I did exactly that, 265 thou, so more than a 1/4"...

 

 

Car sounds great. I would be curious to see if the 52mm TB and the ported MAF ends alone would push it to 400+ HP. Some say the MAF ends are pointless but I put a set on my L31 and gained a few average HP/TQ back when it was a stock engine with headers and a mild cam.

 

Lloyd's cams always sound so good!

 

I was going off memory. Honestly there is ZERO reason GM should have done that other than to purposely choke off the LT4s so they wouldn't be better than the LS1 coming out in the C5 the following year.

GM did the same stupid crap with the 5.7 Vortec in my 99 Tahoe. I compared the spark map from my 99 Tahoe to the one in my 97 Van. The Tahoe had as much as 8° of timing removed in places. Mostly in the high load/lower rpm and midrange. I put the timing map from the Van into the Tahoe. It actually ran like a L31 should after. The lip on the TB was also 2x the size on the Tahoe as it was on the Van. I removed the lip on it. Guess GM didn't want that weak new 99 5.3 Silverado feeling weak next to the old body 99 Tahoe sitting next to it on the lot.

 

Careful mentioning those around here, you'll get your PP smacked! Mine is ported which is pretty much the same thing, it's been that way for 19 years now and I still remember doing it way back when it was a near stock car and it definitely picked up power. Tuners hate them though... Oh well, mine is staying unless I upgrade to a larger meter altogether. I don't see why I can't put a more modern larger meter on the car but I haven't really heard it talked about much.

 

Horsepower sells buddy!

 

Mine is cut-down and ported enough it had to have a resistor soldered into it to get it back into the ball park to be able to properly tune it.

 

If I had bought the Tahoe new in 99 after having had the 97 Van, I would have taken it back to GM and told them to fix this POS! The Tahoe felt like it was towing a boat behind it all the time and the fuel mileage SUCKED. The big old heavy van had much better throttle response, alot more off-idle and midrange torque and just flat ran better. They both had the same trans and gears at the time too. Luckily did not take me too much exploration to find out what the problems were.

Normal L31 Vortec TB ​​​​


The TB that was on my 99 Tahoe L31.

 

I cut that stupid thing completely off of 4.3 in the ZR2 I used to have. Much better throttle response afterwards. Supposedly GM put it on there to soften the off idle hit and keep people from chirping tires at stop lights.

 

I had already removed it several years before on the van. Which is why I was shocked when I saw the one on the Tahoe was 2x as big, lol.

 

For what you have the 52 is plenty. I'm at 440rwhp and running the stock MAF. Leave it alone. Once you get heads then do the 58mm.

 

My Express van MAF has been like this for about 5 years. Runs flawlessly and was not at all hard to tune. Going from a 400 hp 350 running the Marine L31 crossram intake to a 500 hp 383 with a Marine MPI Dual plane, an intake elbow and 87mm DBW throttle body I barely even touched the MAF calibration. Had to make some pretty big VE table changes though. With the 01+ van airfilter housing, the round K&N filter, and 4" ducting with a 90* silicone 3.5 to 4" elbow into the 3.5" MAF it holds 98 KPA @ 6,200 rpm on a 100KPA BARO reading.

 

Cool. All i’m saying is there is no restriction with the stock MAF. Porting it will not increase HP.

 

I don't see how you are not seeing a restriction. At 350 hp I was seeing a restriction in the MAF that was noticeable in a datalog. After I changed my MAF for the one I ported my MAP increased by 3-5 kpa at 5,000+ RPM. The Vortec 5.7 MAF is the same 3.5" MAF found on a F/Y-car LT1 not the smaller 4.3 V6 and B-car MAF.

At 1.5 in/hg a 3.5" maf with the screen is 759 cfm. At 350 hp and 5,000+ rpm on a 350 I still datalogged a pressure drop of 1 in/hg. At 6,000 rpm that pressure drop had increased to 1.5 in/hg. The MAF was reading a peak of around 340 gms/sec before modification.

 

I might get motivated enough to do my own testing, but I'm lazy, so it's more likely id do both because, "what can it hurt besides my wallet"? Lol

 

I wish I knew the MAF frequency limit in the OBD2 LT4 PCM. Would be cool to be able to build a 4" intake and use a factory screened LS6 MAF. The 85mm MAF flows 895 cfm with the screen in place.

 

I thought I seen some company making an adapter to run LS style MAF on the older stuff? I want to say it was analog to digital no?

 

All it takes is a simple plug and play wiring adapter. Also tuning to be able to input the frequency vs airflow map. I just don't know where the frequency tops out on the LT1/LT4s PCM tables. This can limit how much the newer MAF can read.

 

And this is exactly what I wanted to do. If you figure it out lmk. We are talking about the newer plastic meters, correct? Kinda like the ones used on newer GM trucks. Best I can tell is it reads the MAF and IAT all in one piece vs the two separate sensors used on our cars. That's me speculating though.