Author Topic: TRIUMPH T20 CUB - MODIFIED  (Read 58742 times)

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Offline fordboy628

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #60 on: August 18, 2015, 07:58:09 AM »
Scrambler,

What is the exact displacement of your Honda engine?

Just a SWAG on my part:

@ 76.2 rw bhp, (from your PhotoBucket pic), guessing 780cc's (?!?) equals 97.7bhp/liter, not too shabby for air cooled at the rear wheel.

Where does the written 98 crank bhp number come from?

In my world, 76.2bhp x 15% drive train loss (at the most) = 87.6bhp or 112.3bhp/L, pretty good.

98 crank bhp requires a drive train loss % of 28.6%, seems kinda high to me.

JMHO, though.    Punch in your exact displacement and re-calculate these numbers to be precise . . . . . . . .

Also:  Your a/f ratio needs to be lower between 4000 & 5600 rpm to tune out that "dip" in the power curve.    Unfamiliar with those carbs, but it looks like a needle change is in order . . . . . .   or at least "alteration" of the existing needles . . . . . . .    Are your carbs perfectly synchronized?   That can play he** with a/f.

 :cheers:
Fordboy
« Last Edit: August 18, 2015, 08:10:34 AM by fordboy628 »
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Offline Old Scrambler

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #61 on: August 18, 2015, 11:48:57 AM »
Original motor was 736cc...........1mm overbore = 762cc

The 98 was a guess by the dyno tech........from a H.D. shop

We had 50-psi in the tire and noted significant slippage and peeled rubber on the dyno........the tire was quite hot :-o

The tech was short-shifting...........I have no intention of letting the rpms drop below 7500 when changing gears on the salt :-D

The 34mm carbs feed 33mm ported intakes and ported head/trimmed guides. We may have a case of 'big-carb-itis' causing a loss of flow across the needle-jet when shifting gears. Our thoughts were to grab as much of the available air as possible to get enhanced chamber-filling/pressure. 31mm Exhaust valves lead to polished exhaust ports and a 4-1 header. The dyno-test showed improvement after removing a straight-pipe from the header. We have since added a reverse-cone megaphone......no baffles. We also gained HP when the air-filter was removed.........and significant (5-HP) when the timing was advanced several degrees from stock.   

We will continue to play with a ram-air design and we are always open to critique and HELP :-D :-D :-D
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre

Offline Rex Schimmer

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #62 on: August 18, 2015, 02:25:02 PM »
Scrambler said:
"
.......and significant (5-HP) when the timing was advanced several degrees from stock. "

This is a pretty common occurrence with hemi style combustion chambers. The large "chunk" of piston that it required to get some compression interferes with getting the incoming mixture to swirl and reduces the combustion process efficiency which then requires additional ignition lead to compensate. Also the extra piston area and material adsorbs heat which reduces engine power. I also notice that with your head/bore set up there doesn't appear to be a squish area which can also assist in combustion efficiency. Still pretty impressive for an early Honda 4 cylinder engine.

Ram air is not something that can be measured on a dyno and as Tom's experience has shown what may "look" like it should work can sometimes be a step backward. I call this OIA, optically intuitive aerodynamics, i.e. "if it looks good it will be good"! The basics of ram air is that you need to take the high velocity incoming air and slow it down which increases the pressure and will provides air at an the increased pressure to the engine. This requires an inlet that starts small and then increases in cross section at a gradual rate until the air velocity is reduced sufficiently to provide increased air pressure. Not an easy task on a bike like yours but something that could probably be done.

Great project and good engineering! Keep us up to date on your progress.

Rex    

Rex

Not much matters and the rest doesn't matter at all.

Offline wobblywalrus

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #63 on: August 18, 2015, 09:36:57 PM »
Ram air was something I monkeyed around with in the 1970's.  A main jet sized for running into a cool headwind was a lot different than the one needed for a warm tailwind.  Sidewinds had their own bizarre effects.  It was impossible for me to make use of the concept in the varied environments encountered on race days. 

Offline Old Scrambler

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #64 on: August 19, 2015, 12:05:41 PM »
Thanks, Rex.............all helpful info.............I have extensive research into the air-intake designs on modern bikes.............and will continue to work on stabilizing the air in a box before it goes to the carbs.........I have the advice of an air-flow engineer that round tubes and intakes have significant drag, while rectangular or square tubes and intakes only have drag at the corners. 

I have a plan for a big-bore that should have significant squish-band. I take particular note from the positive comments because I wanted to try to exceed what numerous other builders have done to these motors in the 750cc level of competition.

Bo............I am told by everybody's best friend GOOGLE that ram air becomes modestly effective at 100-mph and SIGNIFICANTLY effective above 150-mph. 
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre

Offline panic

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #65 on: August 19, 2015, 05:41:20 PM »
Excellent work, best of luck!

