Cam Timing - Optimum Setting for S4
12-11-2007, 06:05 PM
#16
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So, is there anyone who has made anything like this..
http://tinyurl.com/yte3yt
An adjustable cam for 16v motors? I would think you could sell a couple. I had one on a Volvo Turbo, and I really liked it, played around with a couple of settings before I found my favorite. I would buy a pair, if anyone made one.
http://tinyurl.com/yte3yt
An adjustable cam for 16v motors? I would think you could sell a couple. I had one on a Volvo Turbo, and I really liked it, played around with a couple of settings before I found my favorite. I would buy a pair, if anyone made one.
12-11-2007, 08:25 PM
#17
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Chris, I think with the 2.20 gearing we have any moving up of the power in the rpms would make the car fall flat worse on every gear change. The GT 2.73 will have less rpm drop between gears and you could afford to trade some bottom end for top end (which is how the GT is anyway).
Our 2.20 gearing (and especially highway cruising in 5th gear) needs as much spread of power as possible.
p.s. just my opinion, street driven S4.
Our 2.20 gearing (and especially highway cruising in 5th gear) needs as much spread of power as possible.
p.s. just my opinion, street driven S4.
12-11-2007, 09:17 PM
#18
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Gear drops are the same for all the 928s, EXCEPT for the 2.2 and its 5th.
otherwise, depending on the use of your 928, it would not make much difference. (excecpt technically, baring traction debate from a standing start)
I did a test last night with almost warmed up 305 rear tires at 4000rpm in 1st. at 4000rpm, and near max torque, i rolled on the gas an it burned rubber to redline almost as soon as i was floored. (thats at near 40mph.)
mk
otherwise, depending on the use of your 928, it would not make much difference. (excecpt technically, baring traction debate from a standing start)
I did a test last night with almost warmed up 305 rear tires at 4000rpm in 1st. at 4000rpm, and near max torque, i rolled on the gas an it burned rubber to redline almost as soon as i was floored. (thats at near 40mph.)
mk
Chris, I think with the 2.20 gearing we have any moving up of the power in the rpms would make the car fall flat worse on every gear change. The GT 2.73 will have less rpm drop between gears and you could afford to trade some bottom end for top end (which is how the GT is anyway).
Our 2.20 gearing (and especially highway cruising in 5th gear) needs as much spread of power as possible.
p.s. just my opinion, street driven S4.
Our 2.20 gearing (and especially highway cruising in 5th gear) needs as much spread of power as possible.
p.s. just my opinion, street driven S4.
12-11-2007, 09:22 PM
#19
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they were the stock 85 cams on an S4 engine. (basically, GT without the computer )
it might play into the equation, but the S4 has near the same cam timing settings as the 85 and GT. actually there are some subtle differences, and i wonder why. I think i remember seeing the GT or GTS being 2.1 to 2.3mm (driver to passenger)
i was a little suprised to see and hear such an audible difference by such a small change. Ill i can think of , is that its like tuning a musical instrument.
Its the only change i made and it was very sluggish before from 60-100mph on the way to the track. a dog on the track and my times suffered. after the change, i was thinking, "i got my old car back!" (because there were doubts that the stock 85s would be as good as the Holbert stock GT/85 type cams)
mk
it might play into the equation, but the S4 has near the same cam timing settings as the 85 and GT. actually there are some subtle differences, and i wonder why. I think i remember seeing the GT or GTS being 2.1 to 2.3mm (driver to passenger)
i was a little suprised to see and hear such an audible difference by such a small change. Ill i can think of , is that its like tuning a musical instrument.
Its the only change i made and it was very sluggish before from 60-100mph on the way to the track. a dog on the track and my times suffered. after the change, i was thinking, "i got my old car back!" (because there were doubts that the stock 85s would be as good as the Holbert stock GT/85 type cams)
mk
So all you did was advance the passenger side cam (intake, exhaust?) to match as closely as possible the stock setting of the driver side cam and it made that big a difference? Were these the stock S4 cams or the '85 cams and do you think that plays into the equation?
