v6 GMC information needed

[rwgregory]

Getting parts for the big V-6 is not a cakewalk, but you can get most anything you need for it thru NAPA. Specialty companys like Egge Machine sell complete rebuild kits for them. Just don't try getting anything for them at Kragen/O'rileys, Autozone, Advance, etc. You will be told that they don't exist and you must be mistaken..... As for the trans, The GMC V-6 uses it's own bellhousing that differs from the standard GM V-8/I-6 bellhousing, but the trannys will bolt up to either bellhousing. For an automatic, an adapter plate needs to be used to mate up the V-6 with a GM automatic trans.

[Jacfourteen]

My grandad put 250,000 miles on mine before I got it with the original 305 v6, he said that it didn't matter if he was empty, loaded, or towing it would always get 12 MPG. Keep in mind that my truck has 4.56 gears in it so it's spinning just over 3000 rpm at 60 mph. That engine lasted until 1994 when my brother got his licence and hot rodded it and spun a bearing (too high rpm). Then my dad and I rebuilt a 351 v6 for it and that lasted about 2 years because my dad ran it too fast on the freeway and spun a bearing. So you can tell that they don't like high rpms, I would say keep it below the 3500-4000 range. All the power is below that range anyways, so theres no point in running it that high. I'm not sure about parts availablity for these but I think that the 305 parts are easier to get. My father-in-law also has a 64 gmc with the 305 v6 and he has pulled a old catterpillar D4 on a flatbed up a 10% grade. They are beasts for sure!

[67_C-30]

Originally Posted by 67Mach1

Ok assume I am gong to get the truck, and get a bonded title for it. Assume the engine does not turn over or I cant get it started. Is this thing going to be next to impossible to get parts for a rebuild?

I have plenty of parts trucks to get v8 and I6 doner parts for, If i do a swap would I hve to change the transmission in addition to motor mounts or would it bolt to an I6 or V8 platform?

As rwgregory and Jacfourteen said, parts are not a big deal, and the transmission will bolt to a V8/L6 bellhousing. The engine stands are unique to them, as are the motor mounts. These engine use basically a 3 piece set up to bolt them in a pickup. There's a plate that bolts to the engine, and the motor mount bolts to it. Then the motor mount bolts to the frame mounts. These are kind of hard to find for someome wanting to retrofit a V6 in a pickup that didn't come with one.

[Erl]

If you decide to pass on the truck or sell the motor let me know. I am in Dallas and will come down and get it. I currently have 4 V6's; 2 305, 1 351, 1 478. I could stand one more.

Erl

[68GMCCustom]

Erl I'm about to remove the rear engine mount/front trans crossmember (?) from my bare '68 GMC frame. I also have other various bits and pieces left from switching to a C10 grill and '72 C-10 chassis. PM me if interested.

Oh.....and I apologize for interrupting the thread!

[C-10 simplex]

Also, the first ever american v-6, is also, apparently the most/or one of the most durable?

You probably already knew that, but i decided to add that in there because i really like this engine despite the relatively low mpg numbers.

[67Mach1]

My plan right now is to get the truck to the house. Pop the plugs out oil up the cylinders really good, new plugs wires and either hit the points with a file or replace them, bypass the fuel lines with a boat gas tank and then put on a hot battery. Going to see if the runs after a few hand turns of the block.

I'll check about getting a bonded title which should cost me about 3-400 more and go from there.

I like the oddity of the V6 not too many of them around, If I can get it to be a decent run around truck it will stay. I have the storage room if it comes out so one way or another for now I'll hold on to it.

If the V6 wont run, Ive got a complete I6 set up I can drop in and go waiting in the barn.

I will post more photos after she is picked up...

[C-10 simplex]

To throw some more stuff in(yes, i'm obssesed to unhealthly levels about the whole 6cyl thing), today's silverado with the 4.3 v-6 (which is really a SBC minus 2 cyls) gets 20mpg highway epa rating.

Strangely enough, the LS engine can get 21mpg while being larger by about 70cid in the same truck.

[67Mach1]

Originally Posted by Erl

If you decide to pass on the truck or sell the motor let me know. I am in Dallas and will come down and get it. I currently have 4 V6's; 2 305, 1 351, 1 478. I could stand one more.

Erl

This whole thing has jogged my memory of another GMC V6 I found years ago in a junk yard. The guy said he would never sell it as he drove it around the yard.

