Turbo guys,
I was reading in Maximum Boost (by Corky Bell, good book for you aspiring turbo fiends smile.gif ) last night and was looking for fuel trim/tuning advice. I was hoping he'd have something about control devices (read: electronic) that only kick in after boost is generated.

However, it seems that the only thing he discusses are Rising Rate Fuel Pressure Regulators. You'd infer from his NSX and Miata examples that an MSD, upgraded fuel pump, and RRFPR are all you need.

Now I know this is not true, but I can't remember why. Something about injectors maxing out, or fuel pressure not rising fast enough.

Can someone enlighten me, please?

Thanks,
ac

 

In those examples, he's talking about "turbo kits" that are easy for Joe Consumer to install. And for most cars, that's actually how it's really done. The fuel pressure riser increases per the pressure on the manifold and the stronger fuel pump doesnt give out after 60psi.

It works, but only to a very certain extent. If you want an easy way to bolt-on 35% more power, then the stock injectors with a 100% raise in pressure (and a fuel pump that doesn't mind) can supply the needed fuel.

Look on page 88, he talks about "low boost EFI" applications by using the mechanical stuff you just mentioned (RRFPR, pump, etc) Then after that starting around page 90 he talks about getting into larger injectors and the more advanced computer equipment that's needed.

Not that I'm a junkie, I just happen to have the book at the office for those boring days

-Red-

 

Thanks, I'll re-read that tonight.

I'm looking into maybe just buying some parts from HP.com/UFB and building that kit I planned so long ago.

Onpol told me all I needed for a 5 psi setup was RRFPR, fuel pump, turbo, manifold, and intercooler. I may see if that will get me to my goal and just end up buying the UFB manifold and maybe the turbo.

But if I like it at 5 psi, that setup probably won't do for 7 psi, and I hear that boost is addictive . . .

ac

 

You could PROBABLY get it to 7psi, but it would be a little sketchy.

I would have to say, for up to 10psi you could do a set of 440cc injectors and an S-AFC, skip the RRFPR and do the rest like you were suggesting. It would be a bit safer than just the RRFPR, as massive fuel pressure starts to get scary when you start thinking about it. Who really wants to double (or more) the standard suggested rail pressure across your entire fuel system?

440cc injectors are like $300-350 from RC Engineering, an S-AFC you can get used for $250, and an eclipse pump for $20 would be sufficient. Grab an intercooler (I'll sell ya my Saab 13x9x3 front-mount for $75) and a manifold (Cheuk sells those Champion ones for like $350) and a turbo (T3 brand new is like $550) and you've got a 220WHP daily driver.

It would need some tuning to get exactly right, and an MSD DIS2 unit with the optional BTM component would be a wise idea. Still would be easy to throw together for around $1500 or so...

-Red-

 

Red,
how does an SAFC control the fuel flow at different boosts? It seems like it would compensate for the larger injectors fine at the low throttle points, and would spray enough to keep it from running lean at max boost, but that seems to imply that it would be really rich at all the points inbetween. Or would the stock ECU adjust the duty cycle to keep it from running too lean at the inbetween points?

It just looks like the RRFPR compensates for boost independent of the throttle position and rpm, it allows the stock ecu to compensate for everything else, just bumps the fuel when needed.

Obviously neither is as good as a replacement ECU that can compensate the pulse length and ignition timing as a function of load, TPS, RPM, and boost; but I'm only looking at 38% increase over stock, or 6 psi.

just curious. Thanks,
ac

 

The only reason it works well HERE in the United States is because our cars work on a MAFS system. While it's nice to be able to "watch" boost and react, our ECU can see the amount of AIR coming into the engine and adjust accordingly.

This may be why Cheuk has seen very limited performance ability from the AFC's in Korea -- they use MAP sensors over there and an S-AFC unit is almost incapable of ADDING fuel to a MAP-based car.

