When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If it was a an inline single cam engine the change in timing at a specific point in time eg as a particular valve (call it valve A) opens might be well be linear; (torque required turn the cam will increase with rpm due to friction.) The other factors affecting load on the belt - eg a different valve (valve B) closing tending to drive the cam and reduce belt load at the point that valve A opens would be constant for all valve timing events ie C opens (increasing load) as D closes (reducing load)
For an engine with more than one cam but driven by one belt, the load on the belt that the crank pulley sees would remain the same at a specific valve timing event when considering the effects above but the relative position of the cams would change depending upon which cam (1st or second on the belt) opening a valve etc.
does the force increase at higher rpm? the power required woud be greater, but isnt the force the same , hence the stretch , at equilibrium speed? (i.e. not accelerating) and if it is, the rate of acceleration being so slow, say in 3rd gear, it might be a non factor. kind of analogous to flyweel size and weight being a lot less of a HP loss factor in 3rd or 4th gear due to the acceleration being so much less in those gears.
does the force increase at higher rpm? the power required woud be greater, but isnt the force the same , hence the stretch , at equilibrium speed? (i.e. not accelerating) and if it is, the rate of acceleration being so slow, say in 3rd gear, it might be a non factor. kind of analogous to flyweel size and weight being a lot less of a HP loss factor in 3rd or 4th gear due to the acceleration being so much less in those gears.
Torque required at the cam pulley (force in TB) would be greater due to increased frictional losses but it's likely insignificant. I think that water pump and oil pump would also require more torque to turn at higher RPM due to increased hydraulic losses but I may be wrong about this.
Trying to compute the additional forces associated with changing rpms - ie accelerating the camshafts just does my head in. It's difficult enough considering the changing torques as valves open or close.
It's just occurred to me that on an S4+ no need to mess about with cutting belt covers to see timing marks and sharktuning to set a static ignition timing or anything complex like that.
All that needs to be done is put a 'scope on the traces from the CPS and Hall sender. - Gives you unadulterated crank timing and unadulterated 1-4 cam timing.
Wouldn't get you 5-8 cam timing but realistically that will be closer to the crank timing than 1-4 anyway.
BUMP - someone must have a scope and could do this ?
Torque required at the cam pulley (force in TB) would be greater due to increased frictional losses but it's likely insignificant. I think that water pump and oil pump would also require more torque to turn at higher RPM due to increased hydraulic losses but I may be wrong about this.
Trying to compute the additional forces associated with changing rpms - ie accelerating the camshafts just does my head in. It's difficult enough considering the changing torques as valves open or close.
thats right, the water pump forces will go way up with increased speed, unless it is cavitating.
I think an easy test is to check cam timing at different belt tensioning forces. im sure its a rounding error at best in most all areas of consideration.
thats right, the water pump forces will go way up with increased speed, unless it is cavitating.
The thermostat bypass opens over a certain pressure. Not sure how much this takes off of the water pump load.
Side note: I noticed recently that the t-stats with the smaller disc have a much heavier bypass spring compared to the large-disc OEM stats. I think this may have contributed to the (Chinese) water pump pulley freewheeling on my black car first time on the track.
Originally Posted by mark kibort
I think an easy test is to check cam timing at different belt tensioning forces. im sure its a rounding error at best in most all areas of consideration.
There are many more forces than just tension at work at high rpms, including the weight of the belt, harmonics, etc. Maybe it cancels out, but I'm guessing that each bank will have different timing at different rpms.
The thermostat bypass opens over a certain pressure. Not sure how much this takes off of the water pump load.
Side note: I noticed recently that the t-stats with the smaller disc have a much heavier bypass spring compared to the large-disc OEM stats. I think this may have contributed to the (Chinese) water pump pulley freewheeling on my black car first time on the track.
