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Decat'n a cup 172

Meh i havent. I will at some point when i strap on the matched inlets i have. To stop the emissions light, plug the second downstream lambda hole up, then tape up the lambda under the car ;)
 
Had my 172 decat on the car now for 3 weeks and it's slightly better at the top end of the rev range and much louder, you don't have to get it remapped but I think you get the best out of the decat once u remap it!

Only thing I would say is if you don't like noise don't decat mine stupidly loud but I have removed the center silencer as well with the ktec stealth supersports exhaust
 
so it wont run lean then if i plug the 2nd hole n fix the 2nd lambda sensor up somewhere out of the exhaust?
 
i think the 2nd lambda thing just relates to the engine management light - it may or may not come on (mine didn't and the car the decat went onto afterwards didn't illuminate its warning lamp either) - just a luck-of-the-draw thing; if it does, remove the 2nd lambda and fit a blanking bolt/plug
 
surely though(dont mean to go on), if it reads the same gases reading in post cat after its been decatted, the ecu will be tricked into thiking its running rich when its not? as a result then run lean to compensate?
 
My Cup was de catted but was a silenced de cat with a ktec stealth back and wasn't "that" loud.

But my 172 with just the ktec stealth back is loud enough!
 
someone correct me if im wrong but im sure the post cat lambda is only to measure cat efficiency and it doesnt alter the fueling air in any way. The pre cat one is the only one to measure this straight from the engine so it can tell how the engine is running and adjust it before it goes through the cat.

As for gains and noise, mines got less boomy out the back and the car sounds alot more raw and not so puny as it did. Also noticed vvt coming in a litttle harder and it doesnt pull as well until vvt starts then it pulls like a mofo.
 
mine decat'd runs fine, got both lambers on and it came on after 3 months. turned it off and it aint come back on. well it has now coz shes running sick! anyone know how much difference aftermarket injectors make?
 
someone correct me if im wrong but im sure the post cat lambda is only to measure cat efficiency and it doesnt alter the fueling air in any way. The pre cat one is the only one to measure this straight from the engine so it can tell how the engine is running and adjust it before it goes through the cat.

As for gains and noise, mines got less boomy out the back and the car sounds alot more raw and not so puny as it did. Also noticed vvt coming in a litttle harder and it doesnt pull as well until vvt starts then it pulls like a mofo.
the vvt turns on at about 11k or 12k revs iirc so you wouldnt feel it come on as its already on as you pull off from a stand still. if you are onabout the "5k kick" then that is the engine coming on cam and operating at its optimum revs. i think the vvt is purely there to help smooth the idle out.

mines decated and runs quite rough when cold but once warmed, its fine.
 
11k? Wtf u running? LOL :)

exactly what i was thinking lol! well the 5k kick is the vvt isnt it?

Doesnt the engine activate a solenoid at 5k to turn one of the cam pulleys? which is what the vvt is? similar principle to vtec but obviously not the same setup.
 
yeah, something to do with the cam angle due to the dephaser IIRC

yeah, the dephaser is part of the vvt system. if it is just "coming on cam" then it does it very hard compared to other 16v cars that i have driven. The VVT is designed to give the same principlke as VTEC just it isnt the same setup.

Well to clear it up when i fitted my decat the 5k kick seem to come in alot harder
 
the dephaser comes in at 12-1500 revs right thru to 7k odd, its purpose is quite the opposite to a vtec, a vtec advances the timing after a certain amount of revs, the dephaser is to smooth the idle out on a clio lump, hence why they rattle at idle when worn, the 5k kick you get is the engine running at its highest volumetric efficieny peak
 
i thought vtec was nothing to do with timing, Does the engine not shift to a different cam profile to hold the valves open for longer on a vtec?

so does the dephaser alter the timing throughout the rev range or just at low rpm?
 
can some one tell me if there is a big difference between the normal 172 decat and a silenced 172 decat? I just won a non silenced one on ebay and I'm affriad im going to sound like so ghey boy racer. Is this the case? shall i shall it and get a silenced one? Dan
 
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