Motorcycle Engine Smart

Pros And Cons Of A Motorcycle Powered Smart

I’ll get straight to the point of this page. The only upside of having a motorcycle powered smart is that you can impress people you know who have a particularly low IQ.

But Dey Is Well Quick Bruh!

No, no they aren’t.

What About A 1300cc Hayabusa Engine?

No, that still won’t give you a quick car.

But That Engine Makes 175BHP Stock!

BHP is good for Autobahns, race tracks and winning “Top Trumps”.

OK, time to go back to school.

BHP – Brake Horse Power

BHP only affects the top speed of the car. If you got a car with 100bhp and somehow tuned it to ONLY increase the BHP and you increased it to 500bhp, the before and after car would still do almost the same 0-60 time (taking into account the cross over between torque and BHP as the car accelerates).

The faster you drive, you get increased forces trying to slow the car down. These are from aerodynamic drag, rolling resistance, engine friction, transmission friction, etc. These forces reduce the amount of BHP that makes it from the engine to the wheels. An increase in BHP gives the engine more “top end” power, effectively allowing more power to make it through the transmission to the road. This power increases your top speed.

So, unless you live near an autobahn with an unlimited speed limit, big BHP is fairly pointless.

So Why Do Cars Have Ever Increasing BHP Figures?

Because engine designers generally balance the BHP figure with the torque figure. With these 2 figures well balanced, the car feels better to drive. Car companies know that BHP sells cars to people who don’t know any better. It’s a real life Top Trumps.
Bigger is better, everyone knows that!

What Does Increase The 0 – 60 Time?

Engine torque is the number you need to look at. Torque is the twisting power of the engine.

With high BHP and low torque, the car would go fast but would take ages getting to the top speed.
With low BHP and high torque the car would be quick off the line but have a low top speed.

If you consider that in most countries, the top speed limit is 70mph, anything much faster is a waste. However, no one would buy a car that only did 70mph and if the torque/BHP balance was that different, there is a good chance that the car would feel like a piece of shit to drive.

OK, So Back To The Motorcycle Engine

Let’s look at the torque of the Hayabusa engine in its most powerful standard form.

130 Nm or 96 ft/lb of torque.

Because you have spent your life being fed BHP bullshit, you probably have no idea if that’s good or not. I’ll give you a clue. Have a look at the dyno print out below. This is for a standard fortwo 451 turbo.

108 ft/lb of torque. So, the standard turbo fortwo already has 12 ft/lb more torque than a Hayabusa.

After a remap, the 451 turbo torque increased…

…to 122 ft/lb of torque. 26 ft/lb over a stock Hayabusa.

So, why do you think an engine with a lower torque figure will be quicker?

But The Standard Smart Gear Change Is Really Slow

Yes, it is. That’s why the smart is slow from 0 – 60mph. Not to mention the gear ratios aren’t designed for fast 0 – 60 times. It’s a city car, not a sports car.

So, A Motorcycle Engine Smart Will Be Faster 0 – 60mph!

Yes but not by much. Remember you are comparing it against a standard smart car here. Your best 0 – 60 in a bike engine car will be between 7 and 8 seconds with a perfect pull away.

My Nan’s old Honda Civic does a better 0 – 60 time than that and it weighs twice as much.

In fact, no bike engined smart has ever beaten the 0 – 60 time of Al Young’s modified Roadster with a standard engine. It did a 0 – 60mph in 6.66 seconds (RAC verified).

A Hayabusa Engined Smart Must Be Faster to 60 Than That!

Nope. If you take into consideration that a standard Hayabusa takes 2.5 seconds to get from 0 – 60mph with a perfect get away BUT the smart with a Hayabusa engine weighs 3 times as much.

You can’t cheat physics. 3 times the weight is minimum 3 times slower. This isn’t taking into account the added aerodynamic drag of the car’s body and the extra rolling resistance of 4 tyres with a larger contact patch.

But I Have Seen Videos

Yes, you probably have, like this one.

Let’s break down the footage. Tries to pull away, lurches, almost stalls, full RPM to dump all of the torque, spin the wheels, slowly pull away.

Don’t be fooled into thinking that wheel spinning means the car is quick. The high revving bike engine creates all of its torque very quickly which breaks the traction of the tyre on the road. Once it has done that, it doesn’t take much torque to keep the wheels spinning.

The video just shows you how useless it is. Good for burning tyres, burning clutches, making a load of noise and doing donuts. No good for actual driving, racing or being a quick car.

Other Contributing Factors

A Hayabusa weighs about 260kg. A smart weighs about 3 times that when totally stripped. Near 4 times if you leave everything in.

The clutch and transmission in the Hayabusa engine aren’t designed to deal with a car weighing nearly 900kg. Therefore, you get a load of clutch slip unless you dump the clutch which just spins the wheels.

What If I Change The Gearing?

If you adjust the gearing down enough so it doesn’t burn the tyres or the clutch you’ll either seriously affect the top speed or you’ll have power band issues between gear changes which will affect acceleration.

What If I Use A Proper Car Clutch System?

Great, do that. Any properly built race or track car with a motorbike engine will use a proper car clutch. If you are going to do that, you may as well use a proper car engine with a proper clutch. The problem is that car clutch and gearboxes don’t connect easily to a bike engine and they take up a fair bit of room.

I’ve Seen Bike Engine Smarts Beating Powerful Cars

No you haven’t. All but 1 of the videos I have seen of smart cars beating Corvettes etc have had other car engines fitted, not a bike engine.

There is 1 video of a smart beating a Ferrari where I am unsure if the smart has a bike engine (it does get way fairly slowly so maybe it does) however, the Ferrari driver either lets him win, fell asleep at the start or can’t drive his car because the get away was appalling.

Motorcycle Engined Smarts – Pointless Shit?

Yep. The next time someone says about them, roll your eyes and walk away. If you want to build a quick smart, use a car engine.

But I Want One Because My IQ Is Well Below Average

99% of the bike engined smarts take a year to build and then 4 weeks to end up on eBay. Why put in all that time and money just to sell it almost straight away for a massive loss? Because it’s shit and they are disappointed.

If you want one, keep an eye on eBay. There is usually 2 or 3 a year. Buy it, drive it, realise it’s shit, resell it to some other schmuck.