Suck or blow?

[Starmavin]

I have something I would like to have some opinions on. I am designing a home brewed twin tubo induction for my BMW. Why twin you ask? Is there any advantage to twin turbos? Not at all, doing it will be complicated and hard. But to me it's a fun challange and it'll give those local kids something to beat off too.. Not to mention bragging rites are a bonous.

I have built several turbo systems before. I personaly will be useing the blow through setup, departing from my last setup that was draw through.

I would like to know from other turbo inducted E30 BMW owners their view on "draw through the AFM" or the "blow through the AFM" setups.

My questions are:
1. What style do you use?
2. Why?

[nukeduster]

draw thru

blow thru produces temporary rich states when you close the throttle , the boost still goes thru the afm keeping the flap open til the wastegate can get rid of excess boost

thusly, the ecu still thinks air is getting into the engine even though the TPS says otherwise, and the injectors still keep their predefined pulse widths based off the AFM's (incorrect) readings.

draw thru ftw.

[Starmavin]

So you are not useing a blow off valve to release closed throtle boost?

I was going to try to run two blow off valves in a blow through AFM setup, one before the AFM, and a smaller one after to help prevent "flapper slap". It will be dificult to get the two to work together. Or I'll move the AFM as close to the throtle body as I can so back boost from the intake will minimal. At least I'll have fun trying.

[Hayes]

I read that you have built turbo systems before but you said that there is no benefit to tt setups...I have to disagree, you can run two smaller turbos which will spool faster than a larger single snail. You only have to have each turbo producing half of the overall boost amount instead of a single snail producing all the boost.

That is the conclusion I have come to based on all the information I have read, researched and my own personal thoughts.

Brandon

[94BMW325i]

set your car up like the FD RX7's turbos

[Starmavin]

The set up I was considering would use two T-25s that I had laying around from other jobs and that alone would have taken high RPMs to spool both up. To build it so I can get good (streetable) performance from twins I'd need to find two good 1.4L turbo chargers. Each of the T-25s are built to feed 2.0L motors so if you figure both could feed 4.0L, too much for a 2.7L motor to use effectively. Pluss a single turbo is much less complex (one oil feed and return, one coolant line and return), easier to tune and I don't have the trouble of trying to balance the boost from two smaller turbos (spool up is much more predictable), then you have relibility isues. And in light of all that I am going to save myself the unnecessary drama and revert back to a single turbo. Although it is impressive to have twin turbos is just isn't cost effective, considering that I'm just doing this so the stock 2.7 will go out with a bang to make room for the 750il motor going in its place.....