Cam Timing - Optimum Setting for S4
12-11-2007, 01:29 PM
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Cam Timing - Optimum Setting for S4
I guys, I was hoping that you could help me with suggestions for my cam timing. 
I need to determine the best cam timing setting for my car. Worf928 will be setting my cam timing with the Porken tool as a part of the timing belt system rebuild, and I would like to get the cams degreed as close to optimum for my car as possible. I realize that there is inevitable trade off in some top end or low end torque. I have a 5-speed car (with 2.20 rear end) that I plan to mod towards the more sporty side of the 928 spectrum and plan to use it for track days in the future but it will still be primarily a street car. While I sure don't want to soften my low end too much, but it is enticing to add a bit more top end pull and possibly make the car more revvy.
I've searched through old threads on the subject for the past couple of days and while I did learn a lot about this, I did not see much data for the effects of advancing or retarding the timing on S4's, and really not much at all for 5-speed cars. This thread by Flying Scottsman was helpful but it was mostly about advancing for drivability on automatic S4, and Porken has a lot of very interesting data in various threads, it is focused on advancing cam timing for an AT S3.
https://rennlist.com/forums/928-forum/340190-cam-timing-changes.html
In another thread Kibort stated that synchronizing the cams was a key to extracting performance instead of leaving the stock asymetrical settings, which I though was very interestingl: https://rennlist.com/forums/showthre...ng+performance
So I was thinking both sides synched to 0 degrees (as opposed to factory staggered settings) straight up, or retarded -2 or so? Also, what affects would this have on drivability and reliability?
So, for you Lister's that have done this, particularly on 5-speed cars and S4's, what results did you get from your cam timing adjustments? Before and after driving impressions would be great and dyno charts showing the compromise would be even better.
Is there a sweet spot where I can have my cake and eat it too?
Thanks in advance for any helpful suggestions!
I need to determine the best cam timing setting for my car. Worf928 will be setting my cam timing with the Porken tool as a part of the timing belt system rebuild, and I would like to get the cams degreed as close to optimum for my car as possible. I realize that there is inevitable trade off in some top end or low end torque. I have a 5-speed car (with 2.20 rear end) that I plan to mod towards the more sporty side of the 928 spectrum and plan to use it for track days in the future but it will still be primarily a street car. While I sure don't want to soften my low end too much, but it is enticing to add a bit more top end pull and possibly make the car more revvy.
I've searched through old threads on the subject for the past couple of days and while I did learn a lot about this, I did not see much data for the effects of advancing or retarding the timing on S4's, and really not much at all for 5-speed cars. This thread by Flying Scottsman was helpful but it was mostly about advancing for drivability on automatic S4, and Porken has a lot of very interesting data in various threads, it is focused on advancing cam timing for an AT S3.
https://rennlist.com/forums/928-forum/340190-cam-timing-changes.html
In another thread Kibort stated that synchronizing the cams was a key to extracting performance instead of leaving the stock asymetrical settings, which I though was very interestingl: https://rennlist.com/forums/showthre...ng+performance
my timing is exactly like this. remember, i set the cams to 2mm a side as well. (as opposed to the 1.7mm passenger vs 2mm driver side spec) If you think about it, the line up has nothing to do with cam timing, its the relativity of the two cams, and all the stuff it wraps around. at TDC, thats where the belt grabs both cams with their pulleys. changing timing wont do anything here as the cams move inside the hubs of the cam pulleys.
mk
mk
So, for you Lister's that have done this, particularly on 5-speed cars and S4's, what results did you get from your cam timing adjustments? Before and after driving impressions would be great and dyno charts showing the compromise would be even better.
Is there a sweet spot where I can have my cake and eat it too?
Thanks in advance for any helpful suggestions!
12-11-2007, 02:20 PM
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It is such a lengthy procedure to get to where you can change the timing, that I don't think many have tried back to back dyno runs at different settings.
Kibort is almost right. It's arguably best to syncronize the cams at the same setting, but only when the engine is hot, which is tricky. Otherwise, you have to retard the ĵ side by 1 or 2° if the engine is cold to compensate for engine expansion. That's the reason for the 0.3mm difference.
