Technical Camshaft choice

[JonPiz]

Im rebuilding 650cc engine with 34mm oversized inlet valves and a Weber 28. Is there any point in putting more than a standard camshaft in this?

 

[smart51]

There is, but I've never been able to find out how much. People also port and skim the head and other things. It's hard to say how much each mod does. If I had to guess, I'd suggest a mild upgrade might give you 10% more and a wild cam 20%, but bear in mind that's 2.4 BHP and 4.8 BHP. It only takes you from one kind of slow to another kind of slow.

 

[JonPiz]

I might just fit a new std cam and just enjoy the car for what it is

 

[Bleeding Knuckles]

Hi Jon, If you look at the thread "650 engine questions" (The 650 cam has a duration on 263 degrees (depending on year). A 30/70 cam has a duration of 280 degrees, a 35/75 cam has a duration of 290 degrees and a 40/80 a duration of 300 degrees.) you should get an idea of the differing cam profiles. If you are rebuilding your engine it will take little extra time and cost to 'relieve' the porting in your head to allow the engine to make the best of the larger valves. However, as in all engine upgrades no matter how small don't go mad in only one area as improving the breathing will put extra stress onto the bottom end and without checking can give horrendous problems down the line. Carefully check the wear on your big ends and main bearings and regrind if in doubt. skimming the head a little will also improve engine response and you should not encounter any extra worries that come with radical mods. The carb may need rejetting slightly for good running, but that is simple to adjust. the engine is a jewel and responds to gentle modding and you will find that you will be able to keep up with the modern stuff on our roads!!!! Any questions please ask.
Ian.

 

[JonPiz]

Hi Jon, If you look at the thread "650 engine questions" (The 650 cam has a duration on 263 degrees (depending on year). A 30/70 cam has a duration of 280 degrees, a 35/75 cam has a duration of 290 degrees and a 40/80 a duration of 300 degrees.) you should get an idea of the differing cam profiles. If you are rebuilding your engine it will take little extra time and cost to 'relieve' the porting in your head to allow the engine to make the best of the larger valves. However, as in all engine upgrades no matter how small don't go mad in only one area as improving the breathing will put extra stress onto the bottom end and without checking can give horrendous problems down the line. Carefully check the wear on your big ends and main bearings and regrind if in doubt. skimming the head a little will also improve engine response and you should not encounter any extra worries that come with radical mods. The carb may need rejetting slightly for good running, but that is simple to adjust. the engine is a jewel and responds to gentle modding and you will find that you will be able to keep up with the modern stuff on our roads!!!! Any questions please ask.
Ian.

Thank you so much for your help, I’m sure I will be asking you more questions in the near future

 

[Toshi 975]

There has been loads written about the basic formula for improving power here and on other platforms. Living in an area with a number of long steep hills a standard 500 could be a bit of an embarrassment and frustration to other road users. Various modifications on both 499cc and 650cc engines took care of that and if being able to accelerate uphill with a decent load on board is a “new kind of slow” then I am all for it.

 

[smart51]

if being able to accelerate uphill with a decent load on board is a “new kind of slow” then I am all for it.

I'm sure you know that's not what I was getting at. What I mean is that going from 24 BHP to 30 BHP will not take you from slow to fast, but from slow to less slow. It is better, of course, but it is best to be aware of this before you start than be disappointed after you finish.

 

[Bleeding Knuckles]

And of course don't be disappointed when you get the bill
Ian.