Yet another n00b Supercharger question

[soopachargen]

Correct me if im wrong but if your in need of a plumb back simply putting a atmo unit one will create problems with the ecu and fueling etc.

The fueling problems are caused by the blow off valve letting out air that the afm has already measured so you end up with excess fuel on gearchanges.... with a map sensored motor you wouldnt have this problem because the map sensor reads the pressure after the BOV any way.
this is my layman take on it... anyone wish to add more?

[Crampy]

Correct me if im wrong but if your in need of a plumb back simply putting a atmo unit one will create problems with the ecu and fueling etc.

The fueling problems are caused by the blow off valve letting out air that the afm has already measured so you end up with excess fuel on gearchanges.... with a map sensored motor you wouldnt have this problem because the map sensor reads the pressure after the BOV any way.
this is my layman take on it... anyone wish to add more?

Agreed. A MAP sensored car doesn't really give two hoots whether it's vented to atmospere or to plumb it back.

[m4vr1k]

Sounds like this thread has been nothing but justification for you to use rice boy toys.. If you want a Atmos BOV get a turbo car..

If i wanted your opinion, i would have asked for it, that comment is pointless and immature. I would have expected more from a moderator. No, this thread has been asking if i NEED to have a BOV on a supercharged vehicle...as my knowledge on these kinds of things is limited, and i wanted to make the most informed choice possible. Now that i know that i do, i can go and make my decision on either an atmosphere BOV, or a plumb-back BOV....

[soopachargen]

Disclaimer:In my opinion...

You will want a blow off vavle on your setup so you dont blow intercooler pipes when you close the throttle.

Being an sr20 and having an afm i suggest you run a plum back blow off valve as per an sr20det just to keep the fueling happy. You seem to be able to hear a "psh" from the standard plum back blow off valve on an rb20det so you may still get the sound you're looking for, i havent heard an sr20 with standard BOV.

[m4vr1k]

That sounds like a good idea, might just get hold of a stock SR20DET BOV and make that work...
Cheers

[strap-on]

Good thread i think, dont worry about wank value man, if your cars good enough it wont need wank factor, cars that are made to go good are soooo much cooler than things with rice value

[Mr Revhead]

ok, as vvega said....

TB is after the s/c, so you need a valve to release the pressure created when u close the throttle, as the s/c is still spinning and will be creating boost between it and the TB. so a vent there back into the intake before the s/c is best.

if you fit a vented dump valve itll make a mass if silly noise.

as for fuelling issues, it depends on the system used.
a AFM will have issues, a MAP system wont

[Adamal]

As the S/C is run off the engine, its revs are directly proportional to the revs of the engine, unlike a turbo which will still try to create a positive pressure when the engine revs drop.
Result is compressor surge as the pressure keeps increasing as less of it is being consumed by the engine. That causes the turbo to suddenly halt and be forced to spin the other way (Which is compressor surge). That or its gonna put a huge hole in your intercooler

My paragraph construction is pretty damn messy there, but I think you get the idea

The compressor does NOT spin backwards during compressor surge, air just cavotates (sp?) in the compressor housing making the ta ta ta sound. I have run no BOV on my subaru for the last year or so, no problems with lag between gears

Sorry, poor choice of words. I meant that the increase in pressure puts large force on the turbo, making it want to halt rotating. I think I was pretty tired when I wrote all that

[slighty_sykotic]

Ok,

To sort this once and for all.


Show me proof someone of WHAT is so bad about compressor surge.


My 4agte ran a shit bov that couldnt vent shit all, causing massive compressor surge (and a massive SSQ BOV type noise, like REALLLLLLY loud). A good 6 months of me thrashing it, and the turbo was in EXACTLY the same condition as far as I can tell (ie, perfect).


If it slows the blades down rapidly I can understand how it can't be good for seals/bearings, but if wat SUBARUCONVERT says is true, then air caviation is not going to hurt the turbo as far as I can see.


I know factory cars must do it for a reason, but maybe its to prevent pressure spikes in intake piping more than saving the turbo?.

--Sykotic

[Mr Revhead]

factory = less noise

[slighty_sykotic]

True...


So what nub invented the need for bovs?

[Mr Revhead]

some one running a lot of boost while racing, and found the oldschool turbos lagged a bit

[Zak]

On the topic of super chargers and bov's. On my 20V Engine the throtal body is after the charger, it have a rather large venting bov aswell.

Now, thats all well and good, but the noise it makes is extremely loud, and long. It has a contsant whoosh for about 5 seconds, longer if I am only just under atmo pressure.

As soon as I can I will be changing to a plumb back system purely to shut it up as it is too loud to talk over, let alone people on the street fanging the finger up and stuff...

And way, moral of the story is go plumb back, if you don't you'll regret it

[soopachargen]

On the topic of super chargers and bov's. On my 20V Engine the throtal body is after the charger, it have a rather large venting bov aswell.

i'm guessing thats tims old drift car??

[Zak]

Yup thats the one.

[m4vr1k]

Ive just had yet another wee thought occur to me.
What about when im coasting down a hill. Throttle closed, yet the engine (therefore supercharger) is still spinning.
Will the boosted air simply flow out of the BOV and recirculate?

[Crampy]

Ive just had yet another wee thought occur to me.
What about when im coasting down a hill. Throttle closed, yet the engine (therefore supercharger) is still spinning.
Will the boosted air simply flow out of the BOV and recirculate?

Yes it will. Make sure your BOV is set up right though. Don't screw the top screw down too tight. You'll want it to hold max boost, but also be almost opening when max vacuum is applied to the top of it.

[ants_ae92]

Okay, on my system, unless i figure out a way to replicate the 4AGZE system, the supercharger will still be going when the throttle is closed, so it seems to me that i would in fact need a bov on my system, yes?

You can do it the way you have mentioned in your first post (Put the supercharger blowing into the throttle body). So, yes you can put a BOV on it.

There is a Yellow Ford Capri V6 which goes to the drags fairly often, which uses a similar setup to what you are suggesting. He runs two Toyota S/Cs (unsure if they are SC12 or SC14s) and the compressed air goes through an intercooler and into the throttle. He uses a BOV (can't remember if it's one or two BOVs) and it sounds pretty insane when he's staging at the drags.

Thats Adam Wigg, he lives around the corner hes using 2 sc12s. I think thats power enough as he just can't get any traction as it is!

[Zak]

Ive just had yet another wee thought occur to me.
What about when im coasting down a hill. Throttle closed, yet the engine (therefore supercharger) is still spinning.
Will the boosted air simply flow out of the BOV and recirculate?

Mine will do that for about 5 seconds till the charger turns off, but if you are just going to have yours running all the time, then yes that will happen