When the Holbert car is warmed up, Kibort is probably running: ĵ +2° | ⅝ 0°, because he set the cams cold.
Kibort is almost right. It's arguably best to syncronize the cams at the same setting, but only when the engine is hot, which is tricky. Otherwise, you have to retard the ĵ side by 1 or 2° if the engine is cold to compensate for engine expansion. That's the reason for the 0.3mm difference.
When the Holbert car is warmed up, Kibort is probably running: ĵ +2° | ⅝ 0°, because he set the cams cold.
12-11-2007, 02:27 PM
#3
Drifting
According to Louie Ott, there were no appreciable gains when he advanced and retarded his GT cams and dyno'd the car (..the dyno chart is on his site). I would time them exactly per the workshop manual.
Found it:
http://www.performance928.com/cgi-bi...ss_parent=1125
Found it:
http://www.performance928.com/cgi-bi...ss_parent=1125
12-11-2007, 02:36 PM
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relatively speaking, retarding the cams will give you more top end (rpm) power.
the question you should answer is:
How often are you going to drive your car in the upper rpm range (4500 and up)?
be realistic about your answer, not "I want to" do this or that.
if you are driving 90% street and 10% track (or less), then I would recommend advancing the cams for more low rpm power. this will also help you come off the turns on a road course in some cases.......
---Russ
the question you should answer is:
How often are you going to drive your car in the upper rpm range (4500 and up)?
be realistic about your answer, not "I want to" do this or that.
if you are driving 90% street and 10% track (or less), then I would recommend advancing the cams for more low rpm power. this will also help you come off the turns on a road course in some cases.......
---Russ
12-11-2007, 02:38 PM
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It is such a lengthy procedure to get to where you can change the timing, that I don't think many have tried back to back dyno runs at different settings.
Kibort is almost right. It's arguably best to syncronize the cams at the same setting, but only when the engine is hot, which is tricky. Otherwise, you have to retard the ĵ side by 1 or 2° if the engine is cold to compensate for engine expansion. That's the reason for the 0.3mm difference.
When the Holbert car is warmed up, Kibort is probably running: ĵ +2° | ⅝ 0°, because he set the cams cold.
Kibort is almost right. It's arguably best to syncronize the cams at the same setting, but only when the engine is hot, which is tricky. Otherwise, you have to retard the ĵ side by 1 or 2° if the engine is cold to compensate for engine expansion. That's the reason for the 0.3mm difference.
When the Holbert car is warmed up, Kibort is probably running: ĵ +2° | ⅝ 0°, because he set the cams cold.
Porken, since the S4's have more conservative cam profile than the S3's, do you think that is the reason the S3's respond so well to cam advance in gaining back some more mid to low range? (I would guess thats why the S3's had longer intake runners to help low end w/ such radical cams and no flapper). I would guess that the S4's would respond a bit different to cam timing changes?
Thanks for the info
12-11-2007, 02:41 PM
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According to Louie Ott, there were no appreciable gains when he advanced and retarded his GT cams and dyno'd the car (..the dyno chart is on his site). I would time them exactly per the workshop manual.
Found it:
http://www.performance928.com/cgi-bi...ss_parent=1125
Found it:
http://www.performance928.com/cgi-bi...ss_parent=1125
The factory setting probably is the 'sweet spot' which would make sense.
12-11-2007, 02:44 PM
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relatively speaking, retarding the cams will give you more top end (rpm) power.
the question you should answer is:
How often are you going to drive your car in the upper rpm range (4500 and up)?
be realistic about your answer, not "I want to" do this or that.
if you are driving 90% street and 10% track (or less), then I would recommend advancing the cams for more low rpm power. this will also help you come off the turns on a road course in some cases.......
---Russ
the question you should answer is:
How often are you going to drive your car in the upper rpm range (4500 and up)?
be realistic about your answer, not "I want to" do this or that.
if you are driving 90% street and 10% track (or less), then I would recommend advancing the cams for more low rpm power. this will also help you come off the turns on a road course in some cases.......
