So tuning Individual Throttle Bodies has proven to be quite difficult. At this point however, I feel that I have a handle on what the crux of the matter is and how to solve it (2 feasible solutions).
Here is the discussion from the ENDYN forums:
[i]
Tycho:
Any of you guys ever tuned an ITB setup?
I’m attempting to dial in my newly installed unit and it’s quite an experience.
I’m using MAP currently with a vac plenum hooked to all 4 runners. I have the WOT and low throttle settings pretty much nailed…but mid throttle is rich central.
The main problem seems to be that partial throttle allows the map signal in the 3 runners not having air drawn through them to go to atmospheric…causing the vac signal on the runner moving air to be heavily “diluted.” I see maybe 2 inches of vac at mid throttle positions where I used to see 8 or 9 with a single body manifold…so it goes pig rich in mid throttle regions.
Basically…the MAP vs actual load has gone from being semi linear with a single body to exponential with quad bodies (very shallow slope from 20″ till about 1.8″ vac…then it spikes up and plateus out to 0 vac).
I’m going to give throttle position load sensing a shot this weekend and see how that works out…but I know some of you guys are pretty skilled at dialing in engines and I am far from it…so tell me what I’m “missing”…
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mike_belben:
i have no experience to help you with, but i know for sure that TPS systems dont offer the headaches of map. Jeff Evans could probably shed quite a bit of light for you on tuning ITB’s as he does it for a living.
http://www.evans-tuning.com/
“boosted hybrid” is his SN
ofcoarse i would still love to hear comments on this one for when im stumped on it just the same.
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Tycho:
Thanks mike.
I’ll give TPS a shot today (right now in fact) and will def read though those forums.
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B20C5Turbo:
Quote:
Originally Posted by Tycho
partial throttle allows the map signal in the 3 runners not having air drawn through them to go to atmospheric…
It sounds like you might be connected to a “ported” vacuume source on those TB’s.
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Tycho:
Ported vaccume source?
From some reading of evans-tuning it seems I should make a smaller vac plenum (the one I have is definitely not small).
I got throttle position pretty well tuned this afternoon…will fine tune it later tonight once the roads clear out a bit. Better in some ways…worse in others.
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B20C5 Turbo:
“A picture is worth a thousand words.”
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Tycho:
Here are 10,000 then
http://homepage.mac.com/dgiessel/.P…s/misc/3_10_05/
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CenCODSM:
I think both of you could be on to something here.
Ported vacuum comes from a small orifice in area near (before) the throttle blade such that it is exposed to vacuum as throttle varies. So, verify that your vacuum ports are well after the throttle blades and you can be certain that you aren’t using a ported source (incorrectly). You probably would’ve spotted this however because ported vacuum sources typically give zero vac. at closed throttle, largest vac. at off-idle and back to zero again at WOT.
I suppose that manifold vac. from a single cylinder (with it’s own TB) would be caused by flow across the throttle (restriction). This is only happening 180* of the 720* cycle. And, at that, the flow is only fully developed during the latter 2/3 of that intake event. Manifold vac. is therefore a crude average it appears. Connected to a large enough capacitor, (vacuum plenum) as you have stated, the signal could damp out enough to cause problems. Although I would propose that it would only improve the averaging.
I don’t understand pressure pulse propagation enough to offer more than speculation.
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Tycho:
I’d read that too small a vac plenum causes highly erratic readings (which made sense to me) so I sized mine accordingly…but it seems that those running ITBs with hondata do better with a small vac plenum…so it would seem that I would have to try both to draw my own conclusions.
I’d like to know how Nissan/BMW do it. Toyota cheated with the 20v 4age…with the MAF setup.
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armegedon667:
Those look very much like my gsxr 750 throttles I am currently working with. I know in my case the stock bike efi was speed density and merely t’d the map referance ports together and fed one line directly into the map sensor, no plenum at all.
The ports I am refering to are in the last pic in the top row of the link you have listed above. I assume you currently have these plugged. Maybe deciding to source off the oe injector locations for map vacuum produces some strange effects. Perhaps you should attempt to switch the source of you plunem to the oe referance sources.
