1968 C10 6 cyl to V-8 conversion

[aprilg57]

I have a 1968 C10 that I am converting to V-8. The bell housing, flywheel, pressure plate, clutch & starter all work with the V-8. The problem I have is that the clutch linkage interfers with the exhaust on the drivers side. I'm using a 68 Impala exhaust manifold to be able to use the alternator mount. The angle to the rear appears to be the same as on my 1968 GMC 3/4 ton with a 327. The difference appears to be that the GMC engine is mounted a little further forward than the C10. There are 3 holes in the frame for the engine tower. The GMC uses the front 2. The C10 uses the rear two.
Question 1: Under what configurations were the front 2 holes used? i.e. my GMC has the 4 speed. Is that the reason or is it the fact that it's a 3/4 ton or ?
Is there another manifold that dumps straight down but still has the alternator mount bolt holes on the end that I could use?
April

[lolife99]

V8 trucks used the front 2 holes.
6-cylinder trucks used the rear 2 holes.
There is also a V8 specific and a 6-cyl specific set of frame stands for the enbgine mounts.

[Dano69c10]

Also the manual transmission crossmember is different between v8s and L6s.

[aprilg57]

Thanks for those inputs. Based on those I would assume that there is also a different length driveshaft for the V-8?

[50bomb]

for my 67 chevy c10 longbed it was originally a inline 292 with the 3 speed manual overdrive. I converted to sbc350/th350 and the trans has the short tail. I had to get a longer front driveshft to trans. Paid $50 for a used on at a local salvage truck yard. and for the motor stands/trans crossmember i bought them off a member here for $40-50.

[lolife99]

Originally Posted by aprilg57

Thanks for those inputs. Based on those I would assume that there is also a different length driveshaft for the V-8?

yes

[aprilg57]

Another good input.
Since I already have the engine installed and everything else matches up except the exhaust, I'm going to try a straight down exit left exhaust manifold. I have some from late 50's/early 60's cars. They have the mount holes for a generator to which I can mount an alternator bracket available from many sources.

[aprilg57]

I had another thought this morning. If the engine were to be moved foreward to the front set of holes in the frame, I don't believe the Z bar stud would match up. Was there a bracket that would center the stub between the 2 bolt homes in the engine?
Those of you changing over to an automatic wouldn't have to worry about this. Anyone change from a 6 to a V-8 and retain the MT?

[502ms]

One question I would have is will the transmission/clutch hold up to the torque of the new V8? What trans do you have?

[lolife99]

Originally Posted by aprilg57

I had another thought this morning. If the engine were to be moved foreward to the front set of holes in the frame, I don't believe the Z bar stud would match up. Was there a bracket that would center the stub between the 2 bolt homes in the engine?
Those of you changing over to an automatic wouldn't have to worry about this. Anyone change from a 6 to a V-8 and retain the MT?

Is the pivot point on the 6-cyl block and the V8 block the same distance from the back of both blocks?

[old Chevy guy]

Id have to check to be positive ly sure on the complete answer but I do know SBC has two holes for the pivit ball,not always tapped with threads . What I dont know for sure is there might be a bracket that bolts between the two holes on a 67-72 truck. I will look at my truck and post the answer later.

[aprilg57]

The 6 cyl had a bracket that was bolted to the engine in 2 places and brought the pivot ball out about 10? inches. There is a bracket welded or rivited to the frame with a slot in it for the pivot on the other end of the z bar.
I do have 2 holes tapped for the pivot ball on the V-8. I used the front one which is directly across from the slot on the frame. I'll have to measure to be sure-but I believe the rear one is further back than the distance the engine would move forward if I changed the mounts.
Regarding the clutch being good enough for the V-8, that is a concern since this is the standard 10" clutch. I don't plan to do any drag racing. This is a pleasure truck. If it becomes a problem, I'll buy is new flywheel, clutch, pressure plate and throwout bearing of the 11" variety.
This one has the 3 speed on the column.
I'll do some measuring tomorrow.

