Hey, as the title implies I’ve got a 305 4bbl that I’m pretty sure is an Lg4, that I’m trying to use with my original 350 TPI harness. Could use all the help possible. I’m definitely keeping the 305 in until I can afford a decent engine so a swap is out of the question

 

The ESC should work with the LG4. Obviously, there will be no MCS control for the carb. The TPS can be connectsd along with the VSS, and maybe the TCC will work. There will likely be lots of error codes.

 

Okay, also the previous owner claims to have snipped off all the plugs for the TPI, so all the plugs I have are supposed to be normal engine plugs, but none of the plugs match my engine. So, what wires go where?

 

Since a 1988 did not have an optional carbed engine in the U.S. the "normal" engine would indeed be the TPI for that car. Some of the connectors needed to operate a common LG4 won't even exist, nor will the wiring. The ECM will not have the functions for operating a mixture control solenoid or idle kicker solenoid for the carburetor. If an aftermarket carb is used (without mixture control) a different distributor with mechanical/vacuum advance will probably be necessary, along with all the adjustments to that.

Another consideration is that the electrical connectors and plugs changed design in 1987. An earlier engine will have different design (pattern) connectors.

It will be very helpful to know what model year engine is being installed. Then the wiring diagrams for that engine AND the TPI from 1988 will need to be compared. Missing or incorrect connectors can be replaced, and the older type can be installed where necessary to at least get the critical functions working.

 

Well this is where it gets weirder. I’m going with an 87 LG4 like I said before, but only because it doesn’t have a choke cable. It came out of an 87 base model where it was swapped in place of the cars original V6. I should have clarified that I mean “normal” as in non-essential for a carb engine. What would you recommend I do?

 

I’d like to make this engine function with my digital dash, but if absolutely necessary I’m sure I could find a cheap Ls4, and rwd Trans for it. I’m new to building a roller into a driver, and while I was aware of the headache of wiring, it’s hitting me hardest now 😂😅 so, if a diff engine and trans combo is best I can find it I’m certain

 

No Third Gen ever had a choke cable. They were always electric.

Are you trying to run the feedback carb with it's computer? Or are you going to swap a non-feedback carb like an Edelbrock and a mechanical distributor?

GD

 

Well, my 83 T/A Lb9 had a choke cable but with this one I’m trying to use a stock 4bbl factory carb since I haven’t gotten a performance one yet. Both engine and harness are stock. The difference is the 305 is 4bbl going to 350 tpi harness. (May have strayed off course a lil).

 

Stock carb is simply not appropriate for use on the TPI harness unless it's a purely mechanical carb without the CCC controls (Canada models? And older stuff that's pre-Third Gen).

83 would only have a choke cable if someone added it later. GM didn't use manual chokes in 1983. For that matter even my 69 GMC truck had a hot-air automatic choke. Definitely not stock on an 83.

GD

 

I think the only electrical part is the choke. All the rest is mechanical. I’m trying to make the engine work with the harness unless someone can direct me to a practical engine swap with the harness as snipped as it is

 

forget about using the TPI harness with a carb engine-just slap on a pre-computer distributor and carb and run it. if the TPI fuel pump is still in place inside the tank,you will need to remove that pump and replace with a length of hose and a pickup screen in order to use carb type engine mounted pump.Also provision should be made to operate the transmission TCC

 

It has a mechanical distributor, and I was wondering if an in-line fuel pressure regulator would allow the in-tank pump to continue proper function alongside the on-engine pump? Also what carb would you recommend?

 

Negative. The in-tank pump is running between 35 and 45 psi. It will not tolerate being back-pressured down to 3-5psi for a carb. It must be removed.

For carb - a Holley 4777 of whatever choke and linkage you prefer. Should run well out of the box.

GD

 

Okay, I gotcha. Sounds like I should probably put a better intake manifold

 

Dealers choice. Probably won't matter for a 305.

GD

 

Alrighty, I dig. Any decent intake manifolds from Holley?

 

what intake manifold is on the engine now ? Also may be possible to draw fuel out the return line on the tank as that ends near the pump sock-there will be no debris screen on that line though.

 

I'm sure they make some. But again - IT WONT MATTER on a 305. Just use whatever is already on it. That engine is going to be about 180 HP so *uck it. Just make it run and save your money for a better engine.

GD

 

as far as I can tell it’s a stock GM intake manifold, and I could probably add a few in-line filters to the return. I should have a sending and return though, shouldnt I? My pump has three holes

 

I gotcha. I was thinking that if I add in some performance here, when I get a 350 or something in the Sbc family I could pull it from this engine and put it on the next one

 

Cheapest thing you could do is, take all the LG4 crap off of that, down to the heads and block; and put all the TPI stuff from your car back onto it. Intake, dist, WP, accessories, brackets, etc. Use the TPI wiring harness on it. (duh) Effffff abuncha intakes and carb conversions and all the rest of that.

Yeah 180 HP is pretty much all you're gonna get out of that. Doesn't too much matter what intake system is on top of it. It is what it is.

I should add, you'll need 305 sized injectors; 19 lb/hr more or less. Tuning would probably help but probably isn't "necessary", as in, won't run otherwise.

 

Well he did mention the TPI harness plugs are all cut off. You *could* buy a replacement harness and some used TPI parts and get it working of course - but that's probably a monumental task for someone that isn't intimately familiar with the TPI.

GD

 

Well, as far as tpi and all that... I do know of an 86 T/A in a junkyard that I could purchase and use the engine and harness off of since I know the car has a digital dash. The next logical question would be if I should just yank the trans too since that would give me an entire proper drivetrain

 

Also, given that I got the car just as a chassis I don’t have any of the original drivetrain bits and pieces

 

Oh-I thought just the original engine was missing....in that case you should buy that '86 and take the needed parts:some details will be different,AC hoses,belt drives,etc.but mostly close enough.Is condition of the engine/tranny in that '86 known?

 

I have no clue on the condition of the drivetrain, but since I’m friends with the owner, I may be able to find out