Engine swap question

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PeteG41

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Hey guys, doing a little proactive research and wanted to bounce some questions off the experts. Buddy of mine has a 390 that he pulled out of his f-100, that originally came out of a car. I would guess a Tbird? Apparently it has been bored to a 428, which from what I have read is kind of pushing it, so I am thinking its just a 428 crank effectively making the 390 a 410. The 351c 2v in my mach 1 has already been rebuilt by the PO, quite a few years ago, with one of the cylinders sleeved. I don't have any of the rebuild paperwork and the PO couldn't remember much info besides the sleeve part. I believe I am going to need a valve job, but waiting for the compression test results. My question is, what would I need to do if I decided to put the 390 in my mustang? It was running when he pulled it, and is just going to give it to me as he has no use for it. I am assuming my auto FMX wont bolt up, but the C6, if that's what it is, also comes with it. What all am I looking at to make the swap work? I know the things like motor mounts and most likely tranny mounts will need to be changed, and probably the radiator? Just wondering if that 390 is even a viable option.
 
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Ron Tanzi

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That would be a lot more effort than it would be worth. So my opinion is it not worth it. Your FMX will not bolt up to the FE block. The 390 is heavier than the 351C. I would suggest selling the 390 and C-6 and using the funds to refresh your Cleveland. The 390 was a dog of an engine anyway.
 

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That would be a lot more effort than it would be worth. So my opinion is it not worth it. Your FMX will not bolt up to the FE block. The 390 is heavier than the 351C. I would suggest selling the 390 and C-6 and using the funds to refresh your Cleveland. The 390 was a dog of an engine anyway.
much appreciated for the input. I have been digging around other forums, and it seems like an absolute headache in order to make it work. Mounts, exhaust, drive shaft, yada yada the list seems to go on. My only worry was with my cleveland having already been rebuilt, I am not sure how much more could be done with it. I am no motor expert by any means, but I do know the 351c can only be bored so much. And the sleeve part had me a little worried.
 

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As long as the sleeve was installed properly it should be fine for a street cruiser. Engine overhauls don't always require boring the cylinders. That can only be determined by assessing and measuring the cylinders. If you decide to tear down the engine an engine machine shop could tell you if it's good or not.
 

PeteG41

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As long as the sleeve was installed properly it should be fine for a street cruiser. Engine overhauls don't always require boring the cylinders. That can only be determined by assessing and measuring the cylinders. If you decide to tear down the engine an engine machine shop could tell you if it's good or not.
Oh okay, thank you! As you can tell I am definitely still learning. I guess I was thinking worst case, having already been rebuilt and sleeved with 99k original miles, I was just skeptical as to the overall health of it. I’m mentally preparing myself to have to get a valve job, but will be pleasantly surprised if I don’t. The ole girl took her “maiden voyage”, well for me anyways, 1/2 a mile down the street to my local shop this morning. A somewhat smoky 25 mph but jeez did I have a stupid smile doing it.
 
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Without knowing more about the 390 I agree that it's more trouble than it's worth. Not all 390 were boat anchors, though. The '61 Thunderbird had 375 horsepower, the Z code Starliner had 401 horsepower with three deuces.
 

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If you're looking for a torque monster with lots of available aftermarket parts, the 390 fits the bill.
 

PeteG41

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Without knowing more about the 390 I agree that it's more trouble than it's worth. Not all 390 were boat anchors, though. The '61 Thunderbird had 375 horsepower, the Z code Starliner had 401 horsepower with three deuces.
It’s in storage up in flagstaff, so he’s going to get some numbers on the block, then at least get an idea of what it came out of. No clue why he’s never done it. But cost wise I think a rebuild with some upgraded goodies.
 
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Lots of little things to deal with when swapping. You mentioned the transmission bell housing. Other stuff to deal with off the top of my head.
Linkage, motor mounts, exhaust routing, cooling, suspension (heavier engine), electrical, emissions, accessories (AC/power steering/alternator), throttle linkages and so on.

Just some thoughts to toss at you for consideration.
 

