[MR2] General Car Question

[William Brandt]

Joel - I think we have swerved to an interesting subject - I did catch 
myself after the first post with the realization of a firing order (duh, 
something can't fire simultaneously if there is a sequential order ;-)  - 
although with distributors on the way out and computers controlling 
everything that would be possible.

Then we have a few engines that can turn off sets of cylinders at will for 
fuel economy - Cadillac tried that in the 1980s with disastrous results but 
Chrysler's Hemi V8 is doing that now - although I think with all the 
complexity of such a system the fuel savings isn't that great.

And do the valves still open and  close even though the cylinder isn't 
firing?

They must...

Bill
----- Original Message ----- 
From: "Joel" <priamyd at comcast.net>
To: "William Brandt" <wbrandt1 at sbcglobal.net>
Cc: "MR2 List" <mr2 at mr2.com>
Sent: Wednesday, August 04, 2010 9:48 PM
Subject: Re: [MR2] General Car Question


>I will counter only 1 small portion of Bill's reply (in my usual long 
>winded manner).
>
> Based upon the firing order in the 4AGE (1 - 3 - 4 - 2), it is highly 
> unlikely that cylinders 1 and 3 fire at the same time, and the same would 
> go for cylinders 2 and 4.
>
> I believe that the cylinders fire at 180 degrees from each other. 
> Granted, cylinders 1 and 3 to reach TDC at the same time (as do 2 and 4), 
> but if both 1 and 3 were to fire at the same time (and 2 and 4 alike), it 
> would cause massive power surging on just those portion of the rotating 
> stroke, and leave the other 2 cycles of the 4 stroke cycle to basically 
> wait for inertia to rotate the assembly towards its optimal firing 
> position.
>
> Inversely, if you have 1 cylinder firing at a time, - think of a clock, 
> you'd have a firing at 12, 3, 6 and 9 - and not just 12 and 6.  This would 
> create a constant and fluidly moving rotating assembly that will balance 
> itself.  With ignition happening at 12 and 6, half of your rotation would 
> be, uh, useless and the engine rock considerably and lend itself to 
> violent and unstable behavior.
>
> If you were riding a bike and ONLY applied your leg muscle (ignition) when 
> the pedals reached 12 and only stopped all torque forces at the '3' 
> position, you would be waiting for the other pedal for 1/4 turn - a 1/4 
> turn of wasted motion and possible forward momentum.  An engine operates 
> on the same principle, but with 4 'pedals' instead of 2. :)
>
> Again, I do not say this from a seat of absolute knowledge, so please do 
> not take it as such - this is just my hunch and guess. :)
>
> I have noticed the same thing as Bill - an I4 cylinder engine at low RPM 
> is very rough compared to an I6 engine.  My old 1987 Supra was butter 
> smooth at 800rpm, whereas my Mr2 was considerably rougher.
>
> - Joel -
>
>
> William Brandt wrote:
>> Wayne - I was thinking of trying to answer this but 4 stroke engines are 
>> always a bit of a mystery to me. I know, they shouldn't be.
>> In a 4 stroke engine isn't there only one power stroke?
>> RPMs and power strokes  - well here's a guess - 6 cylinders - 3000 rpm - 
>> 4 stroke - each piston is producing 125 power strokes per minute.
>> (3,000 / 6 / 4)
>> As to your other point I believe in most designs 2 pistons are always 
>> producing a power stroke at the same time for balance and smoothness.
>>  When Mercedes came out with the 5 cylinder diesel in the mid 70s it was 
>> a revolution and something many engineers thought "couldn't be done" - in 
>> that engine the middle "odd" cylinder has its own power stroke while the 
>> other 4 are going 2 at a time (I think!). Usually the 2 power stroke 
>> pistons are at opposite points in the engine for balance (again, "I 
>> think").
>> Here's a good explanation in Wikipedia -
>> http://en.wikipedia.org/wiki/Four-stroke_engine
>>
>>
>>
>> I also don't understand  why inherently next to a V12 an I6 is by design 
>> the most balanced engine. I know when my 2 is idling at 700 rpm it is a 
>> bit rough. I know my old MB I6  - when the motor mounts are decent - is 
>> so smooth at idle as to be almost undetectable.
>> Bill
>>
>> ***
>> I remember from old school engine class it was every other stroke was a
>> power stroke (so 1500 times) but so much has changed. For instance I 
>> don't
>> know how they make a 5 cylinder engine run...fairy dust I think.
>>
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>