13G turbo's can't hold boost till redline - 3000GT/Stealth International Message Center
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Old 03-07-2016, 11:36 PM   #1 (permalink)
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Default 13G turbo's can't hold boost till redline

Alright guys, so here's my story. I have my boost set to 16 psi and it was dropping consistently after 4500 rpm to 12 psi by redline. I had boost leaks in my throttle body which I recently fixed. I thought the problem was solved but I still can't hold till redline. I drop to about 13.8 psi so it's gotten better but still not 100% resolved. I have an evap smoke machine which I use to test for the leaks. My question is this. I have the stock exhaust with an aftermarket downpipe which replaces the main cat and one of the precats. One of the precats is still there. Could this be my problem?
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Old 03-07-2016, 11:43 PM   #2 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

Make sure your wastegates are preloaded properly
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Old 03-08-2016, 12:17 AM   #3 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

I thought preload just affects spool times.
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Old 03-08-2016, 02:06 PM   #4 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

Pre-cats are a massive restriction at higher rpm/ load.
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Old 03-08-2016, 04:44 PM   #5 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

Which 13G's are these? there are many types, the biggest reason why our car's can't hold full boost at redline is more the turbine size, then the compressor wheel, but the size of the compressor wheel doesn't help either.

There also if you have Euro13Gs , that won't hold full boost to redline either.
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Old 03-08-2016, 05:05 PM   #6 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

My UK spec turbos (11g?) Held 16psi to redline, spiked up to 26psi lower down the revs.
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Old 03-08-2016, 05:30 PM   #7 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

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Originally Posted by Warzone View Post
Which 13G's are these? there are many types, the biggest reason why our car's can't hold full boost at redline is more the turbine size, then the compressor wheel, but the size of the compressor wheel doesn't help either.

There also if you have Euro13Gs , that won't hold full boost to redline either.
I believe they are just the tdo4 13g's. I bought them new off of a guy on the forums back in 2004.

Another thing I notice whether it is related or not is if I hold my foot half throttle and it boosts to like 7 psi, as the rpm increases it will also drop by redline.
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Old 03-08-2016, 11:20 PM   #8 (permalink)
Talk about a shortshifter
 
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Default Re: 13G turbo's can't hold boost till redline

Could be clogged or rotted precat but doubtful. No i couldnt go over 14psi when my wastegates were messed up.
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Old 03-09-2016, 01:25 AM   #9 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

Yeah, my precat isn't clogged. I'll gut it out anyway and see if it makes any difference. What about the MBC?

Last edited by yellowVR4; 03-09-2016 at 01:26 AM. Reason: more info
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Old 03-10-2016, 02:18 AM   #10 (permalink)
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Default Re: 13G turbo's can't hold boost till redline

Have you ever been able to hold more boost than that to red line or has it been like that since you installed them?
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