250 I6 to 350 v8: Engine Towers Placement?

[Boyd]

I've been working on my '72 all day getting it ready for the motor swap...the I6 and three speed manual are out and I'm close to dropping the V8 in, but have a question.

Which set of holes do I install the V8 towers in? And more importantly, I'm not sure which tower is for the left, and which is for the right.

I've tried each tower on each side, both in the forward holes and the rear holes and I can't get the bottom bolt hole in the tower to line up with either of the holes in the crossmember. I can get it close in the forward holes, with the bottom bolt hole just slightly in alignment.

I bought the V8 towers from a member on here, so I'm pretty sure they are the correct ones.


(Excuse the cell phone photos please)

This first pic is looking down at the pass side tower in the forward holes.



This pic is the same tower, in the same position...the bottom tower hole only partially lines up with the forward hole in the crossmember.



Assuming I have the towers on the correct side and the forward holes are what I use, do I just put bolts in the top holes and force the tower toward the frame a little to get the bottom hole to line up?

[100%Chevy]

Mines a V-8 and I just pulled the towers off today!
You have them in the right position,so just push it till the hole lines up.
Mike.

[Boyd]

thanks. I got the towers in, now I hit another snag.

What size are the bolts that connect the transmission to the engine? th350 to 350.

[kwmech]

Originally Posted by Boyd

thanks. I got the towers in, now I hit another snag.

What size are the bolts that connect the transmission to the engine? th350 to 350.

3/8'' coarse by 1-1/4'' long, grade 5 minimum

[tp85]

I'm about ready to do the same swap...250 to 350. Did you move the mounts forward, or leave the V8 sitting close to the firewall? I'm still trying to make this decision.

Any tips or list of parts you had to gather up for the swap?

I have the 4 speed manual...

Tom

[brans72]

more pics nd info would be great on this subjects guys. Brandon

[brans72]

bump

[Boyd]

Originally Posted by tp85

I'm about ready to do the same swap...250 to 350. Did you move the mounts forward, or leave the V8 sitting close to the firewall? I'm still trying to make this decision.

Any tips or list of parts you had to gather up for the swap?

I have the 4 speed manual...

Tom

I placed the mounts in the existing forward holes and the engine installed easily. However, after installing the engine and auto trans, the drive shaft is now about 4-5 inches short.

At first I thought it was due to the trans being a short tail version, but I was told that our trucks came originally with short tail automatics. This issue is confusing to me because I've seen others use the forward mounting holes and their drive shaft bolts right up with no problems, but for some reason mine doesn't. I plan on taking measurements and finding a correct length shaft from a junk yard. Or I'll get one a little long and have it shortened.

If you are going to use a 4spd man then you shouldn't have to worry about any other parts besides the V8 towers and a 4spd shifter, which will need to be mounted on the floor.

Unfortunately I didn't take any more pics of the swap, so I can't help there, but since I just did it recently I could probably answer some questions you might have.

[Palf70Step]

Yes the drive shaft is longer for the V8/T350 trucks.. I have been told that if you used the 6 cylinder towers for the V8/T350, it slides it back so that the driveshaft is the same length as the 6/3speed.

[100%Chevy]

Boyd,when I told you where to put the towers,I forgot to mention that mine is a turbo-400 trans.
Sorry for any problem I may have caused you!
Mike.

[NGN]

Hay fellows I just got done with the help of a friend swaping out my three speed for a turbo 350 on my I6 . I know it's not the same but the problem I came across is the auto trans rod to shift link on the streeing column is not the same. I need the longer bent one the three speed one is shorter and straight and also now my speedo cable is short . Luckily my original one piece drive shaft fit . My truck is a short bed . Boyd is your truck a long or short bed I was wondering if four more inches needed will make a difference one or two piece drive shaft. Also Boyd and tp85 your speedo cable might need to be change. I'm sure someone could help out . Hope to help. Nick

[Boyd]

Originally Posted by Palf70Step

Yes the drive shaft is longer for the V8/T350 trucks.. I have been told that if you used the 6 cylinder towers for the V8/T350, it slides it back so that the driveshaft is the same length as the 6/3speed.

Aha, that may be the issue. I thought there was only one drive shaft length for SWB trucks, regardless of transmission. Hope your right Palf!

