Twincam Camshaft detail measurement

[snowyelan]

Could the discrepancy be from the follower rocking in the bore? The cam starts applying force on one side of the bore centerline and as it passes center the follower could be rocking. Since your indicator is off center this would show up in your graph.

[rgh0]

Could the discrepancy be from the follower rocking in the bore? The cam starts applying force on one side of the bore centerline and as it passes center the follower could be rocking. Since your indicator is off center this would show up in your graph.

Good thought and i will check it out

cheers
Rohan

[Ianashdown]

Is the L1 considered to be suitable for road use? Presumably requires larger valve sizes to get this power, which in turn means modified pistons. What CR range is ideal?

Thank you,

Ian

[2cams70]

Could the discrepancy be from the follower rocking in the bore? The cam starts applying force on one side of the bore centerline and as it passes center the follower could be rocking. Since your indicator is off center this would show up in your graph.

Do you need to measure the lift at the follower? Can you measure it by direct contact of the micrometer plunger on the lobe itself rather than the follower? Perhaps try doing it both ways and see what the difference is?

[rgh0]

Hi Ian

The L1 cam is sort of OK on the road but its lack of mid range torque compared to shorter duration (280 to 285 seat to seat) and 0.41 to 0.44 lift cams is noticeable. I have a McCoy 460 inch lift cam in my Elan currently and that with its longer duration of around 290 degrees seat to seat is nowhere near as good on the road as the McCoy 440 cam. It does have about 10 more HP on the dyno at the top end but is no faster in lap times on the track with its lower torque mid-range costing time out of the corners.

You are rarely using 7000 rpm on the road even if you have an engine that will achieve that so no real point in a 300 degree duration cam like the L1 that is best between 5000 and 8000 rpm. The L1 cam is older technology with its lower accelration and velocity. The McCoy 440 lift cam has signficantly higher accelerations that are possible these days with better spring materials and better cam profile generating software. I would like to measure up the QED 420 cam to see what thats like but dont know anyone in Australia who has one sitting around

I have 10.7 comp ratio in my Elan currently which works with Australian Premium unleaded 98 Octane and the 280 degree McCoy 440 cam. Using a longer duration cam I could probably push the compression ratio a little higher

cheers
Rohan

[rgh0]

Could the discrepancy be from the follower rocking in the bore? The cam starts applying force on one side of the bore centerline and as it passes center the follower could be rocking. Since your indicator is off center this would show up in your graph.

Do you need to measure the lift at the follower? Can you measure it by direct contact of the micrometer plunger on the lobe itself rather than the follower? Perhaps try doing it both ways and see what the difference is?

Yes its looks like the follower i am using is rocking in the sleeve slightly. I have some new followers and will do some further measuring to see if I can eliminate the rocking and glitch in the curves. but if its sleeve wear rather than follower wear there is not much I can do to stop it without having a new sleeve fitted

The lift curve measured with just a point follower is different as the initial acceleration with a flat follower is greater as the cam lobe wipes across the follower. I have a 30mm diameter flat follower to screws onto my dial gauge and will do some experimentation with that also but as its a smaller diameter compared to the normal cam follower it may also not give true follower lift expecially for the higher lift larger lobe cams which run very close to the edge of the normal follower.

cheers
Rohan

[rgh0]

Measured up the sleeves in the old soft head i have been using for this test setup and they are excessively worn into the typical hour glass shape. i should have done this check earlier

i.e. 35.10 mm top and 35.15 bottom and 35.00 mm middle compared with a specification of 34.925 - 34.940 mm. i checked the follower movement in the sleeve as the cam goes over centre and yes the glitch in the curve is definitely due to the follower rocking in the sleeve.

I have a 30mm diameter follower that fits to my dial gauge and have set that up to directly measure the lobe. The lobe nose comes very very close to contacting the edge of this follower with the 1.06 inch base circle, 0.412 inch lobe lift cam fitted now. i will do some meausrements to see how well this lines up with the previous follower curve especially when the lobe contact point may be on the edge of the follower for a period and where the glitch occured due to the follower rocking

However away for a week so all that will have to wait a while

cheers
Rohan

[snowyelan]

Hi Rohan,
As a possible alternative you could add a 2nd indicator diametrically opposite the first and average out the 2 measurements. Your indicator may have a similar issue as the follower depending on its internal spindle to bore clearance. Its all in the details, or, in this case, the tolerances.....

[mbell]

The lobe nose comes very very close to contacting the edge of this follower with the 1.06 inch base circle, 0.412 inch lobe lift cam fitted now.

A friend was looking at a head that had been (very) modified for very high lift cams, said it had angled cam followers fitted. I think this was to give more space for the cam nose but might be wrong on that.

[rgh0]

Hi Rohan,
As a possible alternative you could add a 2nd indicator diametrically opposite the first and average out the 2 measurements. Your indicator may have a similar issue as the follower depending on its internal spindle to bore clearance. Its all in the details, or, in this case, the tolerances.....

There is no observable rock in the dial gauge shaft compared to the follower in the worn sleeve as the cam lobe goes over centre and it will be less sensitive anyhow as measuring in the middle of the dial gauge follower compared to the edge of the follower in the head . But until i take some detailed measurements in a weeks time I will not know.

cheers
Rohan

[rgh0]

The lobe nose comes very very close to contacting the edge of this follower with the 1.06 inch base circle, 0.412 inch lobe lift cam fitted now.

A friend was looking at a head that had been (very) modified for very high lift cams, said it had angled cam followers fitted. I think this was to give more space for the cam nose but might be wrong on that.

Interesting that something like this has been done. I have heard of larger diameter Alfa followers being fitted but not "angled" followers. In a race engine you normally have to cut the little half moons in the head and sleeve a little larger and dpeeper to clear the cam lobe nose.

Not sure how angled followers would work as the follower has to rotate slowly in service and the cam lobe is slightly tapered to do that

cheers
Rohan

[mbell]

Not sure how angled followers would work as the follower has to rotate slowly in service and the cam lobe is slightly tapered to do that

I believe the followers were pinned to stop rotation. I suspect this was very high power, short life race engine build...