12-11-2007, 10:54 PM
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Most street-driven 2.20 rear-end 928s spend more time in the lower rev band than do the 2.73s (or 2.xx whatevers that are > 2.20) and thus more torque in the lower regions gives better driveability and Carl's point above stands even though his explanation may not be as technically precise as possible.
12-12-2007, 02:11 AM
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Chris,
The "sweet spot" is the stock setting. If you want to give up some of the low end for better top end torque, you could retard the cams by around 5 crank degrees. That will have the effect of rotating the torque curve around a point at about 4200 rpm. That is the shape of the torque curve stays the same. it just rotates. If you really want better performance, get a set of GT cams or S3 (US'85/'86) cams and put those in. That will make a difference and you'll be pleasantly surprised. You could also keep you S4 exhaust cams and put in GTS intake cams. Adam Birnbaum has that and I believe gained some everywhere as compared to the S4 cams, and for sure better than the GTS intake and exhaust together which are a bad combo.
Edit: With the S4 cams retarded, don't expect the idle to be quite as good as it is now. Small difference. A bit rougher.
The "sweet spot" is the stock setting. If you want to give up some of the low end for better top end torque, you could retard the cams by around 5 crank degrees. That will have the effect of rotating the torque curve around a point at about 4200 rpm. That is the shape of the torque curve stays the same. it just rotates. If you really want better performance, get a set of GT cams or S3 (US'85/'86) cams and put those in. That will make a difference and you'll be pleasantly surprised. You could also keep you S4 exhaust cams and put in GTS intake cams. Adam Birnbaum has that and I believe gained some everywhere as compared to the S4 cams, and for sure better than the GTS intake and exhaust together which are a bad combo.
Edit: With the S4 cams retarded, don't expect the idle to be quite as good as it is now. Small difference. A bit rougher.
12-12-2007, 02:15 AM
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I need to determine the best cam timing setting for my car
Any timing setting will be a compromise because you use the car for different things; same applies to distributor timing.
Marton
12-12-2007, 02:17 AM
#23
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Depends on the speed range you are driving in.
Going 65 for example, in 4th gear on the freeway (5th is too tall ), forces a higher rpm than would be if you were in 5th in a 2.75. This same type of situation is true at many speeds . I was in traffic coming home from the track, and scot with his 2.75 had to bog in 2nd while i was in a sweet spot in 1st in stop and go traffic.
Its not "this again" its just calling it like it is. gears are gears. they work for specific range of speeds. the 2.2 shifts all the gears up a bit (not to the extent of the final drive would indicate, except for 5th)
Yes, on the freeway, if in 5th gear, its nice to have the 2.75 rear end for non downshifting acceleration. (although I prefer a down shift in either) but then again, its nice to have a gear for low wear operation that effortlessly runs the engine at low rpms even traveling at 80-90mph for long drives. That in my mind is true drivability. since ive driven and raced both, i think I can post my opinion.
Mk
Going 65 for example, in 4th gear on the freeway (5th is too tall ), forces a higher rpm than would be if you were in 5th in a 2.75. This same type of situation is true at many speeds . I was in traffic coming home from the track, and scot with his 2.75 had to bog in 2nd while i was in a sweet spot in 1st in stop and go traffic.
Its not "this again" its just calling it like it is. gears are gears. they work for specific range of speeds. the 2.2 shifts all the gears up a bit (not to the extent of the final drive would indicate, except for 5th)
Yes, on the freeway, if in 5th gear, its nice to have the 2.75 rear end for non downshifting acceleration. (although I prefer a down shift in either) but then again, its nice to have a gear for low wear operation that effortlessly runs the engine at low rpms even traveling at 80-90mph for long drives. That in my mind is true drivability. since ive driven and raced both, i think I can post my opinion.
Mk
Ugh. Not this again Mark. The numerical gears drops are the same but the overall gearing at the wheels on the road are different due to the final drive and lay shaft. For your statement to be unequivocally true all final drives would need to be the same too. The facts are that a 2.20 928 at 60 mph in 5th gear will be turning fewer revs than a 2.73 928 in 5th at 60 mph.