Ron Tanzi

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Without knowing more about the 390 I agree that it's more trouble than it's worth. Not all 390 were boat anchors, though. The '61 Thunderbird had 375 horsepower, the Z code Starliner had 401 horsepower with three deuces.
I did not mean to bad mouth the 390 but I would rather have a Cleveland in a car like ours. I have driven a few 390 equipped cars and trucks and feel that the Cleveland is more fun and lighter.

Ron
 
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You have already received some great advice, so I will try to avoid being repetitive. Will E is right on the money with his short list of things you would have to consider with an engine transplant. As far as the 390 being a dog of an engine, that is the reputation it has had for decades, whereas the 428 is considered to be a fairly formidable engine with its larger bore and longer stroke. That said, the 390 and 428 engines have the same physical width, and it is that width that would cause me to take pause with popping either engine into a 71-73 Mustang, much less an earlier year model.

I know the 71-73 Mustangs have a larger, wider engine compartment than the prior year models. That was done so the 429 engine would be able to fit better in the Big Nose Mustangs, as compared to the prior year Mustangs. I know this for sure, in our 1969 Shelby GT500, and in a 1969 Mach 1 with a 390 engine that I worked on long ago, it is/was damn near impossible to remove the spark plugs without unbolting the engine mounts, loosening the tranny mount, and jacking the engine up a bit. And now, yeah, yeah, I can already hear folks telling how they did it with a bit of patience, multiple swivel joints, and perhaps by removing the valve covers. In the case of our Shelby's 428, and the 69 Mach 1's 390, both vehicles had the Thermactor air injection emission equipment, along with the air injection tubes running down to the exhaust manifold port outlets. The tight fit of the engine is bad enough. The intrusion of the Thermactor air injection tubes just makes a nearly impossible situation absolutely impossible without raising the engine up a little bit. At that, it is still a difficult process to go through. The 351 engines are just easier to work on and maintain.

I would be willing to guess, even bet, the wider engine compartment of the 71-73 Mustangs may be just larger enough to accommodate not only the 429 (and even a 460), but the 390/428 engine as well. I just do not know how well the FE engine would end up fitting, as in would it be a better fit, but not "better enough," in a Big Nose engine compartment. For me, that would be reason enough unto itself to opt to keep the 351. Although the sleeving of the one cylinder (and perhaps others also) will technically weaken the block, you could still do a moderate upscaling of performance that would help the engine reach near FE performance, although the monstrous low end torque from the 428 is hard to shake a stick at.

If you do end up doing at least a valve job I suggest you consider doing the following work, whether you build the engine up or not, but especially if you do build it up consider using:
  • Bronze wall valve guides
  • Hardened steel valve seats
  • Perfect Circle valve guide seals (as opposed to the stock umbrella style splash shields)
  • Use a hydraulic roller cam kit
    • If you opt to continue using a flat tappet valvetrain design be sure your engine oil contains Zinc, otherwise you will see your cam lobes and lifters wear out very quickly, even within the first minutes of running ,despite using the proper break-in lubricant for the cam and lifters.
  • Use some nice forged aluminum pistons, but keep the compression under 10:1 unless you prepare the entire fuel system for ethanol being in the gasoline (including the fuel pump)
    • Have the rotating engine components balanced
I really think you will be happy with a well built and tuned 351. In our case I got the GT500 because I never had a big block Mustang or Shelby before, and wanted to experience its performance. Although the performance is impressive, and as much as I love having that Shelby, I must say the 351 engines (C or W) built correctly can do a great job for a street driven pony car. Be aware the rear axle ratio can hold back performance even with a well built engine. The highest ratio I would consider would be 3.0:1, and even that is pushing the edge.

I feel the best compromise for a street driven vehicle for spirited performance, yet being well behaved in terms of engine RPM at 60 MPH, is 3.5:1. The 3.5:1 ratio will have the engine spinning at just under 2,900 RPM at 60 MPH with a final drive transmission of 1:1. With an AOD the RPM at 60 MPH drops to just under 1,900 in 4th/OverDrive gear. That lets us, in our 73 Mach 1, retain the pep we get with its 3.5:1 TractionLok rear axle gear set, while retaining the comfort of only turning nearly 1,900 RPM at 60 MPH as opposed to having the engine spinning at a speed that makes it sound like it could grenade at any moment. Best of both worlds.
 
