Triumphrat

thebiglad · 11-20-2012, 02:42 AM

Quote:

Originally Posted by H3CT1C

Here's a question for the tuners... at what redline will be bike blow up?

As the sig says, I have:
* early '01 790 cams
* shim under bucket conversion
* double vlave springs
* +1.5mm oversize valves
also the following might play a part:
* inlet and exhaust ports have been smoothed and polished
* Wiseco 904

I raised the Procom's rev limiter to 9,000 and everything's been fine for a couple of years. (Yes, I regularly hit the redline.)

This year I made some 48mm headers (internal diameter is 45mm) - and now the bike still pulls quite well at 9k.

I'm quite tempted to raise the redline 100rpm at a time and stop when I feel a dropoff in power... but...

When can I expect everything to let go? 9,050 rpm or 10,000 rpm?

If the bike still pulls well at 9k I would say you are under-geared.

As it's so cheap to change a front sprocket why not try it? You obviously have more than enough power to pull at least 1 tooth bigger on the front sprocket.

H3CT1C · 11-20-2012, 04:15 PM

thebiglad - good point... Funnily enough one of the things I thought I'd do this winter was go to a 520 chain using sprockets from other bikes (the rear is the same as some GSXR or other, and I know there is a 17t front available in 520 pitch....

[edit]

Using AFAMs gearing calculator it would seem that 17/40 is closest to stock (fractionally taller) and that 17/39 is slightly longer still, but still lower than the popular highway gearing of 19/43....

Thanks for the tip!

thebiglad · 11-20-2012, 05:02 PM

Quote:

Originally Posted by H3CT1C

thebiglad - good point... Funnily enough one of the things I thought I'd do this winter was go to a 520 chain using sprockets for other bikes - the closest I'd got to the stock gearing of 18/43 (which I find to be the perfect match of top end and acceleration) was 17/45 - assuming 1 tooth at the front equates 3 at the back my proposed gearing (1 smaller at the front and two bigger at the back) would drop (slightly) overall... Maybe I should look to see if I can get 19/39(38?) (1 bigger, 4(5?) smaller) to increase the gearing slightly....

Thanks for the tip!

For the cost of a front sprocket (£10 off Ebay) I would go for a 19T on the front and see how the bike feels.

H3CT1C · 11-20-2012, 05:23 PM

Quote:

Originally Posted by thebiglad

For the cost of a front sprocket (£10 off Ebay) I would go for a 19T on the front and see how the bike feels.

I was wondering about that - but I have a 530 chain on at the moment and would kinda need to replace it anyway... But you're right... A 19t 530 sprocket would be a fairly cheap solution to test the gearing first before committing to a 17/39 and 520 chain!

thebiglad · 11-21-2012, 02:47 AM

Quote:

Originally Posted by H3CT1C

I was wondering about that - but I have a 530 chain on at the moment and would kinda need to replace it anyway... But you're right... A 19t 530 sprocket would be a fairly cheap solution to test the gearing first before committing to a 17/39 and 520 chain!

I'm not very clear about the differences between 520 and 530 chains, but I can tell you from personal experience that with the std chain set on my bike I changed to a 19T sprocket and there were no issues at all.

What I'm thinking is you could change the front sprocket just for a day to see if you like the difference in how the bike feels before investing big bucks?

H3CT1C · 11-21-2012, 10:07 AM

Yep.... This is kinda what I'd decided on...

B02S4 · 11-21-2012, 07:42 PM

This has morphed into a chain thread. I did a 520 chain 15/47 alloy sprocket conversion on my Speed Four. I personally wouldn't bother doing that type of chain conversion on a Bonnie-based street-going twin.

RickMcCl · 11-22-2012, 08:46 PM

Quote:

Originally Posted by mikeinva

they all should hold together to around 8500 for short burst.Above that things like stock valve springs and conecting rods can let go.But like phil said its no need to rev it passed where the hp is.Stock motors run out of hp way before 8500.Some a good ways below 8000.
To set one up to go 9000+ you better have everything right even the crank needs work.
with streetable cams you wont gain any thing in the 9000+ range anyway.

Mike:

Thanks so much; that clears things up a lot for me!

Happy Thanksgiving to you and yours,

Rick