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Old 12-12-2007, 07:25 PM   #1
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Default Boos tspikeing with the "grainger MBC"

So I floor it in 2ed gear at 4k rpm, the boost sits at 6lbs, then hits 10lbs by 7k rpm. 3rd gear it does the same, 4th goes from 7 lbs to 11 lbs.

Any idea why it does this? And no, im not going to blow the engine. At 11 lbs of boot im at 12:1 A/F. It is annoying not gettting full boost at 5k rpm tho.

1st gear never reaches over 8 lbs, but its so short it doesent matter.
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Old 12-12-2007, 07:45 PM   #2
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what size a/r on your t3? what size exhaust?

for comparison my t3 would hit 13-14psi by 4200RPM with a very restrictive exhaust and unhealthy motor.
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Old 12-12-2007, 08:20 PM   #3
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2.5 inch "home made" exhaust (not too bad, mandrel bent), a/r was umm.. ugh i forget. I think .63 on the exhaust. Is that right?
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Old 12-13-2007, 10:32 AM   #4
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even with a .63 it seems a little slow, however I have no idea what the difference in spool between a .48 and .63 would be assuming all equals.
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Old 12-13-2007, 12:35 PM   #5
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What are you using as the source for the MBC? I'd also check your pipes/BOV as you may have a boost leak at higher psi as 10psi by 7k rpm sounds really, really late.
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Old 12-13-2007, 04:18 PM   #6
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What are you using as the source for the MBC? I'd also check your pipes/BOV as you may have a boost leak at higher psi as 10psi by 7k rpm sounds really, really late.
It is from a tap in the turbine houseing. Its not that it takes that long to spool... it spools to 5 psi very quick, then its like I get boost creep to 10 psi. Should I mess with the spring in the MBC? aka harder/softer? The MBC is almost all the way tight for it to reach 10psi.

I dont think I have a leak, but I guess its possible. I wish I had to dyno, would be easy to check lol.
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Old 12-13-2007, 04:32 PM   #7
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Sounds like the MBC doesnt work at all, and you are just boost creeping to 11+ at redline.
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Old 12-13-2007, 05:45 PM   #8
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Sounds like the MBC doesnt work at all, and you are just boost creeping to 11+ at redline.
no, with the MBC off, it will boost to about 4 to 5 psi and stay there.
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Old 12-13-2007, 06:10 PM   #9
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that would definitely lead me to believe its leaking and improperly adjusted
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Old 12-13-2007, 06:10 PM   #10
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well I got it a lil better, in 2ed gear, sees 10 psi at over 5750 rpm, 3rd and 4th sees 10 psi by 4500
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Old 12-13-2007, 06:53 PM   #11
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that's probably about all you'll get with a .63 housing
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Old 12-13-2007, 07:22 PM   #12
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that's probably about all you'll get with a .63 housing
mk. I wish I acually had the means to explore the limits of the turbo... too bad I dont have a MS and larger injectors.
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Old 12-13-2007, 07:40 PM   #13
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mk. I wish I acually had the means to explore the limits of the turbo... too bad I dont have a MS and larger injectors.
You could temporarily hold the brake down a bit and see how soon you can get pressure up. That will tell if the lack of spool in 2nd is because of lack of load.

Odd you are having issues with spool, it's not that big of a turbo. I have a bigger turbo and spool at around 4200 in every gear, except 1st. My thought would have been restrictive exhaust, but with a 2.5" I don't think so.

NOTE: Just noticed it was on a 1.6 (not being observant). When I had my 1.8 BEGI S5 T3 (Stage 3 .63 A/R) w/ a 3" exhaust I was getting 12psi at about 3900-4000 rpms. So, it may just be the .63 A/R is too big for the 1.6.
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Old 12-13-2007, 07:55 PM   #14
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You could temporarily hold the brake down a bit and see how soon you can get pressure up. That will tell if the lack of spool in 2nd is because of lack of load.

Odd you are having issues with spool, it's not that big of a turbo. I have a bigger turbo and spool at around 4200 in every gear, except 1st. My thought would have been restrictive exhaust, but with a 2.5" I don't think so.

NOTE: Just noticed it was on a 1.6 (not being observant). When I had my 1.8 BEGI S5 T3 (Stage 3 .63 A/R) w/ a 3" exhaust I was getting 12psi at about 3900-4000 rpms. So, it may just be the .63 A/R is too big for the 1.6.
yeah, the .2L can make a pretty big difference. Ill definaly try the brake thing and report back.
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Old 12-13-2007, 07:59 PM   #15
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Originally Posted by cardriverx View Post
yeah, the .2L can make a pretty big difference. Ill definaly try the brake thing and report back.
A .2L would make a significant difference....I couldn't imagine a lamnmower spooling a T3. Sorry, Couldn't resist.
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