1MeanZ

iTrader: (9)

Picking back up where I left off on the writeup, the last pic I posted was of all the cutting done on the driver's side. I did not get pictures of that side as I boxed it all back in and moved the wheel tub in because it was the same as the passenger side.

Once both wheelwells were finished I began to reinforce the rear diff mounts since I knew at that point I wasn't going to move them. There are 2 gussets hidden in the "boxes" made around each diff mount. Compare these mounts to all the other mounts in the first post that others have done and you will see that I've got easily double the reinforcement others have. I did this because when I'm stopping from 140mph at Nelson Ledges with slicks mounted, I don't want something moving around.






Next up I mocked everything back up to test fit the leaf spring, and start working on the bumpstops.

1MeanZ

iTrader: (9)

Next on the list was fabricating the bumpstops. This was one of the trickiest parts of the swap amazingly. I wanted 3" of suspension compression from ride height to the bump stop. To start with I measured the length of my shocks under full compression. I wanted to make sure that my bumpstops protected them from mechanically bottoming out. I ended up having plenty of room with the shocks, the knuckle would hit the body before my shocks bottomed out. So I had to figure out how to package a bump stop that would give me the travel I wanted while not getting in the way of my wheels when the rear suspension was at full droop.

Pictured below was a few shots during brainstorming and mockup. I thought of re-using the stock bumpstops and mounting them on the knuckle. I couldn't come up with a good way to mount them, and they were very large to try to package. One thing not pictured well was the fact that at ride height my knuckle was already close to the body of the car, so trying to get 3" of compression with the knuckle already close to the body was going to be a nightmare.

1MeanZ

iTrader: (9)

The solution to the bumpstop issue ended up being a universal polyurethane bumpstop bolted in the stock sway bar mount holes on the knuckles. Then I cut part of my reinforcing out, made a small perch for the bumpstops and all was well. I put the reinforcing back in the car as you can see in the final photos. In the one picture you can see the piece of scrap I used to make sure I had enough wheel travel. After all the fab was done and packaging compromises were made, I have 2.25" inches compression from ride height before initial contact with the bumpstop.

1MeanZ

iTrader: (9)

Once the wheelwells and rear diff mounts were done, I moved inside to install the roll bar and build the front diff mount. I'm not going to get wordy here, you've all seen a roll bar before, ask questions if you have any. I will however reveal a sneaky trick some of you may know for welding roll bars. I cut holes below the main hoop so it could fall through the floor and be removed from the car to be welded. Then when you reinstall it, I slid my 6x6 plates between the floor and the main hoop and weld it all in. The purpose of welding the main hoop outside the car is that I can weld much better and easier when not inside the car. I also did not have to remove my headliner or anything.

1MeanZ

iTrader: (9)

I also welded the main hoop to the sail panels, shown is the prep, I don't have pix of the welds for some reason....






Here are the reinforcements for the trailing arms boxes...

1MeanZ

iTrader: (9)

The final part of the roll bar install was the front diff mount. I wanted to take some time here to explain here, as this is the one part of the swap that isn't totally correct and I don't have as many pictures as I'd like. The mount I made that bolts to the diff is basically a 3 sided box that bolts to the diff, with a large piece of tubing welded to the top with poly bushings inside. Then the roll bar has a saddle that fits over the mount on the diff. The problem is that there is not enough clearance between the diff mount and the saddle, so when I drive the ring and pinion howl through the roll bar until the diff warms up and the mount moves slightly. Functionally it is fine, but I made it too tight and it's noisy.

87bluebird

what is the gear ratio in these corvette axles? and how much power can they handle?

87bluebird

would it work to do something similar to a 4 link setup coming off the trailing arm mounts? so you don't have to eliminate the backseat. is that what they did on the Zeus performance car. i can't really tell from the pics.

