[Voimakas]

So I was told that improving compression in a motorcycle engine is a great way to increase horsepower. Also in this list was "blueprinting the exhaust" (?). Can someone explain please A) the blueprinting and B) how to increase compression? Thanks. Yes, I'm a noob.

 

[AwwsChwA]

raising compression ratio in any piston engine is a great way to increase torque, but it won't create huge increases in horsepower. Horsepower is related to how fast the engine can run, whereas torque is created based on the forces acting on the crankshaft at any point in time.

So anyway, raising compression is useful. However, it's not as simple as just raising it. There are lost of options...some engines are factory-equipped with dish-faced valves, so replacing them with flat-face valves will raise compression. In most engines, the pistons can be changed out and replaced with specialized (or in some cases different factory ones) units that are designed to raise compression (piston application varies with each different engine). The cylinder head and engine block mating surfaces can be machined down to bring the piston further up into the combustion chamber, which will also raise compression. There are other ways, but these are the most common.

Many things have to be considered when raising compression. The reason for doing it is that it creates higher compression temperatures, putting more energy into the compressed fuel/air mixture, thus creating a more powerful explosion when the fuel/air mixture in the cylinder is burned. But, with higher temperatures come other risks. In most cases, higher-octane fuel must be used to prevent premature detonation of the fuel/air mixture. Also, engines with aluminum cylinder heads & blocks are at greater risk of overheating and surface damage if temperatures get too high. Another aspect that most people don't consider is the increased wear on the connecting rod bearings.

let's say, for example, that your engine has a 9.5:1 compression ratio. If you raise the ratio to 10.5:1 (by any of the methods discussed above), the more powerful explosion of fuel/air puts much more force onto the connecting rod bearings and crankshaft. This will accelerate part wear and eventual failure. I'm no expert, but I've heard from many different engine builders that, for a street engine that will be daily driven and raced from time to time, compression ratio should stay at or below 10.5:1 in order to prevent premature bearing failure.

So, those are some pro's and con's of raising compression. Of course, there are many more aspects to look at. I just chose the most obvious ones.

As for blueprinting the exhaust...this is the art of making each exhaust channel of the engine *exactly* the same. exhausts from the factory are pretty close, but of course are not exact. There may be slight differences in tube size, small dents, variations in tube length, variations in bending angles, things like that. When an exhaust is blueprinted, each tube is made identical to each other. This ensures that each cylinder flows exactly the same amount in all RPM ranges, and will improve performance and throttle response because it improves exhaust pulse balance.

 

[Voimakas]

Thanks

WOW. Thanks a lot. I'm thinking that the whole compression raising thing would probably be bad then cause my cycle will be a daily driver. IT'll have to be, it's the only thing I own.

Are there any other ways that the acceleration of a bike can be made faster without compromising the mechanical integrity of the bike and will allow it to be a daily driver without too many problems?

 

[AwwsChwA]

You're welcome any time, glad I could help. If you have more questions, just ask. If I can't answer em, I'm sure one of the other resident gearheads here can help.

There are lots of ways to improve the performance of any vehicle with an engine. Replacing the air filter with a high-flow unit is a good way to get a small gain. You can also spend some dough (typically a few hundred bucks) and get a high-performance exhaust system for your bike. You can also improve the ignition system to get more performance. Check out www.ignitionsolutions.com and see if they offer an ignition booster for your bike. I have their ignition booster for my Honda CRX, and it really does make a big difference.

So you figured out pretty quick that raising compression isn't so easy, eh? :wink: There's a lot to consider, and the higher the ratio, the more time you have to spend perfecting the air/fuel ratio to make absolutely sure you don't get detonation or other nasty engine side effects.

Basically, just search around for performance upgrades for your motorcycle. Bikes are just like cars, the popular ones all have big aftermarket followings, with lots of performance goodies that are daily-driver safe.

 

[sparty]

in all honesty, the "easiest" way to get better acceleration out of your bike is to sell it and buy another bike that has, well, better acceleration. i mean, you can get small gains here and there managing air flow, but if you're looking for a kick in the pants difference, you're setting yourself up to be let down. but making a sleeper is half the fun, thats why all of those modded hondas are running around. no one expects them to be fast, or at least they didnt. i'm not trying to discourage you, but just giving you the truth. and unless you're looking for a through and through race machine, alot of the higher end modifacations will hurt more than help your daily driver as noted above.

reason being is that engineers have worked manly sleepless nights to get these bikes to be the machines they were intended to be. when we start saying that they were wrong, and didnt have our intentions in mind is when we have to start thinking like them, cover every angle before making a change because, more than likely everything on that bike was put there for a reason. but again, thats half the fun. i'm half ranting because of some of the things i've done to my car and now regret it farther down the road. but all in all it was a good learning experience. so i say go for it, start making that bike the way you want it to be, just proceed remembering that it has to work for you ALL of the time, esp if its your main mode of transportation. good luck.

 

[sime]

in all honesty, the "easiest" way to get better acceleration out of your bike is to sell it and buy another bike that has, well, better acceleration.

actually there is a cheaper way: fit a smaller front sprocket. (lower overall gearing = better acceleration)

what bike is it sparty?