The "Mustang II" IFS Real Info & Debate Thread

mrmustangman357 · Sep 19, 2007

500KR, what you did is what less than .01% of any MII owner would do. You essentially put a frame in your car. You ask if its strong? The question is about loading of the MII applies to its as-installed config, so your app wouldn't apply. I would still triangulate it to the cowl, however, because there are still bending forces, similar to how a semitrailer bows and flattens on a bumpy road

P.S. You are going to have a nose-heavy car

reenmachine · Sep 19, 2007

mikethebike said:
The load is distributed through out the UNI-BODY structure. I think that is why we have triangleulated export braces instead of strut bars.

I'll quote myself from above in case you missed it:

reenmachine said:
...it just seems that people think that since it's a unibody that means the load is shared equally by all of the various members. I maintain that a disproportionate amount of the load is carried by the frame rails...

Gailahan · Sep 19, 2007

I think that when you weld a MII suspension into a car that is in terrible shape ie. rusted through cowl that is when all the problems erupt. Any car that is rusted through is going to have problems no matter the suspension. There are absolutely no issues structurally speaking welding a MII suspension into a mustang that is in halfway decent shape.

rbohm · Sep 19, 2007

bnickel said:
there is a guy on the corner-carvers forum named Boss Bill who has done some torsional rigidty stuff on the 65-66 cars already and our own SN-65 has done some as well.

one of the things i found most surprising was that after installing sub frame connectors (welded in) there wasn't much gain in torsional rigidity. that's not to say that the chassis wasn't stiffened up a bunch, just not much going from the left front to right rear (torsionally)

the reason is that just adding sub frame connectors isnt enough, since they only tie the front and rear sub frames together. i keep saying that in order to truly stiffen the chassis, you need to tie the sub frame connectors to the rocker panels as well with stringers, and build a center cage like the tcp cage. this will stiffen the chassis substantially, and then any change to the suspension is magnified because the chassis is no longer flexing like it was when it left the factory. at that point the mustang ll suspension becomes a moot point unless you are wanting to install a big block in the 65-66 cars. ride and handling improves because the suspension is now working properly, and you dont need the stiffer springs the shelby's got.

Rusty67 · Sep 19, 2007

I'm not going to try and post something in here that I don't know about, that would be dumb. I've read the entire thread so far and there is some interesting stuff.

Something that was briefly mention but not really discussed is the fact that no matter what gauge steel is used, when the steel is shaped or formed it becomes stronger. I think that the shock towers provide quite a bit of support being there because of the way that they are physically designed. The stamping of the steel makes them hold loads and handle force in certain directions better.

I have always said that to do an MII setup right requires more then the kit. Additional bracing is required if you cut the shock towers out. The reason I always tell people not to go with the MII kits is that they seem to believe that all they need to do is install the suspension and not worry about the additional structural bracing that should be installed. If a person says they are actually going to do it right and put in the additional bracing I still don't like going to the MII setup but at that point they are doing it right so I say go ahead.

Also, I think a lot of people like the MII setup because it isn't stock. I think there is a tendency to believe that because a part is not stock that it is better or that having something different then everyone else will help them stand out and make them feel better about thier car. People shouldn't do things to make other people happy, they should do things to make them happy.

reenmachine · Sep 19, 2007

Rusty67 said:
I have always said that to do an MII setup right requires more then the kit.

Others do too and this is why I started this thread. Why have you always said this to people? Based on what direct experience or evidence?

Rusty67 said:
Additional bracing is required if you cut the shock towers out.

You state this like it is universal fact. Again, why exactly is it true?

Rusty67 said:
The reason I always tell people not to go with the MII kits is that they seem to believe that all they need to do is install the suspension and not worry about the additional structural bracing that should be installed.

Any why exactly is this a bad idea? What will happen to them?

I don't mean to pick on you, but your post is a good example of so much of what I am talking about. Statements made to sound like facts, but not backed up by any type of evidence or personal experience.

