44 replies to this topic

[David M. Kane]

Looking at the photos that Doug Nye has been posted from Geoff Goddard's collection, it raised a question I have had for a long time. How did exhaust systems initially become an area of intense focus. My first recall of equal length pipes came in the 1500cc days of Clark and Hill and the early Lotus Indy car days.

What engine tuner started this process?

[A E Anderson]

Originally posted by David M. Kane
Looking at the photos that Doug Nye has been posted from Geoff Goddard's collection, it raised a question I have had for a long time. How did exhaust systems initially become an area of intense focus. My first recall of equal length pipes came in the 1500cc days of Clark and Hill and the early Lotus Indy car days.

What engine tuner started this process?

Hot rodders were experimenting with "tuned" exhaust headers in the late 1950's, and by 1961 or 1962, drag racers were installing these "equal length" headers on cars where custom or aftermarket exhaust systems were allowed. The Granitelli's installed equal length headers on the Novi 4WD cars from the very beginning, I believe, which would mean 1964. As for their installation on Lotus Indianapolis cars, that's because Ford Motor Company's engineers designed them into their engines, from the pushrod V8's of 1963 onward.

Art Anderson

[Tim Murray]

According to LJK Setright in The Grand Prix :

. . . the machines of 1952 and 1953 were not without their attractions and merits. In their engines, designers learned to explore and exploit the improvements in volumetric efficiency made possible by providing separate inlet tracts for each cylinder and by adjusting the lengths of these and of the exhaust systems so as to harness the pulsations that could be stimulated therein. Pioneered by Miller in the early 1920s and then forgotten in racing circles until the idea was revived by HWM and Connaught, these principles had long been known and profitably employed by the makers and tuners of racing motorcycles. In 1952 and the following year the practice became common . . .

Presumably during the reign of the supercharger (in Europe) such tuning sophistication was considered unnecessary. But what of the 'Junk Formula' years in the US when superchargers were forbidden? Did any engine builders/tuners make use of these tuning techniques?

[David Beard]

Originally posted by A E Anderson


Hot rodders were experimenting with "tuned" exhaust headers...
Art Anderson

For a long time I have been confused by the American expression "header".
Is that really a manifold?

[A E Anderson]

Originally posted by David Beard


For a long time I have been confused by the American expression "header".
Is that really a manifold?

Of course, we in the US do call the cast-iron or cast-aluminum exhaust "collector" units "manifolds", but when we see a set of exhaust pipes made from steel tubing, bent and welded together to make some sort of "collector" setup, we think of that as a "header". I suspect the term "header" comes from either plumbing or from steam engines.

From earlier days, I can remember the exhaust pipe system on an ordinary passenger car being referred two in three distinct sections: The head pipe, which connects to the exhaust manifold on its forward end, then to the muffler, and then a tailpipe which conducts the exhaust gasses from the muffler to the rear of the car itself.

The idea of "tuning" headers (and even some cast-iron manilfolds) stems from there being an ideal length at which the flow of the exhaust gasses out from the engine actually can enhance the "scavenging" of these gasses out of the cylinder during the exhaust stroke (on in the case of a two-cycle engine, actually enhancing the out-flow of exhaust to the point where it increases the volume of clean air and fresh fuel in through the also open intake port!). This is why General Motors diesel engines, having been 2-cycle engines--both in truck sizes, and the fairly monstrous railroad locomotive engines, used Rootes style superchargers (the famed GMC or "Jimmy" blowers of drag-racing fame in the US) to further enhance the scavenging of burnt exhaust gas from the cylinder, and increasting the volume of fresh air into it at the same time.

With racing or performance engines, this "tuning" of exhaust pipe length is done to increase the efficiency at a particular RPM range, and by adding curves and bends in the pipes, they can be made equal in length, and if properly brought together at a collector, the velocity of exhaust gas from one cylinder can actually "siphon" remaining gasses from nearby pipes, again enhancing performance.

But: Manifold, in US parlance, denotes a cast iron collecting pipe on the exhaust side, "header" refers to a fabricated steel tubing system.

"England and America, separated by a common language" (George Bernard Shaw)

Art Anderson

[Bonde]

The importance of tuning of exhaust and inlet systems particularly on two-strokes was, I think, realized quite early on. IIRC, such as DKW began tuning their exhaust systems on two-strokes without scavenge pumps in the early thirties, although as I recall, most of DKW's racing engines used one sort or another of often quite sophisticated piston-type scavenge pumps, which may have rendered tuned exhausts somewhat less critical.

