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Pros and cons of a ‘normal’ system with a rising rate regulator or a ‘dead head’ system?

Dead head will be less plumbing and neater IMO but will it provide enough fuel for 4 thirsty 65lb injectors? 

Am I better off using a more normal system with a return to the tank off the rail?

Thoughts/advice/experience/stopbeingapoofandgetonwithit

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Depends on what you mean by "dead head"...

With mechanical pressure regulator some kind return flow is pretty much mandatory. But it isn't that critical where the return actually comes from. It can be from the injector rail or from just after pump with external regulator or even inside the tank with in-tank pump and regulator. There are some slight differences between each solution and it depends on application if these matter or not.

Probably the most important factor is that usually you can't use intake manifold pressure reference with in-tank regulator. For NA engine this isn't big deal. Effective fuel pressure over the injector will vary a bit depending on engine load but since the variation is relatively small compared to fuel pressure it can be easily compensated with tuning. But with boosted engines situation is different. There intake pressure variation is bigger and without manifold reference the effective fuel pressure will drop significantly exactly when more fuel is needed. So for boosted engines a manifold referenced regulator with 1:1 ratio is highly recommended.

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Agreed. And rising rate FPR's are for muppets who can't be bothered to get the installation correctly mapped relying on increase in pressure rather than fuel flow based on load demand. Although many OEM installations are 'dead headed and run NA fine when turbos start to get used for performance then external FPR's and return lines tend to be used more often - for me the latter method works better IMO.

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  • 1 month later...
On ‎12‎/‎4‎/‎2018 at 2:47 AM, Gixer1460 said:

Agreed. And rising rate FPR's are for muppets who can't be bothered to get the installation correctly mapped relying on increase in pressure rather than fuel flow based on load demand. 

can you elaborate a little more on this ?

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2 hours ago, no class said:

can you elaborate a little more on this ?

A rising rate FPR works like a Rising rate suspension linkage which increases stiffness the more it moves. The RR FPR's increase pressure in an increasing ratio more than the boost being applied ie 1lb boost will get, say, 1.1psi fuel pressure, 2lb boost will get, say, 2.2psi fuel pressure etc. These figures are applied on top of the baseline fuel pressure but the mapped injector opening times remain exactly as when mapped NA. The downside is boosted engines require fueling that isn't necessarily linear so could be lean or rich with no way of tailoring it exactly. Also the pump has to supply sufficient flow for NA flow, then added boost pressure + the additional increase BUT generally all pumps decrease flow the more pressure they are required to provide, so a pump that gives, say, 200ltrs @ 3 bar for NA but at 10lbs boost might only flow, say, 150ltrs however if a RRR is used the now extra 11lbs pressure could result in 140ltrs ! ! just when you need the most flow!

Proper mapping keeps a constant FP across the injector (boost pressure increases FP but air pressure is the same so its equal) and increases the injector opening period to match actual demand -- this is the correct way. The RRR way is generally used by people who want to use a non mappable ECU and with ratios of up to 1.7 : 1, the pressure increases on the pump get daft ie. 20lb boost will require FP of 43 + 20 + 14psi = 77psi which will nearly stall most pumps!

Hope that helps ?

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26 minutes ago, Gixer1460 said:

 

Proper mapping keeps a constant FP across the injector (boost pressure increases FP but air pressure is the same so its equal) and increases the injector opening period to match actual demand -- this is the correct way. 

still learning this efi stuff....but this is exactly what I am looking to do .  what's involved in making this happen as in fuel pump / pressure regulator  ? I believe the Microsquirt v3 I have is capable of mapping these  injector opening values in tuner studio  ?  boost pressure increasing fuel pressure  via  GM 3 bar map sensor ?

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3 minutes ago, no class said:

still learning this efi stuff....but this is exactly what I am looking to do .  what's involved in making this happen as in fuel pump / pressure regulator  ? I believe the Microsquirt v3 I have is capable of mapping these  injector opening values in tuner studio  ?  boost pressure increasing fuel pressure  via  GM 3 bar map sensor ?

Yep, with the Microsquirt you can map the injection times correctly. But you will still need a mechanical pressure regulator that increases fuel pressure with boost at 1:1 ratio. This keeps differential pressure over the injectors constant regardless if there is vacuum or boost at intake ports. That makes tuning easier since then the injectors will produce always the same amount of fuel for the same injection period. The MAP sensor is used to tell the ECU how much pressure there is going in the engine so that you can tune right amount of fuel for it.

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