Fto exhaust diameter

[mivecrx]

Going to upgrade my exhaust to a stainless one, what diameter is best? Stock is 62mm, should I stick with that or increase it?

[Myfeckin FTO]

Can't see much of an advantage going with a larger bore exhaust - probably better to concentrate on keeping the flow as non restrictive as possible such as using a decat and even keeping the reasonators/mufflers etc to a minimum. Isn't the GPX exhaust already a larger bore than a GR exhaust? The flange from the Cat is certainly bigger.

Its really about removing the obstacles that prevent optimal air flow right from the induction through the engine and out through the manifold/exhasut system. Any bottleneck (such as a crappy cat or poor induction) will largely negate all your good work elsewhere.

[mivecrx]

I'm not sure about gr gpx bore differences, just interested in mivec models.
I know what you mean about making it as free flowing as possible, I intend to do that but was wondering if going to 70mm would free it up even more or just be overkill. 70mm is very popular on k20 Honda(s).

If I was to get a Mongoose downpipe it would be 63.5mm inside diameter so that wouldn't work well with a stock 62mm catback, in fact it would be terrible so that's why I thought going slightly bigger would help.

[Bernard]

I got mongoose downpipes a few years back and never had a bother, granted I didn't do the fitting myself but still.
They'd hardly sell them if they'd cause problems?

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[mivecrx]

I don't mean it won't fit, it's just the inside diameter is the slightest bit bigger. I think I'll just go with a exhaust to match the mongoose downpipe size of 63.5mm(2.5").