Kaase Boss Nine Engine - Engine Builder Magazine

Kaase Boss Nine Engine

The Boss 429 was a NASCAR special back in 1969 Mustangs and the Ford faithful have been lusting for the Blue Crescent/Shotgun engines ever since. While others dreamed, the die-hard Ford junkies at Jon Kaase Racing Engines worked, and brought the Boss 429 back to life in the form of the Kaase Boss Nine engine.

Imagine a Boss Nine engine singing beneath the hood of your car. On-lookers turn their heads as you roar down the road. You’d be in heaven. Cliff Moore, the operations manager at Jon Kaase Racing Engines in Winder, GA, sees the look of daydreaming customers all the time.

From street to strip, muscle car or show car, street rods to full-out racing applications, Jon Kaase Racing Engines’ Boss Nine replica engine is custom-tailored for many applications.

The Boss 429 was available as a NASCAR homologation special in 1969-’70 Mustangs (and two special Cougars) and the Ford faithful have been lusting for the Blue Crescent/Shotgun engines ever since. While others dreamed, the die-hard Ford junkies at Jon Kaase Racing Engines worked, and brought the Boss 429 back to life on its 40th anniversary.

Kaase’s modern Boss Nine combination is based on a high-nodular cast iron cylinder block that can accommodate 429, 460, 521, or 600 cubic inches and output extends from 500 to 1,000 horsepower. Moore, who has been with Jon Kaase 25 years, says it’s one of the shop’s most popular engines.

“We build these engines for high-end street rods or street cars,” Moore says. “Very few of these engines wind up in the racing market because most guys really want an original Boss 429. We use all modern blocks. We use the Ford SVO block or the Eliminator big block Ford block. It’s your standard bore hone and line hone. We pay really, really close attention to the cam tunnels on the 385 series and make sure that they’re correct size. We use an aftermarket cam bearing, but it’s pretty much just your standard build. We balance the crank, rods, and pistons. It’s a pretty straightforward combination that we can do in about two weeks, if we have all the parts and pieces.”


The 10.30-inch deck height block receives a cast crankshaft in the 460ci version. Engines with 521ci and beyond are founded on a 4340 steel crankshaft joined with 4340 forged connecting rods and Diamond forged pistons. To run on pump gas, the compression ratio is usually limited around 10:1. Kaase caps the short-block with new aluminum cylinder heads fitted with stainless steel swirl-polish 2.30-inch intake and 1.90-inch exhaust valves activated by WW Engineering 1.75:1 aluminum roller rocker arms.

“We have our own cylinder head we call the Boss Nine head,” Moore says. “We also have our own intake manifold, stack injection manifold, a 4150 series intake manifold, and a 4500 series intake. We also have our own valve covers. The way that we designed the head it actually fits a 385 series Ford block or a 429 460 block.”

The cylinder heads are Kaase’s castings and design that look aesthetically as close to the original Boss 429 heads as possible, but they are an improved version. The cylinder heads, the valve covers, the three different intakes – 4150, 4500, and a stack injection intake manifold – rocker arms, and really the whole top end kit is manufactured at Kaase.

In the aftermarket, Kaase uses a lot of Ford Racing products such as the Ford SVO block or the Eliminator products. For cranks, the shop uses Lunati, Bryant, Scat or Callies depending on how much power the customer wants the engine to make or what the application is going to be. Pistons come from Diamond or CP-Carrillo. Rings are all Total Seal. Fuel injection systems come from FAST, Holley or MoTec. Gaskets come from Cometic, and cams come from COMP cams.

“We worked with COMP cams quite a bit on this particular project,” Moore says. “We did a lot of Spintron testing with them on the hydraulic roller applications so it can turn a lot of RPM and not have any issues with valve float. It does have a really long exhaust rocker and it’s a little bit heavy, so it would be really easy to get into valve float with a hydraulic roller. So we spent a couple of weeks on the Spintron and we were able to go in the high 6,000 RPM range without any issues. Ninety percent of these engines are built at pump gas compression right around 10:1 with a hydraulic roller and they produce right at 1.35 hp per cubic inch.”

Something 10:1 you could drive on the street with a hydraulic roller and it will easily make over 750 horsepower and roughly 680 ft.-lbs. of torque. Kaase can tailor the camshaft anywhere from 500 to 900 horsepower depending on what a customer would like to make for power. Of course, the 500 hp would be a hydraulic roller and the 900 hp would be a full roller.