Its not too far from where I will be picking up this other one tomorrow. I may stop by and see if he still has it and if he may have changed his mind.

[67Mach1]

Originally Posted by C-10 simplex

To throw some more stuff in(yes, i'm obssesed to unhealthly levels about the whole 6cyl thing), today's silverado with the 4.3 v-6 (which is really a SBC minus 2 cyls) gets 20mpg highway epa rating.

Strangely enough, the LS engine can get 21mpg while being larger by about 70cid in the same truck.

I'd like to keep it is there any way including swaping out the rear gears to something more road worthy that would get better mileage?

Exhaust? Carb? Air cleaner? Advance timing?

[67_C-30]

Originally Posted by 67Mach1

I'd like to keep it is there any way including swaping out the rear gears to something more road worthy that would get better mileage?

Exhaust? Carb? Air cleaner? Advance timing?

The popular swap is to put a Holley 500 cfm 2 barrell on them, and add electronic ignition. With higher gears, some people have reported some decent mpg numbers. There also people who claim you can get more power and better mpg with higher compression pistons. These engines were 7.75:1, and there are pistons out there that bump the CR up to about 9 : 1. These were used in lot of propane powered V6's. I have always wanted to leave the 7.75 : 1 CR and modify or build a passenger side manifold for one and turbocharge it with a Garrett T3 or even the Borg Warner 6.5L diesel turbo. All you would have to do is have a crossover pipe going from the driver side manifold to passenger side, have an oil feed and return line, some kind of pressure chamber to carb. As low as the these engines rev, there wouldn't be a need for anything bigger. In fact, the small turbos start making boost quicker, and would be more beneficial for this type engine. They already act like a diesel as it is! Just 6 psi of boost will add 75-100 HP and 100 - 130 lb ft of torque to a small block Chevy, so the results should be somewhat comparable. I believe that with the extra torque, that if you kept your foot out of it, it would improve the effeciency of them. That's my theory anyway. You should prove/disprove that for us! The above set-up is what I going to do for my dually before I decided to go diesel. I have done a lot pondering on this, and if I didn't have so many projects, I would have probably tried it. (I have the same type theory for a 292, which would be even easier to turbocharge, but that's another thread)

[67Mach1]

Originally Posted by 67_C-30

The popular swap is to put a Holley 500 cfm 2 barrell on them, and add electronic ignition. With higher gears, some people have reported some decent mpg numbers. There also people who claim you can get more power and better mpg with higher compression pistons. These engines were 7.75:1, and there are pistons out there that bump the CR up to about 9 : 1. These were used in lot of propane powered V6's. I have always wanted to leave the 7.75 : 1 CR and modify or build a passenger side manifold for one and turbocharge it with a Garrett T3 or even the Borg Warner 6.5L diesel turbo. All you would have to do is have a crossover pipe going from the driver side manifold to passenger side, have an oil feed and return line, some kind of pressure chamber to carb. As low as the these engines rev, there wouldn't be a need for anything bigger. In fact, the small turbos start making boost quicker, and would be more beneficial for this type engine. They already act like a diesel as it is! Just 6 psi of boost will add 75-100 HP and 100 - 130 lb ft of torque to a small block Chevy, so the results should be somewhat comparable. I believe that with the extra torque, that if you kept your foot out of it, it would improve the effeciency of them. That's my theory anyway. You should prove/disprove that for us! The above set-up is what I going to do for my dually before I decided to go diesel. I have done a lot pondering on this, and if I didn't have so many projects, I would have probably tried it. (I have the same type theory for a 292, which would be even easier to turbocharge, but that's another thread)

Sounds like a pretty cool theory. As far as testing it out... That will have to be someone else. My problem is too many projects myself. I have so many I cant even keep track of them. Which is why I made a Scrap run last week and have many of them up for sale. With luck I will get down to about 5 or 6 projects by the end of april. In fact with scrap being up a few of them may go that direction once I part them out.

If finding this truck reminds me of anything, they are all over the place out there. Holding onto two or three rusty trucks that are for parts may not be economicaly feasable.

This truck with its solid cab, unless someone makes me a Godfather of a deal, will be staying with me. Thats the bad thing about telling everyone how much something cost you though. Everyone knows what you paid for it.

