Why is the CSi timing so much different than CS?

Stevehose

Stevehose

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Other than higher compression (8 vs 9:1), why are these curves so different? They have the same camshaft and bore/stroke, yes? Max all-in 35 degrees on CS vs 32 on Csi, and a much less later curve all the way up for the CSi. Reason I am asking is that I am researching timing theories and fiddling with my 123 distributor advance curves while taking into account my engine specs: euro piano top pistons, Schrick cam, and 3x Webers. Presently I am aggressively all in at 3k rpm and 35 degrees max, 15 degrees at idle. This is giving me ideas that I should have less timing, not more? I wish I had a dyno in my garage. Thoughts? @sfdon ? @stphers ? @Bueller?

Screenshot 2023-02-26 at 9.50.17 AM.png
 
It’s the compression? Remember also- no vacuum advance on Csi.
Retard only at idle.

You want timing maps for m90 and 10:1 euro spec engines?
 
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I might be wrong, but I think CS use a 264 degree cam, and the CSi use a 272 degree cam, same amount of lift.
 
sfdon said:
It’s the compression? Remember also- no vacuum advance on Csi.
Retard only at idle.

You want timing maps for m90 and 10:1 euro spec engines?
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Yes please! I'm not running any vacuum advance so I will experiment with this.
 
The big differences with the CSi are the distributor with trigger points, ECU, D-Jet electronic fuel injection & (MAP) Manifold Atmospheric Pressure Sensor.

I'm now running a 123 6-R-V-R-IE & use the switched base 'factory' curve. Fuel pressure for the CSi is 29 psi & CSiL is 35psi.
 
Gransin said:
I might be wrong, but I think CS use a 264 degree cam, and the CSi use a 272 degree cam, same amount of lift.
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According to blue books both are the same

"Camshaft identification:
BMW 2,5 CS 1 260°
BMW 2800 CS 2 264°
BMW 2800 CS 3 272°
BMW 3,0 CS 3 272°
BMW 3,0 CSi 3 272°
The 272° camshaft provides better compensation for the output fluctuations due to production tolerances.
Also refer to 13 71 001 for modifications on the intakt cross section opening."
 
Curious @Stevehose. Any reason why you haven’t put a performance cam in your car? Totally seems like a “Steve’s” wheelhouse kind of job. :D

Wladek said:
According to blue books both are the same

"Camshaft identification:
BMW 2,5 CS 1 260°
BMW 2800 CS 2 264°
BMW 2800 CS 3 272°
BMW 3,0 CS 3 272°
BMW 3,0 CSi 3 272°
The 272° camshaft provides better compensation for the output fluctuations due to production tolerances.
Also refer to 13 71 001 for modifications on the intakt cross section opening."
Click to expand...

Go figure. I thought all e9’s had a 272. When I think 264 I think of the US B34.
 
Markos said:
Curious @Stevehose. Any reason why you haven’t put a performance cam in your car? Totally seems like a “Steve’s” wheelhouse kind of job. :D



Go figure. I thought all e9’s had a 272. When I think 264 I think of the US B34.
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Not to disappoint you, Don put a Schrick 284 in the head I got from him a few years ago :cool:
 
I’ll send timing map when I get back to shop. Here is our latest M90 with Schrick Dyno testing Coupe King exhaust against W&N stainless. The Walloth exhaust is great for the stock 3.0 engine.
 

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I should be clear- our maps are for engines built with Schrick cams
 
Heading home tomorrow- been on the road for a couple of weeks.
 
Stevehose said:
Other than higher compression (8 vs 9:1), why are these curves so different? They have the same camshaft and bore/stroke, yes? Max all-in 35 degrees on CS vs 32 on Csi, and a much less later curve all the way up for the CSi. Reason I am asking is that I am researching timing theories and fiddling with my 123 distributor advance curves while taking into account my engine specs: euro piano top pistons, Schrick cam, and 3x Webers. Presently I am aggressively all in at 3k rpm and 35 degrees max, 15 degrees at idle. This is giving me ideas that I should have less timing, not more? I wish I had a dyno in my garage. Thoughts?

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The short answer is the two similar engines breath differently and therefore function differently. Consider different intake manifolds, different runner lengths, interior diameters and the fact that one engine has fuel delivered at the cylinder head inlet port while the other engine’s fuel is delivered much further from the cylinder head. This, along with compression ratio differences, allow for different power outputs, reached at different effective engine speeds. Perhaps . . . this accounts for variations in tachometer “red lines”? Another consideration is the source of comparable data. The Manufacturer amended its shop manual so that reported static compression specifications differed over the years. Some of this may have been due to various market production differences.

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@Stevehose
I had to give up on my 123 because of oil leaks. Another story covered here.
Been running a stock distributor for a while now. I've noticed much easier revving to over 6500.
I just crank in all the advance I can without getting detonation.
Many of the M30 engine gurus that race have always said the M30 likes a lot of advance.
Mines probably at 36 or so.
10:5 compression and custom cam, probably Schrick 284 or so.
Bigger valves and dual springs.

I still have not gotten to the dyno but have that on the list this spring.
Talked to dyno guy a while back and just need to schedule.

Like was said differences in intakes and fuel delivery are probably those curve changes.
Webers are very direct so some pretty good advance early on. When I had the 123 I think I was all in by 3500.
I doubt you can feel those subtleties of those curves on acceleration. Low speed, maybe.
 
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