Boost Referenced Fuel System

ctuinstra

Well-Known Member
Has anyone installed a boost referenced fuel regulator? I'm looking at doing it and would like to know more before going down that route.

i've been working a lot with HP tuners and found a lot of issues with being overly rich at idle and low throttle. The injectors are already running at minimum pulse width so there is no way to lean it out any farther. Reducing fuel pressure should have a big impact.
 

ctuinstra

Well-Known Member
@Justinreed7 is running one. I’ll be running one too on the next bigger build. Not having any fuel issues with my current 60#
I’m surprised you aren’t. I will have to share some of my findings. Bottom line seems to be at low RPM/MAP the injectors just output too much because they are at the min pulse width. Any lower and they seems to become very unstable. During a very short quick WOT and 6K, it seemed that they only reached a duty cycle of 40%. I cannot fathom why anyone would need anything larger unless they are producing tons of HP.

I plan to write up more tonight in the HP Tuners thread.
 

taz_va

Member
Not to sound unhelpful, but did you match your injectors to your flow/power needs? Sometimes people get injectors which are too large, and run into a situation where duty cycle is low, and idle sucks. Some people won't have an issue at lower rpm's based on how much airflow is going into the cylinders. Some folks have turned boost up at idle, for instance, and solved this issue, but it's not something I suggest blindly doing. This also presumes you're monitoring AFR properly.

As to the specific question itself, BRFS's are easy to setup. You usually only see them in high-power setups though (hence the larger injectors). I don't know anything about your build, so I'm not knocking it, just pointing it out. My experience is with LSx motors, but it's similar for the smaller ones. To give you an idea, my last LS2 daily driver build was putting well over 700/700 to the ground, and I wasn't using a BRFS to reduce fuel pressure, just boost it up when necessary. Injectors were matched to the flow/power needs. I don't recall the duty cycle, but it was perfect.

One nice thing about the Goblin and a BRFS is that you can go with a full return if you wanted to, fairly easily, since the engine sits on top of the tank--but that does require an extra line run into the tank, and possibly a pump change. Easier to just pop the regulator into the system and work it from there, by reducing pressure, like you're looking to do.
 

ctuinstra

Well-Known Member
Great question. The previous owner installed the 60# injectors with no other mod other than a ZZP tune and a “CAI”. I see no reason why they would have needed the larger injectors with that setup. I have since installed a smaller pulley (2.9) to increase the boost and potentially need the additional fuel flow at WOT. Assuming I need the flow for WOT, I would rather have that so as not to go lean at WOT, but at what I seen at 40% duty cycle, I’m beginning to wonder the actual need for the larger injectors. Maybe the stock is just slightly too small at full load?

So to answer your question, I’m not sure at this point if we have too much injectors for the demand. From what I read/hear, they are required (or at least strongly suggested) for this set up (Stage 2).

I feel that a boost referenced regulator that is adjusted down to say, 48 psi, might better match the 60# injectors. I just don’t know if that would cause flow issues across the board.
 

taz_va

Member
Good response honestly. The TLDR is you can't go wrong with a BRFS, very easy to install, and it's not going to hurt the build by installing it, just make sure you log fuel pressure / afr / boost, and all the other tidbits to make sure the system is efficient & safe. Here's a little more in-depth response:

I remember when I used to browse the cobalt forums, a lot of people just went with stuff because it seemed right. Don't mistake what I'm saying here, I'm not applying that to you, just making the observation of those other folks. Your situation is you took a setup from someone and now you're refining it, and you're definitely looking to do the right thing either way.

I'm presuming you already monitor fuel pressure, and you correctly surmise changing the rail pressure will change the lb/hr flow of the injectors themselves. Most injectors are rated at 42-45psi, and many GM fuel rails are setup to run 45-60psi stock, and most of the pumps will accept up to 18v. I have no direct experience with the LSJ/LNF's yet, which is why I'm using general experience in my post. What you'll see some folks do is use a boost reference voltage booster, so they choose their injectors so that it's fine at idle, and increases voltage to boost rail pressure, to increase flow as necessary under WOT. Others set things up to bleed fuel off at low-rpm, which accomplishes the same, just in a different way.

If it were me, I'd do some math and run some analysis (logging pressure/fuel burn/afr/etc idle->redline->idle) and see if the injectors are well-matched for the application. I used to have a handy spreadsheet calculator somewhere with hundreds of real-life examples, and the ability to plug in your own data, but I can't find it right now (sadly). If I can find it, I'll post it up for folks.

