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Old 02-12-2014, 06:09 PM   #1
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Default Megasquirt Boost

Couple of boost questions I'm trying to understand:

I've set my KPA to 180 and that gives me a max boost of 11.5 psi at approx 6400 RPMs

1. The boost doesn't hold a steady 11.5 psi just gets there and then the fuel/spark cut hits and it drops. Is there a way of just holding max KPA without the sudden drop off?

2. If it revs upto 6400rpm on 11.5psi would there be any gain by lifting the KPA limit to 200 to raise the boost? With the max power output supposedly 6400rpm before it starts to drop off would I see 15psi before the rev linter kicked in at 6800 ?

I'm not really understanding where the gain is felt by increasing the KPA to get the boost to say 15psi when it takes 6400rpm to reach 11.5psi, or does it get to 15psi just as quickly ??

Bit of a garbled question but I hope you understand what I'm asking.

Thanks and pointers would be welcome.
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Old 02-12-2014, 06:22 PM   #2
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If you're taking 6400 Rpms to reach 11.5psi, you've got a leak, a turbo that's too big, or no boost control.

You should reach target boost in the 3000-4000rpm range, and if you increase that target, you'll see max boos slightly later, maybe 100-300rpms later depending on turbo, then that target will be held until redline.
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Old 02-12-2014, 06:29 PM   #3
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Ah ok, I've got the garret 2560R Flyin Miata Spec turbo.
Also used an EBC with it set at 100% so wastgate only control to get my min which is 10.5psi. With just a few % off on the control settings it gets to 11.5psi. So I think that means the EBCs working. So leak is the probable cause?

Thanks
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Old 02-12-2014, 07:24 PM   #4
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You're not talking about overboost are you?
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Old 02-12-2014, 07:31 PM   #5
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If you can tell me how to post a picture I'll send a pic of the log, I could post a log file if I knew how to do that too.
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Old 02-12-2014, 07:33 PM   #6
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Open what you are setting so it's up on the screen.
Press the print screen button.
Open MS paint.
CTRL+V.
Save.
Upload.
Post.
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Old 02-12-2014, 07:40 PM   #7
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hmmm, im one of the plonkers with a Mac I cant use..........
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Old 02-12-2014, 07:42 PM   #8
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Then do the mac equivalent. Don't tell me you cant, because i know it's possible.
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Old 02-12-2014, 07:46 PM   #9
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Above with rpms at 4000 and boost just over 5psi (these are WOT pulls in 3rd)



Above with rpms just over 6400 and boost just over 11psi (these are WOT pulls in 3rd)

Like I say it never holds a steady boost level on any of my logs.........
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Megasquirt Boost-4000rpm.png   Megasquirt Boost-6400rpm.png  
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Old 02-12-2014, 08:24 PM   #10
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Looks like a classic case of boost creep on the 2560.

Was the wastegate ported at all?

Edit* you can post the log too. Just upload it using this sites uploader... I don't think i'd need Mac software to view it, i don't think. Maybe someone can confirm.
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Old 02-12-2014, 08:39 PM   #11
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This is what if read about boost creep and it didn't seem to relate to what I was seeing at all ?
Boost creep is a condition of rising boost levels past what the predetermined level has been set at. Boost creep is caused by a fully opened Wastegates not being able to flow enough exhaust to bypass the housing via the Wastegates itself. For example, if your boost is set to 12psi, and you go into full boost, you will see a quick rise to 12 or 13psi, but as the rpm's increase, the boost levels also increase beyond what the boost controller or stock settings were. Boost creep is typically more pronounced at higher rpm's since there is more exhaust flow present for the Wastegates to bypass. Effective methods of avoiding or eliminating boost creep include porting the internal Wastegates opening to allow more airflow out of the turbine, or to use an external Wastegates.


I thought my logs were showing a really slow boost rise which never reached it's maximum.
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Old 02-12-2014, 09:01 PM   #12
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If you have a really slow rise to peak pressure, or your boost is a linear line climbing all the way to red line, then you have a boost leak. Check vacuum lines, couplers, clamps, etc.

Make sure your boost protection is above your target maximum boost. If you want 11.5psi, you'll want to set your over boost protection to 12.5 or 13.5, especially while tuning in your MBC or EBC, since you'll just hit a wall every time you try to adjust it.
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Old 02-12-2014, 09:34 PM   #13
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Yeah, he's right. I didn't look at it closely enough.
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Old 02-13-2014, 02:03 PM   #14
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Thanks for the help, think I'm ready for a leak test with my homemade bungs and valve point made, just need to clamp them up and add attach the pump.....





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Megasquirt Boost-34f15aa6-32a5-4e69-839b-0ac8737e6ffd.jpg   Megasquirt Boost-bfcf5eb6-a244-46da-9c28-7e91d2b935b7.jpg   Megasquirt Boost-b0336b1c-c59c-48a6-b72e-b91bf697aa38.jpg  
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Old 02-13-2014, 02:45 PM   #15
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Pretty Cool pressure tester fab... Impressed actually.
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Old 02-13-2014, 03:26 PM   #16
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Cheers, what I'm unsure about is where I should be bunging !!! Some YouTube vids say just put a single bung in the turbo inlet and blow air in through there. Others say bung the pipe from the turbo outlet and bung before the inlet manifold and blow air in at the turbo outlet pipe. Safest seems the later which I'm trying but that's not testing the turbo or any of the engine / manifold gaskets etc. Any recommendations ? Am I going about this the right way or wrong way? Thanks
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Old 02-13-2014, 08:16 PM   #17
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When i did mine i didn't bung anything. Put my tester on the turbo inlet and pressurized.

TB open and TB closed.

You should be able to hear leaks. Some might escape out the exhaust, and into the valve cover.
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Old 02-14-2014, 10:02 AM   #18
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Ok leak test done and there's one hell of a leak on the BOV. I don't understand the internal workings of these things TBH. It's leaking from the join in the casing next to the tiny hole in the side you can see in the photo. The whole barrel spins around, always has but I assumes that was normal.
Attached Thumbnails
Megasquirt Boost-9b92efb5-57b5-4ac8-94cf-495b0e35a7cd.jpg   Megasquirt Boost-a78b3fc8-73cf-4f49-968b-5429ff246461.jpg   Megasquirt Boost-9b92efb5-57b5-4ac8-94cf-495b0e35a7cd.jpg  
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Old 02-14-2014, 11:22 AM   #19
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That would definately have something to do with it.

Can you find information about your BOV online anywhere?

That said, the BOV is SUPPOSED to vent when there is less pressure on the manifold side than there is on the charge pipe side. The next step is to hook everything back up and check to see if your BOV is venting when the engine is running. If you have two people, have your helper rev the engine without a load. If you have air venting out of the BOV while revving then you need to play close attention to the BOV. IF it doesn't vent until the helper lifts (and you get a "Whoosh" sound) then it is working properly.

Let us know.

Last edited by Chiburbian; 02-14-2014 at 11:33 AM.
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Old 02-14-2014, 12:53 PM   #20
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No helper needed, just spin the little bronze wheel in the right side of this picture and the engine will rev.
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