Ok so I have an LT1 camaro, and I want to convert to a SBC setup. with a TH400 and a12-bolt. Wats involve in teh swap? I nkow the rear and trans wont be a problem but what is involved with keeping wiring and lighting to work? gauges too? Any wiring harnesses thta I need to get? Help I need all the help anyone can give!

 

The LT1 PCM supports the speedometer, tach and fuel pump power supply. Without the Opti, you can't really use the stock PCM for anything, particularly the fuel power supply. But you would probably be changing out the fuel system anyway to a lower pressure carb setup. The rest of the instruments, lighting, whatever has no connection to the PCM.

Have you tried posting this in LT1 Engine Tech?

 

No I haven't tried posting it there. Figured this would be the place for it to go. Anyone else have any knowledge on a carb conversion? STarting system? VATS? Is the vats system gone once I remove the computer?

 

Well, this is something I did in an EFI truck. You need to figure out what turns off/on your fuel pump. Yeah, it's the computer, but from what imput. The ignition turns on your pump as soon as the ignition circuit is completed. In my case, it was lack of oil pressure that turned my pump off. That's why some cars (does this include LT1s, probably so) have an oil pressure sending unit and an oil pressure SWITCH.

If you do indeed have a switch, then it seems to be that you want to keep your ECM in the car- don't remove it! So, cut your fuel lines and spice in a return style regulator. You can't dead-head the stock EFI pumps. Also, you need a regulator to get your fuel pressure down to a level the needle/seats on your carb can close. Additionally, don't cut any wires when all you have to do is unplug them. Neatly wrap up your harness and tuck it out of the way. Install your intake, carburetor, HEI distributor and what ever you need to close the hole the opti was in- as you'll be removing all computer controlled functions of your engine. So with all installed, hook up the gas to the carb. Send a hot wire controlled by the ignition to your distributor.

Now, you get the key swith- your pump primes. After turning the key, your engine runs and you develope oil pressure keeping your fuel pump on. As you see, it is important not to chop your harness up or to remove your computer. In this way your speedometer will still work and all of your gauges. Will the tach work? I don't know where it gets it's signal, but it might be retained.

Furthermore, you're violating numerous federal laws by removing the parts discussed in the thread- so be sure you're only using this vehicle on the race track. If you wanted to get an inspection stick.... just realized it's a 1996 car. That means you have OBDII.

You better scrap this ideal or make this your track-only car because you will not be able to get it inspected. You might could have gotten away with this with OBDI, but OBDII will be next to impossible and will only get worse in the following few years. Something to seriously think about.

Studytime

 

I just did this recently, but on a 92 Camaro. Some things are probably similar, some are probably different on an LT-1. Here were the critical connections in my application:

1. Speedo: run by the ECM. Worked just fine after the engine swap. As long as the VSS is still sending it's signal to the ECM it seems to keep working, regardless of what's going on under the hood.

2. Tach: not sure if it's run by the ECM or not but it took it's signal off the negative terminal of the coil- all the complicated guts/wires of the original factory computer controlled distributor that talked with the ECM had NOTHING to do with the tach working correctly (perhaps the tach in a 4th gen still works off the neg terminal of the coil and doesn't care if the Opti is still talking to the ECM??)

3. Fuel pump: at key-on or while cranking the ECM ran the fuel pump. Once running I'm not sure what the ECM looked at to keep it running but it was definitely one of the following- either the oil pressure sender or the tach signal wire (see above). It definitely didn't need to talk to anything inside the computer controlled distributor since all that stuff was long gone when the fuel injection was yanked off.

Literally everything still works on my car- including the A/C! A 92 is a much less complicated car than an LT-1 but probably there are still may similarities in the basic electronic architecture.

I handled fuel pressure regulation with a Mallory 4-port return-style regulator patched into the factory fuel lines up under the hood. Mine is set at 5 PSI and holds onto that pressure faithfully, regardless of engine load or RPM. Basically, a bulletproof solution.

 

Good info so far guys, any places to buy parts i may need or just a general list of odds and ends i may forget?

 

The LT1 PCM is significantly different.... The F-Body LT1 does not interlock the oil pressure switch to the fuel pump. No need to make any changes there. But the PCM looks for the low resolution pulse signal from the Optispark. If it doesn't see that signal in two cam revs, it shuts down the fuel pump. If you don't have an Opti, you won't have a signal from the PCM to keep the fuel pump running - need to rewire to a new source.

