Campeck

ok. HOPEFULLY! (praying for that call) im getting a job soon. which means money that i have nothing but gas and food to spend on. and with moderation and a little dieting I can prolly save up plenty for a modern engine management system for the car.

Geo. tell me more about sequential firing. what is that?

MoonBoy

I suppose I had the 944 intake system in mind without having known(until after I posted) about the AEM valve. In hindsight the valve make perfect sense. I look forward to some dyno results! Good luck!

Geo

OK, we got you thinking! Cool!

Turbo cars have different issues from NA.

First of all, turbos heat the air when they compress it. But the air mass remains constant (only the density changes). Warm air certainly increases the risk of detonation. But remember the air has already been metered at that point. With an NA with a AFM or MAP more air increases the air mass, but the AFM and MAP set-ups are based upon a given VE when they were originally tuned. Change the VE and you change the ratio - the computer gets its measurements from the AFM or MAP, but it doesn't know there is more mass. It's calculating mass based upon previous (and now incorrect) information. When this happens, the engine goes lean and increases the risk of detonation.

What makes a hot-wire MAF superior is that changes in VE don't affect it (unless they are extreme). It measures the mass of air more or less directly. So, if you have a MAF, when you add air, the MAF lets the ECU know there is more air mass and the ECU makes the necessary changes. No leaning of the mixture.

The intercooler won't change the mixture because the air has already been metered and the air mass remains constant (now I'm repeating myself - it's OK though because I'm starting to get old ).

Sam I am

This is my first post, but i have been following these forums here for sometime. I am Mech. engineering student and also agree with serge, It is a fact that bends decrease the flow rate. This occurs because the flow is no longer laminar and has turbulance. This is not the same thing as tube length, you can have as long and straight a tube as you want and still have relatively linear flow. So try to eliminate bends to maximize flow while choosing an appropriate intake length according to where you want your torque curve.

Geo

That is true for the intake runners between the valves and the plenum.

The problem before the plenum is we have a non-optimal system (despite what some like to believe). I'd wager big that the way Porsche designed that intake box was to take a lump of clay, stuff it in the space, and when it was full they knew how much space they had to work with. Don't laugh, I had a friend who worked for an OEM and that is how they designed things like air boxes and ww fluid bottles and such. Some things are not worth spending a lot of time ($$$) designing on a budget car (which the 944 was for Porsche).

Geo

Campeck, I'll shoot some money your way to help you out with testing.

The 944 has batch fire injection, meaning all injectors fire at once. Therefore, one fires 4 times for each time the intake valve opens. This is OK for 1983, but it's not good by modern standards. Modern systems use sequential firing injectors meaning the injector fires once for each opening of the intake valve. This should give you better fuel metering and mixing allowing you to run a bit leaner leading to more power.

Campeck

oh dang! so the injector fires 3 times with its corosponding intake valve still closed?!
frieky.

or when its valve opens it shoots 4 times really fast?

Geo

All injectors fire every time. So for one revolution they all fire 4x. It's not the best methodology.

porshaowner

I've read every post and after 8 pages how come the idea of barrier seperation hasn't been brought up? Are smooth tubes really the way to go? If you get the chance of dyno tuning are you planning on doing a pull with the stock air box and paper filter installed just to get a base number to make sure your ideas are going in the right direction?

Geo

If you read the 8 pages you didn't get the real gist of the topic.

The gains are not from cold air. Testing has shown the under-hood temps to be near ambient at speed. The gains from a CAI come from resonance tuning of the piping.

Others have tried the barrier idea, but it doesn't do much if anything.

Campeck

well.
my car is not stock.
gutted cat. chip. and milled head(slightly)

and right now i have a HUGE leak somewhere in the intake. (my geuss an intake valve not shutting at the right time) letting to much air in. im running VERY lean right now and idling to high. I geuss this will affect the #'s.
in about a month the car goes under repair. maybe this should wait until then?

Geo

Sounds more like a vacuum leak than a valve problem.

If you have a leaking valve it's probably bent.

Campeck

there is no vacuum leak.
I looked twice. both times with intake off. new TPS and idle stabilizer valve.

Geo

Have you done a compression test? That will tell you if you have a leaky valve. And/or you could do a leak-down test.

michaelathome

Don't mean to steal the thread but I thought since we were talking about injection methods and tecniques this kinda fits.

Geo, what would be the benifits if any of this early NA with dual carb setup???

http://forums.pelicanparts.com/showt...hreadid=212390

Michael