Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power? Send us an email at jason.sands@sorc.com and we’ll do our best to answer it.
| The She-Devil truck built by TS Performance had its head studs threaded in one at a time and has survived dozens and dozens of nitrous’d dragstrip passes in the 11-second range. Again, we’d only recommend the single-stud method on low-mileage and new vehicles. Older vehicles should have their old head gaskets replaced, and in many cases it’s also a good idea to resurface the head.
One at a time does the trick?
Question: I was reading the article about your ’97 7.3L Power Stroke injector and head stud install in your May ’11 issue. I have a ’99 7.3L, and I was talking to some folks at a local diesel shop who told me you don’t have to remove the heads to install head studs, you just have to replace the factory head bolts one at a time with the head studs, thus eliminating the need to replace the gaskets. A part of me thinks this sounds great, since it can save $150, but another part of me thinks it just sounds like they could fail earlier.
Will Hanley
-Via email
Answer: The answer to your question is both yes and no. Gaskets will distort, change, leak, crack, and do any number of things over the thousands of heat cycles engines go through as time progresses. We’ve seen one stud threaded in at a time work on the newer common-rail trucks, and the reason there is twofold. As horsepower rises, tolerances are closer than they ever were, which means more attention is paid to the straightness of the head (or heads) and also the deck of the block. A surface that is truer will have less of a chance of blowing out, even with a stock gasket. The second reason this works on newer trucks is that the gasket is still relatively fresh, usually with just 20,000 to 30,000 miles on it at most—plus it’s a newer design. On high-mileage or older vehicles, a fresh head gasket can do wonders—even with just a new set of bolts. It’s tempting to do the studs one at a time because of the labor savings and time factor, but unless your diesel is strictly a drag race or sled pull play toy (and you don’t care if the head gasket blows), we’d save the one-at-a-time method for trucks that are just a couple of years old or have a couple thousand miles on them.
4R100 to 5R110 Question: I have a ’99 Ford F-350 with 4:10 gears, and I was wondering if I could switch over to a newer five-speed automatic transmission to get better fuel economy, and so the engine doesn’t spin so fast while cruising. I don’t tow super heavy—mostly just an open trailer with a race car on it.
John Urgo Camarillo, California
| Old Power Stroke-powered 7.3L Fords are perhaps some of the best tow vehicles around, as long as they are well-maintained and EGT is kept in check. Although many may think tall, skinny tires look kind of goofy, they’re very functional in helping fuel economy and giving the engine a good rpm drop.
Answer: Well, you can do the swap, but we wouldn’t recommend it. High gear (Fourth) on the 4R110 is a 0.71:1 overdrive ratio, while Fifth gear on the 5R110 is the exact same ratio: 0.71:1. The change from four to five speeds was made for various reasons, namely emissions—and to keep today’s higher-revving diesels in their powerband. If it were our truck and we were looking for a little more gear, we’d get it by either putting slightly taller tires on the vehicle (just a few inches will make a big difference) or changing the rearend gears. Since you don’t tow super heavy, the truck can probably make due with 3.73 gears, even while going up hills or in passing situations.
If it’s time to buy new tires, taller tires can have a drastic effect on overall gear ratio. For instance, changing from a 215/75R16 tire to a 235/85R16 tire would net a tire height difference of 3 inches: 28.7 inches versus 31.7 inches. This larger-diameter tire would actually have almost the same impact on cruising rpm as changing the gear ratio in the axles from a 4:10 ratio to 3.73 gears, and the tire route would most likely be cheaper, too.
Camming for Performance?
Question: I have an ’02 Dodge with a 64/65/13ss from High Tech Turbo, 150hp Dynomite Diesel Performance injectors, and I run an Edge box. The truck dyno’d at 420 hp and 1,077 lb-ft on Scheid’s Mustang dyno. I am looking for a little more power and a little quicker spool-up, and my buddies keep telling me a camshaft would be a good idea. Will a performance cam help with performance? If so, which one should I choose?
DJ Morgan
Cosseen, Illinois
| Installing a camshaft is a fair amount of work, but the rewards of better driveability, spooling, a wider rpm band, and fuel mileage can be worth the effort. To see a good example of what goes into a Cummins cam swap, check out “Camshaft Swap” in the April ’09 issue of Diesel Power.
Answer: Well, a cam will definitely help performance, but not in the way you’d expect. In the naturally aspirated gasoline world, camshaft changes can bring hundreds of extra horsepower. With diesels, things are usually a little different. In most cases, if the truck is modified, power will rise—usually to the tune of about 20 to 50 hp (depending on the rest of the engine combination). But there are many other benefits in addition to the power gain. Spool-up time will be greatly reduced, and EGT will also drop. In many cases (as long as you don’t hot-rod around too much), fuel economy will improve. If you have enough fuel and air for high-rpm performance, a performance cam can extend your powerband in the upper-rpm range. It will also allow more air into the engine, so boost will often drop (at the same power level). So a cam can make life a little easier for your turbocharger. In summation, a cam swap helps down low and up top, is easier on parts, and gives a little added power to boot.
As far as which type of cam to choose, it relies heavily on your engine combination, so it’s best to talk to an actual cam grinder about your selection. Hamilton Cams (www.hamiltoncams.com) has done extensive testing on the Cummins engine and offers all sorts of camshafts, from mild to wild. Its 181/210 cam is a popular choice, because it is one of the larger camshafts you can install that doesn’t require fly-cutting the pistons for clearance. In your mild application, we think it would be the perfect choice for that little more you’re looking for.
