About time for the spintron

Heavy lifters create loft. Some loft is desired in this case as it makes for additional duration at high speed. Loft is OK as long as the lifter "lands" on the right area of the cam.

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hm ok that agrees with other engines valve trains not bothered as much by mass on cam side of rockers. It did occur to me that a one use record attempt engine might use cam that would slap valves open extra fast-high then try to slope cam to catch em for somewhat softer landing. It takes a mean hard heart to treat quaint Norton engines like this. !0,000 rpm valve train on top of 10,000 rpm crank pistons jerking, makes us all swoon. Hm sounds like that exhaust flow could make a decent size turbo happy to add its boost to gear up taller-wider for.

hobot said:

Heavy lifters create loft. Some loft is desired in this case as it makes for additional duration at high speed. Loft is OK as long as the lifter "lands" on the right area of the cam.

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hm ok that agrees with other engines valve trains not bothered as much by mass on cam side of rockers. It did occur to me that a one use record attempt engine might use cam that would slap valves open extra fast-high then try to slope cam to catch em for somewhat softer landing. It takes a mean hard heart to treat quaint Norton engines like this. !0,000 rpm valve train on top of 10,000 rpm crank pistons jerking, makes us all swoon. Hm sounds like that exhaust flow could make a decent size turbo happy to add its boost to gear up taller-wider for.

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Keep in mind that valve loft is useful for a race engine where the rpm range and expected life is limited.

Good valve loft at high speed can be bad valve loft at lower speed which may cause damage on a street motor. Jim

Right - O and why I said for a one shot record attempt engine that only had to last a few trips down drag strip, min or two on paved mile runs and 10 miles or so on salt lake. When you started the spintron testing you left our ordinary street Commandos back in dark ages.

I would like to understand a little better about the radiused lifters. Over all lift stays the same but the opening and closing are slowed down, correct? The radius grind on the lifter giving a bit more gentle push off and a gentler landing. It seems like it may reduce the duration just a bit. But maybe not, may just make the beginning and end of the duration a bit slower so that the effective flow should be reduced a little. On the asymmetrical ground lifters it would seem to me that the take off would be almost as fast as the flat lifter but the landing is gentler and drawn out. Am I correct about this? Could radius grinding be a method of making a hot cam more mellow or torquey?
Dan.

motorson said:

I would like to understand a little better about the radiused lifters. Over all lift stays the same but the opening and closing are slowed down, correct? The radius grind on the lifter giving a bit more gentle push off and a gentler landing. It seems like it may reduce the duration just a bit. But maybe not, may just make the beginning and end of the duration a bit slower so that the effective flow should be reduced a little. On the asymmetrical ground lifters it would seem to me that the take off would be almost as fast as the flat lifter but the landing is gentler and drawn out. Am I correct about this? Could radius grinding be a method of making a hot cam more mellow or torquey?
Dan.

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Adding a radius to a lifter decreases the effective duration. That is the duration at a lift that is high enough to provide cylinder filling. Usually .040 to .050 inch.

It does not decrease the seat to seat duration.

It does increase the duration between the end of effective duration and the seat. IE- the ramp duration.

I commonly will add a radius to a flat lifter cam to make it more friendly on the street -without loosing lift. It's often a good way of increasing mid range torque.

You can nearly always add some radius to a lifter if the cam is designed for a flat lifter. A 4 or 5 inch radius is almost always safe. A smaller radius than that and you better be doing some cam mapping to check accelerations around peak lift.

The idea of the non-symetrical grind or profiling the lifter is to control the ramp times while maintaining the most area under the curve for flow. Jim

Jim, would the end game here be developing a special cam with appropriate ramps for the high speed applications envisioned or is this too much of a one-off; best handled by offset cam follower radiuses?

Dances with Shrapnel said:

Jim, would the end game here be developing a special cam with appropriate ramps for the high speed applications envisioned or is this too much of a one-off; best handled by offset cam follower radiuses?

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I wouldn't say I have given up on that idea, but finding someone with a CNC grinder who is willing has been difficult.

