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How a Car Engine Works

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Re: How a Car Engine Works

#161

Post by pdonis »

lutorm wrote: post #128
pdonis wrote: post #114

Earlier quoted context omitted.

Yes, because that means the knock sensor is reducing compression because it senses lower octane gasoline.

Compression is fixed by the engine design. The only thing the ECU can do as a result of knock sensor input is retard ignition and close the throttle (and, on a turbocharged engine, lower charge pressure). Retarded ignition does result in lowered gas mileage, but throttling down does not. It just decreases your maximum available power. Plus, if you notice the decrease in power, your driving is not suitable for compari…

Compression is fixed by the engine design

The maximum possible compression is, yes, since it is determined by the size of the cylinders and the piston stroke.

But retarding the timing amounts to reducing the effective compression--basically you are wasting some of the compression that's available by delaying the spark until the cylinder has started expanding again. I should have made it clear that it was effective compression that I was talking about.

Re: How a Car Engine Works

#162

Post by lsaferite »

lucb1e wrote: post #149
Arjuna wrote: post #42

Hi fellow gear-heads... very cool engine graphics! On a related note, I wanted to add that, if you are not familiar with dual-clutch transmissions [1], they are pretty interesting. One example (many manufacturers offer this type of transmission) is the Porsche Doppelkupplungsgetriebe (or simply PDK) [2], developed by Porsche. It is essentially two gearboxes in one complete transmission package, where both gearboxes p…

My parents' car has something like this (DSG). It takes forever between pressing the gas and actually moving forward. After that the car is fast and has power, it's just not fast to get going when you press the gas, you gotta anticipate. It's really very annoying and I much prefer a normal car, I really can't recommend it to anyone, but maybe it just takes getting used to.

What make/model is their car?

I had a 2006 (I think) VW GLI with a DSG and it was very snappy off the line. It was actually one of my favorite cars ever.

Re: How a Car Engine Works

#164

Post by dragos2 »

polskibus wrote: post #3

This page is really slow on my chrome, wouldn't it be better to divide it into smaller pieces?

It would've been even better if it wasn't a massive gif. I kept hovering and clicking the page the whole time wanting to control the animations.

Re: How a Car Engine Works

#165

Post by lucb1e »

lsaferite wrote: post #162
lucb1e wrote: post #149

Earlier quoted context omitted.

My parents' car has something like this (DSG). It takes forever between pressing the gas and actually moving forward. After that the car is fast and has power, it's just not fast to get going when you press the gas, you gotta anticipate. It's really very annoying and I much prefer a normal car, I really can't recommend it to anyone, but maybe it just takes getting used to.

What make/model is their car? I had a 2006 (I think) VW GLI with a DSG and it was very snappy off the line. It was actually one of my favorite cars ever.

Volkswagen Golf, I don't know any other details

Re: How a Car Engine Works

#166

Post by MrFoof »

coldpie wrote: post #156
MrFoof wrote: post #139

Earlier quoted context omitted.

>All other things the same, a dual clutch is not much faster than a properly-operated manually-clutched gearbox Formula One drivers in the early 90s were the only ones really able to come close, with shift times between 150 and 200ms. The average person is more around 300 - 400ms when shifting aggressively. You can be faster than 300 - 400ms, but not with 100% consistency, especially on downshifts, and especially wit…

I'm a little surprised. I figure most people buying a Cayman S are buying it for fun. I've never driven with a DCT, but most people who have that I've heard from generally say that manual is more fun, while DCT is better in every other respect. Did you find DCT to be at least as fun as manual? I think I'd miss the feeling of nailing the revs perfectly on a downshift while braking for a turn on the track. Any thoughts…

People buy Porsches for fun or track duty. Some for both, in which I'm in the latter crowd. I autocross my cars, and do DEs -- my current MX-5 has been on at least 13 different race courses in the country, including some of the very best (Watkins Glen, Mid-Ohio, Road Atlanta, Road America, Infineon, Laguna Seca, Sebring, VIR, Lime Rock). It's also my daily when I need to use a car to commute.

As for the Cayman S, it's a damn serious car. My load out hits 60 in 4.1-4.2s with launch control, and the 1/4 mile in around 12.6-12.7 @ 110mph (and 175mph in ~49 seconds). A set of Michelin Pilot Super Sports will get it to hold around 1.1g of lateral grip (sustained, not peak). You can't go anywhere near its limits on public roads, except in a straight line. If you want sideways fun, there's the MX-5 and BRZ/FR-S for exactly that.

In a more powerful car (trust me, 325HP is still a lot in a 2900lb car!), DCTs give you a nice quick immediate jolt from the power surging in almost immediately. It keeps a wonderful engine note (and boy does a Cayman S with sport exhaust make some noise) uninterrupted and always on boil. Once Porsche changes its PDK shift levers to those like the GT3 (pull to upshift), those who want to think they're in a racing car with a sequential box can. If I could get PDK-S in a Cayman S, I would and would mostly use the shift lever.

I find most detractors of a good DCT haven't driven a car with one. Additionally, not all manuals are great to begin with, which can be frustrating when you're trying to be quick. The MX-5 is ridiculously good for what the car cost. The Type 997 911 had a great 6-speed as well. My Lancer Evolution VIII MR had an extremely heavy clutch, and I'd say the last few BMW M cars have had a heavier clutch than I'd prefer (and dev money was mostly spent on DCTs). Corvette Z06s and Vipers (last drove a third gen/ZB) require a very deliberate use of the shift lever.

Re: How a Car Engine Works

#168

Post by jotm »

ams6110 wrote: post #151
jotm wrote: post #148

Earlier quoted context omitted.

Ah, carburetors - how I hated those things. Simple in theory, yet so complicated and fickle in practice... I do love old diesel engines with mechanical belt-driven high pressure pumps and mechanical injectors - those things were easy to fix and built to last...

I drive a 30 year old Mercedes diesel as my primary car and it still runs like a swiss watch. You do have to adjust the valve clearance every so often, which is not necessary in a modern diesel or even ones slightly newer than mine.

If it's the 3.0 liter 5 cylinder diesel (OM617) - those are considered to be some the most reliable diesel engines ever made :-)

Re: How a Car Engine Works

#169

Post by coldpie »

MrFoof wrote: post #166
coldpie wrote: post #156

Earlier quoted context omitted.

I'm a little surprised. I figure most people buying a Cayman S are buying it for fun. I've never driven with a DCT, but most people who have that I've heard from generally say that manual is more fun, while DCT is better in every other respect. Did you find DCT to be at least as fun as manual? I think I'd miss the feeling of nailing the revs perfectly on a downshift while braking for a turn on the track. Any thoughts…

People buy Porsches for fun or track duty. Some for both, in which I'm in the latter crowd. I autocross my cars, and do DEs -- my current MX-5 has been on at least 13 different race courses in the country, including some of the very best (Watkins Glen, Mid-Ohio, Road Atlanta, Road America, Infineon, Laguna Seca, Sebring, VIR, Lime Rock). It's also my daily when I need to use a car to commute. As for the Cayman S, it'…

Thanks for the reply :) Hope it's a blast. The Cayman S is my #1 dream car. (I currently drive a Z4 3.0si coupe and take it up to Brainerd International once or twice a year.)

Re: How a Car Engine Works

#170

Post by adolph »

umsm wrote: post #90
adolph wrote: post #55

Earlier quoted context omitted.

See also the awesome fire piston, a relatively ancient technology using the same principles: https://en.wikipedia.org/wiki/Fire_piston

The inventor of the diesel engine based his design on the fire piston technology.

Thats really cool; did not know that.
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