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.
Max-Power first-gen
Question: I’m currently deployed with the U.S. Marines, but my goal is to build an ’89 to ’93 regular-cab Dodge W250 with a 14mm Scheid VE pump, S400 turbo, big injectors, lots of nitrous, water-methanol injection, an aftermarket intercooler, and all the supporting modifications to make it reliable. I plan to run a five-speed Getrag manual transmission with a big, dual-disc clutch. I know the stick will hurt me on the track, but I think the tradeoff for increased horsepower on the dyno and the sled pull track will make up for it. Is there anything else you would suggest for my VE-pump Cummins build?
Lance Cpl. Jordan Duncan
USMC
| For those planning on adding a wastegate to their Cummins engine, Steed Speed offers exhaust manifolds with built-in flanges for mounting external wastegates. There is even a big-daddy, dual-gate setup for applications such as this monstrous 91mm single turbo.
Answer: While we’re not quite finished with our ’89 Ram buildup (we call it Project Rust Bucket), there are a few lessons we’ve learned along the way that we’d like to share with you. The unfortunate truth is a P-pump swap is probably more cost effective than a hot-rodded VE injection pump, but if you have your heart set on being different, we’ll keep our advice based on a Scheid 14mm VE pump with some 6x0.016-inch or 6x0.018-inch injectors.
First off, you’ll need a good 150-gph lift pump, bigger fuel lines, and a fuel tank sump or draw tube to support that 14mm pump. If you’re going to be running an S400 turbo, we’d limit it to a 65mm version for quickest spool-up. We’ve seen common-rail Dodges make almost 800 rwhp with a 66mm turbo, so there’s no reason to go larger than that with a VE pump—especially since they are fairly rpm limited. The fact that you’re running a manual transmission means we’d also go smaller on the turbo to improve lag time during shifts.
Since you’re planning on running a fairly large turbocharger, you might not need an external wastegate, as those S400-frame turbos are pretty tough. We’ve heard of sled pullers running upward of 70 psi of boost without failure when using 75mm S400s. If you still want one for insurance, Steed Speed makes a killer exhaust manifold that has a provision for an external wastegate built into it.
When building your nitrous system, we recommend installing a small (say, 0.025-inch) jet of nitrous on a wide-open throttle switch. This way, you can lift off the throttle to shift, and the nitrous will trigger again when you floor it to help the turbo recover faster. You can always put in larger jets for dyno use, or a second stage if you feel you need more spray.
Cummins engines are pretty stout, so there’s not a whole bunch that needs to be done to the long-block. At your power level, we’d suggest O-ringing the head and adding ARP 625 studs as insurance, but we’ve seen trucks get away with regular ARP 2000s and a non-O-ringed head for a while. After throwing in a good clutch from a company like South Bend, you’ll be ready to rock and roll. And trust us, 500 to 700 hp in a 6,000-pound truck will feel pretty darn fast!
Lemon Squeezing
Question: I need some experienced advice concerning a diesel engine I’m building for crap can endurance racing. In what can be easily considered the epitome of bad decisions, I have acquired a 5.7L Oldsmobile diesel engine for the sole purpose of racing in the 24 Hours of Lemons (24hoursoflemons.com). As if choosing the worst diesel engine in the world wasn’t bad enough, I also have to build it to run reliably for up to 800 miles of hard road-course racing. I’d also like to get 44 percent more power out of it while keeping the engine budget less than $200.
| We’re curious as to why there aren’t more modified Oldsmobile diesel cars. One of the few we’ve ever seen was this Buick Grand National clone, which was powered by a Duramax engine. We featured it in “Darth Vader” (Nov. ’07).
I’ve been looking into reducing the engine’s compression ratio from approximately 22.5:1 to something a little friendlier for reducing peak cylinder pressures. While my budget is poor, I have the tools to make this happen.
How little compression ratio can I run and still have reasonably good cold-starting ability (using glow plugs) in 80-degree weather? I expect the engine to lose some bottom-end torque (and possibly reduced throttle response), but I think I can compensate for the lost power using more boost. My hope is that I can keep peak cylinder pressure lower than running the engine with more compression, and less boost.
So, aside from you recommending a different engine, I anxiously look forward to any advice.
Eric Herbers
Newton, Kansas
Answer: There are many different ways of lowering compression, some of which we would only recommend on a very temporary basis. For a low- to no-buck solution, you could shave the tops of the pistons with a mill, or stack a few head gaskets on top of one another to reduce the compression ratio. A little bit of gasket thickness will cut the compression half a point or more, so putting a few head gaskets on top of one another might seal and might give you the compression you’re looking for. If that is too many “mights,” then we would just stick with putting fresh head gaskets on the engine and leaving the compression alone.
You mentioned boost, but to our knowledge the Olds 5.7L was only offered as a naturally aspirated diesel engine. A while back, we talked to Gale Banks and he remembered seeing internal engine problems at around 15 to 20 psi of boost—not very much compared to today’s diesels—and part of the issue could have been the high compression. If it were us, we’d wastegate whatever turbo we were using to 10 psi of boost for engine longevity.
Finally, in an application such as yours, we’d keep an eye on oil temperature, water temperature, and transmission temperature. If anything takes you out of the race, it will probably be one of these factors, rather than running too much compression. On a normal budget, compression is most often lowered by purchasing new pistons rather than trying to hillbilly something together. But on a $200 budget, pistons aren’t really an option for you.
As far as cold starts, we wouldn’t worry about those. Most diesels will start fine down to about 17:1 compression—even with natural aspiration. There might be a lot of white smoke due to inefficient burning of the fuel, but once the engine is warm, that should quit, too. Good luck on your project, and make sure to send pictures when it’s finished.
Fire-Breathing BMW
Question: I heard there are some BMW diesels out there running 11 seconds or faster in the quarter-mile. I’d like to know how this was accomplished and what kind of tuning is available for the newer cars like the 335d diesel model.
Greg Johnson
Via email
| We testdrove a BMW 335d back in “BMW 335d Road Trip” (Dec.’09), and we still miss it. Running low 14-second quarter-miles in stock form and getting more than 30 mpg at 75 mph are some good indications of why one should buy this hot rod for a super-fun second vehicle.
Answer: We did a little dig- ging, and to our knowledge there aren’t any United States- spec BMW 335d’s that have that much power, or are that fast. There is a company called Burger Tuning that makes a pressure box for the 335d that takes the engine from about 260 rwhp up to 310 rwhp. With a set of sticky tires, the four-door sedan should reach 60 mph in less than 5 seconds and make it down the quarter-mile in the low 13s. If this engine is anything like most other common-rail die- sels, however, there should be an enormous performance potential with more fuel, air, and tuning. We’ve always wanted to see a 700hp 3.0L 335d with standalone engine manage- ment, injectors, turbos, and nitrous, but so far there hasn’t been such a car built. That doesn’t mean it can’t be done, so if anyone out there has a hot-rodded 335d we need to know about, drop us a line at Jason.sands@sorc.com.
