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Thread: Stock M10 121ti, E12, E21, E21/30i head flow comparison

  1. #1
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    Stock M10 121ti, E12, E21, E21/30i head flow comparison

    This is something I found looking on the 2002FAQ. I'm not entirely sure how to interpret these numbers. More CFM down low means? More CFM midrange means? More CFM top end means?

    Is this simpler than I'm making it?

    Modifications make everything difficult but sometimes you can't modify outside design perimeters.

    Some flow numbers in CFM @28inhg

    121 head (with large valves)
    Valve lift___intake_____________exhaust
    .1________73.5_______________51.5
    .2________113.5______________92
    .3________146.5______________127
    .4________173.5______________145
    .5________188.5______________153

    E12 head
    Valve lift___intake____________exhaust
    .1________63_______________57.5
    .2________105______________98.5
    .3________148______________124
    .4________179.5____________137.5
    .5________193______________143


    E21 2.0 head (e21 cars and some very late 2002)
    Valve lift___intake_____________exhaust
    .1_________66________________54
    .2_________115_______________95
    .3_________155.5_____________126
    .4_________179.5_____________142
    .5_________190_______________148

    1.8i head (e21 and e30)
    Valve lift___intake____________exhaust
    .1_________66________________50
    .2_________111_______________87.5
    .3_________155.5_____________111
    .4_________182.5_____________136
    .5_________193_______________143

    Source: http://www.bmw2002faq.com/component/...opic/t,313512/

    My interests are primarily for N/A applications, however I'm curious to know what turbo people think of this.
    "The most important thing is balance." - KT

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    Bump.
    "The most important thing is balance." - KT

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    Incredibly inefficient head design!--Thanks a bunch SOHC. Seriously though, it would be interesting to plot this with a mild cam for each application. It wouldn't be hard to do the math now that we have the baseline numbers.

    The 121 head does seem ideal for turbo cars with a bigger hot side, but the E21 heads would be probably the best option for anyone not wanting more than 250whp with SOHC.

    CFM at different points of lift just means how much air by volume is entering or exiting the engine at different points on the cam profile. Having more airflow at a lower lift will provide faster torque response without sacrificing too much in the way of efficiency. You are essentially looking at the dyno curve of an un, or lightly modified engine(NA). In fact, I would bet that if you plotted these cam/head flow profiles over the dynos of the engines they would be quite similar.

    It should also be noted that 28inhg is a vacuum number, and if I'm not mistaken, that isn't how flow testing is done anymore due to inefficiency of the system itself. The 28inhg, however, does adequately represent the maximum airflow of an NA engine-roughly 14psi-about .7psi below ambient pressure-given the altitude, baro, and temp as standard(sea level, 29.92 inhg, and 15*C).

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    not getting the attention this info deserves!! this is rather interesting. so it looks like the stock e21 head is slightly better overall .5 lift if you take the total flow across both valves, saying that i would think that intake flow is more important on an NA than exhaust. So what is the lift on your cam? this just makes me more curious.
    B Road Blaster

  5. #5
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    https://sites.google.com/a/e21legion...a/m10-cam-info 306 IE is in there. I wasn't sure how to interpret the numbers since they appear to have a different scale from Shrick to Ireland.

    I have heard that the shrick 304 lacks lift (compared to what?).
    "The most important thing is balance." - KT

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    They are so close... I just prefered to work with the e30 318-head because there's less junk in the way and it's a newer casting. No mechanical fuel pump, no injector-holes that you need to plug up with?.. I don't know what you plug them up with, old injectors cap'ed off, no thanks.

    Work with whatever head you want I guess, if you can afford a custom piston that matches the specific combustion-chamber design of your head and the compression ratio/application you intend for you engine or mods you can get whatever power you are looking for, just talk to Tony @VAC that's my best advice.

    I just like the e30 318 1.8l head because it's just a good m10 head simplified for N/A-setup and if anyone wants a turbo if you have the e30 318i intake manifold/fuel-rail setup it's like your 1/2 way there, but I'm not a turbo guy haven't looked into that stuff.

