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Thread: Knock sensors revisited

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    Re: Knock sensors revisited

    So the fast-burn head basically trades off power potential for greater efficiency, and as such only works well up to a certain level of combustion pressure?
    Rob M.
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    Re: Knock sensors revisited

    Quote Originally Posted by Force Fed Mopar View Post
    So the fast-burn head basically trades off power potential for greater efficiency, and as such only works well up to a certain level of combustion pressure?
    I would add the octane of the fuel you are running. The swirl and tumble designs are not exclusive to the 2.2/2.5. The swirl design provides a similar function of the tumble port without using a squish pad. The trick is to try and retain the swirl at elevated power levels. That's where the head porter can make a difference...or some kind of octane enhancement or both.

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    Re: Knock sensors revisited

    Wow, really enjoying the part of this thread on combustion chamber efficiencies. I'd like to add for what it's worth that there are other external variables that can influence detonation as well. Such as the presence of engine oil in the chamber, either from the intake or through the valve, and humidity. It is possible to tune a car on a humid day and experience knock with the same tune under dramatically less humidity.

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    Re: Knock sensors revisited

    Quote Originally Posted by wallace View Post
    I would add the octane of the fuel you are running.
    Octane will buy back spark advance and suppress knock but effort to corrective the main issue(s) will minimize the need.

    Quote Originally Posted by wallace View Post
    The swirl and tumble designs are not exclusive to the 2.2/2.5.
    The swirl design provides a similar function of the tumble port without using a squish pad. .
    Although, a head design to either include or omit squish and the intakes bowl/port to induce swirl are not mutually exclusive.
    In other words, if the material is filled in on the long side of the intake valve within the chamber (to gain additional squish for knock suppression) most if not all of the swirl can still exist and be retained.
    With the 782, the lack of combustion chamber squish is the most significant contributor to knock.

    Quote Originally Posted by wallace View Post
    The trick is to try and retain the swirl at elevated power levels.
    That's where the head porter can make a difference...or some kind of octane enhancement or both.
    Again, the fastburn came in as an emission and idle/mid throttle quality improver but its introduction made it a challenge to reach the previous year Turbo-I rating numbers.
    Even though the need for combustion chamber swirl is reduced on forced induction vehicles, for obvious reasons; a conscious porting effort can retain whats needed to provide pre-boost throttle response.
    This includes decent port velocity and good flow throughout the valve lift range (not just peak) but neither depends on swirl, to be successful.

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    Re: Knock sensors revisited

    Quote Originally Posted by 86TSiGuy View Post
    Wow, really enjoying the part of this thread on combustion chamber efficiencies.
    I'd like to add for what it's worth that there are other external variables that can influence detonation as well.
    Such as the presence of engine oil in the chamber, either from the intake or through the valve, and humidity.
    It is possible to tune a car on a humid day and experience knock with the same tune under dramatically less humidity.
    These details are excellent points - well said !!!!

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    Re: Knock sensors revisited

    Also, from what I understand, "swirl ports" and "fast burn chambers" do not need each other to be in a design. For instance, the 302 casting 318 heads and our 782 "swirl" heads, do not actually have "swirl ports" as I understand it. They only have fast burn chambers that induce swirl when the intake charge flows in. If you look at them you can see this, as the ports are essentially the same as "non-swirl" heads.

    On the other hand, the 5.2/5.9 Magnum heads do have a swirl port design in them, as well as a fast burn chamber.

    Again, this is only what I have understood from reading in various places, if I am wrong please correct me!
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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    Re: Knock sensors revisited

    Quote Originally Posted by Force Fed Mopar View Post
    Also, from what I understand, "swirl ports" and "fast burn chambers" do not need each other to be in a design.
    For instance, the 302 casting 318 heads and our 782 "swirl" heads, do not actually have "swirl ports" as I understand it.
    They only have fast burn chambers that induce swirl when the intake charge flows in.
    If you look at them you can see this, as the ports are essentially the same as "non-swirl" heads.
    On the other hand, the 5.2/5.9 Magnum heads do have a swirl port design in them, as well as a fast burn chamber.

