Reply With QuoteThat sounds great. Glad you could dial in your car right (pun intended). Which adjustable cam gear are you using?
Grand Master
Better better better
8 degrees of cam advance have made the MM head/cam setup a whole new machine. Not perfect but *much* better. Power's much more even and the car pulls strongly on cam and quite nicely off cam.
Car's pinging a bit but it has 89 octane gas, not 92. Swapped in a the stock chip (vs the JC) and the pinging stopped. Next fill will be premium and will put in the JC chip again and see how it does.
I think it would be interesting to try a range of advances from 6 to 10 degrees and see how it behaves....
Bill - Mr. A. Graham Bell seems to have called this one spot on!
Jeff
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy
Major Contributor
That sounds great. Glad you could dial in your car right (pun intended). Which adjustable cam gear are you using?
Brandon J
Major Contributor
Jeff's got the metric mechanic cam gear with 0, 2, 4(+ & -) adjustment.
Korman has this: Offset Adjustable Cam Gear
"Resurfacing the cylinder head retards the camshaft timing. Use this gear to advance it back to specification. Machined for 1,3,5 and 7 degrees of offset. Can also be used to fine tune the power band of the engine."
M30 11/78> P/N 11318606
http://www.kormanfastbmw.com/e34m30.htm
erased due to slander
Super Moderator
Good deal Jeff, the thought just occurred to me that by
by advancing the cam gear one tooth you also advanced the timing the same number of degrees....since the distributor engages in the cam....which could account for a lot of the pinging as well as the improved midrange besides the cam.... just a thought...
Originally Posted by Jeff N.
8 degrees of cam advance have made the MM head/cam setup a whole new machine. Not perfect but *much* better. Power's much more even and the car pulls strongly on cam and quite nicely off cam.
Car's pinging a bit but it has 89 octane gas, not 92. Swapped in a the stock chip (vs the JC) and the pinging stopped. Next fill will be premium and will put in the JC chip again and see how it does.
I think it would be interesting to try a range of advances from 6 to 10 degrees and see how it behaves....
Bill - Mr. A. Graham Bell seems to have called this one spot on!
Jeff
Grand Master
laughing....not according to Martin...! (more)
I suggested this to Martin as we tinkered. He dismissed me!
More seriously...does the timing really advance? The base timing pluse is triggered by the CPS and that hasn't changed, right?
What I do wonder about is the ability of the rotor to correctly distribute the spark. The rotor's tied to the cam and it is HAS advanced right? Also, the rotor has an 'sweep angle' built into it which - i would assume - accounts for the potential advance range in the DME map. That is, the rotor angle allows the tip to be near the correct cap electrode when triggered by the CPS and the adjustment of the DME. Nooooow...if that's all true...
THEN...what happens if you advance that sweep by 8 degrees like we did? Could you have a situation where the spark gets routed to the wrong plug? Or has to jump an excessive gap in the cap and you end up with a weak or no spark, especially at upper RMPs where you have little coil saturation time? I wonder what might happen if you were able to advance the cap by 8 degrees?
Hmmm...or...should I go back and re-read some more of Mr. Bell?
Have to try a g-tech run and see what happens..
Thanks for the chat the other day Bill!
Jeff
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy
Grand Master
Let's try putting +2 in yer turd and see what happens...
Course...I just get to supervise for the next 30 days..dumb doc splinted my hand. Grrrr.
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy
Grand Master
This is good discussion...something that hadn't occurred to me either...changing the cam timing will affect the ignition timing because of the rotor being directly tied to the front of th cam. I am not sure it is a bad thing however if the ignition timing goes along with cam timing...but certainly will change when the explosions occur with respect to crank and piston positions...get too advanced with respect to changing teeth...then you dramatically advance ignition timing. I presume it would be best however to use the custom slide in the adjustable cam sprocket versus jumping teeth to advance the cam thereby preserving original ignition timing. Mark D or perhaps Bill may know about the relationship between the ignition timing MAP, the CPS and what control the DME has over changing advance versus the fixed ignition timing of the distributor/rotor connection to the cam. I would be interested as well. It makes sense that the DME has to override the fixed hardware connection of the distributor to supply a graduated advance as the engine climbs to higher RPM. My interpretation is the CPS is primary to injector firing but perhaps it supplies crank position and speed to the DME to coordinate ignition timing advance as well.
