Engine Design Philosophy

Bernie Benz b.benz at charter.net
Tue Nov 15 09:24:53 PST 2011


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
>>>>>>
>>>>>>
>>>>
>>>>
>>
>>



More information about the 200q20v mailing list