I'd like your all's opinion on this. There's been some recent talk that high fuel pressures will greatly increase the performance of the truck. I believe ramsmoker is running around the 95 psi range, obvioulsy higher than the 60-65 psi that most people with a shim kit or external regulator are running. The only downside I've heard to this high of fuel pressure is a concern with the stock fuel bowl leaking at the o-rings for the drain valve, or blowing out the plastic cap. But, I also think that it's putting extra strain on the fuel pump, thus decreasing it's life.

So, I've got an idea. My external regulator has a boost reference port on it. I can hook it up to a boost line coming out of the manifold, and pressure will rise at a 1:1 ratio with boost. I'm thinking about trying this out. I don't have my fuel bowl anymore, so that's not a concern. I can set my regulator at 60-65 psi with no boost, but when the boost comes on it will ramp up to 85-90 psi at peak boost, in theory anyway. That way, at light throttle, low boost times, the fuel pump won't have extra strain on it, but when the boost kicks up and more performance is needed, the fuel pressure will rise accordingly to help supply the extra fuel. What do you think?

I've pretty much decided I'm going to try this. We all know I've been the test subject for things here before, so I have no problems trying it. I wanted to get some opinions here to see what you all think, things to look out for, etc...

 

Definately sounds interesting. Has anyone run a baseline difference in fuel pressures on overall hp/tq? I'm wondering if something like this will yield higher results to go along with the higher boost, or if it will be diminishing returns. Will you be testing stock pressure vs. shimmed regulator vs. your theory? That would be cool to see the difference and what was affected the most (low rpm, midrange, or high rpm).

 

Sounds like a great idea. My regulator doesn't have that port, only a safety release port that I plumbed a hose down to the frame rail.

 

JT, I think this will absolutely work and wonder why diesels don't have this provision right from the factory. If pump longevity is your concern, then that should solve the higher PSI issue.

I know for a fact that ford gasser poweradder kits come with an adjustable regulator that references vacuum in order to increase pressure in the lines feeding the injectors. Of course those kits come with a bigger fuel pump too in order to supply the fuel, but that would not be an issue with our pumps because it's already made to supply a turbocharged engine and there's no detonation issues.

I'm sure there are PCM tuning parameters to consider with this as well. Since you and Jody are in frequent touch, and you have his chip, I would ask him about those and see what he says. I would be curious to hear his response.

Are you planning on referencing boost to increase the pressure? ON EDIT: I see that you plan on referencing the boost. That Aeromotive has a boost reference port? Or vacuum?

 

If I remember right, and your gallery pics are current, you've got an ITP fuel system. ITP uses the exact same regulator in their fuel systems that I have in mine. ITP just calls it a safety release port, but it's actually a boost reference port. You should be able to do the same thing with yours, as I am with mine. Click here to see the Aeromotive site for this regulator and where you can download thier user guide: http://www.aeromotiveinc.com/pdetail.php?prod=11

Pocket, the theory of stock vs. shimmed (to approx 60-65 psi) has been done by several different members, including myself, before I went with an externally regulated system. The shim showed an increase in performance ove stock. Stock pressures can be anywere from 45-55 psi. I'll only be testing to see if there is an increase in performance as fuel pressure increases with boost pressure.

 

Yes. Start off with approx 65 psi as set by the spring in the regulator. Then, reference boost to increase pressure.

I'll run this by Jody. I've got to call him tomorrow anyway.

 

Cool. I would think the best results would be obtained by somehow trying to stay ahead of the boost with the fuel pressure but haven't really invested any brain matter into it because you can't seem to stay ahead of something that is supplying the signal in the first place. But if you could, it would be a runaway train. Even a delayed increase with reference to boost should still net some real nice results.

 

I've thought about that, but you're right, there's just no way to predict boost. I have considered tapping into the hot side of the intake spider though. It would provide a little more responsive signal, since it would see boost before it goes through the intercooler. I actually plan on moving my MAP sensor line to the hot side, for faster response, and it would be pretty simple to put the boost reference line for the regulator there too. But, I've got an open output on the cold side (where the wastegate hooked into), so I'm just going to try it there first, before I go drilling and tapping the spider.