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If you end up having to do an engine rebuild, instead of spending all the money transplanting a used 390, or worrying about sleeving your block, why not consider buying a different 351C block, building that, and saving your numbers matching block in a corner of the garage?
 

PeteG41

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Lots of little things to deal with when swapping. You mentioned the transmission bell housing. Other stuff to deal with off the top of my head.
Linkage, motor mounts, exhaust routing, cooling, suspension (heavier engine), electrical, emissions, accessories (AC/power steering/alternator), throttle linkages and so on.

Just some thoughts to toss at you for consideration.
Yeah in theory it doesn't seem awful but once you dive into every little thing that it would take, definitely not worth the headache of trying to make it work. Thank you!
 

PeteG41

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You have already received some great advice, so I will try to avoid being repetitive. Will E is right on the money with his short list of things you would have to consider with an engine transplant. As far as the 390 being a dog of an engine, that is the reputation it has had for decades, whereas the 428 is considered to be a fairly formidable engine with its larger bore and longer stroke. That said, the 390 and 428 engines have the same physical width, and it is that width that would cause me to take pause with popping either engine into a 71-73 Mustang, much less an earlier year model.

I know the 71-73 Mustangs have a larger, wider engine compartment than the prior year models. That was done so the 429 engine would be able to fit better in the Big Nose Mustangs, as compared to the prior year Mustangs. I know this for sure, in our 1969 Shelby GT500, and in a 1969 Mach 1 with a 390 engine that I worked on long ago, it is/was damn near impossible to remove the spark plugs without unbolting the engine mounts, loosening the tranny mount, and jacking the engine up a bit. And now, yeah, yeah, I can already hear folks telling how they did it with a bit of patience, multiple swivel joints, and perhaps by removing the valve covers. In the case of our Shelby's 428, and the 69 Mach 1's 390, both vehicles had the Thermactor air injection emission equipment, along with the air injection tubes running down to the exhaust manifold port outlets. The tight fit of the engine is bad enough. The intrusion of the Thermactor air injection tubes just makes a nearly impossible situation absolutely impossible without raising the engine up a little bit. At that, it is still a difficult process to go through. The 351 engines are just easier to work on and maintain.

I would be willing to guess, even bet, the wider engine compartment of the 71-73 Mustangs may be just larger enough to accommodate not only the 429 (and even a 460), but the 390/428 engine as well. I just do not know how well the FE engine would end up fitting, as in would it be a better fit, but not "better enough," in a Big Nose engine compartment. For me, that would be reason enough unto itself to opt to keep the 351. Although the sleeving of the one cylinder (and perhaps others also) will technically weaken the block, you could still do a moderate upscaling of performance that would help the engine reach near FE performance, although the monstrous low end torque from the 428 is hard to shake a stick at.

If you do end up doing at least a valve job I suggest you consider doing the following work, whether you build the engine up or not, but especially if you do build it up consider using:
  • Bronze wall valve guides
  • Hardened steel valve seats
  • Perfect Circle valve guide seals (as opposed to the stock umbrella style splash shields)
  • Use a hydraulic roller cam kit
    • If you opt to continue using a flat tappet valvetrain design be sure your engine oil contains Zinc, otherwise you will see your cam lobes and lifters wear out very quickly, even within the first minutes of running ,despite using the proper break-in lubricant for the cam and lifters.
  • Use some nice forged aluminum pistons, but keep the compression under 10:1 unless you prepare the entire fuel system for ethanol being in the gasoline (including the fuel pump)
    • Have the rotating engine components balanced
I really think you will be happy with a well built and tuned 351. In our case I got the GT500 because I never had a big block Mustang or Shelby before, and wanted to experience its performance. Although the performance is impressive, and as much as I love having that Shelby, I must say the 351 engines (C or W) built correctly can do a great job for a street driven pony car. Be aware the rear axle ratio can hold back performance even with a well built engine. The highest ratio I would consider would be 3.0:1, and even that is pushing the edge.