Some of you may recall bulky but elaborate tuned divergent-convergent expansion chamber individual exhaust pipes on various 3-cylinder DKW and Wartburg-powered Formula Juniors.

Didn't Sir Harry Ricardo also work on exhaust (and inlet) tuning quite early on?


Art,

Aren't 'headers' also sometimes called 'primaries' in The States?

[cosworth bdg]

Originally posted by David M. Kane
Looking at the photos that Doug Nye has been posted from Geoff Goddard's collection, it raised a question I have had for a long time. How did exhaust systems initially become an area of intense focus. My first recall of equal length pipes came in the 1500cc days of Clark and Hill and the early Lotus Indy car days.

What engine tuner started this process?

Exhaust tuning really started to become serious with the introduction of naturally aspirated engines in F1, Coventry Climax , Cosworth, & Repco-brabham ,Ferrari , Maserati were all leaders in the ART of exhaust pipe tuning, with the leading F1 engine suppliers carrying on the science today...

[bradbury west]

I am not an engineer, so............

I understood the lengths to be critical in any case because of the flow of gases in waves, with nodes and anti-nodes, so the end of the pipe had to coincide with where the waves were at their widest divergence, hence race teams sawing off an inch or so at a time to measure bhp, I have been told.. Must have been told that as I could not have made it up.

The 2 stroke bikes found it critical in the fifties and sixties as they extended their rev range, 19,000rpm and 7 speed boxes on 50cc or 125cc engines IIRC from my schooldays, so optimised breathing was critical.

RL

[bradbury west]

BTW, how critical was the exhaust tuning on stuff like low hp F Ford 1600 engines, where every hp counted? From memory they seemed to have rudimentary systems, as did the FJ cars.

RL

[Bonde]

Roger,

In Formula Ford we've actually gone full circle. On the 1600 'Kent' engines we use(d) properly tuned 4-1 "bananas" (IIRC, some of the early FF 1500s had 4-2-1, which was also quite common on FJs), whereas with the 1800 'Zetec' we got that nasty road car cast iron manifold feeding into twin tubes to the cat and hence a single tube tailpipe. On the new 1600 'Duratec' we're back to tuned 4-1 "bananas". Apart from the improved appearance (the 1800 system is equally 'bad' for everyone), the old and new 1600 sound a lot better than the 1800, which always sounded like a long, muffled fart to me - except on our on our FF1800 Aquila, which sounds 'cleaner' due to our long tailpipe ;)

I think many of us who have raced Formula Fords have tried once (or more often when repairs eventually became layers of nickel-bronze, and we we're too cheap to replace the offending pipe with a fresh item) running with a cracked or broken primary pipe - one does feel the power loss and it does show in lap times when that happens. It sounds really weird in-car, too pft-pft-pft-pft, like an old single cylinder bike engine!

In Formula Vee, the early (1200) years called for 4 individual pipes (which was used in Oz well into the 1980s, IIRC). In Europe, 4-1 was allowed I think beginning in 1967 with the 1300 engine, and elsewhere later. The low-powered Vees certainly benefit from the tuned exhaust.

[David M. Kane]

Bonde:

It was in a Royale RP-3A in the day that started this whole thought. I loved the sound and response of that 1600 cc Kent engine.

[Sharman]

As George Mangoletsi said "it's not engineers you need, it's bloody snake charmers"

[Frank S]

Local (Southern California) F-Vees used single-megaphone
tailpipes. The "departure angle" was critical.

Our Rob Walker (not that Rob Walker) made his own
for the McKnight he raced. He went a step farther, welding
some curved leaves and a small central circle into the end
of the megaphone. Looked as if it would create spin in the
exhaust gases.

Rob always ran first or near it, and within weeks a number
of other competitors had produced similar exhausts with
vortex-inducers. Rob just grinned.

--
Frank S

[bradbury west]

Originally posted by Frank S
Local (Southern California) F-Vees used single-megaphone
tailpipes. The "departure angle" was critical.

and within weeks a number
of other competitors had produced similar exhausts with
vortex-inducers. Rob just grinned.

