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Old 02-06-2011, 08:59 PM   #16
Lornce
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Quote:
Originally Posted by mymindsok View Post
Mega Cycle appears not to list any Airhead Cams. You got any inside info?
I had some last summer directly from Mega Cycle. Haven't been to their website since, but it linked to Andrews spec charts within Mega Cycle's site.

Poke around a little more. It's in there.
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Old 02-06-2011, 10:07 PM   #17
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Originally Posted by Lornce View Post
Q. Where does the stock 308 degree cam work best?
A. Depends how it's degreed.

Fact: '77 RS (and every other airhead except the R60/7) used the same cam profile (which determines valve lift and duration) as '79 and all later airheads. BMW degreed (references the cam's orientation to the crankshaft) the cam slightly differently after '78 or '79 (I forget which year the change was introduced) to improve torque/power production in the lower reaches of the rev range.

Increased overlap tends to improve higher RPM power production at the expense of lower RPM efficiencies. The differences are pretty easy to identify on an airhead twin.



It's been a long time since I looked at the specs of the 308 vs. 336 cam (over 20 years). Memory tells me there wasn't much difference in lift, the difference was simply duration. Do you have the specs available from a reliable source?

My experience with the 336 cam in a '77 RS was pretty forgetable. Andrews cams (now mfg'rd by Mega Cycle) produce more impressive performance gains.
BMW advanced the 336's timing as well. The 308 is such a mild cam it is hard to tell the difference. Most think the original timing would have around a 300 rpm higher peak torque. Same with the sport cam. Maybe a bit closer to 500. But you still didn't answer my question. I have a lot of experience with both 308's and only the advanced 336. Pick either 308 or both. It doesn't matter that much.

Read what most serious tuners say about overlap. You will be surprised. The 336 is not a high rpm cam. Chris at San Jose BMW and Dr Curve prefer the 336 for better performance. If I wanted more lift than the 336, I would grind some off the bottom of a 336. It works! 336 lift is 10.68mm and the 308 has 9.4mm. That's 12% more lift. Big diff! Yes, there is room for more but not THAT much more. Remember, that is the cam spec. Then you have a 1.5:1 rocker arm ratio. The percentage difference is the same but . . . . If I was running shorter than stock rods like B+S did back in the day, I might choose a Andrew's cam but I am not. If anything, I would run longer than stock. Sport cams work with stock springs! That is a big diff IMO for a street bike!
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Old 02-07-2011, 07:16 AM   #18
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Originally Posted by supershaft View Post
BMW advanced the 336's timing as well. The 308 is such a mild cam it is hard to tell the difference. Most think the original timing would have around a 300 rpm higher peak torque. Same with the sport cam. Maybe a bit closer to 500. But you still didn't answer my question. I have a lot of experience with both 308's and only the advanced 336. Pick either 308 or both. It doesn't matter that much.

Read what most serious tuners say about overlap. You will be surprised. The 336 is not a high rpm cam. Chris at San Jose BMW and Dr Curve prefer the 336 for better performance. If I wanted more lift than the 336, I would grind some off the bottom of a 336. It works! 336 lift is 10.68mm and the 308 has 9.4mm. That's 12% more lift. Big diff! Yes, there is room for more but not THAT much more. Remember, that is the cam spec. Then you have a 1.5:1 rocker arm ratio. The percentage difference is the same but . . . . If I was running shorter than stock rods like B+S did back in the day, I might choose a Andrew's cam but I am not. If anything, I would run longer than stock. Sport cams work with stock springs! That is a big diff IMO for a street bike!
The difference in timing between the pre and post '78 ('79?) spec amounts to exactly one tooth on the timing gear, fwiw.

Okay, for a healthy high speed touring mount (RS or the like) the 336 cam would probably work okay (in combination with some proper compression, ignition and carburation) and definately stress the valve train less than a more aggressive cam.

But I still don't think it'd be suitable for a sidecar tug.

My application of late has been a GSPD, so I'm more interested in healthy midrange gains for squirting around twisty gravel bends. More aggressive lift and shorter duration (shorter than 336) is what I need. Andrews grinds a cam that works for those apps. You can check with the local KTM doodes on that score...

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Old 02-07-2011, 10:48 AM   #19
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Useful gearing charts here

Based upon stock tire sizes, I'm guessing.

Doesn't consider weight, wind resistance, hills, altitude,etc.
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Old 02-07-2011, 11:00 AM   #20
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Originally Posted by JimX View Post
Useful gearing charts here

Based upon stock tire sizes, I'm guessing.

Doesn't consider weight, wind resistance, hills, altitude,etc.
edit: I'm an idiot and misread Anton's graph.

