Big Block MPFI Pressure regulator setups

[1BadAction]

Intake swap is beginning to take shape and I'm trying to decide what way to go with my fueling. Pump is relatively new, application was a 97 Vortec 454 Suburban so it should have no issue running at MPFI pressures. Keep in mind this has a specialized single fuel rail with a built in pressure damper that houses all injectors at the center of the intake so I'm somewhat limited in what I can do. I've narrowed it down to a few options.

1. Corvette filter/regulator mounted in stock filter location. 58psi. Excellent option, clean, cheap, factory stock reliable and keeps the fuel nice and cool... but they are not vacuum referenced. Since the 7427 doesn't have VAC vs Fuel pressure tables like the LS PCM, this might create some tuning headaches.

2. Aeromotive mounted on the frame rail just behind the point where the braided line jumps from the frame to the engine. Adjustable (will likely run 58psi) clean, possibly more stable pressure, cooler fuel, vacuum referenced so pressure is constant and will have no tuning issue. Cons: 50% more expensive than the vette filter/regulator and not sure how a long vacuum line from the manifold to the regulator will effect the fuel pressure.

3. Aeromotive mounted on intake/firewall before the rail. More traditional. No question in its function. Cons: same as on the frame, more fittings required, somewhat unsightly, AND these setups introduce a ton of heat into the fuel system. At the end of the day this is a tow rig not an all out race vehicle.

Any other ideas? Comments? I'm leaning toward the aeromotive mounted on the frame... but I can probably be swayed.

[brian617]

The 96-00 BBC Chevys with MPFI used a singe fuel rail??

[1BadAction]

Its a marine intake. 100% different from a vortec truck intake.

[brian617]

Got any pictures of yours sans the upper plenum?

[1project2many]

I had some similar questions helping a friend put an LS engine into an S10. In his case we found a fuel rail and came up with a way to change the upper part of the regulator. As I remember there is no access to the Vette regulator in the filter combination assy.

What did Merc originally do for regulator? This seems to suggest they used an external part.

Does the damper look anything like a regulator? I've has some success taking regulators apart and putting them back together using special clamps. Hard to see but this regulator has one of these clamps holding the halves together.


I have built special fittings to install these regulators in places where they were not originally found. Here's one on a smallblock marine intake:


The steel sleeve fitting was made on a drill press. The regulator, a stock part from a Cavalier 2.2, can be rotated to any position.

[1BadAction]

[1BadAction]

Dirty little secret from merc... The mercruiser regulator is a dirt cheap keihin regulator out of a Honda car. Furthermore, the damper is just a regulator with the return port fitting blocked. Earlier motors used the same regulator but the return port fitting was open. That little open fitting is NLA from merc marine, if it wasn't I'd have one on the way.

I've contemplated messing with the fitting, drilling a hole in it, finding an o-ring and giving it a shot. But because of the oddball fittings I'll need for the back of the rail, if it doesn't work I may end up out 70 bucks for nothing.

[1BadAction]

Merc did it a couple ways. Both involving high dollar lines and fueling units that, even in stock applications, are notoriously problematic in both their return forms and returnless forms. Most guys that keep mpi intakes swap over to an external regulator or at a minimum run the return back to their main tank, which is something the USCG frowns on. (Which is why the fuel delivery is so odd in the first place)

[brian617]

Your rail not have this type regulator?

[1BadAction]

That particular pic is when it's being used as a pulse damper (#11 fitting blocked not open) - that's exactly what I have now, can't use the rail without it unless you start cutting, drilling and tapping. If I could find the #11 with a hole in it I may be able to make it work as a regulator.

[1BadAction]

21 in this pic is what I'm missing... If I had a lathe I could cut a hole in the one I have but I don't trust myself to do something that small freehand.

[1project2many]

So is that fitting not part of an automotive rail with keihin regulator?

I have used frame mounted regulators, no problem. Yes, they're costly. At least the good ones are costly. And after catching a couple of cheap Ebay copies leaking I buy the good ones. But my first choice is a factory type installation.

If you want to save time I'd say go with the frame mounted regulator. What you save in $$ trying to use some form of automotive part you'll probably spend in time figuring out what to use and where to get it. Either solution should be vacuum referenced as it will make tuning easier. AE, DE, VE are all in need of careful attention when using fixed pressure fueling and none of the results will be right. There's a fair amount of correction built into new pcm code to make sure constant pressure fuel systems deliver the right fuel to each cylinder.

I see some aftermarket regulators for Honda cars. Any chance a good used one would fit the Merc rail?


Can you open the hole in the rail and mount a single bolt GM style?


I also found this fitting for an AEM regulator... maybe can be used to replace the plugged fitting in the OE regulator?

[brian617]

21 in this pic is what I'm missing... If I had a lathe I could cut a hole in the one I have but I don't trust myself to do something that small freehand.

So if the plug is drilled it returns fuel back through the rail where the two openings are correct?

[1BadAction]

So is that fitting not part of an automotive rail with keihin regulator? I have used frame mounted regulators, no problem. Yes, they're costly. At least the good ones are costly. And after catching a couple of cheap Ebay copies leaking I buy the good ones. But my first choice is a factory type installation.If you want to save time I'd say go with the frame mounted regulator. What you save in $$ trying to use some form of automotive part you'll probably spend in time figuring out what to use and where to get it. Either solution should be vacuum referenced as it will make tuning easier. AE, DE, VE are all in need of careful attention when using fixed pressure fueling and none of the results will be right. There's a fair amount of correction built into new pcm code to make sure constant pressure fuel systems deliver the right fuel to each cylinder.

The AEM regulator would be awesome but I have no clue if it would fit on the merc rail since they don't have the same space constraints in an automotive application. The honda regulators aren't butting up to a rail on the return end, they have a stamped steel nipple pressed in. Here's a pic showing how the regulator mounts to the rail, the return side has that brass fitting with a couple o-rings that slides into the return port.



This is a merc regulator, notice the rubber grommet? I'm not sure if that will seal against the rail or it is there in addition to the O-ring'd bushing. At 150ish dollars for a new merc regulator, plus anywhere from 70 bucks to 200+ each for their specialized fuel lines I would need to run the return, I'd probably be better off going with the Aeromotive regulator on the frame in a returnless style. With a returnless I can tap the inlet on the rail and throw a NPT to -6 on it, if I was to run the merc style I don't have the room to have two -6an fittings.



Going to do a bit more searching today and see what I can find. Good to know the remote regulator will work well though, that's something I was curious about. Corvette regulator sounds like it's out, this thread has given me plenty of paths to follow. I should probably go to a hydraulics shop and get their opinion before I dump a ton of money into something, they may have a much simpler solution.

[Hog]

The 96-00 BBC Chevys with MPFI used a singe fuel rail??

Yup, all the 1996-2000 L29's and L21's had a single fuel rail, right up the middle of the valley. The marine intake is similar in function, different fitment. On the SBC Merc marine intakes, they run at 58psi, but have 2 fuel rails while the Merc BBC marine intakes use a single rail. peace Hog