Gen III HEMI Engine Block – Performance With Heart
Gen III Hemi CGI engine blocks — lighter than cast iron, 3x stronger than aluminum, with 20x less bore distortion. Engineered to deliver 3–5% more torque and power through superior bearing stability and cylinder sealing.
CHOOSE YOUR BLOCK
Four configurations. One material advantage. Every block rated to 3,000 HP.
ACE STREET
The drop-in CGI upgrade. Full factory compatibility.
Full specs, fitment & machine-work notes
ACE BOOST
Tall deck strength meets factory electronics compatibility.
Full specs, fitment & machine-work notes
ACE DRAG PAK
Purpose-built for straight-line domination.
Full specs, fitment & machine-work notes
ACE MAMMOTH
Our largest bore. Maximum naturally aspirated cubic inches.
Full specs, fitment & machine-work notes
Need a different bore, deck, or cam setup? Build your own block →
BYOB - BUILD YOUR OWN BLOCK
None of the four standard variants fit your build? Configure a fully custom ACE CGI engine block with your exact specifications.
BORE SIZE & FINISH
STEP 1Rough bores ship .003" undersize for your machine shop to finish. Honed bores are plateau-honed to final size, ready for ring fit. Bore size does not change the price. Our largest bore, 4.300", is naturally aspirated only.
DECK HEIGHT & LIFTER
STEP 2TIMING DRIVE & CAM TYPE
STEP 3ACE BYOB BLOCK
Complete all 3 selections to continue
WHY COMPACTED GRAPHITE IRON
The material OEMs trust for the most demanding applications on earth.
SUPERIOR STRENGTH
75% higher tensile strength than conventional gray iron. CGI's unique graphite structure creates a material that absorbs extreme cylinder pressures without cracking or distortion.
MAXIMUM STIFFNESS
45% higher elastic modulus means dramatically less bore distortion under load. Your ring seal stays consistent from idle to wide-open throttle — critical for high-boost applications.
THERMAL MANAGEMENT
CGI maintains dimensional stability across extreme temperature cycles. Superior vibration damping reduces NVH and extends component life compared to aluminum alternatives.
FREQUENTLY ASKED QUESTIONS
WHAT IS THE REFUND POLICY ON A PRE-ORDER?
Pre-orders are paid in full at checkout and are fully refundable up until your block enters production. Once manufacturing starts on your serialized casting the order is no longer refundable, but it can be transferred to a different configuration. Email eric@aceinc.shop or call (615) 924-2737 and we'll take care of it.
WHEN WILL MY BLOCK SHIP?
Orders are fulfilled in the sequence received. We confirm your production slot by email once your order is placed, and you'll get progress updates and tracking when your block ships.
CAN I USE THIS AS A DIRECT REPLACEMENT?
ACE STREET is a direct drop-in replacement for factory Gen III Hemi blocks, with full VCT and stock component compatibility. ACE BOOST, DRAG PAK, and MAMMOTH require supporting modifications — each product page lists exactly which parts you'll need.
CAN I RUN BOOST ON THE 4.300" BIG BORE?
No. 4.300" is our largest bore and it is specified for naturally aspirated use only — it is not rated for a supercharger or turbo. That applies to ACE MAMMOTH and to any 4.300" configuration you build yourself. For a boosted big-bore combination choose 4.260" or smaller, or call us at (615) 924-2737 and we'll spec it with you.
IS CGI REALLY RATED TO 3,000 HP?
Yes. CGI's material properties — 75% higher tensile strength, 45% higher stiffness, and 2× fatigue life compared to gray iron — support extreme power levels with proper supporting components.
WHAT ABOUT NHRA/IHRA APPROVAL?
NHRA/IHRA pre-review is complete, with full approval expected in the August 2026 time frame. CGI qualifies as a cast iron derivative material under current rulebooks.
WHERE CAN I BUY AN ACE BLOCK?
ACE engine blocks are sold exclusively direct-to-consumer through our website. Same price for everyone — no dealer markups, no middlemen.
Featured Products
We are building these blocks in the open.
One email a month on where the Gen III HEMI CGI block program actually stands. What moved, what did not, and what we learned.
- Foundry and machining progress from the shop floor
- CMM and dyno results as soon as we have them
- First pick of production slots
Roughly one email a month. Unsubscribe any time.