What are the strengths of Audi I5? Why not I6?

[karlos_s2]

ok. So my friend asks me today why Audi make the I5 motor?? and not I6 motor for example?

I did not haf good answer for this question and would like some Audi experts to offer ideas please

It has been very good in competitions and so (group a..). But it is dynamiclly not balanced by nature such as supra I6 motor and I also am intersted to know why this is?

So.
Why an I5? a 2.2 litre one too! why not 3 litre i5 for example?
Strengths and benifits of this design over other possible ones? (like I6, I4 )
Weaknesses also over other designs?
Did audi just do this to be different from all other makers?? surely not?!

[Corey]

It offered better refinement than an I4 and better economy than an I6. Plus it fitted the engine bay.
I have a design study paper somewhere for this engine dated about 1976, I'll try to dig it out.

[quattroTurbo]

Making it a 3.0 litre would have increased piston size, which would have reduced combustion chamber efficiency and increased internal friction. The 2.2 litre capacity is not only good for economy, but also good for horsepower when combined with a turbocharger.

The Audi I5 stayed in production for around 20 years and proved massively successful in high level motor sport as well as in production cars, which is more than can be said for the Toyota I6.

The last development of the Audi I5 in the RS2 had 315bhp, a figure that is still competitive by today's standards. The new BMW twin turbo I6 3.0 engine doesn't have as much power, in fact its power is matched by the 1984 Sport Quattro I5 engine.

[Urquattro20V]

According to an engineer I know, a 2,3 litre I5 is somewhat of an optimal engine construction. Basically, smoother and more powerful than an I4 without the frictional losses of an I6.

And still room enough for quattro

Some good info here:

http://en.wikipedia.org/wiki/Straight-5

I wish Audi had kept on refining their engine like BMW has with their I6

[mcandmar]

Its more to do with how the engine produces power, an I5 has an unusual firing order and crank staggering, think of an I4 engine there is always two pistons at the top of the stoke and 2 at the bottom, with an I5 each cyl is staggered a set amount from one another so it all runs smoother, and distributes the power strokes more evenly over each crank rotation. The "Characteristics" section of that Wiki link explains it better than i ever could...

God can you imagine if Audi still made the I5 now, what would it be like with another 10 years R&D done to it

[dan_b]

I imagine also that they started from an already existing I4 1.8L engine and found a cost-effective and relatively technologically simple way to increase power in the engine bay space they had available for what ever cars were being developed at the time was to just bolt and extra cylinder on the end?

[Greg_S]

I think you hit the nail on the head dan, certainly a good way of increasing power in the available space

[LHD_Kid]

I understood from a guy who built alot of S1 engines, the 'worm drive' firing order made it the most efficient, there is always a firing cylinder exactly pushing from where the last one takes off (smoothness, I guess) so far as power against frictional losses... Much the same as the guys have said above... So I am sure there is something in it...
As Dan says, I am sure there is also something in the ..."we have a 4 cylinder, what would happen if we whacked one on the end...?" They found it worked well, and hey presto...

[Keeper of The Kitten]

I don't buy the "worm drive" firing thing, all engines fire a cylinder to take up where the last one left off - but certain configurations don't make it evenly spaced (eg 90° V8 engines). No engine fires in order from front to back as it would put undue torsional loads on the crank, hence the reason why I don't think the firing has that much to do with it.

I think there is a lot more to be said about fitting more engine in the same space than there is in the intricacies of the smoothness of the firing order. An inline 6 is theoretically smoother still, but there is no way that a sixth cylinder would fit inline and still retain the basic layout of engine and gearbox. Audi went to a V engine for more than five cylinders.

__MDC__

[S2central.net]

Yes it is not entirely an accident that the pistons from a 16V golf engine are the same (dimensionally) at least as the 1st generation of I5 engines...

That said - its the magic of the funky I5 firing order which give our engines that character. The very 1st one I heard was a neighbours Audi 200 and I was just amazed by the noise of the thing tootling past... Add 4WD and a turbo then things get really interesting !

[dan_b]

I'm interested in the fact that different engine designs have inherently different noise signatures. As we all know, the I5 makes such a distinctive sound, but the V5 from the VW family, which still has 5 cylinders, makes a different noise. Going down, a I4-cyl has a certain noise, which is different from (for those that can remember cars with them) a flat boxer 4. V6s sound different to a I6s, and of course, you can tell a mile off the rumble of a V8!

[S2central.net]

Theres maybe a PHD project in that for someone

[CHEN]

A little off topic, but I heard that the I5 engine was stopped due to laws in the USA which demand a certain gap between front bumper and the engine. Can anyone throw any light on this. Why did Audi stop making such a good engine?

[mcandmar]

When you put it like that i wouldn’t fancy being knocked down by an I5 Audi, first you hit the tank like body work then the iron block engine makes its presence felt ....much rather get attacked by a plastic TT.

The real reason as i see it was to change the layout, the big iron block I5 sticking out ahead of the front axle was never ideal for handling/balance. At the end of the rally days the lighter more nimble Lancias had the edge on the twisty stuff with there transverse engine layout.

[Billman]

I think Audi stoped it because it dint fit to the Serious image they wanted. A I5 with big punch is something for "outlaws" and not for Buissnesmen. But i think they want this "Outlaw" Sportiness for they young buyers only and thats why they are offering small displacement big HP engines in small cars (S3 and TT with 210-225 and now 265 HP from 1,8 and 2 liters).