The Technical Questions Thread

[Dolph_kyas13]

I have a question in regards to the Dakar support trucks, is there a website where one can get specs. I have found the DAF Dakar truck thread on this form. but am looking for more detailed specs on other manufacturers

Thanks for your help

regards

-Jordie

[Sledgehammer]

Jordie, I dont know a greater source of semi-reliable information than Wikipedia.

[ame=http://en.wikipedia.org/wiki/Dakar_Rally]Dakar Rally - Wikipedia, the free encyclopedia[/ame], place to get you started.

[Matra et Alpine]

Why does ABS act in a fast corner ? Today we tested the new Astra and went off. According to the driver he could not brake. ......PS: The test driver was a former racing driver with almost 50 years experience.

Evidnec that experience doens't necessarily mean "good" You said he'd had this before ?
That's because he has exceeded the lateral grip of the tyres. They are basically sliding sideways.
He needed to ( in the past and now ) actually point the tyres back towards direction of travel till they start rotating and acquire some grip and then re-apply braking and/or cornering as the situation requires.
ABS and ESP can't defeat the laws of physics and if there is no grip they do nothing. eg ICE .... OR .... when drivers dont' have the feel for what the grip is when cornering.

Does pulling a car out of gear without putting in the clutch have any negative effects on the components of the gearbox?
It makes double clutching much easier but fear for the transmission prevents me from doing it regularly.

If you have the throttle so that the engine is neither pulling or struggling ( retarding) then puling the cog out won't make any difference. However, out be a few revs and you are putting a stress and creating wear points. Out by lots and you risk shearing a synchro pin. Same with crashign the 'box on the way up.
Race cars and rally cars have done it that way for decades ... but we strip and monitor wear and replace comopnents on them on a monthly basis You EXPECT these things to require replacment during a season.
Not what you want on the street car doing 10K miles a year

If you watch races ( odl school ) where the driver has a gearbox issue you will see them be MUCH more "careful" on the clutch and gear changes to avoid breaking it completely. SOmethgin not in most modern drivers skill set as unecessary. I grew up where a cog breakign was actually quite common, modern manufacturing has brought many benefits

[group c n b man]

Engine Question. Many car manufacturers are talking about down sizing as a way to reduce emissions and continue meeting tougher EU standards. The thing is, the 2.0TFSI from VAG in all of it's applications seem to be more powerful, more economical and less polluting than the old 1.8T. As I understood, smaller displacement led to reduced CO2 emissions and better fuel economy. I also thought that more valves per cylinder also helped improve these. A 1.8 turbo 4cyl with 5 valves per cylinder should be better in terms of CO2 and fuel economy than a 2.0T with 4 valves per cylinder.

However just about every example proves the opposite to be true. Mk1 Seat Leon Cupra R - 225bhp, 32mpg and 211 CO2/km. Mk2 Seat Leon Cupra - 237bhp, 34mpg and 190 CO2/km. Mk1 Skoda Octavia VRS - 180bhp, 35mpg and 192 CO2/km. MK2 Skoda Octavia vRS - 197bhp, 37mpg and 175 CO2/km. Mk1 Audi TTS - 236bhp, 30mpg and 226 CO2/km. MK2 Audi TTS - 268bhp, 35mpg and 191 CO2/km.

This clearly shows that the displacement is not the biggest factor and some of the improvements of the 2.0TFSI over the 1.8T are excellent, especially for the TTS. The 2.0TFSI is the best of all worlds: More power but better fuel economy and emissions at the same time. What I want to know is where have the improvements been made. Is it just the fact that the 2.0 has direct injection or are there more factors?

[LeonOfTheDead]

You have to wonder if the 1.8 engine was a good engine in first place, for as regards fuel consumption and emissions. perhaps it was better than some of its competitors, but perhaps it had plenty of possible improvements.

Consider the new Touareg, which they say it's 200 kg lighter than the first generation. So what? perhaps the first gen was just a pig.

Hypothetically having more valves will help you putting more air into the cylinder as you would use a larger overall area, on the other hand more valves means also smaller valves, which may have worse effects, like difficulties in dimensioning and developing the right turbulence inside of the combustion chamber, or just a too fragile valve. Generally 4 valves are considered the right compromise, while until a few year back 5 valves were used only to reach higher revs.

