Okay, well from the original writeup there was some skepticism on the flow rate of the rather restrictive looking OEM "Check Valves". I could not find my notes on the flow so I redid the test, but more accurate this time with accurate real world conditions in place.

First of all, lets discuss the function of the check valves. They are not check valves. Contrary to popular belief, they are not designed to maintain pressure in the fuel rails. That is why the pump comes on for 15 seconds when you turn the key on. To build pressure. Those Itsy bitsy teeny weeny valves are non-flow restricting pressure snubbers. They have a hole right through the middle of them, so obviously they won't hold pressure. By nature the HEUI injection system creates some serious pressure shockwaves in the fuel. Hook up a mechanical non-oil filled gage to your fuel rail and see what happens. Every time an injector actuates it sends a shockwave through the fuel. Those fittings are designed to dissipate that shockwave before it reaches the fuel bowl, and the fuel pump. Also by maintaining those shockwaves in the rail, a more stable pressure and fuel flow is able to be maintained to the injectors. That is why some will report "romping" upon starting when removing those. The 94-97 trucks are notorious for this. It is from the unstable fuel rail pressure upon startup from those said shockwaves.

Okay, so now that the purpose of the check valves have been established, How do they flow? They are freakin tiny. How can a 444 cubic inch Big Block diesel engine actually run off those?? Quite easily come to find out.

So here is what I did for my bench test. I used a OEM equivalent Walbro pump. I regulated the pressure prior to the OEM fitting to 65 psi. Then used a valve and another gage after the fitting to regulate the pressure to 60 psi to represent actual fuel rail pressure under load resulting in a net pressure drop of 5 psi across the fitting. Remember, it is not accurate to just simply see how much fuel will flow thorugh them into a bucket. If you have 65psi on one side, and atmospheric on the other side(~14psi) you have a 51 psi pressure drop. The higher the pressure drop, the higher the flow.

What we are after here is how well do they flow at 65 psi(pump volume) with a 5 psi drop across them and maintain at least 60 psi in the rail? Well the answer averaged out to .625oz/sec. With some quick math that is 37.5 oz/min, 2250oz/hr or 17.6gph. Per rail. Combined the two rails and you have basically 35GPH of flow maintaining 60 psi in the rails at OEM fuel pressure. In order to drop the pressure below 60psi you would have to be getting less than 2mpg!!

Conclusion? Those restrictive little buggers aren't as restrictive as originally thought maybe?? I know I was bugeyed the first time I saw those things after dealing with gas engines most of my life, but some analytical testing has been interesting. But I am not done yet. I don't live with stock. Nothing I own is stock. So what happens when you raise the pressure by 10psi? Like by using a shim?

Short answer is the flow rate nearly doubles. So now I set my gear to maintain 75 PSI prior to fitting, and 65 in the rails. HiPo. Average was 1oz/sec. More quick math- lets see umm, 1 x 60 is uhhh, umm, Are you smarter than a 5th grader? 60oz/min. 3600oz/hr = 28gph per rail. Or 56gph per rail. You would now need to attain basically 1mph before you drop your rail pressure below 65psi. And remember, the more the pressure drop, the higher the flow.

 

Most informative and interesting! Thanks for taking the time to do those tests!

It sounds as if a bleed return system would work fine by continuing to use the factory vibrolock fittings and lines.

 

Great info, Jason. Thanks for the work.

 

Do we have any fluid dynamics engineering guys on here that could explain the downsides of having these spikes in our fuel, and what instantaneous peak pressures we might expect to see?

If these are reflected as far back as the pump, how is that piece affected?

Would the use of high-pressure "rubber" fuel lines act as an effective accumulator/dampner, and how might fittings and hoses be affected?

Pop

 

I saved my old steel lines when I did my fuel mods and this report makes me want to put the restrictors back in.
Shouldn't be too hard, just cut the ends off and flare the pipe. Then put the flex line back onto the restrictors instead of the NPT fitting that I have there now.

 

Another question, Jason.... Did you leave the tiny screens intact as well as leaving the "check valves"/restrictors in?

Pop, in Jason's Cackle-cure kit I put on my engine, I used the rubber fuel hose he supplied, which definitely showed signs of being somewhat of a shock absorber in the first week of use by progfressively getting quieter each day (for about 5-7 days). I still have the restrictors in place as well.