The LT1 tach is driven off the PCM, not the coil. The PCM is using the Opti pulse signals to determine the RPM and feed the tach. Not sure if you can just run a wire from the coil to the stock 4th Gen tach.

I wouldn't attempt a switch like this without a good wiring diagram. Just about everything you need to know can be determined by looking at it.

 

Are u saying I should get a wiring diagram from the whol LT1 computer setup or for the new wiring that is gonna need to be run?

 

You need both the engine wiring diagrams, and the body wiring diagrams. Chilton's has a semi-decent set of drawings in their F-Body manual, although the body diagram is a little weak, and the engine/PCM diagram doesn't pick up some of the more subtle year-to-year differences. Shoebox has a set of 1995 wiring diagrams on his "Tech Pages", photos of the complete engine wiring harness, with all the connectors labeled, etc. Of course your 96 would be slightly different than the 95, but you're ditching most of the wiring harness anyway.

Its almost like the only thing you would be keeping the stock PCM for would be the speedometer. Not sure if you can even get that signal out of it with virtually nothing else connected. I only use my stock PCM for VSS, IAC and the emissions connections like EGR and EEC. But I still have the Opti optical sensor, and most other sensors paralleled into both the stock PCM and the MoTeC ECU.

 

Ya i just figured I wsa gonna ditch teh whole PCM and engine harness. There's really no need for it once I go carb, just MSD boxes I figured would work out alright, and basicalyl on speedo and autometer guages for all the vitals. I think the only hard part is gonna be the ignition/fuel setup. But that even doesnt' seem that bad

 

Jimmy I Thought I Answered All Of This For You!
Ditch The Pcm And Harness!
You Arent Puttin In A Stock 305 Here You Are Obvously After Performance, A Tach Is A Must Teh Stock One Is Not Even Close To Accureate! Auto Meter Gauges And So One. As Far As The Fuel Pump I Would Put It On A Switch, Alot Of Our Carb Cars Like Starting With Out He Pump On So You Turn The Car On And As Soon As It Fires You Hit The Switch. To Get The Stock Speedo To Work With A 400 You Will Need A Few Things But I Wouldnt Bother! Its A Simple Swap! You're Headers And All Will Work, You Will Have To Cut The Cowl For Carb Clearance.

Just Dig In You'll Figure It Out! And As Far As Emissions There Is A Race Car Weaver You Can Get ........... I Got One !

I Dont Post On This Bord Or Brag About How Fast My Car Is , But I Think Jimmy Can Vouch That I Know All Of This

The Man Haider

 

Ya ya haider u know I just gotta make sure I have all my **** covered, i dont wanna start in on this ignorant

 

Guess I was thinking too hard. Can I get that 15 minutes back?

Studytime

 

I've done this twice. I first carbed an LT1 and now I'm running a gen. 1 SBC. As far as the computer, you don't need it or any of the wires going to it EXCEPT 2!!! Be sure you keep the large purple wire and the only small black ground wire running into the firewall, these are to your ignition so you'll be able to start the car with the key. I made this mistake the first time but I caught myself the second time. As far as fuel system, I used the stock pump and tank for awhile, used an aeromotive 4 port return style regulator. You just need to locate the fuel pump relay which is under the driver's side kick panel. The wire to the fuel pump just needs to be ran to a 12v source, something with current only with the key on. Now I'm running an RCI 12 gallon fuel cell with a Quick Fuel Technology 140gph fuel pump for the motor, and a holley blue pump for the nitrous. Also you have to decide what kind of ignition. I would recommend MSD's pro billet dist. part number 8570 which has the small cap and slip collar cause you're going to need all the clearance you can. It may not be necessary but I always have notched the cowl back to the windshield to make it easier to install/remove distributer, installing/removing and adjusting carburetor. Also, if you're going to a pretty hot SBC with a big roller cam, brakes may be an issue. I'm using a fairly large solid roller and my brakes are sh*t. Cam doesn't produce enough vacuum for power brakes. I suggest a vacuum canister or a manual brake setup. Also, the computer doesn't control the fuel sending unit so you would be able to use your stock tank and have the factory fuel level gauge. Also your fuel gauge and voltage gauge will be the only ones working after the removal of the ECM. Any other questions, just let me know. It's a very easy swap.