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Tycho:
Yeah…thought of that last night right before I fell asleep.
The injector bungs give me sufficient flow to control idle from my vac plenum which is why I used them (perhaps another source of weirdness). I can run my MAP off the regular vac ports on its own and keep my vac plenum the same as it is now (it’s a great volume for brake assist and evap purge).
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Tycho:
Check this out
I was reading that Haltech is great for ITBs because they have a “full throttle” map…well this map is quite simply an open loop RPM fuel map that engages when a certain throttle position threshold (user adjustable) is reached.
So…my SDS does not have this…and they won’t do custom software…so…
I mount a small proximity sensor next to my throttle linkage (or even by the gas pedal) and adjust it so it goes “high” at say…80 percent throttle…when the proxy sensor goes high it switches a relay (or better yet…a solid state multiplexor that can pass analog signals) and bypasses the MAP signal line…sending +5v along the map line to the ECU. This subsequently makes the ECU read +.8 PSI (the highest 1 bar value on my SDS). Since I never encounter +.8 PSI even at WOT (highest I’ve seen so far is -.61 inches…and I’m only 400 feet above sea level) I can tune the RPM fuel values at WOT (with a stable “+.8 psi” value seen by the ECU)…and still lean out all the map values from -.61 all the way to idle vac (about 18 inches). This is great because right now when I breathe on the gas at say 2500 RPM in 5th gear vac goes to -1 inch…which is what it sees at WOT also (tho clearly the engine is not getting as much air under this condition…and subsequently goes rich).
Problem solved. Seems to me one could do something like this with hondata also (if such a feature has not already been integrated). I think if I can get a proof of concept version working, Racetech would take the idea seriously and add the feature in software to their next rev.
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armegedon667:
Well hang on now, being that my ITB setup and engine look to be perhaps a month away from completion, and I am also running an SDS, this intriges me. First, did you try switching the vacuum referance ports? Also, did you attempt to switch the map sensor to a less sensitive 2-bar unit and work within the 1-bar range? Lastly, couldn’t you use Idle TP location for this as well (hmm, not sure if it will ony subract fuel at a specific TP)?
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Tycho:
Yes, I did. Vac ref ports are not the problem. This is something that seemingly everyone with ITBs has experienced…and it makes sense…because only one cylinder “sucks” at a time…so 3 of em (the throttle plates) are big vaccum leaks all of the time.
A less sensitive 2 bar would make the car undrivable (well…in time…there’d be so much carbon buildup from the rich mixture that it would get pretty marginal). MORE resolution if anything is needed (esp in the 4 inch to 0 inch range). That’s another thing I’ve considered…changing the voltage references fed to the sensor so that the SDS sees 19 inches as “0 volts” making it show as -29 inches…spreading my points out a bit and letting me use all 64 to cover my actual range of operation.
Idle TP…that’s an interesting proposition…I was under the impression that it sets that value for that TP and the ones subsequently lower than it also…I will definitely look into that. It would be absolute cake for them to add this (wot map) in software…I wish they’d release their source (or give me a copy) so I could add it in there. That said, I’m still glad I got the SDS over a Haltech or MS as the resolution of the SDS is excellent…and now that they have WB logging it’s near perfect (just need that feature for us ITB people now).
I fould that TP load sense solves the mid throttle issues…but it’s worse everywhere else. To hybridize TP and MAP would be heaven.
Here are my current MAP values (still moving em around a bit from day to day but it’s getting very close). The “problem” is readily apparent… Take a guess at what my mixture meter read as I drove through the mountain pass last week…
[img]http://homepage.mac.com/dgiessel/.Public/ITB.jpg[/img]
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CenCODSM:
I am getting interested in this now. I have a suggestion for you, use just one throttle body for your MAP source. I can’t see any reason not to other than for the benefit of brake boosters and unsynchronized throttle bodies. I don’t know if my bike is speed density or alpha N but they tied all the throttle bodies to the MAP with hose (no plenum).
