MRM331

General Swap Info-Fords

I'm seeing the same types of questions pop up concerning some of the basics of building a conversion using Monster Miata's Ford kit. Since I'm pretty knowledgeable about that particular conversion I thought I'd stick a thread with some of that info at the top. One of our LSx mods could maybe do the same for the LSx guys?

Please feel free to add anything I may have forgotten below or PM me with anything you think we should include. I'll add to this top post as we go.

Here we go:

Kit Vender: Monster Miata- www.v8miata.com
Kit cost: Around $4200 after shipping
Kit includes: Modified Front Subframe, Transmission Crossmember (powder coated), Rear Differential Hanger (powder coated), Rear Differential torque mount (requires welding), Engine mounts, Transmission Mount, Radiator, Coolant fill neck, Radiator mounts (powder coated), Sway bar Relocators (powder coated), Throttle Ball Receiver, 400 pound front springs, clutch master and adapter, stainless steel braided clutch line, adjustable clutch slave pushrod, oil pressure and water temp gauge calibration resistors, T5 transmission short shift adapter, Transmission Tunnel Boot, Heat-Treated axles, rear axle boots (4) and straps, aluminum hub oil seal spacers, Modified Mustang oil pan (powder coated), Miata rear hubs broached to fit Thunderbird axles, Thermal coated headers, Speedometer Cable Adapter, two cooling fans, color instruction manual (cost of manual refunded if purchased in advance)

Cores you need to send out: Front Miata K-frame, Mustang oil pan, Miata rear hubs (about $100 to ship to him from east coast)

What you need find to finish build:
-A Miata (1990 - 2005)
-Some type of Ford 5.0 engine with intake and all accessories
-Fox-body Ford Mustang Bell housing with fork
-Mustang clutch, flywheel, throwout
-T5 world class or non world class transmission with shifter and speed sensor
-7.5 inch IRS differential from a Thunderbird or Cougar
-Half-shafts from the same car as above (you will reuse the CV joints on each end)
-Fox-Body Mustang 5.0 Main, Injection and HEGO harness (all will need to be modified somewhat)*
-Ford A9L ECC-IV ECU*
-A red, 23-tooth speedometer drive gear
-A PM-type starter (One from a 1991 Lincoln MkV is Plug-n-Play)
-About $75 worth of assorted grade 8 hardware - the kit instructions include a list.

What you need to have made to finish the build:
-30.5 inch driveshaft (Mustang one can be cut down)
-Exhaust system

*=not needed if going with a carburetor
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FAQ:

How does the suspension work?
-The kit has you remove the stock Miata springs and swap them onto the back struts. The kit calls for "removing a coil" from them before swapping them back but most builders as of late have not done so. The kit comes with two OEM-quality 400 pound front springs which replace the original fronts. While this will all work on stock struts some type of upgrade, even just to AGX shocks is recommended. This gets you a pretty nice street suspension for very little cost. Most who decide later to track their V8's move up to a complete adjustable coil over setup using at least 500 pound front springs. FatCatmotorsports has a set-up designed specifically for V8 Miatas.

Where do I get a Differential from and how do I make the axles work?
-The differential you need is a 3.27 7.5 independent differential from a 10th generation (1989-1997) Thunderbird or a 7th generation (1989-1997) Cougar. The best have a factory limited slip. To find one look for cars with an "E" listed on the doorpillar tag under "axle". After finding one with an "E" look at the diff tag itself which should read "3L27" if it has limited slip and "3 27" if it is open. If you wish to maintain ABS look for one with ABS mounts on the differential and rings on the axles.
-You will need the front two mounting bushings on the nose of the Ford Differential. You can use the ones from the car you pulled the differential from or replace them with new urethane ones. SuperCoupePerformance sells nice ones for a good price. The front bushings are the same for 8.8 and 7.5 differentials.
-The kit comes with two axles. To make them work you will need to remove the inner and outer CV joints from the Thunderbird's half shafts and put them on the new axles. Instead of using used axles, new half shafts for a Thunderbird can be purchased and used instead. The price for new is not bad. The kit comes with four new axle boots. The inners are replacements for a Thunderbird, the outer are shorter ones from a Taurus. The shorter boots are needed to clear the shocks. The kit comes with a set of no-tool-required bands which will work fine in any southern or dry environment. If your car is going to live in less-than-ideal weather you may want to consider having actual crimp-bands used. The axles interface with the rebroached hubs the kit includes. Since everything is apart it's a good time to replace the rear wheel bearings (stock Miata). The original Thunderbird axle nut can be reused although the safe move is to buy a couple new ones. The same goes for the special 12mm 12point bolts that bolt the flange yoke to the pinion of the drive shaft. You can try to sneak them out with the differential or buy new ones (part# HW1701-about $14 for a set of 4).

