New Team One Cylinder Engine

[Ahmad Rezq]

Hello my friends this is Ahmad Rezq from CURT,
It has been 2 years since we participated in London competition 2012.
we are starting all over again now preparing for 2015 competitions. Our main goal is such to build a simple car and believe me the simplest is always the hardest.
our engine guy came to us with the idea of running one cylinder engine in the new car and he recommended Honda CRF-*‐450X. we made many searches and read many articles state that in the competition the horse power is not the main thing as most of the teams use 1/3 of their huge horse power so by running a one cylinder engine we will reduce about 35-40 kg from the car weight which will give us many advantages we have to put many things in mind to take the decision.
http://www.optimumg.com/technical/it-is-all-about-horsepower-or-is-it/

1 - This is the first year of us to design a car for the competition.
2 - we don't know exactly how the restrictor will affect the horse power of the engine
so can you guys give us some information about the usage of one cylinder engine in the competition , is it a good choice considering this is our first year to design a car ?
how can we predict the effects of the restrictor on the engine?

[Jonny Rochester]

We are using a 450cc single. Our engine guy had calculated that we would not reach choked air flow at any time, so the restrictor would not have a big effect on our power. The engine and gearbox itself is about 30kg dry.

[Bemo]

I don't see a general problem to use that engine as a first year team. What you definitely should have in mind while choosing an engine is the availability of spare engines and spare parts for it in your country. It is propably not a good idea to use an engine which isn't sold in your country/region. If the engine is very common in your area, it is easy and cheap to get spare parts quickly. When I was still an active team member we used a Honda CBR600RR engine. There were several stores in Stuttgart where we could by spare parts for it. It is a big pain if you loose testing time because you are waiting for parts.

[Mbirt]

In addition to evaluating the local availability of engines and parts, I would suggest starting with and engine that has factory EFI so you can use the stock encoder wheel. This means that you do not have to open the engine when you switch to a calibratible ECU. The Honda CRF450X and TRX450ER engines are carbureted and will require custom encoder adaptation that challenges mature teams. Switching to the 2012 WR450f engine with a stock 12-1 VR encoder was a very pleasant experience.

The effect of a restrictor on a single is very easy to predict. If a convergent-divergent nozzle restrictor is placed at the intake port of the engine in place of an intake runner, the size of each induction event will be choked. This creates a flat torque curve and a linear rising power curve. In my testing, this was about 20 ft*lb of torque--quite a reduction from the stock output of the engine. You can model this on any high speed single-cylinder 4-stroke engine (no need to correlate the engine model for this study) in GT-Power or WAVE if you have a team member that is into that.

Teams run theoretically large plenum volumes to get engine torque back to unrestricted levels and prevent the event-by-event choking of the restrictor.

[Jay Lawrence]

Ahmad,

To echo sentiments above, I would advise getting an engine that has fuel injection as standard. This means one less hassle for you to deal with. There are plenty of modern singles that now offer fuel injection as standard. Also, just to clarify some conflicting information above: while the bulk flow of air into a 450cc single may not choke the restrictor (as Johnny points out), each intake stroke is drawing a much larger amount of air (~450cc/induction stroke) than, say, a 600/4 (~150cc/induction stroke). This creates the reduction in torque mentioned by Mbirt.

[Ahmad Rezq]

These are very helpful comments, but there is a vital question i wanna ask. i did read a paper of one of the team said that the single cylinder engine needs forced induction and since we have no experience in turbo or super charger it will be a problem.
another word to say we asked one of the engine suppliers here in Egypt and he told us that the engine will work only 60hrs after that an overhaul must be done. !

[tromoly]

No idea where you heard a single needs to have forced induction, many successful teams run NA singles.

60 hours of running isn't bad at all, my friends who race motocross only put 25 hours on their engines before overhauling, and they do rebuilds once or twice per calendar year.

[Swiftus]

60 hours is good. The race is 30 minutes long.

[Mbirt]

Don't read too much into the random FSAE documents you find online. They're probably penned senior capstone students that had to submit the work for academic credit rather than the work of real multi-year volunteer students that had to do the real work and see the project through.