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Thread: Tech talk: Why 2v heads need more advance than 4v heads.

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  2. #27
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    Quote Originally Posted by 5mall5nail5 View Post
    ........... It's called tuning my friend.
    I have heard that word once,I have to google it.
    My question was,is it detonation limited at 12,or it is where it makes most power?

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    Quote Originally Posted by 5mall5nail5 View Post
    Heh - ouch.
    Not to mention a few 24psi spikes trying to figure out the boost controller.
    But yea 19psi is the limit.
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    Quote Originally Posted by bawareca View Post
    I have heard that word once,I have to google it.
    My question was,is it detonation limited at 12,or it is where it makes most power?
    My personal car was not detonating, but my clutch couldn't cope. Based on lower pressure figures 12 seems about where I'd want to be.

    Quote Originally Posted by good & tight View Post
    Not to mention a few 24psi spikes trying to figure out the boost controller.
    But yea 19psi is the limit.
    Yah - gotta tweak that overboost setting

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    My question is this: We know that 2v heads present much more restriction, which, in comparing megasquirt tables (you're the one to talk to about this, I think) shows up as higher VE. It's not just swirl/tumble that the 24v heads have an advantage in (though I think you're right that the combustion dynamics are what is, partially, what is demanding more timing. If the cylinder pressure is less due to lower VE, then you'll need more timing anyway, right?

    So if we normalize to VE*Manifold pressure...how does the comparison look then? And more importantly, does this limit power in practice? I'm assuming that a less even flame front propagating more slowly in the chamber somewhat increases the tendency to detonate at a given cylinder pressure, but does this effect the tq capability of the engines in question?

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    M20s are in-efficient. Period. Boost fixes a lot of those issues.

    I can has 32v LSX?

    http://www.araoengineering.com/lsx.htm

    They claim 100hp right off the bat.

    My dream engine is a 32v flat plane crank LSX that revs to 9000RPM. I could care less about the power it makes.

    Rob - 2000 BMW Z3 M Roadster | 1986 Porsche 944 5.3L LM4

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    Quote Originally Posted by Robstah View Post
    M20s are in-efficient. Period. Boost fixes a lot of those issues.

    .........
    Compared to what?To be fair,you can compare it to something of it's era,i.e. late 70s

    Quote Originally Posted by Robstah View Post
    ...............
    I can has 32v LSX?

    http://www.araoengineering.com/lsx.htm

    They claim 100hp right off the bat.

    My dream engine is a 32v flat plane crank LSX that revs to 9000RPM. I could care less about the power it makes.
    I was left with the impression that is a BMW forum
    Last edited by bawareca; 03-17-2012 at 01:11 AM.

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    Quote Originally Posted by 5mall5nail5 View Post
    You are running timing figures that I run at 30 psi on pump gas w/ methanol. Extremely soft.
    Pump gas and Meth is different from just pump gas.

    Also I have done lots of testing and i have first hand seen the differences between mbt and what my datalogger is reading from the knock sensors. A fee extra degrees making 10-15whp more is not worth putting a motor that close to knocking.

    I am extreamly happy with the horsepower and torque numbers I end at.. I look to make the maximum safe power.
    Last edited by RK-Tunes; 03-17-2012 at 12:31 AM.
    RK tunes

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    Very interesting graphics Jon, I hadn't considered how significant swirl in the combustion chamber was to burn rate. Until now I had mostly considered CC shape (ie pent roof, hemi etc) for flame propagation.

    For those who have not read it, this article about knock and pre-ignition is related and talks about burn rates affecting octane requirement and CR. http://www.contactmagazine.com/Issue...ineBasics.html


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    Also. Very nice information in this thread jon.
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    Does compression ratio not come into play here?
    not many boosted 2v motors around here running more than 8.8:1 that i know of?

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    http://www.e30tech.com/forum/showthread.php?t=33028

    That is very informative thread with many M20 timing maps posted.Most guys(including me) run ~20 degree @200 kpa and ~ 14 @ 250 kpa with pump gas.if i make the approximation it should be 8-11 degree @300 kpa.I dont see how one can run half of that timing and make reasonable power.
    I wanted to find 24v map for comparison,but looks like they are very secret

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    Quote Originally Posted by BobRoss View Post
    Does compression ratio not come into play here?
    not many boosted 2v motors around here running more than 8.8:1 that i know of?
    It does come into play but this thread is focused mainly on CC swirl and spark plug location.

    High CR will increase flame speed but in a 2V hemi head the flame has to travel a long way around and over the dome of the piston which means a longer burn. Having a longer burn will increase heat buildup and increase the potential for detonation. That is why a pent roof chamber can safely run a higher CR than a domed head and it will require less timing to achieve peak cyl pressure at 14-15deg ATDC
    Last edited by Bwaterman; 03-17-2012 at 12:46 AM.


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    Quote Originally Posted by BobRoss View Post
    Does compression ratio not come into play here?
    not many boosted 2v motors around here running more than 8.8:1 that i know of?
    i run 9.5:1 currently,but didnt go the dyno yet.I will have the results in a month.

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    It´s got more to do with the overall turbulence rather then swirl.

