4.3 V6 into 75 Monza

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4.3 V6 into 75 Monza

Postby My Beast » Fri May 13, 2011 5:28 am

I have a 75 Monza Towne Coupe with the stock 2.3 four banger and 4 speed. I recently bought a complete 4.3 V6 with 4L60E transmission that came out of a 2007 GMC Sierra. It was complete dropout just like it came from the dealer- it is ready to drop in. I have a set of stock V8 frame mounts but have heard that if I use them it will put the engine too far forward. Different people have told me different things so now I am appealing to H Body lovers everywhere- HELP!!! Any comments or advice will be welcomed.
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Re: 4.3 V6 into 75 Monza

Postby BillPappy » Fri May 13, 2011 5:32 pm

This will be a nice swap.. Did you get the ECM with the engine. Also controls the Trans. Not sure about engine mounts. I would have to look at my Blazer with measuring tape in hand.
I hope some will chime in before get out side. What you going to do about the oil pan?

Need pics :)
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Re: 4.3 V6 into 75 Monza

Postby My Beast » Fri May 13, 2011 6:37 pm

I got everything with the engine-ECM, Mass air flow sensor, drive by wire pedal. I am looking for someone to do the swap for me.
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Re: 4.3 V6 into 75 Monza

Postby Kenova » Fri May 13, 2011 10:36 pm

My Beast wrote: I have a set of stock V8 frame mounts but have heard that if I use them it will put the engine too far forward.


You heard right. The 4.3 V6 is 4.4 inches shorter than it's SBC big brother. The V6 mounting pads for the engine mount were moved towards the back of the engine when they dropped two cylinders from the V8. Conversely, the mounts remained the same distance from the front of the engine.
A pair of the Buick V6 mounting plates may come close to being in the right place, but I would think you will still be faced with some fabrication.

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Re: 4.3 V6 into 75 Monza

Postby BillPappy » Sat May 14, 2011 5:58 am

That is what I was thinking Ken.. But was not going to comment on it tell I made sure.
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Re: 4.3 V6 into 75 Monza

Postby My Beast » Sat May 14, 2011 8:09 am

Thanks guys!! I have heard that same thing from several people so that pretty much confirms it for me. My brother had suggested welding a length of bar stock to the bottom of the mounts that would extend several inches towards the front so I could use the stock mounting holes but move the engine back. Another thought- the engine came with the factory mounts still on it from where it was removed from the truck. Would it be feasible to get something fabricated and just drop it in place that way?

Next question is will I need to modify my firewall for the tranny? Same thing- I have heard yes and I have heard no. I would rather not have to if I can avoid it.

BTW- my brother I referred to earlier had a 71 Vega Panel back in the mid 70's with a 69 Z-28 motor and 4 speed in it. Foget all the things he did to the motor, but it would scream!!! Problem was he would drive it, get drunk or high, then blow it up. He would go through the same process again and end up doing the same thing- about four or five times to be exact. Finally sold it to one of his buddies and don't know what happened to it from there.
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Re: 4.3 V6 into 75 Monza

Postby BillPappy » Sat May 14, 2011 10:24 am

I ran a 700r4 trans in my 80 sunbird. It is pretty close the same trans as a 4L60E. It fit like it was made for it. But the 700r4/4l60e pan is so wide it makes for a tougher install.
Now on that note.. One of the later h bodys has a smaller tunnel. I just don't remember what year it is
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Re: 4.3 V6 into 75 Monza

Postby monza75tc » Mon May 16, 2011 1:10 pm

75's had a larger tunnel as was made for the Wankel / rotary. Probably have pelanty of room.

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Re: 4.3 V6 into 75 Monza

Postby tking66 » Thu Aug 25, 2011 3:58 pm

If you have any issues with the ECU or fuel injection and want to simplify it. The Astro/Safari vans had a 4.3L with a four barrel carburetor in 1985 and maybe 1986. You can also use the simple HEI distributor out of that van and wire it to run the basic GM 4-pin ignition module. We did that conversion on a 4.3L we stuffed in a Chevette and it runs great, and the wiring is incredibly simple. Plus the parts were dirt cheap.
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Re: 4.3 V6 into 75 Monza

Postby cjbiagi » Thu Aug 25, 2011 6:01 pm

I think I still have my 4.3 liter badges from my 262 V8 that I'd be willing to sell, that would be a cool addition. I removed them very early in their life so they are in excellent condition. Let me know if your interested and I'll check. cjbiagi@yahoo.com
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Re: 4.3 V6 into 75 Monza

Postby Astre-mutt » Thu Aug 25, 2011 7:57 pm

The mounts are not that hard to make. I can't be 100% sure about the location of the hard points on the Monza chassis, because my 4.3L is in a Astre. I think they must be similar.
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As far as changing to a carb, you will need a 4bbl manifold that fits Vortec heads. The early manifold will not fit. Your 2 chooses are Edelbrock "aluminum", or a Mercruiser 2bbl or 4bbl cast iron.
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Re: 4.3 V6 into 75 Monza

Postby bigguy5994 » Mon Sep 05, 2011 6:41 pm

I appreciate the advice and the posts. Planning on staying with the fuel injection- the engine is complete and ready to drop in place so I'll stick with it for now. I may have to go with an aftermarket cold air intake for clearance but won't really know until I get it put in. As for the engine mounts, it took me a while but finally caught on. An old buddy of mine told me to measure from the bellhousing to the center of the motor mount that is attached to the V6 and it is roughly 12 1/2 inches. Measuring from the firewall that puts them pretty close to being on top of the steering linkage, so if I was to move it forward about an inch it looks like it will clear. Really need to get someone with fabrication skills to figure it all out. Next question is would it be worth it to see about getting some strut tower bracing (kinda like a K brace they use on Mustangs) fabricated to stiffen it up some? I am not planning on trying to race but I do like the feel of flat cornering. I have the factory front and rear sway bars on the car but would like a little more aggresive handling.
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Re: 4.3 V6 into 75 Monza

Postby bigguy5994 » Thu Nov 10, 2011 7:31 pm

Well, after a lot of thought and consideration I decided to sell the engine and transmission. I could not find anyone willing to do the swap for me and the engine was just sitting in my garage, so I put it on e bay and it sold quickly. For now I plan on leaving things as they are (stock 4 banger and 4 speed) but go ahead and get the suspension and brakes up to par and go from that point. If and when the time is right I plan on going with the tried and true 350 with a TH350 trans- go with carb instead of fuel injection and keep it clean and simple.
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Re: 4.3 V6 into 75 Monza

Postby Rickracer » Thu Nov 10, 2011 7:47 pm

I would strongly suggest going with a 700R4 trans, (.70 overdrive, 3.06 first gear, and lockup), you'll thank me later, :wink: 8)
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