SB pipe setup for OS XM

[Aldana]

:unsure: Hello to all tunnels boaters this time I would ask them about this modification, I have a .21 XM stock OB and i have a SilverBullet HP with HTB header for this engine, I think the header should be cut off somewhere to fit correctly and take a good starting point to prove and test my engine.

I appreciate your suggestions

see the pics of it and sorry my bad english

From very far away

Cristian

 

[Jerry Wyss]

well, with the 160* exhaust port timing of a stock XM sleeve you couldn't get the pipe length short enough

with the stuff you have there to get much high rpm operation. It will work fairly well as short as you can get it,

leave a 1/2inch of straight header section and cut the silicone coupler so you have a approx 1 inch and zip tie

it together. Be sure and connect your "stay" wire to something on the O/B,, one of the engine mounting lug holes

using two model airplane wheel collars.

 

[Aldana]

well, with the 160* exhaust port timing of a stock XM sleeve you couldn't get the pipe length short enoughwith the stuff you have there to get much high rpm operation. It will work fairly well as short as you can get it,

leave a 1/2inch of straight header section and cut the silicone coupler so you have a approx 1 inch and zip tie

it together. Be sure and connect your "stay" wire to something on the O/B,, one of the engine mounting lug holes

using two model airplane wheel collars.

Hi Jerry thanks a lot for your suggestion. I want asking you some tips for my TT OB engines, i have a old TT.OB (Blue Box) and red box early edition, I understand that you know about this ob aa lot, please let me know what setup can you sugest me to obtain a better performance in stock and mod form.. like glow plug, prop, height, carburator, pipe?.

 

[Jerry Wyss]

well, with the 160* exhaust port timing of a stock XM sleeve you couldn't get the pipe length short enoughwith the stuff you have there to get much high rpm operation. It will work fairly well as short as you can get it,

leave a 1/2inch of straight header section and cut the silicone coupler so you have a approx 1 inch and zip tie

it together. Be sure and connect your "stay" wire to something on the O/B,, one of the engine mounting lug holes

using two model airplane wheel collars.

Hi Jerry thanks a lot for your suggestion. I want asking you some tips for my TT OB engines, i have a old TT.OB (Blue Box) and red box early edition, I understand that you know about this ob aa lot, please let me know what setup can you sugest me to obtain a better performance in stock and mod form.. like glow plug, prop, height, carburator, pipe?.

Howdy, The TT will run similar to the performance of the XM with just the addition of a pipe. The TT is much more

difficult to get a pipe on it,, the muffler cut-out and relief for the header cup can be troublesome for some people.

The TT has a slight advantage with the geardrive, they like to turn the Octura X637 and X640 prop. I used the X640

most of the time with just the pipe mod and even could turn a X642 running the far outside lane, try that with the XM,nada.

Prop height was normally "bottom of the propshaft bulge" as high as 1/8" above the rear sponson bottoms and a little

less. Angle the motor (slightly "kicked out") to keep the bow of the boat up and weight accordingly.

I used the K&B plugs mostly, 1L and HP, depending on nitro content,, almost any will work for sport use, except "idle bar"

plugs will drop performance dramatically.

Stock carbs will work ok as long as the needles are straight,, have found brand new needles in some carbs were bent.

I use the XM carb on all my mod TT's,, but they have to be turned down on a lathe to have the "carb neck" fit in the TT

"case carb throat". I believe the older TT had a 13.5mm case throat for the carb and the newer is 14mm,, but most important

the carb has to make a GOOD seal in the case throat.

Personally, I've never came even Close! to 40mph with the stock TT muffler in place. There was a guy from Panama (I think

it was) that I cut down a stock TT headbutton, and he got some good performance with that and by pinching down the water

flow at the water exiting the head. Cutting down the water flow is a key method,, it allows the use of more fuel thru the needle.

JW

 

[Aldana]

Great tips ,...now we are organitating a small race here in midle of June and with it sugestion i help a fella with his TT, for me i test my OS with this SB pipe setup, later i´ll make this tips on my TT´s and let you know the results, thanks a lot Jerry

 

[Jerry Wyss]

Another thing, the TT with it's .010" aluminum shim in the head will give you .023" headspace, they have been consistant with this headspace from the begining. Removing that shim will of course give you .013" headspace and would be a good move for any content of nitro down to 30%,, I have not tested 20% or below with that shim out.

This was one of the mods that I had ("Javier" from Panama) do along with the other mods listed in my earlier post. All those mods suggested were done with the stock muffler in place,, but will also be fine with a pipe on the TT.

The XM has a pretty good button "bubble" construction, with a .008" brass shim. For low nitro, I would leave that shim in there and would remove it using 45% and up,, but I would watch my plugs closely using 45%.

JW

This is the best pic's of the TT muffler cut-out that I have