--
Frank S

Sounds a bit like the lemming response to Colin Chapman's forward facing schnorkel on the front of the carb on one of the early 1172 cars, mk3??. It was apparently to stop fuel blowing back into his face, but the others thought it some demon mod. and followed suit IIRC

+++

I seem to recall photos of 2 stroke powered FJ cars, Mitter-DKW?? with large tapered expansion boxes on the exhausts.

RL

[Cirrus]

Ah..... Mitter DKW's



The convergent/divergent exhausts on high performance two strokes are critical to power output. The presure pulse from the exhaust stroke bounces off the convergent part of the exhaust and returns to the cylinder to perform some basic scavenging action. It can be very effective, but it's also very engine-speed dependent. Tuning the exhaust length was very important when I was karting.

[Sharman]

Anybody remember Peco exhaust assisters, I was very suprised in 1963 to see that all the 250 GTO were wearing a similar device at the TT
Gerhard's Juniors were very fast but very fragile engine wise' presumeably the middle pot overheating. They really made a very loud "ringing" noise when you stood next to them

[bradbury west]

John, the Ferrari Peco things were Snap. The ad said "like Ferrari fit". I thought the Peco were just a twin tailpipe with an expansion box, "an ehaust booster"and a rorty noise, certainly on a Morris 1000, (my father had one),whereas the Snap items had some sort of spiral vanes in the exhaust, presumably to accelerate to gases.

RL

[cosworth bdg]

Originally posted by bradbury west
I am not an engineer, so............

I understood the lengths to be critical in any case because of the flow of gases in waves, with nodes and anti-nodes, so the end of the pipe had to coincide with where the waves were at their widest divergence, hence race teams sawing off an inch or so at a time to measure bhp, I have been told.. Must have been told that as I could not have made it up.


RL

It all happens today on the engine dyno or chassis dyno, behind closed doors............

[2Bob]

Then again...

A story has that I have in the back of my mind is that the Geoghans were seen sawing a few inches off the end of the pipe on their newly aquired Lotus 23 during practice (at Lakeside?). They got pole that day. Later on another Lotus 23 had its pipe shortened similarly. It wasn't until after the next days racing that the Geoghans pointed out that they had shortened the pipe so that the car fitted into the trailer properly.....

[Sharman]

Roger
The Peco doodah was described as an extractor, I never cut one up but their sales manager used to race a red Elite, curiously enough, referring to another thread, he and Rod Bloor were very closely matched. I can't remmeber his name.
John

[Manfred Cubenoggin]

2Bob:

LOL!!!

[cosworth bdg]

Originally posted by Manfred Cubenoggin
2Bob:

LOL!!!

Agree !!!!!

[Joe Bosworth]

David Kane started this thread by writing,

"Looking at the photos that Doug Nye has been posted from Geoff Goddard's collection, it raised a question I have had for a long time. How did exhaust systems initially become an area of intense focus. My first recall of equal length pipes came in the 1500cc days of Clark and Hill and the early Lotus Indy car days.

What engine tuner started this process?"

Putting this into some historical perspective, I had started playing with exhaust tuning by 1957 and was constructing several very useful systems with megas and reverse cone megas by 1960.

I certainly wasn't a pioneer by any means, I was following the theories and formulas that were being well published slightly just before my first efforts. An understanding of fluid flow from a couple of engineering units didn't hurt in applying and expanding published works of others.

It seems to me that the guys that were really pioneering applications before that were the single, (and twin), cylinder four stroke bike racing guys on both sides of the Atlantic and perhaps elsewhere but the elsewheres weren't getting much press. The bike guys easily pre-date the 1500 days of F1. At that point in time I don't think that either the dry lakes rodders or Offy roadster guys were paying much attention to exhaust tuning for horse power development.

In my view the bike guys efforts certainly met David's definition of "intense focus".

Having dropped that seed I will be happy to step back and let some of the very bike knowledgable TNFers step in with some dated photo proof to support my view.

Regards

[cosworth bdg]

You very correct in what you are saying about about 4 stroke motorcycle engine tuners... Examples can be found at the ISLE OF MAN T T races going back to the very first events.....

