4 Bolt To 5 Bolt Conv - When Is It Necessary?

Discussion in '1965 - 1973 Classic Mustangs -General/Talk-' started by MTScott, Dec 6, 2017.

  1. Howdy folks, first post here. I've been on the hunt for an older mustang, and/or a falcon. This is a vehicle that will be a fun daily driver, and ideally get reasonable economy (20+ mpg, 25+ would be awesome, but let's be realistic).

    The more practical vehicle to buy is a newer used 4 banger of some sort, but, well, that's boring. They also tend to be a POS that need work anyway. I'd rather work on something I enjoy.

    I come across many I6 falcons and mustangs that are in a decent price range, with a 3 speed. Now, the I6 looks like it could be a hoot to build, so I haven't ruled that out. I'd like to eventually see 200ish HP to the wheel. It seems that could be difficult, or at least expensive with a 200 I6. I could probably live with 150 to the wheel though, and perhaps that is more realistic with the I6. Turbos can solve many problems though.

    I'd also likely convert to a T5 no matter what I do. So it begs the question, why not just put an entire 5.0 drivetrain from a 87-93 in it?. ...and, of course that leads you down the rabbit hole of upgrading your spindles and rear axle control arms, brakes, etc. The only real consistent reason I've heard for this is to handle the weight; however, if you run alum heads and intake on the 302 and remove the no longer needed accessories the 302 starts getting pretty close to the weight of the I6 (from the quick math I've done).

    So, it must be more than just weight... a faster car should have better brakes and handling right? If that is the case, then doesn't a hotter I6 also necessitate the need to upgrade to 5 bolt stuff? I guess my question is "how" necessary is it, is a MUST do?

    Now, i'm not against any of this, but when you start adding up the costs for all of the conversion - well, maybe this car just isn't the proper candidate for what I'm trying to do. I have come across a pretty straight, complete 66 coupe 200 I6 3 speed. It needs paint, cleaning up and standard maintenance done, but for the most part is a great starting point - it is a functional vehicle right now. He also already has decent 4 bolt wheels and tires on it that are near brand new. I just know that the 80-100HP it gets to the wheel isn't going to keep me happy.

    Maybe I'm worrying about this too much, especially if there are grassroots ways to upgrade the suspension and handling (the "kits" I've found are 3000+).
    #1 MTScott, Dec 6, 2017
    Last edited: Dec 6, 2017
  2. ok a few random thoughts here for you;

    1: if you are willing to keep the six, dont expect a lot of power from these engines, without boost of some kind. you can get between 150-175 flywheel horsepower from these engines with a fair amount of ease, but beyond that you need to get into some fairly serious mods beyond simple cam swaps, and bolt on parts.

    2: if you keep the six, and you dont plan on racing the car a lot, then you can also keep the four bolt wheels as well.

    3: the stock rear end wont handle much more than about 200-250 hp at best, so if you plan on more, then upgrade to an 8" rear end. and yes you can modify the axles to use 4 bolt wheels if you like.

    4: a T5 swap is an easy one with this six, there are a number of suppliers that carry the necssary parts for that particular swap. as a side note, the T5 swap kits were first developed by a fordsix member who sold the rights to modern drivelines. just an FYI.

    5: a T5 swap with decent gearing will make the car feel like it has 50-75 more hp than it really has, so dont forget the gearing. also be careful what rear gear and what first gear combination you use, as too much of either would make first gear basically unusable in most situations. a lot of guys started using the 4 cylinder T5 with its 4:1 first gear ratio, and they would use a steep rear gear to take advantage of the overdrive, only to find that first gear was useless. if you do this swap, i suggest using a V8 T5 with its 3.35:1 first gear, and run something like a 3.50-3.73 rear gear. that will allow you run first gear for more than a few feet before pulling for second, and wont have any issues with running the overdrive at 60 and having the engine lug at that point.

