Engine Design Philosophy

[Bernie Benz]

Combustion chamber design likely a factor.

On Nov 15, 2011, at 10:13 AM, Matt Suffern wrote:

> That's fair.  I am cosmetically-biased.  :)
>
> Interesting observation about the included valve angle—I didn't think
> of that.  Any reason why Audi didn't widen the angle so they could fit
> a pair of cam gears up top?  Didn't want a heavier, bigger head?
> Wanted to use existing timing belt hardware on the block?  All of the
> above?
>
> -Matt
>
>
>
> On Tue, Nov 15, 2011 at 12:24 PM, Bernie Benz <b.benz at charter.net>  
> wrote:
>> Your terms “flimsy” and “beefy” show a cosmetic bias on your part,  
>> not a
>> design preference, IMO. The only reason for the chain between cams  
>> is that
>> the two valve banks are to close together to use a single belt or  
>> chain for
>> both cams. If the included valve angle between the two rows were  
>> 90 degrees
>> a single belt or chain could drive both in a much more flexible,  
>> modifiable
>> drive.
>>
>> Bernie
>>
>> On Nov 14, 2011, at 12:38 PM, Matt Suffern wrote:
>>
>>> No point.  I just found it interesting that to perform  
>>> essentially the
>>> same job, Audi chose a seemingly-flimsy rubber belt whereas BMW  
>>> opted
>>> for a beefy double-row (duplex) chain, and was pondering the engine
>>> design philosophies that might have prompted the automakers to go
>>> their respective routes (especially since BMW's M50 is the successor
>>> to their M20, which DOES use a timing belt).
>>>
>>> I suppose I was going for an open-ended technical discussion more  
>>> than
>>> anything else.
>>>
>>> -Matt
>>>
>>>
>>>
>>> On Mon, Nov 14, 2011 at 3:32 PM, Bernie Benz <b.benz at charter.net>  
>>> wrote:
>>>>
>>>> Thought you were trying to compare chains to belts.
>>>> If the chains are of the same basic design excepting for width  
>>>> (single
>>>> vs.
>>>> double) the drive from the crank requires twice the torque (chain
>>>> tension)
>>>> as does that of a single cam. Is this your Q? And if so, what‘s  
>>>> your
>>>> point?
>>>>
>>>> Bernie
>>>>
>>>> On Nov 14, 2011, at 11:44 AM, Matt Suffern wrote:
>>>>
>>>>> The context of the original e-mail:  Single- vs. double-row chain.
>>>>>
>>>>> -Matt
>>>>>
>>>>>
>>>>> On Mon, Nov 14, 2011 at 2:37 PM, Bernie Benz  
>>>>> <b.benz at charter.net> wrote:
>>>>>>
>>>>>> Row what?
>>>>>>
>>>>>> On Nov 14, 2011, at 10:48 AM, Matt Suffern wrote:
>>>>>>
>>>>>>> That would be single- vs. double-row.
>>>>>>>
>>>>>>> -Matt
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Nov 14, 2011 at 1:47 PM, Bernie Benz  
>>>>>>> <b.benz at charter.net>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Please explain your meanings of simplex vs. duplex in this  
>>>>>>>> respect.
>>>>>>>>
>>>>>>>> Bernie
>>>>>>>> On Nov 14, 2011, at 8:21 AM, Matt Suffern wrote:
>>>>>>>>
>>>>>>>>> Someone explain this to me.  Looking through the parts  
>>>>>>>>> catalog I
>>>>>>>>> study
>>>>>>>>> the valvetrain diagram for the 3B.  I notice Audi has  
>>>>>>>>> retained a
>>>>>>>>> timing belt design with a simplex chain to link the exhaust  
>>>>>>>>> camshaft
>>>>>>>>> with the intake.  My BMW 525's M50, by contrast, has a  
>>>>>>>>> duplex timing
>>>>>>>>> CHAIN with, again, a simplex chain linking camshafts.
>>>>>>>>>
>>>>>>>>> Both engines can last upwards of 300K miles.  So why the  
>>>>>>>>> overkill on
>>>>>>>>> BMW's part?  Four more valves to operate (1 more  
>>>>>>>>> cylinder)?  Or did
>>>>>>>>> they just assume people aren't going to do regular  
>>>>>>>>> maintenance like
>>>>>>>>> timing belt changes?  It just seems like an awful lot of added
>>>>>>>>> complexity and valvetrain inertia to avoid a procedure most  
>>>>>>>>> people
>>>>>>>>> assume is going to have to be done anyway.
>>>>>>>>>
>>>>>>>>> Curious.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Matt
>>>>>>>>> Winston-Salem, NC
>>>>>>>>> www.spannerhead.com
>>>>>>>>> _______________________________________________
>>>>>>>>> 200q20v mailing list
>>>>>>>>> http://www.audifans.com/mailman/listinfo/200q20v
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>
>>