DriveShaft?
-The kit does not come with a driveshaft. Fortunately, in many areas of the country there are shops that can affordable make you one or at least modify one for you. If you don't have that luxury Monster Miata can still have a steel one made for you at an additional cost or McCully Racing Motors can make you up an aluminum one.
-The driveshaft must be 30.5 inches from yoke center to yoke center. The slip yoke must match up with a T5 transmission and the flange yoke must match your Ford 7.5 Differential. A good way of getting the correct flange yoke is to remove the flange yoke from the car you pulled the differential from while still in the yard. The flange yoke can be removed from the driveshaft using a pair of vicegrips, a socket and a hammer. Before walking out with the differential bolt the flange yoke back on it and you may get it for free. If you buy an assembled shaft from McCully racing Motors or Monster Miata it will come with the flange yoke
-Another option is to simply have a steel Mustang driveshaft cut down to 30.5 inches. This may or may not cost the same as buying a new one.

How do the Cores work?
-The Monster Miata kit does not use a tube front K-frame like th LSx kits. Instead, the stock Miata front K-frame is modified to work with the 5.0 and exhaust. To have this done you must send your (or a) front Miata front subframe out to California. The kit also uses your stock rear hubs which are rebroached to fit the Thunderbird half-shafts. To minimize the amount of time your Miata is undrivable it is recommended that you find a spare front subframe and set of hubs and send them out Monster Miata. Used front K-frames can be found on eBay for under $100 and some members here who have already done their conversions may have a spare as well. Hubs can also be found pretty cheaply. The cheapest way to economically send the K-frame to Monster Miata is to clean it and degrease it first and ship it unboxed via UPS or FedEx.
-The third part that needs to be sent out is a Ford Mustang oil pan. Since this part is being cut, rewelded and powder coated it has to be almost perfect. If your donor Mustang came from anywhere where it snows it is probably too rusted to use. Even if it's not rusted, any dent and dings could cause it to be rejected. A good idea is to buy a new one online and have that sent to Monster Miata. Dorman or other OEM-replacement pans can be purchased and shipped to Monster Miata for around $50.
-Since a Miata does not have an oil level warning light Monster Miata will typically weld over the bung in the side of the Mustang pan where the sender would have gone. If you are ever planning on adding a oil temp gauge to your V8 Miata this bung is great place to put the sender. Kits are actually sold to add a sender to this fitting. If you do plan on doing so make sure to let Monster Miata know not to weld over that fitting.

Options for Engine Management
-The Monster Miata kit assumes you are using a fuel injection system from a 1988 to 1993 Ford 5.0 Mass-Air equipped Mustang along with an A9L ECU. Included in the instruction book are instructions that walk you through modifying the original Ford harnesses so that they work in a V8 Miata. If you choose to have someone else do the work for you, McCully Racing Motors can take your donor harnesses and modify them for you to make the electronic portion of the build as trouble-free as possible.
-Any other 5.0 Mustang harness/ecu can be used including earlier speed density systems and later SN95 systems. Both can be modified by McCully Racing Motors.
-Stand-alone aftermarket ECU's can also be used ether with the "stock" modified harness or with a completely new harness that you build or have built for your car. Pretty much any system that can be used on a Mustang can be used to build a V8 Miata including QuarterHorse, MegaSquirt and others.

