VTEC Controller
been there done that
Joined: Jun 2002
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From: 916
Originally posted by darkpreludevtir
Everybody keeps saying that you can't tune the VAFC to kick in too low.... but nobody really states why!
I am planning on buying a VAFC2 for my '95 lude, and I had it in mind to have the secondaries kick in around 3500 or 4000 rpm. I suppose it depends on the actual specs of the secondary cam lobes, but I can't imagine it actually harming the output. Can someone explain please!!
Everybody keeps saying that you can't tune the VAFC to kick in too low.... but nobody really states why!
I am planning on buying a VAFC2 for my '95 lude, and I had it in mind to have the secondaries kick in around 3500 or 4000 rpm. I suppose it depends on the actual specs of the secondary cam lobes, but I can't imagine it actually harming the output. Can someone explain please!!
Registered User
Joined: Jan 2004
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From: Australia
Not flowing enough air...
Well I understand enough to know what you mean here, but surely this would only be a problem at low revs, not in the midrange around 3500-4000rpm? At that speed shouldn't the air in the intake manifold should have enough inertia to avoid reversion?
PS - And in reference to earlier comments about changing the VTEC engagement point and its impact on performance figures... It only follows that if your VTEC kicks in earlier then you are going to get access to that greater power earlier and for longer, meaning that your car is going to get faster. Maybe not that dramatically, but it will get faster.
Well I understand enough to know what you mean here, but surely this would only be a problem at low revs, not in the midrange around 3500-4000rpm? At that speed shouldn't the air in the intake manifold should have enough inertia to avoid reversion?
PS - And in reference to earlier comments about changing the VTEC engagement point and its impact on performance figures... It only follows that if your VTEC kicks in earlier then you are going to get access to that greater power earlier and for longer, meaning that your car is going to get faster. Maybe not that dramatically, but it will get faster.
VTEC-Gen4Lude
Joined: Jan 2003
Posts: 34
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From: San Diego
Sooo, by the reasoning that you are applying, setting the VTEC to kick in @ 800rpm would maximize the potential of VTEC motors. NOT the case, actually far from the it!
OK, lets do this Kindergartden style.
H22a lower profile cam profiles = low - mid RPM range power w/ fair to good fuel economy and modest performance.
H22a high profile cam profiles = upper mid and high RPM power with HIGH output and poor fuel economy!
take the case of the H23 , one cam profile for intake and one for exhaust....NO VTEC!
good low end power w/ great mid range up to ~6200 RPM.
Change the profile one way and imrove low to mid range power while hurting high rpm or change it back the other way and improve upper rpm power while killing low RPM power.
well , W/ a VTEC motor you hav TWO " performanc range cams" in one as if we did'nt already know this>>>
use the low rpm range cam too long and upper mid range and high RPM power dissapear.
use the high rpm cam too early and lower rpm power will be under utilized......
OK, lets do this Kindergartden style.
H22a lower profile cam profiles = low - mid RPM range power w/ fair to good fuel economy and modest performance.
H22a high profile cam profiles = upper mid and high RPM power with HIGH output and poor fuel economy!
take the case of the H23 , one cam profile for intake and one for exhaust....NO VTEC!
good low end power w/ great mid range up to ~6200 RPM.
Change the profile one way and imrove low to mid range power while hurting high rpm or change it back the other way and improve upper rpm power while killing low RPM power.
well , W/ a VTEC motor you hav TWO " performanc range cams" in one as if we did'nt already know this>>>
use the low rpm range cam too long and upper mid range and high RPM power dissapear.
use the high rpm cam too early and lower rpm power will be under utilized......
Registered User
Joined: Jan 2004
Posts: 12
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From: Australia
Originally Posted by doodoobrown
Sooo, by the reasoning that you are applying, setting the VTEC to kick in @ 800rpm would maximize the potential of VTEC motors. NOT the case, actually far from the it!
OK, lets do this Kindergartden style.
.........etc etc.....
well , W/ a VTEC motor you hav TWO " performanc range cams" in one as if we did'nt already know this>>>
use the low rpm range cam too long and upper mid range and high RPM power dissapear.
use the high rpm cam too early and lower rpm power will be under utilized......
