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B-Merry

Comparing M10 Cams - BMW and Schrick

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I came across some data while investigating M10 camshafts that I found to be quite interesting, and possibly providing an explanation of something that I did not understand. The data regards the stock BMW 264 cam for the M10, and it is taken from this thread on bimmerforums:

http://www.bimmerforums.com/forum/showthread.php?1309037-stock-m10-valve-lift-and-cam-specs

“These are the specs per the BMW published blue book repair manual:

base circle diameter: 26.7612mm

Cam lift: 7.026mm

Valve lift: 9.13mm (1.3 rocker ratio)

114 deg lobe separation

Duration @ .020": 236*

IVO :4* btdc, IVC:52* deg abdc,

EVO: 52* bbdc, EVC: 4* atdc

Duration @ .011": 264* (This is the equivalent to advertised duration, most cam specs you see are likely measured at this lift)

IVO :18* btdc, IVC:65* deg abdc,

EVO: 65* bbdc, EVC: 18* atdc”

What caught my eye was the 28 degree difference in cam duration, depending on whether the duration was measured using .020” or .010” of lift to demark the beginning and end points of the cam duration measurement.

The thing that I was seeking to understand is this: my mechanic, who has extensive experience with these cars (has worked on them for 40 years, raced them, and built all kinds of engine configurations), indicated to me that he felt the Schrick 284 was fairly comparable to the BMW Sport 300; and that the Schrick 304 is much more aggressive than the BMW Sport 300. After reading this data I began to wonder how Schrick measures cam duration. (i.e., at what lift do they begin and end the cam duration measurement?) Getting a definitive answer has been elusive. I looked at the specification sheet for Schrick cams:

http://www.turnermotorsport.com/image/engine/schrick_tech_2009_BMW_only.pdf

They don’t specify this information, but they do provide a graph at the end of the document which uses a lift of 0.5mm (= .0197”) in defining the duration. (The Schrick catalog uses the same graph and also mentions 0.5mm in its discussion of cam duration measurement, but does not state that this is their standard.) Does this apply to the Schrick M10 284/292/304 cams? I don’t know. But if it does, it seems that when comparing the BMW 264 to the Schrick cams, one should use the 0.02” BMW duration measurement of 236 deg. If this is true then one would expect a somewhat similar adjustment to the BMW Sport 300 cam duration, assuming it too was measured using 0.01”. Since the 300 has greater lift overall than the 264, the leading and trailing edges of the profile may have greater slope (so the transition from 0.01” to 0.02” may be somewhat shorter for the 300), and therefore it seems that the 300 might be more in the 272-280 degree range if measured at 0.02”.

I’m hoping someone on the forum has specific insight into how the Schrick cam durations are measured and whether I’m on the right track here or just completely wrong. Anyway, it does seem safe to say that comparing cam durations without verifying the method of measurement could result in erroneous conclusions.

Also, obviously duration is not the only factor characterizing cam performance. Valve lift and the overall cam profile are clearly important. In this regard, the valve lift of the 264 and 284 are 9.13mm and 9.5mm. The 300, 292 and 304 are 10.0mm, 10.0mm and 10.7mm, respectively.

If I’m on the right track then one would expect the Schrick 284 to differ significantly from the BMW 264 - not a "mild" change as I've seen it described. The 300 would be somewhere in between the 284 and 292; and the 304 substantially more extreme than the others.

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That's interesting about the BMW 300 cam. I had a reground copy from ISKY of the BMW 300 cam in my last motor. It went pretty good but it definitely was not a super high-end power cam. I think the key with that cam, is that it's for side drafts only and still tractable for regular Street driving, thus the reason BMW may have offered it for TI spec motors.

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I don't know much about the technical aspects of either, but I drive an engine built by Bill Holman, one of five I think, that has a Schrick 304, along with dual throttle bodies and 9.5 Mahle pistons.  There is some low end grunt, but it comes on hard, and I mean hard at 4,000 and pulls like a freight train up to 7,500.  My local mechanic sounds like yours.  He doesn't understand why Holman put this much cam in a street car, should never have been more than the Schrick 284, blah, blah, blah.  All I can say is I'll take the 10 miles per gallon.  Try catching me.

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Do not have  a direct answer to your question.  This is somewhat of a "black art" considering not all cam manufacturers and/or regrinders use the same formula to determine duration.  In a prior thread regarding other off-brands, e.g., DeLong, Toby made a similar observation.

 

BMW measures duration from 0.000 in lift.

Most US cam grinders measure it from 0.050", because it's a lot more meaningful in terms of actual flow.

So if their degreeing is at 0.050", that's actually a pretty aggressive cam...   http://www.bmw2002faq.com/topic/65663-delong-mystery-camshaft/

 

 

 

 

 

cam-duration1.jpg     cam_spec.jpg

 

 

ctrp_0805_09_z%2Bcam%2Bdegree_wheel_4.jp

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I bought a used (up) head that had short sections of rocker shafts and two valves/rockers installed, with puny springs.  I believe it had been used to measure camshafts.  

 

This thread made me do a little research online, to try and understand the process involved.  I found this video 

which sheds some light on the 'black art' of measuring.  It showed me that it was a bit more involved than just hanging a dial indicator over the cam, with a degree wheel.  That is what is involved, along with a calculator and a bit more 'technique' than I'd anticipated.  

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Thank you for the replies.