For as regards the down sizing, it's more about efficiency rather than the displacement adopted. The efficiency of an engine is higher at higher loads. An efficient engine doesn't use less fuel as a given fact, and at high loads generally an engine needs quite some fuel, but it also creates more power per each part of fuel than at lower revs (not exactly the same, but generally high loads = high revs, unless you are into neutral).

Now if you consider the amount of power you need on a certain car, even just for marketing purposes, you can get those bhp with a tons of engines each with a different displacement. Of course using a 10 liters engine to generate 100 bhp isn't very smart, as the engine will likely always work at a low load, therefore it will be less efficient. That doesn't mean it will need more fuel though, which is why larger cars do need larger engines.

Now emissions come into the picture, especially if measured the European way, so not considering directly the fuel consumption.
While the fuel consumption is affected by many factors, the emissions levels primarily depends on what happens inside of the engine. Having an efficient engine means, hypothetically, that you convert all the energy of the fuel into power. A larger displacement means bigger combustion chambers, with negative effects on the combustion itself, as the flames is weaker near the walls and therefore the process will be incomplete.
Adopting direct injection and any form of over charging helps mitigating this as the conditions into the chamber are more equal in its volume, as it happens in diesel engine to a larger extent.
At this point its pretty clear that having also a smaller cylinder would help in this aspect, while just having more small cylinders to have the same overall displacement than a present engine would only add complexity and parasitic losses.

Hope this makes sense as its pretty late and should be sleeping now.

[f6fhellcat13]

It is very nice to see Il dottore posting again.
It was lucid enough and very informative.

[jediali]

You have to wonder if the 1.8 engine was a good engine in first place, for as regards fuel consumption and emissions. perhaps it was better than some of its competitors, but perhaps it had plenty of possible improvements.

Agreed. Back in the mid 90s it was competitive but towards the end of its life it was lacking. Its nice to be able to say you have 5vpc just like a ferrari 360 but Ferrari dropped it so that kind of says it. To be fair audi had a good design which did not produce to bad fuel consumption. Sometimes I am quite impressed others not so. Required improvements are the embodiment of the 2.0TFSI.

While the fuel consumption is affected by many factors, the emissions levels primarily depends on what happens inside of the engine.

As mentioned I believe it is all down to combustion chamber/engine breathing design. The ability for more detailed simulation/analysis and control of combustion process in the last few years has really shown. see VAG E888 (new 2.0tfsi) vs EA113 (older 2.0tfsi). Also why has the former got a big gulp of extra torque? similar to the insignia petrol turbo. I need to figure out if either uses HCCP or whatever it is.

A larger displacement means bigger combustion chambers, with negative effects on the combustion itself, as the flames is weaker near the walls and therefore the process will be incomplete.
Adopting direct injection and any form of over charging helps mitigating this as the conditions into the chamber are more equal in its volume, as it happens in diesel engine to a larger extent.

I know very little about cylinder wall heat loss (worse with lots of cylinders) but I am assuming it helps a lot with effciency to have less. Remember also that manufacturers probably want to avoid oversquare combustion chambers because the distance the flame front has to travel is even more. Mercedes, Porsche, Alfa etc used multiple spark plugs for this reason (proabably more power orientated than economy - although mercedes did have 3vpc for better cold startup - im gibbering sorry). I think now manufacturers have developed their combustion chamber design so it cleverly burns the fuel it needs to with 1 spark plug.

[Matra et Alpine]

group -- the engines you cite are POWERFUL ones.
For "normal" usage smaller capacity gives better fuel consumption but NOT better power.
The losses in trying to move LOTS of fuel/air mix through smaller capacity start to increase faster than in a larger engine. Thus requiring MORE fuel to get equivalent power.

If you want the msot power you want then get a BIG V8 and push LOTS of fuel into it.
If you want the best ECONOMY then get a smaller 3/4 cylinder and then add turbo to force mix into cylinder "reducing" gas flow losses on the inlet side.

We can explore more but which is of more interest, economy or performance ?
What balance do you desire and how much power and torque do you wish ?
All these come to play in deciding the "best" engine.
Sadly governments are interested in pollutants first and economy next and power doesn't come in to their laws and regulations

[group c n b man]

I think that the case was the same in the older 30v 3.0V6 - 216bhp, 26mpg and 257 CO2/km. The newer 24v 3.2V6 - 261bhp, 31mpg and 216 CO2/km.
This seems to show that 4v/cyl is more powerful and economical at the same time. Come to think of it, only VAG really tried a 5v/cyl engine and it isn't made any more. Says it all really. Aswell as power and economy advantages, the 4v has been much more reliable, bulletproof infact. However the old 5v suffered some reliability issues, especially coil pack failures.

