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Thread: T-Smec 2.5 G-head Thoughts

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    T-Smec 2.5 G-head Thoughts

    I have been tuning off and on for long time, and often thought that my van just doesn't have the top end power I know it should have. On another thread (http://www.turbo-mopar.com/forums/sh...ome&highlight=) I posted my thoughts on that, and Juggy commented about needing more timing.

    So over the last 2 days i studied lots of different templates, looking at the timing curve and the calculated total timing.

    This is the 'Advance from RPM2' or '00GOVNER'

    Click image for larger version. 

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    In this pic the Light Blue= T-smec G-head cal, Green= swirl head (both 2.5) I noticed that as the RPM goes up the swirl cal adds timing and the G-head does not.


    So i assume that the "swirl" curve is closer to the factory engineered curve of timing needed dependnet on RPM. So instead of using the G-head curve I took the Swirl curve and added 10* of timing to every point so it is the same Shape but more timing. Like this

    Click image for larger version. 

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    Dark blue=Swirl head cal, Green=G-head template, Light Blue= What I did.-

    Result= WAY MORE POWER! the van is now on 4 psi less (12 instead of 16) and according the the Butt Dyno the current low boost cal would smoke the old one.

    That only makes sense to me, that as the engine spins faster it needs more timing Just like the swirl cal. I am not done tuning it yet but now it runs so much better and smoother across the RPM range, but Especially has significantly more power over 4000 RPM.

    IDK but i would suggest that maybe Rob can update the G-head template in T-SMEC. From what i remember that was based off a cal that someone else did. I like some of the drive-ability issues it helps with but its is lacking its potential.

    What are your thoughts everybody?
    Last edited by 1BADVAN; 08-31-2012 at 03:11 PM.

  2. #2
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    Re: T-Smec 2.5 G-head Thoughts

    In addition I believe the Pump Eff table is also off a bit. I started noticing what i would call "Breaking Up" over 5000 RPM in 2nd gear (not in first as it revs so fast). So as i started hunting the problem i noticed that the A/Fs would be a steady 11.5 until 5000 RPM, then it would Drop to 10.8. So the added fuel was killing power.

    So some hunting found that the Pump eff table on the G-Head cal was higher than the others. I adjusted mine to be in-between the 2 but closer to the lower one and it fixed it! Again I think that the template would better serve a wide group if it was closer to the stock curve than this one is.
    I have only one test so far so more adjusting to come.

    Click image for larger version. 

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    Again blue=unmodified G-head cal. Green= unmodified swirl cal. (seems to be the same on whichever i choose)
    Last edited by 1BADVAN; 08-31-2012 at 03:37 PM.

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    Re: T-Smec 2.5 G-head Thoughts

    Well PE tables are different for every engine so that is a given that what will work on yours won't work on Joe's etc.

    As for the timing table, I thought that one was or is for cruise, IE like a vacuum advance on a dizzy setup.
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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by turbovanman View Post
    Well PE tables are different for every engine so that is a given that what will work on yours won't work on Joe's etc.
    Right, what i am saying is that the Template is based off of a custom one. it should be the standard Chrysler one like all the others.

    Quote Originally Posted by turbovanman View Post
    As for the timing table, I thought that one was or is for cruise, IE like a vacuum advance on a dizzy setup.
    No from what i understand that is the base timing, or the timing the computer first looks at and then it adds the timing number (positive or negative) from the MAP tables to get the "Total" timing.

    They talk about about it here starting in post #677 http://www.turbo-mopar.com/forums/sh...map#post862311
    Last edited by 1BADVAN; 08-31-2012 at 01:55 PM.

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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by 1BADVAN View Post
    Right, what i am saying is that the Template is based off of "Joes" it should be the standard Chrysler one like all the others. If my engine with decent mods didn't run good on it a stock one wouldn't like it at all.
    Sorry, not sure what your saying here? Rob's stage cals are slightly tweaked and rely on us to modify the PE table to suit our needs.

    Quote Originally Posted by BADVAN
    No from what i understand that is the base timing, or the timing the computer first looks at and then it adds the timing number (positive or negative) from the MAP tables to get the "Total" timing.

