Hello, I am new here and attempting to convert a 57 Chevy with an Edlebrock carb over to TBI. I have read alot about this(alot of the quality information that I have found came from this site) and thought I was ready to begin the swap until I realized that a Small Cap HEI will not clear the firewall in the 57 with the engine in the stock location. I am wondering if I can use the Mallory Unilite distributor(currently in the engine) and take out or disable the mecahnical advance. I have also been looking into creating a wiring harness from scratch and am wondering if anyone has put together a spreadsheet or list of all the Delphi Part numbers for the connectors and pins needed. If no one has done this, I can try to complile the information. I have found quite a few of them already.

 

A while back I tried putting together such a spreadsheet and it quickly became clear that it is a lot more cost effective to get a harness off JY TBI truck. Usually, a JY pulled harness needs a little cleaning, excess circuit removal, broken connector replacement and you're good to go for a lot less than a new harness. The problem even if you can order all the required connectors the total cost of connectors and wire (SAE J1128) will be higher then if you simply bought aftermarket harness form one of the well know sources. Buying all required connectors shells, pins, weather plugs and wire only makes sense if you are planning to put half a dozen harnesses together.

In case if you need replacement connectors or wire Waytek Wire has a good selection (but it is not complete) of Delphi Packard Metri Pack connectors. Also, be aware that there are multiple flavors of the same connector available as this is done by orienting slots in around connector pins.

Small hat HEI dizzy should clear fire wall - it is no bigger than old points style distributor. Large hat HEI - that's another story.
//RF

 

I took a look at the distributor in the car which is the Mallory Unlite. It is smaller in diameter than the Small Hat HEI. I can barely get my finger between the firewall and the cap. I can take a look and see if it is possible to move the engine forward on the mounts to accomodate the Small Hat HEI. It seems like there should be a way to use the Unilite though so I do not have to go through the trouble of moving the engine.

 

Would a crank trigger be applicable?

 

I was hoping to be able to do something a little more simple. If I have to mount a crank sensor, I think I will see if there is a way to move the engine forward. I thought that in some of the post on this forum people had talked about modifying the original point style distributors to work with the TBI. I thought maybe I could do something similar to the Unilite. I have access to a full machine shop so I can make some mods if need be. I found some information on leaving the distributor mechanical advance and letting the ECM think it is adjusting timing but would prefer to not go that route.

 

Gray - what I am putting down below is an electronics experiment.

Long time ago there was product called points eliminator kit. Technically it can be (possibly) adapted to drive a 7 pin ICM mounted externally of the old dizzy. The tricky part is that GM ICM is designed to detect a zero crossing voltage input from reluctor coil (very low voltage) in its as designed configuration and output of points eliminator is sufficient to drive ignition coil. The two are not (most likely) compatible, but basically do the same thing. It might be a good idea to call Accel or MSD and pick their technical support for a possible (non catalog solution).

//RF

 

Thanks RF for the information. If I am reading your post right, it appears that there may be a way(if I can disable the mechanical advance) to drive the GM ICM with the current output from the Unilite that used to be used to drive the coil. It would seem as you say that this could work. I guess I need to figure out what the output of the mallory is and what the output of the reluctor coil is. Then figure a way to make the mallory output match the reluctor. I work with a guy that is pretty good with electronics so I will ask him what he thinks.

 

A short answer is yes. A long one - may require some soldering. I did a bit of digging into my old notes on ICM reluctor coil interface - pins P & N. There is actually a lot of freely available information out there. In a nut shell - reluctor coil generates an AC signal that swings from about +3 to -3 volts (looks like a sawtooth). When this signal transits through 0 volts the ICM fires ignition coil.
From your stand point you'll have to figure out what is the output of the points eliminator module (PEM) and devise an interface that translates PEM output to zero crossing signal that ICM expects. This is where your electronics savvy friend comes in handy.
Lock out mechanical advance, junk vacuum advance can and you are done - easy right??? Or you can move engine forward couple of inches?

Are you running Pontiac 326 in your Belair??

//RF

 

No it is a Chevy 350 with a T5 in the car. It is actually a 210 Post. The engine has a full Performer RPM kit from Edelbrock on it including aluminum heads. The Edelbrock website says that it puts out close to 400Hp not sure how acurate that is though. The TBI that I am trying to put on it is from a 89 Chevy Pickup. I bored the TBI unit out to 50mm(luckily where I work I have access to the equipment to do this) and am planning on running some 90 lbs injectors in it. I am going to have to get the PEM out of the distributor and play around alittle with the output. Hopefully I can come up with a solution. Thanks for your help RF. I found some similar information on the Megasquirt Website about the reluctor coil.

