A few issues ago we met Mark Marchesan and his feature car R33 Skyline 2.5 Turbo(Mark's Monster). As the owner/manager of Adelaide exhaust shop Exhaust Technology, Mark's in a good position to install a killer 3½ inch system on his car, something he recently completed. Here's the full story on it and some words from an industry expert on mild versus stainless, mandrel versus donuts, fashion and fads... ... The exhaust is the first in a wave of mods to the turbo six that we'll be covered - a progressive feature car!
So what are the ingredients in the new exhaust?
"It's something pretty unique in the way of pipe size; it's not often that we'll go so large. This time we made a full 3½ mandrel with a 3 inch converter and an HKS N1 muffler on the back - so it's a straight through 3½ inch box. And it's got all lagged flanges for easy removal, plus fully linished welds. Maximum loving. A normal 3 inch system sits on there nicely. That's one of the reasons why I went up to 3½ - because I know the opposition can't work tube like that. It's a work of art.
"A lot of my stuff - especially my development stuff - is only ever in mild steel. The only time I'll use stainless is probably for more cosmetic appeal of the rear muffler. You get durability with the stainless converter and for flex I'll use stainless, but I just can't justify, one, the cost of stainless and two, with all due respect, that system won't be on there in 4 years' time. There'll be something else on there.
"But you'll find with such big pipe work that it won't wear out. I've had big mild steel systems go for 6-7 years. The downfall is that when it does go broke and loses all its goodness, it starts to fill the cat up with shit. But you can get about 6 years with a clean up - like dropping the converter and giving the exhaust a quick clean through all the pipe work."
What sort of bends were used - donuts or pre-formed mandrels?
"These were all pre-bent - a bucket load of forty-fives and nineties. The donuts are good but they're hard to weld and they're really light gauge. I think they're about 1.0 or 1.2 gauge. They just suck to work with. Plus, the donuts aren't actually round; they're more oval - so if I had to try to match it through the system it's just too hard to do. The only time I use donuts is when I'm stuck for room."
What sort of welding did you use?
"We MIG'd it all. Exhaust Technology really only uses MIG welders - it's pretty durable. TIG welding is a great thing, but not for a system man - to sit down and TIG a whole system you're only gonna linish back anyway... If I was doing a system in stainless, I'd TIG it, but mild steel MIG'd - that's fine."
Did you use your in-house 3 inch Clean Air cat?
"Yeah, that's one reason why I had to keep it 3 inch - I couldn't get the nipple size up any more. Julian seems to think we can get a 3½ inch cat from America, so once I cfm one I might have a play with that. I don't like going down in size - not especially when we've gone through all that trouble of going up to 3½. But it comes down to if I haven't got a cat; it's not finished. This is probably only a temporary mod, the converter - but I don't know - it still makes good power so I might be able to leave it."
Why did you choose to go for an imported HKS N1 rear muffler?
"The quality of the N1. If you look at the welding and that on it, it makes you want to polish the sucker, you know. They're beautiful and it really suits the car. The 3½ inch Jap boxes are a good thing and I thought let's do something trick. Let's do something trick. And plus, you can't get 3½ inch boxes locally, so that's another thing that provoked me to put on such a big pipe."
Did you need to run a flex joint?
"No. Because that dump pipe's such a long, lanky sucker I've still got to mount it to the gearbox to keep the back part shaking with the engine. These engines don't move that much anyway they're so smooth. And it would've caused a bit of grief to get hold of some 3½ inch flex as well - 'cos then you're starting to get into truck shit. That long, convoluted stainless crap that you can't weld."
How did you make the turbo dump - did you squash the 3 ½ inch pipe or have separate sections welded on?
"Ahh, not 'squashed' - manipulated by putting it in the press and trying to taper it down. That's where we spent probably 4-5 hours - just off the back of the turb. On the inside it's just beautiful and smooth. But even with me internally welding the flange so I can get maximum stud clearance, it's fucking tight. I've got a 3-bolt flange directly off the bottom of the dump, so if I break the engine, I drop off the 3 bolt flange and drop the dump pipe off with the motor. But you'd never attempt to put it back on there because it's tight man; it's really tight."
Were you tempted to fit a separate wastegate pipe?
"I was going to but I decided not to. I fitted up a screama to a friend's R33 and, I mean, they're great acoustically but it's not the car for it. Maybe if you put it on a modified boonga, but not on a supercar you know - that's just stupid. Plus it leaks on idle... I'd make one for my Datsun (1600 SR20DET) but not for the Skyline, man. Plus it's all undeveloped at this stage - big pipes work. The 3½ inch went really well onto the flange plate off the dump and it opens everything right up."
Did you use all of the factory exhaust mounts?
"All factory bar the rear box - and that was purely for cosmetics. There I've used, believe it or not, VN Commodore hangers on the back of it. They're nice and rigid and really durable.