I feel the best compromise for a street driven vehicle for spirited performance, yet being well behaved in terms of engine RPM at 60 MPH, is 3.5:1. The 3.5:1 ratio will have the engine spinning at just under 2,900 RPM at 60 MPH with a final drive transmission of 1:1. With an AOD the RPM at 60 MPH drops to just under 1,900 in 4th/OverDrive gear. That lets us, in our 73 Mach 1, retain the pep we get with its 3.5:1 TractionLok rear axle gear set, while retaining the comfort of only turning nearly 1,900 RPM at 60 MPH as opposed to having the engine spinning at a speed that makes it sound like it could grenade at any moment. Best of both worlds.
Great info! You had me at the spark plugs alone to be honest. Not a snowballs chance in hell I will want to have to mess with engine mounts just to do the plugs. I do like the 351, and I know it is more than capable of being made into a great street motor. Thank you for the info on the valve job! I already had it in my head to do the perfect circle guides, but the rest I will add to the list. And funny you mention it, when my dad was in town helping me work on this last weekend, he mentioned doing the 3.5:1. He had a 71 mach 1 so is very familiar. His just didn't have all of the extra emissions components that mine does. Yes the sleeve part while isn't a huge deal, is what sent me down this road of motor options if it was needed. Here in AZ I am sure it would be easy to find an already rebuilt 351 if thats what it comes down to. Would love to be able to keep the original motor, just trying to get out in front of whatever may come up!
 

PeteG41

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If you end up having to do an engine rebuild, instead of spending all the money transplanting a used 390, or worrying about sleeving your block, why not consider buying a different 351C block, building that, and saving your numbers matching block in a corner of the garage?
Pretty much just read my mind! I have poked around a couple shops here in AZ just to get an idea of what I would be looking at cost wise.
 
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I did not mean to bad mouth the 390 but I would rather have a Cleveland in a car like ours. I have driven a few 390 equipped cars and trucks and feel that the Cleveland is more fun and lighter.

Ron
I agree completely, I have an M code and there is no way I would swap it for a 390. I have had a few FE powered vehicles and like them. Now, if it were a 427 side oiler I would have to think long and hard about it. I'm going to rebuild my 351C as a 408, so the Cleveland would win out, but having a 427 (or even a 428CJ) would be cool. It would be difficult to get an FE to produce the same power as a Cleveland of the same size.
 

PeteG41

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Lots of little things to deal with when swapping. You mentioned the transmission bell housing. Other stuff to deal with off the top of my head.
Linkage, motor mounts, exhaust routing, cooling, suspension (heavier engine), electrical, emissions, accessories (AC/power steering/alternator), throttle linkages and so on.

Just some thoughts to toss at you for consideration.
Have an update for you guys. I had this on a different thread when I posted a video of the motor, and was getting replies of either a dead cylinder or bad vacuum leaks. Since it had been sitting for 7 years or so, I changed the plugs, wires, cap/rotor, points, rebuilt the carb, and put in a new fuel pump. While it idled better, it still had a miss. Well, I heard back from my shop with the compression test and here's where we're at. I have no compression on 4 of the cylinders. They said its not all on one side, but I didn't ask which specific cylinders. I assumed I had at least 1 dead cylinder so at the end of the day 1 or 4 doesn't really matter in the grand scheme. Guess my original compression test was pretty accurate, I thought my gauge was a dud. Now I need to figure out what route I am going to go. Cheaper option is obviously pull the heads, have those machined and throw them back on. On the other hand, which I am about 95% leaning towards, is just rebuilding the whole thing. Looking at $5500ish, from a shop here in AZ. That includes pulling it and installation, as well as upgraded internals, melling oil pump, heads machined. So basically everything brand new. That way I know exactly what I am working with. Thoughts?
 
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I am also in Phoenix. I know a guy who is very familiar with our Clevelands. He rebuilt mine and then sleeved it for me when I messed up and dropped a nut into the intake. He's machine shop only, I don't think he does removals and installations. PM me if you want his info.
 

PeteG41

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You need to find out why the cylinders have no compression. Your shop should be able to tell you without disassembling the engine, beyond removing the valve covers.
I was going to get it home and take them off myself to have a look. I didn't want it to turn into my car sitting at their shop partially disassembled, especially since I am not really prepared to do some costly repairs right now. When I get them off, what exactly should I be looking for? Besides obvious things like valve keepers just sitting in there. I know what that looks like back when I had a 70 cougar.
 
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