ALH Stock cam measurements

The complete lift report is on my kerma-diesel Yahoo discussion group file section.

Summary of lift specs at 1.25 mm (0.050 in) rounded:

IVO 20 ATDC
IVC 25 ABDC
EVO 24 BBDC
EVC 20 BTDC

Peak cam lift= 8.5mm

****and get this:

LDA= 135.8 degrees!!

I must have figured that last one incorrectly because it just seems too wide. The centerlines are at 112.1 degrees.

could you repost this info without all of the abbreviations for all of us newbies?

I'm not familiar with LDA, but based on your valve timing numbers, I calculate LCA to be 112.25 degrees, which is actually very "wide" for such a low RPM motor as the TDI is, but this is a function of the valve/piston clearance limitation that is inherent to this engine. Doubtless to say, any increase in duration by closing the intake valves later and opening the exhaust earlier will only serve to further widen the LCA, which favours higher RPM at the expense of the low.

The numbers agree reasonably with the specs from the Bentley, when you take into account the fact that the measurements are taken at different lifts, and also the likely possibility that the OEM cam has an assymetric profile (back-end profile not the same as front). Because of the very late intake valve opening, in order to not totally kill volumetric efficiency, the leading end of the cam may have a steeper ramp to increase the valve open area, especially at the early part of the intake stroke which is most critical to good VE. If you sketch this out (I have the benefit of CAD), you will clearly see how the discrepancy in reported timings occur (Kerma's numbers show IVO later and EVC earlier than the Bentley).

Kerma, can you share data of your modified cam? Offline if you wish. I have a spec in mind, which I have posted before, and am curious how close or far off I am.

Some work previously done on the subject, just dredging it back up...

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I'm not familiar with LDA, but based on your valve timing numbers, I calculate LCA to be 112.25 degrees, which is actually very "wide" for such a low RPM motor as the TDI is, but this is a function of the valve/piston clearance limitation that is inherent to this engine. Doubtless to say, any increase in duration by closing the intake valves later and opening the exhaust earlier will only serve to further widen the LCA, which favours higher RPM at the expense of the low.

The numbers agree reasonably with the specs from the Bentley, when you take into account the fact that the measurements are taken at different lifts, and also the likely possibility that the OEM cam has an assymetric profile (back-end profile not the same as front). Because of the very late intake valve opening, in order to not totally kill volumetric efficiency, the leading end of the cam may have a steeper ramp to increase the valve open area, especially at the early part of the intake stroke which is most critical to good VE. If you sketch this out (I have the benefit of CAD), you will clearly see how the discrepancy in reported timings occur (Kerma's numbers show IVO later and EVC earlier than the Bentley).

Kerma, can you share data of your modified cam? Offline if you wish. I have a spec in mind, which I have posted before, and am curious how close or far off I am.

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By "LDA" (A.K.A. Lobe displacement Angle) I meant what you call Lobe Separation Angle, the angle between the lobe centerlines.

I am debating whether I should post the modified specs until we see what the "competition" does, and we see the results on a dyno.

What I can say for sure is 231 degrees duration at 50 thousanths lift, and shorter LDA.

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"LDA" (A.K.A. Lobe displacement Angle) I meant what you call Lobe Separation Angle, the angle between the lobe centerlines.

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Sorry for being nitpicky, but I thought it's Lobe Duration Angle? I could be wrong...

A while back, someone posted some flow bench measurements from the TDI head. If I remember right, the graph showed valve-limited flow up to around 0.330" (8.4mm) lift and port-limited flow beyond that. The stock cams barely open the valves enough to reach port-limited flow ever! The valves are restricting the flow through almost the entire range.

This engine is crying out for more cam (regardless of what the "official" statements in the TDI-R tech paper said).

I'm not sure how much clearance we have between valves and pistons. 231 duration (compared to 185) with the same lobe centers would make opening 23 degrees earlier and closing 23 degrees later. The intake valve opening will be 3 degrees BTDC if that's right. This will be cutting it really close for valve-to-piston clearance unless cam profile trickery is used so that the intake valve "follows the piston" for the first bit of the stroke (with an allowance for being out of spec on the cam position).

Needs a little more lift, but not much (just enough to get it into the port-limited flow of the ports). What it really needs is to hang open at that point for a lot longer.

I'm really curious to see how well this works!

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The stock cams barely open the valves enough to reach port-limited flow ever! The valves are restricting the flow through almost the entire range.

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So would a MPG increase be notable from reduced pumping losses?

-Jack

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A while back, someone posted some flow bench measurements from the TDI head.

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That would be mine. /images/graemlins/cool.gif
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This engine is crying out for more cam (regardless of what the "official" statements in the TDI-R tech paper said).

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Maybe not in stock form, but modded...

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I'm not sure how much clearance we have between valves and pistons. 231 duration (compared to 185) with the same lobe centers would make opening 23 degrees earlier and closing 23 degrees later. The intake valve opening will be 3 degrees BTDC if that's right. This will be cutting it really close for valve-to-piston clearance unless cam profile trickery is used so that the intake valve "follows the piston" for the first bit of the stroke (with an allowance for being out of spec on the cam position).

Needs a little more lift, but not much (just enough to get it into the port-limited flow of the ports). What it really needs is to hang open at that point for a lot longer.

I'm really curious to see how well this works!

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Well, I can report that there are no valve clearance problems in my car! I used a thinner head gasket as well.