Boost Dependent AFPR

[TalonJohn94]

So quick question a friend of mine asked me.

Why cant we (DSM guys) just run a "boost dependent fuel pressure regulator" with stock injectors and a bigger fuel pump?

Basically he's claiming that all the fine tuning with ECM link or fuel controllers, etc.. is unnecessary. He's also saying that the injector duty cycle is irrelevant if the pressure is high enough.

And then as a failsafe, you could just install the AEM WB Failsafe device and program an alarm that tells you if AFR falls outside of the exceptable range.

The one thing I mentioned is that you wouldn't be monitoring knock. Other than that, I couldn't think of other arguments.

What drawbacks to his hypothetical setup am I not thinking about?

 

[GSLENK]

hes an idiot. no offense. with increased pressure there is increased resistance, which reduces flow. so the actual increase will not be linear.

duty cycle irrelevant? I wont even start.

If it really could be done, it would have been done. simply it cannot.

Seriously do yourself a favor AND NEVER EVER TAKE ANY ADVICE FROM THIS FRIEND... he's gonna be one of those friends where you pretend to listen and pretend to care, but in one ear and out the other. But since you are friends, be nice.

I would rather have a TUNE then an ALARM as a fail safe. you don't need a wide-band gauge or boost gauge for that matter as long as the ECU can use them. They are just monitors for you to see if anything is going wrong in real time.

 

[GRAVEDIGGER]

Your friend is off his rocker... We do use what is called a rising rate regulator which rises the fuel pressure as boost rises. The problem is that the stock injectors cannot physically flow enough fuel for the air demands presented by larger turbochargers no matter what the fuel pressure is and that is why we have to upgrade the injectors with higher flowing units and then you also have to control them with something.

 

[99gst_racer]

We all already run boost dependant fuel pressure regulators. Even the OE regulator references boost/vacuum. But fine tuning is far from unnesacery. There's far more to tuning than blindly bumping fuel pressure up across the board. We use engine management systems to tune for specific AFRs at specific parts of the RPM band vs. a given load and that's something you just cannot do by simply raising base fuel pressure. It also doesn't make duty cycle irrelevant. It simply lowers your duty cycle a bit. There's still a limit though.

 

[91stocker]

Yep, too much pressure and the injectors will lock shut. But i've never heard of tuning with a afpr. I guess we have all been wasting our money on these fancy tuners and sensors

 

[99gst_racer]

Yep, too much pressure and the injectors will lock shut. But i've never heard of tuning with a afpr.

It was the 90's approach back before great tuning products existed. Kind of like starting a fire with two rocks before BICs existed. It's the caveman way of tuning given the tools we have today.

 

[91stocker]

It was the 90's approach back before great tuning products existed. Kind of like starting a fire with two rocks before BICs existed. It's the caveman way of tuning given the tools we have today.

Haha, afc's are cavemen to me . That's old school right there.

 

[TalonJohn94]

Hey, I have a SAFC!

Thanks for the argument ammunition so far. So far I got:

• Stock injectors just can't flow enough regardless of pressure
• Injectors could get stuck shut
• You wouldn't be able to tune for specific RPM/Engine load conditions

Really what it is is that he want to build a DSM but doesn't buy my argument to do supporting modifications first. He want a quick and dirty recipe for high horsepower while maintaining street-ability. (Hey, don't we all want that?)

99gst_racer: I don't quite understand one part. Does the ECU (stock or otherwise) really consider RPM? I thought it was just airflow, coolant temp, knock sensor and the O2 reading - from which the ECU decides whether to pull timing.

 

[silvreclips]

a lot of the 420a guys use a similar devise to force more fuel in the motor. Its basically a rise rate regulator that ups fuel pressure in relation to boost pressure. So most people run a 12:1 Fuel management unit which increases fuel pressure 12psi for every 1 psi of boost. Its a crude way to get more fuel and it results in fuel pressures over 100psi at times but it does work.

 

[99gst_racer]

Really what it is is that he want to build a DSM but doesn't buy my argument to do supporting modifications first. He want a quick and dirty recipe for high horsepower while maintaining street-ability. (Hey, don't we all want that?)

Little does he know that the best way to make power is a great tune. And the easiest way to blow up a good engine is a poor tune.

99gst_racer: I don't quite understand one part. Does the ECU (stock or otherwise) really consider RPM? I thought it was just airflow, coolant temp, knock sensor and the O2 reading - from which the ECU decides whether to pull timing.

Fuel and ignition timing adjustments are made based on Load VS RPM and Boost Vs. RPM. RPM is always a prime factor for everything in tuning.

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[Calan]

...he wants to build a DSM but doesn't buy my argument to do supporting modifications first. He want a quick and dirty recipe for high horsepower while maintaining street-ability.

Please, PLEASE...talk him into buying a Honda. We don't need another DSM going to the crusher before its time.

 

[WES_393]

Please, PLEASE...talk him into buying a Honda. We don't need another DSM going to the crusher before its time.

Seriously. The dude doesnt even own a DSM yet, and he is already speculating on how to make a billion horsepower without an ounce of work. I know one crowd whos into that mindset....

