331 vs 347 Stroker: Which Small Block Ford Fits Your Build?
A 331 and a 347 are both 289/302-based small block Ford strokers, and in the kits we list the only spec that changes is the stroke: 3.250 in for the 331 and 3.400 in for the 347, both on a 4.030 in bore with 5.400 in rods. The 347 gains about 15 ci; the 331 keeps a higher rod-to-stroke ratio. Choose by how you'll use the car, then have a machine shop check your block.
Key takeaways
- Same bore (4.030 in) and rod length (5.400 in) in the kits we list; the stroke sets the size.
- 331: 3.250 in stroke, 331.6 ci. 347: 3.400 in stroke, 347.0 ci.
- Rod-to-stroke ratio: 1.66 for the 331, 1.59 for the 347.
- Same rod length means the 347 piston's pin sits about 0.075 in closer to the crown.
- Check each listing for crank and piston material and for balance.
331 vs 347 specs compared
| 331 | 347 | |
|---|---|---|
| Bore | 4.030 in | 4.030 in |
| Stroke | 3.250 in | 3.400 in |
| Displacement | 331.6 ci | 347.0 ci |
| Rod length | 5.400 in | 5.400 in |
| Rod-to-stroke ratio | 1.66 | 1.59 |
| Piston pin height vs the other size | about 0.075 in farther from the crown | about 0.075 in closer to the crown |
| Kits we list | Scat 1-94055 (cast crank, forged pistons, I-beam rods); Scat 1-94055BE (same, external balance, flexplate and balancer included); Eagle 14006030 (forged crank, forged pistons, H-beam rods; internal balance design, sold unbalanced) | Eagle 14003030 (forged crank, forged pistons, H-beam rods); Eagle 16003030 (cast crank, forged pistons, I-beam rods); Scat 1-94160 (cast crank, hypereutectic pistons, I-beam rods); Scat 1-94165 (cast crank, forged pistons, I-beam rods) |
Still deciding? Tell us your combo or call 310-784-1010.
Which one is right for you
- Confirm you have a 289/302-family block and have it checked for the .030 in overbore to 4.030 in.
- Decide how the car will be used and whether you plan a power adder.
- Pick the stroke: 3.250 in for a 331, 3.400 in for a 347. Either way, a stroker kit includes the crank, rods, pistons, rings and bearings.
- Pick crank and piston material from the listings (cast or forged crank; forged or hypereutectic pistons).
- Plan machine work: overbore and hone, clearance check and balancing.
- Send us your car, gearing and goal, and we'll help you pick.
Frequently asked questions
Is a 331 or a 347 better?
Neither is better for every build. In the kits we list, both use a 4.030 in bore and 5.400 in rods; the 347 has a 3.400 in stroke and the 331 a 3.250 in stroke. The 347 adds about 15 ci; the 331 keeps a higher rod-to-stroke ratio (1.66 vs 1.59). Send us your car, gearing and use and we'll help you pick.
What is the difference between a 331 and a 347?
The stroke. Both kits we list use a 4.030 in bore and 5.400 in rods; the 331 crank has a 3.250 in stroke and the 347 crank a 3.400 in stroke. With the same rod length, the 347's piston pin sits about 0.075 in closer to the piston crown (half the 0.150 in stroke difference).
Do both fit a stock 302 block?
Both kits we list are made for the 289/302 small block Ford with a 4.030 in bore, which is a stock 4.000 in bore taken .030 in over. The listings don't include clearancing notes, and a longer stroke can need block and rod-to-cam clearance, so have your machine shop check your block before assembly.
Are the 331 and 347 kits balanced?
Per the listings, Scat 1-94055BE is the external-balance version and includes the flexplate and balancer. Eagle 14006030 is designed for internal balance and is sold unbalanced. The other kits don't say balanced, so plan to have the assembly balanced before it goes in.
Ask a Coast High Ford builder
Ford strokers are what we build. Send your engine, goal and transmission, and a Coast High builder will get back to you. Or call 310-784-1010.
Shop this
- Scat 331 rotating assembly (1-94055)
- Scat 331 rotating assembly, external balance (1-94055BE)
- Eagle 331 stroker kit, forged crank, forged pistons (14006030)
- Eagle 347 stroker kit, forged crank, forged pistons (14003030)
- Eagle 347 stroker kit, cast crank, forged pistons (16003030)
- Scat 347 stroker kit, cast crank, hypereutectic pistons (1-94160)
- Scat 347 stroker kit, cast crank, forged pistons (1-94165)
- Small block Ford stroker kits
More guides
- 302 to 347 stroker: what you need
- Ford stroker engine sizes chart
- All Ford stroker and crate engine guides
Written by the Coast High Performance tech team. Checked by CHPTech Nov 4, 2026. Last updated November 4, 2026. Specs come from each manufacturer listing on our store. Questions? Call 310-784-1010.