August 16 (evening) Chris on the sixth and last day of racing:
"Racing finished tonight (Thursday),
and Friday is for record runs. The Indian has run flawlessly and never
failed to start first kick. I've realised there's no way I can get
the record, but I think I've got as much out of the bike as I can. I put
on the 21/42 gearing, and went out this morning and did 79.9 mph/128,6
Km/h on a 185 jet. Changed to a 170 and ran it for the last time this
afternoon, and it pulled 81.5 mph/131,1 Km/h. Big grins all around,
I can't describe how pleased I am. I'm now thinking different gearbox,
and definitely a blower, then I can pinch Lars' soft
[a "soft" record is one set in a class where there were no prior records;
so speeds don't need to be high for this], I'm only a few miles off
it ... oops, did I imply I might be going back?"
Big grins here at IPE HQ too! First, and
most important, it is fabulous that Chris actually made it to Bonneville.
It has been a long trip, starting
in the shed back in England with a dream, a tired engine, a pile of steel
tubing and no money.
Second, I am really happy that the engine
stood up so well to the hard use. There is nothing special about it; it
is the same specification as any other IPE 600cc
741 street engine. So this goes to show how tough these engines
are when put together right - and Chris certainly did that.
As for that last run, I am very happy about
that too. The fact that speed went up with the lower gearing confirms
that the best gearing is around here. According to the gearing table,
to go 81.5 mph the engine must have pulled around 4800 rpm in top gear
on 21/42. So this gearing allows it to over-rev by 100 rpm, while 22/42
has the engine 200 rpm down on the target of 4700, where max power is developed
according to the dyno.
In this way the racing has been a great
success. While I never doubted that the main principle of gearing would
be to gear up if the engine revved more than the target in top gear, and
gear down if it revved less, it is good to see it confirmed so clearly.
And nice to get confirmation that the 170
main jet is about right too. The bike went slower on the bigger 185 jet.
A 185 jet worked best on the dyno at sea level, so the 170 jet is an indication
of approximately how much to jet down for Bonneville in general.
And, Chris? - I knew you'd be wanting to
Click to watch video on
YouTube. This is a new, longer version of the videos posted here earlier.
a "IPE 600cc 741" engine?
Basically a stock 741 engine with bigger
valves, bigger pistons, IPE electronic ignition and Keihin CV carb on an
IPE manifold. Maybe it should be called the "Bonneville 741"? ;-)
Of course it must be put together carefully
(and you need machine tools for this, it isn't just bolting on parts).
But get in touch if you want to build one of these engines and I will do
all I can to help. Even if you are not going to Bonneville with it!
with his 600cc 741 - an engine much like Chris' - will race at the BUB
meet at Bonneville, August 25-30. Here is a brief report
from Neil at last year's BUB.
August 15 (night) Some of the reporting here happens more or
less in real time (if it isn't half a day behind, that is), and Chris just
told me that he actually had 22/42 gearing on initially, not the
21/42 reported earlier. Ah, there goes the neatness of the gearing table...
So, the 80.370 mph Monday means that the engine only turned something like
4500 rpm in top, down 200 rpm from the target 4700. That still indicates
that the initial gearing was pretty close (again assuming that the 4700
rpm power peak on the dyno is correct, but that is all we have to go on).
Chris has put on the 21T front sprocket just before closing time (racing
ends at 7 in the evening and everybody have to be off the salt at 8), so
tomorrow he will be running 21/42 gearing. If predictions are correct,
the engine should be able to pull a few more rpm in top and, possibly,
go a bit faster than 80.370 mph (gearing table says 80 mph at 4700 with
21/42, but maybe the engine can rev a bit beyond that with the lower gearing).
Really looking forward to hearing how that goes!
Chris just posted this fabulous video on
YouTube. It gives a great sense of how vast a place Bonneville is, and
what it must be like to ride there.
Video by Steve Brown. Click
to watch on YouTube.