    Bottom line you got to put some money into it, I got my 84' 318 head for $75 and all said and done about 2k went into it so, my 2 cents. vibrant

  7. #7
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    blocking the injector holes isnt a bad job if you have the head off, i just tapped the holes and stuck a internal hex bolt in, then just dremeled the end the bolt smooth it doesn disturb the intake flow. if i did it again i would get some threaded aluminium shaft to do the same thing.

    looking at that cam data the lift seems to be about the .5 mark by the time you multiply the lift by the rocker ratio (guesstemated ratio)

    the next thing to know would be what head has the most potential for increasing that flow. jst thinking out loud. like i said before most people just seem to use the head they have with no real stand out gains from one of the other.
    B Road Blaster

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    This is glorious, excellent info!! I've spent some time trying to model the m10 in desktop dyno without these numbers, this will just make it that much more accurate.

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

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    I don't think those numbers are that bad give the displacement and the era of the motor. Also, the stock valve lift is only .356" (9mm) with a 1.3 rocker ratio. The largest cam for the m10 (the schrick 336) only has .481" valve lift. These aint big v8's here..

    1.8 head:
    .1-66/50
    .2-111/87.5
    .3-155.5/111
    .4-182.5/136
    .5-193/143

    By comparison, here's a Chevy LS1 head
    .1-83/62
    .2-134/104
    .3-189/136
    .4-222/165
    .5-240/179

    Here's a link with some good info for comparison, including the info Marquis Rex found on some m20 heads:

    http://users.erols.com/srweiss/tablehdc.htm#BMW

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

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    Oh yeah, and I'll be adding this to the faq, I've been looking for this info for a long time. Thanks!

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

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    I must admit... I do take a shine when it comes to that m20 731 head. Possibly on an early eta block? I will say no more.

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    Quote Originally Posted by jrcook320 View Post
    Oh yeah, and I'll be adding this to the faq, I've been looking for this info for a long time. Thanks!
    As have I. M20 people always had the benefit of knowing which head is best, now I suppose we do too.

    Now I guess we must agree on an analysis of different combustion chamber designs for both N/A and turbo efficiency potential.
    "The most important thing is balance." - KT

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    yeah i think the jury is still out on this one.
    B Road Blaster

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    Here's a few thoughts to consider. A smaller port will have greater velocity at lower flow rates, which means it will be more efficient at lower velocities. I'd like to cc the intake and exhaust ports on my old stock 1.8 head and my ported head. It would also be cool to get my head flow tested, for that matter...

    Other things that can and will affect these numbers are combustion chamber shape and design, valve shrouding, and also the valve and seat cut design. A 3 angle (or more) valve job will improve flow at lower lifts. Unshrouding the valves (if they are shrouded) will help improve flow across the board.

    These do NOT represent the power curve for an engine, which is rpm and volumetric efficiency dependant (read port velocity and the engine's ability to breathe). They represent flow capacity of the head at a certain valve lifts only. The stock cam only has about .35" of valve lift, so any numbers above that don't mean anything to a stock engine. Even a 292 only has .385" valve lift, so unless your running some serious cam, anything over .4" is meaningless.

    Interestingly, the 1.8 head flows better on the intake side but worse on the exhaust compared to the other heads, and the e21 and 1.8i heads are much closer at more feasible valve lifts (.4 and below). I would think that better flow on the exhaust would be better for a turbo application (could be wrong there, I haven't read much on that subject). That said, I interpolated the numbers to get .05 increments for better visiblity. I also graphed them in excel... lol. I'll eventually punch them into desktop dyno and see how it affects that program's power estimates for the m10's I have modelled.

    NOTE: This data is in 28" H2O, not Hg as noted in the original post.

    121 head (with large valves)
    Valve lift Intake/Exhaust
    0.1 - 73.5/ 51.5
    0.15- 93.5/ 71.8
    0.2 -113.5/ 92
    0.25- 130/ 109.5
    0.3 - 146.5/ 127
    0.35- 160/ 136
    0.4 - 173.5/ 145
    0.45- 181/ 149
    0.5 - 188.5/ 153

    E12 head
    Valve lift Intake/Exhaust
    0.1 - 63/ 57.5
    0.15- 84/ 78
    0.2 -105/ 98.5
    0.25 -126.5/ 111.3
    0.3 - 148/ 124
    0.35-163.8/ 130.8
    0.4 - 179.5/ 137.5
    0.45-186.3/ 140.3
    0.5 - 193/ 143