Of course I can have masters made which get's a bit expensive for a cam or two and I would want to be damn sure they are what I want before I did that.
I suspect the market for 10,000 rpm Norton cams is pretty thin.

Profiling the lifters gives me the ability to adjust things till I like them so at this point it makes the most sense. I would still like to see if I can get the 86C grind to run at that speed.

Hi Jim, given what you have found with these latest tests, what rpm do you think the PW3 cam would be good for before sending the valves & springs into a tizzy with the asymetrical stock lifters using the IRL springs?
Be interested to see if there is any possibility of the BSA lifters being used . JS may have some input down this path perhaps.
REgards Mike

Brooking 850 said:

Hi Jim, given what you have found with these latest tests, what rpm do you think the PW3 cam would be good for before sending the valves & springs into a tizzy with the asymetrical stock lifters using the IRL springs?
Be interested to see if there is any possibility of the BSA lifters being used . JS may have some input down this path perhaps.
REgards Mike

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With the PW3 -the cam flex put me off of trying to make it work with heavier springs. I am sure it could be helped some with a radius lifter.

The JS2 is different because it is ground for BSA lifters. The different profile means there is nothing to be gained by offsetting or profiling the lifter.

I tried it, I even recorded it. It's with the dozen other complete failures I recorded. Jim

Hi Jim, I'm not familiar with all these interchangeable British parts and wondered why you haven't made some BSA lifters with enough material in the right place to put a radius on like you want to try? If its a matter of not enough time I can understand that but they look like a simple part compared to all the other work you've done. Really interesting read and want to be at the salt flats to see and hear it run!

edgefinder said:

Hi Jim, I'm not familiar with all these interchangeable British parts and wondered why you haven't made some BSA lifters with enough material in the right place to put a radius on like you want to try? If its a matter of not enough time I can understand that but they look like a simple part compared to all the other work you've done. Really interesting read and want to be at the salt flats to see and hear it run!

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Lots of things look easy

I wanted to source some BSA lifters and had a dialogue with SRM, BSA specialists, over a period of time. The stellite foot used on various vintage british designs requires a specialist process to join it on to the lifter. I understand tha this is not only expensive, particularly for low volume, and that cost will come over in the price to you, but it is something not many component manufacturers are doing today.

One assumes that AN have managed to do purchasing at a suitabe volume to maintain the price where it is for stock Norton lifters, whichh use the same process. Way back when BSA were making these parts they had the capability to do it in house.

SRM were prototyping and testing alternative BSA lifter manufacturing processes. They were unhappy with the results after testing, so they did not go to market. (maybe later with more prototyping and testing, I am sure there are a few BSA owners hoping that will be soon).

When Jim said earlier in this thread he had used a set of NOS BSA lifters, I had assumed that was because that is all that is currently available.

Relating to the JS2 cam spintron test Comstock made earlier. Here’s a pleasant surprise. The BSA spitfire/JS0 closing ramp is a perfect match with the 86C. I have been trying to get megacycle to splice it onto the PW3/JS2 cam (price depending and researching). This would give it a gentile ramp and help eliminate bounce. The JS2 gives the same valve action as the PW3 but for lighter BSA lifters and made of billet steel instead of iron.



Looking at the BSA spitfire/JS0, Axlell#3/JS1 and D+/JS3 cams – they nearly match the smooth ramp of the 86C that Comstock has shown us. The difference is that the JS1 (Axtell#3) tail is 5 deg shorter that the 86C which shouldn’t make much diff. The JS3 is the D+ cam (blue) but for BSA lifters and its tail is 10 deg shorter which could make a diff – not sure. None of these cams would have the bounce problem that the PW3 has with its abrupt ramp. So I’m not sure they need changing unless you’re going for a 9000RPM short stroke



Ben G (domni expert) told me that Peter Williams designed the PW3 to get the valves opened and closed as fast a possible. This works great and gives best performance until you get over 8000 RPM when both valves are bouncing and the springs are loosing it.

BTW - last I heard, SRM hasn't given up on the BSA lifters yet and are trying another source.

