davidfarmer

since this device isn't tied into the intake manifold, it isn't a traditional vacuum-controlled device. In other words, most cars use the LACK of vacuum to increase pressure at full throttle.

The C5 hose ties into the intake before the throttle body, therefor you actually might get vacuum at WOT, but NO vacuum at part throttle.

Bottom line, I'm running a custom air intake with no provision for the hose. How much does the OEM regulator change pressure from part/full throttle, and should I bother plumbing it up? I can tune around whatever the pressure is, just don't want the pressure to fluctuate if I don't have it plumbed to the mild vacuum source.

Thanks

FRCTony

It should be plumbed into the intake. I would just run a line over and tee into the brake booster line.

davidfarmer

the OEM setup is NOT plumbed into the intake manifold. It is plumbed into the airbox, which is NOT exposed to engine vacuum.

FRCTony

Can't imagine how it works then...It's always going to read atmospheric.

TYSON1997

No its not going to read atm due to intake restrictions. It will maintain a default of about 58psi with it unhooked. If you hook it to about 20" vacuum you can get about 70psi or so. Mine is just unhooked and tuned at 58psi. But you can buy an aftermarket fpr that just has a screw and can be turned up to whatever you want and tune it with higher fuel pressure if your getting close to maxing out injectors or anything.

davidfarmer

OK, that's great. 58psi is fine.

So it does work "backward" from most regulators.

Thanks!

ToplessTexan

Mine hasn't seen vacuum for years, no biggie. I haven't really seen any obvious assumptions of higher pressure at higher RPM in the PCM either. As long as you've got enough pressure to get the pulse width you need at your target RPM with acceptable duty cycle you should be fine.

Smoke-N-Shot

Kurt, how's it going

xtream1

I have had mine hooked up to a vacuum source for a few years now without any issues. At deceleration I see 20" vacuum and during boost have seen 16#'s. At idle and having approx 13" vacuum I get 53psi and at 0 boost I get 58psi. So, the factory 97-98 regulator does work in both directions at a 1:1 increase rate from a base of 58psi. Also, if you leave it unhooked you should see 58psi steady.

SmoothFRC

for a stock car, leaving it unhooked will not cause any issues.

Many with the 97/8 fuel system will go out and get the adjustible one, as people have reported that the car runs rich from the factory... so they turn it down a little to get a leaner mixture (you would have to research this).

When mine was unhooked, i was seeing 56psi, but my gauge could be off. I have it hooked up to the TB on the pass side.... It does not see vaccum here and only see boost. so the pressure is steady at 56-58psi and will creep up to 63psi or so under boost.

Bill Curlee

I have a brand new still in the box adjustable regulator that i can sell if you need one. Sold the 98 before I had the chance to play with it.

BC

davidfarmer

Bill, let me see what my real pressure is when I get the engine back in the car. If I need the regulator, I'll PM you. If it is reading close to 58, however, I can tune around it.

TurboBerserker

Sorry to bring this back from the dead -- I just found this post while trying to figure out why the emissions hose routing infomation wanted the FPR to connected to "clean air"...

This is goofy.

The reason is this: by doing so, the "vacuum referenced" part of the regulator is essentially defeated. Going to clean air will give you a relative static FPR setting (e.g. it will always read whatever you barometric pressure is). The reason for doing so appears to be in the injector flow rate table of the stock tunes... They are set up exactly as you would for a non-vacuum referenced FPR found in a returnless system.

So, for others trying to figure out a funny running tune (set up for a vac ref'd FPR, for instance), hook the FPR up to vacuum and be done with it