Max airflow?

[90AWDTalon]

Does anyone know the max airflow that a 3" GM MAF can accurately read?

I've searched here and found nothing, I searched google and could only find info on the 3.5" MAF.

 

[90AWDTalon]

I just found a site that listed max airflow, 719cfm. http://dtcc.cz28.com/flow/index.htm

Nothing on max accurate reading yet.

 

[Kevin Jewer]

I ran a 3" MAF up to ~60 lbs/min where I thought it was starting to get flaky, but when I went to a 3.5" it remained the same up to the highest I saw, which was in the high 60s. Turned out to just be the crappy output from the MAFt. This doesn't really answer the question, but it provides some idea of what it is still good to, at least 60. There have to be people out there that have pushed it farther though.

 

[donmagicjuan]

Upwards of 60 lb/min, eh? I think it's time for someone to update his timeslips. . .

 

[Kevin Jewer]

I ran the time listed at 65 lbs/min, but it was a 1.8 60 foot (usually get low 1.60s) and toasted the motor somewhere in 4th thanks to the 255lp. There is a page on my site that details what happened. Once I got over ~55 lbs/min I couldn't keep the car together, mostly drivetrain. I gave up the car at that point since the season was about over (2 years ago), and have since gone 11.5 at 122 in the EVO on the stock turbo. Much easier. But enough about me...

 

[donmagicjuan]

Yikes, it hurts me to look at that. I found your limit approximations of the two 255s very helpful, though. The fact that you only ever saw 0.96-0.98V on your narrowband for all of that should be a real eye-opener for anyone out there tuning with just their front O2 sensor voltages!

 

[Kevin Jewer]

Yes, I was saying that for YEARS and no one wanted to listen to me Finally had some evidence to post. Unfortunately I learned an aweful lot about fuel system capacity after it was too late. That setup had soo much more in it, obviously. At least 50% of my posts are on that particular topic now, I would hate to see anyone lose a motor to something that's so preventable when you have the necessary information.

 

[90AWDTalon]

I asked this question on an autoX email list I belong to, I got a response from a guy who did some research on it and asked around. He said that a trusted source told him that

"Maximum allowable value for gm/sec is 512. But a 3" MAF will max out at about
low 400's. "

I also found on an LT1 forum that max flow was 400g/sec descreened. GM people seem to use g/sec instead of lb/min we use.

512g/sec = 67.89lb/min
400g/sec = 53.04lb/min

I'm currently stuck bouncing between 46lb/min - 47.5lb/min (347g/sec - 358g/sec), I still have the screen on, I found another site that on the ls1 maf at these airflow numbers removing the screen was worth 12g/sec. So it looks like I may be getting close to maxing it out, but I'm not there so it must be something else causing this. I get these same numbers at anything between 25psi and 30psi, or even turning the WOT dial on the MAFT up 10%, I haven't tried higher. Also, my actual AFR is right on the money with my target AFR up to 5500rpm. After 5500rpm I have to set my target AFR extreamly rich to keep my actual AFR were I want it. This is why I thought I was maxing the maf. I still have version 1.3, I ordered the newer version 2.? a few days ago maybe this will solve the issue?

 

[Kevin Jewer]

I really don't like any of the newer MAFts for use with DSMlink where the calibration is done in the maf comp table. The old ones work better IMO.

 

[90AWDTalon]

I really don't like any of the newer MAFts for use with DSMlink where the calibration is done in the maf comp table. The old ones work better IMO.

I'm not using DSMlink, just my own custom chips. I'm trying to do the compensation with the MAFT. I was hopeing maybe there was a change in the code on the newer MAFT chips. Also maybe the having the addition of the rpm tuning mode would help.

I don't know what else to do other than switch to megasquirt, I'd rather stick with my current setup if possible.

 

[Kevin Jewer]

In that case then yes, the newer versions should make it easier to dial it in.

 

[90AWDTalon]

I got the v2.02 chip installed, retuned the maf mode back to were I was with the v1.3 chip. Logged a run, it was the same as the ones I was getting with v1.3. I then switched it to RPM mode turned 6500rpm up 10%. Made another run and the log looked the same as all the others I've done. For some reason the MAFT wont send a higher airflow signal to the ECU, g/rev and injector pulse width the same both runs. I'm attaching the last two logs I made, one with 6500rpm at 0% and the second with run with 6500rpm at 10%.

http://home.comcast.net/~talonawd/whatthef.xls