Big cam vs MAF?

[EaglePerformance]

What is the general consensus as at what cam size, is it better to do with out the MAF?

[GMRACIN]

Different people will have different answers about this;but, I prefer to keep the maf unless you are pegging it.

[EaglePerformance]

The main problem is below about 2k, with a lot of overlap, the air reversion back and forth through the maf causes issues, plus closed loop becomes a problem, what with all the "fresh" air coming through during overlap, maybe if I could figure out a way to not have closed loop enable till after 2k. I suppose the more time spent working over the idle, the bigger the cam the could still be used with a maf.

[angrygoat]

I know on my old LT1, I was able to setup a PE idle. You could use the PE enable vs TPS table to set pe to 0% at idle cells. I'm sure you could use the PE HOT Enable table to do the same thing and then it should be a breeze. If I understand it correctly set you PE ratio to 1.000 in idle cells and adjust VE and MAF accordingly Never played with it a whole lot so I dont know how the transition would be. Warnging: Im a bit of a rookie so take this for what its worth

[Frost]

I know on my old LT1, I was able to setup a PE idle. You could use the PE enable vs TPS table to set pe to 0% at idle cells. I'm sure you could use the PE HOT Enable table to do the same thing and then it should be a breeze. If I understand it correctly set you PE ratio to 1.000 in idle cells and adjust VE and MAF accordingly Never played with it a whole lot so I dont know how the transition would be. Warnging: Im a bit of a rookie so take this for what its worth

the idea is solid but it just doesn't seem to work properly on 98-up F-bodies.

[Cantalope Kid]

Until it max's out X hertz in my opinion or becomes a tuning nightmare. Worth keeping as it adusts for alot of changes in air/temp. that you are not going to enjoy having to adjust at random times in SD mode...SD is over rated like HP/liter for ricers!

[WS6FirebirdTA00]

I keep the MAF as long as I can. I have not had any issues on big cam'd cars either.

[Blown]

So what the general consensus on how to tune low end AFR on huge overlaps. Vacuum helps but only to an extent, then it's a feel thing. I've been experiementing with the cylinder charge temperature bias and filter for throttle response, but the low end decell and idles are always problematic.
WS6, you have alot of knowledge here, whats your MO

[5_Liter_Eater]

I keep the MAF as long as I can. I have not had any issues on big cam'd cars either.

Ditto. I run MAF only (VE/SD disabled) now and even when I had a 238/242 .605/.610 on 112 cam prior to the blower.

[c.w.barber]

242/244 here and i love my MAF.

[golfinz]

Ditto. I run MAF only (VE/SD disabled) now and even when I had a 238/242 .605/.610 on 112 cam prior to the blower.

your not pegging your maf with the blower?

[WS6FirebirdTA00]

A lot of the low end tuning is feel at points on some radical setups. When you get into the big cams, you just know when you have it right. So hard to explain lol you can just hear it and feel it without even looking at the WB most of the time.

[5_Liter_Eater]

your not pegging your maf with the blower?

Not with the LS3 card style MAF sensor in a 4" tube (reduces the frequency) with the IFR cut down a little (reduces the perceived flow), no.

[golfinz]

O cool!

[Cantalope Kid]

O cool!

I was thinking the same thing. Heard it takes a monster to max out an LS3 MAF hertz.

[69lt1bird]

A good example of the LS7 MAF hz on my car was it would only go up to about 9500hz and the 85mm truck goes up to 11611. I had a harder time tuning the LS7 and I didn't feel any gain on 6.0L so I went back to the 85mm for now.

The broader range of frequencies helped me smooth out my tune in maf only mode.

[Eagle]

I recently saw for myself how you can change the perceived MAF airflow by artificially adjusting the IFR tables. Larger IFR values decrease the airflow where smaller IFR values increase it. Definitely a good tip if your flow #'s don't cover the full spectrum.

[5_Liter_Eater]

It's actually the opposite. IFR and MAF numbers have a direct correlation. Larger IFR numbers make you have to increase the MAF numbers and smaller IFR numbers mean smaller MAF numbers.

Take for instance you artificially increase your IFR by 25%. The PCM actually decreases the pulsewidth because it thinks there is more fuel being injected per millisecond. This smaller pulsewidth causes a lean condition which makes you have to artificially increase your MAF by the same 25% to tell the PCM there is more air coming in so it will leave the injectors open longer. There is never really a good reason to do this.

When you lower the IFR it thinks the injectors are smaller so it leaves them open longer which introduces a rich condition so you need to lower your MAF to make the PCM think there is less air coming in which commands a smaller pulsewidth.

[angrygoat]

Now this is why if you scale your MAF to keep under the limits, you have to scale your IFR, spark timing, and cylinder volume by the same % right?

[5_Liter_Eater]

Correct. Any airflow or airmass related table should be scaled. This adds some complexity for the auto guys.