Rusty67 · Sep 19, 2007

Shock towers may not support the load of the entire car to the same extent that the frame rails do but when you remove that much metal from a car and don't compensate for it you are going to have adverse effects. I think its common knowledge by this point in the thread that lack of reinforcement after removing the shock towers makes for an undesirable ride. I suppose I assumed it was understood by this point in the thread.

reenmachine · Sep 19, 2007

Rusty67 said:
Shock towers may not support the load of the entire car to the same extent that the frame rails do but when you remove that much metal from a car and don't compensate for it you are going to have adverse effects.

Like what? And how do you know it hasn't been compensated for by the kit's frame rail reinforcement plates and the huge welded-in crossmember?

Rusty67 said:
I think its common knowledge by this point in the thread that lack of reinforcement after removing the shock towers makes for an undesirable ride.

I disagree. Nobody has said that they did the install this way and got an undesirable ride. 10secgoal said that he rode in a MII-equipped car and that it had cowl shake, but he then said that for all he knew it could have been that way before. Not exactly damning evidence.

There have been several others post that they did the install without anything additional and it works great with no ill effects. What about them?

I have also done the install without anything additional (Heidt's) and the result was wonderful.

Rusty67 · Sep 19, 2007

Ok, look at the car with the hood open. If you remove the shock towers and don't make up for the missing material the car is going to be missing something structural which is going to cause the chasis to flex. If you don't make up for the missing support the car is going to ride like crap. Puting in the proper bracing would make up for it and keep the car from flexing due to the missing shock towers.

jp51mustang · Sep 19, 2007

Don't the shock tower "patch panels" make up the material?

wicked93gs · Sep 19, 2007

they would if they were welded in...but on a lot of kits they are bolt in...which doesnt really help a unibody car....

reenmachine · Sep 19, 2007

Rusty67 said:
Ok, look at the car with the hood open. If you remove the shock towers and don't make up for the missing material the car is going to be missing something structural which is going to cause the chasis to flex.

Not quite so simple. The loads are applied somewhat differently, and the huge welded-in crossmember immensely stiffens the front end.

Rusty67 said:
If you don't make up for the missing support the car is going to ride like crap.

Who says? Yet once again where's your evidence? What about the many here, including myself on numerous occasions, who have done the standard install with great results (excellent ride, excellent handling). Are you unable to put away your preconceived notions in the face of direct testimonial from people who have actually been there and done that?

If many people say something counter to what you believe you ignore it, but if one person says something that may support your belief you hold it up like the holy grail...

reenmachine · Sep 19, 2007

wicked93gs said:
they would if they were welded in...but on a lot of kits they are bolt in...which doesnt really help a unibody car....

True to some degree. It's always better to weld them in from both a structural and aesthetic standpoint. However, bolt-in patches can still contribute to the structural integrity of the unibody. If you think about it, a panel with a bolt securing it every 4 inches isn't really different than a panel with a spot weld securing it every 4 inches. As an aside, welding the entire seam helps, as it does on the entire car. That's something a lot of people do to stiffen the unibody with good results.

66Runt · Sep 19, 2007

Hi Pete,

How does the cross member support loads in the vertical plane at the front torque box/toe board junction?
Which will provide a finer level of moment control give the same width track; shorter or longer control arms?
Which provides a greater potential for progressive damping and heat dissipation, given the same suspension travel: longer or shorter shocks/springs?

My personal opinion is that front suspension is just part of the overall package. The M-II (again in my opinion) is a viable choice when looking to open up the engine compartment to increase the air flow around an engine, or when there is just no room due to a larger engine being installed.
That said I would not choose this combination in a racing application due to the lack of tuning available from the compact structure.
As far as the whole flex issue goes (IMO) it's a matter of using the front sheet metal to build a truss. I'm not even sold on sub cages. I think if properly engineered, stamped panels welded in place would work as well if not better, based on the size and variations of "boxing" that can be provided.
Even a Grigg's suspension would work like crap if not properly installed. (IMO) basing a suspension package on someone’s personal experience is not relative to the quality or design of the product.

reenmachine · Sep 19, 2007

Valid points all.