OK, lets do this Kindergartden style.
.........etc etc.....
well , W/ a VTEC motor you hav TWO " performanc range cams" in one as if we did'nt already know this>>>
use the low rpm range cam too long and upper mid range and high RPM power dissapear.
use the high rpm cam too early and lower rpm power will be under utilized......
I never mentioned 800rpm, for a start. I completely understand that the high(er) lift, long duration profile on the "High" cam lobe in the VTEC set-up will give you terrible performance at low revs and may even give you nice flames out the exhaust....
My question is rather whether the "High" cam is so extreme... Would it really harm output in the MIDRANGE?
Contrary to your statement, there is actually 3 cam lobes per valve in the H22A1, it is the three-stage VTEC engine. Thankyou for your "lesson", and by the way, if you're going to be condescending, learn to spell kindergarten.
Senior Member
Joined: May 2003
Posts: 1,052
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From: Long Island, NY
Originally Posted by darkpreludevtir
Ok, so you chose not to get my point, thats fine...
I never mentioned 800rpm, for a start. I completely understand that the high(er) lift, long duration profile on the "High" cam lobe in the VTEC set-up will give you terrible performance at low revs and may even give you nice flames out the exhaust....
My question is rather whether the "High" cam is so extreme... Would it really harm output in the MIDRANGE?
Contrary to your statement, there is actually 3 cam lobes per valve in the H22A1, it is the three-stage VTEC engine. Thankyou for your "lesson", and by the way, if you're going to be condescending, learn to spell kindergarten.
I never mentioned 800rpm, for a start. I completely understand that the high(er) lift, long duration profile on the "High" cam lobe in the VTEC set-up will give you terrible performance at low revs and may even give you nice flames out the exhaust....
My question is rather whether the "High" cam is so extreme... Would it really harm output in the MIDRANGE?
Contrary to your statement, there is actually 3 cam lobes per valve in the H22A1, it is the three-stage VTEC engine. Thankyou for your "lesson", and by the way, if you're going to be condescending, learn to spell kindergarten.
the point is to add performance when needed, and allow for driveability and emissions at the same time.
as far as the VTEC controller goes...you will want to get one that also allows for minor adjustments of the fuel/ignition curves. otherwise it could do more harm then good, by creating an excessively lean situation at a lower cross-over point. remember that honda uses MAP to determine air entering the engine, not MAF, so by opening the VTEC earlier the computer cannot enrich fuel enough on its own, since its measuring pressure and not actual airflow like a MAF sensor.
anyway, whoever said that opening VTEC sooner (creating a leaner condition) will cause flames at the muffler is wrong. flames out the tailpipe are categorized by an excessively rich running engine.
ie. when a high boost turbocharged motor spits flame on a shift, the blowoff valve is releasing a ton of air (boost) into the atmosphere, that air was already metered by the MAF sensor (a good amount of turbo cars have a MAF instead of a MAP), so the engine thinks its getting more air then it really is.
the result: an excessively rich situation, because the engine still thinks that X amount of air needs X amount of fuel to prevent detonation and make good power.
the popular example is the WRX which uses a MAP (like honda). this allows boost to be vented to the atmosphere since its sampling the intake air charge in the plenum or throttle body, after the BOV.
i would personally recommend the VAFC-II, its more functional in a small way over the VAFC-I, plus it changes color when VTEC engages, and of course its newer.
either way MAP or MAF, both have their shortcomings and strongs.
