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Old 08-25-2004, 08:45 AM   #1
fastlane
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Question When do you need a bigger MAF?

Here is my situation. I just picked up a Garret GT30 turbo and I am planning on installing it very soon. I am concerned that I might need a bigger MAF however. Right now, I am pulling about 3.9v when on boost with my VF39. What is the max voltage the MAF produces and how much correction can I add with the UTEC?

On a side note, I am currently using PE600 injectors and I am planning on swapping in my modded stockers. Can anyone tell me what to set the injector mapping at in OLF?

Thanks!
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Old 08-25-2004, 09:10 AM   #2
big_adventure
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On a WRX engine, you will not NEED a bigger MAF. That said, what model GT30R is the cartridge?

Anyway, the MAF sensor goes to 5.0v, which is a boatload of air. I run a GT30R with an RA Spec-C engine, and I only see 4.9v's on race-gas at 26psi+.

At what engine speed and in what gear are you stuck at 3.9v on that vf39? That's miserable for that turbo - you should see 4.4-4.5v on pump, easily. When I had a vf34 and an FMIC, I saw consistent 4.6v.

-Sean

Last edited by big_adventure; 08-25-2004 at 10:45 AM.
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Old 08-25-2004, 09:44 AM   #3
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it's a -10. 44lb turbo.

For injectors...you can start at 740 and see how rich you will be (with 0's everywhere). I've started them at 800 and it was still very rich on the vf22. Just make sure your fuel trims are semi close.

BTW i'll have a bigmaf with that perrin inlet pipe I'll let you know
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Old 08-25-2004, 10:47 AM   #4
big_adventure
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Thanks Louis -

fastlane - there is no way you NEED a BigMAF with that turbo. Use the stock MAF diameter and tune easier with it.

-Sean
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Old 08-25-2004, 10:51 AM   #5
fastlane
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Thanks for the replies folks. I don't have a log in front of me to reference but IIRC I am seeing the 3.9-4.0v in 5th from 3700-5700.

Hey Louis....definetly keep me in the loop about the inlet as I might not need to bigmaf like I was thinking.
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Old 08-25-2004, 11:02 AM   #6
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You'll see higher maf's at higher rpm's. the engine is pulling in more air. that's your problem. Check the maf at full boost and 7k rpm's.
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Old 08-25-2004, 11:13 AM   #7
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Quote:
Originally Posted by Zackbo
You'll see higher maf's at higher rpm's. the engine is pulling in more air. that's your problem. Check the maf at full boost and 7k rpm's.
That is not ALL ways the case. Some setups will pull more air at alower rpm. Depends alot on the turbo. I run ~4.6-4.7v in the high midrange but because the turbo is so small I only get ~4.4 at redline.

TMS
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Old 08-25-2004, 02:17 PM   #8
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4.8v for me up high on pump, 4.9v on race, both from ~6K up to >8K. It's amazing what a big turbo and big intercooler can do for you.

-Sean
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Old 08-25-2004, 02:20 PM   #9
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Yeah my boost curve looks like ^


TMS
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Old 08-25-2004, 02:22 PM   #10
big_adventure
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On the bright side, you're probably at max boost while I'm stuck below a bar. Except in 6th, my car won't go past 20psi (just getting started for my turbo) until past 4K. Of course, I can run 23.5-24psi on my 93 octane daily-driver map...

The tradeoffs, the tradeoffs.

-Sean
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Old 08-26-2004, 01:44 AM   #11
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the maximum MAF voltage will occur at peak power, therefore not necessarily at redline

Robert
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Old 08-26-2004, 07:46 AM   #12
fastlane
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Could my low maf voltage possibly be from a crack or tear in the stock inlet pipe letting in unmetered air? As it stands, my car seems to run quite well but not as well as I would think it should. I was able to hit 106 mph at the track but that was with a mix of 104 and running about 20 psi. Unfortunately, I wasn't able to get a datalog of the run to see what the MAF voltage was hitting.....
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Old 08-26-2004, 09:02 AM   #13
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Your issue is most likely revs. Take a log and post it...

-Sean
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Old 08-26-2004, 09:31 AM   #14
fastlane
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Will do.
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Old 08-26-2004, 09:48 AM   #15
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Quote:
Originally Posted by big_adventure
On a WRX engine, you will not NEED a bigger MAF. That said, what model GT30R is the cartridge?

Anyway, the MAF sensor goes to 5.0v, which is a boatload of air. I run a GT30R with an RA Spec-C engine, and I only see 4.9v's on race-gas at 26psi+.

At what engine speed and in what gear are you stuck at 3.9v on that vf39? That's miserable for that turbo - you should see 4.4-4.5v on pump, easily. When I had a vf34 and an FMIC, I saw consistent 4.6v.

-Sean


I don't think maf voltage is consistent amongst cars. I have a dyno proven 364whp at 26psi. I was only pulling 4.6v. Overdose has a 13G and pulls 4.3v.
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Old 08-27-2004, 11:17 AM   #16
fastlane
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After checking some logs last night, I am pulling 4.3 - 4.4 volts but it is up in the 6000-6200 rpm range at 17 psi. So I guess I was looking at the wrong place in the logs.
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Old 08-27-2004, 07:21 PM   #17
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Quote:
Originally Posted by bryan carbon
I don't think maf voltage is consistent amongst cars. I have a dyno proven 364whp at 26psi. I was only pulling 4.6v. Overdose has a 13G and pulls 4.3v.
True.. it certainly does vary from car to car. Its an indication of airflow over the sensor itself. If you keep that in mind you are ok.. Inlet pipes, Intakes, elbow pipes, air filters and your air densite and temp all have a pretty drastic effect on those readings.

The other thing to keep in mind is that the ECU cannot read up to 5 volts. The ECu itself will only read to high 200's in Grams... Past that your ECU is ignoring the extra input. From memory thats around 38lbs of air flow.. Any turbo past the 1820 or so will have the ability to max the ECU.. If I flash an ECU I can extend the load columns a bit to gain control back but its limited by RPM. Also note that the higher the RPM, The lower the limit of MAF flow the ECU can read..

The deal... Anything past 38lbs in flow and you need a larger MAF tube to lower the reading across the sensor. This will stop you from pegging the ECu so MAF trickery fueling can work or the ECU can be flashed for the larger pipe to drop the load readings down. In short. Most of us "need" a larger pipe but we get away with it so we dont "need" the larger pipe.... I bet mine is pegged by 5k..



C
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Old 08-27-2004, 08:07 PM   #18
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Clark what you are saying is that people that have reflashes might want to run a larger diameter MAF tube since you have a limited airflow scale to play with. But, people with OLF and a UTEC can in fact almost max out the stock airflow meter with a smaller dia. piping without worry??

Richard
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