I have seen the question "will a biggy back A/F controller be De-tuned by my OBD2 ECU?" several times on here and on Honda-Tech, so I put up some general info on my web page under the tech section about this very subject. This might be usefull info:
and thus your ignition timing will be off since TDC on the camshaft will be different/higher. If you got adjustable cam gears, you could possibly offset the difference.
personally i see it as pointless if you arent going to go the extra step and get tuning. Especially when you dont have the bolt ons to match the exhaust gas needing to be pushed out.
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Blake - Neptune Tuner/Dealer
ALL MOTOR big body honda that will eat your lunch
Last edited by AllMotorBB6; 02-08-2006 at 09:13 PM.
Man, there is a bunch of misinformation flying around here.
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Originally Posted by AllMotorBB6
and thus your ignition timing will be off since TDC on the camshaft will be different/higher. If you got adjustable cam gears, you could possibly offset the difference.
This is only true for OBD1 Preludes (4th gen). On the 5th gen, ignition timing is purely electrical and has no relation to cam phase.
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Originally Posted by Cjanik
on a stock ECU, with no piggyback or other mods, the engine will think you still have stock cams and valvetrain and function like it has been.
This is not true. In reality, aspiration mods will affect your LTFT value, which affects open-loop fueling. This has been proven many times with datalogs done by myself and other members in the past. LTFT seems to be a peculiarity to OBD2 Hondas. In the N/A library, look under the stock ECU section and read the LTFT thread, it should shed some light on this behavior.
The bottom line for you John is that some sort of additional fuel control will really make the biggest difference with the cams. Even a VAFC should work well enough to give you most of the potential of the cams. If you are committed to staying OBD2, the e-Manage is a good choice. Shark has the newer version, and likes it IIRC.
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so even though the lift is larger on the new cams (thus me saying that TDC would be different) the ecu would sense the larger lift and adjust accordingly? I dont know much about OBDII considering all the tuning i have done and learned about is OBDI.
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Blake - Neptune Tuner/Dealer
ALL MOTOR big body honda that will eat your lunch
The bottom line for you John is that some sort of additional fuel control will really make the biggest difference with the cams. Even a VAFC should work well enough to give you most of the potential of the cams. If you are committed to staying OBD2, the e-Manage is a good choice. Shark has the newer version, and likes it IIRC.
thank you very much. I just need new cams/valvetrain anyways, but didn't want to spend money on something that may be rendered uselsss without spending more money.
very helpful, though i can't find much information on in.honda.com to help me with it. Where did you come about this information? just testing?
so even though the lift is larger on the new cams (thus me saying that TDC would be different) the ecu would sense the larger lift and adjust accordingly? I dont know much about OBDII considering all the tuning i have done and learned about is OBDI.
TDC is determined by the piston travel, not the cam. You could have a cam with constant lift, and TDC would not change. The cam merely controls how much air is drawn into the cylinder, and at what time.
The only reason I said that it matters with OBD1 H22s is because the "motor phase" signal is driven off the cam sprocket, so if you change the cam phase at all, the ignition timing will change. On the OBD2 H22s the ignition timing is independant of the cam phase.
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very helpful, though i can't find much information on in.honda.com to help me with it. Where did you come about this information? just testing?
I can't understand what you mean. Which information? The N/A library has links to the most relevant issues to fuel management for the H22, so that would be the first place to start. There's a bunch of stuff under engine management, so you may try reading all of it to get a feel for what's important.
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I dunno if i am just confusing myself even more but im gonna try to explain to you the best i can what i am trying to say and i want you to correct what is wrong with what i am saying.
On the stock camshaft, the lobes are smaller than an upgraded cam. The ignition is setup to ignite just before TDC in order to get the "punch" out of the power stroke. When you install a higher lift cam and the ignition is still sparking at the same point, your going to be losing some of that punch due to it sparking too early. The valves will open and close at different times and the ignition will still be the same.
Now with that said, what i was getting at with my last question was.....is the computer going to see this difference and automatically change the timing based on the different lifts of the cams?
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Blake - Neptune Tuner/Dealer
ALL MOTOR big body honda that will eat your lunch
I dunno if i am just confusing myself even more but im gonna try to explain to you the best i can what i am trying to say and i want you to correct what is wrong with what i am saying.
On the stock camshaft, the lobes are smaller than an upgraded cam. The ignition is setup to ignite just before TDC in order to get the "punch" out of the power stroke. When you install a higher lift cam and the ignition is still sparking at the same point, your going to be losing some of that punch due to it sparking too early. The valves will open and close at different times and the ignition will still be the same.
I think you are confusing yourself.
What I said before is still true. Ignition timing has nothing to do with the cam profile, and never will (on a Otto cycle engine). Optimal ignition timing will always yield a Peak Pressure Point of around 17 ATDC (from memory, I might be a few degrees off). The amount of air charge in the cylinder definitely plays a role in good ignition, but to say the cam is in control of that isn't true.
The whole reason you have different ignition delays in an ignition unit is because the flame speed varies with load and relative piston speed. Thus, for a given flame speed, you would need to begin the combustion chain reaction earlier in order to get the peak flame pressure on top of the piston at 17 degrees ATDC.
While a cam has something you could call TDC, is has no real relation to the crank TDC (or ignition timing). As I said before, the cam only controls how much air is in the cylinder before the valves close, and obviously we want as much air as possible for power reasons.
Performance cams ususally extend the intake duration and lift, and on a well-designed top end this allows more air into the cylinder before the intake valve closes. The cylinder peak pressure is increased, which increases BMEP (and torque increases).
However, the answer to your question about the stock ignition system is no. The stock ignition will never adjust ignition timing. Actually if it senses knock it will retard timing by a fixed amount, but that's it.
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will the ECU change the fuel maps because it knows there is more air getting into the cylinder?
Yes, but only in closed-loop operation.
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will the ECU change the ignition timing because it knows there is more air going into each cylinder?
No, because there is no feedback mechanism for ignition timing.
A/F value cannot be used for adjusting ignition timing, because A/F is laregely unaffected by timing. There are some very cool research areas now about using ignition spark current to derive optimial ignition timing, but that stuff is not production ready and still requires some refinement.
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wont the o2 sensors pickup that my air/fuel mixture has changed and the ECU adjust accordingly?
In a sense, isn't the ECU then trying to counter-act the benefits of the cams?
The O2 sensor is only used during closed loop. If you read the LTFT thread, I have found that closed loop only occurs under 30% throttle. Open loop there is no feedback, so the ECU just uses whatever is in the fuel tables. In that case, something else can modify the fuel parameters and the ECU can't tell.
Just to clear this up, you definitely want closed loop to ensure you have a 14.7 AFR. This will ensure good gas milage and drivability. Open loop is where you want to apply your fuel corrections, because the ECU is essentially blind and uses only the stock fuel maps (LTFT comes into play here though) to run the engine.
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