Definitive answer for I6 to SBC 350 swap.

[Keystone_Hate]

I have been searching for about a month now to find out what is needed to do this swap and I have found a LOT of varying information on motor mounts, engine frame stands, engine location, transmission and bellhousing location and so on. Some say the I6 engine mounts and frame stands work with a SBC, some say they do not work. Some say you can use the I6 frame stands and small block engine mounts, some say you need both for a small block. Etc.

So I am hoping someone can give me a clear answer on this.

I have a 1972 C10 LWB with an inline 6 250 and 4 speed Muncie. Can I literally unbolt the inline 6 from the frame and bellhousing and bolt in a small block?

If so, sweet that's all I need to know.

If not, What do I need? Different engine mounts? Different engine frame stands? What location for the frame stands, front holes or rear holes?

Thanks in advance for any help clearing this up. I am new to all of this and there seems to be a lot of info out there and it's tough to sort out what's fact and fiction.

[Camaroguy]

Originally Posted by Keystone_Hate

I have been searching for about a month now to find out what is needed to do this swap and I have found a LOT of varying information on motor mounts, engine frame stands, engine location, transmission and bellhousing location and so on. Some say the I6 engine mounts and frame stands work with a SBC, some say they do not work. Some say you can use the I6 frame stands and small block engine mounts, some say you need both for a small block. Etc.

So I am hoping someone can give me a clear answer on this.

I have a 1972 C10 LWB with an inline 6 250 and 4 speed Muncie. Can I literally unbolt the inline 6 from the frame and bellhousing and bolt in a small block?

If so, sweet that's all I need to know.

If not, What do I need? Different engine mounts? Different engine frame stands? What location for the frame stands, front holes or rear holes?

Thanks in advance for any help clearing this up. I am new to all of this and there seems to be a lot of info out there and it's tough to sort out what's fact and fiction.

I'm far from an expert but I think you have to move to the rear holes on the frame. I don't know about the engine frame stands if they are different or not, but I am pretty sure the engine mounts are different. They are cheap though and should probably be replaced anyway. Good luck.

[Mike C]

You can use the 6 cylinder mounts with the small block. Just unbolt the motor and pull it out. Swap the flywheel and clutch onto the small block and reassemble. This puts the motor further back but gives better f/r weight bias. Not sure if you will have to rig up a way to utilize the existing clutch cross shaft or not. Should be able to use the straight dump Corvette rams horns in this scenario as well.

[70STOVEBOLT]

No one has mentioned that the trans crossmember is not the same as the inline piece. It is angled differently. Also your driveshaft will determine which holes to mount the engine in on the frame. Otherwise you will need to have one made to the correct length.

[randy500]

The engine will bolt up with no modifications at all to the 250 6 cyl frame stands but not the 292 frame stands. If I remember right the rubber engine mounts from the 6cyl are the same as V8, so remove and install those too.

The clutch Z bar will line up with a hole in the block where you will have to source and install a pivot ball with a threaded end. The threads are 7/16 or 1/2 inch, the ball is not hard to find and is used on 4wd trucks of the same era.
You will have to adjust the linkage from the Z bar to the throw out arm.

A 2wd fan shroud will work with a little longer fan spacer, please use a stock fan as those aftermarket ones suck and are dangerous. A 4wd fan shroud may work, haven't tried that. You will have to source longer radiator hoses, the lower one from a 4wd might work, factory 4wd upper had a metal tube and 2 short hoses, I think a replacement hose is made which eliminates the metal pipe so that hose might work.

[Keystone_Hate]

Originally Posted by firedemon

I just did this swap 250 l6 to 350 I had to change mounts the factory ones didn't fit I used the tubular ones I really like them better than the factory . from what I understand the motor can be mounted in either the front or rear but if you use the front a factory fan shroud and clutchfan will fit perfect . if you use the rear holes your going to have fab work to get it to work . I used a t400 auto trans from a 3ott so I had to change that mount as well I am unsure about your standard

[QUOTE=randy500;7938186]The engine will bolt up with no modifications at all to the 250 6 cyl frame stands but not the 292 frame stands. If I remember right the rubber engine mounts from the 6cyl are the same as V8, so remove and install those too.

QUOTE]

I appreciate everyones input but this is what I am talking about. One says they work, one says they don't. Also mentioned in another reply is a different trans crossmember, which is another thing that's confusing me. I guess this is gonna have to be trial by fire for me to figure this out. It just seems that this swap has been done SOOOOO many time that there would be a unanimous decision as to what works and what doesn't.

[demian5]

Originally Posted by randy500

factory 4wd upper had a metal tube and 2 short hoses

That sounds like crazy talk!

