BritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike Sponsor SteadfastCyclesBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorHepolite PistonsBritBike Sponsor
Upgrade to: Premium Membership | Gold Membership | Life Membership | Vendor Membership | Site Sponsor Membership
Welcome to BritBike Forum!
Member Spotlight
TriVin
TriVin
Warrington, Cheshire, UK
Posts: 154
Joined: May 2006
New BritBike book out!
ShoutChat
Comment Guidelines: Do post respectful and insightful comments. Don't flame, hate, spam.
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Previous Thread
Next Thread
Print Thread
Hop To
#817025 07/22/20 5:04 am
Joined: Oct 2008
Posts: 6,725
Likes: 77
DavidP Offline OP
Britbike forum member
OP Offline
Britbike forum member
Joined: Oct 2008
Posts: 6,725
Likes: 77
The Triumph uses short adapters to mount the carbs to the head, while BSA mounts them directly. Would there be any advantage gained by using those on a BSA?
I'm not using the stock air box, so this is not an issue.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Support Your #1 BritBike Forum!

Check out British motorcycles for sale: British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Joined: Aug 2001
Posts: 8,442
Likes: 44
Britbike forum member
Offline
Britbike forum member
Joined: Aug 2001
Posts: 8,442
Likes: 44
Longer intakes can improve performance.

Long rigid intakes between carbs and head can cause bad vibration effects in your carburettors.


Amateur Loctite enthusiast.
Joined: Aug 2015
Posts: 1,670
Likes: 19
A
Britbike forum member
Offline
Britbike forum member
A
Joined: Aug 2015
Posts: 1,670
Likes: 19
Originally Posted by triton thrasher
Longer intakes can improve performance.

Long rigid intakes between carbs and head can cause bad vibration effects in your carburettors.

Longer intakes can also adversely affect performance.
There are a couple of ways that inlet port length affects performance
1) Ram pipe effect, the port will have a column of mixture travelling at high speed when the inlet valve is open. when the valve closes this column keeps moving due to its inertia and causes a high pressure area of mixture behind the valve, when the valve opens this mixture is released into the cylinder. Unfortunately at lower RPM this column can stall and the longer the port the harder the engine has to suck to get it moving again.
2) Tuned length, the port length can be tuned the same way as an exhaust pipe to utilise the pressure waves created when the valve opens and closes
3) Friction, the longer a port the more of the mixture is in contact with the port wall. The friction between the port wall and the mixture slows down the charging of the cylinder.
An experiment to try, take a 100M length of say 5mm bore tube cut say 20mm off the end. Blow through the 20mm piece of tube, it's easy. Now blow through the 99.98M length, it will be rather difficult


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"
Joined: Aug 2001
Posts: 5,550
Likes: 84
Britbike forum member
Offline
Britbike forum member
Joined: Aug 2001
Posts: 5,550
Likes: 84
Beware of moving the carbs back from the head, fuel tap clearance becomes an issue, check this before committing. i rubber mounted mine, used a mikuni flange adapter bolted to the carb flange , fitted a spigot into the inlet port, rubber between, this solves heat issues and vibration, however running the fuel pipes gets difficult and unless supported the carbs soon droop on the rubbers leading to cracks and air leaks, I fixed that by using t140 carb to air box rubbers. The air boxes are a good thing, yeah. less restrictive than two individual pancake filters , and less gritty than no filters at all, keeps out water too, and have a decent volume to boot, IMO they are a performance aid.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Joined: Jan 2004
Posts: 4,738
Likes: 39
D
Britbike forum member
Offline
Britbike forum member
D
Joined: Jan 2004
Posts: 4,738
Likes: 39
Depends upon what you are trying to achieve.
To benefit from the acoustic wave the intake length should be:
L (in) - 88000 / RPM
Just adding length to a pipe does increase the boundary layer thickness and, yes, if you put a 100M long intake on it will restrict the flow quite a bit. But as Mark was demonstrating on his 65HP A65 post, port shape also matters. Sometimes you need to add length to fit in a good port shape.
The carbs are ideally rubber mounted on the O-ring in the flange so putting them out on a longer unsupported beam will increase the vibration amplitude.
Dr.Gordon Blair developed a computer program to predict the effects of engine parameters but you probably would not want to pay for the computer runs to see if you can get another HP or two out of these antique motors.
Or you can put the head on a flow bench and test various intake configurations.
Or put the motor on an engine dynamometer and test them that way.

