Topic: Benifits from a hot cam?

[Soos]

I was going to do a crazy big bore on my 650(65mm), however i chickened out, and am "testing the waters" with a milder 652cc over bore(61mm).

The cam in the 650 has a little under .300 lift as is, and the hot cam i can get (550's 58b grind, or 58a mabey) is 330 lift.

I have done a thorough cleanup of the head(a poormans head job) polished the valves(just the exposed area past the guides) and lapped the valves in.
Nothing too crazy on the head work, mainly removing casting imperfections, and smoothing out things a bit.




With a overbore this close to stock displacement is there a serious benefit of using a hot cam?
At 300+, it would be almost as much as I have in the bike already.
...cost of bike, boring it out, pistons, rings and new gasket set!!


Would it be beneficial to run with a dyna2000 if i get a hot cam?
Not too sure how much effect being able to adjust the advance would actually be.
I do realize it will be some work just to get the dyna2000 to fit let alone work on my bike.
They don't make a timing plate for the 650.

If nothing else I will be running a RPM limiter if I opt to skip on the dyna2000.


l8r

[Soos]

By the way, I intend on this motor going into a '81cb650c with hardbags and a little fairing.
So I want power, but something I don't have to get 9k RPM to get it.


However my next overbore will be on my stripped down '79, so i'm thinking big with those bores.
Would it be better to have a much larger than stock bore before installing a hot cam?(and dyna2000?)


l8r

[Javier]

nice ride! very tasteful. let me know if you need links to any parts or custom stuff for your 400f, I think I have 15+ links under my bookmarks. enjoy!

   -  javi

[kayaker43]

I wouldn't waste money on the Dyna, others will argue, but its not going to get you any seat of the pants improvement if your stock ignition is optimized. Rev limiter is nice, adjustability is nice if you are constantly swapping parts, but once you find best timing for your present combination, you're good. Its a lot of money for very little if any gain. IMHO.

A race cam will definitely move your power from low to high. Unless its pretty mild, expect to lose low and mid to get more high RPM power. most people miss this, but to work best it also requires a change in exhaust primary length and intake tract length. Can't change intake length on the 650 but a cam tuned for power at 8-9K is a bad match for your average aftermarket header that's tuned for 6-7K. I saw that when running the Yosh TT cam with a hooker header. I thought it was fast until I tried the Yosh short header,. then WOW! Yet the Yosh header wouldn't do much with a stock cam because it was too short. Get them matched and the effects seem to multiply instead of add.

Also a hotter cam will move your powerband up the rev range with or without a big bore kit. I raced stock 550 pistons notched for valve clearance with a Yosh cam for one season and it was very competitive. When I switched to higher a compression 590 kit I was surprised how little difference it made.

High compression and extra displacement will help across the rpm range but if you want to run todays pump gas you can't get high enough compression to make a sizable difference. You have to be realistic about bore increases too. A 50cc increase for instance is still less than 8% so don't expect 20% more power. Its also a lot of money for a little gain unless you are rebuilding anyway

A reasonable cam with the right header is a good payback if you don't mind reving it more. Cleaning up the ports is good and a free flowing air filter is good if you rejet for it, but the stock airbox will give better low end and midrage than pod filters. A full race cam is a bad idea for touring or commuting, you'll miss the mid range too much.

[eldar]

The dyna 200 offers more than just a rev limiter plus at high rpm it IS better than points any day. Not only do you get the rev limiter which is invaluable on hot engines but you can also program your ignition curve to optimize burn pattern So you do not have to compromise any range of ignition like you would with stock, even when optimized.

However, in this case, unless he is going balls out, then no he does not need the 2000. I will still hold to my opinion that the dyna S is still an improvement over points as there was an immediate improvement in everything on my bike when I switched to one.

[bwaller]

I wonder if anyone has or can check to see if the advertized stock lift can be obtained at the spring retainer.

