Hi 6gc,
it's been a while, but it's time to finish this thread. Especially since this place may cease to exist at any moment.. So lets first look at a showcase of the fun things I did with my celica since the last major update:
Autocross!
Track Days!
Drag racing! (which kinda sucks because breaking stuff is not fun... more on that in a bit)
More track days!
Even more track days!
Unfortunately all this fun stuff took its toll on the GT drivetrain. My transmission was freshly rebuilt and upgraded with a TRD helical LSD, but second gear got damaged by wheel hop at the drag strip. It developed a slight whine and eventually grenaded. I did everything I could to avoid wheel hop: new tires, superstrut suspension, a helical LSD, poly, etc. But the launch box is so grippy that you hop no matter what. And in my case it chipped a tooth on 2nd gear, which was the start of the long road to ruin.
I felt really down about this because I took great pride in the transmission I built, only to have it damaged by the very thing it was built for.
Fortunately I was able to salvage and resell the LSD (which somehow didn't get filled with shrapnel) before sourcing a replacement S54-06D from a Beams. This importer KNEW they had me in a tough spot and charged accordingly. I still cringe at what I spent on that replacement trans. But it was June and I needed to take advantage of the rest of the racing season.
From there I avoided the drag strip and focused almost exclusively on track days. It was a total thrill, and I was thoroughly addicted.
Turns out the celica platform is a VERY capable performer, even in FWD form. I was passing cars I had no business to pass, including corvettes, BMW M3's, and even NSX's.
In fact one of my favorite memories is being approached by a driving instructor who was riding shotgun in the corvette behind me. He walked up to my car in the paddock and asked just what the hell I did to it because they couldn't catch me
Good times.
Unfortunately even track days take a toll on the GT drivetrain. The S54 is able to take the abuse, but GT axles are no match, especially if they come from a parts store. Sometimes I found they would develop a click after only ONE round of a 3-round track night. This meant I would be swapping axles pretty much every weekend; which got old REAL fast. If both of those axles look new, its because they are, but one was already damaged a week after being installed.
I was really confused. I wasn't hitting rumble strips on the apex's. I wasn't wheel hopping. I think it was just the sustained 300hp for 25 min at a time that killed these things. Despite this I still felt like I built the ultimate FWD track-capable celica. So I considered that mission accomplished, and started to think about how I can get more reliability out of the drivetrain while simultaneously taking on another project to grow my skills....
Enter the JDM Gt4 floor pan. I decided I wanted to take on the much discussed, but rarely attempted >
>AWD CONVERSION>>.
I unfortunately could not go the route of drilling spot welds and swapping floor pans (more on that later); so instead I thought I could either design a bolt-on sandwhich adapter, or a weld-in set of mounts. Both ways have been attempted in the past, but I wanted this to be different. I wanted it to replicate real GT4 suspension geometry perfectly. I wanted there to be a rear swaybar. I wanted to retain use of the stock fuel fill location. AND I wanted to minimize modifications to the stock chassis as much as possible.
>
>DISCLAIMER:>>>
> >>THIS IS NOT A HOW-TO>>. THIS IS A SIMPLY A LOG OF MY JOURNEY TO MODIFY MY TRACK CAR. I'M NOT RESPONSIBLE FOR WHAT HAPPENS TO YOU, YOUR CAR, OR INNOCENT BYSTANDERS IF YOU TRY TO MIMIC WHAT I'M ABOUT TO SHARE.>>
Anyway, it was time to dig out the remaining bits from my old front clip and give them a thorough cleaning and once-over. The goal was to perform an overall inventory and assessment of where I stand parts-wise
The transmission cleaned-up really well and didn't appear damaged in any way. Most of the other major parts were much the same.
The next step involved throwing the car onto jack stands and completely stripping off the rear suspension. I took GREAT care to make sure the car was on one concrete slab and level. Any twist in the frame would cause huge problems for me in the future, and I knew it. Ages were spent sweating bullets as the car was carefully placed onto a total of 8 jack stands. I HATE lifting cars and screwing around with stands!
And yes, that is a driveway. This project was going to get done outside as I don't have a big garage... This is one of the major reasons I didn't consider doing a floorpan swap. I couldn't leave the car outside with a gigantic hole for months at a time.
