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Old 06-13-2008, 10:53 AM   #1
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Default 98 Grand Prix GTP RWD conversion with LSx/T56

Hello all!!

I have a 1998 Pontiac Grand Prix GTP that I am going to be cutting into very soon here to start this project. It's going to consist of several main parts, so I'll list them here.
  • Rear end frame
    Obviously since I am starting with a FWD car, there will be many issues to overcome here. Without going into great detail, essentially it can be narrowed down into a few key items. First, all of the existing rear suspension will be removed. Then I will have to remove the fuel tank, as it is in the way of both the rear end and a driveshaft. The trunk floor will be cut out, and the frame member that the rear suspension bolts to will be in the way and will have to be relocated. Then I can start building the new rear frame to support the rear axle.
  • Mini-tubs
    Another person I know is undertaking a very similer RWD conversion on his 97 GTP, and he already has the rear frame completed. However, he has noticed that the stock wheel wells are going to prohibit him from running much more than a 275 tire. As I want to run 315's at the least, I decided to tackle this right away by cutting out the old, and building new wheel wells, approximately 5 inches wider than the original. I would go wider except at that point I run into complications with unibody frame rails.
  • Fuel tank
    After much thought about fuel cells, tanks and the like, I decided to fab in a 1990 Caprice tank, with the filler neck behind the rear plate. This will allow me to shave the existing filler door, and will be one of the few external hints at custom work on the car when it's done.
  • Drive shaft tunnel
    Yep, you guessed it.... the stock tunnel is only about half as tall as it needs to be, so that will be cut out and replaced. At the rear this will be pretty easy, and won't even cut farther into the trunk space.
  • Transmission hump
    This part will be a little trickier. I won't know until the cutting begins, but right now my thinking is to cut the entire doghouse out of a late model f-body and fab it in.
  • Front suspension and steering
    The other person that is doing this project is using an f-body k-member, and I am going to emulate him. It's fairly straightforward, the member fits nicely between the frame rails in the engine bay, and just needs some brackets fabbed for it to bolt to. The steering rack will likewise be from an f-body, mounting in the stock location. For support, the front suspension will be staying with the factory MacPhearson strut, but I will be installing custom coilovers here.
  • Driveline
    The current plan is to make arrangements to start with a stock LS1 (LS6 if I can get my hands on one for cheap) mated to a T56. After the car is finished and sitting pretty, all of the loose ends tied down, modding will resume. My eventual goal is a Magnacharger, 600RWHP, and a sub-11 second 1/4 mile pass. This will all be turning a Ford 9" (Possibly 8.8 because of cost, if I can get the same kind of strength out of it) with gears around 3.50 to 4.10.
  • Misc.
    At some point I will be fabbing my own full rollcage. Plans are to keep the car passenger friendly.

Thanks for reading guys! I have learned alot from this section of the board, and it helped me figure out a lot of things in advance. I'll be updating with progress once it starts. The car has a few rust issues that need addressed first.

Comments are welcome, ideas even moreso!
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Old 06-13-2008, 01:20 PM   #2
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Hmm, nice idea. Myself and a friend had some pretty heavily modified GTPs and had considered doing the same swap (mine was a ~350 wheel HP '98 Daytona Pace Car), but both of us went with RX7 swaps instead (lighter and RWD to start with).

Should be a cool swap if you get it all done. I was actually planning to utilize the FD (93-02) RX7 independent rear in mine, though the solid axle will be good for straight line stuff. Panhard bar setup I take it?
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Old 06-13-2008, 01:35 PM   #3
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Its going to be well worth it in the end. My opinion would be to keep the body pretty much stock on the exterior. Give it a sleeper look. Remove the GTP badge and put a WS6 badge in place of it. Basically a Grand prix WS6.
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Old 06-13-2008, 01:35 PM   #4
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my DD is a GP and I only wish it was 6 speed manual trans and RWD. Keep us posted on the progress.

Is this the guy you are talking about
http://www.cardomain.com/ride/2368085
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Old 06-13-2008, 02:52 PM   #5
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that will be a true sleeper when its done, good luck!
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Old 06-13-2008, 05:45 PM   #6
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It might be cool to have something different, but if I were you I'd save my pennies and just pick up a used GTO.
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Old 06-14-2008, 04:11 PM   #7
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On the GTO, I know what you're saying. My budget for this build is 10k, well less than a GTO. And I want a one-off, unique ride.

Measureing for the steel stock now, going to buy the first batch soon. Opinion poll: What size would make a good frame rail? I found some 1/8" x 2" x 4" x15'10" mild steel stuff for $95 a piece, like 10 of them available at a odds and ends supply place. Is that a good deal, and would it make for some good sturdy frame rails? Longest piece I'll be using is only about 40" in a single span.

Thanks for the good words you guys!! I love my GTP (And just so you know, the badges are already gone and I'm running a 3.4 pulley setup) and in the long run I know I'll be happy. The body is staying mostly stock, other than fat tires out back there will be no hints that it's RWD. The interior will also be mostly stock, except I'll be using four bucket seats (maybe from a GTO if I can get a good deal somewhere) and a different center console.


I havn't decided EXACTLY what rear suspension setup I'm going to run..... I'm probably going to copy Michael (the Cardomain link posted, and yes, also the one I refered in the original post) and run a torque arm with triangulated upper link setup. Though, I hear he's having second thoughts about that setup, so I need to talk to him. Too bad I don't have enough room for a 4-link.



