C10 4.3 V6 to 350 swap

[dburbach85]

Hi everyone, and thanks in advance for welcoming me to the Chevy truck fold. I recently purchased a 1987 Chevy C10 (well for whatever reason the '87 year is called the R10, but as far as I know there's no difference). I didn't pay much for it and the previous owner had completely restored the body so there's not a spot of rust or a dent on the truck. Unfortunately, though, I recently discovered that the truck's 4.3 V6 is on its way out. I think the rear main bearing is on its way out as the truck starts to struggle to maintain oil pressure after its been running awhile and a knocking sound beings underneath the engine after 20-25 minutes of driving.

Anyway, all that to say, I want to swap in a 350. Any advice on parts I'll need, engines to look for, and on the work of actually doing the swap is greatly appreciated.

I'm hoping to stick with the TBI setup and the truck has the TH400 automatic transmission in it.

[Engineer]

You will need the TBI top end. Save yourself some hassle and just look for a complete 87~95 TBI engine.

You will definitely need to change your engine mounts to the small block type. Possibly the exhaust, too.

Everything else should be the same. Even the accessory drive, power steering pump, alternator, water pump, A/C compressor, etc. should just swap right over.

[Stewart G Griffin]

Yes, see my thread entitled "engine swap diary:"  i went the opposite way---from v-8 to v-6, but some of my notes should help:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=29914.0

You have it easy because v-8 parts are so easy to find, v-6 not so much:

1) You'll need new mounts, specifically frame perches which attach to the frame---the v-6 and v-8's DO NOT interchange.  But v-8 frame perches are so easy to find--either new, aftermarket or salvage yard.  The actual engine mounts between v-8 and v-6 could interchange but let's do it right.   With v-6 i think the passenger side is clamshell on the engine and mount on the perch.  Whereas driver's side is clamshell on the perch, mount on the engine.  With v-8 both sides the clamshell are on the engine and the mounts are on the perches (i think?)   Why GM did this, i have no idea?

The holes are probably predrilled on your frame for the v-8 frame perches.

2) The v-6's radiator hoses most likely will not work with the v-8.......or they may be too long and could work if trimmed.   The heater hoses should plug right in though.  You will most likely need a new, larger radiator eventually.  But you probably already knew that.

3)  The v-6's throttle cable probably can't work with the v-8 because it's too short, but try it first.  If it doesn't work, not big deal as v-8 throttle cables are so easy to find anywhere.   v-6?  Forget about it----either used or custom build.

4) The v-6 power steering hose and line MIGHT be able to work with the 8.  The low pressure return line can be easily shortened if necessary and the hard supply line may be able to be pivoted foward a little.

5) If you're switching to a carb v-8, then i have no idea how you're going to get the pump situation and fuel lines working, but there's always a way......

6) The vacuum booster line for the brakes MIGHT plug right in or might not.  NOt a big deal as it is cheap.

7) The exhaust WILL NOT bolt up.  Again, no big deal as you have too many choices in v-8 exhaust systems.  Complete bolt in kits are probably available for these trucks.   v-6?  You're on you're own unless you want completely stock, but that has to be welded up too.

Can't remember anything else right now.  But in sum, you have it pretty easy because you're going the normal way of v-6 to 8.   Going the opposite way is a headache.

[Engineer]

Forgot to add the fan shroud won't work, and you may need to upgrade the radiator.

[Stewart G Griffin]

Forgot to add the fan shroud won't work, and you may need to upgrade the radiator.

Yes, the v-6 shroud is too long and i think anyone going to a v-8 should eventually switch to a larger radiator although temporarily the smaller one could work.


Also, i just re-read the original post and you want to stay with TBI.  i think the v-8's injectors are larger which also means you may need a new ECM or chip (?)

[dburbach85]

Thanks for the advice everyone, definitely helpful.

One thing I should have also mentioned, this build will be on a pretty tight budget, so sourcing the engine at the right price is important.

How hard is it to put a TBI setup on a pre-1987 SBC? There's a guy willing to sell me a rebuilt 305 (not as sexy as a 350, but way cheaper) with 0 miles for $500. But the engine is a 1980-85. I already have the TBI intake, throttle body, and injectors off a 350, how hard would it be to make it bolt up?

Also, what troubles would I have with the accessories like the serpentine belt, power steering pump, alternator, etc?

Again, thanks so much for your help!

[dburbach85]

Yes, see my thread entitled "engine swap diary:"  i went the opposite way---from v-8 to v-6, but some of my notes should help:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=29914.0

You have it easy because v-8 parts are so easy to find, v-6 not so much:

1) You'll need new mounts, specifically frame perches which attach to the frame---the v-6 and v-8's DO NOT interchange.  But v-8 frame perches are so easy to find--either new, aftermarket or salvage yard.  The actual engine mounts between v-8 and v-6 could interchange but let's do it right.   With v-6 i think the passenger side is clamshell on the engine and mount on the perch.  Whereas driver's side is clamshell on the perch, mount on the engine.  With v-8 both sides the clamshell are on the engine and the mounts are on the perches (i think?)   Why GM did this, i have no idea?

The holes are probably predrilled on your frame for the v-8 frame perches.

2) The v-6's radiator hoses most likely will not work with the v-8.......or they may be too long and could work if trimmed.   The heater hoses should plug right in though.  You will most likely need a new, larger radiator eventually.  But you probably already knew that.

