cai=running lean, bov=running rich... neither is said to be good while lightly moded
05-02-2003, 09:38 PM
#1
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Car Info: 2005 STI
cai=running lean, bov=running rich... neither is said to be good while lightly moded
hey there. i just got a 2002 wrx that was salvaged (great condition). ive been gettin it fixed at my bros shop and already throwin on some boltons. i read up on this stuff a little but still have questions.
1. puttin a cai is bad cuz it causes the engine to run lean
2. bov (the one with lots of atmosphere or sumtin) causes the engine to run lean when u shiftin.
now, i already have a uppipe, downpiple and hks hyper exhaust installed. i dont want a check engine light on readin that the engine is lean. to help correct the cai, will the apexi afc werk to fix this? and are my current mods enough to drop on the hks bov and cai. this problem has probably been addressed a lot of times but after an hour of searching, i still didnt get a great answer to my problem.
1. puttin a cai is bad cuz it causes the engine to run lean
2. bov (the one with lots of atmosphere or sumtin) causes the engine to run lean when u shiftin.
now, i already have a uppipe, downpiple and hks hyper exhaust installed. i dont want a check engine light on readin that the engine is lean. to help correct the cai, will the apexi afc werk to fix this? and are my current mods enough to drop on the hks bov and cai. this problem has probably been addressed a lot of times but after an hour of searching, i still didnt get a great answer to my problem.
05-03-2003, 12:23 AM
#2
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1. Cold Air intakes have been shown via dynos to do nothing or perhaps even cause the car to loose power.
2. BOV's dont do jack for power either, just make noise... As for lean/rich I have no idea.
2. BOV's dont do jack for power either, just make noise... As for lean/rich I have no idea.
05-03-2003, 08:09 AM
#3
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I would suggest Samco intercooler hoses, lightweight non-underdrive pulleys, and a Cobb AccessECU reflash. If the car's in the shop being worked on, now's a perfect time to ship the ECU out (insured, of course). Those are all minimal cost with noticeable gains (if you don't have any of them already).
05-03-2003, 05:09 PM
#4
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Stock intake is your safest bet. Stick with it til you hit 5-600 horsepower.
BOVs can also be a good mod. Getting a real high quality one increases the consistency of operation and reduces the chance of overboosting. Stock isn't bad, just very quiet. Most AM blow off valves exist only to make noise.
BOVs can also be a good mod. Getting a real high quality one increases the consistency of operation and reduces the chance of overboosting. Stock isn't bad, just very quiet. Most AM blow off valves exist only to make noise.
05-03-2003, 06:16 PM
#5
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i saw in one of the import mags that the cai incresased hp by 13.9. i was thinking of cuttin the cai a little to bring it up a little closer to the car and not to the ground. are there any bad side effects to having a hks bov besides the bad mileage i read about?
05-04-2003, 06:28 AM
#6
here's a little information about blow-off valves and recirculation valves (what is on the WRX).
Compressor surge
The purpose of blow-off valves and recirculation valves is to prevent compressor surge. This happens when the turbo has built boost, and is flowing alot of air into your intake, and you suddenly close the throttle to make a shift. When the throttle is closed, flow has to suddenly stop, and the turbo compressor wheel has to slow down suddenly. This puts a great deal of stress on the compressor wheel and bearings. To prevent this from happening, a blow-off or recirculation valve is placed between the turbo and throttle body that diverts and continue the air flow, allowing the compressor wheel to slow down more gradually.
Recirculation valves
Most modern cars are equipped with Mass Airflow Sensors, which meters the amount of air mass the engine is drawing. With MAS equipped turbo cars, the car maker would usually install a recirculation valve to prevent compressor surge. In this setup, the valve opens to divert the air flow back to the intake stream before the compressor (the non-pressure side of the intake).
What actually happens when the throttle closes and the recirculation valve opens? First air stops flowing through the MAF, as it is easier for the compressor to draw air from the recirculation valve (which is at a higher pressure) than through the air filter and MAF. Basically the compressor would be feeding itself, in a loop. As no air is being drawn through the MAF, the engine management system would stop injecting fuel and ignition, which basically halts combustion (but rpm does not drop to zero as the engine continues to rotate through inertia). The compressor will gradually slow down as the turbine/exhaust side of the turbo drags on the compressor (as there is no exhaust flow from the engine).
As soon as the throttle opens again, the recirculation valve closes, and the compressor starts drawing air through the MAF and combustion resumes. Throughout this process, the engine never runs rich nor lean, and compressor surge is prevented, perfect for the car maker!
