DIY Duraboost Mustang

pres589 (djronnebaum) said:

I'm not a mechanical engineer but I did own an SN95 and read about this a lot. I remember hearing about Fox Mustangs in college that were basically stock with sticky tires that would tear up the area of the car's tub known as the 'torque box' during drag racing.  Something had to be wrong; how could basically straight-line forward acceleration cause this?  Binding is all that made sense to me at the time.

Thin stampings spot-welded to the tub is all the explanation really needed.  Straight line forward acceleration SHOCK LOADS (slicks, remember?) pulling the upper control arms back and pushing the lowers forward.  The tub wasn't expected to do that sort of thing and it was engineered in Ford's "eh, good enough" era.

It gets more fun when track-experienced cars simply start opening up at the spot welds for the floor.

Well, it was also engineered when a Ford 302 from the factory generated 140 net horsepower and the redline was something like 5,000 RPM.  And a lot of those early cars shipped with 2.3 four's or that wheezy inline six from the Falcon.  

In retrospect I should have looked a lot harder at E36's.  I wanted a nice to drive RWD convertible with a back seat and a manual trans.  Oh well.

¯\_(ツ)_/¯ said:

Knurled. said:

Ford's "Escort Bible" describes how to make a proper 4 link to locate the rear axle. 

This, and it boils down to the longest 4 equal length parallel links you can fit- that's what I'd do if I were building a car with a live axle, regardless of size and original configuration.

That said, if you want a Mustang, I'd much rather be figuring out how to get weight out of a later S197 V6 than berkeleying around with the flimsy shell of a Foxbody (I rallycrossed one) or SN95.  If you're going to run something where it all needs to be reinforced, at that point I'd go older and lighter.

I'd do it with three.  Two lower, and one upper.  Not quite how Alfa did it- I would put the link on the other side of the diff to counter torque wedge.  Then add a lateral locator (panhard, Watts, etc), and you are all done.  Interestingly, that's how the modern Mustangs became, and is a HUGE reason why your S197 suggestion is so good.

There was a chance that the SN95 would have done this, but the big issue was that nobody wanted to spend the money changing the rest of the car to make up for it.  

For the OP, given the choices, I'd rock the XR4TI, as the idea would not only pay homage to the Cosworth version, it would be a lot better.

Mustangs are cool, and I support your goal, but Is there a reason why you're not starting with either a Duratec Ranger or NC Miata?

A Duratec Ranger weighs 3000lbs, has tons of room for tires, and a handful of appropriate aftermarket suspension pieces. Leaf springs in the rear probably aren't ideal, but tons of prerunners deal with them well enough. Or if you're planning on fabbing a new link style rear suspension for the Mustang you could do the same for the Ranger. 

An NC Miata weighs around 2500lbs and has a much less controversial suspension than the Mustang. It's much better balanced than the Mustang or Ranger.

The biggest thing with either of these options is that you don't have to spend time or money on a swap. Everything is already there and designed to work well. No engine mounts. No wiring. No transmission/clutch/bell housing puzzles. No stand alone ECMs. Just add boost to get your power goals.

¯\_(ツ)_/¯ said:

To completely go off the established track of this thread... do you really want an XR4Ti?  Because you know I have a couple of them.

you do? i thought you just had the one parts car.

In reply to alfadriver :

Ford did the 4 link to positively locate the leaf sprung Escort axle, first with little 16"-ish long links for the Mk1 and then later the longer links for the Mk2.  Toyota seems to have directly copied it when they made the Celica Group B car, and MRTE appears to have left the lower links (19" long already) stock and just added parallel even-length uppers for the Group B RX-7.

A 3 link positively eliminates bind, of course (and it's what I've done on my cars, because I started with cars with long parallel lower links already) but the nice thing about the Ford way of doing it is that it is simple to do.  Cut two slots in the floor, weld in a couple plates, cover it over, done.

Worked good enough for 240-odd horsepower Escorts and 400-odd horsepower Celicas.

