How the heck can we justify such a small story to show off a new head install on not one, but two vehicles?! Easy: This is Hesco's new inline six-cylinder aluminum head, and it's such a snap to install that you'll have more throttle by lunchtime if you start after breakfast.
We raced down to Jeeps R Us in Laguna Beach, California, as soon as Larie Tales called us to tell us he had one of the very first Hesco heads available. Sometimes we think Tales has better connections than we have, as this was the first we had even heard of it. And we couldn't wait to shoot it: The power numbers we were hearing were astounding-50hp gains on a fuel-injected 4.2L, and 30hp gains on 4.0L inline-six engines! Pretty good for an out-of-the-box bolt-on power gain.
We followed along at Jeeps R Us as technician Abel Estrada (no relation to Eric-yeah, we asked) installed the exact same Hesco head on a 4.2L engine with fuel injection in a CJ-7, and then a 4.0L engine in a Cherokee. Since the 4.2L and the 4.0L have such similar architecture, the same head can bolt onto both (as long as you have a fuel-injected 4.2L-it won't work with a carbureted intake manifold), but you'll see a bigger power improvement out of the 4.2L since the newer stock 4.0 heads were so much better than the 4.2.
The Hesco aluminum heads are 30 pounds lighter than the stock iron head, feature highly improved porting over the original heads, and are set up with heavier valve spring than stock. They come complete and ready to bolt to your inline-six, minus the rockers. As for those, you can reuse your stock ones or purchase Hesco's roller-rocker set for even more power.
Though it's not yet 50-state smog-legal, Hesco is working on CARB exemption right now, and we think they'll have no problem getting it since the intake and exhaust valve are the same size as stock and it retains the same rocker arm equipment. Even without the CARB exemption, we think that it might fly at the right smog-check station, since you really have to look hard to notice any difference from the stock head (once you have a little dirt on it to cover the shiny aluminum-and we know you'll have plenty of that all over your motor, you dirthead).
Driven By NumbersWe got a chance to drive around with the new Hesco head for a bit, and the power improvement was definitely welcomed. Low-end throttle response was greatly improved, and freeway speeds were more easily held going up hills and when racing little tuner cars.
| | Before | After |
| 4.2L (hp) | 157 | 209 |
| 4.0L (hp) | 188 | 217 |