    They talk about about it here starting in post #677 http://www.turbo-mopar.com/forums/sh...map#post862311
    Ok, so what map is that, hard to see what it is, but to me, looks like the "Advancefromrpm2" table? Which is the mechanical advance like a dizzy, not vacuum advance like I thought.
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
    1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
    2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
    2004 GSW TDI, 5 speed, fully loaded, modified.

    Aurora ignition wires for sale. Link to info

    Super60 roller cams or custom/billet cams. Link to info

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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by turbovanman View Post
    Sorry, not sure what your saying here? Rob's stage cals are slightly tweaked and rely on us to modify the PE table to suit our needs.



    Ok, so what map is that, hard to see what it is, but to me, looks like the "Advancefromrpm2" table? Which is the mechanical advance like a dizzy, not vacuum advance like I thought.
    I think i fixed my post to make it a bit clearer. And as for the mechanical vs vacuum basically you are right they work like that. What i am saying is i think the curve on the 'AdvancefromRPM2' table is not optimum.
    Not the right curve, it adds timing at low RPMs but not at Higher RPMs so i changed it so it added timing everywhere, and the results were Great! I will post up my curve in a second if i can pull it up.

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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by 1BADVAN View Post
    I think i fixed my post to make it a bit clearer. And as for the mechanical vs vacuum basically you are right they work like that. What i am saying is i think the curve on the 'AdvancefromRPM2' table is not optimum.
    Not the right curve, it adds timing at low RPMs but not at Higher RPMs so i changed it so it added timing everywhere, and the results were Great! I will post up my curve in a second if i can pull it up.
    Ok, so we are on the same page,

    Yeah, I crank mine too, its not as much as the G-head cal Rob has posted in the Stage IV cals.
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
    1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
    2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
    2004 GSW TDI, 5 speed, fully loaded, modified.

    Aurora ignition wires for sale. Link to info

    Super60 roller cams or custom/billet cams. Link to info

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    Re: T-Smec 2.5 G-head Thoughts

    added a pic and tried to clarify the first post. Thats what i get for trying to type fast inbetween things at work.

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    Re: T-Smec 2.5 G-head Thoughts

    You could have added timing to the map timing tables instead and done the same thing.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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    Supporting Member Turbo Mopar Contributor zin's Avatar
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    Re: T-Smec 2.5 G-head Thoughts

    Makes sense... The G-head is not as "fast" a chamber, so it would need more "lead"/timing to get peak pressure in the sweet spot... I think that's the biggest problem with the cal I have right now, not enough timing and too much fuel.

    Maybe one of these days life will cut me a break and let me spend some money on "toys" so I can get a burner and fix it!

    Mike
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by Force Fed Mopar View Post
    You could have added timing to the map timing tables instead and done the same thing.
    Not true, the map timing tables adds timing to all of the RPM range, what i did adds timing to the parts that need it. or were not given it originally. This is why previously the power would fall off after 4500 now it continues to pull until 5500, like the GLHS i drive

    Quote Originally Posted by zin View Post
    Makes sense... The G-head is not as "fast" a chamber, so it would need more "lead"/timing to get peak pressure in the sweet spot... I think that's the biggest problem with the cal I have right now, not enough timing and too much fuel.

    Maybe one of these days life will cut me a break and let me spend some money on "toys" so I can get a burner and fix it!
    Mike
    edit: I misunderstood what you mean by "lead" initially, if you read this before this edit. Yes it needs more advance or "lead"

    I have done some brief google searching, and found that some SRT4 guys have found this same problems that some cheap vendors would just put a straight line timing advance instead of ramping it up with the RPM and they have noticed that is not optimal.

    In our case this seems to just be a rarely explored with area of the G-headed 2.5. I am just trying to make it better and maybe correlate with you guys to see if my theories so far have a problem.
    Last edited by 1BADVAN; 08-31-2012 at 07:38 PM.

