The dilemma

I want an exhaust system that does one thing but the Government wants it to do another. My perfect system has no back-pressure and sounds like a chainsaw ripping through corrugated iron. The Government wants me to have an exhaust from which nothing escapes: no gas, no noise… just the smell of lavender.

How do I solve this one?

First I dug around in NZ LVVTA Standard 90-10(00), ‘Exhaust Gas Emissions’. These Standards wade through safety, smoke, positive crankcase venting (nasty rubber tubes) and some incomprehensible stuff about fuel injection. The clincher comes in Standard 2.5, ‘Catalytic Converters’. A scratch build after 1 May 2010 needs to have all of its exhaust gases directed through one or more catalytic converters.

Picture 1: Subaru WRX STI main cat with heat shielding removed.

Picture 2: Aftermarket inline catalytic converter. Approx 70mm diameter, max 150 bhp, approx $200. A good solution for a normally aspirated 4 or (in a pair) V6 that has some room around the manifolds.

Philosophical objections and backpressure to one side, cats have four problems for the scratch builder: They are made from expensivium ($120 for scrappers from Pick-a-Part), factory cats are the size of dustbins, they must go close to the manifold, and they run hot – nuclear reactor hot.

Contrast that with my Subaru-powered Porsche RSK scratch build: I’m a cheapskate, Ferry Porsche never left room for cats in a mid engine RSK (“wünschen sie eine pussykatze?”, he was heard to ask), the manifold is surrounded by mechanical bits, and, finally, that close fitted fibreglass body is sure to burn with a merry flame.

Emissions Loopholes

So if cats are too unwieldy for my build do the Standards have a loophole? My devious mind at work, eh. On my reading, these are the exceptions to the Standards:

• Pre 1 May 2008 (perhaps if I built a time machine!).
• Old engine, USA pre-1975, Brit/Euro pre-1990, Aus pre-1986 Jap pre-1985.
• Alternative fuels, LPG, CNG.
• Two stroke (now that’s an idea, I’ve always liked stink-wheels).
• Side pipes as fitted to Cobras and 7s (this is good news for these builders).
• Mostly a racing car, log book and comp license.
• A vehicle that is in the sub category ‘historic replica’ or ‘reproduction’, that is a replication or reproduction of a vehicle manufactured before 1 July 1975 (hey that’s me, a 1957 RSK replica).

The replica exception applies provided that the floor plan makes fitting cats impractical (yep, mid engine, short wheelbase, flat floor, full of pipes and mufflers already); substantially different cross-member than when first manufactured (yep space frame is different to give modern levels of torsional stiffness/side impact); engine block is bigger than in the original (yep again, yippee).

In fact the Standard mentions as possible exceptions large engine replicas of various cars CCC members like to build, 7s, Ford Ts As and Bs, and MGTFs.

My take on all of this is that my 1960 Porsche RS60 replica with its tiny space frame and large engine will not need cats. It will be subject to emissions testing that it should pass if it is in good fettle at the time.

Come on feel the noise

Next a dig into LVVTA Standard 90-20 (02), ‘Exhaust Noise Emissions’. To be honest I can’t really copy the sound of the original four cam Fuhrmann powered Porsche. That engine literally screams, no muffling of course, overlaid with the whine of cam gears and a metallic air-cooled raucous. The Subaru, no matter how loud, will always sound like bovine flatulence.

My reading of the Standards is that for a historic replica of a pre-1960 original or reproduction the limit is 95 dba. Another 4dba is allowed if the engine is to the rear of the driver or positioned within 1.5m of the tail pipe. Wow, am I reading this right, that’s 99dba. And then another 2dba if the engine by design normally makes a mechanical racket (maybe the old Fuhrmann engine would have passed).

Test revs are 4,000 rpm +/-5% (for a 4 cylinder car without variable valve timing) recorded for at least one second and then while decelerating back to idle. Braaaaapp braap braap…

The Standards also say that you can’t adjust the system from within the vehicle while it is in motion so as to exceed the limits above. But if the ECU opens a muffler bypass valve at 4,201 rpm then I guess that’s ok?

(Update - the Club Tech Committee says I'm being a bit cheeky here. I just can't keep adding numbers to make the regs suit - damn)

The Bits

A guy from Chase Distribution spoke to us at a club night and promised large discounts. Well they are true to their word. I couldn’t have had better service. They seem to like the challenge that one-off cars pose. Exhaust parts and their dimensions are all available as .pdf files on the Chase website http://chase.co.nz.

The turbo is worth about 1/3 of a muffler, but Chase thought a Flowmaster replica would still be too noisy especially with the 2.25mm diameter ‘WRX STI’ system I planned. I went with a Tripleflow turbo muffler with the option of adding a hotdog inline muffler later if I needed it.

I added a handy combo pipe, stainless flex pipe, Y, slip joint, hanger and 4 cotton reels. NZ$250. Not bad.

Picture 3: George senior holds the combo pipe. You can see Chase’s extensive stocks in the background.

Now To Build It

I’ll ask Chase to do the welding as my gasless MIG and shaky hand does not produce an even weld, I’d just blow holes in the job – some of the stuff is stainless as well.

Pictures speak louder than words.

Picture 4: The up-pipe is a cut and shut of two stainless stock items. Not much room to spare. This pipe and all nearby lines will have to be insulated.

Picture 5: The angry snail is a tight fit

Picture 6: Out to the muffler. No room for a cat here! The tag will rest on a rubber cotton reel. Chase say only use these in compression, as the rubber will tear if you use a cotton reel as a hanger. Does it melt?

Picture 7: Quite easy really… helped by George senior acting as a human vice while I tacked the pipes. A tip, to avoid awkward measurements work from the engine outwards – not from both ends towards the middle - and use a slip joint or two to take up any slack when your measurement or cutting skills turn to custard.

Picture 8: Chase says to weld the branch pipes together before putting them in the Y. The Y acts as a tail pipe, its right side is a dummy and will be capped. However, a bypass valve could go between it and the muffler intake directly above. One day, maybe…

I’ll ask the Tech Committee to provide comments where I’ve taken liberties with the Standards. The only thing that will issue from the tail pipe will be the smell of lavender and a gentle purr of happy pussykatz.

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