In reply to Knurled. :

Having talked to a Trans Am team that had a 4 link and a 3 link 'Vette- they very much preferred the 3 link.  So....

In reply to alfadriver :

One advantage of the 3 link is that you can play with anti-squat to your heart's content without introducing any bind.  With a 4 link you are pretty much stuck with something neutral if you want to keep happy articulation (and IIRC, those shock turrets welded in for that pic are for something better for around 8-9" of shock travel)

I like a bit of antisquat myself, but I'm also not doing stage rally, which has different priorities.

In reply to Knurled. :

I also like that you can tune the torque wedge with the 3rd link, too. 

Gaunt596 said:

¯\_(ツ)_/¯ said:

To completely go off the established track of this thread... do you really want an XR4Ti?  Because you know I have a couple of them.

you do? i thought you just had the one parts car.

Well yeah, and the rally car.  But I'm not so attached to either of them that I wouldn't be willing to have a discussion if you wanted one- whether that means the parts car or the rally car is really up to your budget 

I do want to get another season in in the rally car, though.

In reply to Knurled. :

You can change antisquat a bit with a 4 link by moving the body side of all 4 arms up or down a bit, IIRC.  I'm pretty sure that effect is why a lot of 4 links lose antisquat as you lower ride height.  And that change shouldn't affect bind. 

alfadriver said:

In reply to Knurled. :

I also like that you can tune the torque wedge with the 3rd link, too. 

Now, before I continue, my current 3 link does have a bit of that in the geometry by design.

What I have gathered from people who have done it to get 100% torque reaction/negation, is that the other compromises you get negate the benefits.  Part of me wonders how much better it'd be if the brake calipers were floated on their own linkage.

My take is, it's better to run shorter gears so that driveshaft torque gets lost as noise relative to the other forces at play.  I loved my 4.78s, I tried 5.43s and found that no, I can't shift 2-3 worth a damn when bumping around on course.

I Had ruled out the duratec ranger as it's too new, and since there's no plug in aftermarket ECU for it, getting it through the plug in emissions testing would be.... interesting. NC miatas could work, but I'm not sure if I would fit in a caged miata, being 6"2 with a tall torso. They are also very expensive in my area. 

In keeping with the mustang idea, looking into the suspension more, I see where there are a lot of inherent weaknesses and geometry problems with the factory design. A three link conversion would be pretty much mandatory, and add a decent amount of cost/time commitment.  Would perform nicely when finished, though. 

¯\_(ツ)_/¯ said:

Gaunt596 said:

¯\_(ツ)_/¯ said:

To completely go off the established track of this thread... do you really want an XR4Ti?  Because you know I have a couple of them.

you do? i thought you just had the one parts car.

Well yeah, and the rally car.  But I'm not so attached to either of them that I wouldn't be willing to have a discussion if you wanted one- whether that means the parts car or the rally car is really up to your budget 

I do want to get another season in in the rally car, though.

I wouldn't feel right buying your stage car, but if the parts car shell isnt a complete rust bucket I think I'd beinterested. 

Gaunt596 said:

A three link conversion would be pretty much mandatory, and add a decent amount of cost/time commitment.  Would perform nicely when finished, though. 

FWIW I am at this exact point in my build now. Over the next 2-4 months I will be cutting out the factory upper link mounts and fabbing up a 3rd link mount. I have swapped my rear axle over to an 8.8 posi out of an Aerostar and will be using the factory 3rd link mount on the side of the diff. Adding a panhard bar, etc.

So Ford controlled the leaf rear of the mk1 and mk2 Escort race cars with a proper four-link setup?  

My Capri was so happy to axle wrap.  If I were to hand you all a big bin of Legos and another Capri (this is a real Capri, not the Mustang one, nor the Aussie/Mazda thing), would you all do that same basic setup again?  Three-link maybe?  This is a mental exercise and nothing more, unfortunately, involving a '73 Capri that is almost exclusively street driven.