Joined: Dec 2013
Posts: 5,613
Likes: 106
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 5,613
Likes: 106
ive experimented just a bit with intake length changes

[Linked Image from i.imgur.com]

^^^this on my not-a-BSA commuter bike. started and ran normally. it's a 5-inch extension that gives a total intake length of 4 inches (intake horn) + 5 inches (tube) + 2 inches (stub) + 2 inches (to valve) = 13 inches. look at the fuel taps. like gavin said, there's clearance issues, which is why i went with 5 inches.

it started and ran normally but i didn't test anything. i just wanted to see whether it would go. a twelve inch piece of tubing can be cut into 3, 4, and 5-inch sections for varying triumph intake tract length from 11, 12, and 13 inches. this is in the range of old panic's intake length predictions from his mathmatical model published in his victory series

i would have preferred to just make longer air horns but these carbs have a weird flange that requires custom mounts on the atmospheric side of the carb.


[Linked Image from i.imgur.com]

Originally Posted by Dick Page
I don't recall the specifics, but I do remember that the results had to be determined experimentally. Too many variables to predict mathematically. Nowadays a computer can probably do it if it is fed enough data.

^^^yes

on the machine i race now, i have the carbs set as close to the head as i can get them, just to try to hold that dimension constant while i mess with exhaust and valve timing. i firmly believe that machines like ours benefit significantly from acoustic tuning of both intake and exhaust systems, but i don't think you can get anywhere quicker with a mathematical prediction over simple cut and test.


I would rather be ashes than dust
Joined: Mar 2006
Posts: 1,669
Likes: 13
Britbike forum member
Offline
Britbike forum member
Joined: Mar 2006
Posts: 1,669
Likes: 13
Chrysler experimented with long tube intake manifolds in the early sixties wedge motors. The longest ones had the carbs mounted over the opposite fenders. Not sure of the physics but they generated more torque at lower rpm. The idea was to get heavy cars off the line quicker. On the more higher rpm motors like the drag race max wedge they went to a short ram.

Last edited by htown; 07/22/20 7:58 pm.

1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


Everything will be alright in the end. If its not alright, its not the end.
Joined: Aug 2001
Posts: 8,442
Likes: 44
Britbike forum member
Offline
Britbike forum member
Joined: Aug 2001
Posts: 8,442
Likes: 44
Originally Posted by Andy Higham
Longer intakes can also adversely affect performance.

Absolutely, or it might do nothing!


Amateur Loctite enthusiast.
DavidP #817098 07/22/20 10:57 pm
Joined: Jan 2014
Posts: 1,090
Likes: 65
N
Britbike forum member
Offline
Britbike forum member
N
Joined: Jan 2014
Posts: 1,090
Likes: 65
Tuning the length is a job for the dyno but Opel and Ford motors i've owned had variable
/split length inlet manifolds.
When racing we found a fair mid range boost from inlets around 12-14 inches. But only
by feel. Most modern motors seemed to mount carbs/inj very close as they rev far higher.

Joined: Oct 2008
Posts: 6,725
Likes: 77
DavidP Offline OP
Britbike forum member
OP Offline
Britbike forum member
Joined: Oct 2008
Posts: 6,725
Likes: 77
I've seen a few bikes with long intake tubes, including some flat trackers. I suppose they're going for more low-end grunt.
The Triumph adapters, part numbers 71-2811 and 12, are only about an inch long, with a slight bend to make the carbs sit level. Different head, different port geometry, don't know if they would have any effect at all.
Gavin, I've been through all that clearance crap with the Mikunis I had on this bike. Had to use 90 degree fuel taps and the fuel lines still went in odd directions. Those fuel taps are now on my T120 to feed the Mk2's.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
DavidP #817251 07/23/20 11:13 pm
Joined: Jul 2019
Posts: 157
Likes: 3
Britbike forum member
Offline
Britbike forum member
Joined: Jul 2019
Posts: 157
Likes: 3
I added spacers when cylinder heat was transferring to the carbs

2 members like this: Semper Gumby, Allan G

Moderated by  Allan G, Jon W. Whitley 

Link Copied to Clipboard
BritBike SponsorBritBike SponsorBritBike Sponsor
Upgrade to: Premium Membership | Gold Membership | Life Membership | Vendor Membership | Site Sponsor Membership
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, | DVD- Manuals & Parts books









Powered by UBB.threads™ PHP Forum Software 7.7.5