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Author Topic: s cams  (Read 6269 times)

ace.cafe

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Re: s cams
« Reply #60 on: February 09, 2014, 07:33:35 PM »
Okay, first I'll reiterate the data from B.W., and fill in the rest of the data for each set, which I can derive from the info that B.W. posted.

Stock AVL cams.
IVO 9*BTDC
IVC  54*ABDC
EVO 72*BBDC
EVC  18*ATDC
Intake Duration 243 degrees
Exhaust Duration 270 degrees
Intake cam centerline  112.5*ATDC 
Exhaust cam centerline 117*BTDC
Lobe separation angle 114.75*
Overlap Period 27 degrees

S Cams
IVO 30*BTDC
IVC 75*ABDC
EVO 85*BBDC
EVC 50*ATDC
Intake duration 285 degrees
Exhaust duration 315 degrees
Intake lobe centerline 112.5*ATDC
Exhaust lobe centerline 107.5*BTDC
Lobe separation angle 110 degrees
Overlap period 80 degrees

S Cams (1 tooth retarded)
IVO 12*BTDC
IVC  93*ABDC
EVO 85*BBDC (Exhaust Cam not retarded)
EVC 50*ATDC  "
Intake duration 285 degrees
Exhaust duration 315 degrees
Intake Centerline 130.5*ATDC
Exhaust Centerline 107.5*BTDC
Lobe Separation Angle 119*
Overlap period 62 degrees

Now, some commentary.

First, the stock AVL cams
The stock AVL cams are a relatively short duration intake cam, with a considerably longer duration exhaust cam, with a little shorter lift on the exhaust by .020"(half-mm).
They open the intake valve quite late, and close the intake relatively early, compared to earlier Bullet cams. This seems to be intended to keep the overlap period short to preserve lower rpm torque, and closing early enough to prevent much reversion up the intake. It's basically a torque cam, or profile which might be used for towing a sidecar, or band-aiding a slow port. It is not a high revving type of cam design. But it has enough to get it up to a reasonable top speed, similar to previous Bullets.
The exhaust cam reflects an attempt to work with the relatively smaller exhaust port, and the lower exhaust valve lift, to extend the exhaust stream velocity over a longer time period, so that the extraction effects might help to better scavenge the exhaust from the chamber during overlap, and help the somewhat slower intake port get moving before the piston starts going down. This is not an unusual practice. It actually is pretty well targeted for the typical Indian Bullet market in India.

The S Cams have a sportier profile, and this is the first time that I have seen specs on the S Cams. I was wondering how they were getting more results from the AVL, and now I know how. The lift isn't really different, although I still dont know if the exhaust cam lifts lower than the intake. Even so, it is clear that the S Cams have much longer duration on both intake and exhaust cam. The exhaust cam is actually in the category of racing cams in terms of duration, but not lift.
The intake cam has similar duration as the Iron Barrel cams have, and similar lift height at max. But there is a big difference in the timing and lobe center. In fact, these S Cams are remarkably similar timing to our Ace Magnum Cams, but without the added lift.
It opens the intake valve earlier than the stock AVL cams, for added overlap, which helps to extend the higher rpms, but may have some unwanted impact at lower rpm torque production. It would be generally considered in the sportier type cam overlap category. This trend continues with the later intake valve closing angle, which is much later than any of the stock Indian Bullet cams. This is also a sportier type of design, also intended to work with a higher rpm range. And the duration allows higher rpm than standard AVL cams, too. It will support higher rpm running, even without any higher lift at the valves, because it gives more time for the cylinder to get filled.
The 112.5*ATDC lobe center of the intake valve just happens to be the same as the Ace Magnum Cams.
The exhaust cam  is a little too long for my taste, but it certainly is not short on duration. It will permit higher rpm running, because it gives plenty of time to get the exhaust out. It opens fairly early, so it will actually work better with higher compression than it would with lower compression. This is fine, and it also happens to be  close to the same EVO timing as our Ace Magnum exhaust cam. But this long duration has a price, which turns out to be what I consider a "late" EVC timing of 50*ATDC. I think this is a little too late, and I think it will have some adverse effects on the low rpm torque. But it will support higher rpm running better. It's in the nature of the sporty cam type it is. For reference, the Ace Magnum Cams have an EVC timing of 32*ATDC.
The overlap period is pretty wide, but not too wide. It has 80 degrees of overlap, biased by 20 extra degrees on the exhaust closing side. Quite a decent overlap period for a sporty cam. It will support higher rpm running quite well, and it isn't too harmful to lower rpm torque, but there will be some effects to lower rpm torque compared to the very short overlap and short duration of the stock AVL cams.

So, in general, I think that the S Cams are a pretty sporty cam set, in terms of timing events. They fairly closely mimic the Ace Magnum Cams for timing, except for that later exhaust valve closing timing that the S Cams have. Other than that, its quite similar in timing, and the Magnum cams just primarily have more lift. I would be favorably impressed with these cams in a stock AVL or also an Iron Barrel Bullet.

