taller camshaft for cb750k?
Topic: taller camshaft for cb750k?
June 16, 2019 / By Cecelia Question:
I have a 1978 Honda cb750k and i want to put a taller cam in it. Is there a cam i could get off of a larger cc bike that would fit or even a website that sells taller cams. I know its going to take some carb jetting. just looking for some info. thanks
taller cams open valves more witch means more air flow through the head. when you install a taller cam in you get way better bottom end, or at least thats what i would think.
Best Answers: taller camshaft for cb750k?
Annette | 9 days ago
As I'm sure you know, the '78 was the last year of the SOHC 750, after that they were DOHC.
When you talk about cams, you don't refer to them as being "taller", but rather more or higher lift, or back in the day we called them high race or 3/4 race depending upon the lift. Just for the record, "race" had nothing to do with racing or going fast.
Lift isn't everything, duration, timing and overlap is important as well. Duration is how long the valve is kept open and timing is when the valve opens in relationship the position of the piston when it opens. Overlap is the amount of time in degrees of crankshaft rotation that both valves are open at the same time.
That said, those are four things that come into play when swapping cams and changing even just one will effect how your bike runs and performs.
You are partially correct when you figure a higher lift cam will increase bottom end. Many "torquer" cams have higher lift than do cams intended to reach a happy medium beteen low rpm power and high rpm power. Torquers usually have less duration, overlap and usually are timed different, all of which enhances low rpm power but at the expense of high rpm power. More radical cams intended for increased power at ultra high rpms often have more lift, duration, overlap as well as timing. They cam generate some impressive power figures but at the expense of low rpm civility. Those engines often aren't happy at less than 4-5k rpm.
The camshaft grind has more to do with power characteristics than does almost everything else.
If you want several more horsepower at the top and moving your redline from 8,000 to 8,500 rpm, look for a '69-70 CB 750. No K1 or anything, just 750. Those bikes had a bad habit of breaking drive chains and then wadding them up between the countershaft sprocket and engine case, busting a big hole in it. Toning down power with the K1's helped. That cam should fit without changing anything.
If you want about 12-14 more horses and a bit higher redline, go for a '77-78 CB 750F Supersport cam. I believe those bikes had different pistons (I know the '75-76 F did) with a little higher compression ratio. As to whether your K pistons will clear the F cam is something you need to ask some experienced CB 750 guys. Sometimes high lift cams require the head be relieved (ground out) so the lobe will clear the head.
If you're looking for more low end power and much better gas mileage but sacrifice several top end horses, go for the cam in the '75-78 750 A, the automatic tranny model. Those engines were tuned for low end grunt to better match the auto power needs. Again, not absolutely sure but I think that cam will interchange with your engine with no problems. The A did use smaller diameter carbs to enhance low rpm intake velocity.
For other cams, you might check the Wiseco website. I know you can still get big bore kits. For substantially more power but keeping the engine tractible, that's the way to go. Like they say, "There ain't no replacement for displacement."
I'm sure I'll get plenty of thumbs down for saying this, but ignore what everyone has said about enlarging the valves, porting and polishing the heads and so on. If you're going for a full bore racing cam, then yes you need to do that to take advantage of the high rpm breathing capability. You'd also need to go with a more freely flowing exhaust and larger diameter carbs.
I don't have a degree from a trade school nor have I been to a training school for every brand bike out there, but rather I've learned the good old fashioned way, by reading and doing. On my own I've studied mechanical, electrical and hydraulic theory, troubleshooting and application and for the last 40+ years I've wrenched on everything from weed eater engines to diesel engines with 300 pound crankshafts, 6 pound pistons and connecting rods the size of a large man's forearm. Not trying to brag, but I do know what I'm talking about. Good luck.
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Originally Answered: What is a good sized camshaft for a 1998 Camaro Z28?
Start by assessing your goals. You will also need to do a valve spring change.
I will make you a camshaft with a 100% love it or I will refund you, guarantee.
People are all going to throw alot of useless information at you. Comparing cams by duration at .050 is just that. Cams have different shapes and therefore, comparing at duration at .050 is 10% of the story. It will get you into alot of trouble in choosing a cam and you will be met with disappointment.
Some cams also manipulate their advertised numbers so that it makes them look more intense on paper. This is especially true with Hydraulic cams in that some advertise at .0045 tappet lift, some advertise at lash point, and yet some advertise at .006 tappet lift. Doing this does not change anything comparing at .050 or anywhere else. But it DOES change the relationship between these points in that it can appear to make the spread look smaller when in fact it is bigger. The bigger spread means a lazier ramp, generally.
