Porting can be one of the best performance mods you do to your bike; especially if it’s a 2-stroke. It can also be the demise of it if not done correctly. You see, the bike factories build the engines to certain specs so that it has the best overall and usable power. So by changing the port timing and dimensions alone, you’re not going to see a huge gain in performance, and possibly a loss. If done right, you will merely be changing the power-curve or peak horsepower, depending on what you’re looking to achieve.
Easier Said Than Done
Porting itself is not a difficult task, but it takes a lot of knowledge and patience to port an engine and produce more power, which is why professionals can charge a few hundred bucks for a simple port-job. If you don’t have experience or training, I highly suggest you send it out to a professional engine builder. Most of them know what they’re doing, and all you have to do is tell them what you want more of (horsepower/torque) and where, what fuel you’re going to use, and they’ll take care of everything else.
Bigger Is Not Always Better…
Any skilled engine builder you ask will tell you that bigger ports alone aren’t going to produce more power. In fact, more often than not, it will reduce power. Like I mentioned before, there’s a reason why the factory made their engine a certain way; to produce the most power over the broadest RPM range. So if you grind off just 0.5mm (.020″) from any of the ports in the wrong direction or location, it will lose power somewhere and gain little to no power elsewhere. Porting is an art; not a job for a hacking grease-monkey.
Bring It To The Best
There are many good bike tuners across the States, so do a little research to find who’s close, in your price-range, or if they can get the job done the way you want it. Eric Gorr (Forward Motion), HPBikes, Pro Circuit, and Max Power are a few that come to mind if you want quality. Generally, the more you pay, the better job will be. But, make some calls to these guys and see what they say. Most of the really good builders are easy to talk to and will get it done right, and fast.
On the flip-side, those of you that are mechanical and willing to do some modifications to your engine (with a risk of ruining it), I will make another article in the future on how to get the most of it while keeping it stock. This is done by blueprinting…
Going from an 85cc motocross bike to a full-size dirt bike is a big jump in weight, size, and height. It can be intimidating when you’re racing against adults and you can’t touch the ground with your feet. Even if it’s a 125 2-stroke, it still feels night and day different than a little 80. If you’re like me (5’6″) and you can barely touch the ground with one foot, an extra inch or two can be the difference between crashing and staying on the bike in a corner or tight single-track trails.
Chopping The Saddle
The most common (and cheapest) way of lowering the seat height is by trimming the seat foam. This is a good time to put on a new seat cover as well! Just take the cover off, trim the seat foam down to the desired size (you can usually take off 1-1.5″ from the middle of the seat and still have enough left). Then you simply stretch the seat cover back over and staple it. This mod is popular because it’s cheap, and pretty much anyone can do it with a little patience. The downside is that there is less foam to sit on, leaving you with a stiffer ride, as well as a curved seat.
Linking Closer To The Dirt
A lowering link is another common mod to lowering the ride height on your dirt bike. It’s an easy solution for short riders stepping up to a full-size bike. It’s a direct bolt-on, and lowers the rear end 1/2″ – 1 1/2″ on most bikes. Cost is probably the biggest factor when considering a lowering link, but it also changes the handling and suspension of your bike. Many riders complain that the pre-load is quite a bit softer, and that the front-end sits higher, changing the rake angle. Handling isn’t affected so much at slower speeds or trail riding, but experienced riders may notice it on the motocross track or at higher speeds.
Taking A Slice Out Of The Subframe
If you really want to go crazy, some guys (and gals) get a chunk of their subframe cut and welded back together to lower the seat height. There are more downsides to this modification, so I wouldn’t suggest it to be first on your list. The more pieces that have to be welded together, the more likely it is to crack or break (so make sure you get a professional to weld it, especially aluminum). Since the subframe is holding mostly the back half of the seat, that’s where most of the lowering is going to happen. Also, if you chop too big of a portion out of the subframe, it may end up causing the rear tire to hit and rub against the fender when the suspension is compressed.
Not only can you get a smaller diameter rear rim, but you can choose the amount of rubber around it. Motocross bikes come with a 19″ rear wheel, but some off-road/enduro trail bikes have an 18″ rear wheel. Swapping for the smaller wheel will lower the rear-end of the bike. Depending on what you have already, going from a 110/100-19″ to a 100/90-19″ rear tire can help lower the bike as well.
Adjust Shock Pre-Load/Sag with Locking Nuts
If suspension set-up is critical, I would not suggest this to be the first way of lowering your bike, even though it’s simple and can lower the bike close to 2 inches. If you look on the rear shock assembly, there will be two locking ring nuts holding the spring compressed. If you haven’t already set your sag/ride height (more on this in a future article), I suggest you do that first. Your race sag should be about 100mm (4″), but if you keep loosening the nuts and spring, it will eventually stop, and that’s where you will have the most sag (lowest seat height). Like I said before, if you are racing or riding hard, I would not suggest going past the proper ride sag because the suspension will be too low and soft. Trail riders can often get away with this (I have tried this personally and it works great in tight single-track).
Moving The Forks Up
In addition to the other mods, you can (or need to), move the forks up in the triple clamps. This will lower the front-end of the bike, and may be required for some of the previous mods because the rear-end will sit lower. Be careful though, and do one small adjustment at a time, because changing things around like this can mess up the geometry and handling of your bike. Take note of all the specs you’re going to modify as a starting point in case you want to go back to it.
Think Before You Act
All of these can change things that require more modifications:
Kick-stand too tall, little seat foam, lower ground clearance, less suspension travel, different handling, ergonomics, different gearing (smaller wheel), etc… And remember, you don’t always need to lower your bike. Being able to touch the ground with two feet isn’t a must, even when trail riding (although it does help in most cases). Just look at some of the top pro racers that are around five and a half feet tall (Carmichael, McGrath, Stewart). With all this in mind, do a little research to find out which one will cause the least trouble if you are unsure. Good luck, and ride safe!