So I've got my a15 running.. After a year designing an efi kit I totally changed tack and went twin dellortos. I will now sell tge efi kit if anyone is interested.

Any way... I'm running a ported polished, double valve sprung head with a stage 3 cam. The total exhaust length from the 4 into 1 collector will only be about 1.3 metres long. It's set up for 2 inch. What length resignatior woukd you suggest? I wondered about a little 250mm job. And what kind of muffler? I'm after a little exhaust tone that is reasonably discreet.

Will build it this weekend after a decision is made.

I might be interested in that efi kit ^^
Some more info on that would be nice :)

I think that 250mm sounds good. I have thought about a Varex? That way you can choose to have loud or discrete?

The collector length depends on your goals:
* Peak HP? If you plan to keep the engine in a narrow range (with close-ratio transmission) this is the way to go
* Broad torque curve? Make it the same length as the factory GX collector

To find the peak HP length, paint the exhaust pipe with a stripe of cheap spray paint. Warm your car then run it flat out through the rev range in first and second gear. Where the paint is burnt off is your optimum length for full-throttle high-RPM power

Varex looks promising if you like the loud sound at times, then can flip the switch for quiet

If you want to avoid loud at all times, use a resonator for power, along with a regular muffler for quietness

Here is the factory GX system



But something like this may be better, attached directly to the resonator



For racing, if allowable, they use no muffler at all. But if you put a resonator at that point it is nearly equivalent. Then adding a full exhaust pipe & muffler makes no difference to the tuning. The resonator effectively terminates the exhaust system as far as length and tuning goes

The total length from the 4/1 is about 1200mm long as it sticks out the back of the cab. I could make it longer to be at back of vehicle but I like the look sticking out the side.

I will be mostly driving as a daily, well actually the wife will :). Il be revving it out but not very often so don't need high performance although I certainly want it to breath.

Will price up a little resignator with muffler this weekend.

The selectable muffler looks awesome but it's out of my budget.