Note that I when I compare profiles I am actually comparing the flat lifter movement to the radiused BSA lifter movement. When flat lifter cams are compared to the same cam made for radiused BSA lifters - the cam and lifter shapes may be different but the lifter and valve movement is the same - for instance - the JS1 lifter and valve movement is the same as the Axtell #3 lifter and valve movement.

Note that I when I compare profiles I am actually comparing the flat lifter movement to the radiused BSA lifter movement. When flat lifter cams are compared to the same cam made for radiused BSA lifters - the cam and lifter shapes may be different but the lifter and valve movement is the same - for instance - the JS1 lifter and valve movement is the same as the Axtell #3 lifter and valve movement.

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JS
taking your above statement as implying that the valve lift profile is the same although the lifters are different, in the case of the PW3 it means that nothing has changed except the lifters. The design features within the PW3 profile that are causing the valve bounce at high engine speeds are there in both flat and radius lifter outputs.
The basic problem with trying to run the PW3 at high engine speeds is the rate of valve accelleration in both opening and closing. For the engine speeds for which the cam was designed (up to 7500 rpm max.) the rate of accelleration is indeed agressive, but was designed to be so in the interests of presenting the maximum area under the lift curve while keeping the overall open duration relatively short. As designed, the PW3 opening accelleration moves from initial valve opening to maximum accelleration in some 18 degrees - nearly 1/5th of the total valve open period to max lift. This is an incredible short time period, and is repeated on the closing side of the profile.

By designing in this manner, PW ensures the valve train has approx. 4/5th of the opening period to slow the mechanism down as the lift moves over peak. Great for control at maximum lift, no valve lofting or valve train component separation.

The problem when trying to push the PW3 into the higher engine speeds is the short period from peak closing accelleration to the actual seating of the valve. It really comes down to a simple problem of time.

Modifying the ramp at the foot of the lift curve is not where the problem originates from, but it comes from earlier on the closing flank.
In an earlier post Comnoz presented a valve lift comparison of a cam with the results of a flat lifter measurement and a radius lifter meaurement super imposed. From the graph it can be clearly seen where and by how much the accelleration differs between the two measured profiles.

By changine the accelleration periods at either end of the design to be twice the original length, while still keeping the maximum designed valve lift, the rate of accelleration is drastically reduced, but unfortunately at the cost of having to accommodate a much longer overall duration.
Not in the interests of general road use I fear, but might have some possibilities in an extended rpm short stroke race engine.

Snotzo

To make sure we are on the same page.

Ist given is that the PW3 cam for flat lifters and the JS2 cam for BSA lifters have the same (or very nearly the same) valve action duration and lift etc.

You are saying first that it doesn't matter what lifters are used - heavy flat stock lifters or lightweight BSA lifters. To answer this question look at Comstocks test of the JS2 to the PW3 cam AND THEN look carefully at my response in a post soon after. Even though Comstock used the best springs he could find for the PW3 cam (Honda). The JS cam with the Beehive springs performed significantly better.

Study the videos that I placed one above the other in my post about the JS2 cam compared to the PW3.
The PW3 with dual Honda springs started valve bounce at 5000 to 5500. The JS2 cam started a tiny bit of valve bounce at 6000.

PW3 had 'severe" valve bounce at 7000. The JS2 had some more bounce at 7000 to 7500 but things did not get bad until above 8000

Now here is where you have to pay attention and make note. When the ex valve starts to bounce it can tangle with the intake valve. This is where you should draw the line on RPM limit for a cam.

The PW3 begins to have ex valve bounce at 7000 and has bad intake and exhaust bounce at 7500.

The JS2 does not have ex valve bounce until 8500 - thats a 1500 RPM advantage of the JS2 over the PW3. There is also spring distress with the JS2 at 8500.

The PW3 gets 2 bounces each on intake and ex at 8000

Also - concerning your statements that the problem with the PW3 is further up on the descending flank. If you look at the 86C cam to the PW3 graph that Comstock superimposed you can see that the descending ramps are nearly parallel and identical. There is more duration and lift with the 86C but the shape is nearly the same - the big diff is the closing ramp and that is obvious.