I should have known better and given Anton the benefit of the doubt.

What was I thinking?


Lornce screwed with this post 02-07-2011 at 07:10 PM
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Old 02-07-2011, 11:07 AM   #21
supershaft
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Originally Posted by Lornce View Post
The difference in timing between the pre and post '78 ('79?) spec amounts to exactly one tooth on the timing gear, fwiw.

Okay, for a healthy high speed touring mount (RS or the like) the 336 cam would probably work okay (in combination with some proper compression, ignition and carburation) and definately stress the valve train less than a more aggressive cam.

But I still don't think it'd be suitable for a sidecar tug.

My application of late has been a GSPD, so I'm more interested in healthy midrange gains for squirting around twisty gravel bends. More aggressive lift and shorter duration (shorter than 336) is what I need. Andrews grinds a cam that works for those apps. You can check with the local KTM doodes on that score...

One tooth? Did you get that info from the same place that says sport cams have the same lift as 308's?

My sport cam isn't in a high speed touring mount and I love it. It has stock 8.7:1 CR. Stock ignition. Before I put the Dells on it worked perfect with slightly re-jetted stock carbs.

IF you are talking about the Andrew grind that Dr. Curve writes about and I have heard Chris talk about, they consider that cam a higher rpm cam than the 336. It has more lift and wider toe to toe as well.

I don't think it matters what bike you have but how you ride. If you are one of those guys that lugs your engine all the time and never revs it over 5500rpm, you won't like a sport cam. It doesn't matter if you are on single track or an interstate. If you are the type of rider that rarely ever lugs his engine and doesn't hardly ever let the revs fall below 3000rpm no matter what cam you have, you will love a sport cam. You will find yourself shifting a lot less often for a wider and more powerful powerband.
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Old 02-07-2011, 11:32 AM   #22
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Originally Posted by supershaft View Post
One tooth? Did you get that info from the same place that says sport cams have the same lift as 308's?

My sport cam isn't in a high speed touring mount and I love it. It has stock 8.7:1 CR. Stock ignition. Before I put the Dells on it worked perfect with slightly re-jetted stock carbs.

IF you are talking about the Andrew grind that Dr. Curve writes about and I have heard Chris talk about, they consider that cam a higher rpm cam than the 336. It has more lift and wider toe to toe as well.

I don't think it matters what bike you have but how you ride. If you are one of those guys that lugs your engine all the time and never revs it over 5500rpm, you won't like a sport cam. It doesn't matter if you are on single track or an interstate. If you are the type of rider that rarely ever lugs his engine and doesn't hardly ever let the revs fall below 3000rpm no matter what cam you have, you will love a sport cam. You will find yourself shifting a lot less often for a wider and more powerful powerband.
No, I got that information by looking at the pieces and figuring it out the last time I installed a cam in an airhead.

If you're still running a stock small valve motor with 8.7cr... and you're happy with it. Why are you being obnoxious in a thread about performance airhead motors?

I have no idea what Dr. Curve or Chris have to say about Andrews cams, though I'm sure their thoughts are sound, given their histories. I'm using the grind that works for good midrange, which is less overlap than the 336 but more lift.

Equipment preparation is important.


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Old 02-07-2011, 11:59 AM   #23
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"Weight, hills etc won't make any difference to gearing results as long as your clutch isn't slipping."

Of course it won't. However, those conditions can sure make you wish your gearing is lower. (Or engine bigger)
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Old 02-07-2011, 12:02 PM   #24
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Originally Posted by Lornce View Post
Maybe in 4th.

Stock 2.91 gears won't pull 5k at 70 in 5th.

I forgot I have my R100 in a /2 frame. I think the older rear end might be lower. I can't remember now.
Still, depending on conditions and weight of the tub, it seems like it should pull OK...?
Don't forget to use a sub-frame.
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Old 02-07-2011, 12:14 PM   #25
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Originally Posted by Uncle Ernie View Post
"Weight, hills etc won't make any difference to gearing results as long as your clutch isn't slipping."

Of course it won't. However, those conditions can sure make you wish your gearing is lower. (Or engine bigger)
Absolutely.

But I've learned that a lot of folks have difficulty visualising gearing and ratios and their effect. An example of which I was responded to above. It may have something to do with the abundance of automatic transmissions out there?

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Old 02-07-2011, 12:17 PM   #26
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Why am I being obnoxious? Why are you? I am not writing a bunch of stuff that just ain't so no matter how you look at it. And I wasn't pointing out that you are being obnoxious but since the cat is out of the bag.

