Holley 500 cfm conversion on a 1966 GMC 305E

[wcstory]

I’m almost complete with the Holley change over. I've been picking away at it but the work schedule keeps getting in the way.

I bought a Holley 2bl carburetor to replace the original single barrel. I am going to be swapping the SM420 granny low 4 speed for a 700R4 so I also decided to swap out the rod linkage throttle assemble for a '72 & up throttle assembly. I'll need the cable assembly to add the TV cable for the 700R4. If I was just swapping the original carburetor for a Holley it would be quicker.

First step I pulled the pedal, linkage and carb - they'll be appearing in the parts forum

I removed the manifold and mounted the Mr Gasket adapter. I scribed the manifold to open it up to match the adapter. I then used a carbide bur to grind out the opening to match. A slow process :pullinghairout: I need access to a miller

With the manifold re-mounted and the Holley seated atop I started on the accelerator cable

The firewall on my GMC was different from pedal and cable swap I found posted. Not sure if this is a Chevy vs GMC issue.

I took a grinder with cutting wheel and removed the old rod pivot mounting attachments. I will weld in a patch when the transmission is out.

I mounted kickdown bracket 20-121, Holley 20-38 throttle stud and Holley 20-95 Throttle and TV cable bracket.

2017-07-09_08-32-44 by wcstory, on Flickr

The throttle bracket I bought was about an inch too close to the throttle stud. I had to cut the end flat and weld on a one inch extension.

2017-07-09_08-33-07 by wcstory, on Flickr

2017-07-09_08-32-12 by wcstory, on Flickr

Drill a .500” hole in the firewall directly in line with the Throttle bracket. My firewall had a stamped flat spot location directly in line. I then used a square file to dress the edges of the hole to accept the square snap in end of the throttle cable. It was apparent the throttle cable I bought was going to be waaayyy too long. After asking on here I found the ends can be removed and the cable cut. I snipped off the metal stops crimped onto the wire rope throttle cable. Remove the firewall end and mark for length. Pull the cable out of the sheath and cut to length. Place the cable back in and put the firewall end back on.

2017-07-09_08-33-35 by wcstory, on Flickr

Take the ’72 and up pedal assembly and cut the upper bracket off leaving the plastic pedal mount base and metal cover with 3 bolts. I found where the pedal seemed correct and marked a hole. I used rivet nut setter to place a ¼-20 rivet nut on firewall. With the assembly mounted I checked fit and feel. I drilled the other two holes and put a rivet nut in. Of course they ended being a little crooked just to piss me off.

2017-07-09_08-31-50 by wcstory, on Flickr

2017-07-09_08-30-54 by wcstory, on Flickr

The upper end of the throttle arm needs to be bent to the right to line up with the throttle cable coming through the firewall. It took a bunch of bend, fit and check trips between the bench vise and the truck. A whole bunch.

2017-07-09_08-29-23 by wcstory, on Flickr

2017-07-09_08-29-54 by wcstory, on Flickr

I clamped the cable and tried the throttle travel and pedal location. Once I’m certain of the location I will crimp a proper stop and solder it in place.

2017-07-09_08-31-26 by wcstory, on Flickr

[geezer#99]

Curiousity question!

What do you use for an adapter to bolt the 700R4 up to the v6?

[Classic v6 GMC's]

Nice write up. The 67-72 pedal set up looks like it works great.

['63GENIII]

While Ive never had a 305, I think its way cool that you're putting a 700R4 behind one. I like what you've done with the throttle cable too. I can relate that it is a bunch of work to get it to fit right. I didn't pull the pivot out and it moved my pedal mount to the left a bunch. Didn't even think of taking it out. I kept the floor mounted pedal and used a couple of Holley linkage bushings on the pin that held the new pedal onto the pedal lever as rollers against the back of the original pedal.

Nice work! Had no idea a 700 would bolt to a 305

[wcstory]

Originally Posted by '63GENIII

Nice work! Had no idea a 700 would bolt to a 305

The GMC v6 line uses their own unique bolt pattern that wasn't shared by its chevy cousin. They did offer a factory powerglide option for the V6. It used a cast iron block to trans adapter and there was a spacer that mounted to the torque converter. The powerglides shares the same bolt pattern as the 700R4 so I'm swapping in the OD tranny.

I'm trying to keep the truck mostly original aside from safety and drivability needs. I added a factory power steering pump and a later year gear box. Seat belts have been added. I'm also converting the single pot brake system to a split system with disc brakes up front.

Originally Posted by geezer#99

Curiousity question!

What do you use for an adapter to bolt the 700R4 up to the v6?

Using the OEM powerglide adapter.

[duallyjams]

Does it have dual exhaust or is that on the list of things to do ?

[geezer#99]

Originally Posted by wcstory

The GMC v6 line uses their own unique bolt pattern that wasn't shared by its chevy cousin. They did offer a factory powerglide option for the V6. It used a cast iron block to trans adapter and there was a spacer that mounted to the torque converter. The powerglides shares the same bolt pattern as the 700R4 so I'm swapping in the OD tranny.

I'm trying to keep the truck mostly original aside from safety and drivability needs. I added a factory power steering pump and a later year gear box. Seat belts have been added. I'm also converting the single pot brake system to a split system with disc brakes up front.



Using the OEM powerglide adapter.

Is the tv cable gonna be long enough?

[wcstory]

Originally Posted by geezer#99

Is the tv cable gonna be long enough?

I may have to move the TV cable Forward. Having Mig/Tig welding setup makes that easy.

[wcstory]

Originally Posted by duallyjams

Does it have dual exhaust or is that on the list of things to do ?

I'm waiting till the 700R4 is in before doing the exhaust.