timing chain upgrade?
05-15-2015, 06:04 PM
#46
Rennlist Member
Ken, I wish I was being sarcastic, that would fit in with the general tone whenever the tensioners are "discussed".
What I am referring to is Greg's description of belt stretch and the relationship to timing. I am not referring to the merits or pitfalls of your tensioner vs. his. I figure you two can continue to hash that out with no end in sight.
What I am referring to is Greg's description of belt stretch and the relationship to timing. I am not referring to the merits or pitfalls of your tensioner vs. his. I figure you two can continue to hash that out with no end in sight.
05-15-2015, 06:13 PM
#47
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Seriously. Get over it.
Same thing that happens with the stock tensioner system, minus the flapping.
To the factory settings. (This is much easier done with the PK32V'r, BTW.)
You must spin the engine with the starter to settle the belt into the gears and equalize the tension between the gears, first.
Equalizing the belt tension should be done using the dial indicator too. This is why you can't set the timing accurately on an engine stand. You may max out the belt tension to try and get consistent results, but what happens when you run it at normal levels? As you have now noticed, the lower tension will affect the timing. Then the belt stretches from new to old. Then it stretches from low rpm to high rpm. Then the engine warms up...etc, etc.
Obviously you are still not listening to what I keep talking at you. It does not get significantly tighter. Under steady state running the tension level with the Audi T/D will equalize in a few seconds when warm. Tensioner. Dampener.
As I say, again and again, the cam timing will always be dynamic, never exactly what one would like it to be. Probably best to either set the cam timing by equalizing the compression on the 1-4 and 5-8 banks, or by picking a particular RPM that you want the cams to be spot on, EG. at max HP, then using a timing light to check/adjust the timing until they hit that target together. Like the cams themselves, there's always going to be a trade-off, some range where it works best.
Same thing that happens with the stock tensioner system, minus the flapping.
To the factory settings. (This is much easier done with the PK32V'r, BTW.)
You must spin the engine with the starter to settle the belt into the gears and equalize the tension between the gears, first.
Equalizing the belt tension should be done using the dial indicator too. This is why you can't set the timing accurately on an engine stand. You may max out the belt tension to try and get consistent results, but what happens when you run it at normal levels? As you have now noticed, the lower tension will affect the timing. Then the belt stretches from new to old. Then it stretches from low rpm to high rpm. Then the engine warms up...etc, etc.
Obviously you are still not listening to what I keep talking at you. It does not get significantly tighter. Under steady state running the tension level with the Audi T/D will equalize in a few seconds when warm. Tensioner. Dampener.
As I say, again and again, the cam timing will always be dynamic, never exactly what one would like it to be. Probably best to either set the cam timing by equalizing the compression on the 1-4 and 5-8 banks, or by picking a particular RPM that you want the cams to be spot on, EG. at max HP, then using a timing light to check/adjust the timing until they hit that target together. Like the cams themselves, there's always going to be a trade-off, some range where it works best.
Have you ever compared what Gates racing belt does compared to a stock belt?
No.
Until you get this basic research done, what you are saying is just your own personal theory...backed by no data, no specifics.
You should actually preface everything you say above with "I think"....or "In my theory". That would be truthful and accurate.....and that is exactly what I've been saying for the past ten years!
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greg brown
714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
05-15-2015, 08:14 PM
#48
Nordschleife Master
What I am trying to currently rationlize is whether the benefits of the high strength Racing belt outweighs passive cam retard. If one is going for maximum change from low to high rpm, you'd want to run the stretchiest belt - the Continental - which I ran on my S3 which peaked out over 310 RWHP, vs my S4 with a Racing which has peaked around 305?
What's nice about the Audi T/D system is that it can absorb anything from the Conti to the Racing and it runs at a lower static tension, allowing more length at high rpm...
What's nice about the Audi T/D system is that it can absorb anything from the Conti to the Racing and it runs at a lower static tension, allowing more length at high rpm...
Wouldn't there be a significant difference in the amount of "passive cam retard" from one side to the other?
Isn't there a significant amount of belt (distance) between the left side of the motor and the right?
So the left side would have the stretch from the oil pump up the side of the motor to the cam gear.
But the right side would have that stretch plus the stretch from the left cam gear, down to the water pump, then back up to the right cam gear.
(Note: I may have the specifics of the belt routing wrong.)
Wouldn't that be almost twice the distance? Which would offer twice the stretch? Which would give twice the "retard"?
How appropriate is it to have the right cam retarded twice as much as the left?
05-15-2015, 09:05 PM
#49
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While we talk about the timing belt tension as if it were a constant all that we measure is the static load of one span with the engine in one position on a cold engine. What is actually happening is quite a number of things but the basic fact is once running there is little or no tension on the span from the crankshaft around the tensioner pulley then up to the passenger camshaft. Which is why it flops around a fair bit. Each span of the belt is pulling a very different load depending on if it is pulling one cam or two plus water pump and oil pump. Different load work being done is a different tension if we could measure it 
Plus the HP required to spin all those things goes up with RPM which is why so many see the belt tension light come on after a high RPM event.
Plus the HP required to spin all those things goes up with RPM which is why so many see the belt tension light come on after a high RPM event.
05-19-2015, 02:54 PM
#50
Inventor
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Since Greg is probably making that up (as He is wont to do - prepare for excuses) and I have been wanting to see if I should retard my S4 cams with the Racing belt anyway, I have ordered a spare set of upper covers to cut a window in each to see for myself.
Note compared to the (non-adjustable) 16V cams, the WSM specs for 32V cams are advanced 2° crank from the cam key centerline. More specifically, the 5-8 cam is advanced 2° measured cold, whereas the 1-4 cam is at 0°. When the engine is warm, the 1-4 cam advances 2° due to engine expansion. (The 'zero' hole on the V2 PK32V'r is advanced so that 5-8 is 0° cold.) This could be a nod toward high rpm retard with a standard belt.
Although it'd be nice if there was a new cam setting for a bunch more power, I'm guessing that it's not going to make a big difference.