Originally Posted by 100%Chevy

Boyd,when I told you where to put the towers,I forgot to mention that mine is a turbo-400 trans.
Sorry for any problem I may have caused you!
Mike.

It didn't cause any problems whatsoever. The way I installed the towers was really the only way to unless I wanted to drill holes in the engine crossmember, which I didn't.

Originally Posted by NGN

...Boyd is your truck a long or short bed I was wondering if four more inches needed will make a difference one or two piece drive shaft...Hope to help. Nick

It's a SWB step. If Palf70step is correct, I just need a SWB auto driveshaft. I'll get it figured out one way or another.

Thanks guys.

[Palf70Step]

Some of the SWB trucks (V8/Auto) came with 2 piece drive shafts also.

[brans72]

So you can use the 6 cylinder mounts and move them forward in a 350 swap for a 67-72 C10 correct?

[Jacfourteen]

Originally Posted by brans72

So you can use the 6 cylinder mounts and move them forward in a 350 swap for a 67-72 C10 correct?

if you had a v6 or I6 when you swap to a small block and you don't want to swap driveshafts then you should use the 250 I6 towers in the rear holes. this will make the engine sit farther back than normal, the only issue this really creates is that you will have to get a 4wd fan shroud (they sit back in this position), get a really long fan extention (probably not good for the water pump seal/bearing), or convert to E-fan (what I did). It makes the dizzy a little tight on the firewall, but as long as you use a small cap it clears fine. Here are some pics of how mine sits. As a note mine was a v6 with 4 speed, now its swapped to a small block and still has the stock 4 speed and driveshaft.

[brans72]

Could you move the straight 6 mounts forward and mount the engine then?

[raycow]

Originally Posted by brans72

Could you move the straight 6 mounts forward and mount the engine then?

Yes. Keep in mind that this means you will be modifying the driveshaft, rear mount and any linkage that connects to the engine or transmission.

Ray

[Jacfourteen]

Originally Posted by brans72

Could you move the straight 6 mounts forward and mount the engine then?

The I6 towers won't line up with the front holes so you would have to modify them to work. The small block towers will line up with the front holes, so if you swap to the small block and want to move it to the stock location you would be better off using these.

[raycow]

Sorry, I finally see what you are asking about. Jacfourteen is of course correct. If you move the brackets to the forward set of holes, you need to drill a new hole in the crossmember.

Ray

[Hubscrub]

mine is in the inline position too no problems i have the 4x4 fan shroud and hei dizzy

[gregg72340]

Ok, I have read this thread 3 times and am thorougly confused. When going from the 6 to the 350 do you need to move the I-6 towers if your using HEI? Also when doing this swap from an I-6/3 speed to a 350/4 speed will a one piece driveshaft work or will I have to switch to a 2 piece driveshaft? and final note its a long bed

[Jacfourteen]

Originally Posted by gregg72340

Ok, I have read this thread 3 times and am thorougly confused. When going from the 6 to the 350 do you need to move the I-6 towers if your using HEI? Also when doing this swap from an I-6/3 speed to a 350/4 speed will a one piece driveshaft work or will I have to switch to a 2 piece driveshaft? and final note its a long bed

Hubscrub is using the I-6 towers in the rear holes with an HEI, so it can be done. I'm not 100% sure on this, but I think the 3 speed and the 4 speed are the same length. If they are then you wouldn't need to change driveshafts, I don't know how this would apply to one piece vs two piece shafts.

[raycow]

A car 4 speed is the same length as the 3 speed, but the truck 4 speed is all by itself. It does not use a slip yoke. Instead, it has a yoke bolted solidly to the output shaft, something like the pinion yoke on a rear end. The 4 speed driveshaft has a slip joint behind the front U-joint and looks similar (except for length) to the shafts used on the 4WD trucks.

Ray

[Jacfourteen]

Originally Posted by raycow

A car 4 speed is the same length as the 3 speed, but the truck 4 speed is all by itself. It does not use a slip yoke. Instead, it has a yoke bolted solidly to the output shaft, something like the pinion yoke on a rear end. The 4 speed driveshaft has a slip joint behind the front U-joint and looks similar (except for length) to the shafts used on the 4WD trucks.

Ray

Alright I knew that some of the 4 speeds were the same length as the 3 ott, too bad it is the wrong one. So to go to the granny 4 speed it would require driveshaft swap/modification.