Boring out a 675 ?

[Petie]

I have heard rumors of the 675cc bieng able to be bored to a 900cc. Is this true? Any help would be apreciated along with new specs.

Petie

[Jamie]

Could it be that a 1050cc Speed Triple is what you are actually looking for ?

[Petie]

No it is not The weight to power ratio would be great and I just heard that you could do it and I was doubting the fact that you could.

[Jamie]

You, Petie, seem to rationalize a larger bore and thus a larger eventual displacement as something which in and by itself would bring advantages in terms of sheer performance, don't you?

Whether the Streety cylinder walls are thick enough (which I doubt) to sustain such an enlargement, the rest of the bike, i.e. its tranny, its radiator cooling capacity, its chassis, its brakes, etc. would be challenged accordingly. So reinforcements aka WEIGHT would inevitably end up having to be added to the bike to make it COPE with said extra displacement and the extra torque and/or power (arguably) accruing from the latter.

Or is either one of us (or both?) missing something? Jamie

[doggy675]

It might be able to go out to 750cc which would be cool

[Petie]

Jamie I totaly agree with everything you have stated and doubt that the stock parts of the bike would be able to back up and handle the power increase. And I thought the same thing along with the walls being to thin that is a very large jump in cc's.
And my intesion with the first post was seeing if someone acctually did it and if it handled it or if my source was talking out of his ***?

[Old Scratcher]

Having just spent a small fortune increasing the size of my Scrambler by 39cc's. I can tell you that if it is possible, it wouldn't be cheap. & I wouldn't be surprised if it was cheaper to trade up to a Speed3.

[Diego]

Petie, I see you also asked this question on the Daytona 675 forum, which really is a more logical place. There are more guys there with a lot more 675 experience than most of us in this forum have, and I see none of them thus far have heard of such a thing being done either.

(I also notice you titled your post there "Boring a 675?" I personally would have written it "Boring? A 675? Are you kidding me?" )

Old Scratcher has analyzed the situation well. The costs would hardly justify the return. If somebody is merely after numbers for their own sake, that may not matter to them. But if results are what count, it would be significantly cheaper to bring the Street's engine up to the performance of the Daytona's by other means, and let it go at that.

And if you wanted to exceed the Daytona's performance, boring the engine out so drastically would still yield minimal results. Apart from reliability concerns arising from the thinness of the walls (if a 15% larger diameter can be accomodated at all), bear in mind that piston speeds at redline are already considered quite high for the geometry of this engine. They lowered redline a bit for the Street because of that, in fact. If you change the geometry further through a radically larger bore, you will have a heavier piston at the end of each conn rod; fully one-third heavier, all other things being equal. Hence, you would also have to reduce redline more, surrendering much of the horsepower gain you might otherwise achieve. The valve diameters and placement would no longer be anywhere near optimum for best combustion, either, and I suspect that would steal whatever little improvement might remain.

All in all, I have to think such a project would be a sad waste of resources.

[Shakey]

I would think that lightening the bike even further and having a tuner have a go at the factory mapping would probably be far less expensive and yield better overall results without compromising reliability. Triumph may eventually build a 750cc along the same lines as the Street and Speed as the competition begins to catch up. I'm certain the tranny and lower end of the Street would support a 750 top end. Triumph has been pretty good about building their platforms in such a manner that they can be expanded upon without much trouble. Look at the parallel twins. The Bonneville went from 790cc to 865cc on the same basic engine/transmission design just by modifying the jugs, cams and fuel systems. As for me, I plan on enjoying the engine just as it is until someone makes a slip on exhaust that really bumps the HP, or an aftermarket ECU that'll be an improvement over the stock module, which is actually pretty darned good right out of the box.

[Thirdway]

You might be interested to learn that according to the tuning specialists working on the same bikes as Maxton for the IOM TT find that the 675 (in Daytona form) is one of the easiest bikes to extract power from. Most other 600s need huge amounts spending on them to gain any increases.

The downside will obviously be power band and longevity.