Preston's 1967 Mustang

[preston]

I'm tired of Ron Schwarz getting all the credit for crazy home built junk , so here is my $xxx,xxx budget Mustang. That's as realistic a number as Ron's $5k budget Mustang.

I guess I better whet your appetite to get some thread views - Twin Turbo all aluminum dry sumped 427 Windsor, 335 tires front and rear, flat bottom floor, custom dual a-arm front suspension, 3 link/watts in the rear, bla bla bla. Totally street legal.

Starting with a GT1/Trans Am inspired honeycomb reinforced space frame.
HOnestly I would probably go back to a standard frame rail setup next time but I fell in love with this build style while studying Trans Am cars. The front snout really is only about 10 lbs lighter than standard roll cage reinforced frame rail style car, but perhaps its stiffer, and it makes mounting a flat floor easier not to mention building it on the frame table

I use a combination of heavy cinder blocks and skip welding to keep the main rails from warping. Most of the rest of the structure I just skip weld and constantly check my measurements and adjust accordingly.









Angle cuts were made with a cold cut chop saw. It was a $500 saw, but it makes very nice quick clean cuts and while the angle finder on it is crude, I use a digital protractor to check the angle of the cuts and sneak up on them. BTW the digital protractor is used constantly on something like this.

Although I was interested in investing in a $45k 1/2" thick surfaced frame table with drilled and tapped holes on 3" centers, I ended up going with MDF boards on my carport floor. The whole surface is angled 0.5 degrees one direction, so I have to keep that in mind but the surface is flat enough. YOu can put a 10ft stick of 2*3 down on it and not see any gaps or air.

Bellhousing tunnel area is formed out of .125 cold rolled, make sure there is enough room to remove the bellhousing with the clutch installed !




Here is the pedal box being fabbed. One huge advantage of my chosen frame design is lots of room for firewall mounted junk nice and low. I am using a hydraboost with dual m/c's with an adapter, so I have a 16" long monstrosity sticking out (I wish !) right at the floor level. AT least the COG stays low, despite the 15lb weight penalty of the booster. But I hate manual brakes on a full weight car.



I built flanges all around the floor, rear firewall, and firewall for epoxying in aluminum honeycomb. I think this hase been very successful on the floor and rear, but was a mistake on the firewall. Doesn't protect against intrusion, and despite my hopes of a "thermos" effect the heat insulation sucks, I had to end up adding stainless shields anyway as well as a crapload of DEI heat shield, so weight savings are zero anyway.




Here is some shots of the honeycomb being glued in. I am using Hysol 120HP or something like that. The honeycomb is from Teklam and is $550 for a 4*8 sheet plus shipping. 1" thick, it is as light as a .050 sheet of aluminum but so stiff you can't bend it over your knees. I estimate I saved about 15 lbs on the flooring vs running diaganol tubes and a 0.63 aluminum floor.

COG was important to me in this car so the main rails are all flat on the floor, and the exhaust runs down the rockers. This keeps the floor low, keeps the driver low, which keeps the roof low, which keeps the body and COG low.







Here is the dash area being constructed. Yes I am still using the original '67 throttle bell crank. You would think a cable would work better here, but there is very little real estate to make it work and I couldn't really find a good pedal that would fit so i used what I had. also, I am using the original wiper system for the most part, and the body is so low on the chassis that I had 1/2" to spare for the wiper motor, and that was after I cut off the motor arm, reclocked and re-welded it. I probably have 20 hours into making the original wipers work that angled square bracket off the front with the circle in it is where it will mount. What you don't see in this picture is the mockup roof I had placed on the chassis to fab it up. Actually its not a mockup roof, it is my roof ! ( and a-pillars).



Here are some pictures of the back end coming together. I am using an underslung watts link with the pivot mounted to the underside of the pumpkin, but as Stielow might say I have "package protected" the use of a Panhard bar, thats the square section of tubing on the lower left of the rear stub where a sliding heim joint clamp can be used. This was about a 6 lb penalty and I'm not using it. You can also make out the sway bar brackets. The sway bar will go through the lower frame rails. They were drilled and a 1.5" .120 tube section welded in.

I couldn't seem to find any pictures with the watts link brackets welded in, but they are just two double shear heim joint brackets on that underslung rail. As i get into the suspension you will see how simple it all is.






If you are like me you are a junky for build threads, so I will be adding to this thread as I feel inspired or if there is any interest in my junk.

[preston]

Some semi-complete pictures of the chassis, note that extra gussetting was added in some places. Total chassis weight without front and rear crush structures was 470 lbs, pretty good considering a Vette frame is 420 with no crossmembers or roll cage.

The lessons learned are

1) the aforementioned firewall should be welded in stainless instead of the honeycomb.

2) I could have used more 2*2 on the lower rail instead of 2*3 for everything (about 8 lbs of weight savings). I used what I had at the time.

