CAR CLINIC: Don’t split hairs, get a Vanguard

Wednesday February 14 2018

I need your help to make a choice between the Vanguard and the Harrier. PHOTOS| FILE| NATION MEDIA GROUP

I need your help to make a choice between the Vanguard and the Harrier. PHOTOS| FILE| NATION MEDIA GROUP 

By BARAZA JM
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Hi Baraza,

Thanks for your informative articles, which I follow keenly.

I need your help to make a choice between the Vanguard and the Harrier.

I have received different views but the Vanguard seems to carry the day mostly because of its 7-feature model. Otherwise the two cars are said to have similar engines, which gives the Vanguard the advantage due to  its spaciousness.

I am looking for a good SUV with few mechanical challenges since  I am coming out of  a bad relationship with a Toyota Caldina 2003 model, during which I had to change two engines and a gear box despite timely and regular servicing and check-ups!

In a nutshell, I want to avoid the regular ugly dates with the spare part dealers and my mechanic (except for regular servicing).

 

Since you are looking at Toyotas and/or Toyota products which are reputedly reliable — despite your ordeal by way of a Caldina — you are basically asking to split hairs. So this is how we will look at it.

You are already attracted to the Vanguard’s space and seat-count superiority over the Harrier’s, so just go for it then. However, to avoid “regular ugly dates” with shop owners and mechanics, as well as untimely engine and transmission replacements, go for cars that either have extensive and well-documented service histories, or have undergone thorough checks to sniff out mechanical time bombs lurking just under the surface.

 

Hi Baraza,

I couldn’t help but chuckle when you advised the fellow inquiring about the Fielder, Sienta, Voxy to “do” his Voxy properly and not tastelessly by attaching a spade to the back door or a snorkel to the front-quarter panels.

On that list of tasteless add-ons, you could have advised him “not add bull bars” and “side steps on a Voxy or Noah”. They are unnecessary, especially the side steps, as you can comfortably plant your foot and board a Noah or Voxy without them since these cars have relatively low ground clearance.

Now, I’m just curious: the other day, I came across a Range Rover Evoque  fitted with four exhaust pipes, which I am sure is not a natural part of the design for the car – at least for those I’ve come across. The maximum are two and I gather the two are the exhaust headers for each arm of the three cylinders on each side for a V6 or four for a V8.I’ve seen multiple exhausts in some Prados too. Is it cosmetic to have 4 exhaust pipes or there are inherent benefits?

Also, on acceleration, that particular Evoque emitted that loud growl and almost typically hissing you hear in turbo- charged Subarus.

I believe the Evoque has a large engine displacement just like the Prado, so why turbo charge it after market?

Keep up the good work.

 

Yea, listen. I’m not sure I’m allowed to talk about Range Rovers anymore after last week’s article elicited a very strong reaction in the form of a lengthy, demand-ridden phone call from the company’s South African-based sub-Saharan headquarters. They were not at all pleased with what I said and how I said it, so for the moment you will understand if I opt to steer clear of any more heat by not talking about their cars.

However, I  can talk about multiple exhaust tips and after-market turbocharging.  Post-sale addition of go-fast bits such as forced induction is done with an obvious goal in mind: turn up the wick on engine outputs. The Prado might have a relatively large engine but there are those who believe they could do with more power and/or more torque, particularly users of the 2.7 4-cylinder petrol. However, it is not common to find modded 2.7s; most people would simply pony up for the petrol V6 or one of the factory turbo diesels, then modify those.

That aside, the multiple-exit exhaust setups you see on Prados are purely cosmetic. Most times those exhaust tips are not even attached to anything and lead nowhere upstream. However, there are effects of tinkering with your exhaust system and that introduces an interesting little topic we call “back pressure”.

Back pressure is the resistance to exhaust gas flow out of the engine as occasioned by the atmosphere and the size of the exhaust pipe. Exhaust system designs factor this in, meaning the length and diameter of your exhaust headers and pipes are not the result of guesswork or plucky whims but in-depth engineering work. Science! Fiddling with these settings by either adjusting the length/diameter or number of functional exits is obviously going to have an effect on how your exhaust system performs.

