M20 Cam Profiles

[reggid]

Profiled a couple of cams, one from a late 320i and one from a late B25 that i have had lying around. It produced some interesting results. I will find another to get a second set of data as well as do a B23 and B27 cam.

M20B20 (L stamped on it)

Peak Lift: 10.00 mm / 9.70 mm
Lift TDC: 1.6 mm / 0.7 mm
CL: 107 / 113
LSA: 110
Duration @ 0.05": 215 / 208


M20B25 (K Stamped on it)

Peak Lift: 9.95 mm / 9.10 mm
Lift TDC: 0.95 mm / 0.45 mm
CL: 112 / 108
LSA: 110
Duration @ 0.05": 212 / 196

[HairyScreech]

very interesting, seems the m20b25 cams have two versions, the normal ones and the ones stamped with a K.
all the b25 cams i have here have all measure exactly 10.3mm lift.

im happy to send over my results from both the lobe and valve.
one thing i did find is that the rocker ratio changes quite dramatically over the range of motion, i gave up trying to make an equation for the rocker ratio as it just changed too much.

would be interesting to compare your numbers to mine.
what set up are you using to measure them? Degree wheel and a DTI?

[reggid]

very interesting, seems the m20b25 cams have two versions, the normal ones and the ones stamped with a K.
all the b25 cams i have here have all measure exactly 10.3mm lift.

im happy to send over my results from both the lobe and valve.
one thing i did find is that the rocker ratio changes quite dramatically over the range of motion, i gave up trying to make an equation for the rocker ratio as it just changed too much.

would be interesting to compare your numbers to mine.
what set up are you using to measure them? Degree wheel and a DTI?

I wasn't intersted in the lobes what matters is what the valve does and variable rocker ratio makes it harder to predict the profile just from the cam alone.

i used a dial indicator to measure valve lift with lash set to zero. My degree wheel was the cam sprocket so i was able to measure at every 3.75 cam degrees or half tooth which seemed to be a good resolution except perhaps at the ramps.

I have heard there are two versions of the B25 cam we only got the 8.8:1 B25 engines with 256k1 engine code (apart from private imports) so that explains the K. It also sort of makes sense to run a smaller exhaust lobe for emmisions and maybe the reason for early B25 out performing the later ones.

I have a B23, another B25, possibly schrick 288 and B27 cam coming plus when i get a 270ish cam from schrick or dbilas.

I will use the same head, rockers etc and makes sure there is no visible wear on the lobes so there is a direct comparison.

[HairyScreech]

iv got a good trick for the degree wheel, at the bottom of this page:
http://www.dprracing.com/pc.htm
There is a timing disc picture, iv printed one out and stuck it onto an old CD.
Also if you twist some wire up to make a little loop then you can line up what degree you want into the centre of the loop, thus removing some of the parallax error involved, makes it much less strain on the eyes.

iv been doing them every degree so far (OCD much?) as iv got concerns over the accuracy on the opening/closing flank and around peak lift dwell. Certainly for the b20 and b25K cams this is not much of an issue as we know they are not going to be the hottest cams but it might be worth it for the b23 and the other b25 cam.

im going to do Si13's alpina cam when i go up to pick up a head from him, i think that is an alpina c2.7 cam.
Would be good to get a proper database of cam profiles up on here so we can make real informed decisions as to what cams are better for each application.

iv got airflow data for both of the standard heads as well, so that allows the airflow to be plotted as a function of valve lift, thus giving real world flow potential as some cams with less lift but steeper flanks may get more air past the valve.

this is great that your taking the time to do this, it will really help everyone in the future.

[reggid]

It is a shame I didn't know what I now know when I did my b31 build 5 years ago I think I would have been better informed. I had a genuine alpine cam that I sent to a guy in the states who profiled it against a b25 cam I will post the graph here when I am at home

[reggid]

i did some more checks and it looks like had an error with my setup with the initial measurements. I am redoing the measurements again. Will update when done.