Nice video Mintgrun. In this example the cam manufacturer provided the defining lift measurement, .05". (Actually, if I understood what he was doing correctly, the 0.05" was the cam lift not the valve lift. The corresponding valve lift with that rocker arm was 0.05" X 1.52 = .076".)

It would be nice to know what Schrick used on the M10 cams. I have emailed tuning@schrick.com asking for this information. If I receive a reply I will post it.

Jim

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Cam mfrs don't have all the other mechanical bits and pieces to give the lift at valve.  They can measure the cam in their shop and that's it.

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Thank you for the replies.

Nice video Mintgrun. In this example the cam manufacturer provided the defining lift measurement, .05". (Actually, if I understood what he was doing correctly, the 0.05" was the cam lift not the valve lift. The corresponding valve lift with that rocker arm was 0.05" X 1.52 = .076".)

It would be nice to know what Schrick used on the M10 cams. I have emailed tuning@schrick.com asking for this information. If I receive a reply I will post it.

Jim

 

Rocker arm ratio actually changes through the rotation of the engine to be precise.  The center of the lash pad isn't always the point of contact.  Duration is usually measured after a certain amonut of lift.  Usually enough to take up the slack in the system or at .050 because that's the amount required to compress the hydraulic tappets or lifters.  On engines like ours, duration is usually measured at the factory lash or no lash.  The importance of schrick cams vs stock cams is the machine required to produce.  You've got to understand the cam is not a symetrical profile.  Schrick cams utilize more agressive ramp profiles which result in better valve train acceleration at high rpm with better flow profiles.

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B-Merry,

 

I think I can explain this one. First a caveat is that I am a Mechanical engineer with many years working in engine performance applications but not a mechanic or someone with extensive M10 experience. Basically I don't know squat about the specifics of the Schrick or BMW cam or how they interact with a M10 system. The 0.020" or 0.010" or 0.5mm or what ever spec you are looking at in which the opening and closing angles are given is an attempt to account for the closing and opening ramp angles. These angles are not shown in the cartoons posted above but exist in actual cams. The ramps exist to slow down the valve seating velocity and lower the initial forces under opening between the rocker and valve stem. There is no hard and fast standard that applies everywhere and for valve train but believe me is the devil is in the details. You can get a Phd in this stuff. If you are able to get a plot of each cam you want to compare I can take a look. Or if you know of people that already have the cams installed I can walk you though how to measure the cam profile in engine with a dial gauge and degree wheel.

 

Long story short if you don't have the specifics go with someone that has objective experience (data is best) with both cams and avoid the sales pitches.

q

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... if you know of people that already have the cams installed I can walk you though how to measure the cam profile in engine with a dial gauge and degree wheel.

I agree that being able to plot various cams (valve/cam lift vs angle) would be very informative. If anyone here has this information it would be great if they would post it. I just assumed this information would be harder to get than the measurement points (.01", .02", .5mm, etc.) for the duration data that they already publish. Maybe Schrick will provide it in a reply to my email.

My point was that if you just look at the 264, ..., 304 "duration" numbers you would think that the 300 and 304 are close, which I don't think they are. If you look at max valve lift you would say the 300 and 292 are similar. But I expect the 292 is somewhat more extreme than the 300, which is perhaps closer to the 284.

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If you read the description in the Schrick catalog, it says that the duration and timing numbers "are shown minus the ramps".  Basically this means that it's the full opening duration of the cam minus the valve clearance ramps.  Which is 0.2mm (0.008in) on the 284 and 292 cams and 0.25mm (0.010in) on the bigger cams.  This agrees with the numbers I measured on a Schrick 304 cam a long time ago.

 

Also, not that it matters that much, but the factory BMW spec of 0.011" is actually spec'd as clearance between the cam and rocker pad, not at the valve.  That number coincides with approximately 0.014" at the valve.  The factory 264 cams I've measured tended to be 264 degrees of duration at more like 0.008", but a few degrees at those really small lift numbers don't really matter much.

 

So technically the Schrick numbers are measured at 0.008" or 0.010" lift depending on the cam, and the factory cams are measured at 0.014" lift.  Close enough to be comparable I would think, if you're just comparing full duration numbers.

 

 

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Heh.  The answer is, you'll like the cam you choose for your own reasons.  Or not.

 

When I measured a bunch of stuff, I found that the ramps played a huge part in how

the numbers flopped around, and that actually graphing out what the VALVE was doing

through a whole cycle gave me the best seat- of- the- pants idea how it'd work in the engine.

 

But keep in mind things like, sidedrafts don't really like a lot of reversion on the street,

and on the track that reversion has to be managed in the intake plenum.  Header and

exhaust flow interacts with everything.  Valve springs are probably the most important thing

to manage as lift, rate and revs rise.

Wet birds never fly at night.

 

And so forth.

 

Your numbers WILL vary.  Mine certainly did...

 

t

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When comparing, keep in mind how the lobe centers ('lobe separation') alter the camshaft's characteristics and performance. -KB

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Thank you for the replies.

Bent - your explanation is quite clear. It seems that the duration numbers are meaningful and useful for comparing that aspect of the cam's design after all. No doubt there's a lot more going on than what the duration and maximum lift data can convey. I do think it would be very revealing to see all of these cams plotted on a single chart for comparison.

Jim

Edited by B-Merry

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I used a cam from Dema Elgin for my race motor. http://www.elgincams.

When selecting a cam all the variables have to be in place. Port size/flow,Rules,Etc.

I am allowed 11:1 comp ratio,Valve lift is limited to .450,stock rockers.

Dema asked for pertinant information that I supplied. G

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