Huge Changes! Manifold, HTA86, Billet Fuel Rails + more


Shortly after I changed out the throttle body for the new Boomba 75mm throttle body, I started to experience some weird misfires. Knowing that I’ve had to replace some ignition coil packs, I pulled the cylinder 1 coil pack and replaced it with a brand new one. I also swapped out all of the spark plugs just to be safe. All of them were clean, but new ones were put in to replace the one-step colder NGK’s that were in there.

The misfire was hit or miss. Sometimes it would pop-up after it got really hot, sometimes it wouldn’t. My suspicion was two things: 1) The Boomba Throttle Body does not have a coolant port like the stock one does. You just route it to back to the block where the stock return line would be on the stock throttle body. I didn’t think it would be a problem, unless the stock throttle body is actually cooling the coolant, making it so that any coolant passing on to cylinders 1 and 3 were at a bit lower temperature. I don’t have any way to prove it, but considering it started happening immediately after installing the Boomba, it was an idea. 2) The injectors or something was clogged, or 3) there was a boost leak on the passenger side TGVs.

With all this in mind, I decided to do some extensive customization when I pulled the manifold to swap out both injectors and TGVs.

I found a used 08 STi manifold and had it custom ported and bored to 75mm, eliminating any restrictions in the intake side. It didn’t make sense to have larger intercooler piping that then was squeezed down to the stock manifold opening. After speaking with another Subaru specialist who had great results with port matching everything (both exhaust and intake), it seemed like a good idea.

I was itching for a tad more power too, so a new HTA86 .82a/r seemed like a great fit for this motor. A Perrin FMIC was also added to the upgrade mix to handle the increased flow and power capacity.

I have always wanted to clean up the engine bay significantly, as the Perrin fuel rails are really kind of an eye-sore. I don’t like the big lines and its whole layout is just messy. After having received the Process West Fuel Rails I decided it was time to make the engine bay look pretty. I took the manifold and intake piping over to PSI to get some custom powder coating! They did a great job and it really has stepped up the overall look.

I tore out the Perrin Fuel Rails and lines and fitted the new Process West fuel rails with custom Earle’s fuel lines and -AN fittings. The fuel rails are -8AN on both inlet/outlet, and all lines from the surge tank and back to the Aeromotive fuel pressure regulator are -6AN.

Injectors were also replaced with hirer rated and higher quality Injector Dynamic 2000cc injectors. ID provides better pulse width data to help resolve any stumbles in the non-linear range.

If you have a keen eye you might have spotted the Killer Bee Upper Coolant Reservoir that replaced the stock one. This was purely to make more space for the turbo inlet, since the stock one is pretty massive and restricts space in that area. It’s a very nice piece and looks a heck of a letter better now!

Big thanks to Phatbotti Tuning for helping me get a near perfect base map, even after all these changes!