I set it up to go pick it up tomorrow. A freind of mine that is off on Mondays is driving my truck and trailer up, I'll finish the deal, he will drive it back and I'll go to work like normal. Picking it back up from him tomorrow night.

see you then with updated photos..

[C-10 simplex]

Originally Posted by 67Mach1

I'd like to keep it is there any way including swaping out the rear gears to something more road worthy that would get better mileage?

Exhaust? Carb? Air cleaner? Advance timing?

i have no idea because of the rpm range of these engines----if you go too high a gear, like 2.56, then the engine might bog down? But then again, with all the torque they produce maybe not.

If it were any of the other gm v-6's or inlines then yes, i would say going to a higher gear may help. Also, with the other gm v-6's, exhaust improvements i'm pretty sure could help.

Just as a longshot, depending on what air cleaner is on there now, if you could get one with the thermac unit built into it, this could possible help mpg a little.

Also, as others have ponted out, HEI or even electronic non-distributor type ignition might help.

[67_C-30]

Originally Posted by 67Mach1

This truck with its solid cab, unless someone makes me a Godfather of a deal, will be staying with me. Thats the bad thing about telling everyone how much something cost you though. Everyone knows what you paid for it.
..

It may sound bad, but I never worry about that. I have been buying/selling/parting cars and trucks for years, and what I paid for it has nothing to do with what it's worth. There's some guys here around here in town that have made negative comments about me "letting stuff get out of our area" because I have sold so many parts on ebay. I tell them to their face that I'd sell them locally, except you want me to give them to you. For instance, if I needed that cab and you said $800, it wouldn't matter that you gave $400 for the truck as long as it was worth it to me and I was willing to give $800.

That don't mean I won't help someone out. I've dealt with several board members here that can attest to that, but when I get something I consider to be hard to come by I, either hang on to it, or sell for what its market value is. There's a couple sets of bucket seats, buddy buckets, and some rust free doors, fenders, inner fenders, and 3 SWB "project" trucks here at my place to prove that very point!

P.S. There was a guy just yesterday that kept trying to get me to give him a price on my '69 SS after I told I really wasn't interested in selling it. I finally shot him a real healthy price, and he said "That's WAYYY more that you paid for it!" I said "Yeah it is, but if you want this one, that's what it will costya." He told me that I thought my stuff was gold. I reminded him that I had never, not once, TRIED TO SELL HIM my car.

[67_C-30]

Originally Posted by C-10 simplex

i have no idea because of the rpm range of these engines----if you go too high a gear, like 2.56, then the engine might bog down? But then again, with all the torque they produce maybe not.

If it were any of the other gm v-6's or inlines then yes, i would say going to a higher gear may help. Also, with the other gm v-6's, exhaust improvements i'm pretty sure could help.

Just as a longshot, depending on what air cleaner is on there now, if you could get one with the thermac unit built into it, this could possible help mpg a little.

Also, as others have ponted out, HEI or even electronic non-distributor type ignition might help.

These engines make their torque peak at 1400 RPM, so they should handle higher gears better than pretty much any gas engine GM has ever built.

[C-10 simplex]

That's true, lower end torque would mean they could handle it better.


Well, in that case switching to higher gears may be the answer to improve mpg.

[67_C-30]

Originally Posted by C-10 simplex

That's true, lower end torque would mean they could handle it better.


Well, in that case switching to higher gears may be the answer to improve mpg.

They're some guys on jolly's website that have claimed 17 - 18 mpg highway with higher gears, and some of mods above. Most of them had switched to 3.08's. It stands to reason that if the engine has more efficient ignition, induction, and exhaust systems, that low end torque would be even better, and should get decent mileage.

[67Mach1]

Originally Posted by 67_C-30

It may sound bad, but I never worry about that. I have been buying/selling/parting cars and trucks for years, and what I paid for it has nothing to do with what it's worth. There's some guys here around here in town that have made negative comments about me "letting stuff get out of our area" because I have sold so many parts on ebay. I tell them to their face that I'd sell them locally, except you want me to give them to you. For instance, if I needed that cab and you said $800, it wouldn't matter that you gave $400 for the truck as long as it was worth it to me and I was willing to give $800.