 

I don't know JT. Just thinking out loud here, but unless you feel your first restriction is at your intercooler, I would think you would get a higher/quicker boost number downstream at the spider/y-pipe right before the heads as this is where the cramming or boost will first build trying to get into the cylinders. I would think it then backs up towards the turbo from there as more air is pushed.

With your new IC, I think you're better served closer to the engine.

I'm thinking the AIH plug is optimum, and already available. A simple T perhaps.

 

Interesting idea, Jeremy. I'll be looking forward to seeing what you find out.

I know from reading I've done that a lopey idle from fuel pressure cranked up is because fuel is leaking prematurely into the cylinders, and this is why it's not the best idea to just crank up the fuel pressure. The optimum fuel pressure is enough to ensure full filling of the injectors but not so much that fuel leaks into the cylinders.... and this is generally 65-70 psi. It will be cool to see if the higher fuel pressure at higher boost where the fuel's in high demand helps performance, but then back down at lower demand such as idle or cruising, you get back to the optimum fuel pressure and don't get fuel leaking into the cylinders. Cool idea, looking forward to seeing your findings!

 

Once again looking at the cross section of the injector, I find it difficult to believe that more pressure is going to do all that much except refill faster.

Other than check valve leakage where and how do these things leak under higher pressure??

 

I agree with you here. But, that's what I'm wondering if it can't be improved upon. By that, I mean at higher demand and RPM, is the injector really refilling up entirely after every time it fires. At 3000 RPM, the injector is firing 25 times every second. I would tend to think that at that point, increased fuel pressure is going to help ensure that the injector is refilled completely.

 

OK you and I are somewhat in agreement about the effects of increased pressure.

HOWEVER: How much more viscous is diesel under pressure than Gasoline?? I mean the gas guys are running much less fuel pressure into their injectors and they DO tend to rev way up past where the computer shuts us down. Even the top fuel drag guys don't run all that much pressure (I think). OTOH, warming up the fuel to say 80*F might acomplish the same result as 20 lbs of extra pressure. Perhaps an experiment with a mix of diesel 1 might be in order?

Finally: what exactly is the end result: more flow or a better pattern? If flow is the result, might not the pcm readjust the injector timing back down into an ineffecient part of the envelope. I'm guessing but I believe that the amount of "on" time for the IDM is what determines fuel spray quantity.

 

I think one large factor in this is the injector pulsewidth. They can be programmed to stay open for a long time, longer than the time it takes the plunger to make a cycle, to ensure that ALL the fuel in there is emptied out and used up on each squirt.

It seems that the higher fuel pressure will help refill the injectors after this, but I don't know how much higher over 70 one could go and still reap benefits from it. Jeremy, this seems like it could turn into a pretty good experiment. Definitely run it by Jody and see what he has to say. I know he can control pulsewidth and such with programming, but I wonder what he'll say about added fuel pressure at the higher boost.

Has Rossi had anything to say about this, yet, in his arena? Bound to get a lot input.

 

I ran it by Jody today. He ran some higher fuel pressures in his truck, and he did say it ran stronger. But, the high fuel pressure caused it to idle rough. He liked the idea of referencing boost, and seemed to think it would work just fine. It shouldn't require any programming changes.

The end result is going to be more flow to the injector. It will not directly affect the pattern, only possibly indirectly by providing more fuel for the injector itself to actually pressurize and inject into the cylinder. The increase in fuel could make for a better spray pattern.

The PCM will not adjust injector timing back down. The PCM has no way of knowing what fuel pressure is being run into the heads. Plus, if I remember correctly, the injector timing is controled purely on a set of tables. The value of the injector timing is found by RMP and throttle position, like 85% throttle at 2200 RPM will give a set injector timing. That timing will always be the same at that throttle position and RPM.

Rossi has been quiet. May not say much, if anything, at least until the tests have been run and some results found.