 

F250 I'm about to install the same kit, on a scale of 1 to 10 how would you rate the over all success of the kit? I've read your great write up but was wanting an update after running it awhile. Idle knock gone? cackle gone? thanks, ~Aaron

 

Aaron, thanks for the kind words. The noise levels are certainly diminished. Seems like it may be getting a tad bit noisier at idle here recently, but once running it's as quiet or quieter than ever. I think that the idle noise increase is a result of either my oil breaking down a bit more or because of a kink in my driver side cackle-cure hose. The oil has been running for a little of 6K miles, and I was hoping to take it to 10-15K, but would only do so if the analysis from Blackstone supporst that move. I'm waiting on the resutls from the 6K sample right now to see if it can go further or if it's near its end.

I didn't notice the kinked hose because it was not kinked at first - probably because of the stiffness of the hoses before use. My son noticed the kink about a month after the install, which I believe to be a result of the hoses softening up a little from exposure to the external heat and internal flow stresses coupled with a little "twist" that evidently resulted from the tightening process on the orifice tee fitting.

The kink will be resolved by one of two methods.
1) loosen the hose and re-tighten without any twist.
2) If no.1 method above doesn't work, I'll shorten the passenger side hose by about 1 to 1-1/2 inches so that the driver side hose gets pulled into a more straight alignment position (I've already simulated that by just pulling the hose over, and it does work).

All that said, I'd do the install again for sure. I've seen egnine performance gains (like mentioned in the report regarding acceleration times), and the engine runs very quiet compared to when I first got it. If my oil is "used up", I'll do another cahnge and will be able to tell right away if that is the idle noise culprit. If the noise is from the hose being kinked under no/low load due to low fuel flows, then I'll know that as soon as I straighten the hose (this weekend).

Hope this helps.

 

Wow, that is great information, stuff i stored away in a seperate fuel system memory bank. I can attest to the major spikes in pressure in the oil and fuel rails when an injector fires. I dont know how many knew that i installed a HPO rail pressure gauge, and i settled in the HPO rail port on cylinder 8 for my gauge hose, right under the turbo compressor side. You can feel the hose pulse when the injector fire, but more importantly, trashed a $50 gauge by not putting a snubber in. At idle, the pressure would jump from 400-750 when the injector fired, but averaged at 600ish. when i was really tasking the system for oil (lugging at low RPM) it wouldnt suprise me to see the needle bounce from 1400-2300 or so every time the injector fired. Over time that bouncing became too much for the guage (imagine, it flicking every time the injector fired!) and on my way from BTS to Mike's house i had to pull over an plug the port. Now the gauge reads 2000psi disconnected, the bourdon tube was very tweaked. Ask JTharvey about the black stuff on the gauge face, i think that was actually oil coming through the gauge. If you stuck your ear beside the guage you could actually hear the injector fire through a 6' hose.

 

So knowing about the pressure spikes, is it better to leave the restrictors in? I have noticed that the regulated return kits that you can buy, eliminate the stock feed lines that contain those restrictors. So which is better?

 

I dont know now, i am thinking that you may want to have on the outlet side only, to prevent those spikes from getting to the regulator. Considering all of this, i still think it is pointless to have that little restricted fitting slowing down the inlet of the fuel to the heads. All of that money for my custom fuel system, and then right before it matters most, stick in a tiny restricted fitting? not on my truck. But, i am pondering the idea of putting them on the outlet.

Just think, all that work Tenn did to those fittings to make them less restrictive and a guy comes on here knowing what he's talking about, saying they are fine. LOL

 

Poor Mike!

OK, restrictors in the feed lines kinda bad...restrictors in the return lines, good?!

 

The way I read this, they won't do their intended job if placed on the outlet of the fuel rail.

 

guzzle, of course if you have the stock dead end style system, put them on the inlet side. However, the pump is so far away from the injectors, that it doesn't transmit those pulses that far, or does it? The thing that can break is the regulator, i would want to have that "snubbed". Now when i say regulator, keep in mind i am talking about a regulated return system, regulator on the outlet of the heads back to the tank, not the stock style.

 

Just the other day I moved my fuel line that goes to the back of the driver side head. I didn't realize it was touching the plastic where the back of the hood meets. You know the rubber strip where the wires run across the back of the engine compartment...Well, I get in, start it up and there is this horrible vibration sound. I shut it down quick thinking I left a piece of the intake loose. After about 20 minutes I see the fuel line touching the rubber strip, grab a hold of it and was very very surprised at the amazing amount of vibration. I moved it away, and the sound in the cab was gone.

Note, my system is a "kwik bleed-off system" except I left the stock feed lines in place and tapped into the heads like the new "cackle kit". It works great.