Injecting you car the EFI way Options

[Mike Bellis]

I work on very complex fuel systems for a living. For fun I enjoy building EFI systems for myself and clients. I have had some inquiries about how to DIY a system. So here anre some pics and a few words... I'll break it down for those not up to speed.





You will see my current project. Don't worry about the wiring. It's still in test phase and I have a shorter harness I'm working on.
This is a TBI (Throttle Body Injection system. The easyest way by far to add EFI to your engine.
Here's a list of sensors needed for most EFI setups...
TPS (Throttle Position Sensor) The TPS measures how far open your throttle is. 1-5 volts in mots cases.
MAP (Manifold Absolute Pressure sensor) Measures manifold vacuum 1-5 volts.
AIT (Air Intake Temp sensor) Measures intake ait temp. Used for TPI or sequencial systems. Not needed for TBI.
Water Temp. Most aftermarket system use a GM sensor.
O2 sensor (measures the ammount of oxygen in the burned exhaust. ECU will adjust fuel level based on this signal)
Oil Pressure Switch. Some systems like the TBI use this switch to shut off fuel with a loss of oil pressure.
MAF (Mass Air Flow sensor) Measures the amount of air going into the engine. Used on high performance systems.
Crank Trigger. Used by the ECU to determine engine speed and adjust the fuel map to suit the engine requirements.
Cam Trigger. Used buy the ECU for a sequencial injection system.
ECU (Electronic Control Unit, the brain of the system)

The TBI system has the injectors mounted in the throttle body on top of the engine. It mounts similar to a carb. These systems can be used on a stock manifold with the correct adapter flange. The TBI is for a mild cam setup but the ECU can be re-flashed for more performance. In the picture above is a Crossfire Injection system from an 80's Corvette. It uses two 400 CFM TB's instead of one. I had to down size the injectors for my 283. The GM computer will learn how the car drives and re-write the fuel map to suit the engine (Closed Loop) using the engine sensors as a referance. During warm up and WOT, the system will run in "Open Loop" mode and use engine speed and TPS signal to adjust the fuel map. This system was used and purchased from Ebay. Total installed price $500.

A sequencial injection system uses both the Crank and Cam signals to determine when each cylinder is at its intake stroke. The injector will fire only during this point of the cycle. A sequencial system has better off idle performance and slightly better fuel economy. The two most common ways to access a Cam signal are to use an Accel Dizzy with a cam output or machine a magnet into the cam gear to use an inductive pickup on the timing cover.




This Picture Is a sequencial system using a F.A.S.T. ECU, GM sensors, Ford dual throttle bodies and Bosch Injectors. For This setup everything was custom fabricated. I used a dual quad manifold and welded injector bungs to it. This system was all new parts. Total installed price $4000. Plus dozens of days of seat time with my lap top writing fuel maps.

I've also used Megasquirt with great results. MS has a great fourm with helpful people just like this site. MS does not need a cam signal because it does not do sequencial injection. MS uses "Bank to Bank" injection. This means to toggles between the right and left cylinders back and forth. There will be slightly lesss performance at low RPM's but at mid to high rpm the difference is neglegable. The really nice thing about the MS forum is that there will be someonr there with a setup similar to yours and they will share their fuel maps. You then use their map as the starting point for yours.

Most aftermarket EFI systems will allow the use of a wide band O2 sensor. A wide band O2 will allow you to run in Closed Loop mode and have the ECU learn how you drive in conjunction with the engine needs. This makes fine tuning of the system very easy.

Most early GM EFI systems can be adapted to any engine. You just need the GM sensors and wire it up correctly. Factory EFI systems are really cheap at junk yards or on the web. Make sure you buy a system as complete as possible. Painless Wiring makes harnesses for most GM and Ford systems.

I hope this helps people understand a little about EFI.

If I missed anything please chime in. Correct me if I made any mistakes.

Bottom line... EFI is easy. Everyone should do it!

[Mike Bellis]

Lets take my 283 FI conversion.

If I were picking a carb I would calculate like this...

CFM=CIDxRPMxVE/3456

CID=283
RPM=max 6000
VE=Volumetric Efficiency 80% (maybe, mild cam, 9.5 comp ratio)

This calculates to a max CFM of 393

So I would look for a carb around 400CFM to be a match for this engine.

The TB setup has dual 400's. 800CFM total. Twice what this engine should need. with the fuel ratio matched to the air this engine runs great. Cruising at speed with little throttle input creates no surging or jerking. If I were to double the CFM again it is concievable that surging could accur. This can be compensated for by "camming" the throttle. Similar to the throttle cam on the 944. This would be done to make the throttle pedal action Non Linear. So at crusing, the pedal opens slightly, when the pedal is pushed to the WOT position the throttle will open at an exponential rate. instead of a 1 to 1 ratio on a linear pedal. No matter how large the throttle body is, the engine is limited mechanically to how much air it can take in.

[computers4kids]

The easyest way will be a TBI from a 1990's GM truck. Almost all of them had TBI. It is not the most high end FI system but it is much better than a carb.

Thanks for the ideas and tips. I'll have to take a trip to the local pick a part and see how available a mostly complete 90's truck EFI system would be and how much they would want....just for a starting point. I know last summer I read and read about adding FI on my motor and the more I did, the more I realized I needed help.

Originally, I thought I was going to get a TPI system off a vette or camaro, but later found because of my Vortec heads, it became much more complicated of an adventure...and costly.

Then I started looking at the TBI systems from Holley. It appeared new plug and play complete kits were around $1100. Their systems appealed to me because they had directions and would be tailored for my motor (somewhat). I just couldn't get myself to spend that kind of money when my car runs great as it is and gets 24mpg on the highway, which isn't too bad. Anyway, not really understanding all the parts well enough, I didn't feel confident enough to purchase used systems or go to the junk yard and pull a system. Heck, I 'm not entirely sure I could find all the related parts you have mentioned that I would need. It would be like "looking for waldo." (IMG:style_emoticons/default/sad.gif) Anyone have a "looking for waldo" book but with pictures of what all the EFI parts looks like and where their normally located? (IMG:style_emoticons/default/biggrin.gif)