While walking the pits at an IMSA race at Sonoma Raceway, NASA Utah racer George Smith noticed something about the pro-built Corvettes that was a little different from the one he’d built. At first he couldn’t quite put his finger on it, but then it hit him: the engines had been moved back in the engine bay.
When Chevrolet engineers designed the C5 Corvette, they moved the transmission from behind the engine to the rear of the car and made it a transaxle, all in the name of improving weight distribution. Smith’s car already had good balance, with 49.4 percent of the weight up front and 50.6 in the rear.
“The Whelen Engineering guys, Ted Marsh, had all the Whelen cars out at Miller Motorsports Park,” Smith said in an interview. “I spoke with Ted a little bit and I was looking at the cars. They had four Corvettes there, and all of them had the engines moved back. I thinking this seems to be a trend.”
Thinking the pros might be onto something, Smith made the same modifications to his car in the winter of 2014-15 season. With help from trusted machine and driveshaft shops, Smith made all the modifications at home in his garage. Of course, this is no casual undertaking, but for racers who perform most of their fabrication and modifications themselves, it is doable.
This isn’t the first time we’ve written about George Smith and his car. You can see previous evidence of his talent and craftsmanship in previous stories. Here’s one from May 2015 and here’s one from May 2016.
“They told me it would alter the weight balance by 1 percent, and that’s exactly what it did,” Smith said.
When he was finished, the weight distribution changed to 48.5 front, 51.5 rear. The added benefit is that he also was able to lower the engine in the chassis by three-quarters of an inch. In terms of benefits, Smith said the modification helps him get off the corners better, but because he also has made other improvements to the car, Smith can only estimate the difference moving the engine back has made, about .02 to .05 seconds per lap.
“The thing I guess I’ve noticed is that before, when I would go out and qualify, I would go out with a full tank of gas because the car seemed to like the weight back there,” he said. “But as I got to about a half-tank of gas, the car would start handling a little less firm in the rear. Sometimes it’s hard to tell if that’s the tires getting used up, getting hot or what, but overall I would say that I don’t notice the difference between a half a tank and a full tank anymore.”
Smith said his brake bias didn’t change, but did have to soften up the front sway bar and add a little toe-out to get rid of a little understeer. What’s more, he no longer fills the tank before qualifying.
So what’s involved? The modification is substantial, and there is no kit you can buy, but we will outline here what’s involved and how to do it. Smith moved his engine back by 2 inches, which is a lot. That meant shortening the torque tube and driveshaft and “massaging” the torque-tube tunnel frame rails to clear the bellhousing. Smith also had to find a way to protect wiring and plumbing from heat from the headers and have new engine mounts made. It also involved a slight rerouting of fuel supply and return lines run inside the transmission tunnel. Let’s break it down one modification at a time.
Driveshaft and Torque Tube
This is probably the easiest part of the job because you just take the torque tube to a trusted machine shop that can cut the front of the torque tube and weld it back together. It’s as easy as writing a check.
“You want to shorten the torque tube on the engine end of the torque tube, because if you shorten it on the other end, you’d have to change the shift linkage,” Smith said. “It just makes a lot more sense to cut the front of the tube.”
The driveshaft that goes inside the shaft is largely the same story. Smith took it to a shop that specializes in driveshafts — every town seems to have at least one — and had it shortened and balanced. Then the real work began.
Transmission Tunnel Frame Rails
To move the engine back, Smith had to “massage” the steel rails that emerge from the transmission tunnel to allow the bellhousing to clear it. Smith used a 6-pound hammer and a flat piece of metal to flatten the rails so the bellhousing would clear. The clearance is essential so there the powertrain remains isolated from the chassis.
“It doesn’t take a lot, but there are a few places inside the tunnel where the bellhousing is going to touch and you don’t want it interfering with the frame,” Smith said. “Even if you could get it to fit in, you’d have a lot of vibration going through to the car, and you don’t want that.”
Smith had to have new engine mounts custom made. Because there’s a strengthening rib on the underside of the subframe, and Smith didn’t think removing them down as a good idea, he had mounts made that accommodated the rib, yet still fastened to the subframe with three bolts. Smith made drawings for a shop to fabricate the new mounts, and they had to build a couple of iterations to get it right.
“It wasn’t the first attempt,” he said with a laugh. “We learned by doing.”
Smith also notched the subframe a little to clear the pan and created some clearance on the right side by grinding off a little of the right side of the subframe. It wasn’t too difficult because the subframe is cast aluminum.
By moving the engine back 2 inches, he crated more clearance between the dry-sump pan and the subframe, so he dropped the engine three-quarters of an inch. He couldn’t lower it any than that because the headers prevented it.
When Smith moved the engine back, it was about time for new headers anyway, but he didn’t have to go full custom. LG Motorsports in Lewisville, Texas, sells a header set that fit the bill. Smith had a good relationship with LG as a long-time customer. Ironically enough, LG Motorsports owner Lou Gigliotti’s racecar was one of the first cars Smith saw with its engine relocated.
“When they designed their long-tube headers, they kind of took that into account,” Smith said. “There’s nothing special about the headers. They’re the standard long-tube headers, but they’re a not as low as some of other brands out there, so they allow you to do this and get away with it.”
Relocating the engine obviously puts the headers closer to the firewall, which meant that Smith had to fabricate an aluminum shield for the plumbing and wiring. There were harnesses, and fluid lines for the clutch release bearing and brake lines. In addition to the aluminum shield, Smith used foil blanketing over the plumbing and wiring.
This is where the job got a little tricky, if it already hadn’t. Because the fuel supply and return lines are routed from the factory down the torque-tube tunnel, and because the bellhousing was so close to the firewall and tunnel, Smith had to relocate them, at least partially.
“There’s not enough room there, so I was given two choices,” he said. “I could either reroute the fuel lines along the frame rails, bring them up the car along the passenger side frame rail or the second option, which was to knock a hole in the torque tube tunnel just before the firewall, run them on the inside of the car and then back through the firewall above the bellhousing.”
Smith chose the second option, then fabricated a metal housing to contain the fuel lines because the CCR says you can’t have exposed fuel lines inside the car. The fuel lines travel up the torque tube tunnel, into the cabin in an aluminum encasement, then through the firewall into the engine compartment above the bellhousing.
Moving the engine back did make removing the heads a little more difficult, but Smith has done that job since the modification and it wasn’t that big a deal. The engine relocation makes some things a bit tighter, but it also made it easier to get the whole engine out, believe it or not. Here’s why.
To decouple the input shaft from the pilot bearing, the engine needs to be able to move forward. With the engine in the stock location, the harmonic balancer would hit the steering rack before the input shaft would come out. With the engine relocated, the engine can move forward far enough for the shaft and bearing to separate. Now, Smith no longer has to remove the steering rack to get the engine out.
All told, Smith did this job as a winter project. The offseason provided him with enough time to do it and tackle each problem he encountered. And he did it all at home in his garage.
“I think the thing that makes it relevant for most of us is this wasn’t high-dollar fabrication-shop work. This is stuff that a guy who is reasonably handy can do himself,” Smith said. “This is not for the faint of heart. You’ve got to be determined to do this. It’s not difficult, actually. Knowing the things I know now, it’s much easier the second time, but I went in blind and discovered one problem after another, and had I known that these were the issues I was going to get involved in, it would have made it a lot easier.”
And he just made it easier for you.