This simple mod gave us 5 horsepower for free

The 3.5-liter 2GR-FE V6 that will soon find a home in our 1991 Toyota MR2 Turbo (which will, of course, no longer be a turbo, but we’ll probably leave the badge on just the same) is a fairly high-spec powerplant as delivered from the factory.

[What does it take to swap a V6 into a Toyota MR2? | Full parts list]

Though it found a home in Camrys and Siennas and Highlanders, the build sheet reads more like something out of a supercar builder’s entry-level division: forged bottom end, roller valvetrain, all aluminum block and heads, and a criminally underrated output figure of 274 horsepower.

We say criminally underrated because nearly every V6 MR2 swap we’ve seen is nearing 300 at the wheels.

Using the Frankenstein Motorworks recipe, which includes headers and a tuned ECU optimized for 93 octane fuel and raises the rev limit, most swappers are easily exceeding factory crank power numbers at the drive wheels.

But even while this increased power is great, more increase is even greater, right?

So when we learned about what essentially amounts to a free tweak that has picked up as much as 5 wheel horsepower in back-to-back dyno tests, we figured we’d do just a bit more tweaking before we raised the engine into our SW20 chassis.

The mod involves some simple porting of the factory lower intake manifold to reduce and smooth the stock injector bosses that jut out into the airflow stream where the manifold meets the heads.

Removing the manifold is simple–a few bolts hold the upper manifold to the lower manifold, and a combination of bolts and nuts hold the lower manifold to the block and heads.

The injector rail is held in place by five fasteners, and the whole project took us only a few minutes, and would have probably only taken a few more minutes if the engine was in a car.

Once on the bench, you can easily see the humps in the lower manifold that restrict airflow.

Knocking them down can be done in a variety of ways. We chose a rotary rasp on a die grinder to knock down the majority of the material, then finished up and smoothed with a finger sander.

The whole process took less than 30 minutes, but that doesn’t include having to run out in the middle for more sanding belts. If you don’t break your last belt, though, the process will be far more efficient.

We sanded to the point where the former hump had neatly blended with the rest of the surface. We were tempted to keep polishing and knock down all of the casting roughness inside the ports, but without the ability to do quick A/B testing, we left the roughness in place.

If we find another manifold, we’ll fully polish the insides of the ports, but some manifolds actually like the small amount of turbulence produced by textured sides. Again, without the ability to do real testing, we’ll just take the low-hanging fruit for now.

If you’ve never done any porting work before, this is a perfect first-time project to get the feel for the process. It’s quick, simple and it’s documented to work pretty well.

How well? Well, here’s a dyno chart from Alex Wilhelm at Wilhelm Raceworks showing substantial gains with no other mods aside from removing the large injector bosses:

We reassembled our intake manifold with some new Mahle gaskets (okay, you will have to buy new lower intake gaskets, they’re about $40, but it’s still a great deal for 5 horsepower), but prior to that, we took the opportunity of exposed intake pockets to clean the valves a bit.

After rotating the engine by hand to close each set of intake valves, we sprayed down the valve chamber with CRC Intake Valve Cleaner. It quickly loosened the accumulated gunk–this engine likely has never seen north of 4000 rpm while doing Camry duty.

After spraying off the gunk, we wiped down the chamber with rags, blew out with high-pressure air, and let it air dry a bit before reassembly.

Our 2GR-FE V6 is now basically ready to install. We need to finish some chassis wiring, but soon it will be time to send it into its new home, now with 5 horsepower it didn’t have a couple of hours ago.