Look what they got away with 1

[BrianGar]

Ill try explain this as briefly as I can.

On the 2.0l 16v vw engine(think 1995ish) they used a bore spacing of 86mm or so.


The head used had been in production for a long time and remained more or less unchanged.

Bring on the Audi v8 4.2L engine, also made by the Vw group.

This engine had a bore spacing of 90.5mm because it had bigger bores.

Clearly they could not have used the same basic 2.0L head dimensions to save a re-jig on the line, could they? Given that the block was longer?

Yes, they could and did.

They used the same basic casting, re-jigged the combustion chamber prints a bit, and sent it off down the same machining line as the 2.0l heads.

I could not believe they did this when I found out.

Check out the first attachment, it shows the 2.0L head. Valves all centred as they should be, all nice and neat, as you would design it.

Now, have a look at the second picture, it has the very same spark plug locations, and valve locations, just that they dont lie in the middles of chambers! Its even worse on the end chambers as the difference increases as you move away from the centre! Amazing huh? Anything to save money and a re-jig I guess, and of course, able to say you now have a 4.2L in your line up!

 

[BrianGar]

And the 4.2L chamber

BG

 

[BrianPetersen]

Hah! That's funny. Are the head bolts similarly offset?

VW does seem very married to the 88mm bore spacing on their in-line engines. Doesn't matter gas or diesel, either.

 

[BrianGar]

Head bolt spacing the same, but end most coolant drillings moved further out.

BG

 

[MiketheEngineer]

So - if you could partially duplicate a good design and save a boat load of money - wouldn't you??

Done ALL the time. Why re-invent the wheel..

 

[BrianGar]

From an engineering point of view, no I would not, the valves on one side of that cylinder would suffer bore shrouding, which would not be present as much in the centre two cylinders.

From a management and marketing point of view Im sure it makes sense though.....but from an engineering point of view...its terrible, sorry!

We all know who pays the wages...but thats not my original point.

BG

 

[MikeHalloran]

To feed a car line that sells 2 million units a year, you need to make 10,000 car sets of parts per working day.

You can't do that with drill presses and lathes unless labor is vanishingly cheap, and it's not, anywhere.

You need full automation, including, e.g., a head machining line that will cost at least several million dollars. You have to run a machine like that for a decade or two to justify the investment.

The math is way different for a one man shop.



Mike Halloran
Pembroke Pines, FL, USA

 

[izzmus]

It was the only way VWAG could (inexpensively) expand the V8 beyond about 4.0l. The short bore spacing is nice for packaging (the old fives are roughly the same length as a Ford four) but a little limiting for displacement.

I greatly admire VW's ability to get mileage out of a basic design. Even beyond using one combustion chamber/cylinder geometry and then multiplying it by four or five or six or eight, there are little things like how the V engines use the same cylinder head on each side, with handedness determined by the camshafts and end covers.

 

[GregLocock]

Given that customer's number one priority is fuel consumption, and manufacturer's is cost and emissions, it scarcely seems surprising to me that niceties that will only affect full throttle performance to any significant degree (if that) are ignored in favour of cost savings.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[automatic2]

I think this highlighs a classic conflict with engineers, that of what they want to be, and that as what they're hired to be. Without knowing the success of the implementation, it could be brilliance.

 

[pauljohn]

I believe Jaguar did something similar with their inline 6 engine in the sixties when they enlarged it from 3.8 to 4.2.

Although they left the head unchanged so the new spacing of the bores in the block left the combustion chambers and cylinders out of alignment.

 

[Peter7307]

Related to the above posts is the dimension used by Rolls Royce for their six cylinder inline engines.

It remained the same for 44 years and there was a paper written on it.
The title was "The History of a Dimension" and the writer was G.S. Grylls.

Link below for those interested:

http://www.rrec.org.uk/Cars/Rolls-Royce_Motor_Car_Engines/History_of_a_Dimension.php

Peter.