Venting and you. BOV information.

[PantherRacer]

OK. The other thread does not CLARIFY why venting a BOV on your CA is bad/might cause it to stumble - cut out. I really wouldn't know but would it have something to do with loss of vacuum in any way? It shouldn't be because of the displacement, smaller engines can have loud *** bov's no prob.

What EXACTLY are the problems, what exactly causes it and what can be done to prevent/fix it?

Thanks.

[datsunboy]

its because CA18's run with a MAF sensor.so the ECU has an input, saying "there is x amount of air in the system".....therefore...."inject x amount of fuel".when you vent the BOV to atmo, you've just lost a whole lot of air, that the ECU doesnt know has leaked out, so it still injects the same amount of fuel as it would if it still had all the air, therefore it would run rich for a short period.

You dont have this problem with MAP sensed engines, as they measure the amount of air at the plenum ( after the BOV/leak ), so all measured air actually goes into the engine

[M374llic4]

I would say as close to perfect explination as I have ever heard.

[PantherRacer]

Great explanation man, great response time too Thank you I probbably need to go look at a pic of the engine but...I guess you can't/don't put the bov b4 the maf then...so any solutions as of yet?other than recirculating? lol

[M374llic4]

No sir, the MAF is before the turbo even. The only thing before it is a filter, its the first thing so that it can measure all the air that comes in, then the turbo compresses it, then in to the intercooler to condense and cool the air then in to the manifold to await its turn to enter through the valves.

what happens is when you floor it, and build up boost then let off the throttle, just because you stopped giving it gas, the turbo doesnt magicly just stop, it keeps spinning pushing air into the intake, since it has no where to go since you closed the throttle it builds up alot of pressure and pushes against the turbo, which is quite bad indeed for it. So the Blow off Valve (B.O.V.) vents that excess pressure in to the atmosphere (atmosphereical blow off valve. sp?)

So now that the MAF told the ecu that, that air was in the intake, it then like datsunboy said, puts the amount of gas it thinks should be there in to the engine and then runs rich and bogs down a tad, just for a second though, till the ecu matches the MAF and injectors back up. Most would not even notice durring normal driving.

As for solution, yes, like datsunboy again said, a MAP (Manifold Absolute Pressure) sensor meteres the air that is Actually in the manifold based on the pressure in the manifold, so if your BOV vents, the sensor tells the ecu instantly, hey, there is less air, so put in less gas!

Then tada! no more bog!

[plv]

so could this be a reason why my has so much turbo lag (other than having a big turbo)? my bov is not recirculated.

[M374llic4]

No, that would not nessecaraly be the case. When it happens its only for a second. Turbo lag is a completely different monster. It occurs when say, you mash the gas from a dead stop, the CA is a small engine so it doesnt flow as much exhaust as say the sr or ka, since exhaust is what spins the turbo, if you dont have alot of it, it takes longer to get your turbo spinning full. Think of a turbo as a multiplier, when you give it a little exhaust to spin it, it multiplys the input of air, which in turn gives out more exhaust, so for every rpm higher you go, the more it pushes in to the engine, the more you get out of it.

In order to get rid of turbo lag, its best to match your turbo to your engine. If you have normal cams, 440 injectors, and a 255 pump, tunning a t3/t4 will certinaly give you some lag, because it takes alot to spin a bigger turbo then say a t25/28. Having a bigger turbo isnt nessecaraly the way to get the most out of your engine. Having a smaller turbo that spools twice as fast will get you up to your peak much faster.

Bigger turbos are only if your engine can handle that much boost in the first place, if your only running 10-12 lbs it makes no sense to run a huge turbo, a smaller one can push that no problem and spool alot faster.

hope it helps : \

[knightrider]

converting to a map system is not the easiest way to solve this problem, all you need to do is buy a recirculating bov, what it does is relieve the presure on the turbo side to the suction side of the turbo, this helps decrease lag by forcing air into the turbo keeping it spooling. a recirculating bov, also called a bypass valve is also good for driveablity. under vacume the bypass valve is open allowing air to bypass the turbo and intercooler and going straight to the throttle body, increasing low end response.

[CaEric]

so would a stock dsm bov work in this case ?

[knightrider]

yes a dsm style bypass valve would work, bosch makes a pretty good one also. the best way to plumb it up is have the bypass valve close to the TB, and have it go across the engine and have the port on the suction pipe point towards the turbo so you dont mess with the maf by blowing air at it backwards.