That don't mean I won't help someone out. I've dealt with several board members here that can attest to that, but when I get something I consider to be hard to come by I, either hang on to it, or sell for what its market value is. There's a couple sets of bucket seats, buddy buckets, and some rust free doors, fenders, inner fenders, and 3 SWB "project" trucks here at my place to prove that very point!

P.S. There was a guy just yesterday that kept trying to get me to give him a price on my '69 SS after I told I really wasn't interested in selling it. I finally shot him a real healthy price, and he said "That's WAYYY more that you paid for it!" I said "Yeah it is, but if you want this one, that's what it will costya." He told me that I thought my stuff was gold. I reminded him that I had never, not once, TRIED TO SELL HIM my car.

Very good points one and all. I too have a few good parts stashed away in the attic waiting for the right project or price.

[67Mach1]

This truck is leaf sprung, and I dont know what rear gear it has, yet. I also have this frame with leaf rear end i think the truck was an I6 as it has the I6 stands still on it.

also unknown rear gear. It was to be made into a trailer. I might have to hold off on that idea now.

[67_C-30]

Originally Posted by 67Mach1

This truck is leaf sprung, and I dont know what rear gear it has, yet. I also have this frame with leaf rear end i think the truck was an I6 as it has the I6 stands still on it.

also unknown rear gear. It was to be made into a trailer. I might have to hold off on that idea now.

Trailers?!? I got trailers too! You sound eerily too much like me (or vise versa).

[67Mach1]

Originally Posted by 67_C-30

Trailers?!? I got trailers too! You sound eerily too much like me (or vise versa).

I was thinking the same thing earlier...

The truck bed trailer has become a bit of a running joke between me and some of my friends. So far I've cut two trucks in half to get ready to make one but never got it finished.

one an 86 Chevy that i ended up taking selling for the bed and this one. However the step bed on this one is better than my 67 GMC step project so most likely it will end up never being finished.

[WyoRoadDog]

Going back a ways in the thread, parts for the 305 are pretty accessible. NAPA is your best bet, as stated, I was able to get almost all the parts for the rebuild on mine through them. The 351 seems to be really hard to get parts for, I was looking in to it, as I picked one up a while back with another 305. Not sure as you get larger (401+) how hard parts are to find.
For mileage, there was a member here in the 60-66 forum that had put a TBI setup on his V6, and said it had helped a lot in performance and mileage. It's something I'm going to look into down the road, but I'm going to get everything back together and running "naturally" first, before adding another variable!

[67Mach1]

The Deal was done today, and almost fell apart before it got started.

To make a long and complicated story as short as possible, the guy ended up wanting another 100 dollars because, get this, Before he could go this weekend and pick up the other cars at the guys place in the country, someone stole all the radiators out of them. So now he needed more for this one to make up for it.

WHOA there Partner. My agreed to price from you now goes up 100 because a transaction with the guy that owned this truck before you purchased it out from under me went sour due to stolen radiators. Not No way but No *'in' way!

Now granted this guy is 87 so after going thru it three times with him that the two transactions are not the same and that we had an agreement, he still wants more money. The he changes gears and says he wants me to bring in one of my other trucks, one that is a stepside so we can trade plus cash to him. WTH!

I fought the urge to leave right then I was so pi$$ed. I guess he could tell how hot I was getting even though I never yelled or raised my voice. I ended up agreeing to give him $20.00 extra and promise to bring one of my trucks by to let him make up the difference he lost on selling it to him. I hope I never see the guy again.

But Wait there is more. After I had a BOS and my friend had it loaded on the trailer, he cam out and said that he forgot to get the rear and front bumper off of of the truck for his friend.

I told him I'd be happy to take them off and sell them to him or take the complete truck off the trailer if he wanted to buy it back. What did I ahve to lose? I figured that since I had a BOS and the truck was loaded it was going to leave with me or the cops were about to be summoned.

I took photos but will have to post later.

Engine does turn over by hand. Rotated it 360 Deg.

[67Mach1]

first set of pics

It was a farm truck so there are dents and dings everywere. The black stuff on it is actually a mossy type substance. I shoudl have gotten a close up photo of it.

In the next few weeks I'll bring to the house. Powerwash inside and out.

The engine had good looking anti freeze in it and the engine was full of oil.

I could shift it out of either R and 1 in to neutral or from 2 into 3 to neutral but it would not make the transition between the two. Could be the reason it was parked? but who knows.

[67Mach1]

set number 2