[demian5]

[quote=Keystone_Hate;7938216]

Originally Posted by randy500

One says they work, one says they don't. Also mentioned in another reply is a different trans crossmember, which is another thing that's confusing me.

You did have a "pie in the sky" request man:

"Definitive answer" on a powerplant swap - LOL

[Keystone_Hate]

[quote=demian5;7938220]

Originally Posted by Keystone_Hate

You did have a "pie in the sky" request man:

"Definitive answer" on a powerplant swap - LOL

I don't think it was a crazy request. How many time has this swap been done? Thousands of times probably? The trucks came factory with a SBC 350. I think there would be a solid straight forward answer.

[randy500]

I hope you got your answer from the posts...

6 cyl Trans crossmember will work
6 cyl clutch will work
6Cyl clutch linkage will work with the ball threaded into the side of the block.
6cyl rubber mounts, I think they are the same.

Overall the engine will be mounted almost identical to a v8 in a 4wd, far back towards the firewall. When mounted there should be HEI cap clearance, might have to install the cap separate from the distributor though.

[randy500]

Factory v8 power steering lines will be short, you might be able to modify how the metal part of them are located and bent but probably have to get some from a 4wd to fit that too.

[randy500]

6 cyl radiator is narrower and as such v8 shroud will not fit because its wider, although the 6cyl radiator will cool the v8 unless in the SW heat.

[Keystone_Hate]

Thanks for the info Randy, and everyone else who gave input. This is gonna be a learning experience, which is why we all get into these things anyway.

[cpnbnanamn]

Originally Posted by Keystone_Hate

Thanks for the info Randy, and everyone else who gave input. This is gonna be a learning experience, which is why we all get into these things anyway.

I'm going to be doing something similar.. Going to a SBC 400 from a 250 I-6 w/ 3OTT. And instead of a direct-drive fan, I'm probably going to go to an electric fan, triggered off of the goose neck with a temp sensor.
As I haven't dug into this yet, I'm wondering about the clutch connections, and adding power-steering (not going R&P). The power steering seems pretty straight forward, but someone mentioned the lines, etc. Also thinking about going hydraulic on the clutch pedal.. Should eliminate the z-bar.

Christ, what am I getting myself into.

[randy500]

The frame stand have some adjustment, less than a 1/4" but sometimes you will have to loosen all the bolts to get the motor mount bolt to fit, you have to do this same thing when changing engine mounts on a V8 truck, so do that if needed.

You will also want to install a front sway bar, its a cheap mod and makes it handle much better, your 6cyl truck shouldn't have one, not factory anyway.

[cpnbnanamn]

Originally Posted by randy500

The frame stand have some adjustment, less than a 1/4" but sometimes you will have to loosen all the bolts to get the motor mount bolt to fit, you have to do this same thing when changing engine mounts on a V8 truck, so do that if needed.

You will also want to install a front sway bar, its a cheap mod and makes it handle much better, your 6cyl truck shouldn't have one, not factory anyway.

It doesn't.. Front or rear.. that's on the list. LOL Even with the 6, it handles like a drunken sailor.. LMAO..

[randy500]

Since I have been giving advice, here comes some more....

Putting a v8 in where the 6 was makes sense to save cost and time, and helps keep the truck on the road, changing to v8 with 3spd manual in the factory location involves a lot of work with minimal improvement. The v8 trans crossmember is different, the clutch linkage is different, the driveshaft is longer and 2 piece, its a lot of parts to get and change, the crossmember is really tough to remove too, it more of a hassle than difficult if you have a lot of tools.

If you do install the v8 in the 6cyl location then just use stock 4wd parts and put short water pump parts on it, that stuff just looks right and the long water pump does not.

When done you also get the benefit of moving the center of gravity to the rear since the engine mounts so far back. IN the future if you decide to change over to auto trans you can move the engine forward at that time...although a short shaft TH350 should go right in with the driveshaft from the 3spd manual...the length should be ok if its stock height suspension, possibly slightly long if lowered.

I hate headers but v8 headers off the shelf fit better in the 6 cyl location too.
Put manifolds on it though, stock ones with the 45 degree bend.

[cpnbnanamn]

Originally Posted by randy500

Since I have been giving advice, here comes some more....

Putting a v8 in where the 6 was makes sense to save cost and time, and helps keep the truck on the road, changing to v8 with 3spd manual in the factory location involves a lot of work with minimal improvement. The v8 trans crossmember is different, the clutch linkage is different, the driveshaft is longer and 2 piece, its a lot of parts to get and change, the crossmember is really tough to remove too, it more of a hassle than difficult if you have a lot of tools.

If you do install the v8 in the 6cyl location then just use stock 4wd parts and put short water pump parts on it, that stuff just looks right and the long water pump does not.

