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After my motor warms up my fuel pressure at idle typically hovers around 30psi. So that's roughly about 5psi less than what it should be. Is 5psi enough to cause my problems?

Mmmmm... sexy teardown pics!

Aw you'll be fine. It'll be just like when I take my scout group hiking. The slowest goes in front to set the pace. You'll have fun because I'll be trying to stay on your tail, and I'll have fun because he'll be trying to stay on my tail. Even the slowest car can break ahead of the group at times, so having more HP in the rear gives everyone the ability to catch up with the car they're behind. It also helps keep the group's speed mostly under control. I'm all for driving dangerously fast, but driving fast as a group in an uncontrolled environment is asking for trouble. I like to think of it as driving irresponsibly, in a responsible way

Do it! I'd have to print it in at least 3 parts, probably more like 6 (2 high x 4 wide), but I'll totally try it out.

So, when are we all going to go for a drive?

Don't forget to include the new turbo, gaskets, hoses, hose clamps, extra bolts that WILL break, a few new tools of some sort probably, exhaust heat shields/wrap, gallons of coolant, gallons of oil, oil filters... I'll spare you the rest.

Is your "buddy" the Internet? :lol: Of course your friend wants you to do a forged build and shoot for 400-450hp. Those are the fun motors to talk about, and it's YOUR money. That's just human nature. Before you set a target on a high HP number do a few more hours worth of research about what kind of maintenance and repairs you'll be fast-forwarding to. More HP usually means driving faster, stopping faster, and turning faster. 450hp is almost double what the car was designed for. That's an awesome thing to shoot for, but all of that extra "enthusiasm" will put more than normal wear on all of the functional bits and pieces scattered throughout the car. Things will start failing before you want them too, and your car could turn in to a death-trap before you realize it. Brakes (not just pads and rotors), suspension parts, bushings everywhere, the clutch, axles, wheel bearings... you get the idea. You're not stupid for wanting more HP, but can you afford everything that comes with it? Doing stupid/awesome things to vehicles is totally fine by most car enthusiast's standards, as long as the builder knows what he's getting himself into (or has a ton of $$$). I enjoy maintaining my family's vehicles, but my financial situation is far from being able to keep up with owning a "built" Subaru. I don't want to keep my car mostly-stock for another 100k+ miles, but my wallet really really really really needs that to be a viable option. That's why I rebuilt my motor back to stock. Yes it was painful, but sometimes reliability trumps driving fast. TL;DR More HP increases the overall cost of owning the car, sometimes to the point of being too much to handle financially.

For their builds they use new assembled shortblocks from Subaru, and swap out the new OEM pistons with aftermarket forged pistons. Then they sell the OEM pistons as new "take-outs". I don't think they sell rods like they sell pistons. So if a successful motor builder starts 9 out of 10 "motor builds" with a new assembled OEM shortblock (per their website), what does that suggest most of us on here should do? Bingo! Unless you really want the experience of rebuilding your motor, it almost always makes more financial sense to just buy a new SB from Subaru.

Heat in general is a bad thing because it's energy spent on something other than moving the vehicle. However, the system as a whole is most efficient when the motor is warm, which is why that's the normal operating temperature. If it were more efficient for the motor to run at 120° then I assume Subaru would have designed it that way. On the other hand, the fuel pump is an electric motor and it doesn't like heat. It's even mounted way back inside of the gas tank just to help keep it cool. I'm in an assuming mood today, so I'll assume that a correctly functioning OEM fuel pressure regulator is designed to be able to handle engine bay temperatures because that's where the engineers put it. If coolant temp looks correlated to my effective fuel pressure then you might be on to something. What heats up with coolant that can somehow affect fuel pressure? I'll also try to log engine bay temp. My EGT probe isn't inside of the exhaust anymore for just this reason. I can't remember if I ever tried it out to see if the probe is accurate at that low of temps (compared to inside the exhaust).

Or you can get away with $0 of machine shop labor if you do it all yourself Check out my (re)built thread if you're curious. I also used a flex-hone for my block and it worked great. One of my cylinders had a large gauge in it (my fault) and honing the crap out of that cylinder more-or-less completely took the gauge out. It's not the most correct way to do it, but the 7.5k miles I've put on it says it's "good enough". My gauge was much worse than your scoring looks, so I'd bet money that a flex-hone will work for you. Plenty-o-pics in my rebuild thread. If you rebuild the block instead of just buying a new one, go to Crawford Performance for new OEM pistons. They're brand-spanking new and only cost $25 each. Send me a PM if you want my OEM cam bolts. They came out easily and are still fully functional. I'm thinking $10 for all four would cover flat-rate shipping (assuming you're in the US) and the inconvenience of waiting in line at the post office.

Food for thought. Would it make any sense if my fuel pressure were somehow related to coolant temperature? On my drive home today I'll try to spend more time at high RPM+low speeds (the middle section in this chart), and I'll also log coolant temp. *Always obey the posted speed limits.