[robert dick]

Prehistoric exhaust tuning :

In 1883, Gottlieb Daimler's first petrol engine, a single in the dimensions of 58/100 mm delivering 0.5 hp at 600 rpm, was tested in a greenhouse in the garden of his house at Cannstatt. His son Paul remembered: "The old man tried in vain to convince mankind that air was necessary for an explosion. The greenhouse played an essential role since we could work there without being seen from the street. The gases were usually led into a cavity in order to absorb the exhaust noise. But once we choose a straightline exhaust pipe which immediately produced more power due to the suction effect."

The 1906 GP Brasier was a four in the dimensions of 165/150 mm delivering 105 hp at 1380 rpm. Its exhaust manifold combined cylinders one with four, and two with three.

[Peter Morley]

I was just skimming through a technical paper given to the SAE about Climax engines and that talks about exhaust systems on the FPE V8 - so they were certainly considering the issues in the mid 50s.
Their conclusions were that seperate (e.g. stub) exhausts were better in this particular case.

[soubriquet]

Aircraft exhausts were designed to give a jet effect by the time of WW2. That technology was developed in the 1930's.

Manx Nortons were making 100bhp/litre in the 1950's, and exhaust tuning was crucial to that.

[cosworth bdg]

Originally posted by Peter Morley
I was just skimming through a technical paper given to the SAE about Climax engines and that talks about exhaust systems on the FPE V8 - so they were certainly considering the issues in the mid 50s.
Their conclusions were that seperate (e.g. stub) exhausts were better in this particular case.

Their conclusions were really subjective & cannot be generalised for all internal combustion engines

[cosworth bdg]

Originally posted by soubriquet
Aircraft exhausts were designed to give a jet effect by the time of WW2. That technology was developed in the 1930's.

Manx Nortons were making 100bhp/litre in the 1950's, and exhaust tuning was crucial to that.

Manx Nortons now we are really taking development, these Nortons led 4 stroke development of which is still applicable today in many forms of motorsport ........

[McGuire]

The concept of exhaust pressure-wave scavenging is practically as old as the Otto engine itself. From The Gas and Oil Engine by Dugald Clerk, 1896, John Riley and Sons, New York:

"It has long been known that in a gas engine exhaust pipe the pressure of discharge is succeeded by a partial vacuum, and this vacuum is again succeeded by pressure, in fact that under certain circumstances an oscillation of pressure is set up in the exhaust pipe, giving a fall of pressure at certain periods after the exhaust valve is opened."

Note Clerk says "it has long been known," and this was in 1896!

Also featured in this book is the 1892 Crossley Scavenging Engine. In its original form this engine used a 7" bore x 15" stroke (577 CID) and at 200 rpm developed 14 indicated hp and 100 PSI MEP, using special valve timing and an exhaust pipe SIXTY-FIVE FEET long (that's not a typo).

This same engine is also briefly described in The Scientific Design of Exhaust and Intake Systems by Phillip H. Smith, 1962, Robert Bentley Inc, Cambridge, Mass. This book can be considered the original popular text on intake/exhaust wave tuning, based in significant part on the work of J.C. Morrison, who published his first paper on the subject in 1931.

The Crossley Scavenging Engine is again referenced in The Grand Prix Car 1954/1966 by LJK Setright, serving as a historical lead-in to around 20 pages of material on the subject of intake/exhaust wave tuning. It's a major portion of the book, as the years in the title correspond rather neatly to the era in which these techniques were developed and realized in Grand Prix cars-- around 1954 on. The Connaught Alta and the four-cylinder BRM, to name two, employed wave-tuned exhaust systems. Of course, motorcycle racing led this trend by a few years... for which we can probably once again thank Leo Kuzmicki:

[Dennis Hockenbury]

Originally posted by Tim Murray
According to LJK Setright in The Grand Prix ....Pioneered by Miller in the early 1920s and then forgotten in racing circles until the idea was revived by HWM and Connaught..... :

Intrigued by this statement by the notable authority LJKS, I reviewed a lot of books on Millers and could not find any evidence to support this statement.

Most of the exhaust systems on the Millers were 8 into 1, and the occasional 4 into 2 systems. I will acknowledge the engineering and artistry used by Miller on his beautifully tapered water manifolds on the 183, 122, and 91 series engines, but alas, no evidence of "tuned" exhaust systems as referenced by David in his original post.

Of course, I am always pleased to be corrected if someone has evidence to the contrary.