The merits of an exhaust system are based on how fast and how efficiently it can get rid of spent charge from within the engine. The exhaust stroke of the four-stroke cycle is partly responsible for this, but it works against atmospheric pressure, which in turn is acting in the reverse direction to exhaust flow. How intense this back pressure is is directly dependent on the shape and size of the exhaust system components. A narrow or restrictive exit will obviously create a lot of back pressure (unwanted effect), but this in turn also means that the exhaust gases will have a higher escape velocity coming out of the engine (desired effect). Think of it this way: when you squeeze the tip of a hose pipe, you are creating a restriction to water flow but you also create a “jet”, whereby the water shoots out faster than it does unrestricted. It sounds paradoxical but it actually isn’t. To maintain the flow rate, the speed has to increase since the size allowance has dropped. The opposite applies as well: a much wider exit means that there will be less back pressure (desirable effect), but also a drastically lowered exit velocity (undesirable), which in extreme cases might be insufficient to completely evacuate the spent charge from inside the cylinder. There is an ideal middle ground where the back pressure and the escape velocity are finely balanced (minimum for the former and maximum for the latter), which is what engineers seek when they design exhaust systems for engines.

So what happens when you get a wider exhaust pipe without any causative reason (such as forced induction or redesigned ports and heads that allow for a higher flow of air)? You reduce the back pressure, which means that you also reduce the escape velocity of the exhaust. During the four-stroke cycle, you might  find that the exhaust stroke is not fully successful; some of the exhaust gases remain within the cylinder, which might mix with the incoming intake charge. The exhaust gases are hot, and they might be hot to the point of causing pre-ignition of the intake charge. They might also disrupt the flame front of the ignited intake charge during the power stroke due to interference with the swirl effect, causing erratic burning of the air-fuel mixture and damaging the pistons and valves.

The exact design of an exhaust system is a dark art, not fully understandable by mere mortals. Besides the size and length of the pipe from header to tips, one also factors in pressure differentials at bottom dead centre versus halfway towards top dead centre, resonance, timing of the exhaust pulses, valve timing, positive and negative initial and reflected sonic pressure waves and how they behave at various engine speeds (rpms), inertial scavenging and how the evacuation of exhaust gases might assist in the efficiency of the induction stroke. It’s a rabbit hole I’d rather not go down so that is that. It is almost quite literally rocket science.

 

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I LIKE THE HONDA STREAM BUT HEAR THAT A TOYOTA IS BETTER AS FIRST CAR

Hey JM,

I want to buy my first car. I have a modest budget of Sh700,000 maximum so I believe I can afford only a locally used car. Most of the advice I am getting is that I should buy a Toyota for a start. However, I like the Honda Stream RSZ. Should I suspend my preference to later when I am “used” to cars? If I go the Toyota route, which is the best option between the Premio, Crown and Allion? Or, with my budget, what would you advise me to get in terms of fuel efficiency, given that  I will mostly use the car for distances of less than 80 kilometres and, occasionally, 200 kilometres. 

 Kev

 

Hello Kev,

Arguments about Kenya being “Toyota country” spring to mind, but let’s sidestep that pettiness for now. For Sh700,000, you are not looking at Crowns, Premios or Allions in particularly good nick, unless you are extremely lucky. Luck is not a factor considered in the purchase of a motor vehicle, since it is neither quantifiable nor determinable.

 You are more likely to find a lower mileage Honda Stream at that price point compared to Toyotas. Also, given that you do short distances, you don’t really need a Crown, do you? Same applies to efficiency. The Crown is a fairly large saloon (compared to the other two) so expect the fuel consumption to reflect that fact.

 

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MY 4WD GOT STUCK IN A DITCH!

Sir,

I have a Honda Airwave 2008 4WD.

One day I got stuck on the Mutindwa railway line simply because there was a small ditch and my 4WD car could not go over it. I thought that since it was a 4x 4, it would handle that easily.

The car also has trouble going up steep roads. Please advise.

Mike

 

“4WD” does not automatically mean “Rhino Charge contestant”, it simply means all the (four) wheels are, or can be, powered. You need ground clearance as well to successfully pull the manoeuvre you were trying to.

What problem exactly do you have with “climbing” steep roads? Does the car bog down and refuse to move or does it move but very slowly?