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PART 12

Pipe Dreams

There is a big difference between an exhaust system on a 4WD and a regular sedan... Ours are more likely to get buggered in a big way. How many times have you been crawling along a track somewhere and looked over to see someone’s hastily discarded exhaust system? Not only is it litter, that’s some poor bloke’s next pay packet lying there.

I needed a new exhaust system to go with the new Calmini headers, so wandered over to see Stuart Vale at Racer’s Choice in Seven Hills. Stuart knocked up the awesome exhaust system and headers on Stimpy the Monster Jimny and really knows his stuff.

Stuart is a mechanic by trade, but moved into custom performance fabrication and exhaust building when he found out, quite simply, that he really liked it. Looking around the workshop, it’s embarrassing to admit that Oscar is probably one of the most under-powered cars ever to grace the hoists here <cough>

The secret to a good system on a 4WD is to tuck it up as high as possible to avoid damage. But if you do manage to bust it, it needs to be sectioned so if you get stuck or mangle it, you can unbolt bits and keep going.

Instead of whacking in lengths of pipe and welding them together, a better idea is to create a flange at each join. This means that if I get hung up on one section, all I need to do is unbolt that one little bit and keep going. Later on, I can just get Stuart to make up another piece and replace it. Stuart does this with all 4WD exhausts to alleviate the problem of us smashing up and buggering our entire system in one hit.

However, fitting up a new exhaust isn’t just about grabbing some pipe and a muffler, and whacking it in. There are more factors involved than what you may think. You first need to consider what you want out of your 4WD, and Stuart will ask you a heap of questions;

Do you want low down or top-end power?
What’s your stock kilowatt figure?
How heavy is your 4WD?
Are you going to be touring and or/towing?
Are noise levels a factor?
Are you after economy or brute horsepower?

These questions are important as they ensure you get exactly what you need and that you don’t lose power. Yep, that’s right... your new exhaust system can actually cause you to lose horsepower if not properly done!

Stuart takes all these factors into account, does a bit of mad scribbling and head scratching, and comes up with all stats he needs to put together the best system possible. And if they haven’t got the bits they need, they’ll make it up for you... as well as roll cages, custom fit braided lines and hoses, custom fabbing, engine building to order and just about every performance enhancing mod or accessory you can think of!

Ok... so the Calmini headers needed to go on first.

Problem one... the gasket supplied by Calmini didn’t fit properly. All the holes were in the right place and the bolt holes all lined up, but it wouldn’t seal properly due to insufficient edging. The outlet holes on the gasket were slightly larger than the ones in the manifold, leaving the bottom edge with only a thin strip to seal it. Stuart advised it would simply go for the weakest point and blow out... not good.

So we did away with the new Calmini gasket (even the old one didn’t appear to be doing such a crash-hot job so it wasn’t an option) and instead used a tube of gasket sealant. A nice thick bead was laid around both the exhaust outlets and header intakes, alleviating the need for an actual gasket. Worked perfectly as expected.

Problem two... the flange for the bottom of the headers was hitting up against the gearbox. I daresay this is another “X-90 thing” that Mr Okamata had something to do with. Michael simply ground a small section out of the bottom flange so it sat flush. With the tricky bits sorted it was full steam ahead for the fit out.

After taking everything into consideration, Stuart decided on a 2in system and selected the appropriate muffler (we already had a Calmini Hi-Performance cat) from probably the biggest stack of mufflers I’ve ever seen. It was then a case of working out where everything could be tucked up, bending the pipe, making the joins and flanges, and whacking it in.

Well, it’s not actually that easy... I was amazed at how complicated fitting an exhaust is! I’ll let the pics speak for themselves. With the system in, Stuart checked for leaks and made sure I was happy with the dulcet notes coming out of Oscar’s.... ahh... bum.

I now have an X-90 that rumbles along pretending to be a two-litre jobbie and cracks a nasty note when I drop the pedal, but best of all... we have the added bonus of more horsepower. We did a before and after check on the dyno and... we got around an 11% increase! After two weeks of monitoring fuel consumption, I’ve worked out I am also averaging an extra 39 kilometres per tank of fuel... which literally puts me back to starting point before putting the 31’s on.

Yay!

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