---Russ
I lost my license for too many speeding tickets once already in the past and had to take remedial drivers ed classes (man was that a drag) so I try not to drive to fast on the street these days....
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12-11-2007, 03:09 PM
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So according to Louie's dyno chart there is about 7 total HP and 2 ft-lbs torque difference between +3 and -3 degrees, which is pretty negligible. So either setting is only about 3.5 HP and 1 ft-lb torque difference from stock.
Really not much difference in where the power shifts in the rev range, both curves look w/in about 100 rpm of each other.....Although after 3k rpms, both the torque and HP curves are a bit more smoothed out and the torque has a healthy bump at 4.5k.
12-11-2007, 03:17 PM
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I have the video of the cams set at the factory settings. the audible sound of the exhaust was noticably different. on the dyno i was down 5-10hp. at the track, i advanced the passenger side cam by the .25mm to near 2mm (was set at factory spec of 1.7) instantly the engine sounded different. Like tuning a musical instrument. my times dropped on the next race, and the sound, heard clearly on the video was noticably different. more of high pitched scream at high rpms vs a thumping V8 sound like the ALMS caddies. went to the dyno and the HP was back as well. based on the sound and the dyno runs, would advise timing of near equal for the two cams. I think one of the GTS or GT specs are closer to equal than the S4, and i dont know why. (im going on memory here, so dont quote me on it)
It was not that hard to check warm. just pull a valve cover and measure the valve depression at 20degrees after TDC. when warm, (not hot) the measurement was still the same as when i did it cold, at 2mm. or couse, i could have been off .1mm or so, but i think the basic message was that i found more power by making this kind of change to the cam timing vs the manual. the only way to really double verify this would be to put the cams back to stock (pretty easy to do) and do a dyno run or listen for that high rpm engine pitch again. ill tell you , at the track, i did 2 sessions and the race and then changed it. it was like a different car. my lap times came back to normal and the sound was different.
Again, later dyno run showed improvments as well. 310rwhp back to 320rwhp.
mk
It was not that hard to check warm. just pull a valve cover and measure the valve depression at 20degrees after TDC. when warm, (not hot) the measurement was still the same as when i did it cold, at 2mm. or couse, i could have been off .1mm or so, but i think the basic message was that i found more power by making this kind of change to the cam timing vs the manual. the only way to really double verify this would be to put the cams back to stock (pretty easy to do) and do a dyno run or listen for that high rpm engine pitch again. ill tell you , at the track, i did 2 sessions and the race and then changed it. it was like a different car. my lap times came back to normal and the sound was different.
Again, later dyno run showed improvments as well. 310rwhp back to 320rwhp.
mk
12-11-2007, 03:23 PM
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"My {S-4-Por-sche} does one-eighty-five...I lost my license, now I don't drive..." 
I found that to be noticeable by the ***-elerometer (w/automatic), you need change the timing by 6-8°. Each degree moved the peaks by rougly 100 RPM.
Changing the intake or exhaust will move the peaks around too, so the factory setting may no longer be the ideal.
I have kinda given up on making a dynamic valve timing device, but I would still like to make a (two-pulley-belt-length-modifying) gizmo, so that I can adjust the valve timing manually, while on the dyno, to find the schweet-spot.
I take it back about Mark's timing being off. I didn't know it was done on the track.
I found that to be noticeable by the ***-elerometer (w/automatic), you need change the timing by 6-8°. Each degree moved the peaks by rougly 100 RPM.
Changing the intake or exhaust will move the peaks around too, so the factory setting may no longer be the ideal.
I have kinda given up on making a dynamic valve timing device, but I would still like to make a (two-pulley-belt-length-modifying) gizmo, so that I can adjust the valve timing manually, while on the dyno, to find the schweet-spot.
I take it back about Mark's timing being off. I didn't know it was done on the track.
12-11-2007, 03:50 PM
#11
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The problem, is that this is kind of shaving hairs. back to back runs are one thing, and ive seen 3-4hp variation, for some reason, usually, my last runs are the best. when the shape of the curve changes, i then attribute it to some change that has been done.