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    Re: T-Smec 2.5 G-head Thoughts

    I haven't messed with tuning much for the above reasons, but I've trolled around and like to learn. Anyway, I always thought it would be best to tune/optimize the engine off of boost first, pretty much tune it for n/a, then modify that tune to compensate for boost... Perhaps lifting the timing curves from the carb'd MP calibrations as a starting point?

    I imagine that it could be a little dangerous if one went to high boost too quickly, but if one were to take their time and start small, it would seem like you'd get a more optimum result...

    For instance, in my experience with other engines, it is surprisingly common for an engine with flat top pistons and 2 valves/cylinder to run their best with 34-38* of total timing all other considerations ignored (yes, there's always an exception, but Cosworths don't follow "the rules").

    It seems like that is where you'd want to start, then back it off 1-2* per PSI of boost, at least as a starting point... But, maybe I'm just coming at this from a different angle?

    Mike
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by zin View Post
    I haven't messed with tuning much for the above reasons, but I've trolled around and like to learn. Anyway, I always thought it would be best to tune/optimize the engine off of boost first, pretty much tune it for n/a, then modify that tune to compensate for boost... Perhaps lifting the timing curves from the carb'd MP calibrations as a starting point?

    I imagine that it could be a little dangerous if one went to high boost too quickly, but if one were to take their time and start small, it would seem like you'd get a more optimum result...

    For instance, in my experience with other engines, it is surprisingly common for an engine with flat top pistons and 2 valves/cylinder to run their best with 34-38* of total timing all other considerations ignored (yes, there's always an exception, but Cosworths don't follow "the rules").

    It seems like that is where you'd want to start, then back it off 1-2* per PSI of boost, at least as a starting point... But, maybe I'm just coming at this from a different angle?

    Mike
    That's what i am thinking. In reality we can't do a no boost but we can do a low boost. I kind of go mid-range my lowest boost is 7 psi but I have tuned at 11psi as i figure it is a safe-ish level to test with.

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    Re: T-Smec 2.5 G-head Thoughts

    Still makes boost if the waste-gate arm is disconnected?... I can see that at the higher RPMs, lots of volume there, but at lower RPM, I would think it would struggle to make boost, maybe act like it has a restricted exhaust (because it does!)...

    At any rate, good to hear I'm not ignorant of some turbo tuning axiom!

    Mike
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

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    Re: T-Smec 2.5 G-head Thoughts

    Quote Originally Posted by Force Fed Mopar View Post
    You could have added timing to the map timing tables instead and done the same thing.
    To edit/ add to what i previously said that yes you are correct i could have added x amount of timing across the MAP tables to get a similar result, IF the RPM curve was good to begin with.

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    Just added a bit more timing so the RPM curve is now 14* advanced over a swirl head. On 11 psi you hear the tires at the edge of slipping (just a bit of squeal). These are not small stock tires either.
    Needless to say i am loving this new power band!

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    Re: T-Smec 2.5 G-head Thoughts

    Cool, really when you compare total timing there isn't that much difference between the two from the factory, except the timing comes in faster and is different in high vacuum. That said, the general concensus seems to be that bathtub heads like lots of timing. The timing curve for them is very much like the old V8's.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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    Quote Originally Posted by Force Fed Mopar View Post
    Cool, really when you compare total timing there isn't that much difference between the two from the factory, except the timing comes in faster and is different in high vacuum. That said, the general concensus seems to be that bathtub heads like lots of timing. The timing curve for them is very much like the old V8's.
    What do you mean? Just trying to clarify. Are you comparing the factory g head cal to the factory swirl cals for the 2.2?

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    Re: T-Smec 2.5 G-head Thoughts

    Yeah, but I could be wrong lol, I'm going off memory and not near my computer. I may be thinking of 2.2 versus 2.5 instead.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

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    Re: T-Smec 2.5 G-head Thoughts

    Just to add, i think my favorite part about this new timing is the amazing increase in throttle response. From a roll stabbing the throttle responds so much faster it feels like a non turbo car. I love it!
    I am planning on going to the track on Friday so i am going to try upping the boost tomorrow to 16 psi with this timing and see how it responds.

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