750 - Cam Choice

Haggis

Haggis

Hero member
Location
UK
Hi All

After my Breganze-bound breakdown, I clearly have to attend to the cams.

The bike is an SF (zero). It has GTL cams fitted at the moment.

I like torque but also ride sportily and like to extend into the rev range. I enjoyed the characteristics before it blew up, but would have liked a bit more 'top' at speed.

Any 750 gurus have info / opinions on cams and how they differ in terms of riding experience?

Thanks in advance.

Paul
 
It depends a bit what sort of pistons you have in there as well.
Small valve head cams may be hard to source. The S had an 8 if I remember rightly. Works well.

What ever people tell you, keep away from SFC cams.

An SF2/3 cam is probably suited, low down grunt and will keep going at higher revs.  Therefore a 7/1.
Don't know how they work on a small valve head though.

Paul
 
Hi Paul h - I've often used 5/C or 6/C cams in the SF's -  amongst intelligent stuff there's quite a lot of bol---ks talked about lack of low end power etc - but haven't done one with the 30mm VHB's - have swapped VHB's for 32mm PHF's on triple type inlet stubs - bike went really well. Best (IMHO) is a 6/c cam with less radius on rockers - my own bike pulls from 2500rpm to 8000+. These cams need  uprated valve springs (got them in stock ATM) - have got a spare set of 5/C's too i think. upping valve sizes will help too and keith's got some nice forged pistons as well!
      Of course the actual performance will depend on how near you have the correct timing - usually all over the place on the twins! - regards - Phil
 
Thank you Paul. And special thanks for offering to post gaskets, very thoughtful and kind.

The pistons are standard SF zero. I am not aware of any changes there.

Are there any clues externally of the head being big or small valves?

P
 
phil37 said:
Hi Paul h - I've often used 5/C or 6/C cams in the SF's -  amongst intelligent stuff there's quite a lot of bol---ks talked about lack of low end power etc - but haven't done one with the 30mm VHB's - have swapped VHB's for 32mm PHF's on triple type inlet stubs - bike went really well. Best (IMHO) is a 6/c cam with less radius on rockers - my own bike pulls from 2500rpm to 8000+. These cams need  uprated valve springs (got them in stock ATM) - have got a spare set of 5/C's too i think. upping valve sizes will help too and keith's got some nice forged pistons as well!
      Of course the actual performance will depend on how near you have the correct timing - usually all over the place on the twins! - regards - Phil
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Hi Phil,

5C is very good combining low down torque and endless revs. I find the 6C less "full" at midrange.
And you're right to mention the need for different valve springs to accomodate the increased lift. It all depends on how much work Paul H. wants to put into the bike.
Way off a simple change of cam.

All the best
Paul
 
Paul H said:
Thank you Paul. And special thanks for offering to post gaskets, very thoughtful and kind.

The pistons are standard SF zero. I am not aware of any changes there.

Are there any clues externally of the head being big or small valves?

P
Click to expand...

Hi Paul,

Pistons will be high comp already then.

If your machine is running 30 mm carbs, it should be a small valve job.

Paul
 
If you use 5C or 6C you have to fit a tuned exhaust system or it will go slower. With either of those it definitely pays to make sure you have at least 9.5 to 1 compression and as Phil said get the cam timing correct. The 7/1 that Paul mentioned is a great all round cam but as said how it works with small valves is anyones guess. Big valve heads seem to pop up for sale from time to time and Wolfgang has definitely got them available. Then you can look a bigger carbs and on and on. As you felt pretty happy with how it went it may be enough to just fit a better exhaust and get the standard motor set up well with correct compression, squish, cam timing etc. As built all of these tended to be quite a long way off spec and can transform a bike.
I have a 6C in my race bike with 10.5 compression and everything else set up to suit, and it pulls really hard from 4000 and is really only happy pulling hard, I wouldn`t want it?s characteristics in a normal road bike.
 
Keep it simple and don"t f===k about with it. :P Enjoy it for what it is ,not what you think it should be ,IMHO. ;)
 
4S is also my favourite for the small-valve head, 7/1 for the big-valver for road use.  Both great all-rounders.

For me, the twins aren't really about top speed, more about mid-range grunt and accellerating out of corners.  But that's just me, and wtf do I know... ::)

piet
 
I'm all over SFCPiet on this one for a 750SF.

The last thing you need is a long duration SFC cam (Irregardless of Valve size or Static Compression) for a Sport Riding Breganzie SF.

For me, the twins aren't really about top speed, more about mid-range grunt and accellerating out of corners.  But that's just me, and wtf do I know... ::)
Click to expand...

Right on. Doesn't mean you can't hit 7800+ rpm with light valves a good valve springs with stock SF Cams. Suggest you don't do it all the time or you may end up in a Hospital.
 
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