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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 12-16-2008, 11:56 AM   #21 (permalink)
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I wouldn't take the Jenks chart as gospel. In my experience the main influences much more, as does the needle height.
IMO Mike is right on target.
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Old 12-16-2008, 11:59 AM   #22 (permalink)
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Quote:
Originally Posted by Ventura View Post
The reason I mentioned Pilots was that I recently fitted 42's to my bike.
With the aid of the A/F gauge I have, I can see the effect real-time while I ride.

The only area where they make any substantial difference is at lower speeds as you start accelerating thro the lower gears
i.e. during around town riding, as revs start to increase, but at lower throttle position.
They made the difference between being at about 13.5:1 (with the 40's) to being much richer at 12:1 (with the 42's) under these conditions.
They obviously also effect the idling mixture, but that can be adjusted out with the screws.
They have NO effect, as you would imagine, at higher speeds, revs and throttle positions.

I'd be a little wary of quoting that graph as the absolute answer to our carb set-ups.
Its an excellent guide, dont get me wrong, but in the experiences Ive had it doesnt show with whole accuracy the range of
effect of main jet, pilot jet or idle screw has.

V.
+1 that guide is wrong more then right what works on 1 motor might not work on another anyway.a/f meter or a dyno with one is the only way to know whats right.
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Old 12-16-2008, 12:26 PM   #23 (permalink)
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Quote:
Originally Posted by sito View Post
My results from Saturday. This is a stock engine Thrux, with airbox delete and dominator sports with no crosspipe on the headers:

1st set of 3 runs:
Mains: 145
Pilot: 42
Shim: 1

2d set of 3 runs:
Mains: 150
Pilot: 42
Shim: 0 (see the severe rich condition at low rpms and how this improved by about 1/3d when I removed the shim?)

3d set of 3 runs
Mains: 145
Pilot: 42
Shim: 0

Ten and I are thinking that I need to find a longer needle. I noticed that Dynojet has an adjustable needle which would seem to be ideal.

Input from the nut gallery?

Thanks...Jack
No crossover on the exhaust? What aftermarket header pipes are you using? A lot of dynos on your configuration have shown low 60 to 65 Hp. The unknown, is the crossover your configuratiuon lacks and I think they had (the other dyno's from similar configurations).
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Old 12-16-2008, 01:10 PM   #24 (permalink)
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Originally Posted by SHILOH View Post
No crossover on the exhaust? What aftermarket header pipes are you using? A lot of dynos on your configuration have shown low 60 to 65 Hp. The unknown, is the crossover your configuratiuon lacks and I think they had (the other dyno's from similar configurations).
His dyno numbers (atlest the one i can see have a 1.0 c/f alot of the ones you see that are above 60 hp have much higher c/f factors .His is a more honest c/f factor and more real world numbers .He is below the average but only like 2 to 4 hp.There are a few of these motors that have made honest hp over mid 60s but very few.most run 57 to 62 hp at wheel. that is with the mods he has.
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Old 12-16-2008, 02:52 PM   #25 (permalink)
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Originally Posted by SHILOH View Post
No crossover on the exhaust? What aftermarket header pipes are you using? A lot of dynos on your configuration have shown low 60 to 65 Hp. The unknown, is the crossover your configuratiuon lacks and I think they had (the other dyno's from similar configurations).
I'm using stock headers with the crossover removed--bought the bike with an airleak at the weld and just decided to nuke it all together.
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Old 12-16-2008, 03:44 PM   #26 (permalink)
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Quote:
Originally Posted by sito View Post
My results from Saturday. This is a stock engine Thrux, with airbox delete and dominator sports with no crosspipe on the headers:

1st set of 3 runs:
Mains: 145
Pilot: 42
Shim: 1

2d set of 3 runs:
Mains: 150
Pilot: 42
Shim: 0 (see the severe rich condition at low rpms and how this improved by about 1/3d when I removed the shim?)

3d set of 3 runs
Mains: 145
Pilot: 42
Shim: 0

Ten and I are thinking that I need to find a longer needle. I noticed that Dynojet has an adjustable needle which would seem to be ideal.

Input from the nut gallery?