87bluebird

i don't know if you have seen it before or not but there's a 69 camaro with the c5 vette irs. hes a link to the website about it. there's a couple of popular hot rodding articles about it here and here


theres also a 69 firebird with the c4 irs i'll post those links tomorrow

1MeanZ

iTrader: (9)

I actually spoke with Jay Cutshaw himself a few weeks ago about his setup. He is a great guy, I wish I lived closer to his shop I think we'd get along well. He has children and wanted to keep his rear seat, which is why he re-used the rear control arm mounts. What he did is exactly what I would do if I put a Dana 36 in my Trans Am, or for anyone else that wanted the swap done on a street car with a normal interior. Jay's car is a show car and street car, and while I feel he has compromised the factory geometry somewhat, I think it still fits the bill for his uses and performs admirably. Not everyone is planning to mount slicks and hit open track days, or run events like the Silver State Classic.

87bluebird

is this your car in this gm high tech performance article.

1MeanZ

iTrader: (9)

yes that is my car. It was featured in April's issue of GMHTP BEFORE the IRS swap.

87bluebird

i have been looking around and it turns out this is a really common swap in first gens. there's even a guy, Wayne Due, that makes a bracket kit. to install a c4 irs in a first gen.
there alot of vehicles that have c4 irs swaps. i even found a bmw E30.
got any updates on your swap. also how close is the c4's track width to our stock width.

1MeanZ

iTrader: (9)

WTF

RED_DRAGON_85

maybe he was saying something along the lines of:
"so much for 'you cant have your cake and eat it too'"
in reference to the 15mpg and 13.7 et... but thats a pretty bad 'cake' if you ask me.
i get 25mpg hwy and probably would run around 14sec et.

InfernalVortex

iTrader: (4)

He's at 4000 feet though. Altitude is evil.

Tom 400 CFI

Still crappy cake. I'm at 4200 at my strip, 7050' at my house. My car runs 13.80's and got 31 mpg on my last outing. 15 mpg in a street car is not cake that I want to eat.

Lets see some more of those sexy IRS Pics!

87bluebird

any updates yet?

Stephen

iTrader: (12)

If a fiberglass car can be built with IRS, why can't a steel car get IRS, without building a jungle gym where the back seat was?

I don't see why it can't be done and less intrusive to the cars interior.

Don't get me wrong. Very cool to get it in & working. I'd just rather have it less intrusive & retain back seat....Or least the area as a "extended cab/package shelf" area.

Dante93GTZ

iTrader: (5)

Things to consider:

#1: Corvettes have a frame
#2: Corvettes don't have back seats (maybe there is a jungle gym back there).
#3: I too would like to see the back seats left in, but then again, I'm not going to attempt this on my car.

Excellent work, tho.

87bluebird

this can be done with out the jungle gym and retain the backseat. the only thing jungle gym does towards IRS is hold the pinion mount in place. but there's other ways to support the pinion that won't take up that space. you can use the corvette c-beam and create a torque arm. or you can make a cross member to support the pinion. or a combination of the those two ideas. or even something else i haven't thought of as long as the pinion cant rotate.

the only other thing in the c4 IRS swap the eliminates the backseat is the trailing arms. 1MeanZ used the stock corvette trailing arms and pads set to the stock corvette geometry in his swap. but you could easily create some new setup similar to a 4 link setup and put the mounts somewhere that wont get in the way of your backseat.

1MeanZ

iTrader: (9)

87bluebird, you've hit the nail on the head, clearly you've been paying attention here!

Stephen, check out Jay Cutshaw's setup in the links in the first post. I spoke with him on the phone recently and he is a great guy, and I now have insight as to why he did things the way he did them. He has kids and wanted to keep his back seat, so he made brackets and mounted the trailing arms where the stock lower control arms were. I believe that that is not optimal for performance, but Jay claims to have good luck with it on street tires.

As for the "jungle jim" that is my way of tieing the front of the diff to the cage so it can't move. I didnt want to use a C-beam or "torque arm" because I wanted room for exhaust clearance. My way is very strong but intrusive. Jay mounted a bar across the rear of the car that anchors where the stock rear sway bar endlinks mount, and tied his pinion to it. It works for light use on street tires, but with a large beam like that I'm sure it deflects in the middle and allows the diff to rotate some. These are all compromises Jay made to keep his car usable, and frankly if I was doing a swap for a customer and they wanted back seat access, I'd do exactly what he did. For someone wanting brutality on the track, I'd copy my method.