I'm not knocking you Snotzo. I respect what you say even if I don't agree. You have a great mind and you can run math circles around me. And I hope to get some help from you with some cam conversions I plan on (waiting for cams to be loaned).

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Here are the PW3 to JS2 comparison test I'm talking about below. I hope I got my facts right.

[video]https://youtu.be/L0_pud6vcuw[/video]

PW3 cam above
JS2 cam below

[video]https://youtu.be/ol5Pp2_FA3o[/video]

jseng1 said:

Snotzo

Even though Comstock used the best springs he could find for the PW3 cam (Honda). The JS cam with the Beehive springs performed significantly better.

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The bounce between the two cams was similar with lower spring pressures.

I used much higher spring pressure in the video with the JS2 cam than I did in the video with the PW3.

The one difference was the JS2 bounce did decrease more as the spring rates got very high where the PW3 would only get better to a point and then seemed to level off.

I can't say for sure, but I attributed this to cam flex which was substantially higher with the PW3 and got worse with additional spring pressure. Jim

jseng1 said:

...This would give it a gentile ramp

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As opposed to a Jewish ramp? 'Sorry; I couldn't pass it up!

Keep it up, guys. This is the thread I jump on anytime I see that it's been updated. I especially appreciate the amazing amount of solid engineering research that's been shown here. Between the graphs and spintron video, I may never get any sleep! I think we've already passed Mr. Yates record for most pages.

Nathan

Comnoz

When racing I always stacked the springs up to the coil bind safety margin and I recommend that in the cam instructions for racers only. I never had a tach - just revved the motor as high as it would go and got to recognize the sound of valve float.

I want to give some credit to Snotzo for his offset lifter contribution. I tried it on the BSA lifters and got a quicker opening ramp accelleration but little or no change on the decending ramp where its needed. I have one more experiment to try though.

Nater - maybe we should try circumcising the lifters?

jseng1 said:

Comnoz

When racing I always stacked the springs up to the coil bind safety margin and I recommend that in the cam instructions for racers only. I never had a tach - just revved the motor as high as it would go and got to recognize the sound of valve float.

I want to give some credit to Snotzo for his offset lifter contribution. I tried it on the BSA lifters and got a quicker opening ramp accelleration but little or no change on the decending ramp where its needed. I have one more experiment to try though.

Nater - maybe we should try circumcising the lifters?

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I always went to about 135 lbs max on the seat. If that gave me a spring that was .050 to .070 from bind it was perfect.

I always figured if you needed more than 135 lbs on the seat with a Norton then it was time to do something else. Jim

JS
I never mentioned the exhaust cam, and was focussed only on the intake as that is also the focus of the spintron runs.
The exhaust side is an issue that I will come to later if it's of interest.

Take any Commando cam that was designed to run with the standard flat follower, measure and plot the lift curve . From this data set it is possible by differentiation to determine velocity, acelleration and jerk.

Take another set of measurements, but this time substitute the BSA lifter for the flat.

You will have the same total cam lift and the same cam duration, but when you examine the acelleration you will note a significant difference. Maximum positive acelleration on opening and closing will be lower with the radius follower than it is with the flat, but negative acelleration up to the nose of the cam will be greater (it slows down faster!).

You will also find the area under the cam lift curve is again less with the radius follower than it is with the flat.

The radius follower eases to a considerable extent the agressiveness of the initial flat follower design, and benefits can result in the reduction of bounce and separation.

In the case of the offset follower modification, the purpose was to keep closer to the flat follower opening rate, but with the offset retain a closing rate very similar to that of the radius follower.

That it has worked is shown on the spintron test runs, and Comnoz has further modified the follower to reduce the opening losses to practically zero.

To design a profile for use with a BSA follower so that it would exactly mimic the measured cam lift of a flat follower design is not an impossible task, but it is hardly necessary for a street engine, and would only be of interest to those involved in high engine speed applications such as racing, drags and such like.

The exhaust valve was not something I was concerned about and I only gave it enough spring pressure to avoid interference -using an old spring.
I only installed the JS springs on the intake. Jim