Vortec MAF sensor upgrade?

[TerryD]

I'm not sure if this needs to go here or in the IFS/NSM forum, but it is fuel injection related.

I've been looking at some bolt on upgrades for the old K2500 and I've seen the Granatelli MAF sensors that have the flow straightener behind the sensing element removed and I was wondering if anyone has ever seen a downside to this for a DD vehicle. I'm also looking at the Volant air intake for it which would, in my mind, help eliminate the need to straighten the air flow as it is a straight shot from the fender to the TB hat. I think they advertise like 35% more air flow capability and if I swap over to a 7.4L TB on my 5.7L, I would think that the MAF would be the next air tract bottle neck. I'm wondering if it is even remotely worth the $300 though or if I could split my factory one, descreen the front half (after the Volant is installed when it's function is negated) and grind out the flow straightener with a die grinder.

 

[dyeager535]

Have you done the flow numbers for the intake side of the 5.7 and 7.4L? (I'm assuming this is the Vortec 5.7L?)

I was actually just playing around with the exhaust side of flow calculations, input CFM requirements are easily calculated via various googled pages.

If you are realistic about the max RPM your motor will see, then intake flow requirements will be easy.

Now, calculations on tubing ID, bends, etc are going to be more difficult, but calculating requirement based on displacement VE and RPM is going to at least give you a starting point.

I know very little about the Vortec stuff, I can only assume that any airflow changes need addressed through programming though. Again only having experience on OBD1 MAF stuff, airflow numbers for the MAF need adjusted as you remove restriction/increase flow. The systems can somewhat adjust, but only to a point.

IMO, and while others may or may not agree, on a street or other low-rpm usage vehicle, all the intake mods in the world aren't going to net a difference worth the expense and effort. Obviously some setups perform much better with a few modifications, but I'd be real surprised if GM didn't have the Vortec stuff nailed down on those motors to about as close as you can get without some serious work. Look at the power change from the last years of TBI, and the Vortecs. Realistically, for all the "improvements" the Vortecs have over earlier (roller cam, higher compression I think, CPI, vastly better heads, etc.) I don't think the power number differences show that there is serious power to be made by some relatively minor mods on the intake side. Oft-quoted spec for Vortec heads, back to back on the same motor, is 40HP...point for me is, if a roller cam, high compression, and CPI is only worth a few extra HP, how much can possibly be extracted on less complex modifications?

Headers are still worth somewhere around 25HP on a small block, my belief is you'd be very hard pressed no matter how much money you spent, to get that much power solely from intake side modifications, with anywhere near comparable time and expense.

Not trying to sell you on headers, but with the cost and work necessary to do intake modifications, and the likely miniscule gains, is it worth it to make any changes at all?

 

[TerryD]

I agree that it won't be an earth stopping gain or anything and I'm already sold on headers (check jba's dyno numbers on a 99 C2500 5.7L).

I was curious if the upgraded MAF housing made any real difference in performance for NA street engines. One thing I could see though, is that with 4.10's and 32's my 70mph rpm is up there a bit. It's one reason I'm liking at the Volant air intake system. Eliminating that >90° elbow out of the factory air box would be a good thing in this instance I would think. I was wondering with doing that, would it benefit from an opened up MAF at the same time.

 

[dyeager535]

What's the current diameter? Really need to know what the intake ducting will flow, and what the throttle body will flow.

This should be obvious, but if not, if the throttle body flows 600CFM but everything before it flows 700CFM, you are limited to 600CFM.

Making some very rough guesstimations for flow based on the exhaust side using this http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/ where exhaust needs to flow twice as much as intake (at port) it appears that ~3" intake ducting would flow enough to support the 1 5/8" primaries on the headers.

This is where the physics starts to go over my head, with diameter of the air ducting, and the bends in it, you should really be able to calculate the flow potential of the air ducting. But first things first, at whatever you determine to be your highest RPM, need to make sure the TB will flow enough.

I would expect that right around 4600RPM your TB runs out of flow. I can't think of one reason GM would undersize the inlet, or restrict it, other than some sound reducing that might cut flow down a bit.

 

[TerryD]

Those are good points and I'll have to research how to calculate those bends. They are not round, so I'll have to do it based on volume I would think. The >90* elbow has a squareish cross section so I'm sure that is to improve it the flow.

I can go up to a 7.4L throttle body which has a larger bore than the 5.0L/5.7L one if I need more there and may do it anyways if I can find one cheap but that will be after getting the less restrictive intake/headers. My head pipes are massive compared to the 1/2ton stuff on our Suburban. I did oil changes on both of them the same day and noticed how puny the ones on the Suburban looked compared to my k2500. I'm sure this has to do with the fact my truck should see higher RPM when towing (designed to run in 3rd at highway speeds?)

Thanks for the input guys, I'll start looking into these things and see what I can figure out.

 

[K85 Octane]

I've seen a lot of guys cut the factory screen out of the MAF sensors and swear up and down the block it made a difference. I've never seen proof of it, no lower 1/8th or 1/4 mile, no dyno runs, no anything. Makes me think it's just in peoples head.

I've seen the Granatelli sensors and thought about one for my s10, but decided no thanks. Sure seemed like the straighter would be a good thing and if the MAF really did out perform the stocker, it might be that it has quicker reaction times or more precise metering. All in all though, the only time you are going to feel more power is at WOT and at that point the engine has it's table to follow and doesn't need a faster reacting MAF. Plus, there are so many other sensors to read to get fuel delivery down spot on that I can't see a PRE-engine sensor making much difference.

 

[TerryD]

Well, I got some pretty hard to deny proof that the screen is needed, at least in an installation where there is a sharp bend before the MAF sensor (meter?)

I was called out night before last at work to look at the FGR air flow meter on our new power boiler (bark burning 1500# boiler and 80MW turbine set). During trouble shooting, the engineering print of the sensing element install was brought up. Turns out there is a honey comb screen in front of the element that is just a 5' diameter version of the one in front of the MAF sensor in my truck.

This is in a pipe that makes a 90* bend to the horizontal about 12-15' before the element is in the line. It is referred to as a a "flow straightener" on the print. So, descreening the MAF in the factory installation or any CAI where there is a sharp bend before the meter is a bad idea.

I had considered that, coming out of that sharp bend, could cause turbulence in the tubing and not evenly distribute the flow across the element causing a false high/low in the reading depending on where the fast moving air stream passed though the MAF sensor. The screen should, in my mind at least, create a slight resistance to the flow and cause a high pressure on the filter side of the MAF sensor. This would aid in distributing the air evenly through the meter. While it would restrict flow very slightly, it would also improve the accuracy of the sensor and provide more even/accurate fuel metering to the engine. This could also very well be the reason for the air splitter cast into the rear of the MAF sensor housing.

Now in something like the Volant CAI where there is no sharp bend between the meter and sensor, I would personally see less of a need for the screen and splitter to be in the air stream and could see them being removed with no ill effects.