If you're making 300 or more, I could see 60# being realistic.. the formula involved simply examines horsepower as a result of injector flow, cycle, and number of cylinders, along with a value known as BSFC (brake specific fuel consumption). If you have a map of your volumetric flow efficiency for the turbo/supercharger & engine, you can come up with your own tailored BSFC. FI for these motors puts BSFC at between .545-.6, from what my research tells me. A few folks claim the stock SC LSJ setup is .58.

I want to say the LSJ's came with 36# injectors, going on what I've heard. This also matches up with the basic injector math where a desired HP results in a necessary flow rate: (HP*BSFC)/(Injectors*Duty): 205*0.58/4*.85 = 34.9. So the stock 205 would need at least 35# injectors. This is based on my presumption of GM using an 85% duty cycle, which I've seen elsewhere. This is crank power of course.

Adding to this, I heard that GM used to sell stage kits for the LSJ, and they included 42# injectors. The first 2 would get you up to 240ish in power. The math shows a need for at least 41# of flow, which lines up with their stage kits. This is just going on what I could scrape online, for their former kits. In theory the math suggests that 42# would support up to 246hp, using the BSFC & DC from above. 60# would support 350hp. Without knowing the parasitic transmission loss, let me blindly presume 15%. So that puts a stock LSJ at 174whp, 42# at 209, and 60# at 298.

If you had a dyno map of the car that would really help. Do you know what your fuel pressure is from idle->WOT? What about your actual AFR & Boost? Stuff like that will help you determine where you need to be. If your duty cycle is 40% and you're still too ruch anywhere, I would definitely think injectors are too large, pressure is to high, or you don't have enough air volume going through the engine to use it all. Sometimes "turning up the boost" really is the answer haha. Seriously though, you're going in the right direction.

Sorry for the long post.. just thought I'd pass on some input. Let us know where you go, this thread could be useful to others.
 

ctuinstra

Well-Known Member
All good info!

I do have a fuel pressure gauge in the line, but I cannot watch it real-time. I believe they are set up to 58 psi on the Cobalt. Being that the factory regulator is simply a spring and ball type (I believe) and not dependent on the pump voltage, it's not easily changed without changing out the spring. Actually, I not sure if it's in the pump or the fuel filter. The filter has a return line on it so I assume it's built into the filter. One could change out the filter to one that has lower pressure across the board. I believe one of the other guys on here did that.

I wish I have the ability to do all of the math to match the injectors but it looks like you did most of it already. I do believe stock it 35# and for whatever reason 60# is the next aftermarket set up. But, as you stated, the GM Stage 2 it 42# I believe. That would be much more realistic. I agree with you, I just don't think we need this large of injectors for this mild of a build. You're math seems very agreeable! I would rather see the injectors peak around 85% duty not 40%. However I need to do some more hard WOT runs and more logging to make sure it's not more than 40#. The problem is that I have no access to a dyno machine, at least not conveniently locally. And I really don't have access to much more other than HP Tuners to be able to see and log what is going on. I do however, have an wideband AFR gauge that I finally figured out how to connect into the new version of HP Tuners and I log that with everything else.

Now reading back to the rest of your post, I would believe we are pushing 209 at least or more, so the 42# might be a bit light for the job on the top end. Now it's a matter of deciding to try 42# and re-tuning or going with the BRFS. The pro with the 42# is that I could get a good matched set and have the values (which I do not for the current 60#) and should just then be able to tune both top and bottom. The con would be that they could be right at the limit of the fuel demand.

Thanks very much for the information, that was a lot of good, real information. You've given me something to think about.

Now, does anyone know for sure where the OEM regulator is, in the filter or pump?
 

JSATX

Well-Known Member
The return pressure valve is a simple ball bearing a spring in the pump housing. I have some detailed posts on it but I don’t remember which page they’re on. I removed mine and went to a corvette fuel filter which has a built in regulator.
 

SliderR1

Well-Known Member
Chad - just throwing this out there - if you really want to get the data on your existing injectors, try contacting Eric Derr at Derr Injector Services in Bowling Green KY. He will totally service your injectors and flow them to give you actual data that can be input into HP Tuners. I sent him two sets of decapped truck 6.0 LS injectors last month. He did all the work and 'matched' a set of 8 for my build for around $135 if I remember correctly...