    Again, this is only what I have understood from reading in various places, if I am wrong please correct me!
    True.
    The 782's contribution to motivate swirl is achieved by having the intake port bowl area (on the long side) substantially filled in.
    Remove that material and the resulting swirl will be eliminated.
    Fixing the chamber... that's a bit more involved.

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    Re: Knock sensors revisited

    Well this has turned out to be a very helpful thread! Thank you very much for all the insights, I think I have a much better grasp of things now and will be working on re-doing my cal here shortly. I think I will start another thread shortly on what would be involved in fixing the swirl head
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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    Re: Knock sensors revisited

    Quote Originally Posted by Reaper1 View Post
    I'd love to have a scanner...just never could afford one when they'd pop up.
    Use mine. I have no real use for it besides diagnosing something once a year on my cars that still have oem ecu.


    To the head differences, a fastburn head should still be able to make decent power no matter how "against the odds things are" but if something has an extremely fast pressure rise that means the spark timing window is very small. That means you can't just "get it close." Its possible that adding 1 degree of timing puts you into knock and 1 degree less is a huge loss of power. Other setups can have a huge window of timing where it seems to make no difference but you still don't knock either. A more finicky combustion chamber is going to have even greater benefits on the dyno with a professional at the helm who knows how to get the most while not going too far.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

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    Supporting Member Turbo Mopar Contributor zin's Avatar
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    Re: Knock sensors revisited

    I'm thinking I'll have a head welded up to allow a "blank slate"... any suggestions as to an "ideal" turbo combustion chamber Ken?

    I like Yates, but, much like we've seen on heavily nitroused engines, such a fast /efficient chamber may be a hindrance at higher HP levels.

    Since this will obviously be more experiment than the average set-up, I'm also thinking I'd do a raised runner, up to the limit of the valve cover gasket surface, if going there is of benefit... I'm just not sure where to "steer" the mix past the valve, seems like some swirl would be in order if just to keep it from "crashing" into the cylinder wall...

    This may be (probably) a 2.0l engine.

    Mike
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    Re: Knock sensors revisited

    Ken - Maybe you have some insight into a question that's been bothering me for a while.

    A G-Headed 2.5 is very difficult to tune. Too much timing and it knocks (seems to handle more timing than a FB head, though), too little timing and the EGT's soar; and performance drops dramatically.

    What is it about the G-Head + 2.5l combination that makes it so difficult?
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    Re: Knock sensors revisited

    I think the increased piston speed is what makes it harder to tune in general, regardless of which head is used. Basically it is just a 2.2 with a stroker crank. However, while I know that it has an effect on timing, I've never been able to get a good answer on what effect it has. I have posted about it on Speedtalk before using a V8 stroker as an example (ie stroking a 318 to 390 w/o changing heads, intake or cam), but nobody really gave me a definitive answer, some even said it wouldn't change. I guess it's fairly rare to stroke any engine w/o changing something else at the same time.
    Rob M.
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    Re: Knock sensors revisited

    I think it is fair to say that the 782 head has some definite improvements that can be made to it, however there is more than 1 side to a combustion chamber. A combustion chamber is a volume. In our case we can change the ceiling and the floor. The ceiling is the head. The floor is the piston. Since I learned about quench, swirl, tumble...all that good stuff, the mismatch of the pistons to the heads for our engines has bothered me...a LOT. A large part of the reason the 782 head is "crappy" is because it really isn't being used to its full potential. There is a quench pad, but the piston crown does not match it, so it isn't used. The dish in the piston allows the charge to go off in a direction away from the spark plug. On top of that, the piston crown does nothing to support the continuation of swirl. It's just a "bucket". To me, if there was a proper piston made to work with the head design, I'm pretty confident that there would be gains in all kinds of areas.