1MeanZ

iTrader: (9)

Onward with the swap notes:

After I had gotten the diff mount finished I mounted the rear diff for the last time. I set the pinion up at 2* nose up and had to have the trans at 2* nose down. This required raising the transmission up quite a bit. My TKO600 is kind of bulky anyhow, so I ended up cutting the trans tunnel completely out of the car to get the clearance I needed.



I went to the junkyard and got another trans tunnel so I could overlap the new one with my old one and get the clearance I needed. It was even the correct color out of another 5 speed car!






I don't have pictures of the process, but when I put the interior back in the car moving the trans tunnel up caused problems. I trimmed the bottom of the console and it all looks stock now, but it was not easy. I also had to make a custom shift plate since my shifter was now in a different position.

1MeanZ

iTrader: (9)

Once I got the tunnel finished, I started on the exhaust. This was probably the most fun part of the project. Anyone that has fought for exhaust clearance on a thirdgen knows what I'm talking about.

After I got the trans lifted for the correct driveshaft angle, I had TONS of exhaust clearance, so I got to work.







I then made my own X pipe with ONE 3" U bend. I cut it in half and welded it back to back. Then I cut off the 2 long legs, rotated them 180* and welded them back on. It worked awesome.

1MeanZ

iTrader: (9)

before I finished the exhaust I finished mounting the rest of the suspension pieces, brake lines, and e-brake cables.

1MeanZ

iTrader: (9)

Moving forward with the rest of the exhaust...

1MeanZ

iTrader: (9)

Then once the exhaust was done, it was time for the moment of truth. I put the car back on the ground for the first time in what seemed like forever. I washed the dust off before the pix.






Here is a quick crappy vid of the exhaust


Here is some in-car footage. Yes thats me biffing 3rd gear
http://www.youtube.com/watch?v=KRET8hdV4Rw

musclecar70sfan

iTrader: (1)

If I was a stranger to thirdgens you would've fooled me into thinking they came factory with IRS. Terrific job!

1MeanZ

iTrader: (9)

After that I drove the car for a few weeks, and moved into our new home so I just drove the car and made sure nothing fell off or broke.

Once I was settled back in I made the rear sway bar for the car. On the street with street tires, the rear sway bar is not needed in my opinion. The car is really low and sprung fairly stiff so it does not have a tendancy to roll over under cornering forces, especially with only the grip from street tires. Knowing the car will see abuse with slicks I started making the rear sway bar. It is not really pretty, it hangs down really low due to packaging issues, but for track and autocross use only it will be fine. I can remove it and reinstall it in about 10 minutes and 6 bolts.

1MeanZ

iTrader: (9)

here is how low it hangs

1MeanZ

iTrader: (9)

The swap is now "finished". Here are some final pix. Next mods will be an Ultrashield road race seat and harnesses, then a new set of slicks

1MeanZ

iTrader: (9)

Thanks, a factory appearance was my benchmark for fabrication quality and fit. I've been to shows and cruise-ins so far this summer and no one notices it. The few people I've told that looked under the car say "it looks like it came that way man, that's nuts" The only giveaway is the rollbar going to the driveshaft tunnel, I have gotten questions about that. Otherwise I cut the factory plastics and covered my fab work with carpet and it just looks like the back seat is missing.

RED_DRAGON_85

its amazing how it all comes together at the end so perfectly.
the great thing about this is that you set the ride height where you want it without having to compromise the geometry at all.
all in all, it looks amazing

Tom 400 CFI

What an amazing project! What a tight package that car is. I love it. All of it. Nice documentation of some awesome work. Props, man. Props.

Guest

Wow, I think I most admire your commitment and dedication to this project. You set out to a major task and tackled it with flying colors...all in the mists of moving into a new house even.

Your craftmanship I can see through pictures is fantastic- your welds are great, your fabricating ideas and skills are impressive.

Great job.

I crackup up where you went to finsih the exhaust and you said "moving forward witht he exhaust". Wrong, you were moving rearward with the exhaust you rednekk

This inspires me to hopefuly someday in the near future get my life back in order and get to that Mimi Cooper project where I plan to stuff a Jaguar rearend with inboard discs into it. (With majorly flared fenders of course)

I am mostly curious as for how the chassis rides relating to rattles and creaks that are the normal daily issues with 3rd gens- now that you have the independant rear suspension. I would bet the car sounds completely different inside when pertaining to road noise.

