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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.

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September 25, 2006 - Posted by | Exhaust

8 Comments »

  1. hi

    after reading your post on exhaust. i have some questions for you. hopefully i can get an answer.

    i am currently driving a 92 Corolla (1.6L) and experiencing a bad FC (9km/l) and therefore i made a trip to fongkim and was told that my cat convertor is spoilt therefore it’s causing me the poor FC. i changed it on the spot. after testing it for sometime, i noticed my FC is still as poor as before and therefore asked Jeff (boss son) and he told me that my piping is bigger in front and smaller at the rear and suggested for me to change the whole piping. But in your post you mentioned that in wouldnt make any difference.

    Do you have any suggestion for me as in to improve my power and my FC? any suggestions would be greatly apprectiated.

    Regards
    andy

    Comment by andy | April 18, 2007 | Reply

  2. Hi Andy.

    More air = more petrol based on stock fuel maps thus poorer FC.

    To improve power and FC, go get a piggyback and proper tuning.

    Changing to bigger piping will not change anything for FC – and power is subjective depending on your car characteristic.

    This is what my friend with a 2000 MT corolla model did and his is damn fast – extractor; remove cat; bigger piping; kuitao exhaust – all at Man.

    Fong Kim in my opinion are carrot choppers

    Comment by gfoo | April 19, 2007 | Reply

  3. Hi,

    I’m new to this region, and was wonedering where in Singapore I can look at auto aftermarket products. Friends say there’s an entire area/district (bliss) dedicated to modders, but are unsure exactly where.

    Plus, how would you rate the prices of these products, in comparison to, say from the UK? Is there a significant mark-up across the board? I would imagine so, since the products have to travel quite a distance to get here.

    I recently purchased a Mk3 Golf (1.6 only – the sadness) and am thinking of upping the power. Any ideas?

    Comment by Norman | May 7, 2007 | Reply

  4. Hi Norman,

    The Ubi area (Paya Ubi and the Ubi Industrial Estate) comprise of many workshops that specialize in aftermarket parts. I won’t say it is market up higher than in the UK, but i know that for the VW, parts are a little harder to come by and it could be dearer due to lack of competition.

    You need to think carefully as to what you want to get from ‘upping’ the power – there is always a tradeoff.

    If you’ve got cash in hand, and do not mind illegal modifications (a $500 fine if caught on the road, but will be fine if you just ensure you swap back legal parts during your inspection) – turbo or supercharge it. This one single mod is still cheaper and more satisfying than any other NA mod you can think of.

    If you want to go legal, you will need to put in some legwork/googlework to find LTA approved parts. For NA modding, you will want to do:
    – ECU reflash or management system + good tuning
    – whole exhaust system (header -> cat -> catback)
    – intake (open pod + any ram air duct or CAI)
    – final drive gear ratios
    – flywheels (if MT), underdriven crankshaft pulley
    – a better ignition system (plugs, cables, coils)
    – better cooling (radiator, thermostat, etc)
    – thinner, but stronger oil – racing-grade fully synthetics

    Some of these parts may not be legal, esp the cat and header, so the same swapouts apply during inspection.

    Please do not waste your time on electrical mods unless you have an extensive ICE system.

    Hope this helps

    Comment by gfoo | May 7, 2007 | Reply

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    Comment by Luk | July 7, 2007 | Reply

  6. Hey,

    Just wanted to if you could recommend a distributor in the UK for the RE Amemiya manifold and exhaust system. Also which induction kit would you recommend, I’ve been looking at the HKS setup but should I consider any Amemiya or others esp. as I’m getting all other RE parts?

    Thanks in advance bro.

    Jay

    Comment by Jay | October 13, 2007 | Reply

  7. I agree with your first statement I have been modifiying cars for years. I see all the time people putting on intakes and after market exhasut systems on cars that LOSE horsepower – like a Civic SIR motor – it retards the timing back which doesnt give you great combustions

    Comment by Chrysler 300c | January 19, 2008 | Reply

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    Comment by removal dpf | November 15, 2011 | Reply


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