L. Ott's dyno run does show that the HP is a little greater at the end, while extending the hp curve a little further.
mk
L. Ott's dyno run does show that the HP is a little greater at the end, while extending the hp curve a little further.
mk
12-11-2007, 04:05 PM
#12
Three Wheelin'
I guys, I was hoping that you could help me with suggestions for my cam timing.
I need to determine the best cam timing setting for my car. Worf928 will be setting my cam timing with the Porken tool as a part of the timing belt system rebuild, and I would like to get the cams degreed as close to optimum for my car as possible. I realize that there is inevitable trade off in some top end or low end torque. I have a 5-speed car (with 2.20 rear end) that I plan to mod towards the more sporty side of the 928 spectrum and plan to use it for track days in the future but it will still be primarily a street car. While I sure don't want to soften my low end too much, but it is enticing to add a bit more top end pull and possibly make the car more revvy.
<snip>
So, for you Lister's that have done this, particularly on 5-speed cars and S4's, what results did you get from your cam timing adjustments? Before and after driving impressions would be great and dyno charts showing the compromise would be even better.
Is there a sweet spot where I can have my cake and eat it too?
Thanks in advance for any helpful suggestions!
I need to determine the best cam timing setting for my car. Worf928 will be setting my cam timing with the Porken tool as a part of the timing belt system rebuild, and I would like to get the cams degreed as close to optimum for my car as possible. I realize that there is inevitable trade off in some top end or low end torque. I have a 5-speed car (with 2.20 rear end) that I plan to mod towards the more sporty side of the 928 spectrum and plan to use it for track days in the future but it will still be primarily a street car. While I sure don't want to soften my low end too much, but it is enticing to add a bit more top end pull and possibly make the car more revvy.
<snip>
So, for you Lister's that have done this, particularly on 5-speed cars and S4's, what results did you get from your cam timing adjustments? Before and after driving impressions would be great and dyno charts showing the compromise would be even better.
Is there a sweet spot where I can have my cake and eat it too?
Thanks in advance for any helpful suggestions!
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.
12-11-2007, 04:08 PM
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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.
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12-11-2007, 05:30 PM
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12-11-2007, 05:55 PM
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I have the video of the cams set at the factory settings. the audible sound of the exhaust was noticably different. on the dyno i was down 5-10hp. at the track, i advanced the passenger side cam by the .25mm to near 2mm (was set at factory spec of 1.7) instantly the engine sounded different. Like tuning a musical instrument. my times dropped on the next race, and the sound, heard clearly on the video was noticably different. more of high pitched scream at high rpms vs a thumping V8 sound like the ALMS caddies. went to the dyno and the HP was back as well. based on the sound and the dyno runs, would advise timing of near equal for the two cams. I think one of the GTS or GT specs are closer to equal than the S4, and i dont know why. (im going on memory here, so dont quote me on it)
It was not that hard to check warm. just pull a valve cover and measure the valve depression at 20degrees after TDC. when warm, (not hot) the measurement was still the same as when i did it cold, at 2mm. or couse, i could have been off .1mm or so, but i think the basic message was that i found more power by making this kind of change to the cam timing vs the manual. the only way to really double verify this would be to put the cams back to stock (pretty easy to do) and do a dyno run or listen for that high rpm engine pitch again. ill tell you , at the track, i did 2 sessions and the race and then changed it. it was like a different car. my lap times came back to normal and the sound was different.
Again, later dyno run showed improvments as well. 310rwhp back to 320rwhp.
mk
It was not that hard to check warm. just pull a valve cover and measure the valve depression at 20degrees after TDC. when warm, (not hot) the measurement was still the same as when i did it cold, at 2mm. or couse, i could have been off .1mm or so, but i think the basic message was that i found more power by making this kind of change to the cam timing vs the manual. the only way to really double verify this would be to put the cams back to stock (pretty easy to do) and do a dyno run or listen for that high rpm engine pitch again. ill tell you , at the track, i did 2 sessions and the race and then changed it. it was like a different car. my lap times came back to normal and the sound was different.
Again, later dyno run showed improvments as well. 310rwhp back to 320rwhp.
mk