~boom
Le Grand Illusion
Joined: Oct 2002
Posts: 1,180
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From: Damascus, MD
Originally Posted by ludeboom
he was right about the 2 cams per engine, there are 3 lobes per 2 valves, but the theory behind VTEC is that you can have "2 different types" of camshafts in the head at one time. A normal profile cam, and a racing profile cam. The engine would idle erractically and under-perform overall if the high cam was used all the time
the point is to add performance when needed, and allow for driveability and emissions at the same time.
as far as the VTEC controller goes...you will want to get one that also allows for minor adjustments of the fuel/ignition curves. otherwise it could do more harm then good, by creating an excessively lean situation at a lower cross-over point. remember that honda uses MAP to determine air entering the engine, not MAF, so by opening the VTEC earlier the computer cannot enrich fuel enough on its own, since its measuring pressure and not actual airflow like a MAF sensor.
anyway, whoever said that opening VTEC sooner (creating a leaner condition) will cause flames at the muffler is wrong. flames out the tailpipe are categorized by an excessively rich running engine.
ie. when a high boost turbocharged motor spits flame on a shift, the blowoff valve is releasing a ton of air (boost) into the atmosphere, that air was already metered by the MAF sensor (a good amount of turbo cars have a MAF instead of a MAP), so the engine thinks its getting more air then it really is.
the result: an excessively rich situation, because the engine still thinks that X amount of air needs X amount of fuel to prevent detonation and make good power.
the popular example is the WRX which uses a MAP (like honda). this allows boost to be vented to the atmosphere since its sampling the intake air charge in the plenum or throttle body, after the BOV.
i would personally recommend the VAFC-II, its more functional in a small way over the VAFC-I, plus it changes color when VTEC engages, and of course its newer.
either way MAP or MAF, both have their shortcomings and strongs.
~boom
the point is to add performance when needed, and allow for driveability and emissions at the same time.
as far as the VTEC controller goes...you will want to get one that also allows for minor adjustments of the fuel/ignition curves. otherwise it could do more harm then good, by creating an excessively lean situation at a lower cross-over point. remember that honda uses MAP to determine air entering the engine, not MAF, so by opening the VTEC earlier the computer cannot enrich fuel enough on its own, since its measuring pressure and not actual airflow like a MAF sensor.
anyway, whoever said that opening VTEC sooner (creating a leaner condition) will cause flames at the muffler is wrong. flames out the tailpipe are categorized by an excessively rich running engine.
ie. when a high boost turbocharged motor spits flame on a shift, the blowoff valve is releasing a ton of air (boost) into the atmosphere, that air was already metered by the MAF sensor (a good amount of turbo cars have a MAF instead of a MAP), so the engine thinks its getting more air then it really is.
the result: an excessively rich situation, because the engine still thinks that X amount of air needs X amount of fuel to prevent detonation and make good power.
the popular example is the WRX which uses a MAP (like honda). this allows boost to be vented to the atmosphere since its sampling the intake air charge in the plenum or throttle body, after the BOV.
i would personally recommend the VAFC-II, its more functional in a small way over the VAFC-I, plus it changes color when VTEC engages, and of course its newer.
either way MAP or MAF, both have their shortcomings and strongs.
~boom
*excellent* summary. :rockon:
Registered User
Joined: Jan 2004
Posts: 12
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From: Australia
Originally Posted by ludeboom
he was right about the 2 cams per engine, there are 3 lobes per 2 valves, but the theory behind VTEC is that you can have "2 different types" of camshafts in the head at one time. A normal profile cam, and a racing profile cam. The engine would idle erractically and under-perform overall if the high cam was used all the time
the point is to add performance when needed, and allow for driveability and emissions at the same time.
as far as the VTEC controller goes...you will want to get one that also allows for minor adjustments of the fuel/ignition curves. otherwise it could do more harm then good, by creating an excessively lean situation at a lower cross-over point. remember that honda uses MAP to determine air entering the engine, not MAF, so by opening the VTEC earlier the computer cannot enrich fuel enough on its own, since its measuring pressure and not actual airflow like a MAF sensor.
anyway, whoever said that opening VTEC sooner (creating a leaner condition) will cause flames at the muffler is wrong. flames out the tailpipe are categorized by an excessively rich running engine.
ie. when a high boost turbocharged motor spits flame on a shift, the blowoff valve is releasing a ton of air (boost) into the atmosphere, that air was already metered by the MAF sensor (a good amount of turbo cars have a MAF instead of a MAP), so the engine thinks its getting more air then it really is.
the result: an excessively rich situation, because the engine still thinks that X amount of air needs X amount of fuel to prevent detonation and make good power.
the popular example is the WRX which uses a MAP (like honda). this allows boost to be vented to the atmosphere since its sampling the intake air charge in the plenum or throttle body, after the BOV.
i would personally recommend the VAFC-II, its more functional in a small way over the VAFC-I, plus it changes color when VTEC engages, and of course its newer.
either way MAP or MAF, both have their shortcomings and strongs.
