SOHC.co.uk Forums > CB750

836cc kit choices - do I need a new cam?

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theshootist:
Hi,

I would be interested on member's thoughts on my SOHC rebuild. I'm having a set of Wiseco 836cc pistons fitted along with a copper gasket. The head is also being flowed, although the valves will remain standard size and I am sticking with the original carbs. Since I'm having the engine apart to this extent would it be a good idea to go to a different cam, along with stringer valve springs etc, or could I just have the existing cam re-profiled or left alone? Some of what I'm reading suggests a cam is necessary to get much benefit from the slight displacement increase, but there are plenty of builds where the standard item is retained.

Many thanks 

MrDavo:
I think it depends what engine characteristics you want, and how you are going to ride it. More cc and nothing else will usually give you more torque and 'rideability', from my experience with performance cams, including a CB750 with a Yoshimura cam, they tend to only work well on full bananas WOT where they give you better acceleration, the rest of the time you lose something in the flexibility and smooth running stakes. They weren't designed to pootle through slow traffic.

I used to have a race bike with full race cams, and big bore carbs, that ran so badly on the warm up lap that I considered going back to the pits, ran perfectly in the race, pulling like a train, then coughed and spluttered around for the slow in lap.

theshootist:
Thanks, point taken.

I didn't say what I was after. I'm not after performance at the top end, a bit more go at the bottom end would be welcome, but I'm fitting the pistons because I'm currently burning oil and have pretty poor performance, so thought I might as well go the whole hog. I'm going to have a word with Kent cams to see whether they can suggest a re-work of the existing cam.

Greebo:

--- Quote from: theshootist on November 10, 2016, 12:07:26 PM ---Hi,

I would be interested on member's thoughts on my SOHC rebuild. I'm having a set of Wiseco 836cc pistons fitted along with a copper gasket. The head is also being flowed, although the valves will remain standard size and I am sticking with the original carbs. Since I'm having the engine apart to this extent would it be a good idea to go to a different cam, along with stringer valve springs etc, or could I just have the existing cam re-profiled or left alone? Some of what I'm reading suggests a cam is necessary to get much benefit from the slight displacement increase, but there are plenty of builds where the standard item is retained.

Many thanks

--- End quote ---

These engines don't like tuning at all, even just fitting K&N's will upsets the running until you getting the jetting & needle settings right, as Mr Davo has mentioned if you are going to race the bike OK go for it, but as he also says it will run like a dog at low speeds..

Take a look at this video
https://www.youtube.com/watch?v=N8tZ8Vmb7HQ

philward:
I've been running a cruz image 836 kit (there standard compression) for about 800 miles on standard cams/airbox/exhaust - plenty of bottom end - 'Hondaman' on .net reckons about 8 bhp on top end. Just fitting same with otherwise standard engine to the CR750 replica I'm building. And at £120ish, can't be beaten in my opinion - trigger rates the cruz image piston which are made by NPR I think (Graham will correct me if I'm wrong - they're good brand anyway)
Phil

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