In reply to pres589 (djronnebaum) :

In your case, I'd do the 4 link because you can buy entire kits of parts for under $400 including shipping.  That is chassis side and axle side brackets as well as the links.

Gaunt596 said:

I Had ruled out the duratec ranger as it's too new, and since there's no plug in aftermarket ECU for it, getting it through the plug in emissions testing would be.... interesting. NC miatas could work, but I'm not sure if I would fit in a caged miata, being 6"2 with a tall torso. They are also very expensive in my area. 

Duratec Rangers started in 01. They're older than the NC Miatas. Reprogramming the factory Computer is the easier and likely cheaper route compared to aftermarket or standalone ECUs. I'm not sure how in depth an OBD2 emissions test would be in your area. Do they automatically fail people with any ECU modification? That would mean nobody is legally running vehicles with aftermarket forced induction, more boost than stock, cam swaps, etc. I don't have emissions testing in my area, but from what I hear, most OBD emissions tests really just look for fault codes, and if that's the case where you are then it should be possible to pass the test with a reprogrammed computer

STM317 said:

Gaunt596 said:

I Had ruled out the duratec ranger as it's too new, and since there's no plug in aftermarket ECU for it, getting it through the plug in emissions testing would be.... interesting. NC miatas could work, but I'm not sure if I would fit in a caged miata, being 6"2 with a tall torso. They are also very expensive in my area. 

 

Duratec Rangers started in 01. They're older than the NC Miatas. Reprogramming the factory Computer is the easier and likely cheaper route compared to aftermarket or standalone ECUs. I'm not sure how in depth an OBD2 emissions test would be in your area. Do they automatically fail people with any ECU modification? That would mean nobody is legally running vehicles with aftermarket forced induction, more boost than stock, cam swaps, etc. I don't have emissions testing in my area, but from what I hear, most OBD emissions tests really just look for fault codes, and if that's the case where you are then it should be possible to pass the test with a reprogrammed computer

mine polls for check engine light function, VIN, and the entire suite of emissions control codes. and while a reprogrammed computer can pass those tests, its very limiting and your stuck with whatever features the factory put in. so any form of Anti Lag, Launch Control, ECU regulated boost control ETC all goes out the window. your only allowed one code to show up as "not ready/disabled" so i cant just go in and turn the codes off, meaning that you have to deal with the ABS system, and the Airbag ECU, as well as the body ECU, to keep the CEL off. far easier to get a pre emissions car and then rip it all out and start from a clean sheet. a plug in ECU is a partial compromise, since I could limp the car to emissions testing, get it through, and then put the aftermarket ECU back in.

In reply to Gaunt596 :

I don't mean to keep harping, and I haven't tinkered with an NC Miata to know for sure if it's the same or not, but at least with the Duratec Ranger, there is no body ECU, no airbag ECU, no computer controlled ABS, etc. From a software standpoint, I think it would really just involve changing fueling and spark timing values within the factory PCM, and that doesn't seem like something that would fail your emissions tests. But I'm just a stranger on the internet, so...

If you want things like computer controlled antilag, or launch control, then those are obviously off the table with the stock PCM, but they'd be off the table with most anything before 2012 too. And aftermarket ECUs that can do those things are probably fairly pricey right?

If what you want is a 250hp Mustang with better weight balance, it seems like aluminum heads for the 5.0 and a tubular K member/control arms would probably take a decent amount of weight off the nose of the car (100lbs or so) and be super easy.

If what you want is a RWD, turbo/Duratec/MZR powered rallycrosser, it seems like Rangers or Miatas would both be lighter than the Mustang and may fit the bill with less hassle/work.

If what you want is a turbo/Duratec swapped Mustang with a bunch of fancy anti-lag and traction control tech then I look forward to your build thread!

I'm not trying to discourage your idea, because I think it has tons of potential. But it does represent a big undertaking, and projects like this tend to languish without ever being completed because of the amount of work needed.

Since the idea of starting with a Ranger keeps getting mentioned, I'll just leave this here:

https://www.locostusa.com/forums/viewtopic.php?f=27&t=19110