MAF and Throttle body sizing

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Sep 2, 2010 | 12:09 AM

shermy2296

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Joined: Feb 2006

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From: Southern NH

MAF and Throttle body sizing

I have a 54 F100 that I've rodded. I put a 91 Lincoln LSC 5.0 HO into it and converted to mass air. I put GT40P heads and Gt40 intake onto it from a 98 Explorer. I put an after market 65mm throttle body(to match the 65mm Explorer throttle body) and long tube headers. I'm using a A9P PCM from a 91 Mustang GT. I have driveability problems at cruise and light load. If I open the throttle , it comes to life with decent power. My question is, should the MAF be larger(or match) than the throttle body(I'm using a MAF from a stock 91 GT which had a 55mm throttle body)? The motor, heads, intake, and throttle body are roughly now equal to a 93 cobra except for the PCM and MAF. Any advice on this would be nice.
Thanks,
Mike
NH

Sep 2, 2010 | 02:47 PM

lew52

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Joined: Jan 2009

Posts: 4,558

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If your using a 65mm TB i would use a 75mm meter.....Lew

Sep 2, 2010 | 09:43 PM

BlueOvalRage

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Joined: Jun 2001

Posts: 2,571

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From: Oxford, Indiana

I agree. The ID of the MAF should be equal to or preferably larger than the ID of the throttle body. A MAF that is smaller than the throttle body will not, however, cause driveability problems. It will only reduce airflow and full throttle performance. What size fuel injectors are you running? If you try to run anything besides a 19 lb. injector with that ECM and MAF combo you will have problems. Another place to look is the throttle position sensor. If it's an older sensor and the signal is getting flakey, it can cause surging and rough running also. There are several other things that can cause your issue, but making sure you're running the proper injector size and that the TPS is working right are the best places to start.