Why forced air over nitrous or engine building?

[john_trickle]

This makes for an interesting discussion always. If the desire is to go fast on occasion for the least amount of money, (on occasion) then nitrous is the way to go. That is of course untill you go big, then you will have to factor in a couple engine builds periodically. I say the phrase "on occasion" because I think most people buying a nitrous setup aren't considering the refilling of bottles dance and if at the track, bottle pressure issues, heaters and other things of the sort. I am certainly not against nitrous, it just has a very specific use and application. After reading this FAQ, look below to reference the use of nitrous with forced air. Now to some facts to support forced air over engine building and/or nitrous. The first dynamic to talk about is the effect on the pistons and rods during normal combustion at say 11,000 rpms. They stretch and compress so much that when building high compression race motors this has to be taken into account when determining deck height. Superbike race teams do not use off the shelf high compression pistons, they use lighter shorter pistons that only have a race worth of life due to this effect. When a more volatile mixture is added in this situation such as nitrous, there is a hammering effect that intensifies the component stress and shortens the component life. That is why you have maybe seen pictures of nitrous motors with a rod coming through the block that are at 100% were putting maybe 250hp to the rear wheel. That is also the reason that there is not a single nitrous bike in the shootout categories placing in the top 10. To run no bar and only be at a 68" wheel base and reaching into low 7 second territory the bike has to push 500 HP. Nitrous bikes will not sustain those stresses where as forced air bikes can maintain that easily for a season. Now for engine building and/or nitrous. In normal aspiration, the term "no substitute for displacment" does apply but in forced air things are a bit different. It is all about containing boost pressure and giving the best chance to the components for wearability. Lets start with the fact that for companies to reach into the stratosphere in RPM to get such high horspower, the bore has to be larger than the stroke. They have been very careful to go as large as possble but yet still have a bike with little chance of failure for the regular customer. This is termed "oversquare". The most typical thing for a motor such as the Hayabusa is to go 2mm over on the bore to give a displacment of 1397. This can cause many issues. If you have ever noticed the skirt height of such a piston compared to the diameter it is amazing in stock form that it works at all much less going still larger on the bore with no extra skirt height. It makes greater wear on the cylinder walls and also the rings and bearings. More wear on those components of course means more component temperature and heat saturation. If those things don't concern you, consider what is needed to go past the 200 hp level, a bore and piston kit won't do it. The cylinders have to be bored and replated with a ceramic coating. This all needs to be done by a reputable company such as Millenium Technologies and of course the oversized higher compression pistons. With simple tuning this combination alone will net around 175-180 hp. The engine needs to breathe more efficiently to utilize the added displacment. Cams and or throttle bodies will be needed. With the aggressive cam shaft, a new spring kit would be a good idea to keep valve float away. With these additions, we can now approach the 225 hp mark. Im not going to give a part pricing run down because even without experience, common sense will tell you that we have just picked up quite a tab. The next issue if you want to reach past the 225 hp point will be to either pay top dollar for the right person to tune a decent 1397 setup, or go bigger with say a stroker crank. After 225 hp, we will now have a fueling issue. Without modifying pressures, that is the capability of the bike. Our throttle body diameter is now also a concern. The now least favorite concern is streetability and wearability. The bearings are now carrying a tremendously different stress as opposed to stock form. The bike feels noticably different even at idle, gone are the days of easy starting and smooth running through town in low RPM conditions. My least favorite part of an all motor build is the lack of tuning flexibility. Once it is set up, there is no controller for the onset of power, amount of power or any of these factors. For me it is like having your cake and eating it to when it comes to forced air anything. The ability to have the motor start, run and perform as smooth as stock all the while having the ability to push more than 400 hp at the touch of a button. That for me is the definition of STREETABLE! These are all of course opinions and not to say that forced air is for everyone. I hope to have just given a few thoughts of consideration as you weigh things out.


john