[smoknbarrels]

I have a big block mind you... I had to modify my own z bar, nothing lined up and the L-6 z bar was too long, even though it has long bracket mounted to the block, still ends up being too long of a bar for a V-8. you might have to do the same thing, just knock a few inches out of the center of it. you are lucky if the sbc has a hole that lines up pretty close... i had to make a bracket on the engine side.

[aprilg57]

Thanks to everyone for their responses. I was able to answer my own question as regards the pivot bracket on the engine side. I looked at my GMC mentioned in my opening message. It has a bracket mounted to the 2 engine bolt holes with the pivot about an inch and a 1/2 forward of the rear bolt. So from you all told me, I should have changed out the motor stands, the rear crossmember (which appears to be rivited in) and bought or fabricated a bracket to mount a pivot onto the engine. Since I didn't this information when I started the project, here's what I ended up with: I took out the 6 cyl. I installed the V-8 using the 6 cylinder motor stands. I bought a pivot from LMC truck that screws into the block. I installed that in the front hole. The Z bar lined up perfectly. I changed the LH exhaust manifold from the 68 to an earlier manifold that exits straight down. I used a new Y pipe that I had left over from an earlier project. The only issue left to address is the alternator mount (a piece of cake). I end up with a single exhaust with 2" pipe so I lose a little power (not an issue for me). About to be on the road!!

[aprilg57]

Just a little more background. I bought the GMC out of the Kenny's Klunckers section of Old Cars Weekly a couple years ago. It was advertised as "rusty but runs good" and the price was $750. It had the original 327 with 97xxx miles and the Quadrajet had recently been rebuilt. I bought it (primarily for the 327) intending to use it as a donor truck. I drove it from Illinois to Maryland and am getting some use out of it. It has just over 100,000 miles on it now. At some point in the future it may become a donor to the C10. If that happens, I'll have everything I need to do the job right.

[old Chevy guy]

Glad it all worked out. Thats what is so awsum about GM stuff in general,you can mix and match so many parts and make stuff work.Try doing what you just did with ford or dodge truck. Probably wouldnt work out so well. Just saying don't anybody get excited.

[hungarian1964]

would you be interested in selling the brackets that bolt to the engine? Not the mounts but the brackets that bolt to the engine

[454C10CHEVY]

whats the difference between the i6 and v8 manual crossmember can it just be moved up or is it different altogether?

[SS Tim]

Originally Posted by 454C10CHEVY

whats the difference between the i6 and v8 manual crossmember can it just be moved up or is it different altogether?

Funny, but my parts manual doesn't show the I6 crossmember. However it does show 8cyl and BB manual crossmembers as seperate applications with different P/Ns.

[454C10CHEVY]

I guess ill b needing one of those i didnt see it in the classic industries book(i could have just missed it) which one are you looking in?

[SS Tim]

GM... I'm guessing you don't follow my posts. :-)

[ZMAR]

I just did the same swap on my 67. I used the old ram horn center straight down exit because of the Zbar mess. does anyone know of the similiar setup but w/ a brand name header?

[Tailgate20]

I'm also deep in this swap. I6 to sbc while keeping the manual 3 in the tree.

I used a ball stud which almost perfectly lined up my bell crank but my clutch isn't disengaging and my floor shifter conversion is to close to the seat to be useful. I'm not sure if i need a new clutch. My clutch seemed to be in good shape when I took it off the I6 and bolted it on my 350. Are they even interchangeable or do I need to find a V8 clutch?

Dynomax block huggers fit this application with slight engine tower mods for clearance.

[Fitz]

The trans crossmember is not a problem. My truck started out as an I6 manual and, as you can see, it grew a few new cylinders and a built turbo 400. I cut and punched out the rivets holding the crossmember in the forward set of holes...just behind the cab mount... and moved it back to the second set of existing holes....so nice of GM to provide correctly spaced holes for a motor and trans that didn't even exist in 1967!

[jpmanyhearts]

Originally Posted by SS Tim

GM... I'm guessing you don't follow my posts. :-)

where do you get one of those books at ?