Project OCD (I bought a car to build tools???) - '67 Mustang Coupe

[ATOMonkey]

How did you set the anti-squat on the subframe? What reference points did you use, measurements, etc?

Also, did you take into account drive shaft angle when you set the anti-squat?

Thanks in advance, these are some of the questions I've been mulling over before I start cutting pieces off of my subframe.

[modmotor46]

Hey ATOMonkey, great questions! I mulled over a lot of them for several months before making any cuts; probably the most time I've spent on a single aspect (rear suspension) of the car yet!!! I do need to give credit to Maximum Motorsports, those guys provided a lot of help in figuring this stuff out.

The reference points used for the IRS are the geometric centers of the LCA mount points. The front LCA on a stock 2003 Cobra is roughly 2.51" higher than the rear. From the beginning of building this car I set the entire car's chassis based on Ford reference material (I used my shop floor as the datum line). As you can see in some of my pictures I used several jack\acme screw type stands to adjust the levels of each reference point. From that point the chassis was set.

I decided to cut the stock IRS mounts off as I didn't want to use any type of bushing. I thought the cradle would be more rigid bolting it directly to the frame, it should also serve to stiffen the frame up slightly too. I designed the brackets to allow me to set the subframe between the Mustang's framerails, make my measurements\adjustments, tack the bracket plates in place then finish TIG welding them on my bench.

The picture below is a version of the measurements for my IRS with respect to the '67. I used Microsoft's Visio to draw and measure the dimensions (pretty cool and simple software for stuff like this). I’m still adjusting the cradle, wheel centerline and ride height to get a more aggressive ride height and anti-squat. Anyway, once those measurements are determined you can calculate the percent of anti-squat. Anti-squat is calculated by taking the Tangent of the IC angle (6.8 in this example) and dividing that by the CG height (h) divided by the wheelbase (l) then multiply by 100 to get the percentage. The formula in my example would look like this; TAN(6.8) / (19/108) * 100. The CG in my calculation is part of the "napkin math" since I don't really know what it will be yet. It takes quiet a bit of playing around with the numbers to achieve the desired results. The anti-squat percentage seems somewhat relative also. From what I've seen on some Corvette forums (good IRS references) their percentages are somewhere in the 60's.





For the pinion angle I plan on using Maximum Motorsport’s Aluminum IRS Diff Bushings. This kit is supposed to allow up to 4.5 degrees of adjustment and recommends a 3 to 4 degree setting. Although it will be a while before I have the drivetrain in it, I’m curious to see where the angle ends up ;-)


Danny,

[cobraguy65]

I think you will like the IRS. I recently replaced the control arm bushings on mine with delrin and added a ford racing diff cover. I have been very happy with the results and would recommend these modifications. Got my bushings from here www.fulltiltboogieracing.com

[ATOMonkey]

That is perfect! Exactly what I was looking for. Great work.

[Motorcitydak]

Cool car and nice to see you are doing it all yourself! That metal bender you have, was it really able to bend that thick plate? Very impressive and I will have to look into that. Also is that the vertical/horizontal band saw from harbor freight? I have been looking into that as well, how do you like it

[modmotor46]

I think you will like the IRS. I recently replaced the control arm bushings on mine with delrin and added a ford racing diff cover. I have been very happy with the results and would recommend these modifications. Got my bushings from here www.fulltiltboogieracing.com

Hey cobraguy65, Thanks for the info; I've been wondering about the FTBR stuff. I've been contemplating their products or Maximum Motorsports. The MM guys are really cool and I have some of their products on my '98 Cobra.

I just ordered some Dynacorn full quarters so I'll be spending the next couple of months working on that. As soon as those are done I'll focus back on the IRS bushings, etc.


Danny,

[modmotor46]

That is perfect! Exactly what I was looking for. Great work.

Thanks ATOMonkey, I'm glad the information is what you're looking for. I've learned a ton from other posts and hope to return the favor along the way!

[modmotor46]

Cool car and nice to see you are doing it all yourself! That metal bender you have, was it really able to bend that thick plate? Very impressive and I will have to look into that. Also is that the vertical/horizontal band saw from harbor freight? I have been looking into that as well, how do you like it

Thanks Motorcitydak. I'm learning a lot doing it all myself but man, it sure is taking longer than anticipated ;-) oh well, it's still fun as hell!!!

The metal bender kit from Swag Offroad rocks! With a 20ton press it's surprising how simply it bends 1/4" plate. Don't get me wrong, you have to apply some pressure to the jack handle but the bends are nice and clean and straight.

Now to the Harbor Freight band saw...best purchase I've made there yet! I've made too many cuts to count and it continues to cut flawlessly - just recently replaced the blade as it broke but not because it was dull. I put too much side load on it cutting a radius in vertical mode :-) It was definetly worth the money for me. I think you'll enjoy it!

Danny,

[rustomatic]

It'll be great to see what this car becomes--I'm one for use of the standard pushrod block, since new cars come with new car motors (and do their new car things). I just have a fixation on old tech in my old cars (old tech that makes driving fun, that is). With that in mind, I've seen the Coyote motor for under seven grand, which does put it in competition with a decent old-school race motor, but then you need the controller for the thing, which is another few bucks...

Is it wrong to like a good cam lope with quiet mufflers? It's kind of like the guard dog you can't see, but know to be very afraid of...

I love the shop; I'm finding that when one has property, there are so many more ways one can get into trouble with hobbies...

[Jetfixr320]

Which bender did you get from Swag? they have two 20ton setups.

[Motorcitydak]

Thanks a lot for the reviews! I will have to pick up one of those saws

[modmotor46]

It'll be great to see what this car becomes--I'm one for use of the standard pushrod block, since new cars come with new car motors (and do their new car things)....

