3.0RB system

Exhaust modifications

Re: 3.0RB system

Postby Doyab » Wed Mar 16, 2011 4:11 pm

What a coincidence this topic has come up. Just yesterday I got the third cat removed. Originally we thought it was 2.25 going into the cat. But turns out it was a dual skin pipe with 1.75 in the middle. So best he could do was use 2inch from cats to flange. If I had my choice again I would have just waited till I got manifolds built with 2 hiflows. But will do that after I get my.supercharger next year. Any recommendations on primarys and secondary pipe sizes and lengths? After removing the third cat. I'm not sure if I'm imaging it but I think I've lost little power real low rpms. But gained abit up top. Also seems to rev easier out of gear.
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Re: 3.0RB system

Postby bradsm87 » Wed Mar 16, 2011 4:14 pm

Robbks wrote:
bradsm87 wrote:U'll still get a cat related CEL with a 200 cell i reckon. The new stuff is SO sensitive. Changing diameter and introducing a restriction that close to the headers is pretty bad for performance IMO.


stock cats are something stupid like 400cpi
the ones i'm using are only 200cpi, so they will flow a lot more for the same diameter.
But i'll step them up to 2" in/ out then into 2" collector
so there's going to be much less restriction than stock.

my tuner has indicated that there will be no issues
IIRC the front 02 sensor is the wideband and rear is just the generic narrow-band.


Both O2's are Narrowband. The rear one just needs to read that whatever cat is in there is doing EXACTLY the same job as the factory cats. Your tuner is right. It will be all good because he will disable the CEL code.

Should be sweet.
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Re: 3.0RB system

Postby Robbks » Thu Mar 17, 2011 8:21 am

I Wish wrote:IRC the front 02 sensor is the wideband and rear is just the generic narrow-band.
Can you confirm this?



hmm, yes. looking at it ECU I/O data the front o2 sensors are narrowband but use 4-wire 02 sensors (twin signal wires that are independent of the vehicle earth, hence why they cost an arm and a leg)
the rear 02's are generic 0-1v, 3-wire.

so the rear sensors are responsible for usual 02 adjuistments to maintain stoich mictures in closed loop.
as for the actual job of the front ones... open loop corrections maybe?
coyote wrote:Sure, a GTR is fast ... but it's about as interesting as listening to grass grow.
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Re: 3.0RB system

Postby bradsm87 » Thu Mar 17, 2011 8:36 am

The front sensors are very high quality narrowbands that control closed loop mixtures. The rear sensors provide readouts to the ECU for it to match against the front to see if the cats are working as expected.
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Re: 3.0RB system

Postby bradsm87 » Thu Mar 17, 2011 2:30 pm

Doyab wrote:Originally we thought it was 2.25 going into the cat. But turns out it was a dual skin pipe with 1.75 in the middle.


This is where I've gone wrong. I made the new secondaries longer, assuming the volume would be about the same with the smaller pipe. It looks like I need to re-do the twins to merge as close to the engine as possible. I bet this is part of the rasp noise too. The twins go for way too long before they merge.
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Re: 3.0RB system

Postby bradsm87 » Sat Mar 26, 2011 9:42 am

SUCCESS!

I moved the merge as close as possible to the engine (350mm further forward and added a small bullet muffler in the space gained and now the rasp is gone. For anyone looking to do an exhaust on a 3.0R, make the merge as close as possible to the engine and put a bullet muffler straight after the merge. I'm in the process of moving interstate at the moment but I'll try and get a sound clip up (a proper one where the engine is actually under load) as I'm VERY happy with the sound.
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Re: 3.0RB system

Postby Doyab » Sat Mar 26, 2011 3:29 pm

so you rekon when i get my extractors made, get them built short and joint close together?
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Re: 3.0RB system

Postby bradsm87 » Sat Mar 26, 2011 6:36 pm

Nah nice and long, just don't merge the secondary pipes foo far back. I'd go 1 5/8 primaries into 2" secondaries into a 2.5" system. 2.25 would also be good but good luck finding good true 2.25" straight through mufflers.
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