Blow-off valves
A blow-off valve diverts the air flow to the atmosphere instead of back into the intake stream. What happens on a car equipped with both an MAS and blow-off valve?
When the throttle closes and the blow-off valve opens, the air-flow from the compressor is dumped into the atmosphere rather than into the engine. However, the compressor continues to draw its air through the air filter and MAS, so the MAS continues to register airflow. The engine management system interprets this and injects the appropriate amount of fuel, and tries to ignite the mixture. The engine does continue to draw some air in from the idle air system, though not nearly as much as what the MAS is registering (remember most of it is dumped into the atmosphere), so in most cases the mixture will ignite but will be very rich.
In extreme cases, on very high power cars where a lot of air is dumped into the atmosphere, the amount of fuel may be too much and cause the car to stall. On most cars however, this is rarely a problem.
Compared to a recirculation valve, a blow-off valve looks messy. But because combustion is maintained through the shift, the turbo and the engine keeps their rpm up better, which translates to better response after the shift.
With a good blow-off valve, you should notice that you are not applying as much throttle when you re-engage the clutch after the shift. This shows the engine is keeping the rpms up higher through the shift.
Fixes
There are some ways to combat the rich condition that arises from the use of blow-off valves. All are electronic devices. HKS offers the EIDS and EIDS-Pro, which work by monitoring the throttle position. When the throttle is closed, the HKS EIDS/EIDS-Pro will attenuate the airflow signal the engine management system sees, which reduces the rich condition. This system is approximate only, do not expect to run a perfect air-fuel mixture during shifts, however, properly tuned it can prevent stalling and substantially reduce the rich condition.
Other electronic gadgets that offers some sort of correction for blow-off valve operation include the Greddy E-Manage, HKS S-AFR, Apexi S-AFC.
Ideally a blow-off valve should be used with an engine management system that does not use a MAS to meter air, for example systems that use manifold pressure or throttle position to determine fuel delivery. In such cases, air being dumped into the atmosphere has no effect on fuel delivery at all. Unfortunately, manifold pressure or throttle position systems require re-tuning as humidity, temperature and elevation changes, and when the volumetric efficiency of the engine is changed. This is usually too much work for most street cars.
Compressor surge
The purpose of blow-off valves and recirculation valves is to prevent compressor surge. This happens when the turbo has built boost, and is flowing alot of air into your intake, and you suddenly close the throttle to make a shift. When the throttle is closed, flow has to suddenly stop, and the turbo compressor wheel has to slow down suddenly. This puts a great deal of stress on the compressor wheel and bearings. To prevent this from happening, a blow-off or recirculation valve is placed between the turbo and throttle body that diverts and continue the air flow, allowing the compressor wheel to slow down more gradually.
Recirculation valves
Most modern cars are equipped with Mass Airflow Sensors, which meters the amount of air mass the engine is drawing. With MAS equipped turbo cars, the car maker would usually install a recirculation valve to prevent compressor surge. In this setup, the valve opens to divert the air flow back to the intake stream before the compressor (the non-pressure side of the intake).
What actually happens when the throttle closes and the recirculation valve opens? First air stops flowing through the MAF, as it is easier for the compressor to draw air from the recirculation valve (which is at a higher pressure) than through the air filter and MAF. Basically the compressor would be feeding itself, in a loop. As no air is being drawn through the MAF, the engine management system would stop injecting fuel and ignition, which basically halts combustion (but rpm does not drop to zero as the engine continues to rotate through inertia). The compressor will gradually slow down as the turbine/exhaust side of the turbo drags on the compressor (as there is no exhaust flow from the engine).
As soon as the throttle opens again, the recirculation valve closes, and the compressor starts drawing air through the MAF and combustion resumes. Throughout this process, the engine never runs rich nor lean, and compressor surge is prevented, perfect for the car maker!
Blow-off valves
A blow-off valve diverts the air flow to the atmosphere instead of back into the intake stream. What happens on a car equipped with both an MAS and blow-off valve?
When the throttle closes and the blow-off valve opens, the air-flow from the compressor is dumped into the atmosphere rather than into the engine. However, the compressor continues to draw its air through the air filter and MAS, so the MAS continues to register airflow. The engine management system interprets this and injects the appropriate amount of fuel, and tries to ignite the mixture. The engine does continue to draw some air in from the idle air system, though not nearly as much as what the MAS is registering (remember most of it is dumped into the atmosphere), so in most cases the mixture will ignite but will be very rich.
