Triumphrat

10-28-2005

Hello everyone, my first time posting..

I was wondering if anyone knows the bore limits for the 865 Speedy? Is it the same engine as the 790 just bored out a bit? If so then would it be correct to say that it could'nt go any futher than the big bore kit the 790 has, if I remember it takes it to 904cc?
I am very tempted by the 05 Speedy but I'm also a bit greedy.....would love to get around the 1100cc mark :-D

Pete_Twizz · 10-28-2005

When you ask about bore limits, are you asking what the stock barrels could be opened out to?

The limiting factor is often heat dissapation. As the bore is increased, the wall thickness is reduced. In some places there is plenty of metal around the bore while other places have less. Where the wall is already thin, it will become very thin with boring and will soon be unable to condust heat away to the fins and thicker areas, causing a hot spot.

If you are asking if an 1100cc big bore kit would be possible, then the short answer is yes.
The long answer, however, might tell you that the engine would become unusable, lacking any bottom end torque, unable to idle properly etc.

Don't take this as 'it can't be done', but beware of the philosophy that says if a bit more is good, lots more must be better.

Keep an eye on the bike press, and don't be suprised if Triumph come up with a bigger twin.

Pete.

iandel · 10-28-2005

If you want to make it bigger, you've got to stroke it. :wink:

WS · 10-28-2005

It would be nice if Triumph came out with a Bonneville look-a-like bike with 500 cc vertical twin and weighed around 300 pounds. A lot more nimble, a lot more fun.

Roadglide · 10-28-2005

You would have to bore it almost 1/2" to get to 1100.
I don't think there is 1/4" of cylinder wall to play with.
Either that or my calculations are wrong.

badrufus · 10-28-2005

I think the service manager at the Kingsport TN dealership is working on a big bore kit (greater than the current 904) with British Customs, for his Thruxton.

http://www.british-customs.com/store/home.php

asphyx9 · 10-28-2005

Southbay Triumph has a 994cc kit, but it does include new cylinders:

994cc Kit

MOBRIT · 10-28-2005

To WS:
Triumph did this, a long time ago. The 'Baby Bonnie' was the Daytona, a twin, 500cc. Don't know the weight, but I'll bet it was under 400 lbs.

Diego · 10-28-2005

I'm pretty sure WS knows this. The observation, "A lot more nimble, a lot more fun," is the answer to a question in another thread about why anyone would've wanted a 500cc like the Daytona when they could have had the 650cc Bonnie.

Bryan · 10-28-2005

You have to remember if you put bigger cylinders on the stock case's you would also have to bore the case's where the cylinders fit. Then you may have to worry about the studs having enough metal around them to hold the cylinders on. May not be worth it except for shot term use such as racing.