Date: Sat, 25 Oct 1997 16:18:32 -0700 From: Mike West Reply-To: Air-Cooled Volkswagen Discussion List To: Multiple recipients of list VINTAGVW Subject: Hot-rodding the Fuel Injection I suppose I should preface this with my curriculum vitae . . The only FI system I own is in a box under the work bench. I have poked at a couple, even cured one . . stuck air flap. Most of the time it's an air leak or clogged injector. . . Then I send them down to a local place I know where they have some decent equipment and expertise. Read a book or two . . . maybe this should be called "Science Fiction" Carburetion is defined in my College Dictionary as: " the process of metering air and fuel to an engine intake system in the proper proportions for combustion". So a Fuel Injection system is a "Carburetor". Based on that, I wrote that piece on "Fuel Injection is Fun!" Some guy recently wrote to me about that article . . . Said he has a '79 with FI and what would I do to get more "performance" out of it. I told him that as I have been lead to believe, the FI system he has is the best performer he can buy for that engine. There is supposed to be a wider band of torque thru the entire power curve. . . . . I suggested he cherry out the FI and jack a fresh engine under it, then get back to me . . . . . :-) The same is true in all cases, what good a big ass carb on a sick engine? Or vice versa? Based on his question and some stuff in my head, you get another article of dubious value . . . :-) How we're going to "hot-rod" FI. Let's take a "virtual" look at one: The first thing you notice is it's butt ugly . . . . :-) Let's face it, there is no pride in the product even. . . There is no polished aluminum or chrome, looks about as functional in the box as it does on the engine. There is no comparison to a set of dual carbs and linkage . :-) You can intuit that those babies do mean stuff. . :-) Throttle body injection still looks cool, it's just a carb with an injector in place of all the needle valves. This was the logical step after the "needle jet" carb. What they had to have, was a way to put the heat sensor and the O2 sensor in the loop so your engine could be tuned "on the fly". Our modern day setup where the injector is in the intake manifold and points at the intake valve is called the "Tuned port injection" I think. I would imagine this was found necessary when they had to put the Exhaust Gas Recirculation system in . . . . The "TPI", as I refer to it above, is reputed to give a better "Volumetric efficiency" meaning it can get more fuel in the cylinder to burn than the throttle body type. The injectors in the TPI sit right in the intake manifold tho and are subject to high heat and vibration . . . Woe . . Here's what I have in mind for the box under the workbench . . It's the complete FI system from a '83 2 liter flat four. I'm going to build a 1904 cc out of a type 1 and strap that FI system on it. I haven't checked the numbers but I think even the injectors will work. If they are too big, I'll get some smaller ones. There is a table floating around on the net giving fuel qty and time etc. with part numbers so it should be no big deal. I mentioned the cheat on the O2 sensor, or was it the temp sensor? I can use these to change any value in the system I want. Stick a potentiometer in the line and have my way with it. My intent is to leave the O2 sensor alone so it reads correct. Using that value, I change the value of the temp sensor to read low which tells the brain to give me longer bursts of fuel. Might still have to dink with the O2 sensor if it gets to fighting with me. I could still get an accurate reading . . . . . I could rig this to read and be adjusted from the dash, same as one of "Claudes Buggies"& Performance. I don't want to. I may have a gage on the O2 sense for a while till I get it tweeked. I need to think on this some more but basically I'd size the injectors such that they would handle my highest rpm fuel requirement. The idle has to be kept in mind also. I just sneaked a peek at Bruce Bowlings Program for sizing injectors and thats all that it does. He give the algorithim of the program for us physicists. . :-) Now if this guy who wanted to tweek his 1600 rig built a big engine to go under his FI, he would have some slightly different problems . . . He has a system with an air box and throttle body for a 1600 engine . . . . So he'd have to round up a bigger air box etc. . . . maybe . . . Maybe just a bigger Throttle Valve which is really an air valve. Sizing the throttle valve should be on the same order as sizing a venturi, still have to pull a vacuum for