I don't think I'm out of the woods yet with the fuel pressure. Here's my logic: (1) Removing the pressure reference line from the FPR causes the FPR to operate solely under spring pressure. (2) The pressure reference line on the FPR helps the internal spring to push less/more, which lowers/raises the observable fuel pressure. The purpose of this is to account for vacuum/boost inside the cylinders that's working with/against the injectors. That calculated difference (cylinder pressure vs fuel pressure) is effective fuel pressure. (3) Effective fuel pressure changes with vacuum/boost at a ratio of 1:1 (on our cars). (4) Because of that simple 1:1 ratio, my effective fuel pressure at any RPM (calculated) should be identical to what the FSM specifies the fuel pressure should be at idle (observed) without the the pressure reference line. FSM spec @ idle w/o ref line: 41-46 psi My calculated effective fuel pressure @ any RPM: 33.2-42.2 psi At the worst times I'm 7.8 psi below spec (41-33.2), and on average I'm 2.38 below spec (41-38.62). Looking at it as reasonably positively as I can, my FPR is at least 2.38 psi out of spec. Is that enough to cause constant problems? Is that enough to cause problems under certain conditions, like when target AFR is close to 14.7? Is that enough to worsen the stumble/stutter issue associated with the FPR?

My formula for effective fuel pressure was wrong in my last chart (duh). It's corrected now, and the chart is a little more useful because the correct formula shows that my injectors (in that particular log) saw an average effective fuel pressure of 38.623 psi.

When are you going to commit to max fuel savings and cover your rear wheels?

It's difficult researching stuff online without finding evidence that supports what I'm already wanting to hear. Example

Here's what's happening during acceleration. Sorry for the busy chart. It's curious that my AFR is a little lean (14.9 per wbo2) in the same range as my stumble zone, and that's right around where [boost(abs)+FuelPres] = 0 psi ± 1 psi. **edit** In my original chart I calculated the combined fuel+boost as Boost(abs)+FuelPres, which is incorrect. I corrected it to be (Boost*-1)+FuelPres. Explained: Negative manifold pressure (vacuum) increases effective fuel pressure, and positive manifold pressure (boost) decreases effective fuel pressure.

Thanks, we're definitely blessed.

At idle I'm a little lower than what the FSM specifies, sometimes way lower. The inconsistency may be enough to indicate a failing FPR. I just don't know very much about this stuff yet. I have the FP set to run at 66.7/66.7/100 so that's not it. I changed it a while ago hoping it would help... nope. On a semi-related note, BtSsm crashed on me yesterday/today when I was trying to view a log, so those crash reports are from me. I don't know how long the underlying issue has been present because I don't usually view logs on my phone. Here's what happened: logging > stopped logging > unplugged phone (tactrix) > selected car profile > navigated to logs > selected the log > tapped "graph" > crash HAHAHAHAHHAHAHAHAHAHAHHA no. A couple weeks ago we found out baby #5 will be here in December, so saving up to replace our minivan is a slightly higher priority than spending extra money on the LGT. I think we'll end up with a 12-passenger Ford or GMC van. I learned how to drive on a 15-pass Ford so the idea of having a big van doesn't intimidate or turn me off like I think it would most people. Anyway, there aren't many affordable options for carting around 7 people plus a yardsale-worth of junk (strollers, wagon, bikes) that my wife usually likes to keep in the van. How she still functions with a minivan and our four kids right now is amazing. Big van bonus: they're as strong as full-size trucks, and you can fit multiple sheets of 4'x8' plywood and 2x4's inside WITH the benches still in. Our van won't look cool at all... but (cheezy grin) it could.

Maybe I spoke too soon. On my drive home I mostly saw 25-26 psi at idle. Sent from inner space.

My fuel pressure sensor is hooked up and working as well as I'd hoped. So far I've only closely looked at the pressure at idle. With the motor warm, here's what I see. What are your guys' first thoughts?

Wow, that's definitely outside of the normal realm of likely causes. Last summer I rebuilt my heads, so I happen to know for a fact that the guides are where they should be. All of those messy details are in a different thread so don't feel bad about missing it. ALL SUGGESTIONS / TIPS / TRICKS are welcome in this thread.

I used high pressure hose and fuel injection clamps.

The engine was running and I had BtSsm open. I really need (want) to get the bluetooth BtSsm adaper. Running back and forth from the engine bay to inside the car is annoying. Ugh, life in a first-world country is such a drag sometimes. For the vacuum ref line. I understand that the purpose is to change the source of the reference, but for whatever reason I also though a longer line was beneficial. For a few minutes I had a 3-ft section of fuel hose instead of the stock ≈10-in, but it didn't change anything so I cut it up into a few pieces to use for my fuel pressure sensor install (1 pc for each side of the T, and 1 pc about stock length to use if I take out the T). How long of a hose are you using? I finally got my fuel pressure gauge plumbed in yesterday and now I have about 8" more line than before.

Uh oh... the guy with the fuel damper thread saw negative things (more misses) when he combined the tightened damper with several feet of hose on the FPR ref line. Coincidentally that's exactly what my current setup looks like, so maybe switching back to a shorter hose will help me.

I moved the FPR ref line from the IM to the BPV, but I didn't see any change in the misses or stumble. I used about 3 feet of silicone hose because that's what I had laying around. It's all coiled up around the fuel lines for now. I "acquired" a couple brass fittings from work this morning so I'll have the fuel pressure sensor hooked up this weekend. I made a fitting last weekend but I couldn't get it to not leak. The threads I put in using my 1/8npt harbor freight tap totally suck. The same tap worked well enough when I used it in the oil pressure sensor in the block, but I used liquid gasket to seal that puppy up good. I'm really hoping to learn something by seeing what the fuel pressure is doing while it misfires.