I've seen it alot on japanese S5's.. but never on american ones..(well none i've seen anyway)

alot of the Nissan guys do it too..





does anybody know the details to doing it? is it straight forward? or do they re-chip the ecu when they do it?



for those that don't know what i'm talking about:

you take the AFM off the intake.. and u basically "replace" a piece of your intercooler piping with the airflow meter... so it's actually metering compressed air rather atmoshperic... closer you have it to the TB the less likely to be affected by air leaks as well as reducing restriction in the intake...

basicaly the closest u can get to being Map without being Map sensor..



i've seen japanese cars with upward of 550hp and big single turbos using this blowthrough method...



anyone have more info?

 

Those cars did not have flapper style AFM's I bet

it's still restrictive, and you're going to have driveability problems with an FC ecu

if you wanted to do something different, you could try to use a Greddy Emanage Ultimate or a MAP ECU to remove the airflow meter without going all the way to a standalone

 

The S4 AFM works the same as the S5 one, so it will work. I can't see any reason why it would cause drivability problems. The problem is the pressure in the AFM can pop the black plastic panel off the top. I have no idea how much boost is required to do that.

This must be done with a fuel controller or reprogrammed ECU though. Because under boost the air flowing through the AFM is denser, the AFM effectively under-reads the airflow and without correction you'll run lean.

This method used to be popular before aftermarket programmable EFI became relatively cheap...

 

the s5 and s4 AFM are nothing alike. i have both and the s4 has a flap that swings back and forth inside. the s5 however has a resipicating "cone" on the indside.

 

yeah I only saw it done on a S5 afm.. obviously because it's a Round tube making it much easier to work with..

i see.. so it does requiring some compensation...

the nissan guys who stick a Z32 afm (hot wire) in their IC pipes don't have to do anything.. it reads the same wether it's in the pipe or on the mouth of the turbo..

i'm guessing it's due to the superior design of the hot wire method?



So did the japanese have a reason for putting it there other than boost leaks?

or because the air is passing through it compressed it affectively becomes a "lesser" restriction?

is that the idea?

Bear with me for a moment:

so theoretically speaking..

if one were to stick the AFM in the IC pipe.. and the toss in bigger secondary injectors

technically u take out LESS Fuel in a blow through setup then a pull through correct? and could run larger injectors with the same fuel controller effectively "increasing" your +/- % range...



or am I way off base here?

 

u misunderstood

he meant the work on the same principle.. i.e a device that "pushed" out of teh way depending on the air blowing over it...

they're both a "flap" of sorts..

e.g. not hot wire or Karman..

 

i think boost leaks/ease of plumbing is the biggie. we've speculated before on a potential power increase, and never came to a consensus. if there is a difference its small

 

I have found that when going with an FMIC (and aftermarket BOV) on a stock ecu FC with the AFM still there, there are driveability problems caused by the BOV not responding as soon as the stocker.

Even though your boost gauge, connected to engine manifold, may not show that you are generating boost, there is actually higher pressure between the turbo and intercooler. You have pressure drop in the intercooler resulting in less boost on the engine side, and you also have the throttle plates only partially open resulting in a greater pressure drop.

So, when cruising along at medium throttle but not in boost, and you lift slightly on the throttle or you shift, the pressure in the FMIC piping actually travels backwards and slaps the AFM door shut for a second, making the car buck. This has happened with most of the aftermarket BOV's I have tried to use, whether or not they have a fine adjustment for opening pressure.

The ones that do have an adjustment, by the time you get them adjusted soft enough to prevent the surge and bucking, then they turn into a vacuum leak at idle and make the car run crappy because of that. So then you find yourself looking for ways to recirculate the BOV to keep it from being a vacuum leak.

I have sometimes gotten rid of this by either running the stock BOV in addition to the aftermarket one, OR replacing the aftermarket one with the stock one altogether, and of course recirculating the stock one.

I mention this because, if you put the AFM in the FMIC piping right after the IC outlet (the most popular spot) then you might increase this effect. Most people put their aftermarket BOV between the turbo and intercooler. IF you're driving under the same circumstances listed above, and the throttle plates close when you lift or when you shift, that pressure wave (however small) will travel back and the first thing it will hit is the AFM flapper, pushing it backwards, making the ecu pull all the fuel for a second and making the car buck.

IF you did a blowthrough AFM, I would say you'd need to relocate the BOV between the AFM and the throttlebody, and you would have to have either the stock BOV there, or an aftermarket one that can be adjusted to open very easily.

 

good good write up, i have been wondering about this for a while now.

 

Thanks for the info RR...

the most common place i've seen the AFM is at the end of the hot pipe right before entering the IC (on the old school greddy FMIC where the pipe comes over the top of the IC...





now that u mentioned all the CONS.. how about some of the PRO'S of putting it there? :p

 

pro's of running a blow through hot wire maf are a more stable idle, and you can run an open to atmosphere blow off valve. BUT if you run an open to atmosphere BOV it has to be BEFORE the MAF. otherwise you will be venting metered air out and your car will stumble or die on decel or inbetween shifts. other than that i can think of any other benefits of a blow through. they are usually more trouble than they are worth. people say they can damage the hotwire or blow open the whole maf casing if you dont prep it right.
I wouldn't run the plunger MAF in a blow through setup. it just seems like a bad idea.

to me it seems the easiest to just get a haltech and run a map sensor instead of the silly plunger maf if you're serious about tuning.

 

pipe over the top is the cold side of the old greddy ic

 

The only problem I see with this is using it with a blow off valve. Depending on where the blow off valve is, and where it vents to, you will have problems with the car stalling.

 

All fuel is cut on deccel anyway isn't it? I believe I read that from Aaron Cake.......

Edit.. yes, here's the quote... I might be mis-reading..
Quoted from: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/premix-dilemma-again-695850/page2/

 

You just like to start **** don't you?

Yes, fuel is cut on 100% decel. But, if you're cruising at 62mph and come upon a car running 57mph, you have to lift slightly. Not enough to put you at 0% throttle, but perhaps you drop from 25% throttle to 15%. This is the circumstance I mention above where the afm is pushed shut for just a second, robbing the engine of fuel, making it buck while still under load.

And (this is just my theory) in a turbo car the intake tract is so long that if you shift under mild load and then try to get back on the throttle this bucking condition can still exist because the old, slow electronics don't respond that quickly. All I can do is give my personal experiences, everyone else can interpret them for what they are worth. Given the number of cars I have worked on over the years, I think I have seen just about everything that can happen with a stock ecu'd FC, modded or not, something most people cannot say.

 

blowthrough is a complete waste on these cars. the stock AFM is so shitty. I can see it on like a mk 4 supra or something, but you might as well just save your time and money on something that allows you to remove the AFM.

 

Well, yes and no. Not trying to rub anybody raw, just trying to make sure the facts are straight... I hate seeing conflicting information and not knowing who to believe. Expectially when the two sources are as reputable as you and Mr Cake.


Good to know Kevin.

 

My original statement was not clear that the TPS has to read zero for the ECU to cut fuel. There is no fuel cut if you are running at 8K and then just close the throttle slightly gradually slow down to 4K.

 

^ bam, nuff said, end of thread

 

my neighbors car has the old style greddy IC, and the bov is plumbed back in to the tid, and it does a lift throttle bucking too.

it feels exactly like how you describe it, lift throttle, bov opens, extra air closes afm, car bucks lean....

 

Cool. Thanks Aaron! Good to know the details.

 

IF it's not the STOCK bov then that could be the issue. The spring tension is too high on some of the aftermarket ones, so regardless of whether they are recirculated or not, they don't open as soon as the stocker.

 

They look nothing alike but they work exactly the same way, which is what I actually said.

I don't think an S4 AFM would be any harder to work with. It's no different to putting a pod filter on, you just use an adaptor.

Correct, a hot-wire AFM is directly measuring the mass flow of the air, not the velocity and temp separately like out AFM's do. So the change in density doesn't matter.

I'm quite sure the most common reason for relocating the AFM was to make room for a bigger turbo on a custom manifold. The turbo usually ends up further forward and there's insufficient room to put both an AFM and a decent filter. It was just a practicality thing, not some fundamental design improvement. The other advantages to moving it are pretty minor. Note that no manufacturers install the AFM after the turbo.

Nope, it'll pose the same restriction no matter where you put it.

Yep, you'd need less positive correction when the secondaries are on, but you'd still need the same amount when they're not.

A plunger-type AFM and a MAF (hot-wire) sensor are two totally different things. FC's don't have a MAF sensor.

Even though it seems like a bad idea to you, it's been done successfully hundreds of times before, and was very popular on heavily modded engines back when aftermarket programmable EFI was prohibitively expensive. There's just not much point to doing it these days.