My 250/3 spped to 350/4 speed swap

[OJ1988]

Just want to chronicale some of my swap details to help others.

When I began to make my swap I looked around and got a lot of different answers from different places about what will work, what has to me changed ,etc....

Hopefully this thread will help others.

First a little background;

truck;

1969 C/10 short bed stepside. 250cu inline 6 cyl. 3 speed column shift.

Truck was all original and in daily driver condition. Only changes were,

Clifford 4 barrel intake manifold
450 cfm holley 4 barrel
Pacesetter longtube headers
HEI distributer.

I drove the truck daily like this for 6 months before I tearing it down for the swap.


New engine,

GM 260hp 350cu crate motor ordered from Jegs.
Added an Edelbrock Performer intake
Numbers matching to the truck Quadrajet carburator

For a transmission, I happened to have a M-20 Muncie wide ratio four speed laying around.



I wanted the swap to be as easy as possible, reuse as much as possible.

SO lets see what I did and learned.

[OJ1988]

So first up was the engine location. The muncie will swap in directly in place of the 3 speed with no changes to the driveshaft, clutch set up, etc...
I liked the idea of this so I would not have to mess with clutch linkage, tranny crossmember or motor mount stand offs.

Here is the muncie,


Stock bellhousing I cleaned up and repainted.


I used a Hays 168 tooth flywheel, and a stock replacement clutch from the local parts store.

Once the old stuff was out, I cleaned it all to bare and strayed some epoxy primer sealer,

[OJ1988]

I bought a v8 z bar and pivot ball and all the little washers and such.

Turned out the v8 stuff would not work in the 6 cyl location.

I ended up using the stock 6 cyl z bar and such. The block mounted pivot ball I used was one listed for a 67-72 V8 4wd. All other clutch related items are stock 6 cyl parts.




For a shifter I tried a few options.
Initially I found the hurst shifter listed for our trucks was discontinued. So, I first found a factory 1966 chevelle 4 speed bench seat shifter. This was too short.

I later discovered the hurst shifter for the truck was still avalible, so I ordered it.
Turns out it will not clear the bench seat with the tranny in the 6 cyl location.
You can not go into 2nd or 4th gear.

This of course required me to do the blazer gas tank relocation which is popular anyway.

Here it is with the seat in stock location moved as far back as possible. Shifter is in 1st gear,


Here it is after the gas tank was removed and the seat mount holes were drilled 3 1/4" farther back.

[OJ1988]

Exhaust:

As you can see in the pic above, the clutch linkage is very close to the manifold with the engine in the 6 cyl mounts.

It appeared there would be no way for any off the shelf header to fit. Since the motor is a stock 260hp, custom headers were just not worth it.

I first went with stock rams horns with the angled outlet, which is stock for the 2wd trucks.

The drivers side interferes with the clutch linkage.
I then went out and found somestraight dump ramshorns, after a restoration of them they for great.


I had also read that if you did this, you could just order the exhaust for the 4wd and it will work fine. WRONG!

I ordered the Heart throb exhaust for the 4 wd, and it was not even close to clearing the tranny crossmember , nor did it allow room for the mufflers.

I am currently finishing up the exhaust and will post pics soon. The heart throb made a good starter kit along with some other random bends. I also installed a jegs h-pipe.

[OJ1988]

Issues with motor in 6 cyl location.

Distributer clearance.

I used a large cap HEI and have plenty of room between it and the firewall. No issues!

Cooling fan/shroud.
The motor sits to far back for a mechanical fan to be effective with the stock v8 shroud. You could add a spacer but I did not like that idea, so I went with an electric fan, and an stock replacement style aluminum radiator.

Radiator hoses,
Lower stock v8 worked great, actually still had to trim it some. Upper was too short. I used an upper listed for a 1977 malibu with a 350.