    I.e the tiny TINY eddy currents created as the piston is pushing up on the mixture.

    Two things create turbulence, air density and engine speed.

    Air density then breaks down into : A combination of air volume and compression ratio.

    Engine speed creates turbulence thanks to faster moving piston.

    Those two also dictate why ignition advance must change with fixed VE over a range of engine speed.

    The flame propogation speed is the results of turbulence. As you start burning a little eddy current it rotates and ignites the adjacent ones, the faster they spin the faster they come in literal contact with other eddy currents to ignite them.

    I think the easiest way to visually this is the mythbusters episode when they where burning gas to blow out pot hole covers, when they stuck a whole bunch of springs and stuff into the pipes that created turbulence as the gas infront of the burn was getting pushed by the rise in pressure behind it, when it moved past the springs little eddy currents where made, when the flame finally cought up with the now turbulent air the flame propogation accelerated faster and faster. Squish area also helps with this in the final push of the piston to the top.


    If we imagine a fixed engine with nothing changing but engine speed you will need higher and higher ignition advance to account for the ignition delay which is a fixed time so that peak pressure can occur at the right moment.

    In the real world two things happen, VE drops after peak torque which causes a need for more advance, however with more engine speed you also get more natural turbulence which requires less advance to be put in. The results are that sometimes after peak torque that ignition advance doesn´t need to be raised as much or at all.

    The less the ignition advance for MBT the higher is the turbulence design of the cylinder, and with that higher efficiency for the given airflow amount as you are creating less work against the engine while it´s on the compression stroke, giving you more final output.

    Given a M20 and M50 engine with the same amount of air density, compression ratio and engine speed the M50 will be more efficient due to plug placement. The M20 is designed with swirl inducing pistons and chamber which helps its efficiency but the M50 has tumble (pent roof) designed which starts turbulence sooner in the piston stroke which ultimately helps with flame propogation.
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    Quote Originally Posted by RK-Tunes View Post
    Pump gas and Meth is different from just pump gas.

    Also I have done lots of testing and i have first hand seen the differences between mbt and what my datalogger is reading from the knock sensors. A fee extra degrees making 10-15whp more is not worth putting a motor that close to knocking.

    I am extreamly happy with the horsepower and torque numbers I end at.. I look to make the maximum safe power.
    Are these knock sensors oem sensors and oem ecu?

    I would like to know , if oem sensors can detect knock when you convert n/a car to turbo car? I mean, I heard that knock frequency changes when the car is boosted. Or can the oem sensors think, the car is knocking but while it is in boost and not knocking.

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    Quote Originally Posted by bawareca View Post
    Compared to what?To be fair,you can compare it to something of it's era,i.e. late 70s


    I was left with the impression that is a BMW forum
    We are talking about 2 valve heads vs. 4 valve heads. Someone has already posted pictures of other make 4 valve heads.

    My point with the M20 and all 2 valve motors is that boost tends to help with the inefficiencies. NA applications will see the biggest benefit between 2 valve and 4 valve heads.

    Rob - 2000 BMW Z3 M Roadster | 1986 Porsche 944 5.3L LM4

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    Quote Originally Posted by 5mall5nail5



    So the reason why a 4v motor might only want 20 degrees where a 2v motor might want 35 degrees is because the flame moves slower through the chamber in a 2v motor and that delta of 15 degrees (hypothetical figures used). So to time it such that the flame is at its most complete state at the end of the compression stroke the initial spark needs to occur that many degrees in advance.

    Just thought some one might find this visual explanation useful.
    The meat and potatoes as some would say.
    Quote Originally Posted by RK-Tunes
    It depends on the set up.
    here is what ive gained from my recent experiences--

    17 psi at 515whp on a m52 at 9* mid range and 13 at redline I saw no knock and the car could have taken 2-3* more timing easy. This a a efficient set up.

    on a less efficent set up at 20psi with a pt61 the car would have slight knock at over 9* in the midrange.

    With 630whp on a 3.2 it was at 20psi it was at 8* mid range no knock.

    At 14psi with 450whp 13-14 degrees in the midrange and 20 up top doesn't knock. This is with a efficient set up. With a cast manifold/ smaller intercooler expect 1-3 degrees less timing.
    Jordan, I'm not questioning your tuning abilities (obviously you've done well thus far), but isn't that very soft even for pump gas? Most people post around ~13*.
    Btw, I'm not a tuner, but in the cases I've seen with soft timing, the EGTs were on the high side. How were yours?
    Also, are you calling "midrange" where torque crosses over the power line?

    Quote Originally Posted by Robstah
    M20s are in-efficient. Period. Boost fixes a lot of those issues.

    I can has 32v LSX?

    http://www.araoengineering.com/lsx.htm

    They claim 100hp right off the bat.

    My dream engine is a 32v flat plane crank LSX that revs to 9000RPM. I could care less about the power it makes.
    Off topic but I bet that would sound awesome!
    I'm not too familiar with flat plane cranks but what are their power making abilities like?
    Last edited by BadBoostedBmwM3; 03-17-2012 at 09:30 AM.
    This is my signature....