There are many more forces than just tension at work at high rpms, including the weight of the belt, harmonics, etc. Maybe it cancels out, but I'm guessing that each bank will have different timing at different rpms.
the t-stat is open at operating condition. your saying it gets more open at high rpm? probably has little or no effect on water pump load. once the t stat is open, the water travels through the small opening in the t-stat around the spring and disc. it cant be made to be "more open", after its further than partially open at near operating temp. its as open as its going to get. if you are saying that it starts to open the rear of the t-stat agains the block so that the flow skips the heads, thats unlikely, as at high rpm, we would see over heating, and thats the opposite to what happens. if you had "freewheeling" it was due to probably your system having air in it, and it needed to be bled.
how did you know or determine the pump was freewheeling? the way the pump is designed , that is probalby unlikey.
as far as tension goes, weight of the belt? its so slow, cant imagine that effecting tension. harmonics yes, when the natural frequensy of the belt at the different pinch points equals the frequency of the cam/rotation vibrations, sure that can add tension. how much? im sure very little.
by your wildest imagination, what could the timing be altered on one cam vs the other? 1 to 2 degrees ? probably again, not measurable as far as effects. Plus, remember, we are taling about acceletion forces being FAR in excess of those that would be due to strictly rotational forces at a constant RPM. so in the end, its probably a non issue.
HI NEW ON RENNLIST...THOUGH OWNED MY 88S4 OVER 20YRS...about the ''j kempf'' tensioner tool...i changed my belt in 2004..light came on a few times...so i ''RETIGHTENED''??? a new belt will stretch somewhat till it settles...this is only common sense..never had the warning again...im buying anothe as i put mine in a ''safe place'' olong with my f/wheel locking tool..when we moved from one side of australia to the other..car never missed a beat.. also done intake
And I've only used the conti belt... tensioned with both the porsche tool and the kempf tool and both seem to be calibrated correctly with respect to each other, and the test load of the 9201 tool from porsche. I have over 140 race days on this engine (S4 stroker 6.4L) over the past 15 years and it still dynos like the day it was built (within 5 hp) no leaks, no noises just pure fun and reliability. I'm worried now that i dont drive it that much anymore , and only race 3-4 times a year now that something will fail due to it sitting in the garage most of the time. BUT, its been an amazing ride .
i think the summary of the tool debate for me was, the tool shows a window of tension, and the belts from Old buggers to S4 are very different and show different tension with respect to the porsche tool.
cheers! you got a clean motor for sure. (BTW) looks great!
Originally Posted by Darren nicolson
HI NEW ON RENNLIST...THOUGH OWNED MY 88S4 OVER 20YRS...about the ''j kempf'' tensioner tool...i changed my belt in 2004..light came on a few times...so i ''RETIGHTENED''??? a new belt will stretch somewhat till it settles...this is only common sense..never had the warning again...im buying anothe as i put mine in a ''safe place'' olong with my f/wheel locking tool..when we moved from one side of australia to the other..car never missed a beat.. also done intake
So, when I tightened my belt, after install, I used the Kempf tool. When setting it exactly in the center of the window, the OEM tensioner still didn't make contact. When tightening it a bit more (2/3s of the window), the tensioner made contact. I buttoned it up and haven't seen the tension light come on.
The curious part of me about all this, is that the engine has its own built in tensioner check system. Why do we need all these tools? Tightening it to the point where the OEM tensioner starts making contact is likely the point you need to go to.
So, when I tightened my belt, after install, I used the Kempf tool. When setting it exactly in the center of the window, the OEM tensioner still didn't make contact. When tightening it a bit more (2/3s of the window), the tensioner made contact. I buttoned it up and haven't seen the tension light come on.
The curious part of me about all this, is that the engine has its own built in tensioner check system. Why do we need all these tools? Tightening it to the point where the OEM tensioner starts making contact is likely the point you need to go to.
um i think this is incorrect...the factory tensioner has to be manually tightened..hence the adjusting bolt...the ''jkempf'' tool measures ''TWIST'' i found it to be very good...as i said a ''new belt'' will still have settling/seating..i got a checklight 2or3 times then never again...that was in 2004...apporox.8000 miles...i also put the ''tool'' and flywheel lock..in a ''safe place'' when we moved from one side of australia to the other....NEVER SEEN AGAIN..
08-21-2011, 01:43 PM
BUT, its been an amazing ride .
BELT TOOL