In the case of the Web 58a, that .330 lift supposedly is produced at the lobe, the actual fiqure at the retainer in the 500/550 is less than that. I kept track of all this useless info but filed it away so well that I can't put my hands on it now! So long story short, unless the 650 rocker is different enough to change the outcome, don't expect to reproduce Webcams lift fiqures.

That being said it still delivers a nice power increase in the 550.

[kayaker43]

Yeah, all my stuff is far away at the moment so I can't check, but I was wondering what the rocker ratios were? I also assumed they were the same for the 650?

Not slamming Dyna, they offer many things and a programmable advance curve sure is nice,.. just talking about priorities or bang for the buck. If more power is your goal, it doesn't give much for the money spent... that amount of money is better spent trying to improve breathing.

[hymodyne]

I've got a 605 cc overbore kit in my 500K1 engine, Mrieck is porting my head and replacing the valve guides. the bike runs on 550K stock carbs with drilled out mains and a 4-1 header and a flow-thru carbon fiber canister. I'm hesitant to jump right into the megacycle mild cam regrind; I'd rather start with the improvements listed above and then go on to add a mild cam later if desired. will I sabotage Mrieck's porting work by not adding a reground cam?
hym

[kayaker43]

You won't get much out of the port job with the stock cam. At least get a 650 cam off ebay for $25-50 since its apart.

[eldar]

Well the dyna S is in improvement and the 2000 is way better. No one gets them just for power. Although in a hot engine, points are not going to get you as much. The main reason is for the features and tuning offered by the 2000.

As for the S, it pays for itself in 5 years or less when compared to the cost of replacement points and condensers. With the added benefit of not having to worry about timing. For many of us, that is the best bang for the buck.

its all good though.

[754]

Generally a cam is run with other mods, hope you have a least a pipe..

 One thing it will do that most other stuff wont is raise your RPM ceiling.

So now you can turn another 2 or 3K higher, which now means you can gear down for better acceleration & still have the same top speed.. but run sporings with it.

[hymodyne]

You won't get much out of the port job with the stock cam. At least get a 650 cam off ebay for $25-50 since its apart.

will a 650 cam fit a 500/550K head? If it will, why do folks pay $$ for a reground one from megacycle, etc.?

hym

[kayaker43]

Its a mystery to me why people are ignoring the 650 cam as a cheap upgrade???  Several have done it but no one has reported back how it felt. I suspect its always done with other mods?

The tachometer gear needs to be swapped and you have to use the old cam sprocket but otherwise its a drop in fit. Even a new one from www.servicehonda.com should be way cheaper than a re-grind?

I bought a 650 cam off ebay for $25.00 and was going to swap it with no other mods and report back, but the cam arrived and was too badly worn to use,... bummer 

The bigger surprise is the big valve 650 head. Even the best ported 550 head won't come close to it and its the biggest reason for the large difference in power between the two,.. yet its also widely ignored as a cheap hop up. You can get these items on ebay pretty cheap too?

[Soos]

how I missed all these replies, I have no idea!!!

Thnx all, I have found out that my main want is available as a stand alone unit.(the rev limiter)
So thats on my list instead of the dyna2000.
And as for a hot cam, I'm going to one day, but not yet.
Mabey on the big bore i'm still dreaming about.


I'm starting a build thread soon to show what I am doing to this bike.
Bags with custom mount, modified rear blinker mounts, Yosemite Sam mudflap, overbore, head job and i'm sure a thing or two more before i'm done.


l8r

[heffay]

nice ride! very tasteful. let me know if you need links to any parts or custom stuff for your 400f, I think I have 15+ links under my bookmarks. enjoy!

   -  javi

YES!   

[c_kyle]

Hey Soos,

what about the US '79 650 cam?  It's supposed to be hotter than the non-US 650Z cam; I don't know the cam specs, though.

Bikez.com has the 1979 US CB650Z producing 63hp, and the other 650Z's producing 50hp.  I don't remember what all the differences were, besides the cam; maybe head work too?