Need help with 964 cam thinking

[Discseven]

964 cams in '85 3.2 street. I'm in a conundrum over my timing and specs.

On one hand both cams are dialed in @ 1.25 mm overlap @TDC (with 0.1mm lash.) And, chain housing covers, oil plumbing to tensioners, saddle, AC supporting bracket, console, tin, valve covers... all those parts are back in place. With that done, now the elephant starts dancing in my head---that being the fact that opening & closings of the valves are slightly retarded according to my measures compared to specs. Question is whether to call 1.25 mm overlap done and move on, OR, take things apart (which I don’t mind doing if there’s sensible reason to) and set timing according to open & closing moments / lobe centers? Am chomping at the bit to keep moving forward BUT second guessing myself is a raised flag I want to consider. Point being, would rather deal with this now when the engine's on the stand in front of me... than deal with it after the engine's back in the car. Being no cam expert by any stretch, am stuck in a fine loop on this one. Help is needed.
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[mikedsilva]

Originally Posted by Discseven

964 cams in '85 3.2 street. I'm in a conundrum over my timing and specs.

On one hand both cams are dialed in @ 1.25 mm overlap @TDC (with 0.1mm lash.) And, chain housing covers, oil plumbing to tensioners, saddle, AC supporting bracket, console, tin, valve covers... all those parts are back in place. With that done, now the elephant starts dancing in my head---that being the fact that opening & closings of the valves are slightly retarded according to my measures compared to specs. Question is whether to call 1.25 mm overlap done and move on, OR, take things apart (which I don’t mind doing if there’s sensible reason to) and set timing according to open & closing moments / lobe centers? Am chomping at the bit to keep moving forward BUT second guessing myself is a raised flag I want to consider. Point being, would rather deal with this now when the engine's on the stand in front of me... than deal with it after the engine's back in the car. Being no cam expert by any stretch, am stuck in a fine loop on this one. Help is needed.
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I'm no expert either, but have found that advancing the 964 up to 1.5mm instead of the 1.26, results in a little more emphasis on torque down low as opposed to the top end HP. It's enough to notice, but not enough to make regret not doing it.

I suspect you'll be happy with your 1.25mm

[Discseven]

Originally Posted by mikedsilva

I'm no expert either, but have found that advancing the 964 up to 1.5mm instead of the 1.26, results in a little more emphasis on torque down low as opposed to the top end HP. It's enough to notice, but not enough to make regret not doing it.

I suspect you'll be happy with your 1.25mm

Mike… your vids speak volumes of your knowledge and the clean lines you work. Way you phrased the situation I’m dealing with is greatly appreciated. Pieces of my puzzle are now clear.

For the benefit of anyone chasing cam timing and dealing with a cam card, it can be a tricky affair. Reason: some measures call for valve lash and some measures are without lash then other measures begin at 0.05 inches of valve lift. Not being the sharpest tack in the board, it’s simple to say that deciphering a cam card spun my head. Am partially venting on the cam grinding industry for making this cam stuff more challenging than it might be. Would be easier if details for each measure given by a card were clearly noted however, faults mine for charging ahead without fully understanding the nuances of how the cam industry presents their specs. My point is, if you’re heading down this path, suggestion is: sort out a cam card’s info fully before shutting off easy access to your cams. I got the 1.25mm right but failed in genuinely understanding the whole of the card data when it was necessary to do so. Now I regret my hast.

Am stepping back from the engine room today—in peace—thanks to you Mike. Tonight or tomorrow morning will decide if opening the engine back up is the way of it or not.

Cam card I’m dealing with:

[Discseven]

If only I weren't so curious, well enough would be left alone...
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[mikedsilva]

Originally Posted by Discseven

If only I weren't so curious, well enough would be left alone...
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You also need to take into account piston/valve clearance. Not sure what pistons you have and whether they have valve reliefs, but the more you advance, the tighter your intake valve clearance will be (and the greater your exh clearance will be).

Check your intake valve/piston clearance first... pay attention to the first 20 degrees after tdc... if you have over 1.5mm clearance throughout, I'd try advancing a little. Then check again. Learn to enjoy the process so it's not a chore.

If that's not your thing, as I said earlier, pretty sure the 1.25 will be fine.

[Discseven]

Originally Posted by mikedsilva

You also need to take into account piston/valve clearance. Not sure what pistons you have and whether they have valve reliefs, but the more you advance, the tighter your intake valve clearance will be (and the greater your exh clearance will be).

Check your intake valve/piston clearance first... pay attention to the first 20 degrees after tdc... if you have over 1.5mm clearance throughout, I'd try advancing a little. Then check again. Learn to enjoy the process so it's not a chore.