3) I would have liked to carry that small tube above the main rails that attaches to the cage side bar all the way from the rear cage post to the front firewall post.

4) there is another 10 lbs I could have whittled out of it in a few places.


Next week I will get into the suspension buildup or the body mounting.

[Payton King]

Thanks for finally posting up your build over here. I followed it over at CC and was very inspired and will enjoy watching the repost over here. Kind of like a "greatest hits" album...without the 2 or 3 year wait.

I have to ask since I am about to start another project, what do you think of the square set-up you are running (335 front and rear)? I have had mixed information, some say it is great and you get to rotate the tires, others say a slightly smaller front (305 or 315) help the car turn better. Thoughts?

I will say seeing the pics of your frame this morning has me re-energized to start my build.

[Ron in SoCal]

VERY impressive Preston!

How did you model the frame dimensions and suspension design? Look forward to more updates on this one...

[preston]

I have to ask since I am about to start another project, what do you think of the square set-up you are running (335 front and rear)? I have had mixed information, some say it is great and you get to rotate the tires, others say a slightly smaller front (305 or 315) help the car turn better. Thoughts?

I'm a far cry from a driving expert, my only track cred comes from 20 HPDE's over the last 8 years and 7 years of shifter kart racing. But it seemed to turn in just fine to me I didn't notice anything strange. Just from a physics point of view that doesn't make sense to me - you turn the front tires 10 degrees and which tire develops a higher thrust angle? A small tire or a large tire? besides, any large bore racing class eventually moves to the largest front wheels they can package, Trans Am, Grand Am, LeMans. Whether that means the same for a street based car is open to debate, but unless you are going for top speed or are horsepower limited, I can't imagine you would want less tire, especially on our front heavy cars. Again what do they run in LeMan spec Vipers and Vettes ? Or the CP guys in autox ?

How did you model the frame dimensions and suspension design?

In this day and age of CNC laser cut Autocad designed wiper motor brackets, I actually find it kind of refreshing that I am so old school. My first try was a glorified ladder frame, and my 2nd try was all designed on Grape which is a freeware modelling software. Once you play around in something like Grape it doesn't take long to kind of "learn" where the structure needs to go for stiffness, and you are package limited for so much of it. So on the 3rd try I already knew the critical dimensions - firewall to rearwall distance, inside rocker dimensions, dash bar height, wheelbase, etc. So from there I literally design it in my head with a few paper sketches and just make sure I have structure near my suspension pickup points (the suspension is modelled in WinGeo). Ater that the cage superstructure is just built like any car with the roof mocked up in place. Speaking of mockup, i guess thats part of it too - constant and never yielding mockup -seat in & out, engine block in & out , roof on and off. Also the front and rear bodymount/crush structures are added later, so that final "fit" can be done with normal fabrication.

I'll go more into the suspension design later.

[preston]

One other thing I wanted to add about frame design - with this kind of "square" style space frame, everything is really easy to keep "square", vs a mandrel bent curvy or OEM type replacement chassis or Ironworks round tube piece of art. I don't remember them now, but when I was in the middle of it I could tell you the required measurement from every corner. It was relatively easy to x-measure and keep stuff square, and all the structure is flat or angle cut square tubing. It doesn't look as inspiring as a tube bent Ironworks extravaganza with the laser cut brackets and gussets, but its about 100x simpler to build and probably a touch lighter too.

[Payton King]

looking forward to future posts

[Flash68]

I saw some posts of yours on CC too and it's great you posted here. Talk about a refreshing project.

I too have been struggling with the squared vs staggered setup for the changes to my car.

[preston]

This car was built with the bigger is better concept. Staggered or non-staggered, I believe in fitting the largest tires you can where you can. If that means 255 on the front and 345 on the back, then try to tune it out with suspension. Use a lot of rear roll stiffness !

Now a pure racer would disagree, might find advantages to lighter wheels and tires. But on our big motor, heavy, pro-touring inspired rides, I just don't see a point in hamstringing the only thing that keeps the car on the ground. I think the wear patterns are different for the front and rear too, so sure you can rotate them, but I find I keep the rear tires on the car a lot longer than the front if I am tracking. Now if you are basing it on economics and/or crash replacement that is something different.

Another idea I have is the car is mostly tuned for the track and the 335 front tires. On the street I mostly leave the suspension alone (because its a lot of work changing stuff around anyay) and my street tires are 285 up front. So that gives me some built in understeer (safety). Not that I ever really push cornering on the street anyway. The downside is that the 285 doesn't fill up the fenders hella flush

I realize we are discussing performance, but c'mon these cars need big tires anyway ! And for performance, a front biased front engined car needs more front tire if you can fit it.

[frojoe]

Originally Posted by preston

COG was important to me in this car so the main rails are all flat on the floor, and the exhaust runs down the rockers. This keeps the floor low, keeps the driver low, which keeps the roof low, which keeps the body and COG low.

This is by far the MOST important aspect of any car build, obviously.