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Discussion Starter #1
Hey there... I'm brand new to the FFCars community and my father & I are starting our journey through the build of our very own Mark IV... hoping to start this coming winter. I was hoping to get some advice and guidance on a few questions we have... the first of many, I'm sure!

We're on a fairly modest budget and looking to build pretty much a standard Mark IV with no major upgrades (i.e. no IRS, no ABS). Looking for a project that'll be fairly simple to do and a resulting Mark IV that we can drive often and not for the track at all.

Hopefully the following makes some sort of sense... but it could be quite likely that I'm entirely off base!! :001_smile:

Our original plan was to purchase a Mark IV Base Kit and then use a '98 GT 4.6L donor car to complete the Mark IV. I started putting all the numbers together to estimate our overall costs using the donor with the base kit. Aside from the extras we will need/want (tires, wheels, body cutouts, powder coated chassis, visors, wings, heater, passenger roll bar, etc)... we also estimated costs associated with the donor, such as the steering rack adapter, replacing the rear axle (to be able to use the FFR 15" Halibrand Replicas w/o the ABS) and sending out the wiring harness to get trimmed down for us. We were then going to sell whatever was left of the '98 GT to recoup a small bit of money.

I then had an idea of a different approach. The '98 GT donor that I have is a very low mileage car (less than 65k), is in perfect condition inside and out and I was able to get it for a pretty good deal. Because of that, I wondered what the cost breakdown would look like if I ordered a FFR Complete Kit and then just use the '98 GT for the engine & trans and possibly the rear-end. My thought on this is based on the assumption that I might be able to maximize the amount of money I could recoup on selling what's left of the '98 GT. I'm thinking I could get quite a bit more out of a '98 GT that just needs a motor & trans than I could if it were completely stripped of everything I needed for the base kit. I'm not suggesting that it'll save me money or even allow it to be a break even deal, but if the difference was only a few thousand... I'd rather have the new parts instead of the donor parts.

Soooo... here's how I see my options:

1) FFR Base Kit
+ existing '98 GT Donor (for everything)

2) FFR Complete Kit
+ existing '98 GT motor/trans
+ existing '98 GT rear end
(sell what's left of the '98 GT w/o the motor, trans, & rear-end)

3) FFR Complete Kit
+ existing '98 GT motor/trans
+ find another Mustang rear-end to use in the Mark IV
(sell what's left of the '98 GT w/o the motor & trans... but WITH the rear-end)

My questions are...

A) Which option would you choose? :001_smile:

B) If I went with the complete kit and decided to use JUST the motor & trans from the '98 GT that I have, what rear-end would you recommend that we get, where would you suggest to get it and how much would I expect to pay for it?

C) If I went with the complete kit and decided to use just the motor & trans from the '98 GT that I have, what happens with the wiring harness? I thought the complete kit comes with a chassis harness, but I assume I would still need some sort of wiring harness for the '98 GT EFI engine/trans? Is it better to take the engine/trans harness from the '98 GT or somehow purchase a new harness for the '98 GT engine/trans to be used in the Mark IV?

OK... now that I just made my questions WAY more complex than they probably are!!... any help, advice, suggestion, recommendation would be incredibly appreciated... or maybe it's to tell me I'm WAY over-thinking it! :lol:

Thanks kindly,
Dave
 

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FFCobra Master Craftsman
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Dave if you are building a roadster I think you will need to plan on a different rearend. If I remember right that rear is too wide for a roadster but will fit under a coupe. Someone correct me if I'm wrong about the roadster. I am doing a complete donor build of a coupe with a 2002 GT donor so if you have any questions related to that ask away or check out my blog for pictures and descriptions
 

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Dave if you are building a roadster I think you will need to plan on a different rearend. If I remember right that rear is too wide for a roadster but will fit under a coupe. Someone correct me if I'm wrong about the roadster. I am doing a complete donor build of a coupe with a 2002 GT donor so if you have any questions related to that ask away or check out my blog for pictures and descriptions
I used a 98 GT for my donor and it turned out awesome, I used the rear end along with the rest of the drive line. The rear end is a little wider so you can't put as big of a tire in the back but it will work just fine.
 