various reasons. Probably grab one off a 1.8 liter bus. . . Also bigger injectors but he can size those off Bowling . . I don't see any need to ever change out his Brain. . . The brain gets it's main signal from the distributor/coil . . . So he gets an air box off a 2 liter Pinto . . . . no biggy . . As long as it uses a flapper with a potentiometer on it, it can be adjusted. Or some similarity . . . I'll stop here briefly and elucidate, whatever that means. . . The flap on the air mass sensor or air box is tied to an arm which sweeps across a potentiometer(variable resistor) and gives a reading between 100 and 300 ohms. . . just a ferinstance, ymmv. . . This reading is piped over to the brain where it tells the brain in voltage, how much air is coming thru there. This number is averaged by the brain and sent on to the fuel pulse sender. This pulse guy reads the value and adjusts the pulse to the injectors to give the right amount of fuel for stoich. ratio. The pulse guy is also tied to the coil, so he knows When to send the fuel out. . . . This is checked by the O2 sensor when the smoke comes out the tailpipe and if it's good, it leaves things alone. If it's not so good, the O2 sensor sends a signal back that is part of the value the brain was averaging in the first place. . . the value is increased or decreased and the new value is fed to the injector pulse guy. . . So if you don't like the way things are working, you take the bull by the tail and Lie to the brain . . . . :-) This particular lie is accomplished by putting a potentiometer in the line to the brain from the flapper potentiometer. Now you adjust the pot to tell the brain it isn't really getting that much air or it's getting more than it really is, depending on which way you want to go on this thing. The brain accepts that value and adjusts accordingly. You dog, you! Other lies may be told by doing a similar deed to the temp sense and the O2 sensor. . . . . You don't like the pinto air box, build your own, some percentage larger from sheet or tube aluminum . . now we're starting to make it pretty! Stick a pot from Radio Shack on the thing and get whatever you like. Same for that throttle body . . it's just a butterfly valve. Nothing electric about it, unless you count the switch that cuts out the EGR at full throttle. Has a small screw that lets you by-pass the valve and bleed air thru for idle. . . As mentioned before, we should be able to cop parts off other makes of cars as long as we understand the principles. Say this guy builds a 1776, probably still use the same cold- start valve and auxilliary air valve . . . . Decel valve, probably still work, haven't looked into it . . Fuel pressure would still be alright, at some point you might need a bigger pump tho I've heard the bottle neck is the size of the fuel lines themselves. The "fuel ring", steel tubing that carries the fuel to the injectors is usually a two piece thing so that would be no problem. . . Saw a "bad" looking Electric Turbo-charger Fan the other day. This could be incorporated. . . . :-) More performance stuff would be getting your injectors balanced. I see an outfit on the net, you send them five or six and they send you four of them back perfectly balanced for volume/pulse- width or some such. Hi teck stuff , , , There are also companies already out there that want to sell you a better injector, better spray pattern they say. . . . There is one possible problem with the Stock Brain, it may have a limit on the rpm. Like, it may not go to ten grand . Me personally, I have to stay somewhat lower than that, I don't have gears to really use that kind of horsepower which is rpm. I'd need that 5 speed gear box. At this point you could go to the CB Performance which uses a programmable ROM chip. . . . big bucks but you're obviously a racer. We probably better put the CDI ignition in too . . .you knew that . . The FI systems are getting better performance if you can believe any of the data that is out there. . . I have no data on TBI vs TPI but it stands to reason that "VE" is a fact and that weighs heavy. . . . The TPI, where the injectors are right in the header, looks to me like it might eat injectors. . . put little finned heat sinks on 'em. Get a shop coat and a tie and go around mumbling things like "pulse width" and "laminar flow". . . . That and a thick wallet will have the girls swarming. . :-) Now we need a chrome air filter . . . . . . west pushing back the dark . . . If you have comments like I'm totally wrong about some part of this well lay them on me. I'll need to correct them anyway. :-) Hot-rodding the Fuel Injection