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Unread 08-06-2013, 04:27 PM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default Re: Vorshlag Shop Truck - 5.3L SWB GMT800

Project Update for August 6th, 2013: Another 10 weeks of driving the GMC "Shop Truck" and I've had two flats, the starter took a crap, and I cracked the F'in brand new windshield - but we've made a lot of repairs, updates, and improvements along the way. We even tackled some new development for the GMT 800 chassis, like the custom-fit Bilstein 5100 shocks, and with Forgestar's help we developed a custom F14 wheel that fits this truck perfectly (never before used on this chassis). We also added a new Alpine head unit and built a kick ass custom stainless exhaust system.


Left: Old Edlebrock shorty headers and ARH Long Tubes. I freagin' HATE shorties. Right: Ghetto old exhaust had fallen off aft of the Series 10 Flowmaster.

The leaking Edlebrock headers were driving me nuts, and the ghetto exhaust (half of which had fallen off in some swamp, I assume) sounded terrible even if you ignored the "CAK-CA-CACK" leak. So we ordered a set of American Racing Headers 1-7/8" stainless long tubes made for the GMT800 chassis, but decided not to use their Y-pipe or cats. We planned on making our own header-back exhaust in house. The standard ARH Y-pipe normally included was a dual 3" into single 3" system, to match the factory exhaust routing, and that just wasn't ... custom enough for Vorshlag's shop truck. Remember: we're trying to show off products we sell as well as the custom fabrication work we do, so a completely custom exhaust was built instead.

After ordering the long tubes... well, we got busy at Vorshlag. Our own cars don't get worked on until the shop slows down, and it didn't slow down for months. So this beautiful set of headers sat around for a few weeks while the service shop was buried in race prep/suspension/fab/repair work (we've since hired another tech, our third, and he's helping pick up the load). I kept driving the exhaust-leaking-truck to drop off and pick up parts, but then the starter began to flake out. At random times the truck would just not crank at all, it took a whack with a hammer to free up the solenoid, then it would work for a day or two more. Looked like the original starter, which lasted 236,000 miles, so we picked up a new Bosch unit for this 5.3L V8. But to get in there to change it, the old headers had to come out. Now was the perfect time to do the new exhaust...

High flow catalysts keep the nasty exhaust gases in check and keeps the truck street legal.

A second reason we kept putting off the header install was a busted exhaust stud. When the starter finally died The True Death, we sent in Ryan to get the broken exhaust manifold stud out of the head (located right at the firewall, of course), which was a bit of a chore. It had broken off flush to the head ages ago and two easy-out bits broke before he went to Plan B. This was when he welded a nut to the end of the broken stud, then carefully ... turned... it... out. Beautiful - no threads were damaged and the guys went on to install the ARH long tubes.

These new full length headers went on and the new starter was installed with new ARP LS1 12-point header bolts. Instead of keeping the standard "ball and socked" exhaust flange which comes on these ARH's and most other aftermarket headers' collectors (which can cut down some exhaust flow), Ryan cut those off. Then he installed a pair of our U.S.-made, all stainless 3" V-band flanges to the collectors. This gives a smooth bore at the header to exhaust junction, thus no exhaust flow restriction. Behind these he added some 3" mandrel bends made of more U.S.-made 304SS tubing, two 3" high flow cats, and a bunch of bends to get the routing over to the passenger side, which has more room than the driver's side (where all of the fuel and brake lines run + the fuel tank is located).

Round case MagnaFlow XL 3-Chamber Mufflers - just turned out to be too big for the space we had.

The plan was for the twin 3" tubing to run back to a pair of MagnaFlow 3" stainless XL chambered mufflers, mounted side by side just behind the cab, then out to the passenger side and exit just in front of the right rear wheel. We had ordered two round case 3" in/out 3-Chamber XL units, but they ended up being too long and had too much girth... hehe, that's what she said. So we went back and found some "suitcase" style MagnaFlow XLs instead.

Square case MagnaFlow XL 3-Chamber mufflers fit side-by-side in the space we had and still have great flow and sound.

These MagnaFlow XL mufflers are relatively new and look quite nice, but most importantly they are priced right. These are not the typical MagnaFlow fiberglass packed straight-thru mufflers, but have routing and chambers for a different sound, and could potentially last longer - who knows? I wanted to hear how a pair of these XL's sounded behind an LSx V8, and that's what this truck has (5.3L "LM7" V8 with aluminum heads and iron block). To me, it sounds like a Flowmaster... which means it sounds good. And these XL mufflers are made of real 304SS, and not a lower grade (409?) "stainless" like the still-painted Flowmaster series 44 mufflers. I think these are going to be a great muffler for us here at Vorshlag and we are going to keep a handful in stock for custom exhaust work.

