rkinney

I am not asking this to get "why would you do that". I'm doing an LT1 swap into a 3rd gen firebird. I was just wondering if an LT1 could use a carb using the GM intake and a 93 ECM to run the optispark for full timing control. I would think that if a TP, Map, and Ect sensors along with an rpm input to the ECM, the optispark should function. The knock sensor could be used and function for timing retard that I wouldn't have with an hei. Any input on this would be appreciated.

camaro350

you could probably sell your stuff and get a good used hei distributer.

rkinney

^^^Please read my post. I stated why I didn't want to use an hei. I have a few hei distributors, that's not the issue. I want full timing control and retain timing retard with the use of the knock sensor.

boosteddragon

iTrader: (1)

subscribed,lookin for same answer!!!! but then again thats tuff using the efi wire harness RIGHT??

rkinney

I planned to use the 93 ECM and harness. I was going to eliminate the injector, o2's, iac, egr, and sec air wiring. Map, tps, ect, opti-coil-module, knock sensor, and vss (for datalogging not function) would be hooked up. I think it will work, hoping the ECM doesn't go into limp mode. I am going to try it and will get back with my results. I'm just about to start the swap.

BIGCAT7274

never done it but i think its doable. why not go with a digital 6 or 7 box? cost?

96TransAmboosted

iTrader: (8)

How is the tps going to send info to the PCM if there is a carb inplace of the TB?

rkinney

Holley and Innovate Motorsports make kits to adapt a TP sensor to a Holley carb.

rkinney

I really just wanted to do it because I like doing things a little different. I also wanted a cleaner looking install with no dist in the back. I'm pretty confident it's gonna work.

slownova73

iTrader: (31)

i dont see why it shouldnt? just my .02, my carbed LT1 was a MO**** FU**** to tune with a distributor, i never ever ever ever could get the timing 100% right on that thing! got it close, but it had room for correction.

vtec

iTrader: (1)

i cant think of a reason to keep the opti after putting a carb on. put a dizzy on there and run a dig6/7 box.

fwiw, i ran a stock ecm, opti, and sbc dizzy for a little while... opti triggered the ecm, and i ran the high voltage through the sbc dizzy. but the only reason i did that is to run the stock ecm with my fuel injection setup. once i got my megasquirt built, i ditched all the factory stuff and went to a crank trigger. if you are running a carb, there is no sense in having an opti hanging out there.

rkinney

If it was going to see more track use, I would prob use an hei and di6/7. It's just going to be a street car that sees the track every now and then. Also, in over 15 yrs of owning an LT1, I have only replaced 1 opti. I know they have their faults, but I'm sticking with it. I have even wondered if an LT1 was converted to 24x components, could the MSD ignition for carbed LS1's be used along with coil packs?

vtec

iTrader: (1)

if its mostly a street car, why are you putting a carb on it? the stock intake/injection would be much better for that.
why are you so against a distributor? i realize they can be difficult to install in a 4th gen, but its been done many times.

rkinney

I'm putting all this in a 3rd gen so the dist fitting isn't an issue. I guess the best answer I can give is that I just want to do something different. I don't like following the status quo. I know that injection would be better for a street car, but a carb will work just fine. The car was originally carbed, although it will have a diff motor, I want to keep it carbed. Thanks for all the input though.

noice

I know this is off topic, but LT1 tuning with a carb is no different from SBC tuning with a carb, it is pretty straightforward.






As for the OP, I'm betting that the computer throws a shitfit when you gut the fuel system off of it. I have no idea how you would tell it to ignore all those sensors.

vtec

iTrader: (1)

I am all for different setups, but what you are wanting to do just isnt the most efficient way of making the spark plugs fire.
having said that, i am not sure if the pcm can tell there is no injectors plugged into it. maybe it will still run the ignition side ok though?

rkinney

I like to experiment, so I will try it. If it doesn't work, then I go with a dizzy. Why is it not that efficient? Besides doing the wiring and ecm install, what's the diff between carb and injection in terms of ignition efficiency. The optispark was fairly efficient with FI. What's lost going to carb? I figured the cel will stay on due to other things not being hooked up. Just not sure if it's going to throw it into limp mode. All the sensors that will affect timing will be hooked up. Just need to look at my editing software to see what codes I can disable. I know emission stuff can be, not sure what else.

vtec

iTrader: (1)

when i said efficient, i meant it in terms of the amount of crap under the hood, on the engine, and resources needed to adjust the timing. the more stuff you use to accomplish a goal, the more chances you have of parts failure, tuning issues, intermittent problems, and things to troubleshoot every time you have a problem.

the optispark is a more accurate design than the sbc distributor, but you dont need that much accuracy anyways to make power. that and it tends to fly apart once you try to spin it 7k frequently. the ability to control timing across the board isnt going to gain any noticeable driveability over a properly curved dizzy, likewise with peak power.

94Z/28M6

You could use the EFI connection kit and use the MSD ignition box . You would not have to buy whole LT1 kit just the wheel for the crank . And just use a vortec distributor for the cam signal .

slownova73

iTrader: (31)

Yea i know that, i just had alot of issues with mine, had a bad module in the HEI, figured that out after countless hours and gas wasted messing with the timing, but i did get it, just took awhile.