-continued in next post-

MRM331

FAQ continued:

How do I make the Gauges Work?
Speedometer: The 1990 to 1997 Miata speedometer is cable-driven. The kit includes and adapter to mate the transmission end of the Mazda cable to the Ford speed sensor. Another option is to carefully remove the speedometer end of the Mazda cable and graft it on to the Ford Mustang cable. Both methods work equally well. The 1999 to 2005 Miata speedometer is electronic. The SN95 Mustang also has an electronic speedometer which it drives using the same speed sensor the earlier Mustangs have. *****It may be possible to drive the Miata speedometer with the Ford speed sensor signal-If anyone knows this for sure please let me know****
Oil Pressure: 1990 to 1994 Miatas have an actual oil pressure gauge with an electronic sender. The kit includes a small resistor that can be added between the Ford sender and the Mazda gauge to make the Mazda gauge work with the Ford sender. Another option is to use an adapter fitting to fit the Mazda sensor into the Ford block. The latter option is more accurate but both work. 1995 to 1997 Miatas can be fitted with the earlier gauge and sender. The actual gauge found in these cars is simply an idiot light made to look like an actual gauge. The adapters needed to fit a Mazda sender in the Ford block are a 1/4 NPT male to 1/8 NPT female reducer (991201ERL) and (if you are not using the Ford standoff pipe) a 1/8 NPT male to 1/8 NPT female 45 degree angle fitting (AT991501ERL).
Water Temp: As with the oil pressure gauge, the kit includes a resistor that can be added between the Mazda gauge and the Ford sender to make it work. Again, the better option is to fit the Mazda sender into the ford block with an adapter fitting. Note that both the Ford and Mazda systems have two separate coolant temp sensors, one is for the gauge and one is for the ECU. On the Miata, the gauge sender is the very small, one wire one on the back of the Miata cylinder head. It's about the size of a large bean. On the Ford, the gauge sender is located on the driver's side of the lower intake manifold. The sender on the other side of the manifold bolted into the heater hose manifold is the ECU sender. That sender must be Ford. The adapter needed to fit a Mazda sender in the Ford lower manifold is a 3/8 NPT male to 1/8 NPT Female reducer (991203ERL).
Tachometer: The Mazda tachometer can be adjusted via a small plastic screw found behind the face. Hook it up the the Ford tachometer wire and, using another tach as a reference, adjust it to be accurate at the range you feel is most important. This method will get you a 2000-3000 rpm range where it is fairly accurate, the rest of the range will be a bit off. The only way to make it 100% accurate is to have a custom face made for it which can be done by Adam of RevLimiter.net.
Fuel Level: This gauge is completely unaltered and requires no modifications to make operate in a V8 Miata.


Do I have any differential options other than the Ford 7.5?
Since the only thing connecting the rear end of the drive line to the front is a driveshaft, you can use the rear end setups from any of the V8 kit venders (Ford or LSx) with the engine/trans part of any other. All eliminate the PPF (power plant frame) used in a stock Miata and require some degree of modification to the rear subframe.
Each will be discussed below:

#1-Monster Miata Ford 7.5 kit
Cost:
Advantages:
-Uses smaller yet slightly heavier iron case 7.5 differential listed above. The added weight in the back of the car helps offset the added front weight which helps maintain a front-rear ratio close to the factory 50/50.
-The smaller size of the 7.5 makes exhaust routing fairly easy.
-The smaller outer CV joint diameter fits without any shock absorber issues.
-Lowest overall cost.
Disadvantages:
-7.5 inch differentials are no longer made and factory support is getting smaller.
-If you cannot find one with a factory limited slip unit the aftermarket ones are not cheap.
-Locating one in a junk yard with limited slip is getting harder.
Modification to rear subframe:
-A torque plate is welded to the front of the subframe to allow the front of the differential to mount.
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#2-Monster Miata 8.8 kit (I have personally never used this kit. If someone has please help me edit this)
Cost:
Advantages:
-Uses the same general design as the MM 7.5 kit
-Still fairly cost-effective (not sure of price increase over MM 7.5 kit)
-Uses the smaller 7.5 outer CV joints preventing having to move outer shock location
-8.8 differentials are still fairly common in junk yards and can be found in both iron case and aluminum case versions.
-A cheap (under $300) Ford limited slip carrier is still available from Ford Racing.
Disadvantages:
-Exhaust routing around an 8.8 is a bit more difficult than the smaller 7.5.
Modification to rear subframe:
-A torque plate is welded to the front of the subframe to allow the front of the differential to mount.
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#3-V8 Roadsters/Flyin’ Miata kit – GM Getrag (I have personally never used this kit. If someone has please help me edit this)
Cost: $1650 to $2760 + cost of differential itself
Advantages:
-Differential can be purchased entirely new
-Several different levels of kits available
-Kit includes driveshaft (cost to have it matched to a T5 may be more)
Disadvantages:
-Highest cost
-Spotty history of GM Getrag differentials in several OEM applications-may be fixed by this point.
Modifications to Rear Subframe:
-Welding of several “tabs” to different areas to provide mounting points
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#3-V8 Roadsters/Flyin’ Miata kit – Ford 8.8 (I have personally never used this kit. If someone has please help me edit this)
Cost: $2250 to $2990 + cost of differential itself
Advantages:
Disadvantages:
Modifications to rear differential:



