Predator 420 HEMI Build Help


New member
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Looking for some advice here. Have experience with 212's but no experience with the hemi 420's.

Currently, the engine is stock except for the stage one kit to hold the place for the Mikuni 34mm and custom exhaust.

Looking for top end performance.

The only part I currently have is a billet flywheel with timing adjustment.

Need to do some porting and polishing at the end of all of this.

Want to install
-Billet rod
-Mod 1 or .308 Cam
-Chromoly push rods
- 65lb dual Springs
-Mikuni 34mm

1: Will the stock spring retainers and keepers work for the dual springs? If not what do you recommend?

2: Is 65lb springs the best option for my build or should I use 50lb springs?

3: 308 Grind Cam or Mod1 Grind Cam? Will I need to clearance the piston to clear the valves?

4: 4.410 or 4.450 Billet rod? Will I run into clearance issues running the 4.450 rod?

5: Mikuni 34mm Round Vs Flat?

6: Is there anything I am missing or anything you would recommend I change?


"Loose Cannon Creations"
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Jacksonville, Florida
The Mod1 cam claims slightly more top end power than the .308 with 3.4 degrees more duration (duh) and only .002 more lift.
The .308 claims to be easier on the drivetrain, which is a good indicator right there that springs as aggressive as 65 lbs. are unnecessary.
I would call ARC Racing to discuss valve clearance before choosing an over-length rod, and what strength rating of valve springs would be more than stock retainers can hold. Tech line (229)435-2647. However, if racing retainers and split keepers aren't expensive, just get them regardless of what the tech facts about them are.
No matter how it ends up, do a squish test before ever spinning the motor over with the starter. Play-Doh is a longtime favorite for that.