Changing out the OEM Fuel Pressure Regulator

[Bang876]

The 08+ STi seems to be plaque with fuel stuttering issues from low rpm of 2800 to around 3000. What I learned was that Subaru design the the OEM FPR to recirculate it back in which creates a vacuum. This in effect hinder the OEM FPR to provide consistence and adequate fuel pressure at all times hence the stuttering at low rpm. The Cobb FPR is actually an OEM part that is modify by COBB so as to provide a straight and resistance free path for the fuel while maintain proper fuel pressure at all times. Its a night and day difference since I did the swapped! The car feels so much more smoother and actually seems faster and more responsive. This is an upgrade I highly suggest to everyone. FYI you will need a retune if you are running stock tune. The reason being is for speed density based cars. There is a load table that needs to be modified if you're going to tune via speed density, otherwise your numbers will be all over the place. Luckily for me I didn't have to get a retune, because my tuner only works with COBB software so and he corrects the load table for every pro tune as standard modifications so my car already had the load tables corrected ahead of time.

THE SHITTY ASS STOCK FPR

Notice how it has a bypass hose that recirculate the fuel back. Thats the issue with the set up, Subaru probably did for emissions reason.

 

[Spamby]

Interesting.
So I'm pro tuned by Cobb themselves. Wonder if it's a no tune swap for me?

 

[HolyCrapItsFast]

I think the necessity for a tune is dependent on how it was tuned prior to the install. If it was tuned to compensate for the stumble, then a retune after the install is likely required because now the new FPR configuration would actually work against the compensations made in the original tune.

I would say if you are on a stock tune and do this install. Then a tune would not be required because the new FPR is accomodating the corrections