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Discussion Starter · #1 ·
Hi all of FSB forum,
I’m looking for an engine to drop into my 1988 bronco as the current engine is toast. I found one engine on Facebook marketplace that has been souped up. The seller describes it as being:
“a 1989 foxbody 5.0 motor with 351 heads roller rockers gt40 intake with 30 lb injectors with MAF bbk fuel rail msd wires and rotor”

My question is firstly:
How much power can I expect this engine to make with shorty headers and aftermarket exhaust?
Then perhaps more importantly: will a M5OD-R2 be able to handle that power?

I’ve heard mixed opinions about this model of tranny. The transmission itself is good- synchros are faulty and it sometimes locks me out of reverse. Given the state of the engine, I think it’s fair to say that it’s been abused. I know that a transmission can work with any realistic amount of power as long as you drive carefully. However, my uncle says that this engine will rip my driveshaft onto the ground, before going on to call it a badass motor.

Is this engine a realistic pairing for a M5OD-R2 that has 140k miles on it? If not, are there any cost effective modifications that I could make to the transmission to bolster it up for such a motor?

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so, it is a stock late 80s bottom end, with stock iron 351W heads (larger valves) and a GT40 intake from an exploder? It'll breathe better at higher RPMs, but otherwise, nothing special.

as for the transmission? I do not think you are adding enough power to do anything to a transmission in good condition, but it sounds like yours may not be.
 
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Discussion Starter · #3 ·
so, it is a stock late 80s bottom end, with stock iron 351W heads (larger valves) and a GT40 intake from an exploder? It'll breathe better at higher RPMs, but otherwise, nothing special.

as for the transmission? I do not think you are adding enough power to do anything to a transmission in good condition, but it sounds like yours may not be.
Are there any reliable indicators of a failing transmission that you could share? When I do the engine swap, I figure that it would make sense to do the rest of the transmission if that needs to be addressed.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Ill say about 240 HP is what a that engine will make. Likely fine for the M5R2. Have you done the shift rail plug swap?
 

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I'm running a M5R2 transmission behind my '95 5.8L with GT40 heads, 1.7 Roller Rockers, Shorty headers, 5.0L/5.8L hybrid intake, PimpX ECU... about a 300HP build... the M5R2 handles it fine, though I haven't really towed anything significant with it yet.
 

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Ill say about 240 HP is what a that engine will make. Likely fine for the M5R2. Have you done the shift rail plug swap?
Agree with the HP... Hard to tell without knowing the cam specs.
But those head are only gonna flow so much. Not sure why whomever built it though it needed 30lb injectors unless they where force feeding it witha S/C or Turbo.
The good news for the trans, sake, is that the power it does have will be higher in the RPM range. So assuming you aren't dumping the clutch @ 4+ rpm it should be easier on it as not gonna have ton of low end torque.
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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I wouldn't trust anything off of the internet personally, unless I fully planned on a complete teardown, and even then I'm leary.

My Bronco got an orileys 302 longblock crate for $1200 when it needed a motor, 1 year warranty, and no headaches, no questions on how it works with my EEC, & most importantly, no guessing games on what sort of backyard rebuild I may have bought off the internet.

Piece of mind has a cost, and that price is not a whole lot more than what a randon stranger off the internet charges on a "trust me, its all gone thru & fresh inside" type of deal. Especially when you consider the cost of going thru what you bought off the internet & all the other odds & ends you need to retrofit this into your Bronco.
 

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Torque is the enemy of a stick shift transmission, not really the hp reading. Also high rpm shifts at full power will find the weakest link of a stock transmission pretty quick. If the motor has a lot more hp than stock, usually the stock clutch will slip before the transmission fails.

Since you are not significantly increasing the torque or increasing the rpm shift points, it should be fine under normal driving.
 

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so, it is a stock late 80s bottom end, with stock iron 351W heads (larger valves) and a GT40 intake from an exploder? It'll breathe better at higher RPMs, but otherwise, nothing special.

as for the transmission? I do not think you are adding enough power to do anything to a transmission in good condition, but it sounds like yours may not be.
"The transmission itself is good- synchros are faulty and it sometimes locks me out of reverse. Given the state of the engine, I think it’s fair to say that it’s been abused. "

other than that slipping, not going into gear, not downshifting or upshifting properly for autos.

for sticks, it really depends on the transmission, you are looking for changing in how it goes into gear for signs of it failing. I've only ever had one transmision failure, and it was a mazda made stick, but it was due to the shift linkage breaking and falling into the transmission...so not really the transmissions fault.
 