Another thing is you've gotta be careful that you mount the pipe with selected rubbers that aren't too rigid - but they have to be rigid enough to support the system and stop it jumping around. I mounted the pipe really heavily where the cross member is because it's not directly mounted back to the floor pan. I've also got lots of rubber mounts going back to the chassis and a really rigid one in the centre."
How much clearance is there with such a big pipe diameter?
"The minimum would be between 10-15 mil. It's clear man; you can run your hand around the whole thing. And to see the pipe on the car it's fucking huge. But if I knew I was going to wipe it out or it was going to rattle, I wouldn't have made it in 3½. I would've just left it at three."
Were you able to keep the factory oxygen and exhaust temp sensors in the factory locations?
"The temp sensor is still near the factory position, but I did pull it back a bit simply because the high flow converter is shorter in body length than the factory one - so the heat temp probe is now probably 5-10cm maximum further down from the cat body. The oh-two sensor is in its factory location obviously - it'd be nice and cool in there now, it's such a big pipe! It's not installed using a simple nut either, they're too bulky and cheap - that's what all the dogs do in town. I get my engineer to make up a half a bucket of oh-two lugs and at least then you know you'll get maximum penetration into the core of the oh-two sensor."
Was it a fairly straight forward system to fabricate, and how long did it take?
"It sucked because it's so big. There's ground clearance to think about and because you can't actually wrap your hands around it so it's hard to linish. Plus all the gear we usually get for 3½ inch is made for trucks and drag cars - its all really big heavy cut flanges and everything. So I had to get flanges cut, and then you don't have gaskets to suit - so it's a fair bit of planning. Probably the assembly of the system was the easiest bit.
"And that took along while. We started on it at about 12 one Friday and all gurgly at about 2 o'clock in the morning I reckon we finished it. It all comes down to the linishing. Man, I spent hours in front of the linisher taking off the welds. And most of the opposition doesn't worry about that - they just leave them all. It's mint. I've never made a good exhaust for my own car - you always seem to take short cuts and bodge things together - but this one's different."
How much would it be for a customer to replicate the system?
"I haven't really sat down and worked out the finer details. A lot of the cost in the system is labour - if I did it through the day, it'd take about 10-11 hours to do the whole lot. So I'd need the car for 2 days - half a day to cool down and plan the system and then a day and a little bit to make it all up. I estimate that with a stainless box, a high flow cat, 3½ inch system - probably close to about $1500-1600 I reckon.
"But if I was to design a system for you, you'd have to give me a ring and plan out the finer details."
Are you happy with the end result?
"Acoustically it's just fuckin' beautiful. It's got this great sound. You can just hear this turb singing away in the dump pipe. I would've liked it a bit louder but probably the biggest advantage of the system is it doesn't have any resonances over the whole rev range. I can hold it in any gear on any incline and have no resonance whatsoever. Compared to the old 3 inch system that I tried on there... But I've only ever heard it from inside the car. Everyone that's heard it has commented that it sounds beautiful, but you don't appreciate it without someone doing a drive-by. And the appearance of the rear box - that's the shoe. That's another reason I went for 3½, you can see it through the spoked wheels and it looks fatter. It makes the most of the big pipe."
What was the previous 3 inch system that you mentioned?
"That was an early day one that was for a customer of mine. It was simply a Dragger and 3 inch pipe work - unlinished and that. He had a bit of grief with it - he moved in next door to a copper and had to pull it off. And I just had to put something on mine... Plus it was good to experience what the customer does too. I used to think these customers that used to complain about droning were pussies you know - just get over it! But it's really annoying - everything vibrates and comes loose, you know.
"But I definitely don't have that now with this system."
How much more power is there now and where did the new system pick up torque?
"The 3½ inch pipe at the start was really disheartening because it didn't make the grunt that we wanted from it. I initially thought the big pipe of the system was what caused it to lose a little bit of torque. But John (Keen) and Julian had a bit of a tinker with it and grabbed an extra 7kW out of it just by - I don't know, just by givin' it a bit of lovin' or whatever. (See "Exhausted Power!") They're in their own world there. In the early days, I used to take in as much input on everything - but it's just too hard now. Everything's more specialised. I'm a qualified brake and suspension mechanic as well, but I've stopped it for that reason - so we can dominate exhausts and get each job spot-on. So to answer the question, after the dyno it made more power over the whole rev range - but before that I had 2 weeks of driving a shitty car. And boost is now holding at about the same - it picked up a little up top."
How has fuel economy been affected with the new system?
"Who monitors fuel consumption? - it's a thirsty pig anyway! I'm always between 3 and 4,000 revs because it's got this beautiful scream to it - so I normally just cruise in third. Naah, fuel economy's a second issue."
Are polished boxes the "in" thing?
"Yeah. And it comes down to designing the system - running some crazy angles. I've never been able to run real big tips and been able to get a good note out of Charades and Starlets and stuff like that. So what we're doing is re-routing the back exhaust part, re-bracketing and changing the angles to show these suckers off. Plus it's a good principle to keep it as straight as possible anyway - but with an emphasis on optimum ground clearance."