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    Quote Originally Posted by VwAlex View Post
    Jon = hpf fanboi his opinion = no value
    LOL you can't be serious!

    Quote Originally Posted by livinginexile5 View Post
    Last time I checked top fuel and funny car were 2 valve motors they are in the 8-10k HP range...

    Additionally with nitro meth being the fuel they run they are required to start their ignition insanely early something like 30 degrees at idle. Can it be called inefficient to burn that early sure but last time I checked the folks concerned with mpg are rarely concerned with power

    I’m in no way advocating that 2 valves are inherently better than 4 valves - I’m just playing devil’s advocate.

    I do believe that there are massive benefits to be had from 4v or even 5v heads but I certainly don't believe that there is inherently anything wrong with the m20/m30/top fuel BBM (big block mopar), because as we all know forced induction has long since been an equalizer of poor intake/head design

    Lastly and certainly not least, since there seems to be so much bashing of the old and so little appreciation of the old(er) engines just remember Offenhauser turbocharged a 4 cylinder 4 valve head back in the 19-teens and made over 1000 HP it evolved into the Indy race engines of the 1980's. Had safety been on par we probably would still be running those engines in one variant or another.
    Again... some people need to read the title. It's not about "how many valves are in engines making the most power". Turbo fan engines make way more power than a top fuel motor. That's not what we're talking about. We're talking about why 2v heads require more timing to make the same effect as a 4v head.... on our BMWs since we're on a BMW forum (though it loosely applies to all combustion chambers). We're not talking about more or less power. We're talking about ignition timing tendencies.

    Quote Originally Posted by gstuning View Post
    Given a M20 and M50 engine with the same amount of air density, compression ratio and engine speed the M50 will be more efficient due to plug placement. The M20 is designed with swirl inducing pistons and chamber which helps its efficiency but the M50 has tumble (pent roof) designed which starts turbulence sooner in the piston stroke which ultimately helps with flame propogation.
    Thanks for your input Gunni. Always appreciated.
    Last edited by 5mall5nail5; 03-17-2012 at 09:50 AM. Reason: Automerged Doublepost

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    Quote Originally Posted by 5mall5nail5 View Post
    Quote Originally Posted by gstuning View Post
    Given a M20 and M50 engine with the same amount of air density, compression ratio and engine speed the M50 will be more efficient due to plug placement. The M20 is designed with swirl inducing pistons and chamber which helps its efficiency but the M50 has tumble (pent roof) designed which starts turbulence sooner in the piston stroke which ultimately helps with flame propogation.

    Thanks for your input Gunni. Always appreciated.
    No one is arguing that M50 is more efficient than M20 and M30.Even if I never saw any of those i will tell that the newer generation [BMW] engine is more efficient than the old one.With other manufacturers 4 V design may be superior in light years than the 2V, but that is not the case with BMW.As one can see from the link with the M20 ignition tables the numbers are pretty close,so are the power levels.

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    Quote Originally Posted by bawareca View Post
    No one is arguing that M50 is more efficient than M20 and M30.Even if I never saw any of those i will tell that the newer generation [BMW] engine is more efficient than the old one.With other manufacturers 4 V design may be superior in light years than the 2V, but that is not the case with BMW.As one can see from the link with the M20 ignition tables the numbers are pretty close,so are the power levels.
    Your problem (along with many others here) is this...

    You're not seeing why most 2V engine designs require more advance then a 4V engine design.

    Stop comparing the timing tables you see on E30tech to others.... the ones you see for "running" setups will be influenced by other factors.

    5mall5nail5 and Gunni are completely correct here.

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    Quote Originally Posted by NOTORIOUS VR View Post
    Your problem (along with many others here) is this...

    You're not seeing why most 2V engine designs require more advance then a 4V engine design.

    Stop comparing the timing tables you see on E30tech to others.... the ones you see for "running" setups will be influenced by other factors.

    5mall5nail5 and Gunni are completely correct here.
    But your post is just some words put in one sentence,and the title of that thread is TECH TALK.I can say that you have never saw a piston in your life,but that has nothing to do with that thread.What I "see on E30tech" is what I see on my map,and is a good refference point.At least it is more than just say someone "You dont know,you dont see....."
    What John said is that M20 needs 2 times more timing than M50,which i dont agree.Plus he never explored the limit,where the power will start going down because he is "clutch limited",according to his post.
    Last edited by bawareca; 03-17-2012 at 11:17 AM.

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    Quote Originally Posted by bawareca View Post
    But your post is just some words put in one sentence,and the title of that thread is TECH TALK.I can say that you have never saw a piston in your life,but that has nothing to do with that thread.What I "see on E30tech" is what I see on my map,and is a good refference point.At least it is more than just say someone "You dont know,you dont see....."
    What John said is that M20 needs 2 times more timing than M50,which i dont agree.Plus he never explored the limit,where the power will start going down because he is "clutch limited",according to his post.
    I've tuned and helped tune about a dozen or more M50-based motors on standalones. I am not going by just my own engine here. An M20 requires more timing than M50 to do the same work. Fact.

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    Post it up!
    I think this is still my tune (car is in the shop still getting the new motor)
    My E21 tune.

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