Alright fellow tuners I made the switch to race fuel (TORCO 110 Leaded) and was retuning the car last night.

Now on pump I was running 60psi of fuel pressure in order to hide enough airflow from the computer using my S-AFC II to prevent fuel cut and had a nice tune at 15psi boost on my new Evo3 16g. With the race fuel I dropped the fuel pressure down to 50psi that I calculated out based on my setup and horsepower goals and hoping I wouldn't have to run such high pressures any longer. Problem is I hit fuel cut at around 5-5.5 grand.

I cant pull any fuel in the S-AFC as I need it to keep the knock down so that option is out. Side note timing is around 15-20. Knock sometimes hits 6 or so. O2 around 0.93v; could I be getting rich knock with the race fuel? What O2 is good for this fuel? Darn high compression 9-1 engine is good for low end power but murder on the knock.

I just boost leak tested the car so that is out

Should I up the fuel pressure to 55-60psi again or

Should I hack the MAF up? I have already removed the lower honeycomb and backed off the screw but I haven't cut it apart yet for fear of ruining low RPM drivability. I've searched a ton on this subject but haven't found much. The VFAQ shows how to hack the heck out of it but at the end the author recants and says he cut too much and destroyed drivability.

If you think I should start hacking; for those of you with experience how much should I hack to start with? I want to keep drivability for the city but need to mask some airflow up top.

Thanks everyone!

I think it's time to upgrade your maf sensor and possibly get a wideband. You can't use O2 voltage to tune A/F ratio's, it's not accurate. I would try to find an Evo maf sensor but if you can't find one of those just get a 2g sensor.

GVR4592 said:

I think it's time to upgrade your maf sensor and possibly get a wideband. You can't use O2 voltage to tune A/F ratio's, it's not accurate. I would try to find an Evo maf sensor but if you can't find one of those just get a 2g sensor.

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Yes I believe you are correct. Side note I also watch for knock and proper timing. The problem is its going to have to be a winter project. (My dad has a heated shop) as the summer here is almost over and my weekends are all booked up. Im thinking I'll go with the second gen maf but it'll take some time to fab everything. Im also hoping to get a wideband this winter.

But for now either I crank up the fuel pressure to hide airflow or physically hack my 1g maf.

Question one; anyone see a problem running 55 or 60 psi fuel pressure? I have supporting fuel system and ball and disc injectors (manufacturer said they handle higher pressures better)

Question two; For those who have physically removed material or "hacked" their mafs how much do I dare take out before drivability becomes an issue. I know people have done this before so please share your results.

Which way should I go?!?!?

Thanks.

Alright I found a nice write up on the RRE sight with pics, but it doesnt give any details as to how the vehicle performed at all. Anyone have anything to add? I think I may follow their lead and start taking material from the lower tube pathway little by little.

Echo5Zulu said:

Question one; anyone see a problem running 55 or 60 psi fuel pressure? I have supporting fuel system and ball and disc injectors (manufacturer said they handle higher pressures better)

Question two; For those who have physically removed material or "hacked" their mafs how much do I dare take out before drivability becomes an issue. I know people have done this before so please share your results.

Which way should I go?!?!?

Thanks.

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First off, looks like you have the 255 pump now is the the HP version of the std 255? The problem with 55 to 60 psi base fuel pressure is the greater the pressure, the less your fuel pump will flow. Our regulators are a 1:1 rising rate, so for every 1 psi of boost you see 1 psi extra fuel pressure. At only 15 psi you'll still be seeing 70-75 psi of fuel pressure on boost. In this range, depending on the pump, the flow really starts to drop off, which is defently something you don't want.

As for hacking the MAF, Im not an expert (Don't need to with 2g & DSMLink) but as far as I know the mod is reversable if you don't damage the honeycomb upon removal. Think most start with removing the bottom section & if this doesn't help enough, then remove the sides. Air chooses its path differently depending on the speed, so your corrections from removing honeycombs won't be linear across the settings.

daren_p said:

First off, looks like you have the 255 pump now is the the HP version of the std 255? The problem with 55 to 60 psi base fuel pressure is the greater the pressure, the less your fuel pump will flow. Our regulators are a 1:1 rising rate, so for every 1 psi of boost you see 1 psi extra fuel pressure. At only 15 psi you'll still be seeing 70-75 psi of fuel pressure on boost. In this range, depending on the pump, the flow really starts to drop off, which is defently something you don't want.

As for hacking the MAF, Im not an expert (Don't need to with 2g & DSMLink) but as far as I know the mod is reversable if you don't damage the honeycomb upon removal. Think most start with removing the bottom section & if this doesn't help enough, then remove the sides. Air chooses its path differently depending on the speed, so your corrections from removing honeycombs won't be linear across the settings.