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'92 Custom w/ '95 MAF 5.0 M/T, 33's, 4.10 LSD
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The M5OD's torque limit is something like 20-25% higher than stock power output, FWIW. Unless the OP's tranny is in poor shape, the given specs of the donor engine shouldn't approach that.
 

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Yo MRL19,
Model: M5OD-R2
Type: Five speed Mazda Overdrive
Years: 88-96 Bronco, F150s
..........97-03 F150s
..........05 F150 (v6)
Engines: 300, 302, 4.2L, 4.6L
Not recommended for mating with 5.8, 460, etc., although some members claim their M5OD "works well with a 5.8" although they have most recently swapped it in.
Model: ZF5
Type: Five speed heavyduty overdrive
Years: 87-99 F2/3/450/superduty
Engines: 300, 351, 460, 6.9?, 7.3
Display:
1.3.(D)
2.4.R
Ratios: ?
Trans code: 2
By member adrianspeeder
 

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Discussion Starter · #12 ·
I wouldn't trust anything off of the internet personally, unless I fully planned on a complete teardown, and even then I'm leary.

My Bronco got an orileys 302 longblock crate for $1200 when it needed a motor, 1 year warranty, and no headaches, no questions on how it works with my EEC, & most importantly, no guessing games on what sort of backyard rebuild I may have bought off the internet.

Piece of mind has a cost, and that price is not a whole lot more than what a randon stranger off the internet charges on a "trust me, its all gone thru & fresh inside" type of deal. Especially when you consider the cost of going thru what you bought off the internet & all the other odds & ends you need to retrofit this into your Bronco.
I was originally looking at long blocks from autozone, advance, and the like. I heard from some local engine rebuilders that they can be sketchy- companies taking junkyard motors, making them look pretty then selling as rebuilt. I bought one for $2k, order was cancelled because they couldn't ship my order until next October. Apparently there's some shortage of blocks.. or supply chain disruptions? That's why I've taken to facebook marketplace. I get my license in April so I want this car driving by then.
If I could get a reputable long block for $1200 from a local shop I would go that route. I just haven't been able to find anything.. in my area at least (NE).
 

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I was originally looking at long blocks from autozone, advance, and the like. I heard from some local engine rebuilders that they can be sketchy- companies taking junkyard motors, making them look pretty then selling as rebuilt. I bought one for $2k, order was cancelled because they couldn't ship my order until next October. Apparently there's some shortage of blocks.. or supply chain disruptions? That's why I've taken to facebook marketplace. I get my license in April so I want this car driving by then.
If I could get a reputable long block for $1200 from a local shop I would go that route. I just haven't been able to find anything.. in my area at least (NE).
where abouts are you located?
 

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If the motor has a lot more hp than stock, usually the stock clutch will slip before the transmission fails.
I was thinking about that last night. The M5R2 and ZF5 take the same clutch, with there being 10" and 11" options that can be used for either. (Did all ZF's get the 11"? Not sure if it was an "upgrade" on both.) The M5R2 can handled 330 lbs-ft, while the ZF5 is either 420 or 470, depending on year. So, the same clutch should be capable of handling mid- to high-400s, otherwise the extra capacity of the ZF5 was never more than theoretical. In which case, that clutch can hold on longer than the M5R2 can...
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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Oh that's great to hear your starting out with a Bronco, and yes it sucks the engine places are suffering the same supply chain issues...

An engine builder is always gonna say remanufactured longblock is a bad idea, as it goes against what they are trying to sell you.

I look at it as if I were buying a starter. Sure I can go to a guy that takes my factory starter, disassembles it, rewinds the casing, replaces the board & all the connections, hot tanks my starter case so it's all shiny & new looking, then reassembles it looking brand new, and a week later I pick it up & pay them $200, or I can go to my local NAPA, tell them the year & make of my vehicle, and they walk out with a box with a fully refurbished starter inside for me for $75 and I leave having spent 5 minutes of my time.

Now that we have a bit more info from you & your situation, a built motor seems like a bad idea on 1st car/truck like this. Sure if its a lifelong dream of having a built motor in a bad ass Bronco, that's awesome, & thats the boat the guys that are commenting on this are in, and yeah, they have bad ass broncos with built motors, but you sound more like a young kid just starting out & excited to get his 1st car, and not to discourage big dreams, but the things you aren't considering are pretty important.