Tom 400 CFI

I am curious about that too. With similar spring rates, I'd expect similar ride quality...but am curious about the real world results.

1MeanZ

iTrader: (9)

Thanks guys for the compliments. Dean your comments mean a lot, I make effort to absorb your input on frrax, and on here under your various screen names over the years

I have a 91 TA with cut factory springs, stock parts, and NAPA cheapie shocks. It handles and drives well and I know how it acts on the roads around here. Taking my Camaro down the same roads really highlights the differences. There is one bump here that is on a 50mph curve. The rear of the TA hops over about 1 inch just driving over it. I've stabbed the throttle and brakes going over the bump in the Camaro and I can't shake it loose.

I've also not lost the the forward bite that I thought I would lose compared to the solid axle and torque arm.

Overall the car is just more stable over the rough stuff, it's that simple.

For another perspective, I'll ask 92RS(real slow) to come in here and give some details about what he thought when he rode in the car for the first time to thridgenfest. This way you guys can get a completely unique perspective from someone else that knows thirgens, then rode in my car...

92RS(real slow)

When I first got in the car I wasn't sure what to expect considering how modified your car is. lets put it this way if you like c4's you'll love this I may even go as far to say that it handles better, and rides better than a stock c4. The ride is so much better than stock no jerking when driving over small hole's our bumps, no rear jumping around either. Overall it's just a much nicer ride.

BG84FBIRD

Looks good man!!

matthufham

iTrader: (5)

that's awesome, came out great!

Guest

I think you are giving me too much credit for knowledge here. I appreciate your respect, but just want to say publically that I really am not the originator of alot of the tech stuff I elaborate on, engineers over the years have developed this chassis dynamics stuff and I am merely just a guy that has studied them and grasp most of what they all have offered over the years of research and development. Where I may hopefully and not arrogantly take credit is taking that information and acquired knowledge and translating it itnto laymans terms for the populous to hopefully better understand. Most people in a lifetime unfortunately do not grasp wntirely what chassis' do in motion and how they are controlled to yeild better tire contact patches.

The things that pussle me that I will never fully be able to research first hand is things like chassis width and length when combines with track sidth and wheelbase- ands "what is the optimum width and lengths of these based on speeds and type of vehicle useage?" These are to me all trial and error when tying to design something from scratch like I want to do to my Mini Cooper as I have been studying chassis desgins and suspensions types over the last few years- and basically looking at what cars are fastest on what tracks. They really boil down to things like Miata's, Lotus Elans, Honda S2000, RX7's, etc...all being quick on autox type courses merely because they all somewhat match in wheelbase and track width. From there, it really boils down to the driver even though all suspensions are a bit different in all of those cars.

Dean

InfernalVortex

iTrader: (4)

Probably the one project I've seen done that I know will never happen to my car... makes me sad. There's just no way I could pull that off... maybe in 20 years if I start learning now.

83C_CamAroZ28

iTrader: (12)

man this a really nice car i wish i can do all of that 2 mine...

Tom 400 CFI

I wonder if we could get an update from the OP about the handling/street manners of this rear compared to the SRA/TA/PHB set up.

I had three 3rd gens, and now a '92 'Vette. I personally think the "handling" of the F body was better, in some ways (many ways, actually) than the Y body cars is now. This is stock for stock comparison, here, and much of it, subjective. But the 'Vette moves around a lot, and exhibits much more trailling throttle oversteer than the F car did, IMO.

I wonder how much of all this perception is b/c of the 'Vettes flexy chassis? I don't know.

rlewi771

how much would you charge to come do that to my car??? Think we could knock it out in a weekend? (hahaha)

1MeanZ

iTrader: (9)

As was briefly noted earlier in the thread, I moved to a new house this spring and have spent lots of time settling, building, moving, organizing, etc. Also, my hitch wont fit the car anymore with the new exhaust, so I had no way to get my race tires to the track without dragging my wife along. Also, 2 of my good friends that I attend track days with have had their cars under construction this summer so we just haven't gotten together. As such, I can't speak to the track performance of the car, which I feel is critical, otherwise this is just a stupid ***** mod and a waste of time and money. I recently purchased a car trailer, my Tahoe is now outfitted to pull it nicely, so stay tuned for next spring when the open track days begin...

