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Author Topic: N/A Exhaust issues  (Read 1491 times)


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N/A Exhaust issues
« on: November 24, 2016, 06:49:48 PM »
Hey guys! I have a 98 R34 with a 25DE Neo and I recently switched out the standard exhaust for a bolt on replacement off a scrapped manual 34. This was a set of high flow extractors and 2.5 inch pipe with 2 coby's (One 200mm from the flange of the extractors and one 3/4 of the way back just before the rear axle) and a smaller standard shaped muffler.  Engine wise it is all totally stock including stock box air intake.

I have a couple of issues with this exhaust such as the first perforated fibreglass filled coby must have been too close to the front and has started rattling. Secondly at idle and low rpm under normal load it sounds really nice and rumbly but over 3500 rpm it loses all of its low note and sounds terrible. It also has an odd almost rattling noise coming from around the extractors but you only hear it on decel over 4k rpm. I have had it on the hoist and can't find anything that would be rattling unless it's actually inside the extractors.

I have decided to build a new 2.5 inch exhaust starting at the extractors as I can get all the parts from STA for around $200 but I have a few questions.

1 - Perforated or Louvered coby? fibreglass or steel wool?
2 - How many coby's? and where along the exhaust? how long should the coby's be?
3 - cannon? standard muffler? what size, brand, type?
4 - Will changing my intake to a pod change how the exhaust notes? What about exhaust wrapping my extractors?

What I am trying to achieve is a nice low note most of the way through the rpm without the cackle/rattle. I want it to be within legal sound limits but other than that the volume doesn't bother me as long as I can actually hear it. On decel any popping and gurgling is totally awesome so i don't care if that happens.

Unfortunately everyone I speak to doesn't own a RB and basically says the opposite of what the last person said so I really have no clue how to get my desired sound.



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Re: N/A Exhaust issues
« Reply #1 on: November 26, 2016, 12:48:09 PM »
Everyone I know has a turbo which has a quietening effect so I believe n/a needs more muffler. Pod will do nothing so don't bother. The most effective mufflers are the oval type but be wary of JDM type one that have a constriction smaller than the inlet and outlet. You will need at least one possibly two mid units - I have used this type:

If you are making a system from scratch you could use a mid unit with an oval muffler at the rear and if it is too loud you can easily add another coby.