67 GMC 305 V6 swap to a SBC 305

[bigwil86]

Hello all, Im new to the site but none the less love these old trucks and have since before i could drive.

Yesterday I made a purchase on what i thought was a GREAT deal on a 67 GMC C15/1500, swb, fleetside pickup truck with the 305v6 and 3 speed on the column. Not until i start thinking about doing a sbc swap that i realize i maybe in a little bit of a pickle. Im at a total lose on the swap and no clue where to begin.

Would it be possible to cut the frame off of 73-87 frame right in front of the fire wall and have it measured up and weld into place on mine after the removal of the front section of my 67 frame. The 73-87 frame would allow for disc brakes, spindles, sbc motor mounts and eventually allow me to install airride suspension a bit easier, or would it just be simpler to swap the crossmembers?

Any help would be greatly appreciated, Thank you!!! Wil

[72freak]

You can put 71-72 Disc brake set up on your rig much easier. There are plenty of easy mods to do what you want without major work.
Pull the engine and trans.....I dont know about the mounts for the V-6 but the V8 will be a direct bolt in with the correct v8 mounts.
Its a pretty basic engine swap.
You can then add power steering and power brakes. With a 67 there will be a little difference in the power steering set up needs.
I would recomend finding a 72 2x4 donor truck...you will then be 5 lug and your wheel options will be MUCh better

[bigwil86]

The motor itself is in amazing condition, no pings, peeks, knocks, or leaks but I would still rather swap in something a little more conventional. Any advice about the x-member?
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[72freak]

Originally Posted by bigwil86

The motor itself is in amazing condition, no pings, peeks, knocks, or leaks but I would still rather swap in something a little more conventional. Any advice about the x-member?

What do you need to know about the x-member? Are you talking about the trans x-member? If you are staying with a 3 speed it should not have to be touched. If you are talking about under the engine that all stays the same also....you just swap the spindles and brke stuff.

[bigwil86]

Did GMC offer a v8 in there c15 truck in 67. Thought it wasn't until 68 they offer a v8.
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[72freak]

Originally Posted by bigwil86

Did GMC offer a v8 in there c15 truck in 67. Thought it wasn't until 68 they offer a v8.
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Yes.....327 was one of them

[bigwil86]

The best I can tell according to autozone, advance, oriellys. The parts search only shows 3 motor options all being V6s. 68 offers all kinds of v8 options. So the only thing I can do is take it out and figure my options from there. The V6 mounts are welded in.
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[bigwil86]

No PM / email sales...thanks for your support

[bigwil86]

i got my truck home yesterday and took a look at the motor mounts and bracket......also just want to say thanks for all the help and advice......we figured out a very easy way to just set the 305 v8 right in place with very minor modification!!!! thanks again...

[72freak]

Originally Posted by bigwil86

i got my truck home yesterday and took a look at the motor mounts and bracket......also just want to say thanks for all the help and advice......we figured out a very easy way to just set the 305 v8 right in place with very minor modification!!!! thanks again...

Now we need to see pictures!!! Try to get some of these welded in engine stands/motor mounts!!

[bigwil86]

Apparently I was wrong bout the engine stands cause mine has the bolts in frame horns but that is a forum on here where a gentleman had the welded in mounts and had to cut and move them for the sbc swap. I'll get up some pics as soon as I get to my comp. I been using the site on my phone.


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[Erik V]

reminds me of my old 72 2wd GMC. 250-6/3tree. I hated how gutless it was, and built a modest 305 out of my mom's old 78 Impala we retired. TH350 swap while I was at it, leaving the 4.11 rearend for a while, boy was that truck quick to ~80, but thats as fast as it'd go.

Done properly you'd never be able to tell from a hood pop. The only tell tale sign in my swap was bolts instead of rivets on the trans crossmember. But I had a parts truck that donated everything to do it factory style.

Those 305's are good basic engines, with headers, intake/carb on stock pistons/rods/heads, my pickup would run circles around Dad's 69 2wd Chevy with a 350/th350. Even when I went to a 3.07 rearend to his 3.73. So keep an eye on the rearend, I dont know what the 305 V6 came with, but the 305 V8 wont like a 4.11 unless you want to snap necks and top out around 80.

Erik

[70cst]

Ok all...
Lets keep the For Sale, Want To Buy, and offers off this thread. Thanks.

[bigwil86]

I apologize about that. Still kinda new to the thread.
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[70cst]

Originally Posted by bigwil86

I apologize about that. Still kinda new to the thread.
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Not a problem.

Oh yes... and from Ohio. Glad to have you on board.

[5150.4.67]

Wow, 375hp from a 305 might be a little high estimate. Ditto for 22mpg. The problem with the 305 is the small bore that restricts you to small valve heads and therefore less flow, not to mention valve shrouding...... now a big cam is completey out of the equation.
About the only decent head for a 305 (without breaking the bank) is the l98 aluminum head. It still retains the 58cc chamber.
Just speaking from experience: I built a mild 305 with 4 barrel FI and Megasquirt and when I was done I was happy. Then it wore off 2 days later and I said to myself, what the hell did i do that for? I could have spent less money and had 50 more hp with a 350!!!
Its fun to be different, but if thats the case, keep the 305 v6. Think of it as half of a GMC v12! (which it kinda is......)

Good luck and have fun!

And welcome! You will learn much here!