When done you also get the benefit of moving the center of gravity to the rear since the engine mounts so far back. IN the future if you decide to change over to auto trans you can move the engine forward at that time...although a short shaft TH350 should go right in with the driveshaft from the 3spd manual...the length should be ok if its stock height suspension, possibly slightly long if lowered.

I hate headers but v8 headers off the shelf fit better in the 6 cyl location too.
Put manifolds on it though, stock ones with the 45 degree bend.

If I'm not mistaken, my 6cyl is already in the rear holes.. Kinda figured I'd have to change the crossmember, and am really wanting to go manual. Haven't investigated the crossmember removal, yet. Still trying to figure out the best option for the manual trans. REALLY don't want a 2-piece driveshaft.
I'm trying to fab as little as possible, really not wanting to fab anything. My welding skills look like a 3 year-old with a severe twitch did it.

[Motorfist]

Subscribed. Swapping a 292 for a 350 later this summer. Good info!

[Tx Firefighter]

Randy knows what he's talking about.

I've done this swap about half a dozen times personally. Pull out the six and drop in the V8. You can even reuse the rubber engine mounts off the six cylinder. Reuse your clutch, flywheel, starter, bolts, everything.

Screw a clutch pivot ball into the side of your V8. It will be obvious where it goes. I buy mine from Classic Parts for about 14 bucks. If your small block is a late model block there will be a blank spot where the pivot ball would screw in. In later years GM quit machining the hole since manual clutch linkages were a thing of the past (this is like TBI and Vortec era engines I'm talking about). Just drill and tap it. You can hardly go wrong, the Z bar points to exactly where the pivot ball needs to be.

Then take a hacksaw and cut about half an inch off of your clutch Z bar since the V8 is wider.

Done deal.

[D-rock1981]

I can't even tell you how many 6cylinder to v8 swaps i've done. pull the 6 out, drop the v8 in, simple as that, thats what I like about chevy.

[Tx Firefighter]

[quote=firedemon;7938667]

Originally Posted by Keystone_Hate

don't know if it is because it is a 67 or what but the 6 mount on the drive side was 1/2 inch off it made the motor sit crooked in the foreword mounting position . when I orderd the new mounts they were from 62 or smoething to 67 and they had 68-72 so there must be some frame difference only thing I can see

We are talking about installing the engine in the rear position where the six originally sat.

I don't even touch the frame stand bolts when I do one. I leave the stands torqued down right where GM installed them years ago.

[Keystone_Hate]

Originally Posted by Tx Firefighter

Randy knows what he's talking about.

I've done this swap about half a dozen times personally. Pull out the six and drop in the V8. You can even reuse the rubber engine mounts off the six cylinder. Reuse your clutch, flywheel, starter, bolts, everything.

Screw a clutch pivot ball into the side of your V8. It will be obvious where it goes. I buy mine from Classic Parts for about 14 bucks. If your small block is a late model block there will be a blank spot where the pivot ball would screw in. In later years GM quit machining the hole since manual clutch linkages were a thing of the past (this is like TBI and Vortec era engines I'm talking about). Just drill and tap it. You can hardly go wrong, the Z bar points to exactly where the pivot ball needs to be.

Then take a hacksaw and cut about half an inch off of your clutch Z bar since the V8 is wider.

Done deal.

Thank you so much. That's the answer I was looking for. You're a gentleman and a scholar sir.
Posted via Mobile Device

[cpnbnanamn]

Originally Posted by Tx Firefighter

Randy knows what he's talking about.

I've done this swap about half a dozen times personally. Pull out the six and drop in the V8. You can even reuse the rubber engine mounts off the six cylinder. Reuse your clutch, flywheel, starter, bolts, everything.

Screw a clutch pivot ball into the side of your V8. It will be obvious where it goes. I buy mine from Classic Parts for about 14 bucks. If your small block is a late model block there will be a blank spot where the pivot ball would screw in. In later years GM quit machining the hole since manual clutch linkages were a thing of the past (this is like TBI and Vortec era engines I'm talking about). Just drill and tap it. You can hardly go wrong, the Z bar points to exactly where the pivot ball needs to be.

Then take a hacksaw and cut about half an inch off of your clutch Z bar since the V8 is wider.

Done deal.

See, now THAT'S a definitive answer. The only caveat I am wondering about is putting a different trans in it. The 3OTT is coming out, too.. not sure what's going back in place of it just yet, but you can bet it'll be a stick shift!!
Thank you, Kevin!!

[raggedjim]

Randy and Kevin hit it on the head, if it is a later block DON'T install the engine until AFTER you have drilled and tapped the z-bar pivot hole! It's easier if done before you install the engine.

I think I still have the drill and tap I bought 30 years ago when I did this.

I gotta tell you though, that thing may be turning some rpm's at highway speeds, I know mine did.

Good luck, Rg