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February 2014 Top Diesel Tech Questions

You've Got Questions? We've Got Answers!

Mike McGlothlin
Feb 6, 2014
Photographers: Jason Sands
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.
Fearsome Ford
Question: I am looking at building a 7.3L puller for the local 2.6-inch Class, and I’m wondering how big of an injector I can run on the street without cracking and how much power I can make without bending the rods.
Brett Smith
Knoxville, Tennessee
Photo 2/4   |   Matt Maier’s ’97 F-250 is an example of a stock-bottom-end 7.3L Power Stroke that lasted approximately 15,000 miles while making 600 rwhp on fuel and 700 rwhp on nitrous. Before bending the Number 8 connecting rod, Matt regularly drove the 230,000-mile truck on the street, towed a 40-foot gooseneck trailer, ran high 11s in the quarter-mile, and even sled pulled all summer long. Matt admits he was very hard on the engine that failed, and that most 600-rwhp 7.3Ls will last a lot longer than his did.
Answer: That is a tough question for a stock- bottom-end 7.3L Power Stroke—mainly because you’re looking to sled pull and drive on the street. In our opinion, forged-rod 7.3Ls venture into “unknown” territory any time they breach the 500-rwhp mark. However, this doesn’t always mean engine failure is imminent. Offhand, we know of several factory short-blocked 7.3Ls making 600 rwhp or more and sled pulling, including Steve Constable’s 300,000-mile ’96 F-250, and a ’97 F-250 owned by Matt Maier of Full Force Diesel.
Fuel wise, anything in the 300/200 (300cc maximum flow, with a 200-percent-over nozzle) or larger area of injector can get a 7.3L to 600 rwhp, but it’s airflow that may be lacking in your case, depending on your local class’ turbocharger rules. Because you’re still looking to drive the truck on the street, we would stay away from 400-percent nozzles, as they’re known to crack due to each hole’s close proximity to one another, making the nozzle as a whole very brittle. A set of 400/200 hybrids or 350/200 hybrids could definitely get you to the 600hp mark, but then you need to worry about finding a tuner to make your bottom end live. Limited timing advance at low rpm is the only way to keep your stock rods from bending, so make sure your tuner doesn’t advance the timing until the 2,600- to 2,900-rpm range. This will hurt torque numbers a tad, but horsepower won’t be affected.
Long-Term Transmissions
Question: I’ve been following Project Rust Bucket (’89 Dodge) and Triple Threat (’95 Dodge), and I would like to know how the trucks’ transmissions have held up in the long term. I realize they were built to handle lots of power, but how are they holding up after years of use?
James Miller
Des Moines, Iowa
Photo 3/4   |   The transmissions in our ’89 and ’95 Dodges have seen a lot of hard use, which included nitrous’d dyno pulls, drag racing, sand drags, and some heavy towing—yet they haven’t skipped a beat.
Answer: Transmission building takes a whole lot of attention to detail, and we’ve been wise enough to select some pretty good builders. As far as Dodges go, our main project truck experiences have been with 47RH transmissions. The 47RH in Project Rust Bucket has a manual-shift valvebody with a trans brake and was built with parts from Diesel Performance Converters, Sun Coast Diesel Transmissions, and J&H Performance. So far, other than a transmission line coming loose and spraying fluid everywhere, we’ve had very little trouble with the transmission, which has seen numerous dragstrip passes, and a couple of 800- to 900-rwhp dyno runs. The truck lives most of the time at about 500 rwhp, which has probably contributed to the cherry-red condition of the transmission fluid and lack of broken parts.
Our ’95 Dodge, known as project Triple Threat, has led an even harder life and has roughly 100 dyno runs and 50 dragstrip passes in the 500- to 600-rwhp range. The transmission in that truck was built by Brown’s Diesel in Riverdale, California, with a Goerend valvebody and billet shafts throughout. Since the input, intermediate, and output shafts are all forged, we softened up the shifts, because there isn’t much flex in the shafts when running all-billet parts, and they have a tendency to snap under hard and quick shifts with the converter locked. With the relaxed shifts, we run a slightly higher risk of burning up clutches in the transmission, but it’s still better than a broken intermediate shaft, which turns the rest of the transmission into shrapnel.
With about 25,000 miles on one transmission, and 30,000 on the other, we can definitely say we’re pleased with the lack of problems so far. Since both vehicles are raced, parts breakage is a real possibility. We’re aware of that and will report on it if anything occurs.
Overkill CP3s?
Question: I’ve read about people who use modified CP3 pumps and also dual pumps on Duramaxes. Is there any situation where you’d need two modified pumps?
James Hildebrand
Via email
Photo 4/4   |   Running twin CP3 pumps is commonplace these days in high-horsepower trucks and will support more than 1,000 hp at the wheels. Kits are available from Pacific Performance Engineering (PPE), ATS, and Industrial Injection, among others.
Answer: Whether you need a stock pump, a modified pump, or two pumps basically depends on the horsepower and rpm levels you’re shooting for. We’ve seen a stock pump make 600 rwhp just fine, but we also found that when the injectors had a large amount of pulse width, it would drop rail pressure—and actually drop power—so we’d consider 600 rwhp a good benchmark for a stock pump. The power you can make with modified CP3s is often up for debate, but somewhere in the 700- to 800-rwhp range is a good guess, depending on your tuner and injector combination.
As far as dual CP3 pumps, we’ve seen more than 1,000 rwhp on twin stock LBZ pumps. Having dual modified pumps is mostly a question of rpm, as spinning 4,500 to 5,000 rpm downtrack will tax even twin stock pumps. At that amount of rpm, there is a very narrow window in which fuel can be delivered and actually make power rather than just heat. That means big injectors and a big hit of fuel all at once, very quickly, which can drain the rail in a hurry with big engine speeds. So while twin modified pumps do have their place, you probably won’t need them unless you have huge engine speeds and huge horsepower.



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