Throttle Body Bore / Spacer
Bore the stock 56mm TB to ~60-62mm, or add a phenolic spacer. Real gains are very small on a stock 4.0L; more useful on a stroker.
The HO 4.0L throttle body is 60mm; the Renix is 52mm. Many vendors and DIYers bore the stock TB to gain a few extra mm of bore. There's also a cottage industry of phenolic 'helix' spacers (Airaid, Spectre) sold with claims of helping atomization. On a stock 4.0L with stock head and cam, the throttle body is not the restriction — the head is. Gains are typically below the noise floor of a chassis dyno (1-3 whp).
On a stroker (4.6/4.7) with a Comp 232 cam, ported head, and the 99+ tube intake, the TB starts to matter. Most stroker builders run a 62mm Hesco bored TB or a Ford 65mm TB adapter. Spacers are still mostly cosmetic — the long, multi-bend intake plenum on the 4.0L dissipates any swirl the spacer creates before it reaches a runner.
If you're already in there for a head gasket or intake gasket job, having the TB bored is cheap insurance. As a standalone bolt-on for a stock engine, skip it.
Why it works
- cheap
- manageable
- real on a stroker
Trade-offs
- minimal on stock 4.0
- snake oil claims abound
Tools required
- socket set
- torque wrench
Parts
| Part | Vendor | Est. price |
|---|---|---|
| Hesco 62mm bored throttle body | Hesco | ~$240 |
| Airaid PowerAid spacer | Airaid | ~$80 |
| Spectre TB spacer | Spectre | ~$50 |
Sources
Related
- 62mm vs 56mm Throttle Body
- Ported Intake Manifold (99+ Tube Intake Swap)
- All Jeep Cherokee XJ guides & tools
- Browse the full DIY database
Written and maintained by an AZ wheeler and driveway wrencher. How we source guides. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.