Airheads don't run right with either setup a whole tooth off either way. I believe they advanced the 308 the same amount that they advanced the 336 which is three degrees at the crank. One tooth is nearly 5 degrees.

At any rate, I am not being obnoxious, I am just pointing out that some of what you are saying is not right. That isn't being obnoxious, it's countering some of your points. Big diff!

I am running a sport cam WITH the stock 8.7 compression. You suggest that the CR needs to be raised to run a 336. No it does not. You suggest that you need to put bigger carbs on. No you do not. You say that you have to run a sport cam above 5000rpm to see any advantages. No you do not. You say that a sport cam has virtually the same lift as a 308. No it does not. You say that a longer duration cam makes for a high rpm cam. No it does not at least a lot of the time. Don't take my word on it, read what some famous tuners say on the subject.

I am not being obnoxious, it just takes a lot of countering to counter a lot of on going 336 folklore that just isn't so but I can leave it at the issue if you can.
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Old 02-07-2011, 01:01 PM   #27
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Last time I looked and compared timing gears, the difference between the keyway and the alignment-marked tooth was more or less one complete tooth. Could be there was a variation in the cam keyway, too? I'm not certain. I have no experience with later 336 cams, only an item suited for a points equipped airhead.

Quote:
I am running a sport cam WITH the stock 8.7 compression. You suggest that the CR needs to be raised to run a 336. No it does not. You suggest that you need to put bigger carbs on. No you do not. You say that you have to run a sport cam above 5000rpm to see any advantages. No you do not. You say that a sport cam has virtually the same lift as a 308. No it does not. You say that a longer duration cam makes for a high rpm cam. No it does not at least a lot of the time. Don't take my word on it, read what some famous tuners say on the subject.
I didn't say compression needed to be raised for the 336 cam to work. I just don't see much point in going to the trouble of an expensive camshaft if you're still waisting your time with lawn mower compression ratios. Personally, I wouldn't bother. It's like putting expensive sneakers on a fat girl to help her run faster. Why bother?

I didn't say anything about bigger carbs.

A 336 cam will show improvements between 5 and 8k. That's a fact.

The difference in lift between a 308 and 336 isn't what I'd call "dramatic".

Longer duration, or more specifically "increased overlap" has long been known to aid higher rpm power production. It's a gas inertia thing. You could read about it.
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Old 02-07-2011, 01:51 PM   #28
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Laugh

Well, your guess about the tooth sounds a bit more like a guess now to me. I will look up the 308 specs when I have the chance and see who is right on that one.

Well, at least you are now wiggling.

I am willing to bet $100 that you wouldn't call my bike a fat girl with sneakers on if you saw it run! Who are you calling obnoxious? The cam is only $200. I don't call that expensive. Why bother? I got right around 33% more power with my stock CR. Big, big diff!

What did you mean then by "proper carburetion". Ignition too?

336 will show gains above 5k? That is not what you said earlier Lornce.

Lift? That isn't what you said earlier either!

Duration? I full well know what a lot of people think about it as do you. Now look into that topic a bit deeper. There is NOT one side to that story!
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Old 02-07-2011, 01:59 PM   #29
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Well, your guess about the tooth sounds a bit more like a guess now to me. I will look up the 308 specs when I have the chance and see who is right on that one.

Well, at least you are now wiggling.

I am willing to bet $100 that you wouldn't call my bike a fat girl with sneakers on if you saw it run! Who are you calling obnoxious? The cam is only $200. I don't call that expensive. Why bother? I got right around 33% more power with my stock CR. Big, big diff!

What did you mean then by "proper carburetion". Ignition too?

336 will show gains above 5k? That is not what you said earlier Lornce.

Lift? That isn't what you said earlier either!

Duration? I full well know what a lot of people think about it as do you. Now look into that topic a bit deeper. There is NOT one side to that story!
You're claiming a 33% power increase from a camshaft? No offence, but you're either wrong, deluded or you're not telling the whole story.

Ermn, yea. Gains above 5k. Just like I mentioned earlier. Hello?

The rest is semantics:
Define a noteworthy lift increase.
Define low-end and mid-range.

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Old 02-07-2011, 02:58 PM   #30
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Originally Posted by Lornce View Post
Interesting. Not accurate, but interesting. I suppose?
The numbers aren't to be believed, but it's sort of useful (I guess?) to compare differences between the various ratios, as long as you realise the speeds aren't accurate or even terribly close to acccurate.

Apparently assumes a 6.6 foot wheel radius for all instances.



The figures at Anton's site roughly agree with my gearing spreadsheet, and mine agrees with the dyno's speedo.

The 6'6" ( 78") is the circumference, not the radius. I base mine on 80" circumference.
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