August 15 (evening) Having spent most of the day thinking about
the problem with the bike accelerating great in first and second gear only
to fall flat in top, it struck me that for the gearing thing to work (gear
down if the bike revs less than peak power rpm in top, gear up if it wants
to rev faster), the engine has to run right to begin with.
But gearing first. I hadn't been able to
match Chris' reported rpm to the timed speeds, but he told me today that
the initial gearing was 21T front and 42T rear (I didn't know which sprockets
he put on at home). The bike went 80.370 mph on this gearing Monday. Looking
in the gearing table,
that is actually spot-on. For 21/42 sprockets the table says 80 mph
at 4700 rpm.
So maybe there is no crazy stuff involved,
except perhaps in reading the tach in the rush of a run? Maybe 21/42 was
the optimal gearing, and the maximum possible speed of the bike is 80 mph?
If so, then it makes sense that it pulls worse and goes slower with Tuesday's
A test of this could be to go down
on the front sprocket. We were optimistic about the speed, and Chris packed
lots of big fronts and lots of small rears. He is on the biggest rear now,
and there are only 20T and 19T smaller fronts to try, but with the 19 on,
the bike should want to rev higher than 4700 in top (we assume that it
is safe to at least 5000; it should rev 5010 if it can get to 85 mph on
19/42). I think it is worth a try as it could confirm that 21/42 was the
best gearing for the bike with the engine running as it does now.
The reluctance to rev out in top, even
on 21/42 gearing, could be nothing more than the big gap between second
and top gears causing the engine to lose its breath, only just being
able to pull 4700 rpm. It is a big gap, the Indian gearbox being sort of
wide-ratio and having only three gears. I think this sounds pretty plausible,
But, coming back to the possiblity that
the engine may not be running right, Grizzy (of Sprint Chout
fame, who has a long career racing and tuning bikes) mentioned that too
advanced ignition would cause the engine to bog down. And Chris advanced
the ignition from the dyno test setting on Saturday. I am not sure what
the reason for this was, but maybe it should be set back to what the dyno
said was best.
Second, on this line of thought, maybe
the main jet is too big, causing the engine to run rich at high rpm when
pulling hard. A test of this could be to close the throttle a little
bit from fully open in top (1/8 of the throttle grip travel, or so) and
see if the engine revs a little bit higher. The problem with such tests
is that there are so few runs - one or two a day, sometimes - to carry
them out, and no opportunity for practice runs. I am really looking
forward to hearing how today went, and if Chris has made any discoveries.
I think what I would most like to hear is a confirmation of the gearing
(118F/48C on thermometer
in the pit tent)
August 15 (morning) Chris on the fourth day of racing (yesterday):
"Following Moen's advice [no, you didn't - see below], I upped
the gearbox sprocket from 22 teeth to 26, the rear sprocket is a 42. This
is a fairly involved job, I have to remove the 2-piece chainguard and the
rear exhaust, then the kickstart assembly. I also fitted new plugs and
did the valve clearances, which meant removing the front pipe and pulling
the distributor out, and holding three spanners, a bastard job, and also
changed the main jet back to a 170.
I finally had it up and running sweetly
by 4 in the afternoon, and by 4:30 we had done the 12 mile run to the start
line and I was ready to go. At this point I must mention Jim and Shaun
who are my crew, and when I'm not running they're Briz's crew along with
David. From a pair of bumbling buffoons a few days ago they have perfected
their start-line routine.
Because of the heat it's not possible
to suit up until the last minute and these two are brilliant. As we move
down the line one drives the van and the other moves the bike while I soak
up some air-con, then (as Shaun says) it's like dressing the King as I
get handed leathers, gloves and helmet which Jim has held to the air-con
vent. They help me zip up and Jim buckles my helmet, the bike's fired up
on the line, Shaun holds the umbrella and removes the sidestand, Jim clips
the safety lanyard to my sleeve zip and folds the kickstart pedal in, the
starter waves me off and they're in the van, blasting up the recovery road.
