1985 K20 350ci Engine Swap Choice

New to the forum, but need some advice for an 85’ Chevy/GMC K20. Bought the truck with ~75,000 miles and was in rough condition. Shortly after having it diagnosed in the shop, the consensus was a new engine would be needed. Hoping to swap another 350ci engine in. I’ve seen a Jeggs ‘Small Block Chevy 350ci Crate Engine Kit’ that includes the following;

• Crate Engine
• Intake Manifold, Gaskets & Bolts
• Carburetor
• Distributor
• Engine Dress Up Kit
• Dipstick

I think this would be a solid choice for improving the power of the vehicle without going too over the top and crazy with things. However, not knowing a lot about engine swaps in general I’d love to hear some opinions or a push in the right direction. Thanks!

I am a do it yourselfer. I would pull out the 350 that is in there, myself, so I know how it all goes when I put it back together. Either rebuild the original or have somebody do it, then put it back together the way that it came apart, with the bolt on stuff that I wanted, with all new accessories. The Jegs motor is probably just as good, but I always like to know whats inside them. I like the challenge, and it saves money too. I always like stuff as original as possible, with a few improvements.

Totally Forgot to mention the transmission combo. The stock one is in great condition, but I’m not sure if it will fit the same. However it being another 350ci chevy engine, I’m thinking it might be possible to reuse the old transmission. Just a thought. Thanks again.

Hey 85K304SPD, unfortunately my mechanic skills aren’t diverse enough to execute a swap myself. I like the idea of a swap myself one day, but at this point in time I feel like it could end up being an expensive mess. What improvements would you suggest for a bone stock K20 if the OEM engine was rebuild to working order?

Well, it looks like you live in Montana, so I dont think that emissions sticker is an issue, (its not an issue here in southern NM), so I would do the standard stuff. Aluminum single plane intake, good 4 barrel carburetor, nice valve covers, roller tip rocker arms, probably a good fitting set of headers and dual exhaust with mufflers. Don't get too wild with the camshaft, but maybe step it up just a little on the lift and duration. Put a new distributor and a new mini starter and alternator. Of course the water pump too.
You can go the next step beyond that and put fuel injection, aluminum heads, roller cam for alot more money. Put a nice new fat radiator in it too.
Other people can probably add to this list.

I will add this to the conversation. ATK is the manufacture of that motor your looking at, at JEGs. We use to by stock remans directly from ATK at the shop and we did so for many years. We use to consider them our go to supplier for resonably priced good quality engines. We stopped using them a couple years ago after a couple bad motors. One was a 360 AMC that cam flattened out on due to a defective lifter. Another was a Chev 350 we installed in a customers square. We went though 3 of them before buying out of the shops pocket at a total loss to us an engine from another manufacture. That manufacture was S&J engines out of Spokane, Wa. They have been very good to us, they have very good pricing and offer various levels of engine building with good explanations, they'll also talk to you on the phone if you like that kind of support.

Long blocks usually have a better warranty than an owner assembled engine. These are heavy vehicles. Generally speaking, performance cams will decrease fuel economy and low-end power.

Although it adds quite a bit to the cost, roller cams are something to consider. Normal oils today are not friendly to flat tappets.

SirRobyn0 said:

I will add this to the conversation. ATK is the manufacture of that motor your looking at, at JEGs. We use to by stock remans directly from ATK at the shop and we did so for many years. We use to consider them our go to supplier for resonably priced good quality engines. We stopped using them a couple years ago after a couple bad motors. One was a 360 AMC that cam flattened out on due to a defective lifter. Another was a Chev 350 we installed in a customers square. We went though 3 of them before buying out of the shops pocket at a total loss to us an engine from another manufacture. That manufacture was S&J engines out of Spokane, Wa. They have been very good to us, they have very good pricing and offer various levels of engine building with good explanations, they'll also talk to you on the phone if you like that kind of support.

Click to expand...

Can concur regarding S&J phone support. I had a long chat with them regarding potential engine swaps for my truck. The gentleman on the phone may or may not have alluded to them doing quite a bit of work for another well known engine supplier on the west coast that many of you may know of.

Thanks for the responses, I’ll check them out.

Go with a dual plane manifold. Single plane manifolds are for high revving horsepower...not bottom end torque, which is what we are looking for in a pickup. An RV cam is also a better choice than something aggressive....again it is all about torque, especially in a 3/4 ton 4x4 pickup.

mcarlo86 said:

Go with a dual plane manifold. Single plane manifolds are for high revving horsepower...not bottom end torque, which is what we are looking for in a pickup. An RV cam is also a better choice than something aggressive....again it is all about torque, especially in a 3/4 ton 4x4 pickup.

Click to expand...

I was gunna ask that when the last guy stated single plane... (i watch engine masters alot). I bought a dual for my next engine swap.

Soundmound said:

Can concur regarding S&J phone support. I had a long chat with them regarding potential engine swaps for my truck. The gentleman on the phone may or may not have alluded to them doing quite a bit of work for another well known engine supplier on the west coast that many of you may know of.

Click to expand...

ks84 said:

Thanks for the responses, I’ll check them out.

Click to expand...

I forgot to mention that the one downfall to S&J is they are a smaller company and most of the time there is at least a short wait for them to build and ship a motor, but that is the only issue we have had.

78C10BigTen said:

I was gunna ask that when the last guy stated single plane... (i watch engine masters alot). I bought a dual for my next engine swap.

Click to expand...

I meant dual plane. Brain F__t. Edelbrock Performer or similar. My apologies.

Your stock engine was rated at about 165-175 horsepower, and it’s tuned for emissions. It has low performance iron heads, with big combustion chambers that reduce the compression ratio to about 8.0 or lower. The Quadrajet is jetted for economy and emissions, and the 4 barrel iron intake is nothing special. Most trucks will have single exhaust.

If you want to improve a stock 70’s engine, the most common solution is a good dual plane aluminum intake, 650 cfm carburetor, moderate flat tappet cam, headers and dual exhaust. Once you get it timed and the carburetor adjusted, you should be up to 275-300 horsepower.

If you swap to Vortec heads or aftermarket aluminum heads, which provide way better flow and higher compression, you will get another 30-35 horsepower, maybe more. You can then also use a little more cam duration, and if you use aluminum heads you can bump up the timing more. If you use a retrofit roller cam it will make it much more durable overall and allow for a more aggressive cam. It’s very easy to get a reliable 350 horsepower and still have the low end power you need in a truck.

It also helps to use a higher stall torque converter that allows the RPM to get higher coming off the line, and swapping to about 3.73 rear end gears should really improve the takeoff. Some of these trucks have as high as 2.73 gears, which really makes them hard to get going off the line.

Fwiw. I just rebuilt an engine at home and it cost me around $2200 including the purchase of the used engine.
To do it again I would have bought an off the shelf, save time money and risk. Just make sure you get a cam that suits your needs