Surprisingly these are both very light mufflers, with the suitcase XL units came in at under 9 pounds each. Cool. One of my unstated goals on this truck is to keep it as light as possible, and we have been dropping pounds here and there along the way.

Left: Here you can see the "H" style crossover tube added, to equalize pressures in both pipes. Right: Both tips exit ahead of the RR wheel.

The final exhaust sounds great - more like an LS1 powered muscle car - but isn't obnoxious at all and the noise level in the cab seems to be cut in half. The entire system is now tucked up above the frame, so if we lower the truck a LOT it won't scrape, like the truck had done on the old muffler. The starter is new, the headers are higher flowing and leak free, the manifold leaks at the header are gone, the exhaust is now 100% 304 stainless steel so it should last forever, and the finished system looks damned good. The Vorshlag crew swapped in some red Taylor 10.4mm spark plug wires and put new Bosch plugs into the heads while they were in there. This truck runs better than it ever has - pulls strong at all RPMs and it easily turns the old, crusty 285mm tires into billowing plumes of smoke!

As you can see, we chose a side exit for both 3" diameter exhaust tubes and decided to forgo any chrome tips or other fancy end treatment - just the raw 3" stainless tubes, cut at an angle to match the lines of the body. This side exit was done to minimize the length of the system, simplify the routing, and to keep from having to do the over-the-axle bends needed to exit at the rear. The rear axle area is going to get tight if we lower the truck more, and the necessary bends always restrict flow. We actually got busy during the install, so Ryan temporarily had the exhaust stop at the end of the mufflers. A couple of weeks later when he had half a day to finish, he made the exhaust tips and added another poly-isolated hanger for that aft section.

We make custom stainless steel, mandrel bent exhaust systems like this for sports cars every week. It isn't the cheapest solution, but it always fits better than Off The Shelf kits. Of course Vorshlag has a keen eye for minimizing weight and making the system route perfectly, so each system we make is lighter and better flowing than virtually any OTS system.


Many of you know we're a Bilstein / Bilstein Motorsports dealer. If you don't, read this Press Release talking about the shocks we sell. We're adding more Bilstein parts to our website every month, but we still have a lot more to add. Anyway, Bilstein makes a wide variety of OEM replacement monotube shocks and struts. This GMT800 is a 2WD version so it has a double A-arm front suspension with a steering rack, coil springs and regular "divorced" shocks (not a coil-over style). The rear is a leaf sprung solid axle with two traditional shocks also.

The ride on this truck was obscenely bad. After 236K miles it shakes, rattles, and rolls over the slightest bumps. The front suspension arms looked okay, but the tie rods were looking ratty and should be replaced soon. By far the worst offender in the suspension were the shocks - and we knew that one or more was shot. Turns out three of them were blown.

New Bilstein 5100 monotube shocks went on the Vorshlag Shop Truck. 5100s feature huge 46mm pistons and silver bodies.

We did some searching in our Bilstein dealer database and found that they made the regular "Sport" (yellow) monotube shocks (with 36mm pistons) for this model/year/configuration of GMT800 truck, but did not have the heavy duty "5100" (silver) Bilsteins with the larger 46mm internal pistons that I wanted. There are a LOT more Sport offerings for OEM shocks than 5100s. We faced the same dilemma on my 2006 Dodge 3500, and I was stuck with Sport Bilsteins when we replaced those (they still rode well). But now that we were a Bilstein dealer, I wanted to push further and see what we could come up with.

Jason took measurements, made some calculations on the proper stroke and body lengths, took into consideration the OEM shock end mounting arrangements at both ends of each damper, dug through our dealer catalog, and ordered up some 5100's based purely on dimensions. The ends were "very close" but we had to drill out one "eye" to fit a larger bolt on the rears, the clevis ends had to be slightly modified on the fronts, but these 5100's eventually fit perfectly at both ends. And man, was it worth the extra effort!

The difference in the ride quality on this truck was Night and Day. Freagin' amazing... it was skipping over bumps and rattling my teeth out before, and now the ride felt smooth yet firm. So glad we went the extra mile and got the 5100's to fit. And while they might need to change when/if we lower the truck more than it already is (it has a stock front height, 2" rear drop shackle), these don't cost a fortune and we can chalk that up to a Test That Worked.

Continued below

Last edited by Fair!; 07-03-2017 at 09:11 AM.
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