~boom
the point is to add performance when needed, and allow for driveability and emissions at the same time.
as far as the VTEC controller goes...you will want to get one that also allows for minor adjustments of the fuel/ignition curves. otherwise it could do more harm then good, by creating an excessively lean situation at a lower cross-over point. remember that honda uses MAP to determine air entering the engine, not MAF, so by opening the VTEC earlier the computer cannot enrich fuel enough on its own, since its measuring pressure and not actual airflow like a MAF sensor.
anyway, whoever said that opening VTEC sooner (creating a leaner condition) will cause flames at the muffler is wrong. flames out the tailpipe are categorized by an excessively rich running engine.
ie. when a high boost turbocharged motor spits flame on a shift, the blowoff valve is releasing a ton of air (boost) into the atmosphere, that air was already metered by the MAF sensor (a good amount of turbo cars have a MAF instead of a MAP), so the engine thinks its getting more air then it really is.
the result: an excessively rich situation, because the engine still thinks that X amount of air needs X amount of fuel to prevent detonation and make good power.
the popular example is the WRX which uses a MAP (like honda). this allows boost to be vented to the atmosphere since its sampling the intake air charge in the plenum or throttle body, after the BOV.
i would personally recommend the VAFC-II, its more functional in a small way over the VAFC-I, plus it changes color when VTEC engages, and of course its newer.
either way MAP or MAF, both have their shortcomings and strongs.
~boom
Er.... seems like there is widespread confusion about how VTEC actually works..... shame.
For a start, the engine does have 2 *camshafts*, as it is like many jap engines, a DOHC. One of these *camshafts*is the intake cam responsible for the two intake valves per cylinder, and one is the exhaust cam responsible only for the two exhaust valves per cylinder.
Each 2 valve pair is operated by a common set of *cam lobes*. There are effectively 3 *cam lobe profiles* per valve (or per two valves, but each pair run off the same set of three lobes so its the same thing). These are used in three stages across the rev range, not two stages!!! These cam lobes are called Primary, Secondary and Mid. The Mid lobe (commonly known as the *high* cam lobe etc) is the lobe which comes into play at the top stage of the VTEC operation. The VTEC system operates by changing which cam lobe is operating the rocker arm driving the valve, not by changing which camshaft is operating as you suggested.
Next, my point about the exhaust flames (which was just a passing comment btw).... Flames in the exhaust are most commonly caused by a phenomenon called "valve overlap" which racing cams and the high cam on the VTEC engines have. If you use these cams at low revs then you will most likely have flames from your tail pipe. Your point about the rich fuel mixture is true, but the most common cause is valve overlap.
I do plan to get the VAFC-II, for this exact reason of tweaking the fuel curve like you say...
Senior Member
Joined: May 2003
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From: Long Island, NY
Originally Posted by darkpreludevtir
Er.... seems like there is widespread confusion about how VTEC actually works..... shame.
For a start, the engine does have 2 *camshafts*, as it is like many jap engines, a DOHC. One of these *camshafts*is the intake cam responsible for the two intake valves per cylinder, and one is the exhaust cam responsible only for the two exhaust valves per cylinder.
For a start, the engine does have 2 *camshafts*, as it is like many jap engines, a DOHC. One of these *camshafts*is the intake cam responsible for the two intake valves per cylinder, and one is the exhaust cam responsible only for the two exhaust valves per cylinder.
fact is that i built my h22a, yea, from a bare block in my goddamn garage.
so before you continue to state the obvious and quote other peoples stuff (like honda and the helms manual
), allow me to remind you of what an attitude will get you.jack shit
btw, most engines do not have alot of overlap (or excess duration).
