There are different kinds of mechanical improvements that can be made to recreational vehicles. Depending on your needs, financial means, or mechanical ability, there are DIY upgrades, and then there are qualified companies that can help with your projects. In my case, I wanted to upgrade the horsepower of my modified quad by increasing the displacement. Today, I’m going to talk about my choice of upgrade and the techniques used by two companies that helped me achieve my goal, Mécanique Sport GM and CVTech AAB.
The most effective way to add horsepower to an engine is to increase the displacement. There are only two ways to do this: boring and stroking. The latter is by far the most expensive way because the crankshaft has to be modified to increase the stroke, which requires some very specialized equipment and experience that very few mechanics have. Therefore, I chose overboring without having to give it a lot of thought.
In my article, I’ll be talking about increasing the bore size. This method increases both torque and power without increasing engine rpm. To achieve this, I called on two companies, each with their own expertise, since not just anyone will take on these kinds of modifications.
There are four steps to overboring:
Assessing the Engine
To determine whether the upgrade would be possible using the existing cylinder, the cylinder had to be checked to see if it was thick enough to take an over-dimensioned piston. In other words, there has to be enough space to use a machining method that consists of shaping the inside wall of the cylinder. If the cylinder was too small, a new cylinder would have to be ordered, along with all the parts that go with it, of course, which would have cost a lot more in the end. After Mécanique Sport GM in Dolbeau-Mistassini examined the piston, I learned that the original one would be perfect for upgrading.
A New Piston
After the cylinder was examined and it was confirmed that it was thick enough to be machined, a new piston had to be ordered, one that would increase the engine displacement from 650 cc to 680 cc. It was a fairly modest change if you consider that it’s possible to modify the displacement by up to 110 cc or more. For a large-scale increase, however, special kits have to be ordered for this purpose, since boring an original cylinder has its limits.
Once the overdimensioned piston had arrived, we shipped the piston and just the cylinder (no seal) to CVTech-AAB in Thetford Mines, a specialist in Nikasil plating.
A damaged or worn aluminum cylinder, or one that needs to be bored again, has to be plated with Nikasil, a nickel silicon carbide surface treatment that’s applied to aluminum cylinders. This plating offers an unbeatable resistance to heat and friction (no flaking or scrapes), unequalled hardness, and a competitive price. Nikasil plating requires a high degree of precision, made possible by specialized tools. The thickness of the new coating is finetuned to take into acount the condition and the dimensions of the cylinder. The final result in each case is a deburred cylinder identical to the original one and ready to be installed. This process helped avoid having to buy several, very expensive parts.
Engine and Parts Reassembly
After the Nikasil plating, the Mécanique Sport GM team reassembled the parts and engine, giving my quad more torque and more horesepower.
NOTE: After this type of modification, the carburetor must be calibrated, as any change affects the air-fuel ratio. A poorly calibrated carburetor can cause the following problems:
- excessive heat
- engine noise with rapid acceleration
- loss of power when the engine is hot
- difficulty starting
- backfiring and exhaust noise when decelerating
All problems that you want to avoid, of course. I’ll talk about this more in my next column.
In short, overboring is a very easy way to increase your quad’s horsepower economically and with a generally favourable end result. Torque and power increase proportionately to the increased displacement, making your quad just a little bit more powerful. If you’re unsure about embarking on this kind of change, I suggest that you visit Mécanique Sport GM and CVTech AAB for more information.
If you’ve got ideas about modifications, or if you have questions about the upgrades I’ve made, please feel free to contact me. I’m always happy to talk about old projects and future ones.