If you install 2x larger injectors, then you can use the AFC to adjust -50% (not exactly, but you get the theory) at every air flow point. The adjustment is seen by the ECU as half airflow, so it sends shorter injector pulsewidths and thus the bigger injectors stay open for shorter durations.

The key here is to keep the MAF return voltage no higher than something around 4.2vdc into the ECU. At that point (or thereabouts) the computer starts to figure out that something is wrong and there's too much air reported. It *assumes* the MAF is stupid and throws an error, rather than assuming you've installed MaDd BoOsT y0 and it's actually GETTING all that air wink.gif

That's why the AFC is able to work alright for low/mid boost situations but nothing really any higher than around 10psi. If you combined an RRFPR with a good Bosch high-pressure pump, a set of 440's and an S-AFC then you could probably run 12-14 psi with some serious tinkering in the S-AFC settings to keep the MAF output under 4.2vdc

If you want to expirement with that, I can provide quite a few settings for you to work with on the AFC. I'm very sure you could run almost 18psi through the stock MAF and still be able to use the AFC to keep the voltage below 4.2vdc... Not sure how long the MAF would last tho

-Red-

 

Cool, thanks Red. Two more questions:

First, what is the flow rate that the MAFS (without changing the signal with an AFC) can handle before throwing the CEL? this leads to question two . . .

Two, do you see any problems with me just upgrading the pump and using a good RRFPR (like the new BEGI unit) and running 5 or 6 psi. Then later (after break-in, learning curve, saving money, etc) upgrading to the 440 cc injectors with the SAFC?

Finally: have you sized the intercooler that is "for sale"? i.e. will it fit in front of the radiator? If so, you may have a p.m. coming . . .

thanks,
ac

 

Red,

You know I didn't think about the S AFC difference in control with the MAF Tibbies you have in the states. With a lot of tinkering, you should get better control with the S AFC than we do with our MAP sensor cars.

Otherwise I agree with you completely. The boost levels where you max out each of these fueling methods is difficult to exactly quantify... like you said... because of different states of tune and inexperience with US MAP based Tibbies.

 

Curtas,

The stock MAF sensor I think "maxxes out" around 17lbs/min (according to Random using his OBD2 system logger) I'm not 100% sure what that correlates to, but you could probably "safely" get 5-6 psi out of it without pissing off the MAF.

And for just 5-6psi, you're certainly able/welcome to use a rising rate FPR and a good pump. In fact, I've got a Venom 12:1 FPR that I've never used before AND have little use for now wink.gif If you want to make me an offer, I'll gladly sell it to ya to.

The intercooler will definately fit between the radiator and bumper on the 1st gen Tibbies, there's a BUTTLOAD of room down there tongue.gif The thing is, you'll still need to "manufacture" some way of mounting it. I can take some pictures if you like. I'm selling it because it's going to be too small for the boost I want to run daily

Cheuk,

You know what's sad is, you kept telling us that you've had bad experiences with the S-AFC unit for tuning and I never could figure out why until I was helping a friend with their Civic Si and a blower -- and a V-AFC. I suddenly realized what you were experiencing: signal from a MAP sensor is a very precarious thing. If the computer sees "too much vacuum" (trying to remove fuel at idle) then it thinks something is wrong. If the computer sees anything above 0 inches of mercury (trying to add fuel at WOT) then it also thinks something is wrong.

The MAF sensor-based ECU's seem to be a lot more willing to "accept" wierd airflow values. Of course it's still a bandaid fix, but I would bet you could get appropriate fueling for up to 12psi with larger injectors/fuel pressure/S-AFC on a MAF car.

Of course, the MAF itself presents a lot of "interesting" problems when dealing with boost...

-Red-

 

Red, pics of the intercooler would be great.

About the Venom unit: how adjustable is it? I've been looking at the BEGI unit that had adjustments for max boost, onset boost, and rate. Downside is, it's $260. That may be overkill, since I'm looking at a small turbo that may be up to full boost by 4k anyway

I went to Venom's site and all they had was a closeup picture. Pretty, but useless.

thanks,
ac