[McGuire]

Originally posted by Dennis Hockenbury
Intrigued by this statement by the notable authority LJKS, I reviewed a lot of books on Millers and could not find any evidence to support this statement.

Miller employed resonant wave tuning on the intake side of the 1922 183 CID engine, with ram stacks on each of the eight separate barrel-valve carburetors. This setup is illustrated on p. 205 of Borgeson's The Golden Age of the American Racing Car; the cut-and-try tuning procedure Miller reportedly used to get the length exactly right (with a stopwatch on the board speedway in Beverly Hills) is described on p. 207.

This is no doubt what Setright was referring to in the statement, which you will note includes both tuned intake and exhaust tracts. Like you, I see no evidence that Miller ever dabbled with wave exhaust tuning specifically.

[Dennis Hockenbury]

McGuire, I noted this as well. Perhaps not surprising that HAM expended much effort on the intake side given his early pioneering work with carburetors.

I was a bit surprised by contrast that the same attention was apparantly not given to the exhaust side. Perhaps it was just not of great importance at the time.

Having heard many, and driven a few Miller's, I can attest to the sheer loudness of the exhausts. While not in the league of a BRM Mk. I or II, they are quite loud for a late 20's, early 30's straight eight.

[A E Anderson]

Originally posted by soubriquet
Aircraft exhausts were designed to give a jet effect by the time of WW2. That technology was developed in the 1930's.

Manx Nortons were making 100bhp/litre in the 1950's, and exhaust tuning was crucial to that.

That's news to me! Piston aero engines tended to just get the exhaust out of the cowlings or nacelles the quickest and shortest way possible, unless the engine was turbocharged, in which case, the exhaust system could be pretty long, convoluted, and fairly heavy (Lockheed P-38 and Republic Thunderbolts had exhaust passages that ran fully half, or more, of the length of the fuselage). Of course, particularly with inline aero engines (particularly the V12's of Daimler-Benz, Junkers, Allison, and Rolls-Royce/Packard) exhaust outlets were angled backward, so the slipstream of the aircraft would aid in scavenging, but that was about it. Radial engines, as a rule, didn't have the feature of individual short exhaust stacks, the B-25D and later variants of the Mitchell bomber being noted exceptions--those had individual exhaust stacks poked through their cowlings--most radials using ring-shaped exhaust collectors, with one or two outlet stacks.

Many confuse the radiator outlet of the P-51 Mustang for exhaust--but if one looks at at the Mustang, exhaust stacks are clearly seen on each side of the cowling--the radiator outlet merely let the heated air exiting the radiator core out into what would have been a low-pressure area behind this unit, thereby increasing the speed of the aircraft.

Art

[cosworth bdg]

Originally posted by cosworth bdg
Manx Nortons now we are really taking development, these Nortons led 4 stroke development of which is still applicable today in many forms of motorsport ........

A lot of the PHIL IRVING idea's came from these MANX NORTON'S... one reason why the 2 valve REPCO - BRABHAM V8'S were so successful in F1 the 1960'S.........

[McGuire]

Originally posted by Tim Murray
According to LJK Setright in The Grand Prix :


Presumably during the reign of the supercharger (in Europe) such tuning sophistication was considered unnecessary. But what of the 'Junk Formula' years in the US when superchargers were forbidden? Did any engine builders/tuners make use of these tuning techniques?

I don't know (I wasn't there LOL) but I don't think so. I have found no photographic evidence at least. Just took a spin through Roger Huntington's great Indy car book and found no sign of any experimentation in exhaust-length tuning in that era. That is just the sort of development Huntington would have picked up on too... right up his alley.

[m9a3r5i7o2n]

More on what McGuire states:

Indy Cars 1911-1939 Ludvigsen, 1923 page 37, Miller 3 Liter straight eight has four twin-throat carburetors with tuned ram pipes angled at what looks like 45 degrees. Also on page 36 is a picture of Jimmy Murphy’s engine which had four single venturi carburetors although the original design has had four dual venturi carburetors. Several other pictures in same book show Harry Miller’s foremost design thoughts. Updraft carburetors instead of side drafts.
The exhausts don't look quite long enought to be of any significance.

Philip H Smith’s book, “SCIENTIFIC DESIGN OF EXHAUST & INTAKE SYSTEMS”, is dated 1962 but there isn't any place I have seen to tell just how well the book was distributed but it sure went thru a lot of reprints!!!

