Dyno numbers and MAF question

[fuzzyGN]

I spent some time on the dyno Friday and came away with a few questions. The combo is an 87 GN with a 206 roller cam, ported heads, RJC PP, 62 mm TB, stock MAF, 3" THDP, MSD 50's, stock turbo, dutt mod stock intercooler, pump gas. The weather was about mid 90's with a slight breeze. We were testing a new boost controller so the boost was only 13 psi for almost all of the runs but some were a little less. Looking at the HP graph, it was going up pretty steep until about 4400 - 4500 RPM then it sharply dropped about 25 HP. Weird. We looked at all of the runs and it was very repeatable. We then started logging MAF numbers and once the MAF pegged at 255 (logging Tlink data also) it looks like the MAF reset to zero, pegged again, reset to zero, and ended up at some number around 200. We also did some steady speed runs at about 4 grand and it would run fine for the first few seconds but then begin to surge several hundred RPM. We couldn't log the MAF numbers but pretty sure that was the cause. As a result the best HP number was 275 at 4450 RPM and about 310 ft/lb torque. Not too bad considering low boost and low RPM potential but still WAY below par. My questions are does a normally functioning MAF reset once it pegs? Is this MAF toast? Has anyone seen this type of thing before? Options? Thanks for any help.

 

[jastrckl]

Yes, normal mafs will do it on a modded car. No, your maf isn't toast. yes, it happens all the time. best option is a chip with a maf lock, that will peg the maf g/s at 255 while you stay WOT, or if you really wanna get serious a speed-density system of some sort that eliminates the maf

 

[ijames]

Or a translator (or translator plus) and lt1/ls1/zo6 maf.

 

[fuzzyGN]

Thanks for the input. So does a chip like a Thrasher have MAF lock? When I had the stock injectors and Thrasher the car seemed to pull much harder in the upper RPM even though it was extremely limited by fuel. If a translator is used the upper MAF limit is basically doubled correct? In that case the MAF lock in the chip would probably not be needed? Thanks

 

[Reggie West]

I am not an authority on the stock MAF sensor but with a stock turbo the MAF should not be maxed out, I would think.

Anyone care to correct me?

 

[jastrckl]

Originally posted by fuzzyGN
If a translator is used the upper MAF limit is basically doubled correct? In that case the MAF lock in the chip would probably not be needed? Thanks

Not quite. It takes both the translator and extender to double the maf range. If the chip is expecting 255 as the peak g/s, there's nothing any new maf will do for you in terms of doubling the resolution. I think the translator may have some sort of built in timout or something since I don't hear about dropouts with it as often. To get a 500+ g/s resolution though, takes the extender chip which is capable of reading g/s above 255 when used in conjunction with an aftermarket maf (the stock delco maf is only physically capable of a certain max frequency output which corresponds to that 255 g/s). The translator+ runs around $250 plus however much you spend on the maf. Something like an me-r is $600 and eliminates the maf, or there's a used accel DFI, etc. All of the above are user adjustable and have at least some timing control. The ME-R just has a set of timings in the typical setup though, street and race.

 

[ijames]

Dip switch 3 in a translator and translator plus is the limiter option. Turn it on and it limits the output to a frequency corresponding to 255 g/s and the ecm will never overflow and give a maf dropout - much simpler than doing it in code in the chip . Turn it off with and extender or extender extreme chip to read up to 512 or 768 g/s.