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07-08-2018, 04:09 PM #106
If you have already invested in the return style hardware I would not spend the monies to go back to the returnless system, Todd. Both systems work well and in the FWIW category most of the race setups opt for the simplicity of the return style system.
The challenge(s) you need to manage are unnecessary heating of the fuel and subsequent return to the tank. Vacuum / boost pressure vacuum line signal delays and attendant uncontrolled return system pressure variances in the fuel rails. The good news is that all are manageable. If you still have a returnless system and use the PID control model that Sullivan Performance developed you can easily handle up through essentially 700 HP.
Things you want to pay attention to for a return style system certainly include placing the fuel pressure regulator away from engine heat. When you do this, you end up using a longer rubber signal hose to deliver the manifold boost or vacuum signal to the regulator. This can potentially produce rich or lean transition points as manifold pressures rise and fall because of the time delay in signal delivery from the manifold through a hose to the pressure regulator. Shorter hose is always better but in a typical balancing headache shorter gets you closer to the engine heat soak problem and longer gets you a manifold vacuum/pressure single timing delay.
When Ford designed the OEM fuel system they had a variation of the signal delay problem that was caused by the tank mounted pumps and normal delays in sensor readings. Their approach was to employ a second pressure test point closer to the injectors and the manifold. The sensor they used was the FRPS. The FRPS measures the delta pressure across the injector calculated as the difference between instantaneous fuel rail pressure and instantaneous manifold pressure.
Once the ECU knows what the actual delta pressure is it calculates a pulse width for the injector that is designed to produce the commanded AFR the tuner asked for. A lot of guys remove the FRPS when they switch to the return style systems because they have been frustrated by blown FRPS sensors prior to the change over to return style. While this is possible to do it is better to leave the FRPS in place, more on that in a minute.
The reason for the FRPS failures in the returnless system is the pressure spikes associated with a poorly adjusted PID — which is what the Sullivan fix . Once you do the Sullivan fix in a returnless system the fuel surges and pressure spikes that kill an FRPS suddenly come under control.
The firs time return style conversions frequently eliminate the FRPS. While the engine will still run w/o the FRPS it will run much better with the FRPS even in a return style system. Remember those lazy to get to the pressure regulator manifold pressure signals that appear with longer hoses between the manifold and the pressure regulator? With the FRPS present the factory ECU can see the effect those slow to arrive signals have on fuel rai pressure. The factory ECU not only sees them it compensates for them by adjusting injector pulse widths in real time to deliver the tuner's commanded fuel charge to each cylinder irrespective of varying fuel pressures.
If you are already a return style system, consider getting the fuel pressure regulator away from the engine compartment heat and reinstalling your FPRS (if you removed it). Your ECU (and your engine) will like you for it.
07-08-2018, 08:52 PM #107
I thought I had posted a pdf of the Sullivan "fix" in this thread. It looks like I did not so here is a pdf copy of it. I lifted this out of the original thread about a decade ago — yeah, its been around that long. Those Sullivan guys were pretty sharp folks.
07-10-2018, 05:33 PM #108
Thanks for info Ed. I’ve read that Kurgan also has the fix for the returnless hesitation. I’m assuming he’s adjusting the same PIDs?
I guess I’m still undecided as which way to go.
For returnless, I still have a factory fuel hat and have squirreled away two junkyard FPDMs. I’d only be focus pumps (unless there’s a better alternative) and a tune away from converting back. The idea of having factory like operation is very appealing. Mainly OEM like start up behavior and not constantly pumping unnecessary fuel.
As for staying return, I’m not exactly clear as to what current components I can use. From what I’ve read in this thread, aftermarket fuel rails with a supply for each and a crossover at the end is ideal. Would the stock supply line work for my hp goals? Would the regulator in the budget return kit work (Division X two port)? Add necessary plumbing and fittings, converting to dead head is adding up to addditional money.
Would there be any concerns with both pumps running, or would staging them be ideal? Also, any known hot restart issues with dead head, or does the pressure in the rail prevent them? Finally, would a re-tune be necessary or recommended?
Sorry for the excessive questions. Thanks again.
Last edited by 67coupe; 07-10-2018 at 05:36 PM.
07-10-2018, 06:59 PM #109
These days it pretty much comes down to what your personal preferences and willingness to buy new stuff is, Todd. Both system styles can be made to work well for your intended use.
If you already have a return style setup the pregnant question is why buy more stuff to go back to a returnless style system. Similar questions going the other direction. Remember, both can be made to work well for you. My suggestion would be to use what you have rather than buying "new stuff".
If you have a regulator with one of the small bypass orfices in the return port, you might want to try it before stepping up to the next larger regulator — $200 or so is a fair amount of beer and pizza. At the 500 HP threshold you might be very satisfied with its performance.
This next comment is not meant to be deprecating. Why not take the best parts you have right now and lets build a 500 WHP engine that does the least damage to your pocketbook and produces the best smileage (smiles per driven mile).
07-13-2018, 08:20 PM #110
Thanks Ed. I’ll start piecing together the lines and fittings to go dead head.
The to do list prior to a supercharger upgrade keeps getting longer...
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