    6: doing a two barrel conversion is recommended, along with a cam swap to a more modern design. a lot of guys run the comp cams h260he grind. this is a nice cam for the street, and very flexible. as for the two barrel conversion, the best is a direct mount conversion, but that requires some machine work. using a two to one adapter loses hood clearance. but both work well. for my 170, i am thinking about using two carbs, specifically the weber 32/36 carbs with their small primaries, and their progressive secondaries.with the carbs set in the right place you get a much better air/fuel distribution in all cylinders making for a better running engine when properly tuned.

    7: upgrade the cylinder head to a later model 200/250 head. they have a larger log and larger valves for better flow capacity. you can do a little pocket porting and smooth out the valve pockets, and open up the exhaust ports a bit, but leave the port divider in the parts department, they dont add enough power to be worth while, and the hassle of installing them isnt worth the effort.

    8: you can run headers if you want, but they are not necessary unless you are building a race engine, and they dont add a lot of power. in fact just converting to dual exhaust with larger than stock pipes is a more effective mod.

    9: if you get an early stang or falcon that has a generator, convert to an alternator. the swap is easy to do, www.gofastforless.com and mustang steve both have the wiring conversion that is necessary for the swap. i did this swap, but i used a one wire conversion kit to eliminate the external voltage regulator, instead of converting from a generator VR to an alternator VR.

    10: if you keep the four bolt wheel pattern, but want to run some late model fox body wheels, you can get wheel adapters that are 1 inch thick to allow you to run the fox body wheels 4x4 1/4 bolt pattern. the nice thing is that the put the wheels in the right place in the wheel wells, and you can run a 205/60-15 tire comfortably.

    let me know if you have any questions.
  3. That was a lot better than random! Great info, and thanks for the reply.

    It seems, that there are ways to convert without costing a ton. I've already found a complete rear axle assembly for $500 local... that's a pretty easy fix. It seems there are many options for converting/improving the front end, and I'd probably want to do that eventually anyway. I guess I shouldn't let this piece worry me.
  4. that rear axle assembly, is it an 8 or nine inch rear? if its a nine inch, you dont need it unless you plan on building a very healthy V8, because even the most powerful small six i have seen built wont stress an eight inch rear end. an 8.8 would be a better choice if you cant find an 8 inch.
  5. I'm going on the road next to make this deal happen. The car i'm looking at is about 4 hours away. This is a stock 6cyl 3 speed, which tells me the rear end is a 7.5.

    I've settled on the idea of swapping in a newer model drivetrain from roller 5.0 car. It so happens there is a 94 5.0 5spd for sale in the same town. he's asking 2400.... I think I can get it for 2k. 133k miles, but the car itself is in need of some love (which for me, simply makes it easier to negotiate)

    We don't need to hash the whole process out, but tell me if I'm being too optimistic: If I start with this 5.0/T5 combo from the 94 I'll be set with trans, bell, clutch, and engine ready to go. Add ford small block engine mounts, and bolt it in. I've seen canned solutions out there for the T5 as far as a crossmember goes, so that seems easy. There are other things too, clutch linkage, oil pan, sump, timing cover, pump, dipstick tube, etc... all solvable and well documented. As far as an early to late model drive train swap, this seems like a fairly straight forward one. Tell me if I'm missing something big.

    One question that might sweeten the deal for me on the 94. Can I swap the 94 axle into the 66 without too much trouble? I'd expect that new/relocated spring perches might be required, but is the axle the right width?
  6. I found my own answer on this...
    65-66 is supposed to be 57.25" wide. The 93 is 59.25" in total width, and the 94 is supposed to be 1.5" wider than that. So, maybe not. I suppose it could work if I ran an OE style rim with less offset.
  7. you did answer your own question here. you might be on the look out for a 75-80 granada/monarch, or a 74 or later maverick. these cars will have the 8" rear end petty much across the line, and i believe all of them are five bolt rear ends and will be a direct fit in place of the 7 1/4 in your mustang.