...

[npez]

That's a cool calculator Nick, thanks for the link. According to that calculator the stock 370cc (or ~35.21lb) injectors will act like 384 cc / 36.59 lb injectors if I increase from 43.5 psi to 47 psi of fuel pressure. I wonder what the max is for the injector if you keep increasing the fuel pressure? If the fuel pump relief valve opens at 65 can we keep increasing fuel pressure to say 60 psi? According to the calculator going to 60 psi of fuel pressure would increase the 370cc injectors to that of a 434.61 cc injector. Hmm. This gets the old gears turning...

Shane,

I'm not sure what the injector itself can handle, but I believe raising it to say 60 may be extreme and cause other issues (leaks, stress on components, etc.) when looking at the fuel sytem as a whole. I was only planning on going up about 10% on the base fuel pressure (approx 47psi)when I go ahead and put in the 555cc Nismos that I have during phase 2a. Close to a 50% bump though - I'd be weary. I've read that on some injectors the margin is only 2-3 psi more over stock base fuel pressure.

Maybe someone with more experience with Nissan injectors can fill us in.

Thanks,Nick.

[qsiguy]

That was more of a hypothetical question. I wouldn't want to push my 14 year old fuel system to 60 psi, I know that would just be asking for trouble. Just curious of the mechanical capabilities of the injectors. Maybe 50 psi....

[SuperHatch]

It's funny that you mention upping the fuel pressure so high, I've actually experienced times when the fuel pressure had to be lowered to not overburden the pumps. In this instance it was a built DSM running 39psi on a 2.0L 4 banger. The resultant required fuel pressure was 82.5psi, and it was easier to lower the fuel pressure a few pounds to ease the load on the pumps, since the injectors were more than large enough. The issue really becomes the ineffective spray pattern caused by lower fuel pressure loads.

When raising the base pressure there is more to consider than if the pump can handle it, as mentioned there is the rest of the fuel system. Also, don't forget that the injector driver has to move that pintle in the injector against a now greater pressure on the backside. This will adversely effect your dead time on the injector, and even though you've now increased the theoretical flowrate, you've decreased your maximum duty cycle. I personally wouldn't go any farther than 47 to 48psi.

[qsiguy]

Good to know. I think that little bit of headroom in my injector output combined with a MAF mod would easily allow me to push up to about 10 psi of boost. As it sits now I'm about maxing both right at 9-10 psi @ 6600-7000 rpm range so I can't really run at that safely. If I could keep the duty cycle < 90% at 10 psi of boost I would feel much better. I'll likely keep it at about 8 psi most of the time but for a run down the track or a quick run on the dyno I'd like to be able to bump it up to 10.

[qsiguy]

So now that we've established what it is we want to do...has anyone tried the cheap e-bay regulators? There are a bunch that meet the requirements we've been talking about in the $30-40 range with shipping. Curious if anyone as tried them and what were the results. I don't really want to drop a few hundred bucks on a regulator if I don't have to. A pressure regulator is a pretty simple device so what problems would one expect from these cheapies? Fuel leaks? Maybe unexpected increase or loss of pressure? A pressure loss would only go as low as OEM spec since the OEM regulator is still installed.

Thoughts? I know I'm a tight wad, I'd just rather spend the money on other mods if I can get what I need from one of these regulators.

[npez]

So now that we've established what it is we want to do...has anyone tried the cheap e-bay regulators? There are a bunch that meet the requirements we've been talking about in the $30-40 range with shipping. Curious if anyone as tried them and what were the results. I don't really want to drop a few hundred bucks on a regulator if I don't have to. A pressure regulator is a pretty simple device so what problems would one expect from these cheapies? Fuel leaks? Maybe unexpected increase or loss of pressure? A pressure loss would only go as low as OEM spec since the OEM regulator is still installed.

Thoughts? I know I'm a tight wad, I'd just rather spend the money on other mods if I can get what I need from one of these regulators.

Shane,

You're not a tight wad - I am very much like you as well. I don't mind spending money but I always differentiate spending money and getting what I need from pissing money away and getting things that I really don't need. I'm with you 100% with that.

Now as far as the ebay units - I did some searches and cannot find anything in a 1:1 boost compatible - some OBX units but they are 8:1,10:1, etc. The best quality item I found (from reading the specs) for the price is the Aeromotive A1000-6. You can see the specs here: http://www.shop.speedunlimited...32401. For $140 dollars it gives most if not all the features of FPRs twice (or more) the price. Qualitatively I have no idea - they've been in business for a while and are everywhere (Summit, all over the internet, etc.) While FPRs are not complex, the last thing I would want is a defect causing a lean condition that sets me back a couple thousand dollars. I will probably give this unit a try as it seems to be a happy medium and let you know how it works out.

Thanks,Nick.

[qsiguy]

I see quite a few that I believe are 1:1. Many say universal and don't give a ratio but are adjustable within a range. I'm pretty sure they are straight 1:1.

Here's one that not quite as cheap as the others.http://cgi.ebay.com/ebaymotors...89443&

This one says in the description "Holds user-defined fuel pressure. (Not a rising rate regulator)". $25 plus $18 shipping. Dozens of them look just like this one, the sellers obviously have varying levels of knowledge on how to describe them.http://cgi.ebay.com/ebaymotors...91653&

Here's one that's described as a 1:1.http://cgi.ebay.com/ebaymotors...37891&
Modified by qsiguy at 10:36 PM 5/20/2008