This may be a stupid question: intake
 

I was thinking about stock intake vs MAF, and it seems to me that the biggest problem is that the flap on the air sensor causes air restriction. Would it be possible to perhaps replace the spring with another that has less tension, and re-calibrate the sensor to create better airflow.

Justin Lerman

The Intake is a different thing than the MAF. The "Barn Door"/flapper is a type of Air Mass sensor/MAF, and it goes at the end of the intake system as does a "hot wire" MAF. The intake is the 2 aluminum pieces with 3 legs on each side of the engine.

There have been some people who have cleaned their flap and gotten better performance, and there have also been some who have "adjusted" (apparently there's a screw) their flap and gotten better performance. I think those who usually get the improved performance are fixing something that has gotten out of adjustment over time.

From what I have read/heard the flapper is not as much of a restriction as you would think, but replacing the "Barn door MAF with a "Hot Wire" MAF is pretty common. For more info read this article.

http://www.angelfire.com/id2/cameronbaudinet/

A company in Europe replaces the stock MAF with a Hot Wire style MAF from a later Porsche as well as some other stuff and gets 26hp.

I'm sure someone with more experience with fluid dynamics will correct me, but it's my understanding that with gas flow (such as air) flow is not significantly restricted until you reach sonic velocity. On the flip side, you can open up the intake too much and velocity will drop to the point where you're not filling the cylinders efficiently. My experience isthat after you've improved the exhaust and fuel systems and reduced rotating inertia, then you can find inprovements with the intake.

then where does all the horsepower come from the hot wire setup

Here's some info I found on a search: http://forums.pelicanparts.com/porsche-911-technical-forum/99842-maf-kit-84-89-carreras-25-real-hp-any-interest.html?highlight=maf

I don't think there's much hp to be gained as a first step. You may gain a few hp as a last step after other mods. You certainly don't have to believe me, but I'm not selling you anything and the poeple selling MAF systems are.

I can also tell you that a lot of MAF "hot wire" setups cost a ton and, I have heard, don't really do much for you. I'm not sure how those fella's in Europe got the power they did, but it was part of a package deal where they changed the exhaust, FI, Computer, and MAF, not just one of those parts. The HP gain was almost certainly due to the package deal.

David, thanks for the thread and the information, probably wont be jumping at the MAF. I would much rather fix up the exhaust and let steve do his magic. OH yeah, and cut some holes in the air box to make it growl! :)

You might also want to check the movement of the flap across the rev range. I had a Mazda 323 with a similar L-Jetronic injection system and the flap was pretty much flat against the side of the intake above 3000 RPM. Basically it was there to help meter the air a low RPMs, but above 3000 RPM it was running pretty much on the O2 sensor and the map.

Since all of the engine's big HP numbers are generated at the upper reaches if the rev range, replacing the flapper may not net you much.

Now if you had a CIS injection system that would be something else entirely.