I'm off the track before them and by the time I have my helmet off with
sweat dripping from it, they've shoved a bottle of iced water in my hand.
This pair are as important as the rider, without them I couldn't do it.
In fact, without the rest of the teams
I couldn't do it as everyone helps each other, be it with tools, advice
or spannering. Finally, after all that work, she ran 5mph ... slower."
Setting tappet clearance.
So, why did the bike
go slower with a bigger front sprocket? Normally, when you want a bike
to go faster, you fit a smaller rear sprocket or a bigger front sprocket.
This makes the rear wheel turn faster at a given engine rpm, and this is
what Chris did, going from a 22T front to a 26T front while keeping the
42T rear. But - as stated in the August 13 morning update below
- this only works if the engine can pull max rpm in top gear, and
the last I heard was 2700 rpm in top. Max rpm in this context is the rpm
where the engine develops the most power - in this case (if dyno data are
correct), 4700 rpm. This is the only thing to keep in mind here. I can't
get the reported top gear rpm and official timed speeds to match the gearing
table (link below), and I am not sure where the
problem is (bad math, bad input data, faulty tach or tach reading?), but
the basic principles still apply.
1) If the bike can pull max HP rpm (4700
in this case) in top gear - and won't rev higher - it is going as
fast is it can.
2) If it can't rev this high in top gear,
gear it down - fit a smaller front sprocket, or bigger rear (even if it
may be counter intuitive to gear down to go faster).
3) If it revs higher than this, it can
pull a higher gear, so gear it up. I hope Chris gets to trying a more realistic
gearing today. Stay tuned...
August 14 (morning) The reporting here is being pieced together
from what Chris gets through to me plus whatever I can glean from other
sources, so sometimes there are delays in getting the whole picture together.
The racers are pretty exhausted by now. Sleeping in tents in Wendover (nearest
town), getting up early for the drive to the salt, getting the bikes ready,
waiting in line for the runs - in full leathers in 110 degree F (43 degrees
C) - lots of working on the bikes in the pit and lots of commuting back
and forth. Just getting from the pits to the start line, and from the finish
line back to the pits, is a trip of 24 miles/38 Km in heavy traffic.
Anyway, I found out this morning that the
misfire was due to low battery voltage. Chris has spare batteres and a
charger, and there is a speedshop/hardware store in Wendover if more batteries
are needed, so it could have been much worse.
Here are Chris' words on the third day
of racing: "Got to our track and queued for nearly two hours. Everything
was perfect, not too hot and a nice tail wind. Dumped the clutch and powered
off the line, into second and she started missing then cut out, so I had
to cruise into the rough salt. The digital rev-counter had cut out so I
knew the problem, the battery, whilst not flat, had gone below 12 volts,
bollocks! Another 12 mile drive to the pits (did I mention the whole 12
miles is chok-a-block with vehicles) and bung in one of the two spare batteries.
The BBC descended like a pack of vultures and bolted three mini-HD cameras
on the bike, and one on me... not literally, I wore a pair of glasses with
a tiny HD camera between my eyes. The temperature was now 110 degrees with
no shade and a pretty good cross-wind. The old girl pulled away nice but
started farting and missing, but eventually ran smooth, the cross-wind
kept blowing me to the left, and when I hit the 2 mile marker it felt much
slower than yesterday [but was actually a bit faster; see below].
I pulled into the exit lane to wait for Jim and Shaun to collect me."
Electronic rev counter serves
as (sort of) voltage monitor, too. I.e. when it stops working the battery
voltage is below 12 volts. Tiny-Tach
has its own built-in battery, so it isn't connected to the rest of the
wiring, and just keeps on working.
The electrical system is
simple. Battery, IPE electronic ignition, rev counter, kill switch + lanyard
to go around riders' wrist so ignition is cut if he falls off (red string
on the right in the picture). Note BBC cameras, too.