 

[gusu]

Seriously. The dude doesnt even own a DSM yet, and he is already speculating on how to make a billion horsepower without an ounce of work. I know one crowd whos into that mindset....

New DSMers?

But seriously, no he is wrong. If you needed additional people telling you he does not know what he is talking about.

Do us all a favor and talk him into buying JDM or Hellaflush, where he will fit in just fine.

 

[TalonJohn94]

He does own one. It's a 1990 (late '89 actually) that is seriously mint. And its bone stock. He's not going to modify it because its FWD and he'll probably want to sell it in the near future.

He wants to get an AWD platform to build. And in fairness he's an all around knowledgeable guy that would probably end up getting it right once he starts building. He just got caught up talking to a friend who tunes R1 motorcycles and other stuff. The motorcycle guy said that ideally you would want to sets of injectors, one primary and one secondary. But the guy also said he gets better results from his rising rate FPR than installing new ECU maps, etc.

And yeah, I will be pressuring him the whole time to do it the right way. You know, "Mod cheap mod twice" and all that. I just didn't really have a complete argument when he brought up the rising rate FPR idea, even though I knew that crude tuning setup was not a good way to go about it.

I especially didn't know that RPM was one of the main drivers for everything, I always thought is was airflow.

99gst_racer: What is the vertical axis there?

 

[Calan]

...ideally you would want to sets of injectors, one primary and one secondary. But the guy also said he gets better results from his rising rate FPR than installing new ECU maps, etc.

This statement alone tells me that he has no clue as to how a DSM (or most any) EFI system actually works. All boosted engines that use a return-regulated fuel supply use a rising rate regulator, as far as I know. It's an integral part of the system's design...not a "tuning tool".

What is the vertical axis there?

That is the VE table in ECMLink, used with speed density setups. The vertical axis is manifold pressure.

 

[GRAVEDIGGER]

99gst_racer: What is the vertical axis there?

Most likely boost for that table, but could also be setup with load in that column. Like 99gst_racer said it's load vs. rpm and boost vs. rpm that we are interested in when making adjustments.

 

[TalonJohn94]

But seriously, no he is wrong. If you needed additional people telling you he does not know what he is talking about.

It was a way for me to learn more about tuning and fuel delivery in general from this forum. Sometimes intelligent conversation is more rewarding than just writing someone off.

What's Hellaflush?

Calan: OK, manifold pressure. Got it.

99gst_racer: So if I, for example, were to use ECMlink (I still use 2G MAS) I would view a similar table but vertical axis would be airflow?

 

[Jon91TSi]

comparison of Lucas type disc injector to Bosch design III to the stock GM multec. - YouTube

Have your buddy watch the above video.. If shows what happens when fuel pressure becomes too high for an injector. The spray pattern can break up (BAD) and then the injector can go static (VERY BAD).

 

[Calan]

That Lucas injector spray pattern ^ is just ugly.

So if I, for example, were to use ECMlink (I still use 2G MAS) I would view a similar table but vertical axis would be airflow?

No.

Airflow calibration for a MAF sensor is one-dimensional and based on measured airflow (in Hz), regardless of the RPM or load. But, target AFR and timing values are always indexed by RPM and load, regardless of the method used to calculate airflow (MAF or SD).

We're drifting a bit OT here, but this page describes the MAF calibration in ECMLink.

 

[TalonJohn94]

Have your buddy watch the above video.. If shows what happens when fuel pressure becomes too high for an injector. The spray pattern can break up (BAD) and then the injector can go static (VERY BAD).

Just watched it and emailed him the link. Thanks a lot for that - very informative. Kinda scary to imagine pushing them to that limit in a car.

 

[Jon91TSi]

And with a 20+ yr old injector anything can happen. It's worth the investment for a set of injectors that can handle the elevated pressure as well as the added benefit of flowing an increased volume. His thought process really goes against the grain.

 

[H@xtGSX]

What's Hellaflush?

RETARDED.

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[TalonJohn94]

Yeah that makes sense. And it was more like a "why couldn't you do this?" type thing asked by him. I'm gonna set him straight before he starts buying parts, I hope. I wish they would have had things like ECM link back when I got into DSMs in like 2001.

I told him that in general, he won't be able to just strap on some dyno queen turbo and start from there. And that there are people that run 11.5 second quarter miles on 14b's.

I'm all about doing it correctly, cleanly and well researched. And that it can be a process. (Of which I admit I am still in the early stages) And I also don't want to see DSMs (especially 1G's ) go to the junkyard before their time. Its possible I get more into the clean sleeper thing than most. Was I the only one admiring the original interior fastener clips and non-faded rear seats on Buschar's white 1GB at Shootout this year, for example?

I know that's getting OT a bit but I can tell you that I will definitely pressure him to do it the right way. I think the DSM crowd is much more knowledgeable than most car followings. And it seems like everyone is super-built these days. Judging from the car show, I might have been one of maybe five guys that still had Mitsubishi turbos and < 1000cc injectors at Shootout this year. Obviously, I'm stretching it a bit.