Adjustable Camshaft Timing Sprockets ==================================== Introduction ------------ Adjustable camshaft timing sprockets allows you to adjust the camshaft timing with respect to the engine crank. Changing the camshaft timing allows you to change the way the engine behaves, for example, more advance (the lobes are ahead of the stock position) gives you more low end, retard gives you more high end. So you may not gain much power, but you may gain in driveability or high end racing. The stock timing is set according to a fixed distance between the crank and the head. If you change the head, shave it, use a different gasket, this distance may be off by a bit which the adj. sprocket can re-adjust. A shorter distance usually results in retard. When your belt slips (due to the direction of rotation) it's usually also in the direction of retard. There are a variety of such sprockets out there, some providing as much as 6 degrees of control in either direction. Keep in mind that the sprocket has 44 teeth which makes each teeth equaly to about 8 degrees of change. This means that you can get away with a sprocket with only 4 degrees of control in each direction. Following herewith are a few notes by the most excellent Peter, and some of the troubles I had as well. See also Greg Raven book, and the archive on camshafts. Jan ============================================================================== Article 18548 of rec.autos.vw: Newsgroups: rec.autos.vw Path: lynx.unm.edu!umn.edu!news-feed-1.peachnet.edu!darwin.sura.net!europa.eng.gtefsd.com!uunet!elroy.jpl.nasa.gov!sdd.hp.com!nigel.msen.com!yale.edu!yale!gumby!calvin!ursa!jtong73 From: jtong73@ursa.calvin.edu (Joanna Tong) Subject: Re: [W] Techtonics Adj. Cam sprockets Message-ID: Sender: news@calvin.edu (News ID) Organization: Calvin College Date: Thu, 5 Aug 1993 16:06:23 GMT Lines: 108 Well guys, I've had my adj. cam sprocket on for 2 days now. I bought it to correct the retarded cam timing I had with the stock sprocket since the head was shaved. I am running the G-grind which also has 1 degree of retard ground into it. I estimate that I was running about 2 degrees retarded+the 1 degree ground into the cam. So I've been experimenting with cam timing these 2 days. First setting was to advance timing 4 degrees on the sprocket. Low end torque picked up noticeably, but the car wouldn't really develop near the urgency at high rpm. I also experienced all kinds of crazy resonances in 1 rpm range. Here's a graph of seat of the pants torque vs rpm: | T | * * * * * * * o | * * * * * * * r | * * q | * u | * e | * | \___________________________________________________ 2 3 4 5 6 7 rpm Set it to 2 degrees advanced on cam sprocket. Now the low end dropped a bit but when it got to about 5000 it dipped in hp and then 500 rpm later almost seems to develop another torque peak. | T | * * * * * * * * o | * * * * * * * r | * * q | * u | e | * | \___________________________________________________ 2 3 4 5 6 7 rpm I now have it set to 1 degree of advance on sprocket. Now the curve looks like this: | T | * * * * * * * ** o | * * * * * * * * r | * * q | * u | e | * | \___________________________________________________ 2 3 4 5 6 7 rpm Seems like these engines have four? torque curves that overlap. One is due to the intake manifold plenum sizing (kind of small) which helps low end torque to in the 3000-3500 range. The '82 exhaust manifold (4-2-1 style) and stock downpipe has short length downpipes which connect to a flex pipe then the cat. I think that due to the downpipes short length it tends to want to help at around 5k rpm, but really can't because by that time the diameter of pipe used is restrictive. So the length is kind of too short for the diameter used. If they had sized the pipe the same diameter and made longer downpipes it would have been better. The G-grind shifts the torque curve about a full 1000 rpm to the right compared to the stock cam - comes on about 4000-5000 rpm and goes till about 6000 when it starts dropping off. Intake runners on the A1 style manifolds are about 14 inches long (I think this is what I measured) including the port length in the head. So it should help at about 6k rpm. The problem is that with the G-grind set to stock cam timing it only marginally helps. So I think that G-grind should be set to a retard position for best power. Sure you'll lose some low end but not too much. The trick is to lose