Anyway, I got the GT suspension out quickly as I had previously applied antiesieze to every single bolt and nut when installing my poly bushings (antisieze OCD pays off ppl!). I pushed the GT stuff off to the side and deadifted the impossibly heavy GT4 subframe onto the transmission jack before carefully maneuvering it under the car. My main goal was just to see what the major interference's are, and to look for any common landmarks with the JDM floorpan. This was the point where I needed to know whether there was a major reason to abandon the project. I knew others had done it, but I didn't know what they sacrificed in terms of suspension positioning to get things to fit. Like I mentioned before, my goal was to replicate the actual GT4 perfectly.
I quickly found that absolutely nothing looked similar, but that there were two points on the frame rails, and two other points on the rear bumper that were located identically between the USDM and JDM floorpans. I knew I found my design datums.
I remember laying back onto my creeper after staring at everything for a while. It was clear that trying to gauge things this way was a waste of time since I was just guessing at what the positions were supposed to be. I gave up for the day and went home.
That night I started researching hand-held 3d scanners. I thought I could create a 3d scan of my JDM floor pan and overlay it onto a scan of the USDM pan. This would be great as it would show me where everything would need to be positioned...But have you seen the prices??! Holy **** O.O Not to mention the resolutions aren't very good, and it's difficult to get a quality scan on a large surface in lower light situations. Maybe this has changed now, but at the time it wasn't a viable option..
So, I decided I would need to build a development Jig
Good thing I have access to, and am handy with a bridgeport
I didn't have a welder and was thus forced to create my jig from steel L-brackets and 2x4's. The jig was built on the JDM floorpan, obviously making sure to capture the subframe mounts and common datums.
Aaand the final product just before mounting onto the car. This was actually a huge pain in the ass to make. It looks simple, but precision is everything, and that's difficult to achieve with these materials.
When installed, the four GT4 subframe mounts would float in air, showing me exactly where I need to build my design towards.
Once the Jig was in place, I could see where the rear subframe would need to be positioned. I made sharpie marks on the car and removed the jig before sliding the GT4 subframe in. It was immediately clear that the differential collides with the spare tire well...
It was also unfortunately pretty obvious that my idea of building a bolt-in 'sandwhich' adapter wouldn't work. There simply is no room to build a strong box frame that would clear both the chassis rails and the OEM AWD subframe. Nor would there be room to capture the GT4 swaybar mounts points without creating diving-board features. The only way to proceed would be to either reverse engineer the 205 subframe and build a bolt-in replacement from tube/square stock, OR design weld-in mounts.
Here's an example of what I mean by replacement subframe. I would have to reverse engineer the GT4 subframe to get locations on all of the differential and lateral arm points. Then I would have to design frame members that bolt into the stock GT mount locations...I marinated on this for a long time and decided that weld-in mounts were the easiest way forward. I just wouldn't be able to do a good job on a custom tube frame without proper 3D models of both floor pans and OEM subframe.
Side note - I did look into CMM services in my area. I figured they could measure all of the major points on my subframe and generate a digital file that I could model from... but like with the 3D scanner, it costs big $$$
After deciding the path forward I busted out the trusty vibratory saw... This was the point of no return and I was a bit nervous to do it. But with the help of a plumb line and a sharpie, I cut a perfectly straight line on a bulbous sheetmetal feature. Years later this is still one of my greatest fabrication achievements lol. I can't believe I was able to cut it so that a 90 degree flat panel sits flush all around. But anyway you can see that the subframe now clears the chassis.
I couldn't leave the car outside with a big hole in it so in went a patch panel. I kept imagining mice or spiders getting inside and obliterating the interior, so I may have gone overboard with the tape. What you see is only the first layer haha.
Now that I knew where the subframe needed to live, I decided to start searching for the missing parts identified earlier. I am forever grateful to my friends on here who gave me access to Toyodiy.com. Those diagrams answered so many questions and saved so much time.
Everything that's circled was missing... I could feel my bank account starting to quiver. It knew about the UK exchange rate. It knew about the GT4 Tax. And it knew I show no mercy.
Also decided to throw in some poly because... racecar dammit!.
