You're looking at it right. I set the base timing of the motor (factory settings). Then I adjust the manifold pressure timing...ie -18 degrees of timing at 16psi. There is also fuel RPM and then manifold pressure fuel. MP fuel richens the mixture as your MP raises.
That tune is just my noob tune. Haven't dyno tuned it, but will once we the new motor squared away and install the MS (I'd like to ask for your help if thats okay when the time comes).
so it's clear bawareca was only posting to hear himself talk... WTH kinda garbage was that...
one thing to consider is that your not aiming to reach peak cylender pressure at TDC. At TDC there is no leverage on the rod to push on the crankshaft so all the pressure is basically wasted. Many people incorrectly think more timing is allways better until it pings but this is not true because if you spark to early, then your making peak pressure to early when the rod cannot transmit its power to the crank. The result is you pound out the rod bearings and overheat the piston.
I was taught that most motors regardless of design make best power with a peak cylinder pressure around 12-15 degrees after TDC, with the effective power stroke essentially being over at around 20 degrees past TDC. So when you say a motor is running 20 degrees of advance, it really has about 32 degrees of crank rotation to complete the burn vs a motor running 10 degrees of timing which has about 22 degrees of rotation to complete the burn. Bottom line is timing tuning is all about burn rate and dialing in peak cylinder pressure to where the motor can make most efficient use of it.
That is a good point.It also shows that the rod ratio has a lot to do with the timing,i.e. how long the piston has to travel before it reaches the point of maximum leverage.That also explains a lot why there is such a big difference between M20 and M30 timing.
I was looking at old data for euro M20s with ignition distributors.There is roughly 13 degrees difference between M20B20 and M20B20.As they are using the same head and piston design,same intake and exhaust,and very close CR the difference can be explained with the different rod ratio mostly.
This message is hidden because bawareca is on your ignore list
-Kenny
'89 535i Twin Turbo Project
My assumption would be he knows rod ratio is different and thus piston velocities, but does not think this is the main cause for ignition timing difference.
Bore size is 84mm for the m20 versus 92mm or whatever it is for the M30.
The bore size difference would make a big impact IMO.
Rod ratio is largely irrelevant to required timing. The important relationship is that the locus of peak pressure occurs at the appropriate crankshaft angle.
Because a high rod ratio increases piston dwell, one could argue that the effective combustion chamber volume is smaller during combustion and therefore less advance is required, but the influence is marginal.
You need more advance as RPMs increase because the crankshaft is going faster. Everything is referenced to crankshaft angle.
-Kenny
'89 535i Twin Turbo Project
Wonder what a pile of junk gen1 Chevy big block requires...
Here's my m30 at 20psi. It was set to about 15* before tuning and it
was a complete turd with that low of advance.
Last edited by YellowBed; 03-20-2012 at 11:20 PM.
You're running 91+methanol, right? Otis runs like 26 degrees on E85 at the top of the cells. I just don't want any M30 bros to see that map and grenade their engine on pump only. btw, what nozzle are you running for meth, I'm setting mine up soon
No idea on gph but cooling mist said it was good to 500hp when I bought it 5-6years ago.
The pump is cut back to 85% So probably on the too big side.
bingo. Plus different cumbustion chamber shape. Rod ratio in my opinion is mostly irreverent and not worth concerning yourself over at this level. I saw a graph once about the difference in piston speed and position between a 5.7 rod and a 6 inch rod and the difference was so miniscule as to make me laugh. There are so much more important things to concern yourself with.
Everybody has opinion,but there are interesting facts here:
E21 323i ("77-82) distributor no# 0237 302 006
with quoted timing at 22 degs at 1500 rpm
E21 323i late- 0237 302 032 same timing quoted as above
323i 1982-1983 dist no 0237 302 038
19degs at 3000 rpm
323i 1983-1984 dist no 0237 302 040
16 degs at 5000 rpm
323i 1985-1986 dist no 0237 304 025
16 degs at 5000 rpm
320i/6 1982-1983 dist no 0237 302 037
26 degs at 3000rpm
320i/6 dist no 0237 302 039
23 degs at 5000 rpm
320i/6 dist no 0237 304 024
23 degs at 5000 rpm
(from http://sites.google.com/site/e21323i...timing-numbers ,but there are many other sources)
For someone who doesnt know, M20B20 and M20B23 share the same 80 mm bore and the same old and inefficient spherical combustion chamber with slightly domed or flat pistons,same intake,exhaust,etc and a very close CR. There are roughly 7 degree difference between them under high load.Pre 83 are Bosch K-jetronic,84-85 are L-jetronic.
OTOH even the most conservative M50 table shown here runs 20 degree @100 kpa (N/A engine).
Last edited by bawareca; 03-21-2012 at 11:21 AM.
Very few people tune their turbo car at 5000 RPM @ 100 kPA. It's actually very hard to get the engine there.
You're also referencing bosch timing figures to guys who are submitting basemaps. Very few people have standalone tuned NA motors. It also depends where on the 100 kPA line you look.
Sorry,but the tittle says "Why 2v heads need more advance than 4v heads",and there was discussion about idle timing on the previous page.So what it is?
Timing is timing,no matter if it is controlled via points or MoTec .
2v heads do need more timing than 4v heads - they have, intrinsically, less efficient combustion chambers. We've been over this already.
You're looking at basemaps for turbo M5x motors and comparing them to NA M20 maps at 5000 RPM and (assuming) 100 kPA. Again, I have yet to tweak the timing on an M50 at 5000 RPM and 100 kPA. I can't get the load to stay there long enough to warrant adjustment from a calculated starting point.
Last edited by 5mall5nail5; 03-21-2012 at 12:45 PM.
I am finally out of that discussion,because it is changing the subject with every post However i think there was something interesting for everyone,in different areas
If you really want to prove that you are correct you can multiply your (super conservative) map by 2 and feed it in a M20,or feed Otis's map in M20
You are becoming very irritating the way you quote literally. I've mentioned 1.5 - 2.0x throughout this thread. When an M20 is at 25 degrees under load an M50 may be at 16 degrees... 16 x 1.6 = 25... move on. The subject is not changing you just post so strangely its hard to understand whether or not you are reading the same thread. An M20 takes more time. PERIOD. I don't know what else you want to hear. A half dozen capable people have agreed. The rest of the world is not devastated to find this out but for some reason you're like... fighting it. M20s take more timing than an M50 PERIOD. FACT. The end. The most ridiculous part of your posts in this thread isn't that the rest of us aren't debating whether or not they require more timing or not, but WHY. The first post explains, in the most basic form, why a 2v head requires more than a 4v head. I feel like you're arguing with me that 6 cents is not 6% of a dollar when really we're talking about whether or not sales tax applies.
I get it you disagree with me that's fine, go on your way and do your thing - you're confusing me and surely dudes who are trying to figure this out.
Last edited by 5mall5nail5; 03-21-2012 at 02:10 PM.
Not really. When you're relying on mechanical advance, be it via a vacuum pod and/or centrifugal, you have a fixed timing curve to work with, all you can do is move the whole curve up or down by turning the distributor body.
That data lists the distributor PN precisely because they all have different curves.
Trying to compare them based on a single operating point is meaningless.
-Kenny
'89 535i Twin Turbo Project
Bookmarks