[PantherRacer]

Keep the simple explanations going guys , hopefully there won't be any questions left unanswered for anyone else who would need an explanation etc.Whenever the information is all clear/verified a mod can link to it in one of the stickys (they're kinda locked)

[biosehnsucht]

my recirculating "BOV" is on the hotpipe and goes straight into the intake pipe a little behind the MAF.. I need to get pics of my setup so I can point things out like this

[kota2240]

Im running the hks ssqv into the atmosphere. I dont have any problems, thats probably because this bov knows how to seal!

[rico05]

I too run a SSQV, and unless I do a long vent (slow shift after hard accel...ya know...to make the BOV pop off loud and clear ) and either hit the brakes or engine brake, there is no stumble.

Another viable solution is to set up the MAF as a blow through. You plumb the MAF into the cold pipe (cut out a section of pipe, and hold the MAF in place with couplings and clamps) and make sure that the MAF is after the BOV (just put the BOV on the hotpipe) and it will work.

Problems:1. Have to modify the cold pipe. And a stock square CA coldpipe will not accomodate the round MAF.2. Can easily ruin the MAF after only a few months. KA24E MAFs (which many run, inlcuding myself) are cheap to come by (I've paid less than $20 for all 3 MAFs I have bought).3. If the MAF is too close to the throttle body, or turbo, or a bend in the piping, turbulence and pressure waves can confuse the MAF, throwing off your readings, and then giving the wrong fuel.

Really, switching to a MAP based system is usually far superior because of the speed and range of many modern MAP sensors as well as the ECUs that are setup to run them.

Or as stated above, you can just recurriculate. Most major tuning companies provide or sell recurric kits for their popular BOVs. But I am a ricer, and I love the vent of a BOV.....I've wanted to have a car that made that noise since I was a kid, and every time I hear my SSQV sing, I fall in love all over again.

[biosehnsucht]

You can hear my PROF Sheepdog BOV just fine recirculated if you're actually next to me.. altho I'm not sure if thats cause its a dual outlet system (if there's enough pressure difference to open it far enough, it will atmos BOV through the back of it as well as recirc)

[PantherRacer]

But I am a ricer, and I love the vent of a BOV.....I've wanted to have a car that made that noise since I was a kid, and every time I hear my SSQV sing, I fall in love all over again.

So it's not a real serious problem, like other things in life, there are compromises. I'm gonna let it RING.

[biosehnsucht]

It can cause problems.. or not. I think usually most of the time if you're having actual stall out issues its going to be because something else is also wrong and this just makes it worse enough to stall from too much fuel :P

[CaEric]

can u guys post some pictures of these setups ?

[rico05]

I clean my plugs once a month, and buy new ones about twice a year. That is the only real downfall to venting: Killing your plugs. I also like to run 7s, which they seem to be more susecptible (sp?) to fouling vented anyway. I may switch back to 6s and pull a little timing out (I am running about 3* advanced now)

[knightrider]

heres some pictures and quick pros and cons sorry best i could do in 5 minutes.

blow through setup

[knightrider]

BOV to atmosphere

[knightrider]

recirculated setup

[rico05]

See, that blow through is WAY too close to the TB. Maybe Mitsu MAFs are more stable than the Hitachi ones we get, but that has to be freaking the MAF out. I saw this setup on a S14 w/ SR that had the MAF on a straight part of the cold pipe, comming up from his front mount on its way up to the bend at the throttle body. IIRC it was about 18" from the TB.

[fanta]

The DSM appears to be running a GM MAF; you can see the "MAF Translator" box to the left of it.

[knightrider]

yes, the first picture is of a dsm running a gm maf, and it is quite close to the throttle body.

[biosehnsucht]

I generally read 18" being a good distance from turbo or TB.. and "not too close" to bends..

[datsunboy]

the distance from the turbo/supercharger/throttle body/bends definately matters!were having big problems at the moment with my mates car that is a CA18DET converted to supercharger, and the MAF is way too clost to the s/c, and the turbulence is causing the MAF to read too high, and run rich as hell.

problem is though, we cant really move the MAF anywhere else!starting to think of putting some sort of honeycomb grid inside the piping to try get rid of the turbulence.