Keep the comments coming gents, and feel free to suggest a rear suspension setup..... That's still the biggest question in my mind.
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Old 06-14-2008, 09:22 PM   #8
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man that will be cool, I would try to find a wrecked F body and cut the tunnel out of it and take everything you need.
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Old 06-15-2008, 02:23 PM   #9
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If my poor memory serves me; was'nt there an AWD concept Grand Prix from GM with a V-8 in the early 2000's? If so maybe someone would have pictures of the concept piece to help you engineer the RWD aspect of the project. My wife has a fully loaded 02 Grand Prix 2 door, and I always said why couldnt GM have made this V8 RWD from the factory. They are really comfortable cars, and the design is still relatively modern, that makes them all around good cars, only problem is the power comes out of the wrong axle. LOL
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Old 06-15-2008, 02:40 PM   #10
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For frame rails, I would just use a 2x3 set that is already made. This guy has quite a bit of stuff. This is where I am going to get my Cavalier stuff when I'm done with my Impala.

http://cgi.ebay.com/ebaymotors/Front...2146QQtcZphoto
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Old 06-15-2008, 04:38 PM   #11
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Quote:
Originally Posted by LS-10 View Post
If my poor memory serves me; was'nt there an AWD concept Grand Prix from GM with a V-8 in the early 2000's? If so maybe someone would have pictures of the concept piece to help you engineer the RWD aspect of the project. My wife has a fully loaded 02 Grand Prix 2 door, and I always said why couldnt GM have made this V8 RWD from the factory. They are really comfortable cars, and the design is still relatively modern, that makes them all around good cars, only problem is the power comes out of the wrong axle. LOL
It was called the Pontiac G8...

Google it, it will show up.

It was at the Chicago Autoshow back in like 2002.
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Old 06-15-2008, 06:21 PM   #12
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I couldn't find it there. They had the G-Force, and a concept called the PONTIAC SOLSTICE? LOL. They also had the Razor. MAN O MAN how I wanted one of those Mopars.
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Old 06-15-2008, 06:28 PM   #13
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The G8 used an AWD transaxle from an Aztek. It also had a two piece driveshaft to an IRS rear end, and GM broke it every time they tried to make a pass on the track. It was very poorly designed. It's also not the topic of this thread.

Since I need a lot of steel for some other parts of the car, will the 2x4 work for me? I am going to be putting rails tucked up inside the rockers, and they will be pulling double duty as SFC's.
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Old 06-15-2008, 10:24 PM   #14
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I don't see why it wouldn't work. I don't know what you want to use for a rear suspension, but the same guy has 4 link and ladder bar setups that use the 2x3 as well.
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Old 06-15-2008, 11:25 PM   #15
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They had that car at the GPG back in '01 and made all the GP guys crazy in hopes they would build it. I had my '00 GTP which I loved, and same as everybody else wished it would have been a manual and rwd.

FireFox, good luck with your project. You are doing something a lot of people have dreamed about at some point.
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Old 06-16-2008, 12:03 AM   #16
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This should be good. W-body fo' life.
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Old 06-16-2008, 09:50 AM   #17
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My feeling is if W-bodys had been RWD and had a manual option, GM could have saved their time with the GTO, and the G8 would still be a few years away.

Thanks for the support guys!!! If anyone spots a good deal on an LS1/T56, feel free to toss it my way.

I have a question as well.... What are some of the best routes to under body protection these days? I would look into that truck bed liner stuff, but that has to be heavy, and I'm all for a lighter option. I want to protect this baby when it's done.

Updates: I was poking around my rocker panels again yesterday, and man are they bad. At this point I'll be replacing pretty much everything behind the GT/P body cladding. So I will be tucking those 2 x 4 beams up in there and tying the whole frame of the car together. It'll also be a great place to tie my roll cage into.
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Old 07-07-2008, 10:51 PM   #18
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Small update: I started cutting the floor pan and drive shaft tunnel out of a late model F-body to see if I can't fab up a way to put it in my car, instead of making it all from scratch. One interesting thing I found which I did not know about was the fact that the floor pan isn't the same level on each side.... The drivers side is lower. So that may complicate things.

In other news, the battle against rust is maybe 50% done with in the rockers, I'm close to being able to assemble my SFCs and getting everything buttoned up. The frame is going to be stiff as a mother when I'm done with that.
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Old 07-08-2008, 08:48 AM   #19
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Need some PICS.

Thanks.
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Old 07-08-2008, 09:55 AM   #20
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GM did this to a Monte Carlo and had Hot Rod promote it as if it would get built if enough people wrote GM to make it happen. They used a modified F-Body floor pan. That's the direction I'd head.

My guess is that you'll reconsider running 315's in back unless you want 1 bucket seat or seats made for really little kids. Also consider how low you want it. Getting really low makes packaging that much harder.

I think this would be really cool if it ends up looking stock, no tube frame or tinwork interior. That's the tough part.
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Old 07-08-2008, 09:55 AM
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98, arm, bar, body, caprice, conversion, driveshaft, grand, gtp, ladder, lsx, pontiac, prix, replaced, rwd, swap, torque, trans, wt56


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