ribs

I'm in the process of building a turbo 4A-G for my 1st gen MR2, and doing this on a budget, I'm trying to figure out any parts I can reuse from my pile of junk from my 951.

One piece I had laying around was the stock 2.5 bar FPR from my 951, that worked fine, but I replaced it with a 3 bar unit. I just wanted to know if it was a rising rate pressure regulator, as this would be adventageous to my application, meaning that I don't have to try and source another FPR. The stock 4A-G FPR is fixed, while the supercharged FPR is rising rate, but rare/expensive. I'll still have figure out if the 951 FPR adapts to the 4A-G fuel rail to see if this is viable at all, but it would be good to know if there is any reason at all to use it.

This motor is getting stand-alone fuel and spark management (megasquirt and megajoltlitejr), so tuning for a RRFPR won't be a problem, and I may be able to get away with smaller injectors giving me better idle and off boost drivability. TIA,

-rich

Sam Lin

It is rising-rate, that's why there's a vacuum line hookup on it.

Good luck
Sam

dand86951

I don't think the stock 2.5bar is a rising rate, i.e. raising fuel pressure more than 1 psi for each psi of boost. It does maintain the 2.5 bar differential as boost rises IIRC. Most of the adjustable regulators really just adjust the starting point. Some can be adjustable and rising rate such as increasing fuel pressure by 1.3 psi per pound of boost.

Ben Z.

Sam, I'm not positive, but from what I recall we may have just witnessed a very, very rare event: You might not be 100% correct on this one!

Rate implies slope, and to me, a rising rate would mean the fuel pressure would not be linearly related to the pressure in the intake manifold. I thought that it was in our cars, but there is a good chance I'm wrong. You probably just meant that the fuel pressure is not constant, in which case I'm being even more of a jerk. Anyways, good luck with the project car, rich!

Oh yeah, Sam are you finished with school (if so, congrats) or did you decide to try something different?

EDIT: and I was beaten to this by like half an hour, didn't think I was that slow.

Sam Lin

Ahh, you're right, I got rate mixed with pressure - my apologies, and thanks Dan and Ben for correcting me. It is a linear 1-1 rise rate.

Sam

ribs

Thanks guys! I'm pretty sure that the stock 4A-G regulator only lowers fuel pressure according to vacuum, but doesn't raise it for boost. If this regulator is capable of keeping fuel pressure the same relative to boost, I will probably use it (if it can be easily adapted to the 4A-G fuel rail). I'm a little weary about using 550cc injectors on a 1.6L motor, especially since the megasquirt ECU doesn't do sequential injection (I can set up 2 banks, which may help a bit), and the injectors I am using are high impedence, which makes it even more troublesome, but hopefully I'll be able to get it to idle without much trouble. If anyone is interested, this is the gist of the motor I'm putting together:

-4A-GE 7 rib shortblock (cast iron, larger rod & main journals than older motor, more reinforcement)
-4A-GZE pistons & rods (8:1 compression, forged, H-Beam rods, all from supercharged motor)
-4A-GE large port head (TVIS dual runners, 16V, wide angle DOHC, aluminum, etc.)
-Head and block were rebuilt before being sold to me
-T3 super 60 turbo (still trying to find one)
-custom equal length tubing iron manifold (from here...haven't bought this yet either)
-Volvo 740 intercooler (huge!...going in the trunk, getting ducting)
-welding my own exhaust and intercooler pipes
-Megasquirt Fuel Injection computer (megasquirt DIY DFI...already put this together)
-MegaJoltLiteJr. Ford EDIS controller (MJLJ homepage...already have this put together too, and I picked up and EDIS system out of an escort from a junkyard for $15 or so)
-550cc S5 RX-7 turbo II injectors, brand new, on their way
-A bunch of other minutia

Currently, the bare block is sitting on an engine stand in my garage...I'm going to attack it with carb cleaner later this week, send the crank out to get balanced, and start putting the motor together soon.

Other people running my same set up get between 250 and 300 HP to the wheels with reasonable amounts of boost and good tuning. I'm going to strip a lot of crap out of the car, too, so I am hoping to get a net weight of around 2200 pounds, with 250-300HP...it should be a fun car when I get it all together. Then I have to do a suspension...grr...

-rich

Sam Lin

That should be a fun project, you've got everything you'll need to run it well, and it's a durable engine with plenty of potential.

Sam

Paulyy

what is the highest rate for the stock 2.5 bar FPR under boost?

- paulyy

JohnKoaWood

OMG, this might just be one of the oldest resurections to date!...

Paulyy

saves jamming the forum with threads,

now someone answer my question

dand86951

I don't think there is a limit for the regulator. Bosch may have some max pressure safety rating but it will most certainly be over 100psi. The limit would be from the fuel pump. The stock regulator should maintain the 2.5 bar differential up to whatever boost you go depending on whether or not your fuel pump can deliver the required flow at that pressure.

Paulyy

so would there be any chance of the stock 2.5 bar FPR failing?

dand86951

There is always a chance any FPR can fail. What pressure will you be expecting it to run. If you run 30 psi boost the FPR will be working at 68 psi. That is not excessive nor should it lead to any failure.

Now again your fuel pump and injectors have to be able to handle that pressure.

Rogue_Ant

68psi is fine for both injectors and pump. The bosch pumps are actually quite adept at high pressures.
And the stock 2.5bar FPR is a 1:1 rate regulator.

Paulyy

Thanks guys for that info
Theres nothing wrong with the FPR ran some tests on it.