SUZUKI DR600
Paul Berryman returns... at last!
Twenty-seven brake horsepower: it’s not much by any standards, but it’s all that my beloved DR600 churned out when I got it in 2014. To give some equivalence to this number, it’s 18 less than Suzuki claimed in the original sales brochure, and also in the same rear wheel horsepower zone as Honda’s modern-day CBR250R; a bike so dull it makes even a wet sandwich seem like fun to eat. To be fair to the DR, the riding experience wasn’t ever entirely anaemic, even though it had all this power missing. It’s always been fun to jump on, but I was surprised after a few weeks of owning it that it didn’t cope with any kind of hill ascent without shifting down a cog. Now, this is a 600cc single, and if there were one thing I expected it to do well, it would be climb to hills without needing to be fed lower gears. An enquiring dyno run giving just 26.73 paltry bhp confirmed it was a real rather than imagined problem. Ok, but what should it make? The 45bhp in the sales brochure should point towards a real-world bhp figure of around 36-40 at the back wheel, depending on the usual dyno-reading variables of temperature, air-pressure, type of dyno, correction factor used, and even the skill of the operator. So, there was work to do to find between nine and 13bhp to get this DR back on the money. Those of you that have been paying attention to amongst the slowest progressing projects ever on CMM (and there is real competition for that title) will already know that the DR has been through a full top-end overhaul with 1mm oversize piston which registered a 5bhp gain, to a better, but still not quite right, 32.23bhp. More recently, the new cam-chain fitted at Tony Galea’s camchain services in Essex felt like it had finally got the DR to where it needed to be. The old cam-chain had been so worn that the timing was half a tooth out and was also causing a huge lack of punch. The top-end refresh I’d done had helped but, according to my finely tuned arse cheeks the fresh cam-chain had really moved things on. Was 36bhp now possible? I reckoned it was. Was 40bhp on the cards? I was less sure, but there’s only one way to find out – dyno-time!
When it comes to dyno-time, it’s always my old muckers at MSG Racing between Aylesbury and Thame to whom I turn. They dyno’d the DR before, so it’s where we needed to go for a ‘like-for-like’ reading. Dyno figures between different tuning shops can vary wildly, regularly by as much as 10%. Some of the UK’S most popular tuning shops also have the highest reading dynamometers. By accident or design, I wonder? Think about it, would you be happier with your tuning shop giving you an 182bhp or a 200bhp motorcycle? Come the day of reckoning on the big roller, the bike was generally in good/ standard nick, with the aforementioned 1mm oversize piston from the later DR650 fitted (the 650 gets its extra cubes from stroke as well as bore) so we had 13cc more than the original 589 that it left the factory with. Also deviating from stock was the jetting. Somewhere along the way I’d also gone up on the main jet from the original 135 to a 137.5 – nothing much alarming about that, and I certainly didn’t think it was going to make any real
difference on the dyno. There was, however, something else I’d changed since the last dyno visit, which seemed like a good idea at the time. I’d fitted a new silencer to the Micron headers. I say new, but it’s old, and it’s actually just a shed-found 90’s period Micron can leftover from my FZ750. It just needed a custom link-pipe adapter from ebay to fit to the link pipe (made to order, around £10 – see pic). Aesthetically, it’s a good job there’s a side cover hiding the confusion of ‘creative thinking’ that links the incongruent exhaust parts together. With the bike assembled, it looks pretty cool, but with the side panel off it looks like something made by the losing team on junior Scrapheap Challenge. It replaces another Micron, which albeit made for the DR, was really heavy, rusty, not repackable and very noisy. I had long harboured a fundamental dislike of this exhaust and was delighted to replace it, but truth be told, exhausts are like opinions – you’ll never have to wait long before you hear one and not all of them are good! Anyway, I’ll cut to the chase. Today’s run on the dyno was a simple strap it on, warm it up, and get a figure with no subsequent messing about or adjusting. And the result was…. Well, it was both good and not as good as hoped. Let me explain. The rules of bar room bull mean if you’re talking power output, always pick the big numbers. That means peak power (yeah – that bit you hardly ever use). Looking at those on the DR this time out we had a gain. Did we get
to 36bhp? No. But we did get to 34.26, up 2.03 bhp, or about 6.3%, which is a useful (but still not target matching) increase. Where things get interesting is either side of peak power. A little farther back down the rev range there is one point where the gain reaches a whopping 13.2% (measured change was from 26.5 to 30bhp at 45mph in 4th gear). So, that’s where the extra seat of the pants power I’d been feeling was truly coming from. It’s a huge increase by any standard, and if we’d carried that gain on to the top end, we’d have chugged past the 36bhp target with ease. Whilst that didn’t happen at the top end, what did occur was the bike’s willingness to hang on to the gear for another few mph – the dyno chart (pictured) shows the DR running out of puff at 68mph on the old cam-chain versus 74mph on the new one. It’s a really significant change in this motor’s usability and it’s easy to feel when you ride it. So, am I satisfied? Well, yes and no. The cam-chain swap has been brilliant and I’m 1000% chuffed I had Tony Galea do it. However, whilst initially proud of my new free-breathing exhaust made from bits lying around in the shed, I’m now looking at it and asking if it’s really doing the job. Always a man ready to do things properly, Gav at MSG has suggested getting back on the dyno on a quiet day when we’ll plug in the fuel/air ratio meter and see if there are some gains waiting by properly testing jet/ exhaust combinations. Top man. The finishing line is in sight. From its wheezy original 26.73 bhp to today’s chunky 34.26bhp, our gain is already good. With one more push, however, I want to see if we can really pip that long-held 36bhp threshold and finally just enjoy riding it! cmm