Most street-driven 2.20 rear-end 928s spend more time in the lower rev band than do the 2.73s (or 2.xx whatevers that are > 2.20) and thus more torque in the lower regions gives better driveability and Carl's point above stands even though his explanation may not be as technically precise as possible.
Most street-driven 2.20 rear-end 928s spend more time in the lower rev band than do the 2.73s (or 2.xx whatevers that are > 2.20) and thus more torque in the lower regions gives better driveability and Carl's point above stands even though his explanation may not be as technically precise as possible.
12-12-2007, 02:33 AM
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Chris, I think with the 2.20 gearing we have any moving up of the power in the rpms would make the car fall flat worse on every gear change. The GT 2.73 will have less rpm drop between gears and you could afford to trade some bottom end for top end (which is how the GT is anyway).
Our 2.20 gearing (and especially highway cruising in 5th gear) needs as much spread of power as possible.
p.s. just my opinion, street driven S4.
Our 2.20 gearing (and especially highway cruising in 5th gear) needs as much spread of power as possible.
p.s. just my opinion, street driven S4.
12-12-2007, 03:29 AM
#25
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Thanks for the info Louie. I don't plan to change cams right now but will definately keep the GT cams or GTS intake cams in mind as a future mod. I will likely stick with the stock 'sweet spot' for now. I don't think I will retard the cams since it is a stick and feels plenty torquey down low as it is. Only thing that I'm still trying to figure out is if it would be worth it to 'synch' the cams as Mark described. Any thoughts on the effect of that?
If you are putting on a new cam belt and/or sprockets, don't spend a lot of time getting real close reference right then. Wait until you have several thousand miles on the belt & sprockets before you tension them and take your reference. The timing will change a little between new belt and used belt.
12-12-2007, 03:53 AM
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I suppose there are different methods to "sync" the cams, and everyone has their favorite. I've used a timing light to measure the cam timing difference between a cold and a hot engine and come up with numbers that show that the left side (drivers) cam advances about 2 crankshaft degrees when it gets hot and the right (pass) side advances about 3 crank degrees. It's kinda hard to tell the difference between 1 crank degree (0.5 cam degrees) so you can take those numbers as one step better than an educated guess. Since the cam timing is most important when the engine is at operating temp, I do my sync testing when it's up to temp. I measure compression on each side as soon as possible after it's been shut down. That way you don't need to take time to disassemble anything other than remove the plugs. Remember to open the throttle and let the engine turn through the same number of compression strokes (5 or 6) for each cylinder. Average the compression readings on the 4 cylinders on each side. The side that is retarded will have lower compression in relation to the other side. Then you decide whether you want to advance one side or retard the other side to get each side the same. Whether you advance one side or retard the other side depends on what engine characteristics you want. Use Ken's tool to make the adjustment on the side you want to change. One or two degrees is noticeable on compression. Put the rotor back on, run the engine up to temp again and take another compression reading. When each side is equal, or as equal as you want to take the time to work with, measure the cam timing on each side with Ken's tool. Write it down where it won't get lost and that's your reference for cam timing and cam sync. Better yet, take a picture of the Porken tool in place so there is no doubt later as to how they were set. If you have to get in to change sprockets or for some reason disturb cam timing, you can always get back to your reference. If you want to change cam timing on both sides for a performance check, you can change both sides from the reference with Ken's tool.
If you are putting on a new cam belt and/or sprockets, don't spend a lot of time getting real close reference right then. Wait until you have several thousand miles on the belt & sprockets before you tension them and take your reference. The timing will change a little between new belt and used belt.
If you are putting on a new cam belt and/or sprockets, don't spend a lot of time getting real close reference right then. Wait until you have several thousand miles on the belt & sprockets before you tension them and take your reference. The timing will change a little between new belt and used belt.
12-12-2007, 04:40 AM
#27
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The 2.75 rear end also comes in handy for the ability to hit the rev limiter in 5th gear when on the Autobahn.
12-12-2007, 07:06 AM
#28
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12-12-2007, 07:47 AM
#29
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both early and late MY 928 are simply geared too low on 5th and really need 6th for autobahn. Several engines have been destroyed due to combination of high revs and well known oiling problems in 928 engines.
12-12-2007, 12:08 PM
#30
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