    E21 head
    Valve lift Intake/Exhaust
    0.1 - 66 / 54
    0.15 - 90.5 / 74.5
    0.2 - 115 / 95
    0.25 - 135.25 / 110.5
    0.3 - 155.5 / 126
    0.35 - 167.5 / 134.0
    0.4 - 179.5 / 142
    0.45 - 184.8 / 145.0
    0.5 - 190 / 148

    1.8i head (e21 and e30)
    Valve lift Intake/Exhaust
    0.1 - 66 / 50
    0.15-88.5 / 68.75
    0.2 - 111 / 87.5
    0.25- 133.3 / 99.3
    0.3 -155.5 / 111
    0.35 -169 / 123.5
    0.4 -182.5 / 136
    0.45- 187.8 / 139.5
    0.5 -193 / 143
    Last edited by jrcook320; 03-14-2017 at 05:23 PM.

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    You double posted E12 heads. What are you trying to say...
    "The most important thing is balance." - KT

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    left to right
    1.8, 121 t, e21 2.0

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    http://www.bmw2002faq.com/component/...opic/t,355426/

    Thought I'd copy some more information. This is again from the 2002faq. Its regarding porting an M10 cylinder head and the 2 barrel manifold that it comes with on a 2002. Enjoy.
    "The most important thing is balance." - KT

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    Well, it's kinda hard to say without knowing what 121 w/ big valves means. If it means 1.8 sized valves then I'd pick the 121. On the intake side, all other things being equal, low lift flow has a big influence on things as the pressure drop is greatest during valve overlap due to the vacuum created by the exiting exhaust gasses (engines don't operate at a constant pressure drop), especially if you have a properly tuned headder/extractor for the rpm range you want to make power in.

    Flow bench numbers on the exhaust side aren't as menaingful (I didn't say meaningless) because the actual pressures and velocities are way larger than what it is practical to do on a flow bench, but again low lift flow is crucial to making good power.

    In both cases, I'd give up a little higher lift flow for significanly better low lift flow, especially on these engines as they don't have terribly high max lift to begin with.

    That all being said, that opinion is based upon the figures presented. If you want to talk ported heads the 1.8 has more potential at the disadvantage of larger combustion chambers.

    If you're truly interested in this subject, I highly recommend that you read "How to Port & Flow Test Cylinder Heads" by David Vizard. Also in this book is how to build a flow bench for approx $75.00 USD (assuming you have a reasonably powerful shop vac). If you're a good scrounger and bargain hunter you can do it for less. I know because I did.

    There is one thing I question about those flow numbers and that is the 28 in Hg pressure drop figure, Industry standard is 28 in H2O. That's a big difference.
    Last edited by e21Terry; 08-17-2012 at 08:56 AM.
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  19. #19
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    I think 121 with big valves implies that its a 46mm intake 38mm exhaust like the rest of the M10 heads. 121ti had this setup.

    I know nothing about flowbenches so I can't really comment. I just copied this information from a fella who did it on the 2002FAQ forum.

    You have a good point about the lift. The M10 head is limited by how much lift it can have by the size of the cam journal (or bearings, forgotten my terminology), unless of course you go for an eccentric setup and slot in a 328 or 336.

    I'm curious as to why you say the 1.8L head has more potential? Is that potential to flow, or just potential to make best N/A power overall? Whats the reasoning behind that?

    Yeah I think someone mentioned the in Hg measurement. If you have a flow bench, I'd love to see what you come up with to compare it to what we have here. After some pretty extensive searching on the internets, this was the best I could find. That being said, considering the flow potential of M10's and M20's are pretty close in terms of head design, I found this fellas findings: http://speedtalk.com/forum/viewtopic.php?p=83856 to validate the findings of the M10 flowbench tester. Its probably safe to say that its possible its not exact, but its pretty close?

    I'll let you be the judge sir.

    In the meantime, I shall quote a few paragraphs from Graham Bell's Four Stroke Performance Tuning, (Third Edition 1998) for the builders out there to keep in mind.

    "The Cylinder head is the most important area to be considered by the serious tuner. Its design has more bearing on the end result, performance-wise, than any other component of the high performance engine. There is no way in which high horsepower can be obtained if the head won't flow efficiently, and in turn burn that air fuel mixture efficiently.

