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Old 01-13-2016, 02:26 PM   #1
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Default 5x racing FPR for boost

So I have been wondering about the 5x racing FPR.

5X Racing 1990-1997 Mazda Miata Adjustable Fuel Pressure Regulator

Would this be a useful tool to increase pressure a little at idle especially since a lot of injectors want more pressure than the 43 psi stock 90-93 fprs.

I am using stock rx8 injectors 03-12 Mazda RX8 420cc - Yellow Body #195500-4450
on a 99 fuel rail in my 1.8 vvt

The RX-8 workshop manual shows a fuel pressure range of 54.4-65.2psi and a fuel injector volume range of 356-404cc/min for the RX-8 yellow injectors.

I have flow force 610cc injector on the bench to install later. I am not man enough to tune them yet. LOL

But aren't they set modded factory gt500 injectors? I bet they have more pressure at stock than 43psi.

Just a thought I contacted 5x and the FPR is still boost referenced 1 to 1 still he thinks it will boost idle/vacuum fuel pressure but has never done boosted, I don't know where and I cant find it now but I saw a post someone turned it up to 58psi at idle:

"Our regulator is designed to operate in the exact same manner as the stock regulator. It is essentially the stock regulator with an adjustment mechanism built onto it. It uses the same vacuum line, so boost/vacuum would operate as it would on the stock configuration."

John 5X


"I can't say exactly what the upper end of pressure can be, as we designed them and really only use them to reduce pressure and lean our mixture on our Spec Miata race cars. It will increase pressure too (I've done that before to test them), but I suppose it really depends on the potential of the fuel pump.

We don't rebuild the guts of the regulators, we modify the "can" the guts are in to add an adjustment mechanism to the top of it. We have a proprietary machined aluminum "can" that we press onto the OEM regulator that allows you to turn a set screw and statically set the pressure. We do a thorough pressure test on the provided cores to make sure they're not leaking, but other than that, you will be operating with an OEM regulator that's externally modified to be adjustable. For what it's worth, the OEM regulators are very robust and we've only seen one or two out of the hundreds that we didn't feel comfortable modifying, so I'm sure if yours works correctly now, it is fine."

John 5X
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Old 01-13-2016, 03:43 PM   #2
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If it were my car, I would stick with the factory regulator. You won't gain enough by bumping the base pressure to justify the cost.

If you need to bump the base pressure to get more out of your injectors (i.e. if you have 1000s and are trying to stretch them to 450whp on E85), then you're going to have so much fuel pump that the stock FPR will be overpowered at idle anyway, in which case you'd want something like a Fuelab FPR.

If you're running stock internals, the 610s will be more than enough, even at 43psi base.
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Old 01-13-2016, 03:45 PM   #3
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I don't think rx8 ev6's like higher pressure either.
You're thinking new style ev14's

Throw in the FF's, don't even waste time with the rx8's
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