    Ken, on the filling of the long side of the intake port in the bowl, I seem to remember that there is a very slight offset on one side of the bowl. From reading what others have said over the years, and seeing the work of people that really know what they are doing with that type of port work, I was under the impression that that was part of what starts the swirl of the charge. The rest is directed by the chamber shape (and to some extent the valve and valve seat). I agree that filling the long side would certainly help, but it's important to note that it's not just an arbitrary filling.

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    Re: Knock sensors revisited

    I don't even run one anymore. Flashing for no dam reason all the time. I set the timing to factory and run 15psi. It's held up for a month so far.

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    Re: Knock sensors revisited

    Quote Originally Posted by roachjuice View Post
    I don't even run one anymore. Flashing for no dam reason all the time. I set the timing to factory and run 15psi. It's held up for a month so far.
    Well that's what 5DIGITS saying, is that the swirl head will work good up to 14-15 psi, after that it gets really sensitive to knock and require a lot of timing to be pulled to keep it from doing so. The chamber isn't designed to work well at higher boost levels.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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    Re: Knock sensors revisited

    Quote Originally Posted by ShelGame View Post
    Ken - Maybe you have some insight into a question that's been bothering me for a while.
    A G-Headed 2.5 is very difficult to tune. Too much timing and it knocks (seems to handle more timing than a FB head, though), too little timing and the EGT's soar; and performance drops dramatically.
    What is it about the G-Head + 2.5l combination that makes it so difficult?
    Trapping efficiency, piston dish OD, and piston speed (elevated piston temps) are all contributing factors.

    Trapping efficiency:
    Trapping efficiency is higher on the 2.5L that it is on the 2.2L which equates to higher cylinder pressures.
    Working with higher cylinder pressures in turn has an effect on the amount of spark advance that can be used.
    The quote listed below is posted on the Allpar website.

    Dyno tester Ed Poplawski wrote,
    “I worked on this a little bit. We ran Fast Burn heads on the 2.5L and the big advantage that I remember was that with the Fast Burn head, wide open throttle spark timing was lower than with the standard head, so you didn’t have to worry about spark knock too much and you didn’t need premium fuel. That made a big difference for the turbocharged engine.”


    While it states that the spark reduction was largely due to the fastburn head it may be more accurately stated as "spark timing was lower than the 2.2L using the same cylinder head", for reasons indicated above.
    Likewise and respectively, both engines will tolerate more spark advance with the G-Head.


    Piston dish OD:
    The piston dish diameter was changed between the 2.2L and the 2.5L.
    This negatively affected the amount of squish when compared to the 2.2L using the same head.
    Additionally, many subsequent aftermarket forged pistons, for both applications, have the squish band reduced.
    A wider band with a slightly shallower dish may provide a compression bump with enough squish/quench to maintain the same level of spark advance, under the same boost conditions.

    Click image for larger version. 

Name:	Pistons.png 
Views:	110 
Size:	320.9 KB 
ID:	49392

    Piston speed:
    The elevated piston speeds on the 2.5L will increase the piston temperatures.
    This will also increase, for obvious reasons, as boost is elevated and aggravates the engines sensitivity to knock.
    As many are aware, this is also the reason why the later 2.4L turbo charged engines incorporated the use of oil squirters to counter act piston temperatures.

    As reference, the values below indicate the approximate RPM's for a 2.0L, 2.2L, and 2.5L when the piston speeds are equalized.

    2.5L - 6000RPM

    2.2L - 6800RPM

    2.0L - 7700RPM

    To put things into perspective, the desire to run a 2.5L engine to 6500RPM is much like running a 2.0L to 8300RPM and may be something to consider during the next up-shift.
    Last edited by 5DIGITS; 03-26-2014 at 06:54 AM.

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    Re: Knock sensors revisited

    Quote Originally Posted by ShelGame View Post
    Ken - Maybe you have some insight into a question that's been bothering me for a while.

    A G-Headed 2.5 is very difficult to tune. Too much timing and it knocks (seems to handle more timing than a FB head, though), too little timing and the EGT's soar; and performance drops dramatically.

