Explain these cam specs to me

[scott s]

 Hey Guys! Long time no post.....

 I still have my '63 ragtop, but have ventured into the world of classic motorcycles for the last couple of years.
 This is sorta off-topic, but I know you guys will understand this and can explain it to me in terms that I can understand.

 I have a '78 CB550. I've ported and polished the head and will be doing a 1.00mm overbore. I also have a CB650 cam (a popular upgrade).
 Can someone explain these cam specs to me in "VW terms"? For example, am I in the Engle 110 range with the new cam, or is it getting into the FK 8 range or (Am I making sense here???)

 Anyway, here are the specs:

Stock (1974) CB550 cam


1.36 exh.       lobe              1.38 in.
1.110           base circle       1.110
0.252              lift              0.272



CB650 cam


1.39 exh.       lobe               1.40 in.
1.110            base circle       1.110
0.280             lift                0.293


 I'm obviously gaining some lift (.021 on the intake and .028 on the exhaust), but how much of a change is that, comparatively?  I don't have the duration specs in front of me, but I'm told that they're the same for both cams.

[Ian Godfrey]

Not an expert....  the new cam is like ratio rockers, assuming the the duration is the same you have more lift so if your heads breath OK power goes up and more lift normally increases the duration either side so either the cam is more rampy or maybe there is actually a bit more duration at checking clearance. So its like putting 1.25 rockers on a vw cam designed for 1.1's. more flow, hp up a bit, rpm up a bit.

[martin]

20 thousands is almost nothing, so not much of a real difference.

[Ohio Tom (DdK)]

.020" is almost %10. Thats like .050" extra on a VW motor.
noteworthy..

[martin]

Maybe noteworthy, but it won't do much for performance. Even .050" extra is not even a 1/16" which is .062". For more power you need a substantial increase in lift. This vid shows what real lift looks like when you have a half an inch of lift at the cam with 1.4 ratio rockers http://www.youtube.com/watch?v=xX3iaHUI-SA&list=UUQM6yUWtw-pjn_dmwhXhP2g&feature=plcp

[JVance]

Maybe noteworthy, but it won't do much for performance. Even .050" extra is not even a 1/16" which is .062". For more power you need a substantial increase in lift.

0.050" is worth 15-20+ CFM of flow, depending on the cylinder head.

This vid shows what real lift looks like when you have a half an inch of lift at the cam with 1.4 ratio rockers http://www.youtube.com/watch?v=xX3iaHUI-SA&list=UUQM6yUWtw-pjn_dmwhXhP2g&feature=plcp

Wrong vid? Your comments below indicate only .455" of lift at the valve 

It is a custom Web Cam Grind # 218. Valve lift is .455" and duration is 280 degrees. Duration @ .050 is 242 degrees on a 112 degree lobe center. Not that the lift is higher with the 1.4:1 rockers that are being used.

[martin]

OK, not quite half an inch, but you get the idea of high lift watching the vid.

[JVance]

.455" lift isn't .700" (.500" cam + 1.4:1 rockers).

[martin]

So maybe we need an expert on here. Is it .455 x 1.4 = .637" ? Note that an extra .020 on these numbers would mean nothing, btw.

[JVance]

A Web 218 has .455" lift at the valve with 1.1:1 rockers; that would be 0.414" lift at the cam. With 1.4:1 rockers, your lift would be .580". Of course, this is simple calculations from the advertised values; your builder, having degree'd your cam, set-up your rocker geometry, and checked for clearance to coil-bind, can probably confirm the exact lift at the valve.

You're welcome to discount the extra .020" of lift if you want; it certainly will mean more to Scott having a much smaller cam. Of course, if the new cam isn't ground isometric to the old one, there may be other improvements we cannot account for by simply calculating max lift, such as the duration the valve remains open above certain lifts (e.g. .150", .250", or even .350" if he should run 1.4:1 rockers).

[scott s]

 Well, this is a very popular swap for the SOHC4 crowd. Everyone reports a positive "seat of the pants" gain with no loss in driveability.

 I ported and polished the head, removing casting flaws and resahping the area around the "football" (valve guide). I match ported the intakes and just removed the catsing flaws on the exhaust side (I'm told the exhaust side doesn't really need any help on these engines).
  We polished and lapped the valves.

 Here are some pics:




 I can't find the duration specs on these cams anywhere, but I'll keep looking. I'll also try to find out the rocker arm ratio.
 These changes, along with a 1.00mm overbore (a 3.5% increase in displacement) ought to make a difference.

[scott s]

[Ohio Tom (DdK)]

3 angle valve job would add power for sure.

The pics look nice.

[scott s]

 Still looking for stock duration and rocker arm ratio specs.

 For reference, here are some WebCam performance cams for the 550. They have a good bit more lift, though.

http://dynoman.net/engine/cams/webcams_honda.html

[scott s]

 And some info a fellow SOHC'er sent me:

"Here's the info I have on the CB550/650 cams. Unfortunately I do not know the rocker arm ratio and have not seen that info published. Would like the answer to that question also. The text below is cut and paste from articles and notes from others on the forum.

OK I found specs for Yosh cams.

Street special part# YH500-121-00

IN opens 20 BTDC, closes 50 ABDC  .278 lift
EX opens 50 BBDC, closes 20 ATDC  .307 lift


TT Special race cam  #YH600-122-00

IN opens 27 BTDC, closes 57 ABDC  .324 lift
EX opens 56 BBDC, closes 27 ATDC  . 336 lift


From another post, the lift on stock cams is:

CB650    IN .280 
            EX .293

CB550    IN .252
            EX .272

It looks like the 650 isn't too far the Yosh street cam as far as lift, not sure about timing?
In corresponding with hymodyne I guessed the 650 cam would have about .020 more lift than the 550 cam. Kayaker's #'s say I was close. I also guessed about 10 degrees more duration at least on the intake.
think .030 or so more lift would have a miniscule effect on ramp angle, but more duration would add to it. No matter what, lift is good, but its the timing that matters. The most important timing event as far as "feel" is intake closing. Closing later moves power up the rev range because it gives more time to fill at high revs. "

[scott s]

 I was also given some specs for the stock CB550 cam from a 1980 Action Fours catalog:

 intake duration 240*
 exh. duration    245*

 intake lift     .300
 exh . lift       .280

 Using the numbers I posted earlier, this would give me a 1.1:1 rocker ratio, right? (.300 divided by .272 equals 1.10. Using the same math for the exhaust side gets me 1.11.)

 That would mean the CB650 cam has .322 intake and .308 exhaust lift at the cam, right? (And possibly more duration)
 Those kind of lift numbers put me in the FK10-ish  or larger range, right?

 EDIT" I'm told that the CB650 cam has about 8 degrees more duration, so that would be approx. 248* int. and 253* exh.
  All this combined DOES seem like a good increase and is somewhere between the Yoshi "Street Special" and "TT Special" race cam.

 Thoughts? I know you guys understand cams more than most people.... 

[Ohio Tom (DdK)]

My rule of thumb for VW motors is that every 10deg more duration equals about 700-1,000rpm shift upward in powerband.

Seriously, in my earlier post I mentioned that you should look at having a 3 angle valve job done to those heads. It will make a significant difference. Especially in lower lift scenarios. It's about getting the most of the lift/duration that you have.

I got a buddy who does Harley stuff and VW heads on the side. He can lay down some seriouly cool multi angle valve jobs. They will make any head work better.