    Many tuners go to extremes, cramming as much air into the cylinder as possible, only to have a combustion chamber that won't burn the mixture efficiently. Personally, I am unimpressed by air-flow figures; they tell very little about how well a head has been modified. There is no point in getting a lot of mixture into an engine unless you can manage to burn it at the right time, and if you try too hard to get high flow figures, you can easily end up with a combustion chamber that won't burn effectively. While I believe a gas flow rig is an aid in head development, I also believe that it is possible to look at a port and decide whether or not air would like to flow through it. A port that is nice and straight and has no projections will generally flow well. Until recent times many engines had a head design so horrible that to create an improvement was relatively simple.

    It has always been thought that there is a direct relationship between high air flow numbers and high power output. In principle this theory sounds correct, but in practice it does not always work out that way. At one time a factory racing department picked the best high-performance heads off the production line for modification. After being ported, each head was flow checked. The heads that recorded the best results were kept for the factory racing team, and the supposedly inferior heads were sold to selected privateers. The interesting thing is that on the dyno, the engines with the heads that produced the best air-flow figures actually recoded power outputs no better than the engines with average flow heads. After this discovery the factory tested all their heads for power output, before any were released to the private teams, and the found that some of the average heads they ha been selling produced the best power."

    Great read and design reference this one. Lots of empirically derived data to back up his claims.
    Last edited by FranzE21; 08-17-2012 at 11:07 AM.
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  20. #20
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    Quote Originally Posted by Big John View Post
    I'm curious as to why you say the 1.8L head has more potential? Is that potential to flow, or just potential to make best N/A power overall? Whats the reasoning behind that?
    I haven't flowed a m10 head so this is speculation on my part, but I'm fairly certain that with proper development with valve & seat geometry the 1.8 head could be made to flow at least as well as the 121 at low lift. Combine that with the better higher lift figures of the 1.8 & you've the best of both worlds.

    I built my bench 20 some years ago, with a home brewed venturi meter (you said your governer's a ME, he can explain) to measure flow and did all my testing at a constant 28" H2O pressure drop which was the gold standard at the time and was working on Ford V8. I was limited in what I could do as far as valve & seat angles because I didn't have the equipment & had to send it out to get changes which gets expensive. I'm in the process of updating the bench now to incorporate Vizard's concepts and hope to be flowing m10 1.8 & m42 heads in the near future. I came up with the idea of making slip - fit valve seat inserts that I can make on my metal lathe with various geometries that can be easily switched in & out which will greatly lower the cost & time to test a large range of configurations. Also, I can grind valves on the lathe with the tool post grinder. Then, when I find what I believe to be optimal, I can send a head out to be cut to my specs once. Brilliant, eh? If anyone has old valves they want to donate, I'd appreciate that.
    Last edited by e21Terry; 08-17-2012 at 11:33 AM.
    "The water was not fit to drink. To make it palatable, we had to add whisky. By dilligent effort, I learnt to like it." Sir Winston Churchill

  21. #21
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    Quote Originally Posted by Big John View Post

    You double posted E12 heads. What are you trying to say...
    Finally fixed this...

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

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    VERY useful info itt. when port flowing heads it always nice to go as high as possible to see when the flow starts dropping off then you can plan to lift to that number so you hit the highest flow twice on the cam profile (while opening and then again while closing) instead of just once.

    But, as was mentioned, M10 cams dont lift very high. So prep to do alot of head work. the first thing i always do is get the biggest valves and give them a 4-angle head. I also found that if you build up a little ramp with welding material in the intake tract where it bends right before the valve, you increase air velocity and flow. Unshroud the valves as jrcook said and then have it extrude honed and you know the rest.

  23. #23
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    After reading Vizard's book, there are two things I'm particularly interrested in investigating. One is fairing (streamlining) around the valve guide, and the other is valve seat angles less than 45 deg. A shallower valve seat angle produces more "curtain" area for a given lift and can significantly improve low lift flow.
    "The water was not fit to drink. To make it palatable, we had to add whisky. By dilligent effort, I learnt to like it." Sir Winston Churchill

  24. #24
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    Heres and interesting video ive always liked.

    [ame="http://www.youtube.com/watch?v=sY10X0WDoUo"]http://www.youtube.com/watch?v=sY10X0WDoUo[/ame]

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