Pro-tip DO NOT purchase the front and rear diff mounts. They absolutely destroy the feel of the car for minimal gain and I reverted back to stock as soon as I could.
The four bits in the top left image were all purchased used from the UK. They literally looked like they were plucked off the deck of the titanic when I recieved them, which was really irritating because they cost a lot. Fortunately I have a very good friend who blasted and powedercoated them in exchange for a 6pack.
Also decided to go ahead and just buy new rear shocks and bushings. We're talking about 20 year old parts here, so some freshening-up is pretty much required. I'm just thankful that most of my stuff is rust-free.
Meanwhile I also started thinking my way through how to handle fueling. It was clear that I couldn't use the stock GT4 tank, and I didn't really want to go all-out custom. I was still trying to limit the scope of this project and a from-scratch fuel cell felt like a huge undertaking. Fortunately a company called ATL makes these special 12 gal 'well cells'. Specifically intended to fit into your spare tire well.
This approach also has its drawbacks, but I felt like it was the easiest path forward. Plus I had a pretty good idea of how I would be able to retain the stock fill location.
Have you guys heard of CAD? Cardboard-aided-design? It's something I learned about when watching a fantastic youtube series called Project Binky:
https://www.youtube.com/playlist?list=PLGSO...Y5MTQg1qjtxA_nq These dudes are my heroes and I learned much from them. They use cardboard to map out all of their work, and so I was inspired to try something similar to acquire the shape of my floorpans. A custom cardboard contour gauge! Complete with BBQ skewers! It actually worked pretty well
Once constructed, I simply lined the gauge up with the sharpie marks I made earlier and pressed it against the floorpan. Then I placed the fresh contour onto a sheet of paper and spray painted over the skewers to get a template ready to be glued onto some foam board. Not the most accurate method, lots of areas to introduce errors, but a great way to start
Here is the end result of the custom contour gauge. Just to give you an idea, this took 3 hours to make. These things are simple in concept, but difficult to actually execute.
Not bad for $20 spent at jewel. One thing to mention is that by this point I had decided on the configuration for the weld in mounts. Some time with a napkin made me realize that all the mounts really had to do was prevent the subframe from falling towards the ground, and resist lateral forces during turns. To achieve both of these things (and maximize weld area) I would build a bridge between the two stock frame rails for the front pair of mount points, and 'hook' into the same frame rails for the two rear mounts.
This naturally makes use of the strongest structure on the car, and allows welding to some really thick metal. Plus, it doesn't require massive removal of existing floor pan, only the addition of more structure.
Anyway, I later graduated from foam boartd to more sophisticated materials such as balsa wood, Popsicle sticks, and painters tape. Don't scoff, this is honestly the most efficient way to rough out a design. I promise things will get a bit more interesting later on
The basic process involved bolting in the development jig, taking measurements, cutting panels from balsa, trial fitting, adjusting, test fitting with actual subframe, making adjustments, scrapping designs, etc. Very boring and tedious stuff.
It's hard to convey how many iterations I went through at this stage. It was all maddeningly slow progress because the materials I was working with tend to bend and deflect. It's very difficult to keep things perpendicular, flush, straight, and unstressed when you're lying on your back in January with only inches of clearance from your nose.
Not to mention I had to install and remove the jig about a million times between iterations and I only had a few hours every weekend because sunlight is a limited resource in the winter.... There were many points where I wanted to just say F-this and go buy an STi, or 3D scanner. Same price basically.
BUT, I'm pretty dumb. And dumb people are persistent so I eventually got to a balsa prototype that I was happy with. I was carrying it triumphantly to my car to go home when the wind picked up and ripped it apart in my hands....
Weeks later I had recreated the prototype and got started on digitizing it in my favorite CAD software. At first I took the laborious approach of using grid paper and a vernier caliper to draw the contour as a series of points on a sketch plane in the software. I later found a simpler method but it still sucked.
The result of all that work was these two initial extrudes. These were the beginning of my 3d model, and would serve as the backbone of the rest of the project. Why go through all this effort? Well I was toying with the idea of being able to make more than one of these, all identical.
Many hours of work later I had my first set of digital prototypes...
Anyway, that's all I can stand to type up for now. Stand by for future updates
This post has been edited by enderswift: Nov 24, 2019 - 4:03 PM
