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Old 05-14-2013, 11:59 PM   #1
Fenrir
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Stock Direct Injection PSI

I've done some searching and haven't come up with anything (apologies if it was mentioned somewhere else already, I did search for a good 20 minutes here and on google), so figured I'd start a new thread.

Has anyone been logging the PSI on the HPF system? I've been seeing some strange numbers, and want to compare against a different logging solution. I'm using a DashHawk with custom PIDs entered in. Fuel PSI is hitting 3k at WOT at times according to my logs, curious if anyone else has been paying attention/noticed similar results or if my logs are just bunk. Attached the logs if anyone cares to look. Nothing exciting, just a few 2nd/3rd gear rolling pulls.
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Old 05-15-2013, 08:42 PM   #2
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Originally Posted by Fenrir View Post
I've done some searching and haven't come up with anything (apologies if it was mentioned somewhere else already, I did search for a good 20 minutes here and on google), so figured I'd start a new thread.

Has anyone been logging the PSI on the HPF system? I've been seeing some strange numbers, and want to compare against a different logging solution. I'm using a DashHawk with custom PIDs entered in. Fuel PSI is hitting 3k at WOT at times according to my logs, curious if anyone else has been paying attention/noticed similar results or if my logs are just bunk. Attached the logs if anyone cares to look. Nothing exciting, just a few 2nd/3rd gear rolling pulls.
3,000psi sounds about right. The DI system has to inject fuel into the cylinder at full compression at the top of the stroke when cylinder pressures are at their highest. That's how a DI system works...this is why the Direct Injectors have metal hardline's unlike the flexible fuel hoses of the port injectors, it's also why the DI system has a separate mechanical fuel pump as the electrical fuel pump in the tank cannot pressurize the fuel to a high enough PSI for use in the DI system.

For reference, Diesel engines have used Direct Injection exclusively for years. Diesels have compression ratio's on average anywhere between 16:1 and 25:1 (vs. the 86's 12.5:1) and Diesel direct injection systems often operate at 25,000psi or more on the bigger commercial diesels.
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Old 05-15-2013, 08:45 PM   #3
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3,000psi sounds about right. The DI system has to inject fuel into the cylinder at full compression at the top of the stroke when cylinder pressures are at their highest. That's how a DI system works...this is why the Direct Injectors have metal hardline's unlike the flexible fuel hoses of the port injectors, it's also why the DI system has a separate mechanical fuel pump as the electrical fuel pump in the tank cannot pressurize the fuel to a high enough PSI for use in the DI system.

For reference, Diesel engines have used Direct Injection exclusively for years. Diesels have compression ratio's on average anywhere between 16:1 and 25:1 and Diesel direct injection systems often operate at 25,000psi or more on the bigger commercial diesels.
Yeah, quite familiar with the systems in general. My Speed3 runs around 2k PSI on an upgraded pump (1500-1600 is average on the stock pumps, which were notorious for going bad, but that's a whole other thing altogether...), so I was just curious where these cars sat on the stock system. I wasn't so much questioning 3k because it seemed high, as much as trying to gauge where my datalogging is at as I'm using a fairly unconventional method.
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Old 05-15-2013, 08:48 PM   #4
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Yeah, quite familiar with the systems in general. My Speed3 runs around 2k PSI on an upgraded pump (1500-1600 is average on the stock pumps, which were notorious for going bad, but that's a whole other thing altogether...), so I was just curious where these cars sat on the stock system. I wasn't so much questioning 3k because it seemed high, as much as trying to gauge where my datalogging is at as I'm using a fairly unconventional method.
Ah, I cannot attest to the accuracy and precision of your data logging solution however as long as your readings are consistent then you should be able to use them in your research I don't know what the compression ratio of the Speed3 is but I know that the PSI needed for Direct Injection increases Logarithmically compared to the compression ratio. So therefore the a system with a higher compression ratio will need MUCH more PSI to overcome cylinder pressure.
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Old 05-15-2013, 08:49 PM   #5
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Ah, I cannot attest to the accuracy and precision of your data logging solution however as long as your readings are consistent then you should be able to use them in your research
Not without accurate readings I can't.
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Old 05-15-2013, 09:28 PM   #6
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I've seen 3K pressure too.
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Old 05-15-2013, 10:04 PM   #7
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3,000psi sounds about right. The DI system has to inject fuel into the cylinder at full compression at the top of the stroke when cylinder pressures are at their highest.
Just wanted to point out a small detail, in concept this is how you might think DI should work but it depends on the particular system and the operating conditions. Also the fuel should never be injected at the top of the stroke otherwise there would be no time for the fuel to mix with air before ignition, I believe the direct injectors on these Toyota systems fire halfwayish up the compression stroke, but it's possible that they fire on the intake stroke too (I can't quite recall).

