CT15B turbo cannot hold 18psi? - MR2 Owners Club Message Board
 
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post #1 of 10 (permalink) Old April 18th, 2017, 11:20 Thread Starter
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CT15B turbo cannot hold 18psi?

From the beginning of my Gen4 swap I have ran either the CT20b or billet CT20b turbos which I was thrilled with both. Now running the ct15b after having to sell my billet 20b. Im trying to run 18psi but it will not hold the boost at all and just doesnt feel has enough oomph as the 20b's (ran a 12.6@110 with billet 20) car currently feels as a mid-high 13 sec car. It seems to spike up to 18 then immediately drop down to around 15 and slowly go down from there. Im running a ball and spring type mbc from ebay that in fairness did just get at the same time as I installed the 15b. Although I had run same type (ball & spring) mbc (twosrus and hallman) with no boost holding issues and holding to redline. Does the 15b simply struggle with holding boost, especially 18psi?
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post #2 of 10 (permalink) Old April 18th, 2017, 11:23
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Small compressor wheel and weak wastegate spring = unable to hold boost to redline.

Try the ATS Sweet 16 billet upgrade.

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post #3 of 10 (permalink) Old April 18th, 2017, 12:04 Thread Starter
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I plan on the sweet 16 soon as funds allow. Will the billet wastegate help with this issue on the the 15b?
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post #4 of 10 (permalink) Old April 18th, 2017, 12:12
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I doubt it.
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post #5 of 10 (permalink) Old April 18th, 2017, 14:12
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15b is a quick spool small OEM turbo, what did you expect? I'd be surprised if it held 15psi.

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post #6 of 10 (permalink) Old April 19th, 2017, 09:39 Thread Starter
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I expected it to perform at least like the older stock ct20b.
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post #7 of 10 (permalink) Old April 19th, 2017, 15:04
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It's smaller than the 20b but as such can spool very quick. It's not all about max boost.

Jim
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post #8 of 10 (permalink) Old April 19th, 2017, 17:11
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Quote:
Originally Posted by benckj View Post
It's smaller than the 20b but as such can spool very quick. It's not all about max boost.

Jim
more comparable to the CT26 until it's billetized

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post #9 of 10 (permalink) Old April 20th, 2017, 09:37 Thread Starter
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Originally Posted by benckj View Post
It's smaller than the 20b but as such can spool very quick. It's not all about max boost.

Jim
The difference in spool is minimal and certainly does not make up for the lack of power compared to the 20b. Seems like even the ct26 held boost better as it would slowly lose steam up top and boost creep back down in the higher rpm. This feels like it just falls off a table, which make me wonder if its the mbc, wastegate acutator, or the actual turbo characteristics. Car ran w/ gen4 and billet 20b 12.6@110 (shouldve been low 12 had I known how to launch properly), now it feels like it struggles to be a high 13sec car.

Last edited by neemo6; April 20th, 2017 at 09:40.
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post #10 of 10 (permalink) Old April 20th, 2017, 09:55
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Originally Posted by neemo6 View Post
The difference in spool is minimal and certainly does not make up for the lack of power compared to the 20b. Seems like even the ct26 held boost better as it would slowly lose steam up top and boost creep back down in the higher rpm. This feels like it just falls off a table, which make me wonder if its the mbc, wastegate acutator, or the actual turbo characteristics. Car ran w/ gen4 and billet 20b 12.6@110 (shouldve been low 12 had I known how to launch properly), now it feels like it struggles to be a high 13sec car.
i'm guessing weaker wastegate actuator combined with tiny compressor wheel = no bueno

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