66Runt said:
How does the cross member support loads in the vertical plane at the front torque box/toe board junction?

It does not. What it does do is increase the torsional stiffness of the front subframe. It also essentially eliminates relative motion between the left and right side suspension mounting points, which is a lot of what the export brace/monte carlo bar & cowl structure are meant to do on a regular suspension.

66Runt said:
Which will provide a finer level of moment control give the same width track; shorter or longer control arms?

Longer.

66Runt said:
Which provides a greater potential for progressive damping and heat dissipation, given the same suspension travel: longer or shorter shocks/springs?

Longer.

I see where you're going with this, and that's not what the discussion is about. I've repeatedly stated that I'm not arguing that the MII is the perfect suspension for all applications or that it's the highest-performance setup. I simply set out to counter the mostly unfounded and oft-parroted claims that installing a MII suspension ruins your car's structural integrity.

66Runt said:
My personal opinion is that front suspension is just part of the overall package. The M-II (again in my opinion) is a viable choice when looking to open up the engine compartment to increase the air flow around an engine, or when there is just no room due to a larger engine being installed. That said I would not choose this combination in a racing application due to the lack of tuning available from the compact structure.

Nor would I choose it for a racing application. But it's up to the task of street performance and spirited driving. Not that compact structure means that it can't perform. Try to hang with a shifter kart next time you're at the track.

66Runt said:
basing a suspension package on someone’s personal experience is not relative to the quality or design of the product.

Correct, just as trashing a suspension system based on no real evidence or even that personal experience isn't an indicator of the quality or design of the product.

ron67fb · Sep 19, 2007

The big pink thing is the apron, where the shock tower is bolted into. F is the suspension force at rest, bump, whatever. Now, leaving the apron in but having a gaping hole where the tower itself used to be, is that so bad? After all, the square part of our "pink thing" is still there, although with less triangulation since the middle part is now gone. Triangles are more resistant to twist than squares.

I also don't see how a crossmember will provide much torsional rigidity when simply welded onto the frame rails. The mount should be extended onto the apron structure; remember triangle. Does a large crossmember help? Yes. Should the crossmember support ALL the torsional loads? I personally think not.

mikethebike · Sep 19, 2007

66Runt said:
Hi Pete,

As far as the whole flex issue goes (IMO) it's a matter of using the front sheet metal to build a truss. I'm not even sold on sub cages. I think if properly engineered, stamped panels welded in place would work as well if not better, based on the size and variations of "boxing" that can be provided.

Right. Back in the old days when Jag and Lola built unibody tubs with suspensions hanging off we called it a monocoque structure. Worked for the Lola that became the GT-40 and again for the GT-40 Mk.IV.

68GT500KR_Vert · Sep 19, 2007

It's more like this.

Or This:

ron67fb said:
View attachment 361981

The big pink thing is the apron, where the shock tower is bolted into. F is the suspension force at rest, bump, whatever. Now, leaving the apron in but having a gaping hole where the tower itself used to be, is that so bad? After all, the square part of our "pink thing" is still there, although with less triangulation since the middle part is now gone. Triangles are more resistant to twist than squares.

I also don't see how a crossmember will provide much torsional rigidity when simply welded onto the frame rails. The mount should be extended onto the apron structure; remember triangle. Does a large crossmember help? Yes. Should the crossmember support ALL the torsional loads? I personally think not.

reenmachine · Sep 19, 2007

I'm gonna let it ride for a while to see where the awesome paint shop action leads!

68GT500KR_Vert · Sep 19, 2007

Reen,

I'm just illustrating that the force makes no difference on the shock towers because the MII suspension is on the frame rails and the frame rails and body extend back and work like a leaver. There is no weight in the engine compartment sheet metal.

It's just like you said, when it was original the springs put weight on the shock tower, but the shock towers too were welded to the frame rails. the only thing i could see the braces for were tower stability. and add rigidity to the compartment's walls. But the car's weigh has nothing to do with the sheet metal; it's on the rails.

Basic engineering.

The "Mustang II" IFS Real Info & Debate Thread

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