The S Cams with the one-tooth retarding on the intake cam are starting to get into a timing range which I consider close(or into) the "out of bounds" area for timing in a normal engine. The 93*ABDC intake closing event is really very long, and the port that I saw in the AVL would have to rev quite high to be able to support that late of an IVC event. And at the same time, the late intake opening timing shortens the overlap period enough to likely impinge on the overlap period needed for such higher rpm running that would be necessary to work with that late of an IVC event. Lobe centers in the 130 ATDC range are not typical in regular engines.  So, I think that retarding of the intake cam on this S Cam set is a little too extreme for my tastes.
The exhaust remains the same as before, since it is not retarded.

The side effects of this are that any time an intake cam closes the intake valve something like 20 degrees later than the cam that was taken out of there, there will be some compression effects. I would expect that the engine will need to go to a higher compression piston, and/or a 535 piston to take best advantage of this cam set. I realize that Bill Harris had installed this set retarded by a tooth, and his compression test didn't change much. I don't have an answer for that, but I wouldn't expect that situation to be typical. I think that was an anomaly which cannot be counted upon to happen. It shouldn't happen, given the specification change. I just can't account for it. When we do this sort of thing in the Iron Barrel, it always needs a higher compression piston to compensate for the cam timing change.
Anyway, be advised that you MIGHT likely need to use a higher compression piston and/or 535 piston to get the most out of this cam set. Obviously, it can work without that, but if the compression is brought up closer to max for the fuel being used, it can work even better. We always do it.

So, there you have it.
The S Cams are a pretty sporty cam set, IMO.
If I were using them myself, I would install them "on the dots" and do a compression test to see if I needed to increase it with the new cams. Always do a clearance check for piston-to-valve clearance, as B.W. suggests, when installing new cams, and/or increasing compression.
I would like to see them in an AVL with our port job and our hi-ratio roller rockers, pushing over .450" lift. That would be a real nice package there.
« Last Edit: February 09, 2014, 08:01:16 PM by ace.cafe »
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Re: s cams
« Reply #61 on: February 10, 2014, 09:22:33 AM »
Thanks, Ace!
 Just for clarity, the Electra X AVL engines have a rocker ratio of 1.1:1, so the valve lift will be a little more than the height of any cam lobe operating either of the valves.
 Also, I think the valve bounce is caused / aggravated with the STD cams, because the lobe is little more than a sudden 'blip' and the valves might be closing very suddenly and violently without much / any contact between cam follower and closing flank of the cam at critical RPM's, that they tend to bounce open again, off the base circles.
 With the 'S' cams having a longer duration, perhaps, even if a follower and closing flank of a cam lost contact with each other, soon after full lift perhaps, the valve may be closing before the base circle arrives under the follower and in doing so, softens the 'blow' and allows the valve to seat smoothly at the end of the cycle and the engine can carry on producing revs and power.
 B.W.

ace.cafe

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Re: s cams
« Reply #62 on: February 10, 2014, 12:37:13 PM »
B.W.,
Well, that little bit of rocker ratio is very helpful in a situation like this. So, I'm happy to hear that.

It seems to me that that the factory picked a spring that was just barely adequate for the  stock bike rev range application. Maybe they even intended it to be a type of rev limiter.
« Last Edit: February 10, 2014, 12:42:16 PM by ace.cafe »
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Re: s cams
« Reply #63 on: February 10, 2014, 12:51:42 PM »

It seems to me that that the factory just picked a spring that was not quite properly spec'd for the application.
I don't know about that, Ace, because I modified things a bit and fitted the Hitchcocks competition double valve spring set, as used for some 'Iron' engine tuning jobs, but they failed to stop the valve bounce. The standard AVL set up is a single, very strong spring, but this is no good either, obviously.
 I don't know if any reasonable spring set up would properly control the valves with the standard cams installed. I presume the exhaust valve probably bounces hard as well, but the inlet valve bounce will be killing the revs. Also, as already stated elsewhere, the valve stems and collets are receiving severe punishment when this valve bounce occurs and I have heard of several cases where the pushrod ends get thrown out of their [too shallow] sockets in the rocker ends, causing roadside breakdown - these rocker end sockets could do with some improvement, too.
 B.W.

ace.cafe

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Re: s cams
« Reply #64 on: February 10, 2014, 01:03:46 PM »
We will soon find out if the beehive springs will solve this on Tooseevee's head.

If they don't,  then it looks like there will be a lot of cam changing happening with the AVL engines.

Regarding the rockers, I would like to put the roller rockers on all these things, but I am concerned that the budget is too high for a lot of folks. It would require a new piston and pushrods, etc., along with all the head mods. That could get beyond many people's price range.
« Last Edit: February 10, 2014, 01:12:25 PM by ace.cafe »
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Re: s cams
« Reply #65 on: February 10, 2014, 06:02:13 PM »
Hi,

the stock rockers do seem pretty substantial, is there scope for lightening and polishing them safely?

Regards,

A.