If that's not your thing, as I said earlier, pretty sure the 1.25 will be fine.

Am calling my pistons stock but others have questioned this...




Intake piston/valve clearance below. (Was done from zero lash counting rotations of the adjuster screw until contact with piston was made. 1 rotation = 1mm.)

Degrees from TDC | Clearance in mm
- 26.5 | 9.5
- 20.0 | 7.23
- 14.8 | 5.9
- 09.5 | 4.89
- 06.7 | 4.45
- 03.0 | 3.9
- 01.0 | 3.6

TDC - Overlap

+ 00.1 | 3.5
+ 02.0 | 3.4
+ 07.5 | 3.28
+ 09.5 | 3.1
+ 14.5 | 3.25
+ 20.0 | 3.6
+ 25.8 | 4.52
+ 29.1 | 5.25
+ 33.0 | 6.1

Working on engine is a meditation of sorts. Time does not exist. Thinking is focused on a singularity. I quite enjoy that mindspace. Several days ago Webcam (Laurie) advised advancing the cams for more low end. Ian, in conversation suggested the same. Then, you followed suit. Thought about it for a while concluding a return trip would be quite worthwhile.

Am very curious to compare timing by lobe center as opposed to Porsche timing. By "Porsche timing" I'm referring to lift/overlap at TDC with 0.1mm lash.
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[mikedsilva]

that's heaps of clearance.
what does your exh valve clearance look like?

What was your deck height?

[Discseven]

Originally Posted by mikedsilva

that's heaps of clearance.
what does your exh valve clearance look like?

What was your deck height?

I did not check exhaust valve clearance (yet) Mike. After measuring intake, I figured if that clearance was good, exhaust would be too. Bad assumption? Am disassembling later today with exhaust check on the menu for tomorrow.

"Deck height," distance from the crank's centerline to the top of the cylinder? That measure I did not take. I did look at each piston after installing the cylinders with the cylinders retained and rotating each piston through TDC. Made sure no piston's edge passed beyond a cylinder's edge. Rods and cylinders are stock.
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[Discseven]

Exhaust piston/valve clearance below. (Was done from zero lash counting rotations of the adjuster screw until contact with piston was made. 1 rotation = 1mm.)

Degrees from TDC | Clearance in mm
Negative numbers are degrees ahead of TDC
- 26 | 4.2
- 18 | 3.15
- 12 | 2.75
- 07 | 2.69
- 04 | 2.67
- 02 | 2.75

TDC - Overlap | 3.2

+ 06 | 3.75
+ 12 | 4.25
+ 15 | 4.55
+ 25 | 4.58
+ 35 | 4.75

This and the intake clearances in post #6 were done with the overlap timing at 1.25 mm at TDC. I subsequently advanced the timing to 1.45 mm.

According to Webcam's cam card, the .05" intake opening (zero lash) spec is at 5 degrees BTDC. As that card reads, this would seem to be with a 1.25 mm overlap at TDC. I could not get the relationship between the Porsche mm method and the degree settings to correlate. My .05" reading with the 1.25mm setting was consistently at 1 degree BTDC. Advancing the cams to 1.45 mm increased the .05" open measuring to 3 degrees BTDC. To extrapolate for the sake of doing so, it appears that a 5 degree opening BTDC (as the cam card specs) would require a 1.63'ish mm overlap setting. That is provided the numbers calculate in linear form---am not sure they do and am no cam expert by any stretch of the imagination.

Lift and duration are very close to cam card specs but not dead on. My lobe centers were off some degrees compared to cam card spec but this fits with the .05" openings as noted above.

Having worn out my welcome at Webcam, am not going to discuss this matter with Laurie any more. So where am I with all this?

To deal with cams, obviously one must be careful with everything. Establishing TTDC, setting a wheel accurately, readings done with the .05" with zero lash method, the Porsche overlap readings in mm with 0.1mm lash... there's ample opportunity to make a mess of things going back and fourth between these methods of cam timing. Am I confident in my numbers / confident in my cams-to-crank relationship? Yes. Bearing in mind that someone else noted (not in this thread) that they did not get the cam card specs to correlate... am notably not alone in this cam card lack of correlation.

Bottom line... I'm good with 1.45mm matched sides at TDC overlap (my pref is +low end torque.)

...Thanks Mike for your participation in this journey.
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[mikedsilva]

Originally Posted by Discseven

Degrees from TDC | Clearance in mm


TDC - Overlap

+ 00.1 | 3.5
+ 02.0 | 3.4
+ 07.5 | 3.28
+ 09.5 | 3.1
+ 14.5 | 3.25
+ 20.0 | 3.6
+ 25.8 | 4.52
+ 29.1 | 5.25
+ 33.0 | 6.1

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What is your intake valve clearance, when at the 1.45mm setting?
I usually find around the 11/12/13 degree mark, to be the most critical usually...