M.L. Anderson

[D-Type]

Originally posted by cosworth bdg
A lot of the PHIL IRVING idea's came from these MANX NORTON'S... one reason why the 2 valve REPCO - BRABHAM V8'S were so successful in F1 the 1960'S.........

And don't forget that the top end of the Vanwall engine was effectively four Norton Manx engines in a water jacket.

[A E Anderson]

Originally posted by m9a3r5i7o2n
More on what McGuire states:

Indy Cars 1911-1939 Ludvigsen, 1923 page 37, Miller 3 Liter straight eight has four twin-throat carburetors with tuned ram pipes angled at what looks like 45 degrees. Also on page 36 is a picture of Jimmy Murphy’s engine which had four single venturi carburetors although the original design has had four dual venturi carburetors. Several other pictures in same book show Harry Miller’s foremost design thoughts. Updraft carburetors instead of side drafts.
The exhausts don't look quite long enought to be of any significance.

Philip H Smith’s book, “SCIENTIFIC DESIGN OF EXHAUST & INTAKE SYSTEMS”, is dated 1962 but there isn't any place I have seen to tell just how well the book was distributed but it sure went thru a lot of reprints!!!

M.L. Anderson

Of course, a lot of this discussion is coming from the early 21st Century, trying to look back at race car developments from 50, 60, even 75 or 100 years ago--in other words, when such as intake and exhaust design was in its infancy, correct?


It's pretty hard, I think, to bear in mind that a lot of engineering was, in the 1920's, even teh 1930's, still pretty close to "cut and fit", "trial and error".

Art

[cosworth bdg]

Originally posted by D-Type

And don't forget that the top end of the Vanwall engine was effectively four Norton Manx engines in a water jacket.

Look at the way naturally aspirated engine development has headed since manx nortons...........

[cosworth bdg]

[i]

Philip H Smith’s book, “SCIENTIFIC DESIGN OF EXHAUST & INTAKE SYSTEMS”, is dated 1962 but there isn't any place I have seen to tell just how well the book was distributed but it sure went thru a lot of reprints!!!

M.L. Anderson [/B]

Yes a lot of reprints, i have one such reprint

[Allan Lupton]

Originally posted by robert dick
Prehistoric exhaust tuning :

The 1906 GP Brasier was a four in the dimensions of 165/150 mm delivering 105 hp at 1380 rpm. Its exhaust manifold combined cylinders one with four, and two with three.

Have you got, or can you tell me where to find, a photo of this?

The earliest example of this that I have otherwise heard of is the 1921 Coda Diatto-Bugatti T23.

The Coda system left it as two exhaust pipes, as I expect Brasier did: the next milestone is combining the two into one which must have been done between the Wars, but I can't find it in any good photo.

[robert dick]

Pierry's Brasier in the 1906 Circuit des Ardennes (copyright Daimler-Chrysler archives) :




The Brasier had a side-valve L-head engine : one intake and one exhaust valve per cylinder, in the same valve pocket, operated by one low mounted camshaft.
It is not apparent in the photo if Brasier combined two into one in the endpiece of the exhaust pipe.

[Allan Lupton]

Excellent photo: all the contemporary magazines' Brasier photos I could find had the bonnet shut.

[VAR1016]

Just stumbled on this interesting thread.

The story of the Richard Brasier is fascinating; how sad that there are no photos (those referred to having apparently disappeared).

With regard to exhaust tuning in general, I recall reading somewhere that Freddie Dixon (with much bike experience) may have used such techniques on his very fast Rileys in the 1930s. While no expert on Bugattis I have noticed that Bugatti manifolds e.g. on Type 35s appear to have quite a modern layout certainly by the standards of the time.

Lastly when Ferrari took over the Lancia D50 cars they did away with the manifolds and replaced them with four equal-length pipes running the length of the car on each side. The Lancia V-8 had of course a 90° crankshaft which makes manifold design and installation very tricky; perhaps this explains Coventry-Climax's findings regarding stub exhausts referred to earlier in this thread? And Tony Vandervell laughed at the Type 801 Ferraris, referring to the shattering noise from their exhausts, saying "that's where all your power's going!" The Vanwall cars were very quiet in comparison; note the design of the exhaust system!

Paul

Edited by VAR1016, 22 November 2009 - 17:11.