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Do you really have your heart set on that 98? a 99 to 04 will get you the PI SOHC
There are some big differences in the engine and your ability to add more power
and available speed parts
I.E. one of the big cheap HP gains is to swap a set of PI heads and intake to a 98 and earlier car
3650's have some 1-2 shift crunching that lead to as needed recalls.
I'm not trying to discourage you but a PI SOHC and a later 3650 may save you bucks down the road.
Milage is not a big deal on these engines ask any taxi fleet owner
I went the donor route also stating with a 02 GT with 24k on it there is almost none of it left at this point due to build creep and many happy miles of driving
 

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The rear end can be narrowed to fox width by getting rid of the abs and running fox width axles for wider wheels, so that is a non issue. There are even options to keep abs with wider wheels, but that gets complicated.
It is your decision, but many of the mustang parts will need painted and rebuilt, even with low mileage. Just depends if you want to do a bit of extra work to save some money. The 98 is only rated 225hp, so you may be wishing for more hp quickly. Luckily, it responds great to mods (especially the pi swap). Also, seals deteriorate, regardless if mileage, expect valve seal and main seal leaks, just due to age. Again, mileage isn't so important. I have a 97 gt with over 220k and runs great. Just a small puff from the valve seals occasionally.
 

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Your rear end will work with some modifications. A '94-'98 rear end can be used with the FFR 15X9 wheels if you bring it to Fox width by swapping axles and caliper brackets with the package from North Racecars:

North Racecars Brake Solutions

'99 and later use a wider housing and can not be brought to Fox width without cutting; '93 and earlier are 4 lug with drum brakes. There is no "off the shelf, straight from the car" Mustang rear that will get you Fox width with 5 lug discs without modification.

Jeff
 

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Discussion Starter #8
Thanks so much for the responses! Yeah… I figured out pretty quickly that there would be a rear-end mod of some sort no matter what. If I went with a ’93 or earlier, I’d need the lug conversion and if I went with the ’94-’98, I’d need to lose the ABS and swap the axles & calibers.

The ’98 was definitely not my first choice and was originally thinking of going ’99 or newer to get the extra HP, but availability & price was the deciding factor on the ’98. For now it’ll get us in the Mark IV and then leaves us some room for engine upgrades later down the line by either adding mods to the ’98 engine or eventually swapping out the entire engine/trans as another project 10 years from now! This a project my father and I have wanted to do for quite some time and he wants to make sure we do it while he still can… that means making some sacrifices in order to get started sooner rather than later.

I’ll definitely be pulling the ’98 GT engine & trans for the build, but since I think I might be able to get a better return on what’s left of the ’98 GT as a whole if it has the rear still in it, I think I’m going to look for another rear… even if it’s the same as what I have. Any recommendations on where to look for a used rear?

How bout my questions regarding the wiring harness? From what I understand, the complete kit will come with all the wiring for the chassis, but I’ll need a different harness for the ’98 EFI engine/trans. Is there somewhere I can get that harness?

Thanks kindly,
Dave
 

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FFCobra Fanatic
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If you can find an old turbo t-bird rear the sticks had 3.55 posi the autos have 3.91 get a set of ranger axles and you got five lugs there's a particular ranger years but I've forgot which
I have one in my car but got all the brake mounts and axles from North race cars
When you get to wheels go with the bigger 17 inchers rubber for 15's is getting tough to find at good prices
A wire diet is the way to go but the first cars just had the whole thing stuffed in there and got trimmed out later you can get a lot of help here with that if you do it yourself but it's a big job
 

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I had a 96 GT donor but put in a 98 Cobra motor. I learned a few things along the way. I wanted 315's in the rear so I went with North Racecars fox length axles and added his cobra brake brackets. I modified the rear GT calipers to fit Cobra rotors that I upgraded to (they are vented and slightly bigger than GT, and I added ABS ala GregM on the Forum. Let me know if you have any questions on the rear config.

If you use the 98 GT motor, you will have less HP than you would if you used a Performance Improved (PI) version in the later years. If you super/turbo charge it, doesn't matter so much.

You will need some kind of engine management for the EFI as you have things like Throttle Position Sensor, Mas Air Flow Meter, Crank Position Sensor, Wasted Spark coil packs, fuel injectors and so forth. Probably the easiest would be to have Art at Wirediet.com clean up the donor wiring harness (strip out unneccessary stuff and shorten wires) and have your ECU from the donor re-programmed for no PATS, EGR, CATS, etc.

Or you can tackle that yourself leaving all of the smog/antitheft stuff attached from the donor. Also the ford ECU controls things like the radiator fan through the PCM in the donor and the gas vapor recovery system. So you have to be careful what wiring harnesses you need to save, even if you use the MarkIV complete kit chassis harness.

Telorvek makes a wiring harness kit that lets you create a new harness for the donor ECU and has terminal connection box for troubleshooting. You can mount the ECU in the trunk if you like. But you still have Pats/EGR/programming issues listed above.

Or you can go a little exotic with an aftermarket EFI and it's associated wiring harness for their computer. I am going with a MegaSquirt and the wiring they provide. I have to come up with connectors for the injectors, coils, sensors, etc. And there is a huge "learning curve" to programming it myself. But what a journey it is turning out to be. hth Bill
 
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