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Discussion Starter #1
Hi guys
I was looking at the cheap & crappy cast alum inlet manifold and decided to polish it - easy job - undid the clips to carb & manifold slipped carbs away, unbolted it & with a little W&D sanding (600/1000) and polishing it came up looking great - Job doen start to finish on about an hour.
Now I have a couple of questions for the experts out there - the inside of the inlet has 2 small ridges on the lower surface & I remember seeing a video (can't remember if it was a Motorne or Brit Iron video) where they ground these ridges down. My questions are:
a) what are these ridges for in the 1st place? I assume they are there for a reason - maybe for better mix of fuel/air?
b) by grinding them down and smoothing the inside what effect would that have?
Look forward to any replies!
Cheers
Steve
 

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Triton,
I ground them down. I might have believed that they were cunningly designed turbulence generators, if Triumph hadn't made such a thorough dog's breakfast of the rest of the inlet tract. I had porting mismatches in the head to manifold joint approaching 1/8"! I made a pair of locating studs by cutting the heads off a pair of M6 machine screws, so I could put the castings on and off easily, then ground the head and manifolds to match with a dremel. Smoothed the inlet tract as far into the head as I could reach. Then turned my attention to the rubber carb/manifold adapter, and found the rubber sticking way into the flow path over 1/2 the circumference. Sanded them fair with sanding drums in a dremel.
Now, lore and the literature all say you need "some" roughness in the inlet tract to generate turbulence, but I have yet in 40+ years seen anyone suggest "how much." I installed "Turbulators", don't remember the size, but they were slightly too large, and a hacksaw cut brought them in to size. I like the idea of getting symmetrical turbulence all around the circumference, and between the two carbs.

I haven't dynoed it, my butt says it made a difference, and I had to go up to a #145 set of jets.
(I have an '07 Thrux, same setup as yours.)
Anyhow, losing the ridges doesn't seem to have done any harm.
Redhawk
 

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Discussion Starter #3
Triton,
I ground them down. I might have believed that they were cunningly designed turbulence generators, if Triumph hadn't made such a thorough dog's breakfast of the rest of the inlet tract. I had porting mismatches in the head to manifold joint approaching 1/8"! I made a pair of locating studs by cutting the heads off a pair of M6 machine screws, so I could put the castings on and off easily, then ground the head and manifolds to match with a dremel. Smoothed the inlet tract as far into the head as I could reach. Then turned my attention to the rubber carb/manifold adapter, and found the rubber sticking way into the flow path over 1/2 the circumference. Sanded them fair with sanding drums in a dremel.
Now, lore and the literature all say you need "some" roughness in the inlet tract to generate turbulence, but I have yet in 40+ years seen anyone suggest "how much." I installed "Turbulators", don't remember the size, but they were slightly too large, and a hacksaw cut brought them in to size. I like the idea of getting symmetrical turbulence all around the circumference, and between the two carbs.

I haven't dynoed it, my butt says it made a difference, and I had to go up to a #145 set of jets.
(I have an '07 Thrux, same setup as yours.)
Anyhow, losing the ridges doesn't seem to have done any harm.
Redhawk
Nice job Redhawk - I like the "turbulators"!!
Thanks for the info - I did grind the ridges down but didn't go so far as to check any "into air" condition of either the manifold or rubber adaptor - DOH!:rolleyes: (Being an aero engineer, I just assumed they would match to begin with! I forgot my own mantra- Never assume anything!)
So since taking them off is a fairly quick thing I'll do just that and make sure both manifold & adaptor match the inlet.
Cheers
Steve
 

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Well, Triton, ya got me thinking, always a dangerous thing for a Past Commodore of the "Can't Leave Well-Enough alone" Club. I've been meaning to do something about that OEM rubber carb adapter. As I said, I sanded it to "pretty good," but it just bugged me. Whatever the air/fuel mix is doing after going under the slide and through the throttle butterfly, it sure as Hell ain't laminar. Kewel, we need some turbulence, but it also means no nice boundary layer for minor mismatches to hide in, and I don't know what the configuration of that rubber is when installed. Probably not the same as on the bench.
So, it being cold enough to liquify methane in NJ today, I turned a couple of alloy spacers to the ID and OD of the carbs and manifolds, 3/8" long. Slid them into some 1 3/4" ID cooling hose, and installed with the stock clamps. The carbs pulled up to the spacers with a "clunk", no play, and they look good in a mirror, standing on my head.

