TBI Motor Swap

I’m going to replace the tired 305 in my 76 Jimmy with a rebuilt 383 TBI roller motor, anything to worry about, like will the accessories off my 305 all fit? I’ll obviously need new valve covers since I believe they’re center bolt style, it’s a one piece rear main seal so new flexplate, this is not a later Vortec motor so the manifold should be the same, I’ll have to verify the fuel pump boss, am I forgetting anything else?

You may not have fuel pump provisions on the TBI block,probably will not. So an electric pump will ne necessary. When I did mine I bolted a factory mechanical pump to the block. Used my electric pump as a pusher blowing through the factory pump. That way I was able to retain all factory lines and appearance. Plus the factory pump with the return line regulates the fuel pressure, keeps the electric pump from deadhead and keeps the electric pump and fuel cool due to bypass,just like the factory did.

I had to click a few times on your avatar to see the wide screen shot:

but that is a mighty fine looking thing to be putting a hotter engine to, maybe with a bigger exhaust. Do you have TBI vehicle to pick off of, or is it going to be all catalog new?

goldpack said:

I had to click a few times on your avatar to see the wide screen shot:

but that is a mighty fine looking thing to be putting a hotter engine to, maybe with a bigger exhaust. Do you have TBI vehicle to pick off of, or is it going to be all catalog new?

You must be registered for see images attach

Click to expand...

Thanks, I just bought it with the understanding that it had the original 400 but after driving it I realized it was a little under powered so curiosity got the best of me and I discovered someone swapped in a 1981 305, yuck. So I’m buying a reman roller motor to install over the winter, not looking for insane power just enough to push this brick down the highway without putting my foot through the floor.

Ricko1966 said:

You may not have fuel pump provisions on the TBI block,probably will not. So an electric pump will ne necessary. When I did mine I bolted a factory mechanical pump to the block. Used my electric pump as a pusher blowing through the factory pump. That way I was able to retain all factory lines and appearance. Plus the factory pump with the return line regulates the fuel pressure, keeps the electric pump from deadhead and keeps the electric pump and fuel cool due to bypass,just like the factory did.

Click to expand...

That’s brilliant, so you cut the arm off of the pump and bolted it to the block so it looks factory?

fishwater said:

That’s brilliant, so you cut the arm off of the pump and bolted it to the block so it looks factory?

Click to expand...

I would not have thought to use a mechanical fuel pump as a pressure regulator but agree the idea is brilliant. If I ever end up at the point where I have to switch from TBI to carb I'll keep that idea in mind (probably not anytime soon).

fishwater said:

That’s brilliant, so you cut the arm off of the pump and bolted it to the block so it looks factory?

Click to expand...

You may not have to cut the arm. See if the relief is cast into the block just no pushrod hole drilled.

In your initial post, are you saying you’ll use your current intake manifold that’s on the 305 on the Tbi motor?

If you are ordering a reman, I don’t believe there’d be much of a difference price between an L05 tbi engine and an L31r vortec engine. You’ll get better heads and go from 8.5:1 to 9.5:1 compression. It’s probably a 30-40hp difference between the two…

I think your buying an intake manifold either way.

^^^ center 4 bolts are different angle on your 305 than on TBI heads you can grind the holes to the correct angle otherwise you are buying an intake. If your intake is cast iron grinding is going to be tough. But there are factory 4bbl manifolds with the correct angle in the junkyard if that's the route you want to go. I think you might be better off with the vortec heads depending on camshaft profile and rpm operating range. A 383 isn't going to have factory compression ratings due to different displacement. I'd bet they are both the same or dam close.

I’m looking at two different budget 383 builds, both are 9.5 or 9.0 compression. One is fancier with stainless valves and Melling HV pump, supposedly 410 HP/460 torque and the other is a more basic stock type build with 365/425, both have new steel cranks and Silvolite or Sealed Power cast pistons and roller cams.

Neither build is a high end, max effort type of build with forged internals, I just don’t see the need on this one, I just want a good cruiser that starts every time I turn the key. It’s really a shame because the 305 currently installed runs great, leaks out of every orifice but runs really smooth, it’s just completely gutless and it’s all hills up north where I typically head every weekend. Fortunately there’s a little room left in the budget for me to buy the new motor so I’m disappointed that I was told the truck had the original 400 but it’s not the end of the world since I can do the labor.

Look at the rpm where they make power in relationship to where you are going to spend most of your time driving. 410 horsepower at 7000rpm means nothing if you never go past 5500rpm and you definatly don't want your torque peak outside of your normal driving rpms

Any of these builds have options for octane or alcohol ?
(economy on wallet, )

Ricko1966 said:

Look at the rpm where they make power in relationship to where you are going to spend most of your time driving. 410 horsepower at 7000rpm means nothing if you never go past 5500rpm and you definatly don't want your torque peak outside of your normal driving rpms

Click to expand...

Both have torque down low where needed and max out at 5400 RPM like the old RV/Tow style cams.
.462/.480-218/226 @50 with 111 centerline for 456 ft/lbs
.460/.480-216/224 @50 for 365 hp/425 ft/lbs

YakkoWarner said:

I would not have thought to use a mechanical fuel pump as a pressure regulator but agree the idea is brilliant. If I ever end up at the point where I have to switch from TBI to carb I'll keep that idea in mind (probably not anytime soon).

Click to expand...

It's can be a little more involved than just bolting on a pump,depending on how much pressure you are trying to drop.You may need to drill the bypass orifice progressively bigger until you can bypass enough fuel.