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Luckily I havent had any problems with losing flow. The Walbro 255 flows rather well.

Ive allready removed the lower honeycomb years ago.

Im going to start to remove material now from the inside of the lower passageway like they did on the RRE websight write up. I'll take out a little then make a run and see how much it changed the airflow and go from there.

From researching I havent exactly found the data Im looking for but it looks like just from removing some material from the lower passageway people have been able to increase flow a bit. Hopefully I can hide enough flow up top and yet keep drivability down low. I would really like to not have to crank up the fuel pressure any higher than my 50psi that the base fuel consuption calculations designated.

I'll post my results as soon as I can free up some time to do all this as summer is a very busy time of year for me.

Thanks.

255 flow well, yes. 255 flow well at high pressures, not so much. Again is yours the 255 or 255HP, as this does make a difference at the higher fuel pressures you'll be seeing. The std 255's flow drops off much quicker, right around the area you'd be seeing. I can't find the chart I'm looking for but I found another one that will give you an idea of what I'm talking about, with flow vs pressure, it's abit down this page:

http://www.stealth316.com/2-fuelpumpguide.htm

Also have you atleast re wired the pump?

daren_p said:

255 flow well, yes. 255 flow well at high pressures, not so much. Again is yours the 255 or 255HP, as this does make a difference at the higher fuel pressures you'll be seeing. The std 255's flow drops off much quicker, right around the area you'd be seeing. I can't find the chart I'm looking for but I found another one that will give you an idea of what I'm talking about, with flow vs pressure, it's abit down this page:

http://www.stealth316.com/2-fuelpumpguide.htm

Also have you atleast re wired the pump?

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Hey daren, I think this may be the chart you are talking about: http://www.vfaq.com/pump-Walbros.html. Hope this helps.

Good information thank you. Luckily it doesnt look like Im at a lack of fuel even up top according to my logs and safc graph. I havent had to add a ton of fuel up top. Right now my curves skirt pretty close around 0% or so. Im just hitting fuel cut when the maf count gets too high.

I think I have the regular 255. No I havent rewired the pump yet.

zippyshoe said:

Hey daren, I think this may be the chart you are talking about: http://www.vfaq.com/pump-Walbros.html. Hope this helps.

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Thats exactly the chart I was looking for (why would I try & find the chart on the vfaq, only the first place you should look for this kind of info )


Now you can see how flow drops off as pressure goes up & how the reg 255 drops off much quicker then the 255HP. That 55-60 psi base pressure that you were talking about earlier puts you right in the bad area. Sounds like your fine now at 15 psi but with a non rewired pump & if you up the boost at all, I think you will start to run out of fuel pretty quickly. Defently get that pump rewired as pump flow is directly related to voltage & the voltage with the factory wire is much to low. If you want to compare pump flow vs voltage, RRE has a test listed on their site to give you an idea of the difference it makes.

daren_p said:

Thats exactly the chart I was looking for (why would I try & find the chart on the vfaq, only the first place you should look for this kind of info )


Now you can see how flow drops off as pressure goes up & how the reg 255 drops off much quicker then the 255HP. That 55-60 psi base pressure that you were talking about earlier puts you right in the bad area. Sounds like your fine now at 15 psi but with a non rewired pump & if you up the boost at all, I think you will start to run out of fuel pretty quickly. Defently get that pump rewired as pump flow is directly related to voltage & the voltage with the factory wire is much to low. If you want to compare pump flow vs voltage, RRE has a test listed on their site to give you an idea of the difference it makes.

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Cool thanks for the advice. I will try tuning the car without turning up the fuel pressure. Maybe I'll get a chance for a rewire this winter. Also if hacking the mass some doesnt work I think I'll install a second gen mass this winter as well. I'll be sure to update this as I go along.

Thanks.

I just received a very helpful pm from Pneumo I'll post it to help others researching this hacking subject.

Quote: "I hacked the maf a little at a time to see how it changed things. When I had my maf hacked like the RRE page the car still drove nice and didn't hit fuelcut. When I hacked it more I noticed the car would stumble at very light throttle. I also had to do some wierd things to the SAFC settings to partially compensate, but the light throttle stumble never completely went away, and the fuel trims kept moving up and down.

I'd recomend hacking the maf like the RRE page first, and if you need more airflow after that just go with a 2G maf, or EVO maf. "

Here's another comparison of a 255 vs. 255hp. Pics are from walbro:



You can really see the benefits of the hp at higher pressures. Also, you can see the benefits of the pump rewire.

Many have run the walbro at 14-15 volts w/ no issue and really eeked out significantly more flow.