The 425hp Beast aka Mighty Mouse

Our poor project vehicles. Each of them has literally seen, hundreds of modifications over the years. To make matters worse, our job is to give the products we test a royal beat-down each time we bolt or weld on a new component. To add insult to injury, the foundation of our test mules (think: engine, transmission, etc.) take the same beating, but get none of the glory – a truly thankless job. Which brings us to our 5-part feature article – You too can build a 400+ horsepower, reliable engine in your spare time.

About 10 years ago I installed a TBI fuel injected Chevy 350 motor and a Turbo 350 transmission into our FJ40 – both of which were freebies. The engine had been swapped in and out of other vehicles since 1986 and I lovingly named it my ‘mystery motor’, since the innards and mileage were completely unknown. To this day, I still couldn’t tell you if it is a 2 or 4 bolt-main engine, and aside from adding oil to it every few years and conducting the minimally required maintenance, nothing had changed and it served us well.

It was on our last trip to Moab, UT for the Easter Jeep Safari, that the years of punishment began to show the effect on the mystery motor.  I came off the top turnbuckle on several hard-core trails specifically selected to give a few new products a good beating, and the mystery motor started showing signs of its age. A few more valve rattles, a little more blue smoke from the tailpipe, and a recent, notable lack of power are all this poor motor was capable of producing. It is now time for a new mill to be transplanted and, as the saying goes, “Go big, or go home”.

Our old, mystery motor

Our new, 425 HP engine

I made the decision to build my own engine for various reasons that I’ll speak to later in this article. Nonetheless, I enlisted the help of real experts and our good friends at GM Performance Parts, Lunati, Holley and PSC (Performance Steering Components) to pick their brains. After several days of dialogue, questions and technical discussions, they finally convinced me to build, with their help, a 400+ horsepower, 383 cubic inch, fuel injected, Chevy stroker motor. This mighty mouse motor will be adorned with the finest components Holley, Lunati and GM Performance Parts as well as  a few other power adding superstars.

Here are the highlights of the motor specs, but as I mentioned, we’ll break this article into a 5-part feature to not only tell you what we built, but why and how we built it, step-by-step. Consider this engine-building guide our gift to you, our fellow 4-wheeling friends.

Engine Highlights: 

• GM Performance Parts 383 Stroker Block, 1-piece rear main seal, 4-bolt main – part # 88962516
• GM Performance Parts Serpentine Accessory Drive System w/out A/C – part # 12497697
• Lunati fully balanced rotating assembly
• Lunati “SledghammerSledgehammer” Forged steel stroker crank
• Lunati “Voodoo” cam, roller rockers, push rods, double-roller timing chain and lifter set
• Holley Stealth Ram multi-port fuel injection system – Part #: 91603211
• Holley aluminum 2.02 heads – Part #: 300-552-1
• Holley billet aluminum high-performance distributor
• Pro-Tru aluminum flat-top pistons
• High Performance engine bearings
• MSD Ignition 8.5 mm super-conductor plug wires

Part 1 – Design Plans & Engine Prep

Sure, we could have ordered a turn-key engine to drop into our ailing FJ40, but we wanted to build our own mill for a variety of reasons. First, we wanted to show you that almost anyone can build their own engine. Second, there’s a level of gratitude and pride that you will have when a buddy or onlooker says “wow, that’s a sweet engine!”, and you reply “thanks, I built it myself”. Third, we could design an engine that fits our specific needs, instead of getting an engine that someone else designed.

With that said, we put our call into GM Performance Parts and Holley to have discussions about our needs, which were quite simple; We wanted a small block Chevy engine primarily because of its reliability. The availability and the low cost of parts were primary reasons too. We also wanted a motor that started its power curve at low rpm’s, had gobs of power on tap at high rpm’s for our occasional mud runs and sand dune blasts, and would provide years of trouble-free service – oh yeah, it had to run on pump gas too.

Holley and Lunati ultimately put together a very extensive and comprehensive set of engine components that would make up our project mighty mouse motor. Shortly thereafter, the components started showing up at the 4X4REVIEW shop and the project formally began.

After the GMPP 383 block showed up, we loaded it up and took it over to our friends at Schmidt’s Automotive in Indianapolis, IN – a famous speed shop that builds engines ranging from direct OE replacements to 1,500 HP nitrous-burning monster mills for top-fuel dragsters. The GMPP crate motor comes ready to assemble, but given that this engine would have the finest components available from Holley and Lunati, and we wanted a perfect build, we decided to have Schmidt’s give it the royal treatment. Schmidt’s performed several key services to our block, such as:

• Align Hone – ensuring that the crank journals are perfectly true and honed.
• Bore and Hone – Schmidt’s bored the cylinder walls .030” over and then honed them to exacting standards
• Block True Deck – Schmidt’s took a few thousandth’s of an inch off of the deck (the part where the heads are bolted to) of the engine to ensure it was perfectly square
• Jet Clean – they then cleaned the mill with special solvents and cleaning systems to ensure that even microscopic amounts of metal shavings were no longer present.

While Schmidt’s was at it on our mill, we had them install new cam bearings and check all clearances on the block, since the connecting rods for a 383 stroker motor swing wider and can come in contact with the cylinder skirts, causing catastrophic failure – never a good thing. The engine is now fully prepped and ready for assembly.

Yes, crate motors do indeed come in crates	The GMPP Serpentine Accessory Drive System	The GMPP Chevy 383 small-block stroker engine	Lunati rotating assembly, Wiseco pistons, Holley aluminum heads, etc.
Schmidt’s performing an engine boring process	More Schmidt’s machine work being performed	Our new engine. Just kidding, this is one of Schmidt’s top-fuel, dual-stage nitrous monster motors	A sneak-peek at our new Mighty Mouse Motor

Next article… Part 2, The Lower Engine Build