Diesels are different because they don't inject fuel then ignite it, the two processes happen simultaneously so the diesel injector has to be able to supply fuel at maximum cylinder pressure which is much higher than even the pressure at the end of the compression cycle.

The high pressure is not only because you need to get the fuel straight into the cylinder instead of just pump a bunch into the intake tract (which has more room), but also because the shorter amount of time the fuel has to mix with the air means you want it to vaporize more quickly.

Aside from less heat soaking into the fuel from the valve and head, another benefit is having fuel go straight to the piston, so that less ends up on the cylinder walls, the piston gets a little cooling, and more fuel is concentrated around the spark plug.
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Old 05-16-2013, 10:23 AM   #8
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The Mazdaspeed 3 engine could be considered an early generation GDI system. It uses swirl injectors. Newer GDI runs up to about 20MPa, similar to what OP is seeing (3000psi=almost 21MPa).

The current generation diesels run up to 180-200Mpa. The newest systems coming out are about 250-300MPa.
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Old 05-16-2013, 03:27 PM   #9
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The Mazdaspeed 3 engine could be considered an early generation GDI system. It uses swirl injectors. Newer GDI runs up to about 20MPa, similar to what OP is seeing (3000psi=almost 21MPa).

The current generation diesels run up to 180-200Mpa. The newest systems coming out are about 250-300MPa.
Sure, that's why I was looking for a baseline as I couldn't find any information elsewhere on the system in this car.

Thanks everyone for the info, looks like my data is accurate so I can move forward.
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Old 05-16-2013, 05:11 PM   #10
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Yeah, quite familiar with the systems in general. My Speed3 runs around 2k PSI on an upgraded pump (1500-1600 is average on the stock pumps, which were notorious for going bad, but that's a whole other thing altogether...).
I thought I recognized your sn, I'm running a CPE full replacement and still only see 1600 psi, what the heck are you doing to get 2000?

Also, DH seems to be working on the 86? Maybe I won't sell it when I part out after all...
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Old 05-16-2013, 05:30 PM   #11
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I was using the torque pro app to monitor the pressure of the high pressure rail from the ECU. At idle i was getting around 750, light load was about 1500 and high load floated around 1900. But i stopped mentally tracking it a while back, dunno if my memory is accurate.
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Old 05-16-2013, 06:11 PM   #12
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I thought I recognized your sn, I'm running a CPE full replacement and still only see 1600 psi, what the heck are you doing to get 2000?

Also, DH seems to be working on the 86? Maybe I won't sell it when I part out after all...
Big turbo and I don't run CP-e garbage.

In reality it's around 1900+, but it'll hit 2k.

DH seems to work just fine. Lots of stuff it monitors. Although when the DI turns off, it gets very confused and the fuel rail pressure just keeps counting up.

I also noticed a slight discrepancy between the digital speedo in the dash and the DH speedo, but I'm not too worried about it.
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Old 05-16-2013, 06:36 PM   #13
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Do you run KMD pumps then?

I also see ~3k in my logs for the FA20's I have logged.
Also noticing the creeping of rail pressure while DI is off.
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Old 05-16-2013, 07:09 PM   #14
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Originally Posted by arghx7 View Post
The Mazdaspeed 3 engine could be considered an early generation GDI system. It uses swirl injectors. Newer GDI runs up to about 20MPa, similar to what OP is seeing (3000psi=almost 21MPa).

The current generation diesels run up to 180-200Mpa. The newest systems coming out are about 250-300MPa.
Yes, the stock maps target from 2.5 Mpa at the lowest load up to 20Mpa at WOT.
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