the least amount of low end, maximizing mid range torque, while running it retarded enough so that at about 6k there is good cooperation between the intake runner length and the cam timing curves. This will extend the overall area under the curve. The point being that these cars come with some fixed torque curves due to factory selection of intake manifold lengths, plenum volume, and exhaust manifold. You can change the exhaust downpipe to the Techtonics one for better midrange and somewhat better top end (they sized the pipe diameter right and the length is ok too), but you really can't adj. the intake manifold. The cam itself has a curve but you can only move it up and down a bit with the sprocket. Sometimes what helps one torque "curve" doesn't help the other and you have a dip in the overall curve (the sum curve of all the different curves). I think it is interesting how the factory changed the intake manifold on the '85 and up golfs. Plenum volume is up over the A1 manifolds and runner length is also up about 2 inches. Increased plenum volume should decrease low end response but help power, while increased runner length should help the low end but kill some off the top end. The A1 manifolds also have straighter runners as well, while the A2 manifolds make a bit more curves to lengthen the runner length (how much varies with which runner). Sometimes I wonder what the factory thought they would gain by all this. The point of all this is I hate compromises! It would be nice to not have to set the cam timing to minimize disharmony among the various different torque curves. BTW, have any of you out there experimented with cam timing? Have you found a setting that works best? I wouldn't mind trying it. I think I'll call techtonics about what the recommended setting is. Another side effect of retarded cam timing has been a rougher idle. Oh well enough rambling.... Peter Tong '82 Convertible with Audi 80 2.0 motor. ============================================================================= From rvborgh@Calvin.EDU Thu Nov 3 16:03 PST 1994 Date: Thu, 03 Nov 1994 19:03:15 -0500 (EST) From: rvborgh@Calvin.EDU (Raymond Vander Borgh) Subject: Re: Retard To: jan@UG.EDS.COM X-Envelope-To: JAN@FSHPP1 Content-Transfer-Encoding: 7BIT Status: RO Hi Jan, On my car moving the cam sprocket counter clockwise retards the cam, and the other way advances it. I'm talking about the center part of it that rotates (the adjustable part). Last week I tried a full 8 degrees of retard, and the top end was improved but the low end was too soft - throttle response suffered, and so I moved advanced it a bit. At any rate, I believe the cam sprocket rotates clockwise, so if the timing mark that lines up with the front top deck of the valve cover gasket surface is above the surface of the deck then the timing is retard. The way I have my car currently set up I don't like it either - I have it too advanced or something - the problem is that I don't really have the time to mess around with it too much - by the time I get home its dark already - and I'm pretty exhausted. At any rate, hope this helps! best regards, Peter T. ------------------------------------------------------------------------------ From rvborgh@Calvin.EDU Mon Nov 7 15:10 PST 1994 Date: Mon, 07 Nov 1994 18:10:00 -0500 (EST) From: rvborgh@Calvin.EDU (Raymond Vander Borgh) Subject: Re: Retard To: jan@UG.EDS.COM Message-Id: <9411072310.AA01432@Calvin.EDU> X-Envelope-To: JAN@FSHPP1 Content-Transfer-Encoding: 7BIT Status: RO Hi Jan, you wrote: > ** this is correct. Just unloosen the hex bolts and pull out the > wrench and turn it - not much to it at all. Might be worth it actually > to get your G60 dialed in just perfectly - but talk to Darrel V. about it > first. Thanks Peter, Funny, I was thinking pretty much the same last night while rereading Greg Raven's book (I don't know why I did not re-read this book earlier, because he has all my mistakes in there word for word, "The belt will probably slip", "it'll take a couple of tries to get the alignment right", etc). ** I like Raven's book - all in all I think that it is pretty complete. There are some details that he leaves out, and sometimes I couldn't figure out why he was doing/saying things should be done a certain way - then when I was messing around with the ignition systems myself I figured out why. In any case, he claims that there is a bit of slop between the crankshaft and camshaft