[Chris James]

I have a 1985 k10 single cab short bed Silverado with a 700r4 transmission and an anemic 305 engine. I'm strongly considering replacing it with a 350 tbi I have from a 94 z71 stepside. First question is will it bolt up to the existing motor mounts and the 700r4? I'm also guessing I need to update the wiring harness and ecm for the fuel injection. Is that all I should have to do or am I gonna have to dive deeper?

 

[geo1]

It's the little things that will be time consuming,it would be easier if you're donor vehicle was a 87 tbi,then you could have all the right brackets, including gauge cluster, right? yours doesn't have a cel light

 

[RayVoy]

Does your 305 have a throttle body?

 

[Chris James]

Does your 305 have a throttle body?

No is just a carburetor on it

 

[RayVoy]

OK, the 350 will have a TBI, you can buy a 3rd party computer to do engine management.
You'll also need to add a couple of O2 sensors (maybe 4 depending upon the computer you buy). The number of O2 sensors will also depend upon the exhaust config you use.
Do you need cat(s)? Again, depends upon computer requirements.

Fuel pump, your 305 probably has the mechanical fuel pump bolted to the block, if the 350 has the mechanical pump, your good to go; if not, you'll need an electric pump (low pressure).
If your 350 has a plate over the pump mounting area, you may be able to bolt on a pump.

Motor mounts should work fine.

700R4 will bolt up, not sure about its shifting needs, someone else can probably help us with this.

 

[Chris James]

OK, the 350 will have a TBI, you can buy a 3rd party computer to do engine management.
You'll also need to add a couple of O2 sensors (maybe 4 depending upon the computer you buy). The number of O2 sensors will also depend upon the exhaust config you use.
Do you need cat(s)? Again, depends upon computer requirements.

Fuel pump, your 305 probably has the mechanical fuel pump bolted to the block, if the 350 has the mechanical pump, your good to go; if not, you'll need an electric pump (low pressure).
If your 350 has a plate over the pump mounting area, you may be able to bolt on a pump.

Motor mounts should work fine.

700R4 will bolt up, not sure about its shifting needs, someone else can probably help us with this.

Damn I would have never thought about o2 sensors! Thanks for the heads up!

 

[xPosTech]

I'm pretty sure the 700R4 needs a TV (throttle valve) cable for shift control. It also uses a lockup torque convertor with brake switch unlock. If the TV cable is not adjusted correctly it can damage the tranny. You must have the correct linkage on the TBI/carb.

http://www.superchevy.com/how-to/65138-adjusting-tv-cable/

https://www.cargurus.com/Cars/Discussion-c16546_ds639067

Ted

 

[RayVoy]

Thanks Ted

 

[The Heater]

You will need to put an IN TANK fuel pump so it pushes the fuel from the tank. You will need more pressure than a mechanical pump will provide.

 

[RayVoy]

You will need to put an IN TANK fuel pump so it pushes the fuel from the tank. You will need more pressure than a mechanical pump will provide.

He wants to use throttle body injection, it requires the same pressure as a carb

 

[The Heater]

My truck has throttle body injection. I had the same model truck, older, with a carburetor. The latter had a mechanical pump, the former, my current rig, has a pump in the fuel tank and the pressure is WAY more than in the truck that had the carburetor. Now, my truck is a 1994 and things may have changed by then. It is also a 454, but so was the prior truck. Fuel pressure for TBI on my motor is substantially higher than the carbureted version.

 

[RayVoy]

Fuel pressure requirements for throttle body injection (and I'll add, sitting on a 350) is 12 lbs per sq in.

And, thinking you may be on to something @The Heater , I checked the pressure specs for the mechanical pumps.

Appears you are correct sir, the mechanical pumps output only 6 to 9 psi, so they need a hand.

I think I would just use an external to tank electric pump, bypassing the mechanical one.

 

[The Heater]

My truck has been modified internally and it has Edelbrock 110 cc aluminum heads with custom built rocker assemblies, roller cam and valve train, different cam profile, etc. So when Blood Enterprises put the truck on the dynomometer and began to reprogram the ecu they discovered the normal fuel pressure was too low to obtain the desired Fuel/Air Ratio. They said it was around 30-33 lbs. There is a regulator in the truck for the fuel pressure, so they modified it to squeeze more pressure out of the stock fuel pump, which is in the tank. A fuel pressure regulator would be a cheap item to add to the fuel line just to see what your pressure is, so if the engine is not running right you can try to increase the pressure if you are going to try to use a mechanical pump.

But I can tell you that my shop (above), which is very sophisticated and designs proprietary engines for an exotic car builder in MI, told me a mechanical fuel pump would not produce enough pressure for my TBI. I have a Gen IV Big Block, which has a port on the block for a fuel pump (newer versions of the block do not), and I had asked them the question when we were trying to solve the low fuel pressure issue after all the engine modifications. But again, this is a 454, not a 350, but I would think there would need to be more pressure for that engine, too.

 

[RayVoy]

Hey, you won, I already gave you win credit in my previous post. At least the part about the mechanical pump not pushing sufficient pressure.

Just one thing, the regulator will let you reduce pump pressure (reduce and smooth); but I don't think you can increase pressure in a mechanical pump.

 

[The Heater]

Oh, no, man, I wasn't trying to win any arguments. I don't know anything about 350 engines with TBI. The Big Block could be different. When you said they used a mechanical fuel pump I was assuming that GM changed things by the time my model truck was being produced. But I wanted to throw my two cents out there, and that is all it is worth, for the potential purchase of a motor or for any possible work to make everything go together.

 

[RayVoy]

Hey, we are good, I was only teasing.