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#1 |
Registered User
![]() Join Date: Jun 2006
Location: Cape Cod, Ma.
Posts: 236
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Holley 500 cfm conversion on a 1966 GMC 305E
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. ![]() 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. ![]() ![]() 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. ![]() 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. ![]() ![]() 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. ![]() ![]() 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. ![]()
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1966 GMC 1 Ton 305 V6 SM420 4 speed - retired Fire Dept Support Truck from Little Falls, NJ My GMC Photos |
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#2 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,626
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
Curiousity question!
What do you use for an adapter to bolt the 700R4 up to the v6? |
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#3 |
Senior Member
![]() Join Date: Mar 2015
Location: Arizona from Overland Park Kansas
Posts: 3,968
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
Nice write up. The 67-72 pedal set up looks like it works great.
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Current projects: 1966 Chevy Custom PS PB A/C BBW 283 v8 3 speed OD 1966 GMC Long Step 1966 GMC 3/4 ton Custom PS PB Sport trim 351 v6 1966 GMC 3/4 ton 4x4 Custom PB 305 v6 np435 1960 GMC Custom 1968 GMC 3/4 ton 4x4 Short Bed 1962 K20 Tow truck 1961 GMC Extended Suburban Panel and a few more |
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#4 |
Registered User
Join Date: Sep 2008
Location: San Carlos, Ca.
Posts: 3,048
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
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
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Chris '63 k15 long step Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205 ![]() 52" front and 63" rear spring swap D44 / 14bff - disc axles Milemarker 9K and 10.5K hydraulic winches 63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29 |
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#5 |
Registered User
![]() Join Date: Jun 2006
Location: Cape Cod, Ma.
Posts: 236
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
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.
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1966 GMC 1 Ton 305 V6 SM420 4 speed - retired Fire Dept Support Truck from Little Falls, NJ My GMC Photos Last edited by wcstory; 07-10-2017 at 04:35 AM. |
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#6 |
Registered User
![]() Join Date: May 2007
Location: Deale Md
Posts: 4,663
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
Does it have dual exhaust or is that on the list of things to do ?
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James 63 GMC V6 4speed carryall 65 chevy swb bbw V8 auto 68 K20 327/4 speed, buddy buckets 2002 GMC CC Dually Duramax 64 GMC lwb 3/4 V6 4speed SOLD 66 GMC swb bbw buddy buckets SOLD IG duallyjams The only thing that stays the same is constant change! |
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#7 | |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,626
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
Quote:
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#8 |
Registered User
![]() Join Date: Jun 2006
Location: Cape Cod, Ma.
Posts: 236
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
I may have to move the TV cable Forward. Having Mig/Tig welding setup makes that easy.
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1966 GMC 1 Ton 305 V6 SM420 4 speed - retired Fire Dept Support Truck from Little Falls, NJ My GMC Photos |
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#9 |
Registered User
![]() Join Date: Jun 2006
Location: Cape Cod, Ma.
Posts: 236
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Re: Holley 500 cfm conversion on a 1966 GMC 305E
I'm waiting till the 700R4 is in before doing the exhaust.
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1966 GMC 1 Ton 305 V6 SM420 4 speed - retired Fire Dept Support Truck from Little Falls, NJ My GMC Photos |
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