Based on your photo, I'm not sure your side positioned air intakes are "visible" outboard of the slipstream from the chassis ahead of it. I'm guessing that (as seen from above) they are inboard of some component shapes in both directions.
All fluid transfer depends on pressure differential - high to low, nothing else. If they're not in a high pressure area (relative to the box interior) you have nothing except engine vacuum. You may need an entry device far away from the box (and suitably ducted).
Have you done any yarn or smoke tests?

Offline Old Scrambler

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #66 on: August 20, 2015, 03:14:29 PM »
Panic...........thanks for taking an interest :-) :-)

The bottom of the box has a rear-facing intake about 3/4-inch tall by 3-inches wide. Its design was different from all other CB750 models and helped to move the red-line on the standard F2 and F3 models from 8000 to 8500 rpms. The outer 'add-on' ducts are indeed slightly in-board of the outer edge of the motor block. I have shaved the head fins to match the block. My knees are pressed against the rear edges of the airbox and feel quite a bit of air-pressure when over 100-mph.........that could disappear when at higher speeds. The effort was only to catch 'some' additional air but not to expect any ram-air affect.

Last year we had two 1-inch hoses, one on each side of the neck, with flared 'bell' intakes, leading along the frame (wide tank tunnel) and then formed into a wide-radius 180-degree bend and stuffed into the bottom intake. We had a new K&N filter in the box. It seemed to work but when I shifted from 3rd to 4th at 9,500 rpms (about 113 mph) the motor bogged and would not recover. I backed off on the throttle and saw no improvement.  We changed jets and made one more run with even worse results.  On the subsequent dyno run (no hoses) the motor struggled at 9000 rpm and showed rich on the A/F.............we removed the bottom of the box and filter and showed immediate improvement with the motor running clean and clear into the mid-10,000s.............then we moved the timing a few times until we found the sweet-spot and the motor ran crisp, clean and QUICKLY up to 11,300 rpms.   
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre

Offline tauruck

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #67 on: August 20, 2015, 11:07:05 PM »
I built an air box for my Sportster bobber but as the bike wasn't a runner at the time we tested it on my buddy's bike.

He's a qualified HD mechanic, did all the courses etc. but is also a Chevy Big Block nut case.
He went up three sizes on the jets because the Dyna motor breathed too well with my contraption.

I'll shoot some pics and post them later.

Offline tauruck

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #68 on: August 21, 2015, 10:17:25 AM »
Here's the box sans the three metal rings that fit in the opening.

Offline tauruck

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #69 on: August 21, 2015, 10:21:59 AM »
I know it looks like something you might see on a Top Fuel or Funny car motor but it works.
No restrictive HD filter.
I used a breather fabric that we used on the Mazda Rotary race motors sandwiched between a metal mesh thing I thought up.

Offline Old Scrambler

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #70 on: August 21, 2015, 09:06:45 PM »
T. Thanks for the comment..............and pics..........Was the intake facing forward?  How did it perform on the street...........or wherever it ran?
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre

Offline tauruck

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #71 on: August 21, 2015, 09:20:14 PM »
Facing forward and ran on the road.
This thing works but it was on a Harley.

I guess it might get clogged up on the salt but it was way better than the OEM HD "air box".
Each inlet is 38mm.

Offline wobblywalrus

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #72 on: August 22, 2015, 01:11:00 AM »
Dennis, the air horn should have rounded rather than a sharp edge, and it should be a harmonic distance from the intake valve seat at the peak torque rpm.   The butterfly or inside face of the carb slide is reflective.  It should be at a half harmonic from the intake valve face at the rpm when you want grunt at partial throttle.  The air going into the bellmouth should be as cool, calm, and clean as practical.  A proper air box will help.  It can hold the filter and have an intake where the air is cool.  Also, by virtue if it being a box, the air inside is calmer than on the outside, and this helps.   

Offline Peter Jack

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #73 on: August 22, 2015, 01:15:55 AM »
Do you have a picture of the underside Mike?

Another nice piece of work by the way!  :cheers: :cheers: :cheers:

Pete
« Last Edit: August 22, 2015, 01:18:13 AM by Peter Jack »

Offline Old Scrambler

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Re: TRIUMPH T20 CUB - MODIFIED
« Reply #74 on: August 22, 2015, 12:21:18 PM »
The custom-design Sportster intake is indeed very COOL.......LOOKING. It allows the carb to breath.............but it may be more of an 'anchor' than a helper on the salt at 'high-speed'.

Bo...........all good info...........but I don't plan on having any 'slide-obstruction' when at WFO :-D  The dyno tells me the box with air-cleaner was very restrictive. The attempts on the salt-runs indicated rich conditions and that gear-change transitions need to be at higher RPMS in the upper gears.............maybe I need a closer-ratio set of gears or a six-speed :|

Three of us went to a Steam & Tractor Show yesterday............found a genuine JAGUAR wrench and took a few pics of a 100-HP Steam-Tractor rolling through the power parade and later operating a saw-mill. 
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre