WTK. AFM goes before the Turbo, or after the

[corrajem3]

intercooler. I have seen a lot of photos having it after the interooler, but also few models have it at the turbo intake.

Which is the best location, which is the gain or loss at each location? I'm thinking to install it at the turbo intake, because i think that in the other location may the air pressure of the turbo may cause damage to the flapper of the AFM.

I'm not an expert, my mechanic recommend to me to do it in this location. So which is the best way to do it??

Regards

1989 325 I Turbo (Next Wednesday)
1988 M3

[Paul]

Correct install it before the turbocharger.

[corrajem3]

everybody not agree with that. For this reason I'm posting it, looking for additional feedback.Do you have it there? have you or any friend has tested it, at the other side?

I hope to complete my installtation this Thursday, and even though it was already moved before the Turbo, I will like to know the constraints or benefits or having in the other side.

Regards

Jose

[captdaddy]

Check this link, there are several post on this topic in the archives, just do a search.


http://bimmer.roadfly.org/bmw/forums/forcedinduction/1086126-1.html

[TurboBimmer]

Mine is before the turbo, but I think that will limit my power one day.

Why? The way I see it, is that under high air velocity, high boost and high RPM, the AFM creates a restriction to the air being sucked by the turbo. Imagine this theorical scenario.: The turbo sucks so much air to create very high boost that there is a vacuum created between the AFM and the turbo inlet (theory). Since atomospheric pressure at the inlet of the AFM is 14.7PSIA and the outlet is 0 (vacuum created from the turbo) , the maximum airflow is equal to the pressure differential vs the restriction. (14.7 psi maximum)

If the AFM was after the turbo, there would be no restriction in the inlet of the turbo. At the AFM, there would be a pressure drop cause by it's restriction, but since the wastegate controls the boost acording to the intake pressure, the turbo would only work harder to create the desired high boost, which wouldn't be possible with the AFM before the turbo.

That being said, I think that for low to moderatly high boost, having the AFM before the turbo is OK. On my M42, the CR is lowered to 8:1 and I was able to make 20 psi of boost. My clutch was slipping bigh time, but that's another story. May be if I go to 25 or higher psi my AFM will be a bottleneck, but so far, it is not.

[///ARINUTS...]

I am thinking of installing my AFM right before the throttle body. it seems to be that the air going into the engine is best metered there, otherwise the ECU will read a false air Flow and temperature. Also if you have a blow off valve after the AFM then you are dumping metered air which will throw the A/F ratio off (too rich). Sure you will have to adjust the AFM a few times to get it right. Probably the spring will need to be a bit tighter so the velocity doesn't smack it open.

Anyway, My vision for my system is something like this:

Air filter, pipe, Turbo, pipe, Blow Off Valve, pipe, intercooler, pipe, Air Flow Meter, Pipe, Throttle body.

Can you picture it? Does anyone see problems with that set up?

[Paul]

Perhaps, but why would every manufacture using AFM mount them before the turbo?

Do you think the AFM is designed to handle 14+psi? I doubt it would last very long at those pressure and temperatures.

I don't think it would really be much of a restriction, if your still using the stock AFM at 20+psi something is wrong, a rising rate fuel pressure regulator isnt a good idea in the first place. Time to invest in proper engine management.

I got my clutchnet clutch, looks very nice, hope it holds up better then the centerforce did...

[ChrisM]

[TurboBimmer]

Paul, you finally got your clutch!
I'm still e-mailing back and forth with clutchnet.com for information and prices. They are not fast to answer, like 1-2 weeks!
Did you get the 6 puck? Is it a double diaphragm PP?

[Paul]

Ya its a sprung 6 puck with the heaviest pressure plate they can make. Very nice looking piece, pressure plate is fairly light compared to my old centerforce and the disc looks top notch. I'll have it all back together for this weekend and I'll let you know how it feels. It's not a double diaphram PP.

[Paul]

They don't manage fuel, its a bandage at best and not reliable. They seem to be popular for low boost applications and superchargers, problem is they don't provide correct fuel requirements under boost. You can get away with it at low boost levels, not ideal but at higher boost levels they are just dangerous to engines and fuel systems. Increased fuel pressure = less flow, which is why they are increased in ratios 4:1 (fuel pressure:boost pressue) now if the flow is reduced as the pressure increases what do you select the ratio to be optimum for? Peak boost? Proper engine management is the answer, properly sized fuel injectors, normal fuel pressure, proper tuning, do it correctly or pay for it later.

Wonder why they don't use them in factory cars?