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Jun 16, 2009, 11:01 PM
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#1
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Evolving Member
Personal Sales Rating: ( 0)
Join Date: Apr 2009
Location: Santa Rosa, Ca.
Posts: 247
Drives: 2005 Evo VIII
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how much boost taper is normal?
I am fairly new to the evo scene. I recently installed a boost gauge and been reading on here about where oem boost readings are. I guess mitsu set the factory tune to have the boost taper a bit. Here is my question, I found an open road to test my car, in second gear 90% throttle I will boost to 20psi, then it tapers down to 15. 3rd gear at wot it stays at max 14 psi. Kind of weird but it also seems like its hitting a wall, not as responsive in 3rd as it was 2nd trying to accel from 5500 rpm on up,hmm... but in 3rd and 4th it just stays at 14 psi max. I was under the impression it should taper down to ~17 psi, so its quite a bit off. My car is a 2005 gsr, completely stock except for licp, evo 9 DV, and a perrin crank pulley (came with car when purchased). Also with new oem plugs gapped at .024". When I replaced my dv to the evo 9 metal one, I noticed my dv clamps were kind of loose. I want to go through and check all my clamps again, but I dont think that is the issue. I also am not sure if its my tb shaft seals, partly because I am able to boost to 20 psi, just wont hold past 14 psi. So any ideas that might help, thanks.
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Jun 17, 2009, 04:14 AM
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#2
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Location: Mesoamerica
Posts: 3,468
Drives: 2004 RS
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It's pretty easy to build a boost leak tester. Test it for leaks first.
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Jun 17, 2009, 05:00 AM
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#3
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Newbie
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Join Date: Apr 2009
Location: central nj/tampa fl
Posts: 50
Drives: nitrous built dohc vtec 94 ej1
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thats right where ix turbos taper to. i know you have an 05 but they share the same 10.5 hotside. once you get more bolt-ons you'll be able to hold boost better.
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Jun 17, 2009, 05:58 AM
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#4
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Evolving Member
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Location: Santa Rosa, Ca.
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Drives: 2005 Evo VIII
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Quote:
Originally Posted by evoluvinevo
thats right where ix turbos taper to. i know you have an 05 but they share the same 10.5 hotside. once you get more bolt-ons you'll be able to hold boost better.
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interesting. I am gonna do a boost leak test, but I also wanted to make sure I am not trying to diagnose something that is completely normal,heh. I have been trying to do a search on the perrin crank pulley, someone told me that due to it not having a dampener my engine could be pulling timing, reading knock from it. 
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Jun 17, 2009, 06:07 AM
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#5
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Location: central nj/tampa fl
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Drives: nitrous built dohc vtec 94 ej1
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not dampening vibrations in the rotating assembly isnt enough for it to register as knock. only occurrence from an undampend unbalanced crank pulley is accelerated bearing wear. as far as doing a boost leak there arent any leak issues with your car. 20 is avg peak boost and 15 is avg boost taper by 6500 on a bone stock no-bolt ons 9....its sad. to reiterate what i said before once you start getting bolt-on's full exhaust,intake,uicp and ic you'll hold boost much better and reach peak boost your actually tuned at.
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looking for a special edition apex silver or graphite grey evo 9 in central florida area.
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Jun 17, 2009, 08:21 AM
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#6
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Location: Oak Harbor, WA
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Drives: '05 Tarmac Black SSL VIII
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It never hurts to do a boost leak test every once in a while.
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Jun 17, 2009, 09:25 AM
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#7
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Evolving Member
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Location: Santa Rosa, Ca.
Posts: 247
Drives: 2005 Evo VIII
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Quote:
Originally Posted by evoluvinevo
not dampening vibrations in the rotating assembly isnt enough for it to register as knock. only occurrence from an undampend unbalanced crank pulley is accelerated bearing wear. as far as doing a boost leak there arent any leak issues with your car. 20 is avg peak boost and 15 is avg boost taper by 6500 on a bone stock no-bolt ons 9....its sad. to reiterate what i said before once you start getting bolt-on's full exhaust,intake,uicp and ic you'll hold boost much better and reach peak boost your actually tuned at.
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Good news,thanks.. well not so great, boost taper sucks. But good to know im most likely ok. I have a oem crank pulley I want to swap back in this weekend. The specs are nice from the advertisements for the perrin piece, but it just seems better to have a dampened pulley, imo.
Previous owner had this car pretty much stock except for a turbo timer and a perrin pulley. Interesting selection of first mods,  .
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