While a lot of these engines are reproduction engines for original ’69 or ’70 Boss 429 cars, others have ended up being used in full-out drag racing, offshore racing and powerboats, and road course applications.

“This engine covers a really wide range of power and different applications,” Moore says. “It boils down to how much power they would like to produce and really the only difference is the camshaft selection and valve train selection to match the cam.

With 500 to 1,000 horsepower to offer, and up to 1,500 hp when supercharged, it’s no wonder the Kaase Boss Nine engine catches customers daydreaming and on-lookers turning their heads.

Engine of the Week is sponsored by Cometic Gasket

To see one of your engines highlighted in this special feature and newsletter, please email Engine Builder managing editor, Greg Jones at [email protected]

You May Also Like

2,662cc Air-Cooled and Turbocharged VW Engine

This 1969 Volkswagen Beetle was just $600 when Steve Dalton bought it in high school. Having tweaked the performance of the car every year, he’s gone way past that mark and several iterations of the VW engine. Today, it’s a 2,662cc air-cooled and turbo’d VW with a bunch of aftermarket goodies.

There’s just something inherently awesome about seeing a Volkswagen Beetle wheelie off the line at a dragstrip. It’s even cooler when you know the engine making it happen is also a VW and not some sort of swap. We caught up with Steve Dalton, the owner of such a Beetle, during Sick Week 2024. His air-cooled and turbocharged Volkswagen engine competes against a sea of V8 horsepower, and it holds its own, so we wanted to know how the 1969 Beetle and the VW engine got to this point.

Volkswagen Beetle’s Air-Cooled and Turbocharged Engine

This Volkswagen Beetle cost owner Steve Dalton $600 when he bought it back in high school for use as a daily driver. Every year since he’s owned the car, the Beetle and its engine have gotten some sort of performance upgrade to the point that it is at now. Steve is a regular on the

ProCharged 572 cid Big Block Chevy Engine

Inspired to build a hot rod with all its systems exposed, Leroy Edwards used his 50 years of mechanic experience to build this cool-looking car himself. Powering this hot rod is a ProCharged 572 cid big block Chevy engine with nitrous adding an extra kick. Check it out!

big block Chevy engine
Twin-Turbo 6.4L Gen III Hemi Engine

After rebuilding his ‘Lil Red Express truck for the past two years following a collision during the Midwest Drags, Rick Russell got back to drag-and-drive competition at Sick Week 2024. This time, ‘Lil Red Express featured a twin-turbo 6.4L Gen III Hemi engine!

Lil Red Express
All-Billet K24 2.2L Honda Engine

We’ve known JBR Engines owner Jose Bello for a few years, and well before that, we knew his shop was one of the premier shops in the Honda and import engine scene. During a recent visit, we got to see an all-billet Honda K24 2.2L engine coming together for a customer looking to improve upon his 5.86-second quarter mile time!

Other Posts
Turbocharged Nissan SR20 DET Engine

For a number of years now, Derek and Rita Cho-Sam of DRZA Auto in Tavares, FL have been among our top Nissan engine shops. When we realized that Sick Week would be rolling through their part of Florida, we made arrangements to stop by and see DRZA in person. Derek and Rita gave us a

Nissan SR20 DET engine
Kevin Smith’s Turbocharged 388 cid LS Engine

Kevin Smith, owner of KSR Performance & Fabrication, has been a big part of the drag and drive community for a while now. His shop, in addition to all the performance and fab work it regularly does, stays open during events like Sick Week, so competitors can utilize the lifts and tools to get back

KSR LS engine
Alex Null’s 6.4L Ford Powerstroke Engine

During our trip to Dallas this year, we spent a day in Weatherford and visited Alex Null and Summit Diesel. We were treated to the details of Alex’s own 6.4L Ford Powerstroke engine build he is finishing up for a race application. It’s our Diesel of the Week brought to you by AMSOIL INC. Related

6.4L Ford Powerstroke
Single-Turbo 6.4L Powerstroke Engine

After a few different things fell into place with trucks and other 6.4L Powerstroke engines, Alex Null, owner of Summit Diesel, was able to build this particular 6.4L Powerstroke into a race engine for his Ford F250 and the 7.70 index class. Check it out!

6.4L Powerstroke engine