A little bit of cam timing goes a long way. You don't really need a big cam, you need one with steep ramps and very gentle closing ramps. This way, you get the job done with lifting the valve so the cylinder head is where it is happiest in the flow curve at the same time that the piston is at max velocity in the cycle. This is known as valve timing. It is very critical in separating an engine that accelerates and one that does not. It is also very critical in influencing cylinder pressure as well as how well the cylinder head builds velocity inside the ports. The camshaft is the single link between the engine and cylinder head and without it, a cylinder head means nothing to an engine. Camshafts are also the means of changing the engine's air flow appetite, as well.
You can REALLY turn the car into a pig if you start playing the cam selection game. Especially if you start to throw a load of exhaust cam timing at it and combine that with a really wide Lobe Separation Angle. Combined, these will destroy low rpm cylinder pressure and cranking compression, the engine will accelerate lazy, eat lots of gas because it's WAY down on torque where you need it, and it will scream for compression. Sure it will have a choppy idle, but if the car won't get out of its own way, how cool it sounds at idle is really trivial, in my opinion.
You have to consider what your goals are and what you want to accomplish/have to show for it when you are finished.
Feel free to email me and I will discuss with you appropriate choices once I understand what your end goal is. If you still choose to go elsewhere after we talk, then that's ok, too. At least let me educate you on how to feel your way through all of the MEGA mass produced junk cams out there, and which are mostly being peddled by those you expect to be in the know but are largely inexperienced in designing cams AND building engines. In addition to that, a couple of the really big names have piss poor quality control. Don't believe me, buy 4 of the same cam from them and check every one of them in the same engine using the same timing chain and degree wheel/dial indicator. You will learn very quickly that they are all over the place and there is little consistency. Hence part of what I mean when I use the term Mass produced junk. They are cheap and for good reason. That said, talk to a few pro category racers not being fed sponsor money from them and I am confident that a great many who are willing to talk to you will tell you that they would not run one of those cams if you gave it to them for free. When a cam company spends advertising Dollars to the tune of well over 1 Million per year, I feel that it screams that they have to beat their cams into the public's brain by marketing them to death for people to use them. Most racers start with them when hey are entry level and don't know better. However, when they get turned on to something else, very rarely do any of these guys EVER look back.
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You have to realize that the designers make motors to run at optimum performance. Putting in a taller lobed cam will have very little effect unless the head is ported to increase the airflow. This includes bigger intake, and exhaust valves. Stock porting restricts the airflow when if you have oversized cams. Porting, and polishing the heads is the best way to go, and if you go that far, you might as well do the valve job too.
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I agree with jon, with the exception that factories often dutune a bike slightly(at least back then) to meet EPA rules. There are gains to be had with a cam swap, the trouble is there were plenty of cam manufacturers offering various grinds for your bike back in th 80's, now, not so much. It only makes sense to do some porting while you've got it torn down too. And then, there's no replacement for displacement! These things tend to snow-ball, at least with me. Check out Carpy at cb750cafe.com, he's making some pretty fast & cool rides out of these ol bikes. Also cyclexchange.com has some performance parts for these engines, not sure about cams.
Very cool bike! Good luck with your project!
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I'm with 'ricer', but want to know the why behind your quest !?!?
Added: Without the heads being ported, possibly some valve work, you're looking at some big bucks. Why?
To be the 'baddest' sounding 78 CB 750 on the block? (exhaust should be the next quest).
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For a person i remember five'7 and beneath quick and five'eleven and up tall. For a lady five'three and beneath quick and five'eight and up tall. A guy that's inbetween those numbers are quick however no longer that quick and tall however no longer that tall lol and a lady that's inbetween is the ideal peak IMO.
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taller cam... valve piston clearance??
have you looked at CB750 hondas from different years.. they made them untill at least 2002
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Originally Answered: Am I going to grow any taller?
Holy smokes, a GIANT. Odd that you are the only one so tall. Who's your daddy? I have heard of cases of kids being swapped at birth. Perhaps there is someone very tall in the family history.
I used to love the show as a kid "The Friendly Giant" ... Height can be impressive. I was in the U.S once and stopped at a Tim Horton's while there. The size of those guys were massive. I couldn't get over the height. I'm about as tall as your dad.. So you can imagine how stunned I was looking up. I heard that it may be something about the hormones in the meat and produce. So eat a lot of beef if you want to grow more. Although I don't think those additives have a good effect in future according to cancer studies. I really think you are tall enough now though.
Just so you know, your body isn't actually fully grown until between age 21 and 25. (In fact one of your internal organs doesn't reach full extent until age 25 but I just forget which one right now.. DUH)
In case you are curious: http://www.youtube.com/watch?v=eDigdsYNA1E