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loss of backpressure from fitting a decat; tiny bit of loss power?
Topic Started: Mar 29 2009, 12:55 PM (316 Views)
irishgerard
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Stage 6
hi guys i recently fitted a decat to ny levin purchased from solid fab, but now starting out in low revs it lags power. Anyone shed any light on why this might happen and how i can sort it? In running a stock exhaust but was told it shouldn't make a difference. Thanks!
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chiksluvit
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[OO\_____/OO]
you don't really want any back pressure from your exhaust system... .
it's normal to feel a slight drop of torque at low rpm with a decat since the scavenging effect is not as great with a cat...
then again VVT helps minimising the drop in torque.
I don't have VVT and I only felt a slight drop of bottom end torque when I fitted metal cat... and it's a huge metal cat too

maybe service the car, reset the battery and see if it improves.. otherwise it's just physics, you're trading a bit of bottom end torque for more top end power..
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hogan1
Stage 4
i also noticed this, it's like there is a flat spot in the low revs
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JohnnyBZG
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Needs to Try Harder
Also make sure the decat is sealed properly...get some good gaskets..
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doug20v
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toyota head.. honda hater
@irishgerard have you noticed amy power difference since fitting this?as im going getting one this week and fitting it to my standard system,
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irishgerard
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Stage 6
it lacks power from about 2k to 3k revs it sounds nice when getting to top end... not really noticed much dfferece although i havnt driven the shite out of it yet.
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andy_bzr
stage 4
i kind of had the same and for me it was the gaskets!! they are shit hust put on the old ones with abit of sealer and its fine now has a lovely rasp from 2-3 k and then at top end
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JohnnyBZG
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Needs to Try Harder
Initially when I put the 5Zigen system on (with the supplied gaskets) if I suddenly went WOT, it made a farty sound as the gaskets weren't sealing well, and then as the revs raised it started to vibrate like a (woodwind instrument) reed. Felt a complete turnip when overtaking people, that's why I went back to the original gaskets....solved it all.
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andy_bzr
stage 4
so i guess then we agree that its the gaskets that are the problem! if the gaskets are any use than the whole thing isn't
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nismoe
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Levin-headed
no my gaskets were sealed, stuck with the toyota ones. we started it after fitting(was up on a lift) and checked for leaks none there. went for a spirited drive put her back up on lift checked for leaks again and it was airtight.
I still think if you have a/m header and/or catback exhaust, fitting a decat will affect your low end and only gain minimal top-end unless you have the ability to remap maybe then a significant gain may be achieved :idk:
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BZ-G
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aka Hyper Rev 4...
nismoe
Mar 30 2009, 01:04 PM
BZ-G
Mar 30 2009, 11:51 AM
in the past, i had a decat with stock exhaust and it worked great.... :idk:
stock exhaust yes but when i put the decat on my bz-r with hks hi-power cat back i cant say i noticed any real gain at any point and noticed a loss in low end grunt. changing back to a 'greener' levin tonight ;)
some aftermarket exhaust systems don't suit/like decats, for example the PEII i had in the past did improve slightly with a decat on but it produced the same power as the stock exhaust with a decat (had dyno runs to test the power), so i just fitted my stock exhaust back on....
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TRUENOSAM
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Stage 6
Mine developed a flat spot after fitting a de-cat pipe.


I did a ecu hard re-set (disconnecting the battery for an hour) and all was good. Flatspot cured :)
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irishgerard
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Stage 6
Might have to try that tommorow see if it changes anything :cheers:
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dog-tag
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Stage 5
yep thats what i did! i changed my lambda and everyting wonder what was wrong, the ecu just needed resetting! gaskets are a big big thing and i also noticed a lack of low power on mine too..
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