In extreme cases, on very high power cars where a lot of air is dumped into the atmosphere, the amount of fuel may be too much and cause the car to stall. On most cars however, this is rarely a problem.
Compared to a recirculation valve, a blow-off valve looks messy. But because combustion is maintained through the shift, the turbo and the engine keeps their rpm up better, which translates to better response after the shift.
With a good blow-off valve, you should notice that you are not applying as much throttle when you re-engage the clutch after the shift. This shows the engine is keeping the rpms up higher through the shift.
Fixes
There are some ways to combat the rich condition that arises from the use of blow-off valves. All are electronic devices. HKS offers the EIDS and EIDS-Pro, which work by monitoring the throttle position. When the throttle is closed, the HKS EIDS/EIDS-Pro will attenuate the airflow signal the engine management system sees, which reduces the rich condition. This system is approximate only, do not expect to run a perfect air-fuel mixture during shifts, however, properly tuned it can prevent stalling and substantially reduce the rich condition.
Other electronic gadgets that offers some sort of correction for blow-off valve operation include the Greddy E-Manage, HKS S-AFR, Apexi S-AFC.
Ideally a blow-off valve should be used with an engine management system that does not use a MAS to meter air, for example systems that use manifold pressure or throttle position to determine fuel delivery. In such cases, air being dumped into the atmosphere has no effect on fuel delivery at all. Unfortunately, manifold pressure or throttle position systems require re-tuning as humidity, temperature and elevation changes, and when the volumetric efficiency of the engine is changed. This is usually too much work for most street cars.
05-04-2003, 06:29 AM
#7
got cut off sorry,
Converting recirculation valves to blow-off valves
Generally recirculation valves are simpler in construction than blow-off valves. With the better "blow-off valves, the valve is designed to vent whenever the intake manifold (after the throttle body) pressure is much lower than the intake pressure between the compressor and throttle body. ie. they operate on the difference in pressure seen before and after the throttle body.
With most factory recirculation valves, the valves operate with just the intake manifold pressure. ie. whenever the intake manifold is under vacuum, the recirculation valve will be open. This is not a problem because the MAS still correctly meters airflow, since the entire intake is a closed system. However, taking a recirculation valve and having it vent to the atmosphere like a blow-off valve instead of back into the intake will create problems -- the recirculation valves open whenever the intake manifold is under vacuum, even at idle, and when this happens the MAS does not accurately meter the air the engine is drawing, and the engine management system will not be able to idle the engine properly.
A cheap fix is often to replace the spring with a stronger one, so the recirculation valve is only open when a great deal of vacuum exists. During shifts, the intake manifold develops more vacuum than it would at idle, so the spring would be selected just so the recirculation valve is not open at idle, but will open when the vacuum is higher during shifts. The problem with this approach is that the recirculation valve will remain open even after there is no need to relieve pressure, and also they will also open during deceleration from speed. A converted recirculation valve can create unnecessary problems, and we recommend using a proper good quality pull-type blow-off valve or just keeping the recirculation valve system as it is. !
Converting recirculation valves to blow-off valves
Generally recirculation valves are simpler in construction than blow-off valves. With the better "blow-off valves, the valve is designed to vent whenever the intake manifold (after the throttle body) pressure is much lower than the intake pressure between the compressor and throttle body. ie. they operate on the difference in pressure seen before and after the throttle body.
With most factory recirculation valves, the valves operate with just the intake manifold pressure. ie. whenever the intake manifold is under vacuum, the recirculation valve will be open. This is not a problem because the MAS still correctly meters airflow, since the entire intake is a closed system. However, taking a recirculation valve and having it vent to the atmosphere like a blow-off valve instead of back into the intake will create problems -- the recirculation valves open whenever the intake manifold is under vacuum, even at idle, and when this happens the MAS does not accurately meter the air the engine is drawing, and the engine management system will not be able to idle the engine properly.
A cheap fix is often to replace the spring with a stronger one, so the recirculation valve is only open when a great deal of vacuum exists. During shifts, the intake manifold develops more vacuum than it would at idle, so the spring would be selected just so the recirculation valve is not open at idle, but will open when the vacuum is higher during shifts. The problem with this approach is that the recirculation valve will remain open even after there is no need to relieve pressure, and also they will also open during deceleration from speed. A converted recirculation valve can create unnecessary problems, and we recommend using a proper good quality pull-type blow-off valve or just keeping the recirculation valve system as it is. !
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