For a review of street performance, I covered that a few posts above, 92RS(real slow) also posted his comments after riding in the car. After driving the car quite a bit on the street, I still stand by all the comments made. The car is stable and composed over the rough stuff. I have pushed the car on the street, and it's adhesion is downright un-nerving even with cheapo Sumitomo tires. I look forward to great results with new slicks on a closed course where I can really push it.

Tom, you may "feel" that your f-bodies handle better, but nearly any autocross event, or track day will prove that theory wrong. I also feel that the vette's chassis is not that flimsy, especially when compared to a thirdgen. Again, many people's experience on the street is very different from actual times obtained at an auto-x event or track day. C4 Corvettes are very strong performers, even today, head and shoulders above any thirdgen when it comes to handling in a competition environment.

I like to build and design. I like unique mods. If my goal was to have the fastest car I'd sell my junk and get a C6. However I like thirdgens, and I enjoy projects and improving performance. I enjoy the process of hotrodding, I'm not in pursuit of ultimate perfection. I think my thirdgen is 100x cooler than a stock C6 that some guy just bought, simply because it's something I made myself. My car displays many things you can't easily buy, like skill, creativity, and uniqueness. I think that is what hotrodding is about. I think that is what many of us here do.

Tom 400 CFI

Thanks for the post. I hope that you can post back to this thread next spring, when you get some more objective (track) results.

I find it interesting what you say about the 'Vette/F-bod comparo, b/c back in my F-bod days, my car compared very well to any stockish C4. Better, in most cases. My car was made up of all stock parts (mostly 1LE stuff) except for the addition of SFC's and STB. This was in Auto-x. Never road coursed that car.

Also, I cannot believe that the Ybod has a stiffer frame than the F-bod...even w/the roof on. Roof off, it's terrible (the Y car). Is there any objective data out there on the F car frame?
I had three F cars; only one had SFC's/STB the rest had no frame additions. My current 92 is my first C4 (had a C6 prior) and it is pretty bad, in the frame flex dept. Way worse than I can remember my F cars ever being.



. That is a well said statement! I feel the same way about my T/A -everything about that car was "all me", by the time I sold it, and I was proud of it.
My C6? Eh. Same as every other C6 built by GM. A friggin' monster on the track...but not that fun to own, and very little pride. I was digging reading your perspective.

383tpimachine

Very nice.

built91Z28

Absolutley awesome work. I love fabrication and this is some of the nicest work I have seen. I completely agree with you about it being cooler because it was built, not bought. That was one of the reasons I did my exhaust the way I did. Everyone said you cant have true dual and ground clearance. I have 8" of clearance and I'm lowered 2". You just have to be willing to make it. Not everything can come out of a catalog.

Guest

3rd gens hands down can be made into about the best handling cars in the world (pound for pound/ dollar for dollar). Its why I love them.

My 3rd gen would turn circles around my C3 Vette, both are extensively modified. The vette has about 5X the power though and I eat Vipers and such for lunch. I grew up in and around Vettes, I have driven just about everything out there including many C6's (but not a C6 Z06 yet) and have driven them hard. I would not go as far to say they are monsters, they are sofa's on wheels. THey are very tame and easy to drive. They are geared for the masses that can now afford that High School dream car.

You want to see a monster Vette? here you go. 0-60 in 3 seconds. All of this run you see is the car in 1st gear only doing up to 70 mph on a little autox course here in So Calif back in '93. This car puts down 540 rwhp, and tachs 8500 rpms-(yes, 70 mph in 1st gear with a Mincie M22 Rockcrusher- you should see it pull in 3rd gear)

If my Camaro had half the power this car does...and racing rubber like this does, the camaro would clean my Vettes *** in autox runs.

http://www.youtube.com/watch?v=8owSV...eature=related

Dean