[OJ1988]

AS for cutting the hole for the shifter, I crawled under the truck, looked at the end of the tranny, where the shifter mounts and drilled a hole straight up from there into the floor board, then from the top I just cut a 4" square around it with a cut off wheel.

Any questions so far?

[OJ1988]

Here it is near completion, with a 650 holley that was latter replaced with the quadrajet. Sorry for the grainy Iphone pics, if anyone wants to see anything in particular, let me know and I'll get out the good camara.



I wanted it to look kinda stock. Most importantly I wanted it to be realiable and easy to work on.

I converted to an internal regulator alternator at the same time as well.

[Toms1968]

Nice build thread. Lots of usefull information. I hope your happy with the swap. Where did you get all the washers and what not for the Z bar, and the stud ball for the side of the block?

[OJ1988]

I think u got the stuff from the truck shop.
I order most resto stuff from them and lmc
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[OJ1988]

Another trans related issue. On the 3 speed the speedo cable cones in on the driver side, and the Muncie has it on the pass side. I rerouted the cable over the steering column and it was able to reach the Muncie.
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[saskgreen]

Great thread. This is what I am planning on doing to mine aswell. Will definatly be using your info.

[propanemudtruck]

Good post! Hope things work out good with this project, it's clean and effective!

[OJ1988]

Thanks guys! Just hope I can save some trouble for other people.
I'm right at a year on this, but during the swap I have also rebuilt the entire front suspension and brakes with 1975 parts. Used cpp 6 lug rotors, poly urathane bushings, cpp 3" drop springs, toxic shocks, cpp shock brackets, cpp sway bar, and so on.
Perhaps I'll cover all that as well later on.

I am also working on the rear stuff.

It is getting real close, and I can't wait.
Once it's on the road, my real project, the 88 iroc will come back to the build stall in the garage.
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[OJ1988]

Another issue was the throttle linkage.
A lot of guys swap to the later cable style.
I chose not to.
The linkage on it was fabbed up for the Clifford holley combo.
No way was it going to work.
I grabed one off a v8 1969 in a junk yard.
It looked awful and was way to long as well.

So I took a chance and ordered a custom linkage kit for a 1969 camaro from jegs.
It looked killer and works perfect as well!
Added the standard return spring set up as well.


On the front of the motor, u added a jegs balancer. 6 1/4" model.
Water pump is a cheap aluminum long version.
Painted it all orange to look stock!
Pulleys were yanked off a small block laying on the ground in the junkyard.
Alternator brackets were a cheap chrome set painted black as well.

For a starter I used a compact model from jegs as well. I have the same one on the 55 and it works great. They sound cool too!
I like the added clearence as well.
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[OJ1988]

Just pulled rear end cover off to change the fluid, and this thing has 3:73 gears in it!
I would have been super excited about that 3 or 4 years ago, but not now with $4.00 a gallon gas.
Now I'm thinking rear gears swap or trans swap. There is a guy making 4th gear overdrive for Muncies though.
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[OJ1988]

Little did I know at the time that these trucks still used a short waterpump with a driversside mounted alt. That explains the intereference I had with the stock fuel line.

I am currently finishing the rear suspension and Blazer tank install. Hope to drive this thing soon!

[OJ1988]

I ended up getting a numbers matching quadrajet, well if this truck had come from the factory with a 350 and manual trans, it would be a numbers matching carb!

[RdoubleU]

OJ - Can you give the hurst shifter part numbers you used with the bench seat?

I am looking at which shifter stick to use in my application and am looking at

Hurst Part #'s
5386900
5384331

Just wanted to avoid the same issue you found with the seat and the shifter height

[OJ1988]

Here is the shifter I used,

http://www.hurst-shifters.com/?wpsc-...et-gmc-3910002

[OJ1988]

Just wanted to ad, I got the truck running and driving, put about 4000 miles on it in 3 months.

Ended up selling it to a guy in Charlotte North Carolina and replaced it with a 1971 Camaro.