Car Efficiency Experiments

[thunderhead]

The result was an 18% to 25% improvement in efficiency -- at the cost of increased clutch wear and the need to recharge the battery.

http://tudor-pirate.livejournal.com/64591.html

[drdongle]

What kind of car?

[thunderhead]

A petrol Suzuki Samurai.  The wings are made of checkerplate (heavy) and the wheels are oversize with off-road tyres (bigger resistance, speedo underreads by 13%).

Although the figures are just over 18mpg, the 13% extra means it's actually nearer 21mpg.

It's the only petrol car I have on the road.  My VW camper has been off road for years; and my kitcar is in pieces waiting for an electric motor to arrive.

When the kitcar is back on the road, I'll rip the Samurai up to make a Dutton Amphijeep -- probably another electric one.

[Norm]

   If you really want to experiment and possibly

get startling results ...try inflating the tires

to 10 or 15 ...use lighter weight oil in the engine and lower viscosity lube in the drive

train. Probably void the warranty on your vehicle?

                   ( :>) Norm.

[pyrocasto]

To 10-15psi, or 10-15 more?

10psi=flat tire

My truck stays at 40-42psi, right below max. Helps out quite a bit I've noticed, but have to let some out in the snow.

[zap]

I do the same and it helps alot Chris. Ride is a bit harsher but hey, it's a truck. Keep an eye on your tread and wear pattern. Even tires inflated well below stated load ratings can have wear accelerated unevenly if alignment or balance is slightly out, from what I've noticed.

[hiker]

i dont see ......

driving wide open-burns more fuel..

driving in high gear and slipping the clucth to take off-surprized you didnt throw a rod throu the crankcase..lugging down your engine is hard on all kinds of parts..

better off just driving senceable...

[Norm]

 I meant to say 10-15 psi Above Average.

                  Norm.

[thunderhead]

i dont see ...... driving wide open-burns more fuel..

Driving wide-open does burn more fuel, but it also generates more power.  If driving wide-open consumes double the fuel but means you only need to have the engine working for 40% of the time, it's still be a win.  Evidently it is. :-)

Given the air resistance goes up as the square of speed, and so the energy per mile overcoming air resistance goes up linearly as speed, for a car to give the same MPG at 30mph and 60mph is evidence that the engine is only 1/2 as efficient at 30mph as 60mph.

My understanding of the mechanism is that the pistons extract energy from the burning mixture by expanding it and so lowering its pressure.  When the mixture's pressure approaches that of the atmosphere, no more energy can be extracted -- the same force is on both sides of the piston.  So the higher the starting pressure, the greater fraction of the energy can be extracted.  

The throttle lowers the pressure of the mixture in the cylinders -- so best efficiency is with the throttle wide open.  

driving in high gear and slipping the clucth to take off-surprized you didnt throw a rod throu the crankcase..lugging down your engine is hard on all kinds of parts..

I wasn't slipping the clutch to take off (any more than usual), I was using the clutch to disconnect the engine for most of the time, and leaving it to idle.  Think of one foot on the floor or the other, but never both.  When taking off I'd select a low gear (normally first) and floor it.

The thing I'd be most concerned about when driving at low revs and wide throttle openings is oil pressure, especially as the engine is over 100,000 already.  But then, if I broke it -- the engine is over 100,000 already.  I'm talking about a beat-up old 4WD with outrageously disreputable bodywork that I paid £400 for and intend to break for parts -- but not engine parts.

As you say, I'm better off "driving sensible", and that is what I'm doing now the experiment is over.  I just wanted to see if it would make a difference, and if so, how much.

It does, and a lot.  So I've convinced myself that my understanding of engine efficiencies is correct, and that I know how things like the Prius work.

I don't imagine myself driving like that again, except possibly if we have another fuel strike.  But in a few weeks, now the weather's warmed up, I'll get the kitcar electrified and the Samurai can become an occasional use vehicle.

[Bruce S]

Thunderhead;

 If you're still watching this thread.

I have a few observations.

With the information you sent. This would explain why those little 5hp Briggs lawnmower engines run so very long on such a small tank.

Think about it... once they are  started they are running pretty much flat out wide open all the time. At least the ones around my neighborhood anyway.

I use an electric one, so I don't use these anymore.

I'm a bit curious about the alternator giving up at the higher rpms. These things are notorious for wanting higher rmps to get the charging output.

Anyway thanks for the test.

BTW: A little disappointed to see that the Samuri only get 13mpg our 5.7l chevy with 4wd and 305Ms gets with nasty driving habits better than 16 in the city.

And the 165k+ Ford f100 gets even better and it's on a carb.

Cheers

Bruce S

[thunderhead]

This would explain why those little 5hp Briggs lawnmower engines run so very long on such a small tank.

And it explains why generators do the same thing.  So an electric car with a generator to give longer range would be about as efficient as an ICE can be.

'm a bit curious about the alternator giving up at the higher rpms. These things are notorious for wanting higher rmps to get the charging output.

That's the opposite of what I meant.  The problem was that driving along with my toe on the floor at 2000RPM in 5th doesn't do much for the alternator.

BTW: A little disappointed to see that the Samuri only get 13mpg our 5.7l chevy with 4wd and 305Ms gets with nasty driving habits better than 16 in the city.

We have bigger gallons than you: I make it about 18mpg.  It's still very poor.

The problem with the Samurai is that it's big and heavy, and on agricultural tyres.  The checkerplate wings probably take it to 1300kg or so, from the stock 1000kg.

I've been poking around scrapyards looking for standard tyres on wheels that will fit -- I don't want to dispose of the Camac 4x4s that are on it now when we're planning to go look at more smallholdings in Ireland in a month or two.  So I need more wheels.

I'm only commuting in the Samurai while I put an electric motor in the Quantum.  The problem is, the wife keeps giving me jobs to do at the weekend, and my boss gives me jobs to do during the week.  I'm sure many of you know how it is. :-(

But I'm glad it's not finished today: I look out of the office window and I see snow drifting past.  In England, with our government's inability to deal with a few flakes of snow, that means 4WD is a good idea.

And the 165k+ Ford f100 gets even better and it's on a carb.

The Samurai's on a carb too.