    What is it about the G-Head + 2.5l combination that makes it so difficult?
    Interested in hearing more about this also.
    Slug has flashed the CEL indicating knock since she has been fully rebuilt with JE forged slugs. Has indicated knock retard on OTC 4000 also. Still running 2.5l with G-head (MP mild port +1). Now running flashable though with 3 bar. Tried both +40's and now scaled for 95#/hr.

    I'm getting concerned when I do get Mini back together I'll be in the same boat.
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  18. #58
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    Re: Knock sensors revisited

    Quote Originally Posted by Reaper1 View Post
    I think it is fair to say that the 782 head has some definite improvements that can be made to it, however there is more than 1 side to a combustion chamber. A combustion chamber is a volume. In our case we can change the ceiling and the floor. The ceiling is the head. The floor is the piston. Since I learned about quench, swirl, tumble...all that good stuff, the mismatch of the pistons to the heads for our engines has bothered me...a LOT. A large part of the reason the 782 head is "crappy" is because it really isn't being used to its full potential. There is a quench pad, but the piston crown does not match it, so it isn't used. The dish in the piston allows the charge to go off in a direction away from the spark plug. On top of that, the piston crown does nothing to support the continuation of swirl. It's just a "bucket". To me, if there was a proper piston made to work with the head design, I'm pretty confident that there would be gains in all kinds of areas.

    Ken, on the filling of the long side of the intake port in the bowl, I seem to remember that there is a very slight offset on one side of the bowl. From reading what others have said over the years, and seeing the work of people that really know what they are doing with that type of port work, I was under the impression that that was part of what starts the swirl of the charge. The rest is directed by the chamber shape (and to some extent the valve and valve seat). I agree that filling the long side would certainly help, but it's important to note that it's not just an arbitrary filling.
    BTW, it costs about the same to get the correctly made piston (hey vendors!) as it does improperly designed pistons. Who will be the first to market a proper piston? Nobody You can get this stuff done yourself but you shouldn't have to for a platform that still has some market.

    I also bank ZERO $ into obsessing about pistons speeds because the baddest import engines start off with high piston speeds and they keep stroking them more and not looking back. They do what is necessary to prevent knock be it modified pistons, whatever. If you build the shortblock and design the pistons exactly the same and ignore pistons speeds or heat, that is your fault, not the engine's.

    Now, spending all that time modifying a cylinder head and you plan on putting an off the shelf improperly designed piston in, again, your fault when things don't work.

    Less spark advance is not a bad thing. A sign of a good turbo setup is needing less spark advance. Bad tuning practices carried over from older tech/poorly designed cylinder heads need to die. Just because its hard to tune something using backyard techniques does not mean that engine combo is junk. I don't like spending money so I would probably avoid the hard to tune cylinder heads so that backyard techniques will be good enough.
    Last edited by Ondonti; 03-25-2014 at 10:54 AM.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  19. #59
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    Re: Knock sensors revisited

    I've honestly just given up on the whole tuning these cars thing. I saw jack ----. Only thing I've got on my tune right now is scaled for injectors and map and no over boost. That's it. Stock timing. Stock everything else. Got soooooo tired running in and out the house flashing tunes and going out and beating on the car trying to see a change then cracking ring lands on multiple occasions. Done. Stock tune ftw. Afpr for fine tuning the afr. Done. Keep it simple.

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    Re: Knock sensors revisited

    I got decent results, 80mph in the 8th in a 3300 pound race weight fwd is decent power, but I spent A LOT of time burning cals, like 1 or 2 everyday. I also had forged Wiseco pistons so no ringland worries I have run up to 25 psi on mine, but after 17 psi it was definitely in the realm of diminishing returns. The 80mph was on around 20-22 psi though.

    However, I never really could get it to not flash the knock light at those levels either, even with the knock threshold raised significantly. Now I know why
    Last edited by Force Fed Mopar; 03-25-2014 at 10:55 PM.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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