synchronization from the factory. ** yeah, I know there is but I just wonder what the factory tolerances are. Actually, I was thinking the other day about how much stress that woodruff key must go through - esp when you are installing a high lift cam. If you think about it, it makes sense. However, he also claims that anything less than 2 degrees wont be noticeable. ** this is not true at all. I've been playing around with my cam timing of late and can tell you that I can notice about . degrees worth of change. Then engine will sound different and torque characteristics change enough for me to notice. Your previous comment about the engine running quieter with the cam timing retarded is something I've also noticed - how the CO is set also makes a big difference in how harsh the car sounds - esp during cruise type conditions. I STILL haven't figured out what setting is best for my car. The other day it was raining outside and when I pushed on the gas the car went into wheel hop. After this episode at idle the car would just want to die. Luckily I was close to home. Got home and plugged in the dwell for the fuel injection - no reading at all and I couldn't hear the frequency valve either. So I checked the grounds for the OXS system and it turned out that the OXS ground lead had been shaken off during the wheel hopping episode. The reason that it had been wanting to die was that the CO was too rich. With the ground unconnected (computer off), I tuned the CO by ear until the engine was running as smoothly as possible. Then hooked the computer back up. Lo and behold it ran better and with more power. Still not enough for me though. Anyways, back to your 40-60 time: 3.7 seconds is just as good if not slightly better than the stock SLC - that is good midrange torque in my book. I still haven't timed mine yet - I'll let you know the #s when I do though. Darrel is at TechTonics? **yes regards, peter tong ------------------------------------------------------------------------------ From: rvborgh@ursa.calvin.edu (Raymond Vander Borgh) Newsgroups: rec.autos.vw Subject: Re: [W] G60 + AT CAM = No Power? Date: 1 Nov 1994 23:25:47 -0500 Organization: Calvin College Lines: 28 Message-ID: <3974cb$ph2@ursa.calvin.edu> References: <1994Oct24.205229.31116@cc.usu.edu> <3941ik$ano@lipari.usc.edu> <16 980@comton.airs.com> NNTP-Posting-Host: ursa.calvin.edu This past weekend I took a trip to Ann Arbor to visit my sister at U of M. For better freeway response I advanced the timing and shifted the torque down lower. I originally had the adjustable cam sprocket at 4-5 deg. retard for good top end. At the 4-5 retard setting the torque peak was around 5k or perhaps a little above that, but the bottom end lost the same amount. I'm still experimenting with the cam settings to see what the best setting is = a good balance between the top and low ends. At certain settings the engine runs quite a bit harsher I've noticed - can't exactly give the reasons, but this is how it is with on my motor.... peter tong '82 2.0 8v Cabby ------------------------------------------------------------------------------ Newsgroups: rec.autos.vw Path: usc!howland.reston.ans.net!europa.eng.gtefsd.com!news.umbc.edu!haven.umd. edu!purdue!news.bu.edu!olivea!uunet!spstimes.sps.mot.com!mogate!newsgate!mark From: mark@wdc.sps.mot.com (Mark Shaw) Subject: Re: [W] Timing belt adjustment Message-ID: <1994Nov3.203124.4888@newsgate.sps.mot.com> Sender: news@newsgate.sps.mot.com Nntp-Posting-Host: margay.sps.mot.com Organization: Motorola Western MCU Design Center References: <92115@olympus.wustl.edu> <1994Oct28.193252.28880@newsgate.sps.mot. com> <393pqq$90n@lipari.usc.edu> Date: Thu, 3 Nov 1994 20:31:24 GMT Lines: 89 In article, (Jan Vandenbrande) writes: |> Could anyone explain to me what they'd expect from being one or |> more teeth off in either direction for the camshaft settings? |> Something like: |> |> One tooth against the direction of rotation == ?Less low end? I have not seen any concrete numbers other than AutoTech's comment that advancing the camshaft by 4 degrees will help the low end torque. The only problem with this is that there are 44 teeth on the camshaft sprocket, so you only have 8 degree increments. hence the reason for those adjustable camshaft sprocket wheels. The BOSCH Handbook has an interesting discussion of the effects of valve timing (see pages 368-370, 3rd Edition) in which they make the following statements: 1) 50% of the exhaust occurs as the exhaust valve starts to open slightly before BDC during the highest pressure point in the exhaust cycle. >From this it appears that changing the exhaust vlave timing has little effect on the volumetric efficiency. On the other hand: 2) There is always some vlave overlap as the exhaust and intake are open at the same time. Some intake charge is lost out the exhaust and some exhaust is mixed with the intake charge. 