Exhaust Theory: Tuning Guide for Aftermarket Exhausts

I’m going to say it right out. Modern, post 2000 cars with small engine capacities (1.8l and below) should NEVER EVER install aftermarket exhausts if you want a speed increase (the Renesis 1.3l is an exception as displacement is nearer to 2.6l). You’ll get better sound no doubt, but you’ll never have more than just a couple of percentage points in bhp increase, if at all.

Aftermarket exhaust systems worked wonders for older designs such as the Corolla for a simple reason – the stock exhaust setup was crap – it had very small pipework that strangles the flow – just so that Toyota can get the fuel economy and emissions they advertised. So anything that made the pipes bigger and gave better flow did wonders for the Corolla.

Nowadays manufacturers can’t afford to throw away any spare power or fuel economy and modern exhaust systems are highly efficient “straight through” systems. Manifolds are still usually cast iron for durability but with longer runners and twin outlets that then lead into a long twin tubular downpipe. In essence it’s a productionised version of the tubular 4-2-1 performance manifold.

Exhaust systems really do help in higher capacity engines, and especially where exhaust gas temps are very high – that’s why aftermarket exhausts really do work for highly modified cars, race cars, and especially so for the hot Renesis engine. One thing that stops peak performance of engines is overtly high internal temperatures, and that’s usually caused by restrictive manifolds and exhausts – this especially becomes an issue in forced induction or lean stoich situations. So what’s recommended? A proper 4 branch tubular manifold and straight thru silencers.

But beware of systems that boast bigger bores / pipe diameters and all that rubbish. Lose the finely tuned bore sizes that manufacturers intend to be and you’ll lose power – it’s a factor of mathematics.

So what does RXReviews recommend? If you own an RX-8 or any other performance car,

1. Keep the pipes stock. Dun fuck with perfection
2. Change the muffler to a proven Jap rotary tuning brand – Autoexe, knightsports and RE Amemiya are good bets.
3. Change the catalyst to something that improves flow, WO changing bore size or destroying your emissions. the Knightsports metalit catalyzer is a good one to get
4. Change your manifolds. Here, I’m recommending RE Amemiya – race proven on the 4AT.

If you own a typical 1.6l car, don’t bloody waste your time. Do not kuitao at Man, Do not change pipes at Fong Kim, Do not get aftermarket exhausts from Supersprint, Remus, etc. Save your money and just get yourself a good dinner at Morton’s with foie gras or something.

Sponsor Singapore’s A1 Grand Prix Team? You’ll need at least US$1m handy

Preview: Green Drop-in Air Filter + REVi Ram Air Duct

Fresh from the States and lying in my storeroom: the Green high-performance drop-in filter for the stock RX-8 airbox, and a spanking new REVi Ram Air Duct from Racing Beat. For those that have been following my mod antics over the months, you’ll know i’m searching for that perfect price-performance solution for the RX-8 4AT.

Now my Apeximota – the Simota carbon fibre box + A’Pexi open pod filter intake solution works great – there is no loss in low end, gains in the mid and high end, and the car feels so much livelier. The only problem? It’s really LOUD – a hair under the same dB levels as the AEM.

Green Filters have been all the rage in Europe for some time now – the cotton material they use is far superior to K&Ns, they use less oil so there is less chance of ever mucking up the MAF, definitely better filtration performance in tests – just all-round better than an K&N. Check out the BMW, Porsche and AMG forums – Green is a mainstay there. In fact, Green is the standard OEM filter for all AMGs in Europe i believe.

So my theory? A high-airflow drop-in like Green will retain the heat/vacuum benefits of the stock airbox, perform as close as possible to an A’Pexi, get fresh cold air using the ram air duct without compromising water-damage (e.g. the AEM) – and tadaaa – a quieter with much better performance than the big-name/big-pricetag brands out there.

I’ll post a review once it’s set up.