August 13 (evening) Third day of racing. Now on a 170 main jet,
with plugs looking good, still on the same gearing, the bike ran 80.370
mph/129.32 Km/h in a bad cross-wind. It developed a misfire at 3800
rpm. Gearing changes tomorrow.
Chris took a snapshot of the course layout
in the program, so you can get an idea of the geography. Course 4 (far
right) is where the slower vehices run (and "slow" is relative here! The
Poteet & Main Speed
Demon streamliner went 427 mph/687 Km/h today - on the long course).
Anyway, the T's on the map shows timing points - at mile 1, 2 and 2-1/4
on the short course. The curved lines are the return roads. These are taken
if a run goes well. If something goes wrong, racers are to turn out to
the other side. This way it is clear to rescue crews (at the "fire" stations
on the map) if everything is OK or if someone needs help.
Results from Saturday's runs are
now on the SCTA
website (yes, they are a bit behind, but all this is being done by unpaid
Race course layout at SpeedWeek
August 13 (morning) I suggested to Chris last night that he
lowered the overall gearing in an attempt to let the engine pull
higher rpm in top gear. The 741 was actually dyno tested back in England,
but I have been wanting to save writing about that until there was a good
context for it (like the final speed here on the salt, for example), so
a full discussion of that will have to wait a bit. There were basically
three objectives with the test.
1) Get a baseline jetting for the
carb. With the "thinner air" at Bonneville, no doubt a smaller main jet
would be needed, but it is a huge help to know what jet makes the most
power at seal level.
2) Determine the best ignition timing.
This, again, might need changing at Bonneville (not least to match the
race fuel), but a baseline is hugely helpful.
3) Find out at what rpm the engine
develops maximum power. And, almost secondarily, what max power actually
is. The reason the rpm is more important than the power is for gearing
decisions. Max HP - together with an estimate of frontal area (bike + rider)
and aerodynamical drag - gives an indication of the potential top speed
which, of course, is useful as a guide. But you have to tweak things to
actually get close to this.
It turned out that the engine developed
max power at 4700 rpm, so I based the gearing
table (.pdf) on this. Obviously the bike will go the fastest - if gearing
is optimal - at the max HP engine rpm. So, the way to go with this is to
first get the engine to pull 4700 rpm in top gear, and then adjust the
gearing in small steps. If the engine wants to rev more, higher gearing
should be tried. If it won't quite pull 4700 in top gear, lower gearing
until it does. As can be seen on page 6 of the table, speeds from 80 mph/129
Km/h to 124 mph/200 Km/h can be adjusted in steps of 1 or 2 mph with different
sprocket combinations. Bigger steps can be tried until things are closing
in. Sorry if this sounds complicated. It really isn't. The final goal is
clear, it may just take a bit of work to get there. The bike will go as
fast as it can with a gearing that allows it to pull peak power rpm in
Another benefit (apart from making it easier
to pull max rpm) of lower gearing is that the "gaps" between gears get
smaller with lower gearing, making the rpm drop at shift points smaller,
and making it easier to stay in the power band. This is particularly a
problem with a relatively low-power bike with a three speed gearbox. Revving
a little beyond 4700 rpm in second (maybe 5200 or a bit more) may help
land the engine near its max power rpm after the shift to top. Or at least
closer to this, the lower the overall gearing is. Looking forward to seeing
what gearing changes Chris decides to make today, and what the outcome
If you are looking at the gearing table,
Chris has front sprockets from 19T to 28T (so fields for smaller sprockets
in the table have grey text) and these rears: 34T, 35T, 36T, 39T and 42T.
The fields with grey background are for those sprocket combinations that
lie outside realistic limits. The green fields are for the target rpm of
4700. I hope it makes sense - and I hope I got the math right!
August 12 (evening)
On the second day of racing, Chris and the
741 ran 78.814 mph/126,81 Km/h, so speeds are starting to creep
upwards. "After doing a plug chop it looks like the jetting's sorted
as they're a nice light grey, but it wouldn't pull over 2,700rpm in top.
