[Philip]

What are the pros and cons of each? At a recent car show I noticed all the other TPI motors did not have a mass air flow sensor like mine does. It cleans up the looks, but can it run as well with out one and how will it affect mpg"s?

 

[72chevelleTPI]

What are the pros and cons of each? At a recent car show I noticed all the other TPI motors did not have a mass air flow sensor like mine does. It cleans up the looks, but can it run as well with out one and how will it affect mpg"s?

They are both good systems. The MPG's are about the same. 85-89 models had the MAF, 1990 and up used a MAP sensor instead. The MAF system is 10% forgiving on modifications such as aftermarket cams. With bigger cams you lose some manifold vacuum which is critical on the MAP setup. The loss of vacuum doesn't affect MAF setups as much.

 

[Tom Mobley]

What Stephen said. The MAF systems tend to not be very tunable or forgiving of rough idle cams. If you've got a stock or near stock engine that stuff doesn't matter much. Are there performance issues with the MAF system?

 

[The_Punisher_454]

Many people with TPI smallblocks convert to speed density running the $8D code, which was the most performance oriented code of that era's computers.
MAF has its strengths and weaknesses, and so does SD. And sometimes these strengths and weaknesses go back and forth between the two. Later PCM's handle MAF with bigger cams better than the older computers did. Overall though most people go SD. Also be aware that some later MAF setups like the LSx engines are capable of using both MAF and SD, and many people are running these engines on a alpha-n scheme at idle (RPM vs. TPS) with the more radical cams.

 

[RB69SS396Conv]

Theoretically, MAF is better, because it actually measures the mass of the air the engine is taking in, which allows it to meter the right amount of fuel. S/D merely tries to "infer" how much air there is, based on vacuum (MAP), throttle position, and so on. So a MAF system is inherently more likely to be accurate, and more likely to be able to handle changes in engine displacement, air density, ambient temp, and so on, since it directly measures the actual "number" of air molecules. That's why most newer FI systems use one.

OTOH, the implementation of the MAF in the TPI cars, was weak at best. The MAF only has 8-bit resolution. That is, it only has 2 to the 8th power, or 256, possible discrete values of flow that it can report; and since it was set up in the software so that those are steps of 1 gram per sec, that means it can only accurately meter from 0 to 255 g/sec, which is something like 375 CFM of air. So this limitation isn't a factor of MAFs in general, but rather the crude implementation of it in the early TPI, that was the best that could be done with the limited computing power available at the time.

Another more universal issue with MAFs is that the sensing element itself is usually very small, and its location in the intake tract is therefore critical; so, for example, a Frod one is about ½" in diameter, located in a 3" tube or whatever, near the wall of the tube off to one side and right behind an elbow, such that turning the tube one way or another will position it in or out of the actual air flow. I've seen those cars where they REFUSED to idle or otherwise run right, and merely rotating the MAF element 180° or whatever, dramatically altered how they acted.

And of course, there's the simple size (diameter) of the TPI MAF itself; it's big enough for a stock 305 intake tract, but once the intake flow is improved and/or the engine's CID is larger, it becomes a restriction. It's already a restriction to a 350 in stock form, let alone a modded one.

For these reasons and others, the TPI MAF setup is not as popular as the later S/D version.

 

[ZZ69chevelle]

A MAP sensor is a lot cheaper to replace than a MAF sensor too. No MAF burn off relay and related wiring needed either, or in the case of 85, seperate module on the ECM.

 

[The_Punisher_454]

You may notice that on moany MAF systems they place the MAF quite a ways upstream from the throttlebody. If you must use a MAF and have a large cam You'll want as much isolation from intake pulsing as possible. Any reversion will be measured as positive flow. And any leaks downstream of the MAF will throw the mixture WAY off, more so than vacuum leaks on an SD system.
That all being said, some MAF systems work really well. On the thirdgen.org boards there is a guy using a '427 computer (mid 90's pickups) with MAF on a TBI. Its custom code of course, but it works really well. Do a search on that board for "$0D MAF TBI" and you should find the thread.

 

[stealth71]

One nice thing about the MAF is dry nitrous tuning is pretty simple and safe.

 

[Philip]

Thanks for the input. My MAF is quite far from the throttle body and I beleive the 350 motor is stock. It runs well and gets 18 - 22 mpg so I think I will just leave it alone.

 

[RB69SS396Conv]

Since you've got it there and all working and it's doing what you want, and it's NOT a trivial matter to change it (ECM & harness), then there's not alot of sense in changing it over. The "theoretical" differences are outweighed by "practical" considerations.