adisco
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Boost drop :/
Car: Mr2 turbo 1991
Problem: Ive got a problem with boost drop that i still havent figured out. Boost will get up to 17psi and will drop down to 12-14 psi at around 5000rpm onwards...
With my old set up i ran the following mods:
-2.5inch exhaust with knocked out cat
-Aftermarket side mount cooler
-Standard ECU with FCD
-Ct26
-Turbotech manual boost T set to 17psi (these are pretty reliable, used them on many of my other cars i used to own.)
I than upgraded ecu to Blitz Acess ecu, i also upgraded turbo to CT20b and that didnt fix the boost drop.
I need ideas on what i could try to resolve this boost drop pls:
So far its not:
turbo
actuator
ecu
Other possibilities? aftermarket IC? Standard knocked out cat? Ideas please.
Thanks for reading, ADZ.
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Mrskylighter
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Re:Boost drop :/
2012/07/04 20:59:07
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Have you disconnected the T-VSV valve from the wastegate?
On the wastegate there is two hose connections.
One goes to the turbo compressor or intercooler pipe.The other goes to a valve under the inlet manifold which the ecu uses to limit boost when the engine is cold or when knocking etc.
If you haven't already done so, block off that second connection on the wastegate so you only have the one conection to the turbo compressor or IC pipe.
Does that sense?
If you have already done the above then i have no idea what the problem is :)
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adisco
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Re:Boost drop :/
2012/07/04 21:51:45
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Ye ive already done that thx. Any other ideas?
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just_ace
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Re:Boost drop :/
2012/07/04 22:15:43
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I wonder if you just getting a spike to 17psi, but stables at 12psi?
Or possibly ign break down in higher rpm?
Wouldnt think boost leak.
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MR2QIK
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Re:Boost drop :/
2012/07/04 23:05:58
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MR2QIK - "The Little Car That Could"  320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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adisco
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Re:Boost drop :/
2012/07/04 23:29:16
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just_ace
I wonder if you just getting a spike to 17psi, but stables at 12psi?
Or possibly ign break down in higher rpm?
Wouldnt think boost leak.
I may or may not be. In my opinion its not because ive started with 10 psi and gradually upped my boost. Holds 17 psi from 2 800rpm to about 4500rpm and than the dropping starts...
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adisco
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Re:Boost drop :/
2012/07/04 23:30:50
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MR2QIK
What BOV are you using?
Standard BOV... Is the knocked out standard cat maybe causing the boost drop?
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MRTurbo
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Re:Boost drop :/
2012/07/05 14:01:41
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Even though you may think the Turbotech MBC can ruled out, I would still try another MBC and also check the length of vac hose to the actuator etc. shorter the better.
Also the standard downpipe and Cat is pretty restrictive regardless of thw guts having been knocked out of it.
1990 SW20 GT 3S-GTE Targa 2001 Honda CBR600F4i 
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adisco
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Re:Boost drop :/
2012/07/05 14:43:58
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MRTurbo
Even though you may think the Turbotech MBC can ruled out, I would still try another MBC and also check the length of vac hose to the actuator etc. shorter the better.
Also the standard downpipe and Cat is pretty restrictive regardless of thw guts having been knocked out of it.
Yea, the vac lines are pretty short. Guess ill borrow mates BC and make sure that its not my boost T. After that i guess all that is left is downpipe, and if that doesnt fix it, ill look at the cooler, as i dont know what brand my aftermarket cooler is...
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just_ace
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Re:Boost drop :/
2012/07/05 17:23:36
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The std dump wroth cat punched out should still allow decent boost to redline shouldnt drop that much.
Either way should still get a 3 in dump.
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TRD2000
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Re:Boost drop :/
2012/07/10 09:04:30
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my first thought would be that the turbo just cant get enough air through to sustain 17psi as the revs get up and you use more air.
if the turbo CAN sustain it, my next thought would be that perhaps your intercooler core is too restrictive to flow the higher mass flow rate of air and the pressure drops.
if it's not that then possibly the exhaust manifold/adapter for the new turbo has something wrong, but another possibility..... but have you considered where you're reading boost from? has it been from the same point the whole time or have you changed from teeing into the wastegate line to direct on the manifold or vice versa?
has it EVER held 17psi? or is that just a target you think you should be getting?... it's not uncommon for turbos to drop away in the top end as either their compressor can't flow air or they start to choke up the exhaust and come out of their efficiency bubble.
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EssDub
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Re:Boost drop :/
2012/07/10 10:51:15
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From experience, that sounds exactly like the type of spiking you get from MBCs. Are you using a Tee-piece with a ball and spring arrangement for surge control? Is the controller as close to the turbo as you can safely get it? (in accordance with its instructions). MBCs are typically slow to respond to fast-spooling turbos, my Turbosmart MBC took around a second or so to regulate the boost on my old car, running at 1bar - It'd spike to 1.3bar then drop back. adisco
just_ace
I wonder if you just getting a spike to 17psi, but stables at 12psi?
Or possibly ign break down in higher rpm?
Wouldnt think boost leak.
I may or may not be.
In my opinion its not because ive started with 10 psi and gradually upped my boost. Holds 17 psi from 2 800rpm to about 4500rpm and than the dropping starts...
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