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Re: s cams
« Reply #66 on: February 10, 2014, 06:44:37 PM »
Thanks, Ace!
 Just for clarity, the Electra X AVL engines have a rocker ratio of 1.1:1,
 

Hmmm. Compatible with the UCE/Iron Barrel engine ?? Say yes !

ace.cafe

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Re: s cams
« Reply #67 on: February 10, 2014, 07:09:29 PM »
Hmmm. Compatible with the UCE/Iron Barrel engine ?? Say yes !

No, the AVL has a large rocker housing with shaft type rockers. The UCE has block style rockers like the older Bullet, but not the same.

Theoretically, a billet housing might be made to use these AVL rockers, but it wouldn't be worth the effort for such a small change. We can do the billet housing for the UCE,  but we will do it with roller rockers and more lift ratio. Then the improvements will be more worthy of the expense.
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Bill Harris

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Re: s cams
« Reply #68 on: February 10, 2014, 08:04:09 PM »
There are several people out there that have installed 'S' cams in AVL powered machines.  I think it would be helpful to understand the benefits of the 'S' cams, where the rubber meets the road, if you with 'S' cams installed, would give us your experience, on this thread.  What it took to install the cams and how the cams effected your performance with out and or with other modifications to your bike. 

My experience with 'S' cams are:
I had intake valve to piston interference.  To remedy this, I timed the exhaust cam to the timing marks and the intake cam one gear tooth retarded.  The 'S' cams fit right into the timing chest just as the stock cams did.  No alterations to the chest needed. The bike runs very good.  I'm getting more RPMs out of the engine.  Don't know just how many, I don't have a tachometer.  The bike can make 75 mph in forth gear and 80 mph in fifth.  I got 160 psi on my compression check with the 'S' cams, intake cam one gear tooth retarded.  I got 155 psi on the stock cams timed to the marks.  These compression checks were made with a 30mm PWK flat-slide carburetor, K&N pancake air filter, and a free flowing, upswept exhaust with the Indian made classic short silencer installed.  I also have very good low speed throttle response.  The bike is running stock gearing with a 18" rear wheel.  The engine has a very useable and predictable power ban.  All of this is on 87 octane fuel.  I'm very happy with the performance with these modifications.  I think the 'S' cams are a good addition to the overall performance of the Harris Scrambler.   

Cheers,
Bill
« Last Edit: February 18, 2014, 04:29:24 PM by Bill Harris »

ace.cafe

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Re: s cams
« Reply #69 on: February 10, 2014, 08:42:12 PM »
Hi,

the stock rockers do seem pretty substantial, is there scope for lightening and polishing them safely?

Regards,

A.
Adrian,
I would say yes, but obviously there would be limits on the amount of metal to remove. Lower moving mass is good for higher revving. Polishing is more for removing pits and sharp inside corners, or any other surface imperfections, for the purposes of removing likely stress - risers that may develop into cracks. The polishing part can be done all you want. The removal of metal needs to be judicious,  using your best judgment, so as to avoid weakening the part.
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ace.cafe

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Re: s cams
« Reply #70 on: February 10, 2014, 09:01:05 PM »
Bill,
It sounds to me like you got the results that I would expect from the mod. And you obviously did a careful job with all the right checks to be sure that it would be okay, and you found a piston - to - valve clearance issue, and you corrected it, and you did the compression tests with the results in the area which we would want.
So, I am not casting any doubt on your installation or results. You diligently executed a successful installation,  using proper methods.

However, there are variations in Enfield parts and castings which can be seen when dealing with one machine to the next. Yours might have been one way, but we might see differences in other engines. Apparently Paul has noticed these variations too. There could be any number of reasons for it.
So, you did the right things, with all the proper methods, and got a good result. I applaud you for that.

The results should be mostly seen in upper rpm power, with little or no reduction in low rpm torque noticed, as long as care is taken to be sure that the compression did not fall from the modifications.  If it does, we have some remedies to deal with that, on an individual basis, based on what is being seen in the particular engine in question.

BTW, 80 mph with stock gearing is probably very close to 5000 rpm in top gear. Depending on how high the sidewalls are on your rear tire, it might be just a little above or below that rpm.
« Last Edit: February 10, 2014, 09:06:31 PM by ace.cafe »
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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Bill Harris

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Re: s cams
« Reply #71 on: February 10, 2014, 11:56:21 PM »
Thanks, Ace

Royal Enfield people are good people

Cheers,
Bill   
« Last Edit: February 15, 2014, 07:13:38 PM by Bill Harris »

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Re: s cams
« Reply #72 on: February 15, 2014, 08:16:09 PM »
The machine I installed the 'S' cams into, with the inlet cam retarded by 1 tooth left here today. The owner arrived by train and rode it home some 70 miles or so. I asked him to let me know how it all went and he phoned to say it went very well and he is very happy with it. That will do for me.  ;)
 B.W.

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Re: s cams
« Reply #73 on: February 15, 2014, 08:43:27 PM »
+1  :D
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ace.cafe

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Re: s cams
« Reply #74 on: February 18, 2014, 12:42:45 AM »
Yep.
If they are happy, that's what counts.
Good to hear.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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