Redefining Classic: The 300HP Cummins Heartbeat of a ’72 K5 Blazer

An Excellent Cummins Swap in a Vintage Classic

We’ve all heard the expression that something is so clean you could “eat off it,” but it’s hardly ever true. Even in show trucks, there’s usually parts that are dusty, or oily, or have secret rusted bolts. We can confidently say that this is not the case for Jim Martin’s ‘72 K5 Blazer from Northern California. The paint is gorgeous, the engine bay is pristine, and even the underside is absolutely immaculate. It’s probably one of the cleanest Cummins swaps we’ve ever seen, and that’s saying something.

The re-power on Jim Martin’s Blazer is about as clean as any we’ve seen, and the color scheme goes wonderfully with the Medium Blue of the engine bay. At 300 hp and 800 lb-ft it may not make huge power, but it motivates the K5 quite nicely.
A simple large universal air filter setup feeds one of the few performance modifications, an upgraded compressor-wheel turbo, which connects to a non-intercooled crossover.

Now Blazers are classics, but they’re also known to not have a ton of power, and to get horrible fuel economy with the factory gas engine. Guess what solves all that, a diesel! Jim’s Blazer has been swapped with a classic 12-valve Cummins out of a ‘91 Dodge. The factory 160-hp engine is kind of a snoozer, so Jim’s Cummins has been upgraded with a turned-up fuel screw, governor spring kit, upgraded compressor wheel, and now makes approximately 300hp along with 800 lb-ft of torque. Reliability issues like the killer dowel pin have also been addressed. Power is routed out through a custom muffled dual 3-inch exhaust system.

If you’re wondering about cooling, it’s actually fairly simple, with a large single electric fan squeezed in to do the job, since the Blazer doesn’t do any towing.
Diesel engines don’t create vacuum, so a hydroboost brake setup off of a ‘94 Dodge Ram was incorporated into the braking system.

Jim likes to shift his own gears, so he chose an ultra-strong NV4500 out of a ‘94-’98 12-valve Dodge as a suitable manual box. The five-speed transmission was adapted to the First-Generation engine with a starter, engine plate, and flywheel out of a Second-Generation donor truck. This manual was then further adapted to an NP205 transfer case out of a First-Generation truck. As you can see the driveline is a mishmash of First and Second-Gen parts, but it works.

There’s a lot going on underneath the K5. Here you can clearly see the NV4500 five-speed transmission and NP205 transfer case, which has been adapted to the Cummins with Second-Gen hardware.

With the diesel engine and trans swapped in, there was still the issue of getting the truck to go down the road. Jim accomplished this with such niceties as a Readhead steering box with a crossover link, while the clutch and hydroboost braking system were adapted from a ‘94 Dodge donor truck. Axles that were study enough to handle the diesel power were swapped in too, with a GM 14 bolt in the rear, along with a Dana 60 out of a 1-ton truck up front.

Out back is a 4.10-geared GM 14 bolt that is mounted on 6-inch lift springs from Off Road Designs. The rearend is also equipped with such tricks as a True-Trac posi, anti-roll and traction bars, and an electric over hydraulic parking brake.
The front Dana 60 is out of a ‘82 1-ton K30, also has 4.10 gears, and is on the same 6-inch lift (which helps clear the Cummins oil pan). Also visible is the Redhead steering box and cross-over steering.

Now we get on to what Jim calls “the glitter stuff,” which makes the truck look the way it does. There’s 17-inch polished wheels by US Indy Wheels, and Ididit steering column, Car Tunes custom stereo, and Taylor Wings cargo box. A lot of it is functional too: like the Autometer gauges, and the Speed Hut Speed Box electric-to-mechanical conversion for the speedometer. The interior itself also has a 6-point rollcage built by David Virga and custom bikini top by West Coast Custom Interiors. Jim sits in comfy Corbeau seats, and there’s LED lightning throughout. You might also think the paint is custom but it’s actually a factory Medium Blue PPG hue.

Since 15-inch wheels look way too small these days, Jim optioned for a more modern look, with 17×10-inch US Indy Wheel slotted rims, and 37×13.50R17 Cooper SST Pro tires.
The interior is as clean as any other part of the Blazer. Visible here are the Corbeau seats, custom rollbar, and AutoMeter gauges.
The rear of the K5 also houses Corbeau seats, which are securely mounted to the rollbar.

You have to stand there for a minute to take Jim’s Blazer all in. It’s not just one thing that attracts your attention but everything that is so well-done. He’s modified virtually every part of the vehicle, but the fact that he’s retained a factory-style look is perhaps the best of all. Jim would also like to credit Ken Imler from Imler Diesel and the original owner Andy Byrne for their help. We’d like to credit Jim for building such an awesome ride, one that’s definitely worth featuring in the pages of Diesel World.

There’s a little bit of custom storage in the form of a stainless steel locking cargo box by Taylor Wings. Also hidden in the rear are the Blazer’s 6×9 speaker (of which there are four.)


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