I have searched but I have come up short. I'm looking to get the most out of my stock fuel lines without having to upgrade to bigger lines. I want to get atleast 400rwhp this Friday when I go to tuning and I want to know how dangerously close am I getting to maxing out the flowing capacity of factory lines. I've heard/read many different rumors/opinions, but nothing conclusive. Here's where I'm coming from.
Last time we dynoed my car everything was going great until we turned up the boost. The car put down exactly 300 rwhp at 9 psi. As we went up in boost we noticed a major drop in fuel pressure as the rpms climbed (pressure would drop about 15-20psi). My tuner figured it was either the fuel pump's fault (maybe a faulty Walboro 255), or the pump wasn't getting a constant 12v and the 1600cc injectors were pulling too much fuel and the lil Walboro couldn't handle it. I though other wise but I changed pumps anyways. Since then, I switched to a TT Supra pump, and wired it up to a constant 12v relay. Something tells me that there's something else to it.
I don't know when was the last time my fuel filter was changed (I've owned the car for 2 years, driven about 15k). I have no way in checking if my fuel pressure still drops but I think I would of blown up since then if it still drops, since I've been boosting 15 psi and I've been fine.
So my question is this. How much boost/power can our stock fuel lines and filter handle? Am I going to be flowing too much fuel pressure and volume through the stock lines and filter that would actually give me a problem? I have a friend that keeps telling me to switch to a -6 fuel line so I'm safe, but I've read many people's set ups and not many do this mod.
BTW, I'm planning on putting on my new fuel filter before we go tuning this Friday. Thanks for reading this mess I call a thread

 

While I haven't verified this, I have read several times that the stock lines are supposed to be good for over 400rwhp.

 

anyone else?

 

Considering each set of conditions is different, it's really hard to say. I've seen some people running a LOT of power on the stock lines. I'd get a fuel pressure gauge and find out for 100% if you still have a pressure drop.

BTW, I remember one from a LONG time ago. Pettit had a car that was not too modified, and always ran lean on the top end. They tried all sorts of stuff to figure out why the fuel pressure was having problems. Turned out one of the metal fuel pipes on the bottom of the car had been squished and was restricting the fuel flow. They fixed that and the car was good to go.

If you're having fuel pressure problems, first step is a new fuel filter and fuel pump voltage, which sounds like you're heading in that direction. But, you won't know for sure if the problem is solved until you do some testing. Just back off the throttle if you see the fuel pressure go south!

Dale

 

I doubt that you would need to go to -6 lines to support 400HP. While it's cheap and easy to tap the ends of the stock rails for 3/8" NPT and put -6 fittings in them, buying enough -6 line to go all the way back to your fuel pump (or doing it with new hard line) is going to cost you an arm and a leg.

Replace your fuel filter. Now.

Are you using the factory pressure regulator + solenoid? Considered that the regulator may be to blame?

 

I have an Aeromotive fuel pressure regular and have a guage on it.

 

have you tried to hot wire (wire your fuel pump straight to the battery) your fuel pump? this would easily solve any problems about if your fuel pump is getting constant voltage. in anycase, i would change that fuel filter asap!

 

Like everyone said, change your fuel filter. Since you don't know how many miles are on it (not to mention you put an additional 15k on top of that), you should really change it ASAP.

 

To solve your current problem without getting involved in a major project, do as suggested already - check the fuel lines for damage, fresh fuel filter, test the fuel pressure regulator to make sure its working properly, and do a fuel pump bleed down test to make sure the lines are holding pressure and leaking back through the fuel pump connection in the tank.

Several members of the Forum have run well in excess of 400rwhp with stock lines. Ari/rx7.com was running deep in the 9's and Steve Kan was deep in the 10's with stock fuel lines. Several other forum members run in excess of 400rwhp with stock lines. I don't think fuel line size is the problem but larger fuel lines will help the system operate more efficiently (lower pressure drop) so the fuel pump can operate at a lower pressure where it flows more volume.

I've got -6 lines and wish I would have done a test before to have something to compare and see how much actual pressure drop.

Jack

 

Jason from the rx7 store told me the stock lines hardlines are good for 500-550rwhp
I don't think the fuel filter is ever really a problem but thats purely a guess

 

Oh and this is a really ******* dumb thing to admit to. Come on man imagine all the money and hard work in putting in a new engine. I say you are very lucky. I had the same pressure drop on the dyno the first time tuning with 850s, 1600s and the m2 boshe pump. we tried changing the fuel filter, hardwiring the pump, and even switching to a walbro that made 650rwhp on a supra. Nothing worked during that tuning session : ( 2 months later we put in 2 supra pumps and changed the new aeromotive regulator which was found to be a bit faulty and then the problem was solved. My car was tuned for the fuel pressure drop the first session. So I immediately knew when we had fixed the problem because at ~4500rpm where the drop was happening when I was running 13psi+...as soon as I got to that rpm after changing out the regulator and putting in 2 supra pumps the car fell on its face because the fuel pressure stayed all the way up around 60 and it was getting that extra assload of injector dump to make up for the previos pressure drop.