At best you'll get 16mpg if your bronco was stock, but you start building a motor up, your gonna have a 10-12mpg Bronco. I sold my 79 Bronco cuz the 460 at 10mpg cuz it was so bad on gas & replaced it with an 85 Bronco with a 351, that got 14mpg & it was astounding how much less money I spent on fuel every week. Kept that one almost 10 years with no problems at all.

The other part of the equation is the cost involved. If you buy a built motor, and the seller actually is honest about it (doubtful) and it's a solid motor, & you hook it all up, your factory EFI computer, which is expecting a stock motor, isn't gonna work for this motor. Now your looking at another $1000 for a stand alone computer to make it run right & then paying a guy another $500 to map your fuel curve, it just a rabbit hole you really don't want to venture down, especially on a limited budget.

In my opinion, a junkyard 5.0 truck motor for a couple hundred bucks, that runs, would be a much better soloution to get you started on your Bronco obsession, which is a lifelong thing by the way.

My 1st Bronco, a 79, was when I was 16, I'm 48 now, and on my 4th Bronco, but I can assure you, not much more mature than I was at 16, just a little wiser.
 

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Discussion Starter · #17 ·
The other part of the equation is the cost involved. If you buy a built motor, and the seller actually is honest about it (doubtful) and it's a solid motor, & you hook it all up, your factory EFI computer, which is expecting a stock motor, isn't gonna work for this motor. Now your looking at another $1000 for a stand alone computer to make it run right & then paying a guy another $500 to map your fuel curve, it just a rabbit hole you really don't want to venture down, especially on a limited budget.

In my opinion, a junkyard 5.0 truck motor for a couple hundred bucks, that runs
Thanks for the response, I greatly appreciate the effort and info that you put into it. It's good to know that there's a whole community of people like me who spend way too much time on their cars- probably 500 hours worth of reading during the past year in my case.
Upon reviewing the modifications to the motor, it seems that its been rigged up to breathe better and accommodate future mods, but shouldn't be too powerful compared to stock. I'm hoping that it will work with my stock EFI computer, because a Holley EFI system is $$$. If I would need to buy that, I might have to back out on the purchase as I'm planning to go check it out tomorrow. As of now, I'm going to use the camshaft from my stock 302 as I've heard its not bad for low end torque, but I'm open to an aftermarket one.

My reasoning for choosing this motor for $1000 as opposed to the $500 JY motors that I've seen is simply that some degree of work has been put into it. Whether its objectively a better motor or not, someone put time into this to install the modifications. If they did that, I think it's a better bet in terms of reliability compared to a JY motor. Plus, it's not that much more expensive once I buy all the other stuff I need for the swap.

Previous owner said he was going to swap it into a ranger but ended up abandoning the project.

MPG is a concern of mine. Obviously I'm driving a bronco so I can't expect anything great but 15mpg sounds pretty damn good. When the car ran somewhat well (one rod knock), I made about 10mpg but I idled it in my driveway a lot because it's fun to hang out in.

If I'm wrong about this conclusion please let me know. Many people on this forum have much much more knowledge and I appreciate it all. I'm just a kid trying to get his bronco on the road.
 

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The guys that have done these swaps can comment on computer issues and how compatible it may or may not be, its just not my area of expertise, but I look at it from the perspective of, if I were trying to do this, what my concerns would be.

I believe an 89 Mustang 5.0L uses a roller cam, and your 88 truck 5.0L is a flat tappet cam, so you would need to change out the Mustang lifters, pushrods, to accommodate the flat tappet truck cam... aka, another $750 or so. And again, not my area of expertise on mustang vs Bronco, but the more knowledgeable members here that are very up on motor internals can fill in where my limited knowledge stops, which is in the shallow end of that pool. Which is why I buy crate motors for stock applications, and have paid big dollars for my #s matching motors to be built by experts, cuz they all bolt in the same.

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I wouldn't count on 15 mpg. If you reach that, you're certainly in the upper tier of Bronco efficiency. I average a pretty consistent ~13 mpg, with a typical range of 12.5 to 13.8 (and a high of 14.8 ... yes, I've been trying to reach 15), which is higher than many report. That's with a 302. And even having swapped to a manual transmission, I've only seen maybe 0.5 mpg improvement on average.
 
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