If you have 3 as above though, that sounds like heaps. Which is why I asked about your deck height.

[Discseven]

Originally Posted by mikedsilva

What is your intake valve clearance, when at the 1.45mm setting?
I usually find around the 11/12/13 degree mark, to be the most critical usually...

If you have 3 as above though, that sounds like heaps. Which is why I asked about your deck height.

Way I figured clearance at 1.45mm is to subtract 0.2 from the 1.25mm measured clearances. (0.2 being what the advance in timing added to valve height.) You note 11,12,13 degrees being the most critical. As my data harvesting would have it, I did not get clearance figures for those degrees! Way I looked at it at the time, the curve---as I saw it in my mind's eye---showed no reason for concern. Even if going to a 1.45mm setting. Now, since you raise the topic, am compelled to sketch this out to genuinely visualize the clearance and curve...



This sketch plots the intake clearance in mm and degrees starting @TDC going to 20 degrees. Points are my clearance figures at the 1.25mm overlap setting so I'd subtract 0.2mm from these clearances to arrive at the 1.45 setting clearances. You good with that? The dashed line is the estimated clearance as degrees move forward. The open space in the plot is the "critical missing clearance data." What I conclude from this plot is the possibility for the tightest clearance (at 1.45mm setting) to be around 2.8mm. Would you agree with this projection? Am not wanting to lead you here. If you KNOW this 11,12,13 degree area to be dramatically different than a curve that would be deduced from this plot, say so. I'll have something new on my plate!

On the "deck," I did not measure either the crank to the cylinder tops or the piston top edges to the cylinder top edge. I did eyeball the latter to check that no piston edges were, each at TDC, higher than the cylinder edges. Am curious what you're considering in regard to deck height?

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[PeteKz]

Karl, great graph. Thanks for keeping us informed.

[Discseven]

Originally Posted by PeteKz

Karl, great graph. Thanks for keeping us informed.

Hey Pete... This has been an interesting journey. Advice you provided in the prior thread is great stuff! Thank you. Mike and I discussed clearances with the question being why mine seem to be rather abundant. Did I mess up the measure taking? Couldn't leave that in doubt. Went back in to find out. I did not. With the 1.45mm setting I advanced the cam timing to (from 1.25), the clearance measures are insignificantly changed. The data gap in my graph is filled in with my tightest reading being 3mm.
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[PeteKz]

You're using a different cam than I am. It is what it is. I know the M1 cam was designed to use all the clearance and duration possible with the stock style 3.0 and 3.2 pistons. That is probably what accounts for the 1-2mm differences in clearance between yours and mine. Put the engine back in and run it!

[eastbay]

If I read above correctly, the 1.45 is 3 degrees advanced? Maybe you could squeek 4 degrees?

I installed 964 cams at 1.26 on my last build, so will look forward to your driving reports.

Years ago I played with the 4 degree keyways on domestic V8s. The difference between 4 retarded and 4 advanced totally changed the character and drivability of the motor.

[Discseven]

Originally Posted by PeteKz

Put the engine back in and run it!

Moved engine to shop (from condo workspace) yesterday. Getting there... mm by mm.

Originally Posted by eastbay

If I read above correctly, the 1.45 is 3 degrees advanced? Maybe you could squeek 4 degrees?

I installed 964 cams at 1.26 on my last build, so will look forward to your driving reports.

Years ago I played with the 4 degree keyways on domestic V8s. The difference between 4 retarded and 4 advanced totally changed the character and drivability of the motor.

Correct Eastbay. 1.45mm @ TDC with 0.1mm lash = 3 degrees advanced timing. With 1.25mm = 1 degree advance, quick math suggests that every 0.1mm of adjustment = 1 degree of advancement. To be at 4 degrees, lift projects to be at 1.55mm. This being dangerous math, anyone reading this is advised to do their own measures and calculations given one's own particular engine config.

Having pizzed around with these cams for I won't say how long---with pleasure I might add in order to learn new stuff---calling this "done" has been creeping up on me.

Mike proposed timing to 1.5mm. That was my target. I bounced around for a while above and below 1.5. Eventually got to 1.45 torqued on both sides. At that point, is it worth chasing 0.05mm? For F1 guys it likely is. My call was no. Both sides being matched was more important to me. And there were other things to deal with.

Commentary on what performance is... I look forward to it!

In all this cam business, and as a side note, a look at where this all started...



That rocker "infected" its partner cam lobe. And so the getting of the 964s and what has amounted to a fine journey into camland.

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