The Knowledge - Velocette Owners Club

B.7. Racing and High Performance -
L #35 The easiest way to get your Viper to go faster, is to fit a Venom barrel and head. Better yet,
a Thruxton barrel and head! I have a Viper clubman, and it won't do over about 90, with a fairly fresh
motor. But, I remember at Montlhery several Vipers, and in discussion with their owners, they all
claimed to get over 100mph out of them, with no great trickery. Any thoughts on this, fellows? P d'O
#54 Try shedding some pounds. This is easier to do to the bike than the rider. A 50 pound reduction in
stock bike weight should be close to trying to gain 5 hp on a Viper. I have a Venom based racer that is
down to 240 lbs with fuel and oil (non-stock frame). It makes a big difference A box of clean spark plugs
and a selection of sprockets will do wonders. Spend the time dialing in your carbs and ignition. Make
lots of high-speed runs and immediately take those plug readings. A crisp running engine can add an
easy 5 mph to the top end
L #36 I am taking up sprinting using a 1937 MSS running on methanol with an 1 3/16 inch 10TT9,
running on a standard M18/2 with standard followers. The clutch is to Thruxton spec. In my first year
my key objective is to be able to slow the beast down, as currently it has a rigid MAC 6 inch hub (frame
and forks are MSS/KSS). I seem to have been spending the last month converting a cast MAC/MSS 7
inch front hub to fit the webs. Turned up lots of 5/8 inch to ½ inch spacers (in titanium), and converting
a 5/8 inch diameter spindle to having ½ inch BS Cycle ends. Titanium is a funny metal; do you know
you can get it to ignite when you turn it? I have been researching the subject of speed. First thing is to
speak to all the fast Velo boys at the meetings; they are only too pleased to be of help. Secondly there
have been some excellent articles on tuning Velos in Fishtail and Fishtail West by Nick Vann, Dennis
Quinlan, Bill Melville, Marin Violette, Robert Gussman, peter Witman and Laurie Nunn. These appeared
in a reprint of the technical articles in Fishtail, by our American cousins.
#59 While you are busy tossing the weight off your frame, think about getting some serious weight off
your valve train. That will help you raise the rev limit. Velos breathe fairly well with the 17/8 cam.
Problem was they tangle valves just over 6200 rpm (Venom). Actually they seem to be pulling hard until
then which indicates that power is still being made. Lightening the valve train will allow the revs to
increase. There is a problem with this though, as the revs increase the stresses on the crankcases built
substantially. As such, at the same time you lighten the valve train think about using parallel roller main
bearings or machine a steel top hat reinforcement piece for the drive side main bearing if you stay with
the taper rollers. The drive side case is definitely a weak point. I run a 9.75 to 1 compression ratio,
Sommerton polydyne cam, and my rev limit is 7,500 rpm (self imposed). I have run it out to over 8,000
rpm (undergeared and I wasn’t going to let that Manx get past me on the long straight) and the bike is
still pulling hard. I wouldn’t try go to this level without extensive engine work. I have lots of mods,
titanium bits and extensively reinforced engine cases (and even they have cracked). Many bikes tend to
run out of breath as the revs increase. The Mac, for example, with its mild cam just tends to let you
know that there is no gain in wringing the throttle any more, time to shift.
L #64 I am a member of the local WA Historic racing Club and have a '38 Mac. I'm having trouble
with second gear, it broke and I am advised by those that know that this is a common problem and the
best way out is to replace it with a pre-war MSS box, or it will just continue to happen. Any thoughts? I
am having great difficulty in finding a replacement 2nd gear in Oz. The Mac has close ratio gearset
and close ratio sleeve gear, SW springs, triumph front wheel, and runs on Methanol. The barrel has
had the cast iron fins removed and replaced with shrunk-fit alloy roundies for better heat dispersion. I
was using Castrol "R" but due to the difficulty in obtaining it and the high cost, am flushing out the
system and replacing it with a 50w oil, any suggestions on what to use given that it does not get very
cold over here and we do a maximum of about 6 laps per race, three races a day plus 2 practice
sessions. 4 others from our local Velo club are also racing this year having built up pre-war 350's to
come and play! We are trying to encourage other pre-war machines as this class is just me at present,
so I'm looking forward to solving a few minor niggles before the season starts.
#65 I have checked the spares lists of the major suppliers in the UK and no one has this gear available
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