From: darling@simlab.arc.nasa.gov on behalf of Dave Darling [darling@simlab.arc.nasa.gov] Sent: Tuesday, May 04, 1999 8:41 AM To: C. Monnett Cc: 914 Subject: Re: [914] 2.0 FI modifications? At 7:59 PM -0700 5/3/99, Chris Monnett wrote: > I'm wondering if anyone out there knows how to tweek of modify the >FI system on the 2.0 Basically I interested in getting every ounce >performance out of the car. Does anyone make a slightly bigger >injector? Are there any benefits to putting a cone filter on? If any >one knows how to get the most out of the system I would greatly >appreciate it. I won't make any claims to being able to get the "most" out of the D-jet system. However, there are some basic points to consider. First, an internal-combustion engine is an air pump. The better flow you can get into it and out of it, the better it works and the more power you will make. In general, a flow path that has lots of bends does not flow as well as a path with few or no bends. The stock air cleaner bends the air 270 degrees before it gets to the throttle body. If you removed the stock cleaner and put a cone filter over the top of the throttle body, you might very well see some increase in power. You will *definitely* see an increase in noise (OK, you'll *hear* the noise), and in engine wear. You might be able to rig up a separate box with an air filter to connect up all the vaccuum hoses that used to go into the air cleaner--that will help quite a bit with the engine wear. (Unfiltered air is bad...) And, of course, you could no longer drive or even park the car in the rain, unless you fabricated some sort of water shield. And I'd be surprised if you actually got much power out of it. I'm sure it would *feel* faster--after all, when you spend money and it sounds "meaner", it *always* feels faster. But I'd be surprised if a dyno showed a large improvement. A set of Kerry-Hunter headers (or the old Garretson headers, which I hear Pete Webber is making now) and a high-flow muffler would also do some good with the air pump. Of course, you lose your heater that way. The next basic point is the air:fuel mixture. There is an all- around optimum mixture, an optimum power mixture, and a less-well- defined optimum fuel economy mixture. The D-jet was designed to keep the mixture somewhere near 14.7:1, which is the all-around optimum one. Optimum power is about 12:1, which is slightly rich. But the power gains are really quite small there, from what I read. Anyway, if you really want to get that particular smidgen of power, then you will need a way to monitor the mixture. The O2 sensor in the exhaust is a popular and relatively easy way to do this. You can mount a single sensor in an area common to all four exhaust streams, and then tweak the adjustments on the D-jet system to get the reading you want. Or, you can mount sensors in all four exhaust streams (near the head is best) and try to find some way to tweak the cylinders individ- ually. Sadly, the O2 sensor is not a very good indicator at full- throttle. I'm not sure why, though. Anyway, most changes you can make (and still run a D-jet system) are going to give you very small increments of power--if any. Wholesale substitutions of the FI components, like fuel injectors, is likely to only give you a car that runs as good as or worse than the original. If you're serious about getting a little power here and a little power there, you'll need to book a bunch of dyno time. Get all of the changes you are thinking about making all lined up ahead of time, then go to the dyno and try each one out. Dyno time is rather expensive, so try to get the changes done and tested quickly. If you come up with anything that works *really* well, please let the rest of us know! --DD Dave Darling 74 914 2.0 (decapitated) darling@simlab.arc.nasa.gov "OFF WITH ITS HEADS!"