George
5-10 Grand Master
that'd be my vote, i've played around with the later 4 cyl rwd volvos that had refrence mark sensor controled ignition, but they still have a adjustable distributor (same housing as the hall trigger just no guts) and you can move the distributor but the timing light don't move
all america wants is cold beer warm cat and a place to take a poop with a door on it
Grand Master
Jeff...if you have a timing light, before you jump a tooth, consider putting a light on it to measure the ignition timing to a mark on the damper. Then move the cam a tooth and measure the ignition timing again. The advance curve should be the same based upon the DME ignition timing MAP but the question is will low RPM initial timing be changed by moving the cam sprocket a tooth and not changing the adjustable cam sprocket slide position.
George
Super Moderator
I'm not certain how much effect it will actually have, I couldn't find any
information about this a long time ago on computer spark controlled cars that used crank sensors but still had dist... I was wondering how they determined advance before they started using knock sensors...
Anyway what i came up with was, on a normal dist, like i grew up working on there was a fixed amount of centrifugal advance built into it... meaning as the distributor rotated faster, internal weights would fly out connected to the dist shaft, the further they moved out the further rotor would advance the timing, then they used various vacum advance systems to advance or retard the timing depending on manifold vacum and or carb port vacum... this way they could advance or retard in a purely mechanical manner based on engine speed and vacum or load.. Then when i started seeing a lot of the pointless, sensor less dist. on computer controlled cars where it was just a body that routed spark... I noticed when looking at them that the outer contact area on the rotor was really wide much wider than an older dist....This is what allows the computer to advance the timing or retard the timing without the rotor position changing... This wide strip is so wide that its always in contact with the cylinder thats currently firing regardless of how much advance or retard the computer cranks into it.. my guess is that the factory sets it up for the spark to occur somewhere near the center of that rotor outer contact area at around 15 degrees advance, this was when the computer retards the spark theres plenty of contact still touching the contact on the dist cap and when it advances the timing theres still plenty of contact with that brass strip..
Now when you advance it by moving the cam gear one or more teeth,
I don't know if the cam was just ground different from the dist indexing point or not...but if you moved it a tooth or more how far do you have to go until you reach the point that the postion of the rotor will be too far away from the contact on the dist cap when the computer is calling for full advance based on engine speed ,load ,temp, tps setting etc...There will be a point at which that rotor is going to be closer to the next cylinder on the cap in the firing order and it will just jump to it instead... So my answer is that no I don't think it will advance the timing, until you go too far and then it really will advance the timing at high advance conditions... I don't know if you'll hit that point or not... If you do you may have to come up with a way to reindex the dist to back it up some so the rotor contact area is widest over the cylinder you want it to be on... I'm just speculating here since i haven't played with the bmw cam timing and don't know what the limitations are in the movement...but it seems to me that anytime you start moving the cam and the dist moves along with it, you're going to have to eventually come up with a way to move the dist back to its original relationship to the crankshaft position sensor... Since you have 6 contacts in the dist cap and they are 60 degrees apart from each other, you'd have to set the crank on tdc number one and look at the rotor relationship to the dist contact to determine how far you could move it until the next contact in line is closer for the spark to jump to... But Martin is correct in that your static timing at idle should still be unchanged.. until you move it to the point that the next contact is closer...something interesting to think about ... measure the width of the contact area on the rotor and the distance between contacts on the dist cap and then look at your starting point at tdc....It'll be obvious at high rpm ,high load , when you've moved the dist too far...
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