VTEC motors have some of the highest, either way, flames at the muffler are not caused by more air (as you previously stated), its caused by unburned fuel.
turbo cars have minimal to zero overlap.
thats why boosting a DOHC VTEC is futile without dialing out overlap on the cam gears.
Registered User
Joined: Jan 2004
Posts: 12
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From: Australia
Originally Posted by ludeboom
im glad you can copy a bunch of stuff you read somewhere and paste it here
fact is that i built my h22a, yea, from a bare block in my goddamn garage.
so before you continue to state the obvious and quote other peoples stuff (like honda and the helms manual ), allow me to remind you of what an attitude will get you.
jack shit
btw, most engines do not have alot of overlap (or excess duration).
VTEC motors have some of the highest, either way, flames at the muffler are not caused by more air (as you previously stated), its caused by unburned fuel.
turbo cars have minimal to zero overlap.
thats why boosting a DOHC VTEC is futile without dialing out overlap on the cam gears.
fact is that i built my h22a, yea, from a bare block in my goddamn garage.
so before you continue to state the obvious and quote other peoples stuff (like honda and the helms manual
), allow me to remind you of what an attitude will get you.jack shit
btw, most engines do not have alot of overlap (or excess duration).
VTEC motors have some of the highest, either way, flames at the muffler are not caused by more air (as you previously stated), its caused by unburned fuel.
turbo cars have minimal to zero overlap.
thats why boosting a DOHC VTEC is futile without dialing out overlap on the cam gears.
I'm not stating the obvious, I am trying to clear up some of the confusion here... Most ppl assume its a 2 stage engine.... its not
YES!! flames in the exhaust are caused by unburnt fuel!!! How does unburnt fuel get to the exhaust? by going straight from the inlet to the exhaust
when both valves are open due to overlap. Race spec engines and yes, vtec engines have overlap. Anyway, thats not the point!!! do you even know what my original question here was?
Registered User
Joined: Jan 2004
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Originally Posted by darkpreludevtir
Not flowing enough air...
Well I understand enough to know what you mean here, but surely this would only be a problem at low revs, not in the midrange around 3500-4000rpm? At that speed shouldn't the air in the intake manifold should have enough inertia to avoid reversion?
PS - And in reference to earlier comments about changing the VTEC engagement point and its impact on performance figures... It only follows that if your VTEC kicks in earlier then you are going to get access to that greater power earlier and for longer, meaning that your car is going to get faster. Maybe not that dramatically, but it will get faster.
Well I understand enough to know what you mean here, but surely this would only be a problem at low revs, not in the midrange around 3500-4000rpm? At that speed shouldn't the air in the intake manifold should have enough inertia to avoid reversion?
PS - And in reference to earlier comments about changing the VTEC engagement point and its impact on performance figures... It only follows that if your VTEC kicks in earlier then you are going to get access to that greater power earlier and for longer, meaning that your car is going to get faster. Maybe not that dramatically, but it will get faster.
Its not the speed of the air that causes your car to bog out when vtec engages to low. More air = more fuel. If the RPM is to low, then you are running to rich, because the engine speed has not increased to a point where the air/fuel ratio is creating power, but is low enough to where you are flooding the engine. (this also causes the flames, not just overlap. You have to much fuel left in the chamber after the firing of the sparkplug, so it gets dumped out the exhaust and ignited when it reaches the tip of the exhaust pipe, where it mixes once again with burnable oxygen. The temp of the exhuast gases ignite the mixture of Oxygen and Fuel.)
Originally Posted by ludeboom
at the muffler are not caused by more air (as you previously stated), its caused by unburned fuel.
Remember, gasoline is not flamable with out air. Since the amount of exhaust gases is greater than the amount of remaining unburnt fuel, the fuel does not burn until it reaches the outside of the exhaust tip. At the edge of the exhaust tip, there is just enough back pressure to pull in fresh air (that has oxygen) to make the air/fuel mixture greater than that of the exhaust gas, which then makes the unburned fuel flamable.