[truckster]

Just for comparison, I built a 350 and put it in an 83 Chevy Caprice Wagon. My next-door neighbor had the same car, except his was an 84 and had the 305. Mine had more power and better mileage.

[cam.man67]

So, why do you want to get rid of the 305v6? Great motors.

[bigwil86]

Im sure the are great motors and extremely torquey but the parts avalibilty is getting almost none exhistint and apparently they are kinda a pain to work on plus as heavy as a 10 ton tank. The build specs on the SBC 305 Im putting together will allow me too produce about 375 hp and still get approximately 22 mpg. and at todays prices that means something. lol. I'll be running a mildly built 305 SBC, 700R4 Trans, 4.10 Gear.

[Warrens69GMC]

Originally Posted by bigwil86

..... SBC 305 Im putting together will allow me too produce about 375 hp and still get approximately 22 mpg. and at todays prices that means something. lol. I'll be running a mildly built 305 SBC, 700R4 Trans, 4.10 Gear.

Curious on the build of the 305 - 375hp and 22mpg isn't easy in these trucks, and a 375hp 305 isn't mild...

[406 Q-ship]

Originally Posted by bigwil86

........The build specs on the SBC 305 Im putting together will allow me too produce about 375 hp and still get approximately 22 mpg. and at todays prices that means something. lol. I'll be running a mildly built 305 SBC, 700R4 Trans, 4.10 Gear.

A 350 would be the better choice and will get the gas mileage if built right. 4.10's will not get you 22 MPG even with the 700R4, 3.42 is the steepest gear that might be possible to achieve 22 MPG. That kind of mileage in a truck would be impressive unless you switch to one of the later model LS series of engines, the older SBC Vortecs will get is to but a bit more of a struggle.

[N2TRUX]

Originally Posted by bigwil86

....
Would it be possible to cut the frame off of 73-87 frame right in front of the fire wall and have it measured up and weld into place on mine after the removal of the front section of my 67 frame. The 73-87 frame would allow for disc brakes, spindles, sbc motor mounts and eventually allow me to install airride suspension a bit easier, or would it just be simpler to swap the crossmembers?

As you have discovered, its not necessary to swap clips to gain V8 mounts and disc brakes. You can look for 71-72 brake system but they aren't as readily available as the 73-87's. The later system is cheaper for replacement parts too.

Take a look here "Drum to Disc" conversions 67-70for a great guide on the subject.

[bigwil86]

Yea, I'm in the process of trying to find a 71-72 c10 donor truck now. But as for the 305 v8 I'm building its a 305 with 4 bolt mail splade caps for added durability, speedpro/king bearings, 305 X-beam rods with dome pistions, 200cc ACR aluminum heads with 202/160 valves, 1.6 aluminium roller rockers, screw in head & rocker arm studs with polylocks, Jegs 468/488 lift cam with 110 lobe separation, dual plan weiand highrise intake with 650 cfm holley. I run this exact same set up a 83 S10, I know the GMC is a bit heavier so the gas mileage may fall off a bit but after the motor is tuned the numbers are good.
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[406 Q-ship]

Originally Posted by bigwil86

Yea, I'm in the process of trying to find a 71-72 c10 donor truck now. But as for the 305 v8 I'm building its a 305 with 4 bolt mail splade caps for added durability, speedpro/king bearings, 305 X-beam rods with dome pistions, 200cc ACR aluminum heads with 202/160 valves, 1.6 aluminium roller rockers, screw in head & rocker arm studs with polylocks, Jegs 468/488 lift cam with 110 lobe separation, dual plan weiand highrise intake with 650 cfm holley. I run this exact same set up a 83 S10, I know the GMC is a bit heavier so the gas mileage may fall off a bit but after the motor is tuned the numbers are good.
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That combination will never get 22 MPG, even in a vega. The 2.02 heads will NOT work on the small bore 305 (valves will hit the cylinder bore), 200 port is the size you run on a really healthy 350 and bigger not a 305. That Cam is HUGE in a 305. Do yourself a favor, if you want that kind of a combination do it to a 350. Even a 350 in that combination will be a bit lazy bellow 2800 RPM.

[BIGKEV]

Originally Posted by bigwil86

Yea, I'm in the process of trying to find a 71-72 c10 donor truck now. But as for the 305 v8 I'm building its a 305 with 4 bolt mail splade caps for added durability, speedpro/king bearings, 305 X-beam rods with dome pistions, 200cc ACR aluminum heads with 202/160 valves, 1.6 aluminium roller rockers, screw in head & rocker arm studs with polylocks, Jegs 468/488 lift cam with 110 lobe separation, dual plan weiand highrise intake with 650 cfm holley. I run this exact same set up a 83 S10, I know the GMC is a bit heavier so the gas mileage may fall off a bit but after the motor is tuned the numbers are good.
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Not trying to piss in your cornflakes, but those heads and that cam are both WAY to big for the small bore of the 305 IMO. The 3.736 inch bore makes it hard for a 305 to effectively "pump air" making it easy to over cam or over do it on heads. Don't get me wrong here I'm not one of those all 305's are junk guys. For a truck this big I'd run around a 170-180cc head, and something around ,450 max lift. With 1.6 rockers your going to bring your lift up to .499 int and .521 ex. How much stall are planning on running (your going to want +/- 3500 rpm depending on rear gear)? How often are you going to spin the motor to 7000 rpm in the that big truck? I know 305s make great power on paper, but on the dyno it's usually a different story. At the end of the day do what makes you happy