-Still more to add-

-Jason

tbone heller

Great write-up! To add to it, there is also some fasteners that need to be purchased as outlined in the assembly manual. Be sure to keep the 12mm 12point driveshaft-to-flange retaining bolts when you purchase your differential.

rookie

Fantastic write up. This is gonna save a bunch of questions for a lot of people. Thanks Jason. Can you add the type or size or where to get the fittings for the oil pressure and water temp senders to get them to work correctly? That will save more time.

MRM331

I have those part numbers on file. I'll add them in.

-Jason

charchri4

This is a Ford rear end tag.

Thunderbirds and Cougars that show an "E" axle code on their door pillar tag usually have a 7.5 inch limited slip differential. Once you see that look under the car and look at the differential itself. If it reads "3L27" it's a Limited Slip with 3.27 gears (ideal for a Ford 5.0 Miata). If it reads "3.27" it's an open 3.27. These are the axle codes:

Code Ratio
1.. 3.58C
2.. 3.55C
4.. 3.42C
5.. 3.27C
6.. 3.73C
7.. 3.07C
8.. 2.73C
9.. 3.31C
53.. 3.58C
A.. 3.63C
B.. 2.47C
D.. 3.42L
E.. 3.27L
F.. 3.45C
J.. 3.85C
K.. 3.55L
M.. 2.73L
R.. 3.45L
W.. 3.73L
Y.. 3.08C
Z.. 3.08L

If you find a W let me know and consider it sold...

http://www.coolcats.net/general/axleinfo.html

MRM331

I'm adding a few blank posts so that I can add all info to the top. I'll delete any we don't need when its done.

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MRM331

I'm adding a few blank posts so that I can add all info to the top. I'll delete any we don't need when its done.

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MRM331

I'm adding a few blank posts so that I can add all info to the top. I'll delete any we don't need when its done.

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MRM331

I'm adding a few blank posts so that I can add all info to the top. I'll delete any we don't need when its done.

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MRM331

I'm adding a few blank posts so that I can add all info to the top. I'll delete any we don't need when its done.

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jonbon88

Hi Jason,
I am posting this with information about the SN 95 T-5 transmission speedometer. As you know the speedometer and sending unit is electronic for the SN 95 Mustang. All that is needed is to replace the sending unit in the transmission with a 93 Mustang mechanical one and install the red gear and cabe adapter. The speedometer does seem to read a little off in the higher gears. Reads higher. I am going to compare it with GPS to find out the difference.

sebz

Toi dont have to replace thé unit Just add the mustang speedo cable

MRM331

So the units are the same? That's what I thought.
You can use the electronic signal to work an NB electronic speedometer I believe.

Bernie51

My Canadian 1990 Miata has been converted to Ford engine etc by the previous owner. I know nothing myself about the mechanics or electrical works of a car.
The power to the DRL (which is also the signal light) fluctuates from a high of 11.5 down to 0.
Can you tell me very specifically the route of the power wire (green in this car) backwards from the light itself back to the signal light arm.
Thanks

Lateralgeez

Headers:
Hedman 89500 (passenger side) 88400 (driver side)
Hedman 88420
Martin's
Regular shorty headers facing forward

Do these work?
Speedway 9300201 block huggers - work with GT40P heads, requires mini starter