SteveM928

I know that the earlier cars don't have any cam timing adjustment, and that the cam sprockets are just located on the ends of the cam using a key and keyway method. I think the idea of a variable cam timing device, that would change cam timing while driving, would be a good idea. For a fixed cam timing change why not just use offset keys for the cam sprockets though?

PorKen

I need to adjust the vacuum modulator, it shifts down too easily now.

I keep saying to myself, well, this is as good as it gets, but I am still amazed that there are still small, but noticeable improvements to be made. The car was a total pig when I bought it - I never thought it would be as nice to drive as it is now.
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heinrich,

You have to leave off the middle and left TB covers in order to install the gizmo, and the 32 valve cars use the covers for the distributor cap? With custom covers, maybe.

The 32V engines have adjustable pulleys anyways.
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SteveM928,

Offset keys would work, but this setup is easier to install, and more finely adjustable. I've worried about the strength of offset keys also.

The plate gives me a platform to build on for a variable system.

SteveM928

How strong would they have to be? The bolt on the front holds the sprocket on the cam. The cam timing on the later cars is adjustable. That key never even touches the sides of the slot in the sprockets on those cars.

PorKen

SteveM928,

The passenger cam gear would be a good candidate for an offset key, 2 or 3 degrees would get the cams pretty close.

If you did not have to change back and forth often (emissions tests), then a 3 degree for the crank gear (for the 3 speeds especially) would work.

If anything, it would give me more timing belt slack to work with for a variable system. I could retard the crank gear by 6 or both cams by 3, and then have only to advance...

Anyways, where to buy an offset key?

drnick

porken,

what would be achieved through varing the valve timing?

drnick

porken,

what would be achieved through varying the cam timing?

PorKen

Took her up to 130; she pulls much better over the century. The accelerator feels like I'm stepping on a big juicy steak; less pedal required for the same speeds.
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drnick,

To paraphrase Wall Street: "Torque low, Horsepower high".

Advancing the cams raises and moves the torque peak down in rpms, at the expense of maximum horsepower. Retarding should raise the HP max + peak, while sacrificing TQ.

My goal is to make a 7 degree movement. 3 advanced below (4000?) and 3 retarded over. In theory, +5 TQ, 600 RPM lower, moving to +5 HP (600?) RPM higher. Overall, HP should be 10 higher than the fixed 3 degree advance.

Someone's bound to ask: "why all the work for 10 HP?". Answer: "Because it's there". Real answer: driveability, especially with the 3 speed automatic.

heinrich

"The accelerator feels like I'm stepping on a big juicy steak"

sparks

porken,

recently replaced head gaskets, and had heads surfaced. Was 1/2 tooth off prior to that too. My car had 77k miles at time of purschase and engine did not look "messed" with.

PorKen

sparks,

How's you're idle? A little 'lumpy'?

sparks

porken,

Yes it was. idle was "hunting" too. I suspect a vacuum leak. Motor being re-gasketed now. It was not smooth. I'll know more whan it's all toegether and running. Sure would be nice to have cams in sync.

918-S

I'm new to the 928 motor. I have a 1980 euro spec "S" motor in a Porsche 914. The project is nearing completion. I'm renewing the timing belt now. I noticed the right cam gear (passanger) timing marks don't line up perfectly. The left cam and crank are right on. Is this normal? I thought this may be from an off brand belt torerance or something. would your device correct this or is acceptable?

Sorry about the link. I thought it would go directly to the progress thread on the 914club.com BBS. I'll post some pics here.

progress of the Alien

PorKen

Just back from the dyno with the new setup. Cams sync'ed, 3 degrees total advance.

Rear wheel SAE: 190 HP/220 TQ (* 20%: 228 HP/264 TQ)

The torque curve is now a plateau. Near dead flat at ~220 from 3100 to 4300 rpm. When I last dyno'ed at 3 degrees, without the sync, it was peakier.

No increase in peak power, but torque levels are higher, farther down in rpm now.

My city gas mileage has improved, even with the dyno runs!!!
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sparks,

Please PM me or post when you have your engine together, I'm curious to see if the gasketing helped or if you still have the same idle.
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918-S,

Your 300HP 914/8 is going to be insane to drive! (I couldn't find any pics or topics easily with your link, post some pics, or a more direct link, please.)

From my experience, I can say that even a few degrees of advance/retard moves the HP/TQ levels around and that matching the marks on my engine made the idle smoother, and improved acceleration with the automatic.

A small movement of the cam gear doesn't look like much, but it actually a few degrees. For example, from one edge of the cam V to the other is about two degrees (four at the crank).

Ideally, I would think that since your car is so light, you would want to retard your cams slightly, to reduce the low end torque (wheelspin), and raise the HP.
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I'm looking for an offset key to get the marks close. Then I'll use my gizmo to dial it in perfectly, and make adjustments over time.

918-S

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918-S,

Your 300HP 914/8 is going to be insane to drive! (I couldn't find any pics or topics easily with your link, post some pics, or a more direct link, please.)

From my experience, I can say that even a few degrees of advance/retard moves the HP/TQ levels around and that matching the marks on my engine made the idle smoother, and improved acceleration with the automatic.

A small movement of the cam gear doesn't look like much, but it actually a few degrees. For example, from one edge of the cam V to the other is about two degrees (four at the crank).

Ideally, I would think that since your car is so light, you would want to retard your cams slightly, to reduce the low end torque (wheelspin), and raise the HP.
...

I'm looking for an offset key to get the marks close. Then I'll use my gizmo to dial it in perfectly, and make adjustments over time. [/B][/QUOTE]


Thanks for the info. I thought my link would go directly to the thread on the 914club.com BBS. I'll post some pictures on this site.

Do you know where I could locate off set keys to achive what you suggested?

sparks

porken,

I'll post results, but will be a while. still waiting on a few parts. The BMW belt tensioner you found, what is the part number?