 

Ok I did some more looking today and it appears that the GM Ignition Control Module conditions the ouput of the reluctor coil from the distributor and then sends a square wave to the ECM. It appears that the square wave that goes to the ECM could easily be produced with the PEM. I am needing some help in understanding what all the ICM does now. If I just send the square wave straight to the ECM and bypass that portion of the ICM does this effect the coil firing function of the ICM.

 

do not forget that ICM receives timing signal (EST) from ECM to advance or retard timing on the next coil fire. Also dwell is being taken care by ICM.

//RF

 

I did a bit of cruising - check out pertronix website

http://www.pertronix.com/

I would suggest that you talk to their tech support. It is possible that have done a solution that you are looking for - OE points dizzy converted to drive 7/8 pin ICM.

//RF

 

If I bypass the ICM for the Reluctor Signal being converted to the square wave, can I still use if for the other functions. I will try to contact Petronics next week and see what they have to say. I think I might just be able to bypass the part of the ICM that I am not using and hook it up as normal for the dwell and est.

 

So basically you'll have no timing control by ECM. - It should work, but you'll loose the ability to program timing which is allows greater flexibility over wide range of operating conditions. With this approach your dizzy will have to perform all timing chores and just send a reference pulse back to ECM. IMHO it is a compromise and it will limit performance potential. I would not take this approach, but that's because I hate to leave performance on table.

//RF

 

I was actually hoping that I could just bypass the ICM portion that converts the zero crossing sine wave to a square wave. Then feed a square wave to the ecm straight from the PEM. Then use the ECM to control the coil as normal through the ICM. This should still allow the ECM to control the timing, I think. I think but am not sure that the part of the ICM that converts the zero crossing sine wave to a square wave is independent of the portion that the ECM communicates with to control the coil and timing. I might be missing something here though and apologize if so.

 

FYI Painless makes a universal TBI harness...
http://www.summitracing.com/parts/PRF-60101/

 

Use a stock GM ICM no matter what. Even if you need to remote mount it to the firewall. Just be sure to give it a heat sink.

There is secondary handshaking that goes on between the ECM & ICM. Along with other pieces of that puzzle that make using a stock GM module the best way to go.

IIRC, Dave's does conversions of points distributors to HEI 8 pin modules and pickups.

RBob.

 

I was always planning on using a stock ICM. I am trying to figure out how to get the ICM to work with a Mallory Unilite distributor.
What I am trying to do.
The Unilite can be modified to put out a square wave for cam position sensing. The stock small cap HEI puts out a zero crossing sine wave that is input to the stock ICM which converts it to a square wave that is sent to the ECM. The ECM sends a signal back to the ICM which in turn fires the coil at the correct timing. What I am wondering is if it would be possible to By-pass the portion of the ICM that converts the zero crossing sine wave from the small cap HEI to a square wave and feed the square wave directly to the ECM. Then let the ECM feed the signal back to the ICM and fire the coil at the correct timing. It seems like this would work but I am not sure if the two functions of the ICM are independent of eachother.

 

No bypassing of the stock ICM. This is what I was trying to say. Use the proper reluctor type pickup and feed it to a GM ICM (notice I keep mentioning a GM ICM, not an accel, not a standard, not a pertronix, not a ---fill in the blank---), a GM ICM.

With enough work what you are envisioning will work. But to get it to work is more effort then just doing it the GM way to begin with.

RBob.

 

I would like to use the stock GM ICM the way it is suppose to but the small cap hei will not clear the firewall in the 57. I would have to modify the unilite distibutor to use the reluctor. I thought it might be easier to just bypass part of the function of the ICM but didn't know if it would work.

 

You know you can turn the distributor so that the module faces the front of the intake.. Don't know if that would give you the clearance, but I suspect it would.

 

The diameter is actually to big. I was looking around on a couple other sites and it looks like the engine in this car is sitting back a little further than it should be. In looking I found that the stock 57 had a points style distributor in them and there should be enough room for the small cap HEI. I am not sure why there isn't in this car. It is a tight fit between the fan and radiator so maybe it was done for that reason. I am going to look more into moving the engine forward since there appears to be no easy solution to getting the Unilite to work as is. I think if I can get it to move forward .5" I would be good. Thanks to everyone for the help.