3) The amount of valve overlap can affect engine performance over its operating range and affect emissions (particularly HC and NOx). >From these it could be assumed that little change occurs if you move BOTH the opening of the intake and the closing of the exhaust, with maybe a minor increase in interanl EGR for moving them both earlier. 4) The real important point (and Bosch underlined this one!) is that closing of the intake valve has a big effect on the volumetric efficiency: Close early, better low end Close later, better high end Apparently most variable valve timing designs really tinker with this. In the extreme cases (i.e. misplaced timing belts) I would expect the following behaviors: TOO ADVANCED (i.e. the camshaft sprocket timing mark is BELOW the top of the head when the flywheel is at TDC). This should cause some forcing of exhaust into the intake manifold as the intake valve is opening sooner during the exhaust stroke. Maybe even some backfiring into the intake at startup. There should be a loss of power as the piston is bucking closed valves during the exhaust stroke and sucking on closed valves during the intake stroke. Also the charge efficiency would be low. I would however, expect the engine to be able to start, and run. Should also burn valves, as the exhaust is opening sooner into the higher temp, higher press expansion cycle. TOO RETARDED (i.e. the camshaft sprocket timing mark is ABOVE the top of the head when the flywheel is at TDC). This should cause very low compression, as the intake is still open as the piston is starting the compression cycle and some charge is lost. Power would also be lost as some of the exhaust may also be drawn back in as the exhaust valve would be open longer during the intake stroke. I have seen this case personally and the engine will not start, but spins really fast during cranking. The failure mode of a "slipped" belt should be towards more RETARD as the driving torque on the belt is mainly from the camshaft. Too much torque drive at the crank sprocket with resulting slip would spin the crank sprocket ahead a few teeth with respect to the timing belt. And too much torque drag from the camshaft sprocket with resulting slip would cause the timing belt to move ahead a few teeth with respect to the camshaft sprocket. Both cases result in more teeth appearing between the camshaft and crank sprockets towards the forward side of the engine. Voila, a net retarded camshaft (and possibly a retarded spark if the crank sprocket slips and adds more teeth between it and the intermediate shaft sprocket. I don't know if this explained anything, but it's one shot at it. Mark ------------------------------------------------------------------------------ From: porban@eeserv.ee.umanitoba.ca (Peter Orban) Newsgroups: rec.autos.vw Subject: Re: [W] ? on timing & belt skipping a tooth Date: 3 Nov 1994 18:55:45 GMT Organization: Electrical Engineering, U of Manitoba, Winnipeg, Manitoba, Canada Lines: 20 Distribution: world Message-ID: <39bbnh$6ql@canopus.cc.umanitoba.ca> References: <39b5on$gbv@hacgate2.hac.com> NNTP-Posting-Host: ic11.ee.umanitoba.ca In article <39b5on$gbv@hacgate2.hac.com> 00j4043@ccmail.emis.hac.com (TR Sills) writes: > >A couple of days ago there was some discussion on how a car will react >when the timing belt may have skipped a tooth. If this was the case >though, what would you read when you check the timing on the flywheel? >Wouldn't it too now be off? ... It depends where the belt skipped a tooth. It could be at the crankshaft, could be at the camshaft, or at the intermediate shaft. It probably skips at the crankshaft, as that is the smallest wheel, it has the least amount of tooth in contact. When mine skipped, all the power went, I could bearly go home, and then just adjusted the ignition timing. In another 20K km the whole belt was gone, I was stranded. Peter orban@nrcamt.nrc.ca ------------------------------------------------------------------------------