3)  The v-6's throttle cable probably can't work with the v-8 because it's too short, but try it first.  If it doesn't work, not big deal as v-8 throttle cables are so easy to find anywhere.   v-6?  Forget about it----either used or custom build.

4) The v-6 power steering hose and line MIGHT be able to work with the 8.  The low pressure return line can be easily shortened if necessary and the hard supply line may be able to be pivoted foward a little.

5) If you're switching to a carb v-8, then i have no idea how you're going to get the pump situation and fuel lines working, but there's always a way......

6) The vacuum booster line for the brakes MIGHT plug right in or might not.  NOt a big deal as it is cheap.

7) The exhaust WILL NOT bolt up.  Again, no big deal as you have too many choices in v-8 exhaust systems.  Complete bolt in kits are probably available for these trucks.   v-6?  You're on you're own unless you want completely stock, but that has to be welded up too.

Can't remember anything else right now.  But in sum, you have it pretty easy because you're going the normal way of v-6 to 8.   Going the opposite way is a headache.

Thanks for all the info Stewart! Couple questions,

1. why were you wanting to go V8-V6?
2. I'm a little confused on the engine mount vs perch, could you explain the difference? Are they 2 different parts?

[Stewart G Griffin]

1) Mainly because i like the engine---also for MPG (although in my case my MPG actually dropped compared 350 and 305.  i think this engine is worn out) and also since i mainly use the truck for transportation and occasional weekend type hauling, like going to the hardware store, i felt i didn't need an 8.  Also i will say this the v-6 WILL cruise along at 65 or better just as well as a 305 or 350.

Another big reason was space---with this new setup i can actually stand inside the engine compartment---makes it easy to work on the engine.

2) This is an 8 cylinder perch and mount (driver's side):



Here is a 6 cyl perch and mount, passenger side:


6cyl driver's side:


So, basically the perch is a tower/extension to the frame that the mounts bolt to.  Some cars use them, some don't.  i think the smaller monte carlos and camaros, for example do not use them----the mounts bolt directly to the crossmember in those cases ( i think?).

The v-6 and v-8 perches WILL NOT interchange without serious modification as in using a cutting torch and welding as the 8 has 2 bolts to the top of the frame and 2 bolts to the crossmember, whereas the 6 has 2 bolts to the top of the frame, 1 bolt to the SIDE of the frame and one bolt to the crossmember.

Also, notice that the driver's side v-6 perch has the clamshell bolted to it (instead of usually the mounts bolt to it) and the passenger side v-6 perch has the mount bolted to it.  i think the reason why they did this is because the v-6 shakes at idle, but i'm only guessing here.  But with v-8, both clamshells bolt to the engine and mounts bolt to the perches.

[dburbach85]

Thanks so much, that cleared that right up. Looks like I need to find some perches!

I really appreciate it!

[dburbach85]

1) Mainly because i like the engine---also for MPG (although in my case my MPG actually dropped compared 350 and 305.  i think this engine is worn out) and also since i mainly use the truck for transportation and occasional weekend type hauling, like going to the hardware store, i felt i didn't need an 8.  Also i will say this the v-6 WILL cruise along at 65 or better just as well as a 305 or 350.

Another big reason was space---with this new setup i can actually stand inside the engine compartment---makes it easy to work on the engine.

2) This is an 8 cylinder perch and mount (driver's side):



Here is a 6 cyl perch and mount, passenger side:


6cyl driver's side:


So, basically the perch is a tower/extension to the frame that the mounts bolt to.  Some cars use them, some don't.  i think the smaller monte carlos and camaros, for example do not use them----the mounts bolt directly to the crossmember in those cases ( i think?).

The v-6 and v-8 perches WILL NOT interchange without serious modification as in using a cutting torch and welding as the 8 has 2 bolts to the top of the frame and 2 bolts to the crossmember, whereas the 6 has 2 bolts to the top of the frame, 1 bolt to the SIDE of the frame and one bolt to the crossmember.

Also, notice that the driver's side v-6 perch has the clamshell bolted to it (instead of usually the mounts bolt to it) and the passenger side v-6 perch has the mount bolted to it.  i think the reason why they did this is because the v-6 shakes at idle, but i'm only guessing here.  But with v-8, both clamshells bolt to the engine and mounts bolt to the perches.

One more question, am I correct that the photos show the perch/mounting location for the V6? Are the holes to the right in the frame and crossmember where the V8 perches would mount?

[Stewart G Griffin]

Yes, the 2nd and 3rd pictures are v-6 and the new perches would have to be moved forward about 4.5".  There should already be holes drilled for the v-8 perches.

[dburbach85]

Thanks, I very much appreciate the help!

[zieg85]

Here is a picture showing the top mounting holes on a 1986 C10

Green arrows V-6 orange is where the V-8 ones go.  I am eventually doing the same to mine

[dburbach85]

Nice! What about the crossmember? Is there another hole it attaches to there?

[zieg85]

Nice! What about the crossmember? Is there another hole it attaches to there?

Yes.  As you can tell where the V-6 mounts with 3 bolts the V-8 has 4 bolts and all the cross members have the needed holes.  Stewart's frame never had a V-6 as they were 85 and newer so he had to drill