Dougs951S

As some of you may know, I'm about to install a bolt on HX35 turbo on my car, and I thought that before I converted the car to true MAF, I would do a little experiment to see how much power I could eek out of the factory AFM. I took it apart and very carefully ported the inside of it, smoothing down any sharp bends or obstructions in the airflow path and slightly enlarging the ID of the passages without altering where the door closes. Unmodified, the AFM is capable of flowing ~480 CFM at 60 degrees ambient which works out to about 330 horse. I figure I might gain a few percent from the porting and for the purpose of my experiment I will assume that my AFM will flow 500 CFM. As I understand it, when the AFM signal maxes out at 4.8 volts, the DME dumps in a bunch of extra fuel. More power can be made beyond this hard signal limit do to this, but fueling is out of control and not being regulated in the traditional sense. If one had enough fuel capacity what, if anything could be done to tune around this? I have heard of some racers making as much as 400 hp on the AFM, but I dont know how this is done. With a large turbo and big injectors, what is truly the absolute limit of what can be done with an AFM? My main reason for being curious about this beyond simply seeing what can be done is that seeing as how my car will be running with the AFM at least for a short time, I'd like to extend the resolution of the AFM ad be able to run some reasonable boost in the 15-16 psi range without exceeding the flow limits.

Dougs951S

Yes, a holset. I realize the car badly needs a MAF, but I'm working with what I have at the moment and I'd like to see what I can do with what I have on hand. I dont understand your comment. At 1 bar, an HX35 should flow just a touch over 1000 kg/hr, right at the limits of a ported AFM.

Reimu

Where did you pick up that 480cfm figure from?

Dougs951S

1000 kg/hr flow rate of the stock AFM = 36.66 lbs/min times density of dry air which is 13.076 feet^3/lb = 479.36 CFM.

Rogue_Ant

It's been a few months since the last time you stated that Holsets are not a good turbo for gas cars. So, do you have any proof/data/logic yet?


Doug, have you flow-tested the AFM? The AFM typically maxes at 4.6 volts. Additionally, I've had stock turbo cars max the AFM output, which is definitely lower than ~37lbs/min.

Rogue_Ant

Yep, I didn't think you would bother to actually produce a reasoned argument.

Just fine. And all of them are making significantly more power than your V8 conversion.
Nice try for a distraction though.

Dougs951S

Truthfully Joshua I haven not performed my own flow testing on the AFM, but I have seen 1000 kg/hr quoted a few times, and it seems to coincide with the ~320-330 hp figure that is always spoken of.

Dougs951S

Lets please not derail this thread. Rob, you have offered me good information in the past, made me some very generous offers of help when I was in a bind and generally seem like a nice enough guy. Myself and others obviously have different opinions than you on using these turbos on gas cars so lets agree to disagree. I asked a specific question in this thread and I would like comments herein to pertain to what I asked. Thanks.

Rogue_Ant

Yes, please explain to me how a to read this magical compressor map! I really don't understand how a basic flow vs pressure graph works.

And I definitely need you to explain how different a CI engine is verse an SI one. Does one run on pixie dust?

Take your "I'm smarter than you" insults elsewhere. You aren't capable of learning, none-the-less teaching.

Sorry for the OT Doug, my BS meter gets full every once and a while.

Rogue_Ant

And it might be close, but I would guess a little high... Probably closer to 30-32# depending on the condition of the AFM.

Dougs951S

Nevermind..

No worries

Dougs951S

For some reason, now I feel like I need to get defensive here. There is no need to question where my ideas come from, I certainly can think for myself and rationalize something like a turbo swap. It isnt a secret that people from many other car circles are using these turbos, mustangs, honda, dsm, audi, vw, chevy, to name a few. They are all happy with it, and the general opinion that you seem to disagree with is that they spool well, make good power, are durable as hell and cheap to rebuild. Using these turbos on gas engines is not an isolated thing that just a few guys who drag their talons or Evos are doing. I doubt so many people could be wrong, or just flat out lying about their impression of their turbos. That being said, no, I did not get this idea from somebody just because they have "vendor" status. I got this idea because I think its a good idea! I asked for some input, and the people on this board that are knowledgeable in the area that I asked about jumped to help me. Some are vendors, some are not. All of their input is valued. I'm pro anything that makes my car go faster, more reliably. Bottom line.

FYI I got my holset from a guy who had it on his 1.8 liter audi. He said it was awesome, spooled fast and never stopped pulling. I asked him why he was selling it, he was getting rid of the car and was putting it back to stock. No issue with the turbo.

Reimu

So does the afm work fine until it becomes too much of a restriction for all the air or would adding a maf alone increase power at any level? (in peak power terms here)

Eric_Oz_S2

Yes you can tune around the afm limits. The ecu does not dump extra fuel, the load calc will simply max out the afm input component and then only scale for rpm. You can tune around it using the wot maps. If you go too far, I would guess the pt maps may be a problem. Ie if you max out the afm under pt then you may have some difficulties.

Tom M'Guinn

I have ZERO proof of this, but have to believe the primary limitation of the AFM is the voltage scale and not the air flow. The snorkel and boost pipes would appear to represent bigger restrictions than the AFM. That's not to say a MAF won't flow better, but I suspect the AFM can flow enough air for more HP. At a certain airflow level -- say 300hp -- the barn door opens all the way. Any additional boost/air beyond that point cannot be metered by the AFM. If you scaled down the voltage from the AFM to say 80% of it's natural output, and used a speed density approach for additional flow, I bet a nickel you could push 400hp through a stock AFM... Purely my bench racing speculation however....