Thanks...Jack

Hello Jack;
Your bike are suppose to have 62 RWHP at sea level with the Power Pack that you have.
The main reason for your low numbers are the lack of crossover in your headers.
Try to install a set of stock Thruxton headers and pull another dyno run.
I had the same problem few years ago.
With your same set up, no crossover my bike barely make 53 RWHP, swapped for OEM THruxton headers and voila a big increase in HP.
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Old 12-16-2008, 04:42 PM   #27 (permalink)
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Quote:
Originally Posted by TPUSA View Post
Hello Jack;
Your bike are suppose to have 62 RWHP at sea level with the Power Pack that you have.
The main reason for your low numbers are the lack of crossover in your headers.
Try to install a set of stock Thruxton headers and pull another dyno run.
I had the same problem few years ago.
With your same set up, no crossover my bike barely make 53 RWHP, swapped for OEM THruxton headers and voila a big increase in HP.
Ah ha!! thanks for the tip--I'll get on it asap.

Jack
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Old 12-16-2008, 05:09 PM   #28 (permalink)
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2 into 1 into 2?

Quote:
Originally Posted by TPUSA View Post
Hello Jack;
Your bike are suppose to have 62 RWHP at sea level with the Power Pack that you have.
The main reason for your low numbers are the lack of crossover in your headers.
Try to install a set of stock Thruxton headers and pull another dyno run.
I had the same problem few years ago.
With your same set up, no crossover my bike barely make 53 RWHP, swapped for OEM THruxton headers and voila a big increase in HP.
Verry interesting thread guys!.. I always suspected the crossover pipe was just there to split the flow between the two mufflers for EPA noise control. But it probably reduces overall backpressure during high rpm operation(i.e., full throttle max HP)

I see that D&D publishes a Dyno chart showing their 2 into one header vs. a stock Thruxton (see below)

They are showing 63 hp as a baseline for their jetted bike, and 72 hp with their 2 into 1 header. If it's true, then the scavenging effect (#1 cylinder pulse creating a suction in the collector as it passes thru just in time to pull the gas from cylinder #2) has a huge effect on power! The OEM balance pipe helps some over 'TT-style' individual head pipes, by reducing exhaust backpressure...no real scavenging like a 2 into one.

I would like to see someone make a more traditional 2 into 1 into two header for the Thruxton that you could mount stock or aftermarket pipes to. I just like the 'traditional' look of two tapered reverse cone pipes. Twin mufflers also help to keep the sound level low without resorting to a giant single canister like the Zard. I made up a quickie drawing of my concept in AutoCad just to get my idea across, and it's posted below:



I did a quick search and didn't see anything like it as being available for the Thruxton. Has anyone seen such an animal? I would be willing to build one to try, although it would probably eliminate my center-stand. I would also make it a 'big-tube' header...1.75" (45mm) pipes to flow some real gas.

Any comments?
Cheers,
BLIGHT:
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Old 12-16-2008, 05:46 PM   #29 (permalink)
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Quote:
Originally Posted by blight View Post
Verry interesting thread guys!.. I always suspected the crossover pipe was just there to split the flow between the two mufflers for EPA noise control. But it probably reduces overall backpressure during high rpm operation(i.e., full throttle max HP)

I see that D&D publishes a Dyno chart showing their 2 into one header vs. a stock Thruxton (see below)

They are showing 63 hp as a baseline for their jetted bike, and 72 hp with their 2 into 1 header. If it's true, then the scavenging effect (#1 cylinder pulse creating a suction in the collector as it passes thru just in time to pull the gas from cylinder #2) has a huge effect on power! The OEM balance pipe helps some over 'TT-style' individual head pipes, by reducing exhaust backpressure...no real scavenging like a 2 into one.

I would like to see someone make a more traditional 2 into 1 into two header for the Thruxton that you could mount stock or aftermarket pipes to. I just like the 'traditional' look of two tapered reverse cone pipes. Twin mufflers also help to keep the sound level low without resorting to a giant single canister like the Zard. I made up a quickie drawing of my concept in AutoCad just to get my idea across, and it's posted below:



I did a quick search and didn't see anything like it as being available for the Thruxton. Has anyone seen such an animal? I would be willing to build one to try, although it would probably eliminate my center-stand. I would also make it a 'big-tube' header...1.75" (45mm) pipes to flow some real gas.

Any comments?
Cheers,
BLIGHT:
Well, you have a motivated buyer here, if you'd like me to somehow commission the build. i would certainly be able to provide the "after' dyno run with consistent variables. Finding used headers is going to be a bit*h.

jack
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Old 12-16-2008, 06:39 PM   #30 (permalink)
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yea Thruxton headers new are high if you cant find some used you would be better off going to D&D 2INTO 1 and selling your new mufflers you have.You need Thruxton headers they are better then bonnie headers because of there shape.I have a set of bonnie headers i will sell but dont think they would help you much.Maybe you could try some of the bike junk yards.
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