[pimento]

It's not as if these engines are all else equal other than valve count, so it's not really feasible to state that it all comes down to that.

[Matra et Alpine]

Well 5 cyl was a beast.
Let's remember the Works Audi QUattros with that block pushed out to 700 hp
Also, Honda dominated with the RC211 engine which was a very narrow V5.
It has advantages, just not enough to accept the extra space an extra cylinder adds.
Thus why most compact small engines are moving to 3 cylinder.

[LeonOfTheDead]

It is very nice to see Il dottore posting again.
It was lucid enough and very informative.

Thanks dude

Well 5 cyl was a beast.
Let's remember the Works Audi QUattros with that block pushed out to 700 hp
Also, Honda dominated with the RC211 engine which was a very narrow V5.
It has advantages, just not enough to accept the extra space an extra cylinder adds.
Thus why most compact small engines are moving to 3 cylinder.

I think he was just referring to 5 valves per cylinder rather than 5 cylinder engines.

As a matter of fact, small car and big engine, can't beat that.
Call Aston Martin, ask for a spare V8, and then buy a Cygnet.

[culver]

When comparing motors via the cars they are installed in remember you are no longer comparing apples to apples. As an example. Take my SAAB 900 turbo. I typically get 30mpg going 75mph on the freeway. I once got 23 mpg under near identical conditions. My engine didn't change but the roof rack full of crap might have hurt my mileage.

That's an obvious example but it does show how with no changes to the powertrain I can change the car's mileage. Consider that the higher mileage might be due to better aero, lower rolling resistance tires, different transmission etc. Without being able to factor those things out it's hard to say if it's really the motor that's more efficient.

My father's 2008 Passat 6spd 2.0T gets the same mileage as his '98 Passat 1.8T. Both are manual but I suspect the taller final gear on the 6spd makes more difference than the two motors. However, I also suspect the new motor is more efficient thanks to DI and simply a newer design.

Also, to some degree, displacement and mileage aren't well correlated. If we are talking 5.7L vs 2L then I expect to see a real difference (though a comparison of the Corvette to S2000 shows they can be surprisingly close). However, when you are talking 10% difference in displacement there are a number of other factors which could improve mileage. The same is true for power vs mileage. Some technologies such as direct injection, increasing compression ratio, etc have almost/no negative impact on steady state cruise fuel consumption while allowing for higher peek power.

Other times mileage remains unchanged due to other factors. When BMW offered the 525 and 530 in the US the 530 basically matched the mileage of the 525. The reason was the 530's extra 0.5L of displacement allowed for longer gearing. So the car didn't really have any more passing power in top gear but the 3L motor was spinning slower than the 2.5L. Net result the 3L was just as fuel efficient on the highway yet had more power when you downshifted. That doesn't tell us if the 3L was really more efficient, only that the total combination of gearing and motors were equally efficient on the highway.

[Kitdy]

Well 5 cyl was a beast.
Let's remember the Works Audi QUattros with that block pushed out to 700 hp
Also, Honda dominated with the RC211 engine which was a very narrow V5.
It has advantages, just not enough to accept the extra space an extra cylinder adds.
Thus why most compact small engines are moving to 3 cylinder.

Why did the move from 990cc to 800cc make Honda change their engine from a V5 to a V4?

EDIT: Is direct injection permitted in MotoGP?

[Matra et Alpine]

The GP went from 2-stroke 500cc to 1litre 4 stroke.
With other rule changes they expected speeds to drop.
Instead the engineers squeezed awesome power and performance and so they decided then that they had to reduce the engine size from 1 litre to 800cc.
It's a new 4 cylinder engine.

Direct injection is allowed, BUT because bike engines rev high and are MUCH smaller and lighter than their car alternatives then injection has always been a problem. It's fairly recent that ANY injection has been made to work on street bikes

I'd also suggest that the bike packaging probably reduces the difference from trumpet injection to direct in cylinder. Bikes have run single sleeve carbs per cylinder for decades and many car "upgrades" have involved replacing car designed carbs with bike inlet designs.
Must go do some checking with the bike guys