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Old 10-10-2018, 08:09 PM   #1
VB242
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Default Why does my boost drop off?

I can build 24psi but after I get over ~5k rpms it drops off rapidly down to 15psi. My internal w.g. actuator is 7psi without the MBC, is this my problem?
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Old 10-10-2018, 08:17 PM   #2
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What kind of MBC?
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Old 10-10-2018, 08:24 PM   #3
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Black voodoo something off of eBay, ball and spring type.
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Old 10-10-2018, 08:29 PM   #4
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I should have asked what turbo also. Did you ever keep 24 psi? the springs get whooped up sometimes and stretching it may help
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Old 10-10-2018, 08:35 PM   #5
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Too small of a turbo, too small of a turbine housing/wheel, or the cylinder head doesn't flow.

You have MS, post a MSQ and MSL.
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Old 10-10-2018, 08:41 PM   #6
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Quote:
Originally Posted by 2turbotoys View Post
I should have asked what turbo also. Did you ever keep 24 psi? the springs get whooped up sometimes and stretching it may help
http://forums.turbobricks.com/showthread.php?t=344024
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Old 10-10-2018, 09:46 PM   #7
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Ah, ok. I'm slowly backing away cause I know nothing about turbocharging Kjet, my B21 runs on Megasquirt. Just curious tho, do you put boost through the CIS plate?!? That thing is tiny. But it sounds like tryingbe is right about something being too small, especially the wastegate, that's asking a lot from an internal wastegate. Also from that thread it seems this is not a new problem, it hasn't ever pushed 24 psi consistently. Isn't that out of the compressor efficiency range?
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Old 10-10-2018, 09:56 PM   #8
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Quote:
Originally Posted by 2turbotoys View Post
Ah, ok. I'm slowly backing away cause I know nothing about turbocharging Kjet, my B21 runs on Megasquirt. Just curious tho, do you put boost through the CIS plate?!? That thing is tiny. But it sounds like tryingbe is right about something being too small, especially the wastegate, that's asking a lot from an internal wastegate. Also from that thread it seems this is not a new problem, it hasn't ever pushed 24 psi consistently. Isn't that out of the compressor efficiency range?
No, just the K-jet intake manifold, 2" compressor discharge up to 2.5" ebay intercooler to 2.5" piping to K-jet intake. Siemens 72's stuck in the k-jet holes on the head. Here's a link to a datalog from tonight. I'll post up the msq from my phone in a minute
https://drive.google.com/file/d/10z6...ew?usp=sharing
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Old 10-10-2018, 10:11 PM   #9
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I really think that is too much exhaust flow for the internal wastegate, they just aren't that good, that's for stock applications, that being said I did constantly put 20 psi through a ported 15g for a couple years, but it didn't like it, turbo hot side coked up with white **** and cooked the bearings. Idk, if you have to run that much boost to get the power level you want, I would run a bigger turbo with less boost. Also you haven't said if it ever consistently ran 24 psi, is this a new problem or it just doesn't do what you want. Maybe someone else has some ideas..
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Old 10-10-2018, 10:41 PM   #10
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Msq, what a challenge to upload grr
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Old 10-10-2018, 10:55 PM   #11
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I don't follow your logic, maybe if it was over boosting, then the waste gate hole would be too small. This is a China Bay td05-20g supposed to be good for 400-500hp with their waste gate actuator and waste gate port. Maybe with my gearing it just won't hold the boost? It boosts 21psi in first, 23-24 in second 24psi in the third then drops off as I accelerate, it holds 24 a little longer in 4th then I run out of road.
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Old 10-10-2018, 11:25 PM   #12
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I'll check for a boost leak after the tropical storm goes away
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Old 10-11-2018, 12:28 AM   #13
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How is the return pressure on the actuator? The 15g ones are pretty sad, so even with an MBC they would still creep down since the actuator couldn't keep the gate closed at higher rpm. You could try a helper spring on the gate just for testing, see if that helps.

Also what Harry suggested, could be the exhaust side is too small and becoming a restriction.
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Old 10-11-2018, 07:48 AM   #14
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I went ahead and ordered a kinugawa adjustable waste gate actuator. It doesn't seem like the motor is getting choked off, I think the waste gate is getting blown open.
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Old 10-11-2018, 08:23 AM   #15
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The MSL you gave only shows 22PSI max and it also said you didn't stay in WOT long enough. Stop letting off at 5000RPM



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Old 10-11-2018, 08:37 AM   #16
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Quote:
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The MSL you gave only shows 22PSI max and it also said you didn't stay in WOT long enough. Stop letting off at 5000RPM



Operator error? Probably, I thought I had a couple good 3rd gear pulls though.
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Old 10-11-2018, 08:43 AM   #17
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Quote:
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Operator error? Probably, I thought I had a couple good 3rd gear pulls though.
Did you even check your own log?!?!
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Old 10-11-2018, 08:52 AM   #18
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Quote:
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Did you even check your own log?!?!
I was drunk and needed to go to bed after figuring out how to post the link, so no. But it sure seems like it drops off in the car.
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Old 10-11-2018, 09:05 AM   #19
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Quote:
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But it sure seems like it drops off in the car.
That's just mean your top end is not setup for flow, ie. head, cam, turbo, etc.


Get an adjustable cam gear, put it on the dyno, get a baseline, then retard the cam gear couple of degree, make another pull, repeat until you like where you have power band.
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Old 10-19-2018, 01:14 PM   #20
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So the 24# kinugawa w.g. actuator didn't make much difference, do I actually need the eBay header? Head has stock valve sizes, ipd turbo cam.
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Old 10-19-2018, 05:37 PM   #21
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Quote:
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So the 24# kinugawa w.g. actuator didn't make much difference, do I actually need the eBay header? Head has stock valve sizes, ipd turbo cam.
Sorry, but I didn't follow, what engine?
If you are hoping to run 24psi on a small turbine wheel, you might be asking too much.

That's very high boost with most redblock/whiteblock with a TD04 turbo!
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Old 10-19-2018, 06:59 PM   #22
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Quote:
Originally Posted by 8DOM8S8AN View Post
Sorry, but I didn't follow, what engine?
If you are hoping to run 24psi on a small turbine wheel, you might be asking too much.

That's very high boost with most redblock/whiteblock with a TD04 turbo!
It's supposed to be a td05 housing I have 3" side exit with 11" glass pack, minimal exhaust restriction
This turbo
https://www.speedyracer.com/Turbocharger-TD05-DSM-20G
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Old 10-20-2018, 11:33 AM   #23
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Quote:
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So the 24# kinugawa w.g. actuator didn't make much difference, do I actually need the eBay header? Head has stock valve sizes, ipd turbo cam.
Post your revised MSL.
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