Did some searching around and I know its a common thing to do with lots of engine swaps (to fit exhaust components, intercoolers, etc).. but has anyone ever written up a detailed account of their trunk cutting experience?
A while back I made a custom side exit exhaust... which I've grown tired of and I'm looking to do something different again. I'm open to cutting my trunk since I rarely drive the car anymore so I don't need the space. Just wondering if someone has taken any measurements of exactly where they cut and the process by which they stitched it back up, what the panel looked like, etc etc.
It is good to see you are still around. I did a few search's and did not come up with any write up either. Just a lot of discussions about the subject or pictures of it already completed. Most just cut the bottom out, the area that reduces size in the trunk, and just go from there. That seems to give the most room and still maintain some trunk space.
Warning: Truck is a Structural part of rear framing and Many Cut part or all of it then find out that causes problems. Is why most areas are Not simple thin sheet metal.
Front of truck is also the Strut Tower bracing. Way more bracing some "added" aftermarket bracing on top of towers that does little to nothing. Bottom of truck is basically a Beam ties the rear lower frame and cradle so can't move.
Even if you "Find" a write-up to mod the trunk, most are useless and have problems but most don't bother posting that info months to years latter. Some junk them by then for various reasons. Worse many have sold to first sucker that have no clue how bad the truck mods can be.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Warning: Truck is a Structural part of rear framing and Many Cut part or all of it then find out that causes problems. Is why most areas are Not simple thin sheet metal.
Front of truck is also the Strut Tower bracing. Way more bracing some "added" aftermarket bracing on top of towers that does little to nothing. Bottom of truck is basically a Beam ties the rear lower frame and cradle so can't move.
Even if you "Find" a write-up to mod the trunk, most are useless and have problems but most don't bother posting that info months to years latter. Some junk them by then for various reasons. Worse many have sold to first sucker that have no clue how bad the truck mods can be.
Ogre, the sides and bottom of the lower trunk well are not tied to the lower frame rails, nor do they provide any structural support to the spaceframe.
This is the area that some people cut out to make room for their exhaust.
The upper trunk does provide structural reinforcement, as you described in your post. Lower frame rails bracing is accomplished by the rear cradle mounts and the rear impact beam.
Man I needed to see that, I have been staring at the hole in my trunk for 5 years now. Someone needs to start selling the precut trunk floor, maybe even with those plug holes cut out, I wonder if its possible to rivet that in also for the non welders among us?
Yes, as Orgre said; don"t cut the top brace as this links the strut towers. You can move back the sheet metal below the brace to give youself more room, as I did. I have a great big turbo sitting on the back exhaust manifold! I fixed the gaps with sheet steel which was riveted afterwards. I still have a usable trunk.
After having done several 3800SC swaps and one 4.9L swap we have never had to cut the trunk one bit . The exhaust system that was used did not even require removing the trunk heat shield. Was also able to achieve acceptable (3800SC) to relatively low (4.9L) exhaust noise. Don't cut the trunk. You don't need to and your significant other will appreciate it. Even with the full trunk, you only have enough room for two small carry on pieces of luggage. Cutting that trunk gives little room for anything. I you do decide to cut the trunk then, who's going to buy a car like that?
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
I had to "modify" the trunk to get enough room for the muffler and cat to fit. If you look at the trunk from the side, the bottom of the trunk is slanted from the front of the car up to the back of the trunk. I cut that slant off, bringing the "front" of the trunk bottom up about 3" . Now the trunk bottom is flat, but still pretty deep, and gave me room for the muffler to fit without hitting. To finish off the bottom, I bent the cut edge of the trunk in about 1/2" all around ( slitting the edge every 3-3" makes this pretty easy). I then fit a piece of sheetmetal to fit into the trunk bottom. Once you have the fit right, put some weight into the trunk on the new sheetmetal, then go underneath and drill 1/8" holes through the bent tabs through the new floor pan, and secure with pop rivets. You could also weld. Seal, and then wrap with heat reflective material ( I used mighty mat 1/4" http://www.bgf.com/products...degrees/mighty-matt/ ). The stock heat shield can go on top of the MightyMat if you have room- I did.
Thanks for the welcome back guys... it's definitely been a while. And thanks for the links and info so far.
I previously had a magnaflow full size muffler in the back without having to cut the trunk but the welds on it weren't great and the crushed pipe was awful. It was something patched together to quickly get the car on the road after my 3800SC swap years ago.
The challenge I am having is that I no longer have the crossover pipe on my 3800... I am running the ZZP power logs, the front one I modified to dump downwards instead of up and over the transmission. So I somehow have to get a dual exhaust to fit around and in the compartment back there...
Wtfb, is Lunatic still around (if you know him)? Would he be willing to share that pattern for the trunk floor?
Here's how I did mine with both manifolds dropping straight down. This is on a sbc, but similar design should work with 3800. Front side manifold drops down and follows the stock exhaust path under the engine. Rear manifold drops down and connects at a y just before a turn into the muffler. I used a stock Fiero muffler that I modified for 2.5" inlet and outlets as well as adding a bypass valve. No trunk cutting needed.
The only picture I could find of it:
[This message has been edited by liv4God (edited 05-09-2020).]
To make an exhaust that fits without truck cutting you will need a Spintech crossflow muffler. Fits like a charm. Here is part of what it looks like on my 4.9L swap.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Thanks for the welcome back guys... it's definitely been a while. And thanks for the links and info so far.
I previously had a magnaflow full size muffler in the back without having to cut the trunk but the welds on it weren't great and the crushed pipe was awful. It was something patched together to quickly get the car on the road after my 3800SC swap years ago.
The challenge I am having is that I no longer have the crossover pipe on my 3800... I am running the ZZP power logs, the front one I modified to dump downwards instead of up and over the transmission. So I somehow have to get a dual exhaust to fit around and in the compartment back there...
Wtfb, is Lunatic still around (if you know him)? Would he be willing to share that pattern for the trunk floor?
Yes Shayne (Lunatic on PFF) is still around and we talk once in a while. I will ask him.
------------------ 86 GT built 2.2 ecotec turbo rear SLA suspension QA1 coilovers on tube arms
