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Old 09-12-2008, 06:52 AM   #1
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Corvette C4 IRS Conversion

Ok so some may be familiar with my conversion at this point - but i've had a few requests to bring it over to this board, so here it goes.

The suspension is about 95% done, so this post will be somewhat retrospective.

It may take me a little bit to get all the info posted - as its turned into 30+ pages of posts on other boards. This will be the abridged version

Quick recap:

built the car, and ended up with way too much power for what the stock rear could handle. traction was a huge issue, and i was hesitant to stick we all BMW parts due to the cost (driveshaft shop axles, etc) The car is alot of fun as of now - but not getting traction till 3rd or 4th was wearing thin. Racelogic's traction control only went so far.

couple goals i had in mind:
- fully adjustable (camber, toe, instant center)
- unbreakable
- affordable parts
- good balance of street / strip
- and partially just a project to do

had some good suggestions, but decided to move forward with a C4 (84-96) Vette IRS swap.

main benifits:
- 3.5" axles!
- aluminum , light weight
- Dana 44 diff (unbreakable)
- domestic parts are cheap!
- 4 link
- still an IRS.

Here is what a C4 vette IRS looks like

Half Shafts

Tire size evolution

205 - 245 - 315

trying them on for size - Hoosier Drag Radial (315/35/17)

making clearance

So how is all this going to work?

Subframe will be constructed from 2"x2" .083 mild steel tubing.

Just ordered a set of CCW Classics. 7.5" up front, and 11" in the rear.

Once all is said and done, i'll drop the car off at a local chassis shop for a chromoly cage to tie it all together

As off last night, i'm working on a jig to position the rear at the exact locations to build the subframe around.

Subframe will be welded off the car, and then tied into the chassis as one unit.

a long way from home


made some more progress.

CCWs show up friday! hope i can get them mounted too, well at least the rears


here's what the subframe will look like


got some more parts in today

stopped by S&W race cars, where i had some of the custom brackets waterjet cut

test fit

also picked up some 2 x 3 tubing, and this drop down cross member. There should be enough room for the driveshaft to some through, and the exhaust to fit on the lower left corner. This is just in place for mock up, there will be 1/8" steel plates welded to the rocker panel first

tomorrow the wheels show up! can't wait.


wheels showed up - getting tires mounted now



600hp beast
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Old 09-12-2008, 06:52 AM   #2
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back from a long day at the shop. Had my buddy jon up, and we were able to bang out some ish

jon brought up his wheels for me to check out and, and we tried his 15" welds on my hubs - they fit! which is awesome, because now i will be able to run a more conventional drag tire if needed

so first thing first, i cleaned up the rocker panels so we could get some 1/8" plate welded to them for the subframe to tie into

we then got the front half of the subframe cut out and tacked together.

with everything positioned, we marked where the four link bars intersect

took it back over the welder, and tacked it all in place.

we have some scrap welded to the 1/8" side plates so that we can set the subframe in without too much struggle. end of this tube will be boxed in

theres still some debate on track width. Jon thinks i need to move the wheels in more, and he is probably right. I need to get the 4 link bars for the passenger side, and get both wheels in there before i make that decision.

we ran out of steam before we could get the other bars cut to length that run front to back - but theres always tomorrow


so i was able to crank out some work the past two days

have the front half of the subframe all welded up

tonight i finished up some work on the back part of the subframe with the diff mount, etc. we were able to position the diff in the car for the first time and get a glance at how the axles will in up

we sectioned out a good bit of the stock axle..

back view

bottom view

front view


got some parts back from s&w that i had waterjet cut..

- new rear diff mounts, with two mounting holes so i can 'raise the body' without effecting suspension geometry

- upper shock mount tabs

- diff bracket for camber adjustment rods

I also picked up some 3 piece rod ends and chromoly tubing to make the camber adjustment rods.. damn that shit is way too expensive, but they only had the 3 piece stuff in stock in both right hand and left

This week i also machined up some lower shock mounts, which will bolt to the wheel spindle housing... the stock corvette actually had a monoleaf spring so there was no provision for coilovers. My mount bolts into where the shock would bolt to

