Cars Room Quiz (1 Viewer)

[SlipStream]

The easy question has a trick-question odour to it. I'll lock in D - tyres are constantly slipping over the road's surface at any speed and never grip to their maximum potential, ever. Because they're constantly slipping, they are subject to friction and consequently all tyres will wear away regardless of how hard they're driven (some will just wear quicker than others).

Hard: I'm just going to take an educated guess for this one. Individual throttle bodies are fairly rare and the performance advantage musn't be too much greater than that of a large singular throttle body leading into a plenum chamber (which is the most common intake design for supercars and also high-hp custom turbos, like the APS XR6T which has actually had the Falcon individual throttle body intake manifold replaced in favour of a plenum set up with a single, large throttle body). I would imagine some of the main advantages would be: quicker throttle response, improved fuel vaporisation from the injectors leading to greater efficiency, easier starting... that's all I got.

 

[shortygb]

B), and the hard one...umm...no idea.

 

[braad]

Hard: I'm just going to take an educated guess for this one. Individual throttle bodies are fairly rare and the performance advantage musn't be too much greater than that of a large singular throttle body leading into a plenum chamber (which is the most common intake design for supercars and also high-hp custom turbos, like the APS XR6T which has actually had the Falcon individual throttle body intake manifold replaced in favour of a plenum set up with a single, large throttle body). I would imagine some of the main advantages would be: quicker throttle response, improved fuel vaporisation from the injectors leading to greater efficiency, easier starting... that's all I got.

ditto with D for 'easy'

leading on from the ITB....would it increase the ability to individually tune the cylinders? i'd like to say increased air-flow...but they arent on drag cars are they? :/ are they on the V8SC?

hmmm...nice question :uhhuh:

 

[loquasagacious]

The easy question has a trick-question odour to it. I'll lock in D - tyres are constantly slipping over the road's surface at any speed and never grip to their maximum potential, ever. Because they're constantly slipping, they are subject to friction and consequently all tyres will wear away regardless of how hard they're driven (some will just wear quicker than others).

Hard: I'm just going to take an educated guess for this one. Individual throttle bodies are fairly rare and the performance advantage musn't be too much greater than that of a large singular throttle body leading into a plenum chamber (which is the most common intake design for supercars and also high-hp custom turbos, like the APS XR6T which has actually had the Falcon individual throttle body intake manifold replaced in favour of a plenum set up with a single, large throttle body). I would imagine some of the main advantages would be: quicker throttle response, improved fuel vaporisation from the injectors leading to greater efficiency, easier starting... that's all I got.

No trick in the easy question.

Getting close on the hard abit more on the pros needed....

 

[petar13]

It's probably all to do with the 'quicker idea'. As there's one throttle body on each cylinder, there is a far lesser volume of air to be controlled (as opposed to just one for the whole manifold). So it just goes through quicker - you get the better throttle response, as Slip said. Using the air pump metaphor, the air (fuel too) is basically 'pumped' into the cylinder much more efficiently.

I guess each of the bodies can specifically control the amount of mixture for each cylinder, maintaining good ratios for efficient combustion, at a whole range of RPMs. So you probably end up getting a broader power band, as opposed to what you would get with a single body.

I remember reading about this as a performance mod a while back. Outrageously expensive. I know that just the one throttle body for a E32 BMW 750 goes for $1500-$2000. I could only imagine the cost if you were to put twelve of those into that engine. These things do eventually need replacement, and I'm guessing the reason that the individual bodies on the XR6T were pulled out of production, was because come replacement time, you would be looking at half of the car's whole value (if not more).

 

[loquasagacious]

Now I knwo its christmas and all but thats no excuse not to be racking your brains to solve car quizes.

In terms of ITBs petar and dylan are close enough but no ones nailed the easy one yet.

 

[SlipStream]

Ahh well, thinking about it you said the tyres' maximum traction.. which isn't necessarily 100% I guess. A car can make a certain amount of power - i.e. maximum power could be 100kW - but it isn't 100% power, because cars are nowhere near 100% efficient.

And I've already had my go. Kieran pick someone to go

 

[loquasagacious]

Ok you are using the maximum available traction of your tyres when they squel - when they smoke you are exceeding this eg you are trying to use more than you have.

As far as ITBs go petar is probably closest. The advantages are:

A conventional set-up has differing lengths between air entering the manifold and entering the combustion chamber this creates inefficieny.

The smaller throttle bodies mean that they can react quicker this creates a quiker (much like four valves rev higher than two) and crisper throttle response.

There is also the issue of greater airflow important because power = air+fuel+spark.

Disadvantages are the complexity especially if turbochargers are involved.

 

[SlipStream]

Take it away petar!

 

[petar13]

Me again? Ok, then....

EASY - Which of the following is true about diesel engines?
A) Many new common rail diesels utilise a twin-spark configuration.
B) The high cylinder compression ignites the diesel spontaneously, facilitating the power stroke
C) Due to high compression ratios, diesel engines can rev quite highly
D) The need for glow plugs is only pertinent in countries with high year-round temperatures.


HARD - How does cooling induced air improve power output (i.e. by means of intercooling, etc)? What actually happens?

 

[SlipStream]

EASY - B

HARD - Cooler air is more denser than warmer air so holds more oxygen and is more combustible. There are two types of intercooling - air to air and water to air. Air to air is most common, and uses air as a medium to remove heat whereas the less common water to air is basically like an inverted radiator where the water/coolant removes the heat from the charged air. Hot air is also more prone to damaging detonation (don't want that in a turbo car) so with high boost applications an intercooler is mandatory. However intercoolers don't cool air like an air conditioner, they just remove a lot of the heat. If you were to put your hand in front of intercooled air you'd burn yourself.