I, of course, worked from a formal engineering drawing, the key to success.
Redhawk
 

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Steve,

As fun as it may be to think that Triumph actually designed and incorporated vortex generator "ridges" into the stock manifolds, the sad truth is that they (the ridges) are a byproduct of the casting process/machining.

By all means, do polish the insides of the manifolds. Do you have the longer 790cc manifolds, or the shorter 865cc versions with the Phenolic spacers? A port match to the spacers would bring the biggest gains short of pulling the head and doing a proper port matching/polished job.

/Mike
 

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Discussion Starter #6
Steve,

As fun as it may be to think that Triumph actually designed and incorporated vortex generator "ridges" into the stock manifolds, the sad truth is that they (the ridges) are a byproduct of the casting process/machining.

By all means, do polish the insides of the manifolds. Do you have the longer 790cc manifolds, or the shorter 865cc versions with the Phenolic spacers? A port match to the spacers would bring the biggest gains short of pulling the head and doing a proper port matching/polished job.

/Mike
Hi Mike
I thought as much when I saw how crappy the surface finish of the casting was! I'm sure it was a Motorne.com video I saw where they blended them out (didn't understand the running commentary in French though!) - can't remember if they polished them after or not. Redhawk mentioned he thought leaving them slightly rough on the inside to generate some turbulence. BTW The outside looks fantastic polished - a 1000% improvement for very little effort.
Anyway if you match the port to the phenolic spacer I guess you have to match the spacer to the inlet manifold too! Oh well I guess that's on next weekends to do list!:)
Thanks all for the info! Wonder if there are any other experts out there with any further input? (maybe one or two of the triumph designers/engineers read these blogs?)
Cheers
Steve
 

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Discussion Starter #7
Excellent!

Well, Triton, ya got me thinking, always a dangerous thing for a Past Commodore of the "Can't Leave Well-Enough alone" Club. I've been meaning to do something about that OEM rubber carb adapter. As I said, I sanded it to "pretty good," but it just bugged me. Whatever the air/fuel mix is doing after going under the slide and through the throttle butterfly, it sure as Hell ain't laminar. Kewel, we need some turbulence, but it also means no nice boundary layer for minor mismatches to hide in, and I don't know what the configuration of that rubber is when installed. Probably not the same as on the bench.
So, it being cold enough to liquify methane in NJ today, I turned a couple of alloy spacers to the ID and OD of the carbs and manifolds, 3/8" long. Slid them into some 1 3/4" ID cooling hose, and installed with the stock clamps. The carbs pulled up to the spacers with a "clunk", no play, and they look good in a mirror, standing on my head.

I, of course, worked from a formal engineering drawing, the key to success.
Redhawk
I salute you:bow:
May I just say you have WAY too much time on your hands!!:D
Great job - like to see a photo with everything in place!
PS Like the Engineering Drawing - better than some I've seen at the very well known aircraft company I work at :D)
Cheers
Triton
 

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60to80 grit finish is all you need.Dont put anything extra in the intake there to small as they are ,same goes for the carbs there to small to.
 

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"May I just say you have WAY too much time on your hands!!"

Hey, I'm retired, got the motorcycle of my dreams, a heated shop, a lathe, and a day that never saw 30ºF. That combo gets to critical mass real quick.
Redhawk
PS; Once drew up some serious mods to a motor yacht design on an (unused) airline barf bag.
 

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Discussion Starter #10
"May I just say you have WAY too much time on your hands!!"

Hey, I'm retired, got the motorcycle of my dreams, a heated shop, a lathe, and a day that never saw 30ºF. That combo gets to critical mass real quick.
Redhawk
PS; Once drew up some serious mods to a motor yacht design on an (unused) airline barf bag.
Hey Redhawk - Good for you - I'm just WAY jealous!:)
 
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