Rustomatic, I'm still torn - like an old shoe! I so want the ol' bump stick shuffle in the '67. I'm talking a high lift roller setup that sounds like your standing at a drag strip. However, I priced out building a 408 - stroked Windsor...wow, the cost of building just the long block I want is more than the complete Coyote engine (less the control pack and oh yeah, an alternator). Granted, the 408 parts list started with a FR Boss 351 block and AFR 205 or 225 heads, etc.

My plans eventially include a supercharger on whatever direction I go - love the whine!!! Muscle Mustangs and Fast Fords dynoed a Coyote with a Kenne Bell 2.8L supercharger - at 15lbs boost it made over 700HP! and Ford has an all fordged version of the Coyote now with a lower compression ratio (9:1 vs 11:1).

Anyway, at the rate I'm going right now it'll be this time next year before I need the engine.


Danny,

[modmotor46]

Which bender did you get from Swag? they have two 20ton setups.

I bought their standard 20 ton press brake without the adjustable back stops. It wouldn't fit the 12ton press I already had (and love because it has the separate pump and pressure gauge). So, I first bought some metal and expanded the width of my 12ton press...well long story short - It didn't work! 12 tons is NOT enough pressure to bend 1/4" plate. I guess you could probably heat it to the point of making the bend easier but I don't know at what point that would be - you certainly don't want to harden or temper it in the process. I ended up buying some more metal (7.25# channel) and built my own as pictured earlier in this post, picked up a 20ton bottle jack at HF on sale and with a coupon :-) and all was well. The Swag press is well worth the money. What's cool is it's just an accessory and not a dedicated unit so it's pretty versatile.

The funny thing is I never ended up using the 1/4" pieces I bent for the IRS brackets (switched to 10GA). Although I'm sure I'll need them somewhere along the way for something else.



Danny,

[ATOMonkey]

Regarding metallurgy.

You can't really screw up plain carbon steel by heating it. In fact, it's preferable to hot work plain carbon steel to avoid weird stress concentrations. Or if you do cold work the steel, you would bake it after at about 300F for 8 hours to stress relieve.

The steel you're working with is likely hot rolled plate, so it's about as soft as carbon steel gets.

Cold rolled plain carbon is harder, but again, heating to bend the part only relieves the additional cold work stress you're imparting.

[turboclevor]

modmotor46

what all had to be modified on the cobra IRS to make it fit the first gens? i have a 69 coupe that i want to put one in

[modmotor46]

Hey Turboclevor, sorry for the long break and late response. I've been tied up on a number of other projects.

Since I did not want to use the factory mount points on the IRS cradle, new mount points had to be custom built. I could have just built my own brackets similar to the ones DVS Restoration sells but was looking for something a little different. The overall goal was to set the cradle up higher in the chassis for a lower stance and CG and to also make it more rigid. The DVS website actually gave me the idea for modifying the cradle. Search his website for lowered cradle. The biggest part of the modification was the positioning of the custom brackets. I simply cut the factory rubber bushing mounts on the IRS cradle completely off just under the round sections that actually hold the bushings. The front cradle tubes had to be brought inward by removing a 2” section on each side (to clear the 67's rear frame rails) and the rear tubes were shortened by 1 ½”. Pics earlier in this thread demonstrate those modifications.

I had to modify the trunk extension pan so the rear portion of the upper control arm mounts would have clearance. I used a planishing hammer to make the humps in that pan prior to welding it in as I was replacing the trunk floor anyway. Once the cradle mods were done I built my brackets in sections, clamped these sections to the 67’s frame rails, set the cradle into position under the car with lead screw type jack stands (this step is where a lot of measurements take place), tacked the cradle to the brackets and then pulled it out for finish welding.

The only other modifications were due to the use of coil-over shocks. I used QA1 DS303’s and had to build the shock mounts for both the lower control arm and the upper mount point. I’ll post some pics this weekend of the shock mount work. Oh yeah, I also built some frame rail inserts (pics earlier in the thread) to make the mount points more rigid. Some simple anti-crush sleeves would probably have sufficed but my OCD kicked in and I ended up building some pretty solid inserts to spread the load.

Hope all this information helps.


Danny,

[AstroCreep]

Great information in this thread. Very inspiring.

[modmotor46]

Thanks AstroCreep. It's been pretty fun going this direction (with the IRS) hopefully others can use the information.

[85coupe50]

Great build. Can't wait to see more.

[modmotor46]

Here are the modifications I made in support of coil over shocks. Anyone who has worked with an IRS knows there is very limited room for a coil over setup. In the end, the mounts I made and position of the shock relative to the motion of the lower control arm is for the most part a compromise - overall I think they will work out fine! I had to fabricate both the upper and lower shock mounts. For the lower mount, the LCA had to be ground down as there is a lip around where the stock washer\nut would go. I bent some 1/4" plate to slip over the LCA's factory shock mount location and then drilled a hole where I welded (front and back) in a Grade 8 bolt. The upper mount was bent from some 10GA sheet and welded to the rear cradle bracket. Spacers were turned out of aluminum stock.

Shock size was based on positioning the LCA near parallel with the floor. I mounted one of my Cobra wheels (17x9 with a 275-45x17 MT ET Street tire) and the top of the tire comes within an inch of the quarter panel lip. I plan on going with either an 18" or 19" wheel so it should tuck in under this lip - shooting for a wheel with an offset somewhere around 45mm. Anyway, the shock I ended up with was a QA1 DS303. That shock allows for a ride height of 11" (perfect for the confined space) with a compressed height of 9.5" and an extended height of 12.625".











Danny,