 

[petar13]

You got it in one, Dylan. It's all yours.

 

[SlipStream]

lol, fair enough. Turbos are my area of expertise

EASY - What does the S and F stand for on Ferrari's Racing Emblem (see my avatar)?

a) Spa de Ferrari
b) Scuderia Fiorano
c) Scuderia Ferrari
d) Spa de Fiorano
e) Sicily de Ferrari

HARD - How do compressor bypass valves (blow off valves) prove beneficial in a perfomance context?

 

[DaddyK]

Easy C

A BOV prevents damage to the actuall turbo by releiving the excess pressure which is built up, but it also does it without sacrificing the boost response, crappy BOV's can't hold the pressure in which results in the turbo boosting poorly. Uhm, thats all i can really think of performance wise.

 

[55psi]

Easy C

A BOV doesnt necessarily increase performance, as all it does is releases the air pressure being sucked in by the throttle body and when it shuts, the air is then released via the BOV. What a BOV helps is to decrease turbo lagg and a good BOV can keep boost very well so u dont have lagg spikes. If there wasnt a BOV the air that was once sucked in by the TB will return back through the turbo blades and slow the turbo down a little bit while causing a fluttering sound causing turbo lagg. The air coming out of the BOV can go into the atmosphere or it can go back into the intake system(plumbed back)

 

[SlipStream]

Easy C

A BOV doesnt necessarily increase performance, as all it does is releases the air pressure being sucked in by the throttle body and when it shuts, the air is then released via the BOV. What a BOV helps is to decrease turbo lagg and a good BOV can keep boost very well so u dont have lagg spikes. If there wasnt a BOV the air that was once sucked in by the TB will return back through the turbo blades and slow the turbo down a little bit while causing a fluttering sound causing turbo lagg. The air coming out of the BOV can go into the atmosphere or it can go back into the intake system(plumbed back)

Beh, close enough.

Imagine the turbine and compressor impeller spinning at 150 000 rpm+ at high revs. The pressure in the intake manifold is, say 16psi. As soon as you take your foot off the pedal, the throttle body butterfly (that little round flap) closes instantly - the air being pumped at high speed into the intake plenum is suddenly bunched up behind the throttle body butterfly with no where to go - but the compressor is still whirling away at those awesome speeds.

The turbo is still pumping the air at the same speeds but into a far greater space behind the throttle body butterfly (normally it goes straight past, into the intake plenum and down into the cylinders). It can't just keep pumping air, there is a limit. This is where we face an issue called compressor surge, where the compressor impeller has to slow down (rapidly) because it can no longer pump air into that little space. This is all happening in seconds, mind you.

Imagine as soon as you have changed gears, you come back onto the throttle - fully. You need boost, right? Well tough luck. The turbo is now spinning at about 10 000rpm because of compressor surge - it had to slow because it couldn't pump air at such high density. You'll have a flat spot as you come back onto the throttle while the turbo spools back up to 150 000 rpm or so. This puts a big dent into acceleration.

The idea of the BOV (or Compressor Bypass valve as it is professionally known) is to vent this build up of pressure behind the throttle body so that the compressor does not surge and slow down - by venting the pressure, the BOV keeps the turbo spinning so when you come back onto the throttle, you have 11psi of boost instead of about 3psi. You're already a lot closer to the max boost pressure (I think I said 16psi), so you're already going faster thanks to the BOV. Mainly used in race applications, like all race technology it made its way back to the street somehow.

So there's the reason for a BOV - to keep the turbo spinning after you come off the accelerator.

Remember mate, you're not allowed to use Google or whatever to cheat. This thread is about honesty - so keeping this in mind, take it away!

 

[55psi]

u saying i was cheating?..
Its all my knowledge my friend, i summarised all that HUGE quote in just several lines. COME ON
Anyways QUESTIONS.

Easy - What is the most common problem with rotary engines?
a) Snapping conrods
b) Busting apex seals
c) Overheating
e) Leaking oil from sump

Hard - What's the difference in responsiveness and power between a turbo charger and a supercharger? And why is there a difference?

 

[loquasagacious]

Hmmm

Easy:
None of the above: using prodiguous ammounts of oil and needing often rebuilds....
In lieu of that - C....

Hard:

A turbo is more responsive and provides more power. This is for several engineering reasons.

Firstly because a supercharger is driven off the engine it in itself is not very responsive and will just build power (eg psi eg supercharger rpm eg engine rpm) as the engine winds up. So it is only as responsive as the engine - and given that the supercharger is actually a load on the engine it arguably reduces engine responsiveness. A turbocharger is also more responsive in a negative manner eg without a Compressor Bypass Valve (CBV)[BOV] it will rapidly respond to a closed throttle by winding down the boost.

A turbocharger can provide more boost and more boost means more power. It can provide more boost because they can spin faster (thus compressing more air), as Dylan was saying they can be cranking at up to 150,000rpm. This compares to a supercharger whose rpm are going to be much much closer to engine rpm because it would be (virtually) impossible to gear from say 5,000rpm to 150,000rpm.

So there you have it turbos are more responsive and provide more power.

 

[55psi]

i dunno if ill give that one, but very close

 

[petar13]

Well, high compression turbo rotaries do have a tendency to result in apex seal failures/leakage. And anyway, as they get worn away with use, there is a greater chance for failure. Just don't quite know what you mean by 'busting' - it's not like they explode, or anything.