I think that half of your MAP/TPS non-linearity is due to your large throttle area per cylinder. (~38mm itbs?) I think that two 60mm throttle bodies on a common plenum manifold would flat-line the MAP at about half throttle or less too. Four 30mm ITBs would be area equivalent to a 60mm…
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armegedon667:
This may seem silly, but are you using closed loop operation? I wonder if you were to lean out the map values in the ranges you are having trouble with and enabled closed loop if drivability would be improved. You could then tune WOT and idle only and let the ecu take care of the in-between.
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Tycho:
36mm throttle plates…and you are totally right. However…this is the nature of ITBs. I mean…if I ran 30 or 25mm plates I’m just starving the engine in the very locations I installed the ITBs to gain power in.
Gave a 1 TB vac signal a shot last night…fluctuation central! Even with a little hole in the vac line to stabilize the signal. However…an idea came out of it. If one wrote software to “sample” the vac signal and “hold” the biggest vac signal for a period of one engine cycle (just tie it in with the RPM sensor) then you would get a very very nice MAP spread vs actual engine load. Theoretically the max vac signal seen over the period of one engine cycle (720 degrees) with ITBs should be pretty close to the vac signal you see with a single TB. You’d be looking at map only when the cylinder being sampled is having air sucked into it…then ignoring the signal for the other 3 strokes where the throttle plate is bleeding air into a non volatile runner. Just a simple software problem (I think this feature would be absolutely killer for ITB combinations). Perhaps I can make an in line circuit betweeen the MAP and ECU that will do this on its own (would not be able to sense the period of the motor (RPM) unless I got a bit more abitious (I could pull the TACH off my coil pack) but I could cook up an arbitrary timing value that would work ok).
It’s a pulse flow world…and ITB’s accentuate that point…to the chagrin of the MAP sensor (and the averaging that occurs when all 4 runners are tied to a plenum). Boils down to -5″ (vac at a cyl when it’s drawing air at part throttle) + 0″ + 0″ + 0″ (the other 3 runners that are “chillin”) divided by 4 = 1.25″ vac at the sensor.
I have been playing with closed and open loop. I really have the map tuned in fairly well for stoich between just above idle all the way to say -3″ vac (it gets just slightly richer throughout the vac range…as vac drops off). The drivability is getting very very good at partial throttle now.
The main issue is that the partial throttle and WOT vaccum values overlap due to the flakey (diappearing) vac signal at partial throttle. So if I enable closed loop to “handle” things up to -2.5″ vac…then it tries to go stoich on me when I go WOT in the hills…resulting in some pretty harsh things under the hood. There needs to be a second set of MAP values for throttle positions exceeding a certain threshold.
Essentially what is needed is both a MAP and TP configuration…where at a pre set threshold the system switches from map (maybe at 35 pct throttle) and goes to TP load sense. TP load sense sucks at partial throttle period. MAP sucks at anything more than partial throttle with ITBs.
A WOT map (I may even configure a 3 input multiplexor and a second proxy sensor to get MAP (0-35 pct), TP1 (35-70 pct), and TP2 (70-100 pct) giving me low, medium, and full throttle ranges) gets me “close enough” to that hybrid combination for the tune to be “very good” (enough for me anyway).
An interesting side note is that the robotics class I am taking currently involves extensive programming of the 9S12C32…a familiar part number for MegaSquirt 2 users. If I were better at writing higher level code (to make a software interface) I could take this project on (I find MS software to be pretty “weak”). Tho the non computer interface of the SDS is something I really like (main reason I got it). It’d be a real easy system to add these features to I’m sure (with the access to the source code).
I think the take home lesson is that there is a solution (from what I can tell both methods outlined here should work fairly well) to tuning ITBs throughout the load range with excellent streetability (BMW does it pretty damn well). It’s not overly complicated and can be done without MAF. It just needs to be done…but the market pct running ITBs is horribly small so it’s not been worth anyone’s time to make a “good” solution yet.[/quote]
Of course I’ll be posting updates here and in the endyn forums with the results of the 3 input multiplexor solution. Should be quite acceptable for now (it’s killing me not being able to bury my right foot (and the car next to me) when I have my “nice” map loaded).
-Tycho