View Full Version : Funky way of making AFM and BOV co-operate?

08-03-2006, 02:09 PM
Well, it's 1am here, and after a LOT of coffees and ciggies, I have had a rather interesting idea...(instead of writing up this damn thesis :bigthumbu )

Y'know how a BOV makes a car with an AFM go a little haywire when it vents due to the BOV messing up the AFM reading, why not do something like this guy has?


And then mount the BOV before the AFM, this way, the AFM only measures what's going to the TB, rather than what's going into the turbo...

With a side-feed, this could work even better as you could practically have the AFM strapped to the TB.

Or do I really need a good slapping to the head for even thinking of it? :hehe:

08-03-2006, 03:14 PM
I thought about this myself but I was told that AFMs begin to give out skewed readings with very high flow air... But I don't know ...

08-03-2006, 03:22 PM
The AFM will read air temps that are too hot that way. I'm not sure how an extra flapper door in front of the air stream would affect the BOV operation...if the AFM opens/closes it could cause the bov to vent prematurely...

08-03-2006, 07:43 PM
I gave that suggestion awhile back, and got all negative comments. It kinda does make for an odd air stream. The afm's insides aren't really all that smooth.

You can try it, then let us know.

08-03-2006, 08:36 PM
Theres a thread about this already.

I dont know what youd search but its been beaten to death.

Theres been a few people that have done it that "say" it works. However they have never provided a full modlist, and a dynosheet with a fuel trim chart to prove it doesnt mess the afrs up.

Think about it. Its a flapper door. If you install the thing AFTER the turbo the SECOND the pressure changes it opens all the way. You either have OFF or ON. There would be no happy middle ground (not saying the AFM is all that accurate in the first place). Not to mention the AFM has the IAT in it as well and as Chris said it will not reflect an accurate temprature and the fuel trims will already be off.

I just cant see the engine running right set up like that. You need a blow through MAF setup before you can start running like that.

However, theres a guy on the MR2 board that rigged up a way to let SOME of the air recirculate while letting the other part of it vent. Theyre saying it runs good, transitions properly and sounds pretty damn good.

08-04-2006, 12:01 AM
Arh, OK, my bad >_<

/me goes off to try searching again...

Bingo, found it :D


Sounds better to wait for nuke to work his magic :D

08-04-2006, 06:30 AM
You guys realize Im crazy right?

I actually pulled out mathmetical equations and shit in that thread.

Whats wrong with me?

08-04-2006, 06:59 AM
haha. The only thing I see wrong with the equation is a messed up non smooth air flow.

The afm should be right before the manifold realistically. This "it's not going to read the correct temp." bs is bs. You have an intercooler. That's going to change the temp.

If there's air in the system I don't imagine the flap closing.

08-04-2006, 02:46 PM
angryyoungnpoor: It's just that the stock ECU makes corrections that are based on ambient temp, not manifold temp. This makes a difference. That means that the stock ECU indirectly infers something about intercooler efficiency. And besides, the stock sensor has a heat range that is appropriate for ambient temperatures, which are much cooler than manifold temps.

I have also tested the AFM as it is...it already is an on/off switch practically, placing it after the turbo wont help. Remember that air post-turbo is compressed, therefore you are getting more air in the engine for a given deflection angle of the AFM door.

All theory...in practise does it matter that much? Well, we mostly run off the charts rich anyways. So who knows.

I'd rather just get rid of the damn thing and tune it with a wideband. So thats what I'm doing.


08-04-2006, 03:54 PM
Uhhh... hot air is compressed more than cold air?

08-04-2006, 08:20 PM
The main thing that everyone is missing her is the AFM measures flow of NON compressed air. When you compress air it gets heavier. So it wil mess the flow up.

I dont understand what there is to get or not to get about this. Even in that thread and clayton was saying it works, blah blah blah, no dynosheet showing it did anything positive or negative, and no a/f ratio sheet showing me how lean/rich that car runs without that AFM in its proper place.

Until someone does that and shows me ideal as stock A/F ratio with the same mods we wont knwo for sure.

08-04-2006, 09:52 PM
I think the main problem is the pressure. It's a flow meter and therefore does not correct for the pressure. If it was an air mass meter it would have worked maybe.
The temperature, i think, is not relevant anymore as soon as you change anything like IC, boost pressure, turbo size etc. Because then the relation between intake air temp. and air temp. at the manifold changes.

08-04-2006, 10:38 PM
No its relative.

We arent talking about what the engine sees, we are talking about what the ECU thinks its seeing.

If you have that AFM in the turbo stream the ECU is always going to see 120+ degree temps and fuel for it.

08-05-2006, 04:23 AM
You know what it really fucking comes down to? AFM's/MAF's FUCKING SUCK... Why they EVER invented such a horrible device I'll never know.

08-05-2006, 04:39 AM
wait wait wait, Im soo used to the Trans AM its not even funny, so this AFM thingy has a flapper valve inside it? how F-up is that???

08-05-2006, 05:17 AM
You know what it really fucking comes down to? AFM's/MAF's FUCKING SUCK... Why they EVER invented such a horrible device I'll never know.

Cause theyre efficent as fuck for their native systems.

Stock to mild modded, theyre fine.

They adjust for VE, and take care of it. Theyre good at what they were designed to do within the operating parameters set to do so in. Start modding and thats a different story. Resolution runs out and it becomes an on/off switch.

So in ways theyre better than MAP and MAS or MAF but in lots of ways theyre not...

08-05-2006, 05:59 AM
I'd rather have MAP from the get-go.

08-05-2006, 06:39 AM
Then you should get a 3rd gen. I think most around here like them. ;)

btw, edited my first post.

08-05-2006, 06:46 AM
Eventually I'll go AEM EMS or some shit...

08-05-2006, 08:47 AM
No its relative.

We arent talking about what the engine sees, we are talking about what the ECU thinks its seeing.

If you have that AFM in the turbo stream the ECU is always going to see 120+ degree temps and fuel for it.

So what you're saying is... the afm detects the air before the turbo... :hot: air.. =non dense air. Which then sends a signal to the ECU saying to give this much fuel for this much air... I can understand this much, because the air that is in the system is already accounted for. What I don't understand is how it can be at all accurate if the temperature of the air is 15 degrees cooler, or more once it hits the fuel.

I think the ideal thing to have done was to have something before the turbo to read the amount of air and something before the manifold to read the temperature of the air.