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.
New/Stock Transmission Questions
Question: I just bought a '96 Dodge Ram with the Cummins engine that has 200,000 kilometers on it, and the transmission was rebuilt 100,000 kilometers ago. My question is: Is there anything I can do to keep the transmission alive as I add more power? I heard these transmissions weren't that good from the factory, but since it was already rebuilt, I am hoping there are some tricks I can do on a budget.
Nick Emery
Kakabeka Falls, Ontario, Canada
| If you’re willing to hover around 400 rwhp and don’t play with locking the torque converter in earlier gears, you can get away with good clutches, a low-stall converter, and a shift kit on pretty much any transmission built between ’89 and ’02.
Answer: We've heard this before on the Internet, and there's really no basis for Dodge transmissions being "bad"-they were simply designed to operate at a certain power level. The big culprit for starting this rumor is the factory torque converter, which is designed to always keep the stock turbocharger up on boost. This means the stock converter is relatively "loose" or will slip until about 2,000 rpm-even in stock form. As power levels rise, the converter will slip more and more, until it's mostly just creating heat and not transmitting power effectively.
We've seen stock stuff hold 500 to 600 rwhp for a very limited amount of time-never longer than a few months. If you're only looking for 300 to 400 hp and are willing to spin the engine to 3,500 rpm or so, then the stock transmission and converter will actually work pretty well. At that rpm level, however, engine modifications such as valvesprings, locks, and retainers are highly recommended.
If you're willing to spend the money and your truck isn't sled pulled or drag raced, a triple-disc torque converter, performance valvebody, Alto clutches, a billet input shaft, and a performance flexplate can handle virtually any horsepower level, as long as the transmission builder is competent. With labor and installation, this type of transmission will usually cost around $4,500 and should last for decades.
As for your case, having just had the transmission rebuilt, we would take it to a local shop and have it adjusted for higher-rpm shift points and see if they can boost the line pressure. In Project Rust Bucket, our '89 Dodge D250, the stock 727 automatic held 514 rwhp with a just Trans-Go shift kit and a low-stall torque converter, so having a performance transmission on a limited budget is definitely possible.
Naturally Aspirated to Turbo Swap
Question: I purchased an '85 4x4 Toyota 2.0L diesel from a friend with a blown engine. After finding out the pistons hit the heads and the engine was not re-buildable, I sourced one out of Canada. I have about $4,000 in the truck and really don't drive it because it is gutless. I'm a diesel enthusiast and bought the truck for that one reason alone. It is naturally aspirated, and I would like to put a turbo on it, as well as upgrade the fueling system and exhaust. Bottom line: I need more power!
Robert Lopez
Santa Fe, New Mexico
| Justin Wheeler’s 6.9L IDI Ford proves old doesn’t mean slow. With a dropped-compression engine, modified injection pump, and a 63mm turbocharger, the Blue Oval put down 356 rwhp and 674 lb-ft of torque.
Answer: We get quite a few of these emails from old diesel car owners, IDI truck owners, and other folks who have gotten their hands on naturally aspirated diesels. For you folks, there is good news and bad news. The good news is the stock engine can be upgraded with a turbo to roughly twice the stock power level. The bad news is there's usually no kit for this type of work, so the entire turbo system will have to be fabricated.
Also, modern turbodiesels have a compression ratio of about 17:1, which is a lot lower than the 20 to 22:1 that older naturally aspirated diesels have. This means only a limited amount of boost can be run (about 8 to 15 psi) without damaging the engine, often in the form of bent connecting rods or a blown head gasket.
The fuel system can remain largely stock, although the injection pump must be turned up to provide a power increase. There's usually enough room in the stock injection system to do this, without modifying the injectors or injection pump. If more power is desired, the compression can be dropped down to 17:1 or 18:1, the boost increased, and the injection system modified-but this effort is beyond most enthusiasts.
Maximum Pressure- 200 psi?
Question: I was talking to a friend who claimed that some tractor pullers run more than 200 psi of boost! I know it's common for modern diesels to run 30 psi-or even more when modified-but it seems a little ridiculous to claim nearly 10 times that amount. Is there any truth to these numbers?
Ken James
Tampa, Florida
| These days, even single-turbo tractors are capable of more than 100 psi of boost, highlighting the serious turbocharger technology that goes into these applications.
Answer: Well, we hate to break it to you, but your friend is right! In fact, we've heard as high as 300 psi on some pulling tractors, but the strain on the engine at those types of boost levels is incredible.
The turbochargers on these behemoths are some of the most interesting pieces in the diesel industry. They're usually in three stages: two turbos blowing into a single turbo, which then blows into another single turbo before entering the engine. Holset turbochargers (most commonly known for their HX35 and HY35s on Cummins engines) are upgraded with different compressor wheels, modified housings, and even different centersections in order to work on high-boost tractors.
The sizing of these turbochargers (which are run on 500-plus-ci diesels) is as large as the boost numbers they provide. A likely combination for a four-turbo tractor could be something like twin HX80 turbos blowing into an HX82, blowing into an HX83. The toughest, strongest turbo in the whole arrangement is usually the highest-pressure charger, because it will have the insane job of trying to further compress air that may already be at 100 psi or more.
Before you go out and try to build a 200-psi setup for your daily driven diesel, remember that these pulling setups require nearly every part of the engine to be aftermarket. Compression must be dropped severely-sometimes as low as 10:1-and pistons and cylinder heads are often made out of steel for extreme strength.