My SS/SC came with the 42 lb injectors, but my build has sort of stalled and I haven't gotten that deep into the tuning yet.
 

ctuinstra

Well-Known Member
Chad - just throwing this out there - if you really want to get the data on your existing injectors, try contacting Eric Derr at Derr Injector Services in Bowling Green KY. He will totally service your injectors and flow them to give you actual data that can be input into HP Tuners. I sent him two sets of decapped truck 6.0 LS injectors last month. He did all the work and 'matched' a set of 8 for my build for around $135 if I remember correctly...

My SS/SC came with the 42 lb injectors, but my build has sort of stalled and I haven't gotten that deep into the tuning yet.
Very good information! It’s always bugged me that I don’t have the exact flow rates and don’t know to trust what is programmed. Then that leads to we don’t really have a flow rate for the MAF with the new intake set up. Ugh, a guy can go quickly down rabbit holes.

It would be interesting to see how the 42# work for you.
 

taz_va

Member
Glad to be of some value. I believe for the Cobalts, the pressure regulator is in the fuel bucket. See this post for a picture of it:

I don't believe the filter has a return line, it's a canister with 2 ports--in/out. The evap line runs between the tank and the intake of the Cobalt, perhaps this is what you guys are mentioning?

Your HPT puck allows for external sensor input (as you just discovered with the AFR). It's easy to include fuel pressure and boost in that as well, just by running an extra sensor wire from each, to the puck--presuming your senders are digital. I always had spare senders in my bags just for that purpose, screw them in place and wire them up. It's not the worst thing if you can't log those items simultaneously, it just makes things easier.

I got to thinking a bit more about your situation yesterday--does the tune properly reflect the injector flow? I'm not saying you did anything wrong, but maybe the guy before you didn't set it up well to match their flow.

Also, relating to the possibility of going with a boost reference setup, don't forget you have to tune for that as well. It's not difficult, just takes a little patience.

Here's a link from the Cobalt forum relating to tuning for 60# injectors, which I ran across while looking for something unrelated:

Here's one relating to tuning for the return setup:

Keep us posted on your progress.
 

taz_va

Member
Another random thought, if you're at 40% DC at WOT, and your trims/afr look great, you really have plenty of room to up the boost. I was reading somewhere that the ZZP people hung out, that you didn't really need 60# until you were passing 18lb of boost. That 40% DC just really sticks in my head haha. The good thing is you aren't running lean.
 

Lonny

Administrator
Staff member
The fuel pump is marked supply and return.
15555271063011692052074.jpg


This image shows the fuel pressure regulator.
15555272073811664910988.jpg


These are the supply and return lines that go to the filter.
1555527356728436661086.jpg


This is the filter, it free flows through all three ports.
15555274521701341873886.jpg


If someone wanted to use an external pressure regulator and needed a return line they could remove the internal regulator and hook to the return port on the top of the pump.
 

ctuinstra

Well-Known Member
Glad to be of some value. I believe for the Cobalts, the pressure regulator is in the fuel bucket. See this post for a picture of it:
Good info here. I understand now how the regulator works in this system. With the return line at the filter, I guess it just loops the fuel there after the pressure is at it's limit.

Only one huge question, they mention "Remove the end cap on the rail and mount the regulator", how the heck does one do that? I didn't know that was even possible. More research I will need to do here. Love this idea.




I don't believe the filter has a return line, it's a canister with 2 ports--in/out. The evap line runs between the tank and the intake of the Cobalt, perhaps this is what you guys are mentioning?
As you seen with Lonny's post, there are two lines going to the filter. One is a return.



Your HPT puck allows for external sensor input (as you just discovered with the AFR). It's easy to include fuel pressure and boost in that as well, just by running an extra sensor wire from each, to the puck--presuming your senders are digital. I always had spare senders in my bags just for that purpose, screw them in place and wire them up. It's not the worst thing if you can't log those items simultaneously, it just makes things easier.
I'm using an MPVI2 and the puck is a horribly overpriced unit just to add one more signal line. I was able to use the serial data out of the AEM gauge and map that into the scanner. No cost since my donor already came with the AEM AFR gauge. Pretty sweet until you forget to unplug it from the always hot line. Battery was dead in one day.



I got to thinking a bit more about your situation yesterday--does the tune properly reflect the injector flow? I'm not saying you did anything wrong, but maybe the guy before you didn't set it up well to match their flow.

Also, relating to the possibility of going with a boost reference setup, don't forget you have to tune for that as well. It's not difficult, just takes a little patience.

Here's a link from the Cobalt forum relating to tuning for 60# injectors, which I ran across while looking for something unrelated:

Here's one relating to tuning for the return setup:

Keep us posted on your progress.
Planning on it.
 
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