Fuel Pump Adequacy
 

Ok so I have a 2002 Miata VVT with MS3 and MK Turbo Kit.

I set it up at 8 PSI, boost creeps to 10 PSI but that's fine, just tune for it. Maintains 11.6-11.8 just fine.

I put in the boost controller, turned it up to 15 PSI, and tried tuning, no matter how much fuel I throw at it it's running as lean as 12.6 under high-RPM (>6000) operation. Duty cycle is exceeding 100%.

I've got the FlowForce 640cc injectors as provided with the kit.

I think I need a fuel pump upgrade, everywhere I read I just find conflicting information. Some say the FP and FPR and adequate up to 300 HP. Some say it's not. Some say you just need a Walbro 190HP. Some say you don't. Clearly, I'm running out of fuel somewhere, because with 640cc I definitely shouldn't be running out of injector.

Let's set the record final and straight in this thread. For >200 HP in an NB2 Miata, do I need a fuel pump upgrade?

It's never a bad idea to buy a proper fuel pump (how old is yours now? 17 years?) and have enough headroom for future mods.

A DW200 is like 90$ and fits PnP, just go for it. Installing is pretty easy and takes about an hour.

I've already got a 190HP and install kit on the way. I'm just trying to figure out why fuel pump info is so conflicting. Some say it can handle the power, some say it can't. Maybe my pump is tired? Who knows.

It's because stock pumps are old and at various states of tired. A new fresh pump might keep up but at 15psi your approaching 300 crank HP so why bother. Stab the 190 and get back to chucking rods out of the block.

a 190 LPH pump is plenty for your HP level.

have you watched your fuel pressure under load?
if the pressure is dropping i would assume a weak pump.
if the pressure is fine i might look at the injectors themselves.

Change your filters at the same time. Seen clogged filters rob a lot of power.

Stock 1990 fuel pump with flow force 640s and pushing 15psi on the old 1.6 #sendit

I seem to remember something about the NB FPR being referenced to ambient, rather than the manifold like on NA Miatas. So as you increase boost pressure, the pressure differential across the injectors decreases reducing flow for a given duty cycle. Have you checked your fuel pressure to confirm that the pump is running out of steam?

EDIT: Glad to know my memory isn't failing me:

https://www.miataturbo.net/engine-pe...5/#post1291056

In other words, you may still have an issue even with a new pump because the FPR is not increasing rail pressure for boost. If the pump doesn't fix it, then you will either need a new FPR (preferably manifold referenced, maybe even convert to a return-style fuel system) or larger injectors (which will flow more fuel for a given pressure differential).

Is there a way to convert to a manifold referenced setup to increase rail pressure while maintaining the returnless setup?

I would suggest upgrading your relay and wiring while you install a new pump. The stock one is known to be weak.

https://www.miataturbo.net/general-m...p-relay-95629/

Yes

You don't need to get a vacuum referenced fpr for 300whp ( which you will get nowhere near with the turbo you have now ). All you need is a better fuel pump which is sounds like you've already got coming. I run 550's with a 255 hp walbro and I'm making 296 at the wheels with duty cycles in the 85-90% range. Your old pump can't keep up, it's likely dropping pressure up top which is why you can't get any more fuel no matter what pulsewidth you are asking of your injectors

Sounds good. I might put together some stuff to have a manifold-referenced fuel pressure regulator, utilizing as much factory hardware as possible.

The NB fuel system is ambient referenced, but it's also starting at a higher pressure. NB fuel pressure is ~58psi, and NA is ~43psi. At 15psi boost pressure, the fuel delivered by the injectors should be about the same.

UPDATE:

Upgraded to the new Walbro FP. I had to retune damn near the entire VE map! Apparently not only was the stock pump possibly inadequate, but was probably on the verge of failing.

Well there you go kids, if you're going turbo just upgrade your fuel pump!

Yeah, this should really be done even if as a maintenance item.

The advice in the wiki saying stock pump is good for stock block was probably more applicable when the average pump wasn't 15-20 years old.

Probably would have been fine if it was a new stock pump.

Exactly which pump did you use? If you went to big it may be to much for the regulator to handle which could also explain why you had to retune the entire table.

Possible, but the difference in price is so small. Besides, leaves room for more upgrades!

Walbro 190HP. I think the old pump was so tired that I had to throw a ton more VE to get it to correct AFRs, autotune actually had to pull out a ton of VE.

I only needed to return the portion of the table with positive manifold pressure, 100+ kpa. The vacuum portion of the map didn't change much, if at all.

Did you ever check old and new pressures?