Will 3½ inch systems become commonplace?
"As much as possible, I'm gonna try and push it. But when I start quoting it, all the opposition will start doing the same - but they'll fuck it up. I've just gotta keep the systems down as well - I can't just go and spend days or charge 2½ grand for it or something. Especially for something that could be replicated in Japanese as well. But I don't want to follow the Japanese trends, you know. I want to use the Jap boxes but still hook them all up with our pipe work, that way I can get more clearance and custom position on the back box.
"I've got another 3 ½ inch system in a - fingers crossed - 9 second LJ Torana that's a muffled system, as well as a few 3½ inchers in our sport sedans and now on the Jap stuff.
I'll bring it on. And as time goes on, the better the flanges will get, the better the cats will get and the faster I'll be about to fit them up. Next I want to do a 3½ pipe on a four banger like a SR20 Silvia. That's it, because I know the opposition can't make it - not like we can anyway.
Yeah, 3½ inch is the shit I think."
Contact:
Exhaust Technology
+61 8 8272 7500
www.exhausttechnology.com.au
Mark's Monster, Part 1
Mark's Monster Part 3 - The Roll Cage and Course Car Preparations
Mark's Monster Part 4 - The Wheels, Tyres and Suspension
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Exhausted Power!
When Mark told us that he was disappointed with the performance of the Skyline with its new (huge) exhaust, we arranged for the car to be placed on John Keen's DAT Dyno and a mixture analysis done. Firstly, though, how much power did the car now have? Power peaked at 143kW (192hp) at the wheels - but what did the car have as standard? Unfortunately, in Mark's enthusiasm to have the new exhaust fitted, a 'before' dyno run wasn't undertaken on this car, however, another (apparently healthy) 2.5 litre R33 turbo Skyline recorded only 110kW (147hp) at the wheels. If (note: if!) the second figure is indicative of the breed, that's a pretty healthy power increase. So why was Mark unhappy? The mixtures partly tell the story:
Road Speed
(km/h in second gear) |
Power
(kW at the wheels) |
Boost
(psi) |
Air/Fuel Ratio |
| 37 |
41 |
6.1 |
12.8 |
| 48 |
52 |
6.4 |
12.3 |
| 58 |
66 |
6.9 |
12.1 |
| 66 |
75 |
7.0 |
11.9 |
| 76 |
86 |
7.2 |
11.6 |
| 85 |
92 |
7.5 |
11.5 |
| 94 |
106 |
9.7 |
11.3 |
| 101 |
121 |
9.7 |
11.2 |
| 113 |
123 |
9.8 |
11.1 |
| 123 |
125 |
9.3 |
11.1 |
An air/fuel ratio in the elevens is too rich for maximum power in a turbo car running standard boost - the mixtures needed to be leaned-out to the low twelves for better results. This was achieved by a deceptively simple modification - pulling off the vacuum/boost hose leading to the fuel pressure regulator. As a result fuel pressure doesn't rise with boost, so less fuel will be admitted through the injectors. (Note: this sort of mod should not be undertaken without the use of an accurate air/fuel ratio meter allowing the results to be monitored! Another note: it also means that the air/fuel ratio will be richer at light loads - but the oxygen sensor feedback loop should be able to cope with that.) With the fuel pressure lower on boost, the following test results were gained:
Road Speed
(km/h in second gear) |
Power
(kW at the wheels) |
Boost
(psi) |
Air/Fuel Ratio |
| 48 |
55 |
6.3 |
13.2 |
| 60 |
71 |
6.8 |
12.9 |
| 65 |
77 |
6.9 |
12.8 |
| 76 |
90 |
7.1 |
12.6 |
| 87 |
98 |
8.2 |
12.5 |
| 97 |
121 |
9.6 |
12.4 |
| 102 |
133 |
9.6 |
12.3 |
| 111 |
136 |
9.8 |
11.8 |
| 124 |
144 |
9.1 |
11.7 |
You can see that on the basis of these results, power has gone from 125kW to 144kW at the wheels! But hold on, what about that 143kW figure mentioned in the first para? All these figures show the difficulty of accurately testing any turbo car on a dyno - power is all over the place as the intercooler gets hot and cold, ignition timing is automatically retarded and advanced. We could say (as many others do!) that this isn't the case, but it's wise to be realistic...
However, on the 'snapshot' runs performed to get the tabled data, power is clearly higher with the slightly leaner air/fuel ratios being used. This also showed on two ramp-mode power pulls you can see on this dyno graph (green line shows power before the fuel pressure hose was removed, blue line after). The dips in the power curves at very high rpm are not related to mixture problems - instead, access to the ignition timing maps would be needed to tune this out.
Conclusion? With a big exhaust the Skyline runs a bit too rich for best power, but leaning-out the full-load mixtures is a no-cost hose-pull away. 'Course, full programmable management (or even a good interceptor) would be better again!
Julian EdgarContact: DAT Racing
+618 8277 4222
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