(note, the mount is not tightened to the housing in this picture)

i'm hoping tomorrow i get to crank out some work on the car. I want to be able to get my axles on order and figure out the driveshaft.. then its on to doing sheetmetal work


welded up the back part of the subframe. Adding the upper shock mounts, the new diff mounts and fabb'd up the front diff mount

got everything back into the car - and used a plumb bob to drop points onto a piece of plywood to check alignment of everything, and then tacked it all to the car

then i reassembled everything to double check fitment, and it all seems right on

messed around a little bit with the rod ends for the camber adjustment bar.

next will be axles and driveshaft and finish welding of the frame. I'm trying to decide mig or tig. I have the mig in the garage, but would have to tow the car down the street to the tig

also, gonna order up some springs and my fuel cell tomorrow


scary to see how much was taken out of the axles (for mock up only)

got my 15gallon fuel cell in today, and finished up the camber rods - complete with all the spacers and whatnot

test fit (like if it was made for the car)

shot of the back with 90% of the junk bolted up. Just need the real axles and to make the toe adjustment rods..

oh and some sort of sway bar

also picked up this beast to help with some of the sheet metal work


got a second to mess around tonight. Tried my hand at my first panel. Turned out ok, but the bead roller is hard to get the hang off - it wants to go all over the place

spend alot of time this weekend drilling spot welds and removing the existing trunk floor. here is what was left

and now my new panel

also mocked up my toe adjusters. need to weld something to the diff cover for these to attached to

sway bar tube mounted.. (pardon my semi crappy mig weld on that one side)

and now for the good stuff - new axles!

bummed out that my drive shaft isn't here yet.. DSS is taking a good bit of time. Called frank today and he said "well i'm not sure why its not done, i guess thats why you are calling huh?"

thats all for now....

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Old 09-12-2008, 07:16 AM   #3
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i'm so f****en shocked.
that's sooo awesome.you must be tired.
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Old 09-12-2008, 07:21 AM   #4
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Nice work! Looks like a fun project... now I have to ask, what is powering your beast that you are getting 3rd AND 4th gear wheelspin??!

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Old 09-12-2008, 07:27 AM   #5
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very cool.

what motor is in this thing? Are you only going to use it for the drag strip, and what front suspension are you running?

Originally Posted by vlad
Do you know anybody else who built that many bad ass E30s?
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Old 09-12-2008, 07:28 AM   #6
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Wow impressive. I think last I saw your other thread was on BF.c

So whats under the hood?
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Old 09-12-2008, 07:31 AM   #7
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hey guys thanks

under the hood is a built s52 - low compress motor, running 22psi on a GT35r.

I made 562whp and 580 tq back in april and that is kinda what lead to this project - i was sick of spinning tires all the time

i'll post some more of the suspension build in a few

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Old 09-12-2008, 07:45 AM   #8
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ok so on to cage fab.. I decided to do this in house after getting some quotes and long lead times


here is some pics of the mock-up.

need to weld in my 6x6 plates here

nice match of the body

anchor points for rear of cage

lots more to fit and adjust. door bars, i'm still trying to decide if i want to do swing out. and there are two more diagonal bars that go in the hoop / cross bar to the rear subframe cross member


oh man, just got back from a long day at the garage. working on the tin work, and got the floor plates welded in for the main hoop

the passenger side was a bitch because the stock wheel well is all over the place to account for the fuel tank fill

pro street anyone?

then i switched over and formed and welded the floor plates - not an easy job with 1/8" metal


more worky


did a little work this weekend - but not as much as i wanted too. It was just too damn hot out in the garage...

the car is finally sitting under its own weight.. still needs some adjustements for camber / toe ,etc. And the car will be raised up another inch or so. I was happy however that it rolled in and out of the garage smoothly. it all needs to come back apart before its done for painting, etc. but i needed to be able to roll the chassis around to take it down the street to TIG weld the cage.


i guess i'll update this thread more often since my other one got locked ( on BFC)

finally got the correct parts in for my drive shaft shop drive shaft.. 3" chromoly

mounted up nicely, but i needed to clearance the tunnel and temporarily get rid of the ebrake.

plenty of clearance about the 2x3 cross member which is important because i designed the whole suspension to be able to drop down 1.125" inches to different mounting holes for added wheel clearance but still maintain the correct geometry. Also got my rear drive shaft hoop in

also worked on getting my subframe bars fitted to tie the subframe 2x3 crossmember to the roll cage.. this was a major pain in the ass. you can see my e-brake filler plate here. i'll probably have to mount something on top of this for e-brake

hoping to take off work friday and tig the cage..