I'm not alone with this problem, but tomorrow I'm going to thrash its bollocks
off in first and second, and see if it'll hold the revs in top. It felt
shit-hot, pulled like a train until I hit top (third) but got a bit twitchy
as the side winds blew me to the left."
The starter officials who direct proceedings
at the start line, and everybody else working at SpeedWeek, are all SCTA
volunteers who are spending their holidays in the best way I can think
of. Today Chris' starter was Jill Iversen from California, who is
racing a 741 of her own, though not here this time. Jill holds the SCTA
record in the A-VF 350 class (F = fuel other than gasoline, 350 since her
engine is 500cc and gets the SCTA side valve discount on engine size, see
bottom of page for more on this) at 106.001 mph/170,56 Km/h and has gone
92 mph/148 Km/h on gasoline after 5 years of tweaking and tuning. More
about Jill's super neat 741 racer here.
I wonder if Chris told Jill that he is also from California
- albeit in Norfolk, England!
August 11 (evening)
Chris on the first day of racing: "The
rookie orientation took a couple of hours and we got our first glimpse
of the track while being taught start-line procedures for both the rider
and the support vehicle, then it was time to get leathered up. I would
be running on the "short course", one mile run up and another timed every
1/4 mile, then shut down and peel off to the right, and wait for Shaun
and Jim to collect me.
I was expecting severe nerves but for
some reason they stayed away, but my hands were shaking uncontrollably.
I have never worn full leathers and I have never worn a full face helmet.
Anyway, the old girl fired up first kick. The starter walks over to you,
snaps your visor down and points to infinity (and beyond).
My revised clutch worked a treat and
it fairly roared off the line, but just wouldn't pull full revs. I went
through the traps at 71.110 mph/114.42 Km/h which aint much until
you take into account we are 4500 feet above sea level
[actually the equivalent of 7500 ft or 2200
m when you factor in the temperature] and my engine is 70 years old.
Blasting up the track is hard to describe,
all you can see are the rows of 1/4 mile markers disappearing over the
horizon. During the run I felt no emotion, I just fixed my eyes between
the markers and listened to what the engine was telling me. After the run
I was out of breath and my heart rate had definately gone up, but boy,
what a buzz! We had a short drive back to the pits, a mere 12 miles/19
Km. The crowds had grown to thousands and spectators lined the whole run
After a plug chop I fitted a smaller
main jet, going from a 185 to a 165, and advanced the ignition. She is
running on 110 octane race fuel, and hopefully I will get her to pull more
revs, so it was 12 miles back to the pits, or a 24 mile drive for each
run. This time the bike was fitted with two cameras and the BBC had one
on the start line and another halfway down.
It pulled like a train off the line,
with a super-neat shift into second and a bit of a fluff into third, but
bear in mind this is only the second time I've ridden her [no real
testing opportunities in England, and at SW the racing vehicles can only
ride on the course, during official runs; no test riding allowed, unlike
at the BUB event at Bonneville later this month]. It was pulling well
to the first mile marker, but still wouldn't pull maximum revs, so tomorrow
I am going to start trying different sprockets and a smaller main jet.
Speed for second run was 72.322 mph/116,37 Km/h."
Chris has main jets for the Keihin CV carb
from 140 to 200 with him, as well as five rear sprockets and 10 fronts
- and a gearing table to show speeds compared to engine rpm with various
combinations of front/rear sprockets - so there is lots of adjustability
available; he test fitted the most likely sprocket combinations at home
and noted chain lengths for each.
If you wonder about the cameras etc, BBC is
doing a two-part documentary on the British racers, first part was the
preparations at home, and part 2 the actual racing at Bonneville. I think
it will be shown sometime in the fall, and there will probably later be
DVDs for sale.
Firing up first kick.
Infinity lies thataway...