then everything needs to come back apart for paint.. fuel, auqamist.. then its pretty much ready for the road


took the day off work yesterday and got the cage fully tig'd.

still need to do the door bars though


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Old 09-12-2008, 07:48 AM   #9
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slowly making progress.. i'm hoping to get the car primered underneath, seem sealed, etc.

got the front and sides of the tubs done. really makes it look cool.

think there will be enough room?

only one more panel to make (what would be the panel behind the back seat). then i just need to finish my welds here and there and start to re-assemble

other cool thing is the stock rear door panels still fit! so it will look super stealth with some carpet covering everything in the back.


little update

trying to finish up the door bars before i seriously throw something at the wall.. frustration trying to get everything to fit - and i'm not at all happy with the swing out hinges i bought but i'm trying to make them work.

short end of it is - the door bars can't be in place for 'street mode'.. the door panels get in the way - so most likely i'll just run the door bars at the track and pull the door panels off

hope the door bars are up high enough - they are supposed to pass through between your shoulder and elbow. But i have a feeling i'll be tearing the door bars out within a year and going to a full 10 point cage so it probably won't matter much

and i've finished all of the sheet metal panels

if you can't tell - the project is starting to wear a little thin on me


little update since i'm having a slow day here at work

I had to revise my camber rod mounting points on the diff as the pressure bent them outward when i set the car down..

so i had another plate waterjet cut that goes behind the rod ends. prevents the bolts from being able to spread out.. I'm most likely going to weld in a plate between the two plates to make a U channel of sorts

I also got the diff cover back from having a chunk of aluminum welded on to mount the tow adjustment rods.

now i gotta spend some time cleaning it all up and powdercoating it before it goes back in the car


killed some braincells tonight, and epoxy primered the underneath.. looks cool now that its all one color.

next, to slather on some seam sealer and then undercoat


finally found my memory card for my camera. then i lost it again, then i found it all in the matter of hours. but here are some new pics after the undercoating.

some of the pics don't lend themselves to how great it turned out.. i had some friends over last night who were amazed at how much different it looks now over just two weeks ago.

and now i'm starting to lay out the fuel components


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Old 09-12-2008, 07:53 AM   #10
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Jay post up the vid of it. Your fab skills are killer dude!!!!!!
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Old 09-12-2008, 07:57 AM   #11
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Originally Posted by Good & Tight View Post
Jay post up the vid of it. Your fab skills are killer dude!!!!!!
thanks again!

haha i'll get to the video.. gotta keep them in suspense

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Old 09-12-2008, 08:21 AM   #12
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did a little bit of work over the weekend. started in on the braided lines for the fuel.

I also finished up my camber bracket and did some powder coating.. Accidentally used the wrong red on the calipers, but i kidna like it

here is how the camber bracket came out, with the extra back piece and boxing it

and started bolting up some of the components.. tomorrow i'm going to throw in the diff, axles and driveshaft


made my -10 fuel rail, its huge!

old verses new

got all my lines made, and new regulator and filters installed

primered and undercoated the truck

tonight i should be able to finish getting the tank installed and hopefully fire it up..

although i don't have brakes yet, so i can't drive it around for a few more days


key was turned! all went well. i'm uploaded a video to youtube here.. just shows the suspension and a loop around the parking lot at low speed

i'm super happy with how the first test run went.. really no problems at all.

the car sat lower than i wanted when i first pulled it out, as it settled more than i expected. I cranked up the coils about 3/4" and might do another 1/4 to 1/2 before i leave them

ok here it is


crazier videos to come ones i finish up a few small details. like bolting the seats in

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Old 09-12-2008, 09:58 AM   #13
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Jay, you are crazy, in a good way ! LOL.

P.S. How much hp in your green e34 ?
Mtech1 v8 build thread - https://www.r3vlimited.com/board/sho...d.php?t=413205

OEM v8 manual chip or dme - https://www.r3vlimited.com/board/sho....php?p=4938827
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Old 09-12-2008, 10:04 AM   #14
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thanks man - yes i am certifiably crazy at this point. haha

the e34 is Jon '5mall5nail5' on bimmerforums. his build isn't finished yet, but he is shooting for between 800 to 1000whp i would say

600hp beast
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Old 09-12-2008, 10:40 AM   #15
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Damn, what a beast.

Do you plan on having such things as license plates on this thing?

Just incredible, you shame us all.


Closing SOON!

Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

Thanks for 10 years of fun!
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