Ha ha. I did the same math and came up with similar conclusions. The 5.3 L replaced my 4.0 L, so the difference in my application is that the LS is about 1/3 bigger, and should pump 1/3 more air….provided all else is equal, which is a huge MAYBE!
I believe the 2003-2004 Disco has the same MAF sensor as the 2001 Disco, but the 2003-2004 MAF sensor is mounted in a slightly larger tube. This larger tube is, presumably, to account for the larger volume of air the 4.6 L pumps when compared to the 4.0 L. If the increased area of the larger tube is proportional to the increased size of the engine then the net result may be the MAF sees the same volume/velocity of air. Hmmmmm!
So an increase in area of the tube that the MAF is mounted in would need to be proportional to the increase in the volumetric size of the LS 5.3 engine. My calculations show me I need a 3 inch MAF tube, which is a quarter inch bigger than the stock 2001 Rover MAF tube to get an accurate MAF reading that the Rover PCM can use properly. However, a 3 inch MAF still presents a sizable restriction in the air intake system…..better, but not great.
And, super importantly, I don’t know if my any of my assumptions are even close to accurate. Mostly wild *** guesses.
What we need is a MAF that can be mounted in a large intake tube, but with the ability to adjust the output of the MAF electronically…..or translate the GM MAF signal into something the Rover PCM can work with. Sorry….fantasizing a little here.
I agree with Captain Aaron that the stock air box is a big air restriction. My unscientific experiments point to the filter media versus the air openings, which I calculated to be bigger than the MAF, in terms of area. I ordered an in-line air filter, as suggested by the Captain and already used by Boostle in his truck, to bypass the factory air box. I’ll provide comment after it is installed and tested. I think I’ll also try installing a vacuum gauge in the air intake system to measure the impact of various components….more restriction should result in higher vacuum readings, so swapping out various components should help me pin down the most efficient system.
I’m 100% certain I’m over thinking this, but I love a good puzzle.

 

I'm waiting for parts for my LM7 5.3 right now. And after a week more of traveling in between, I get to throw my .020" over, BTR "torque cam" in and get it back together with all new innards. My plan on air intake is now to add a snorkel, modify the airbox for a cone filter inside it and no baffles, adapt the Rover MAF to a 3" section of tube (as a salute to middle school math- Thank you Mrs. Cutton) and get a little tuning done.

 

I read over a bunch of stuff on this again and did some math. I think I may have found a relatively straightforward way that the MAF cartridge could be inserted into a larger tube (in theory, 4 inches), and provide the ECU with accurate data. However, it might take crowdsourcing some data gathering / experimenting to make it work. I'll follow up after I do some preliminary tests over the weekend.

 

So it occurs to me as I am rreading the discussion the problem might be easily solved with a little trial and error testing. Measuring the maf reading with a data logger for some representative conditions (WOT, 3/4, 1/2, 1/4 - across full rpm ranges) and then plugging the maf sensor in to a larger LS sized tube and comparing the readings. Honestly probably the only on that matters is WOT as every other opening will be proportional. Although a proportional sized tube sounds logical, we might find that the stock sized LS inlet tube is close to appropriate. Assuming LR did their job on the tube sizing so that at WOT there was little to no restriction, the same is likely true with the stock LS sized tube. There was an Australian company selling an aftermarket THOR intake manifold front half because they said it was an intake flow restriction for the 4.6, that restriction was downstream of the MAF so MAF tube itself may not have had a significant restriction. The other thing that could be done with an external input would be to measure the MAP at the MAF sensor on the stock engine and the LS tube - size the tube to have similar MAP at similar rpm. My Camaro MAP at WOT is very close to 100kpa, never measured the Rover but I bet it is similar. LR did a pretty good job of getting max power and torque out of that 4.6. If you look at the torque figures they are higher than 4.8L LS torque figures at significantly lower rpm (cam profile).

 

This is exciting. As an aside, what is the output to the rover ecu? 0-5 volts? How about the LS? Haven’t looked at wiring yet but maybe a second LS sensor wired into the Rover circuit ?

 

Is anyone using the HP22 TCM on the HP24 with an LS and oversized tires and no Rover MAF?

 

Why use both MAFs? Swapping in a bigger motor, just to neck down the intake seems counterintuitive. MAFs are made application specific, meaning each is designed for a specific intake size and location within the intake piping. But they all read the same thing. The LR ecu and the LS ecu both need a signal. One MAF, two outputs.

 

yes this would be ideal if possible

 

I decided to run some experiments after doing some math regarding mass air flow. Here is my particular case:
99-02 MAF internal diameter: 2.75in
LS intake tubing internal diameter: 3.62in (guess the advertised 4in was external)

Therefore, air in the LS tubing would be moving at roughly 57.8% of what it would be moving the Rover tubing. To correct for the deficiency in flow, I calculated a multiplier of 1.73x.

I cut a hole in the LS tubing, pulled my MAF out of the housing, and put the cartridge in the larger tubing for a test. I cut the MAF signal wire and added a small amplifier to modify the MAF signal before it reached the ECU with the desired multiplier.

And… that is when I figured out that my MAF was dead. So, it appears have been testing out the no MAF theory for a while now. I don’t know how long it has been like that, but it appears it still will work okay without it.

I pulled the another MAF out of my 2003 Disco (internal diameter of that housing is just over 3in). After establishing that this MAF actually worked, I fiddled around with the amplifier readings compared to the readings from the LS MAF. At idle it appears to be slightly high, but that may be a result of not having a screen to help with laminar flow. I need to build a better setup before I test further (and get another MAF). Also, I figure that having readings a tad high might be better, because it may lead to the transmission using additional shift pressure.

I don’t know if this will end up being usable, but I will keep playing around with it and see how it goes.

 

Excellent info all around!
I had a good conversation with a Compushift distributor and transmission specialist last evening. He seemed to know the owner of HMG, the maker of Compushift controllers, personally. The impression I got was that the supply of Compushift controllers has been hampered by international chip production and the Covid debacle. The problem may be remedied soon. Fingers crossed.
He shared some opinions on our MAF quandary. First, because our LS engines flow more air for the same RPM as the Rover engines, the Rover MAF most likely is putting out an incorrectly elevated signal to the Rover PCM, causing higher transmission line pressures. Second, he pointed out that higher line pressure may prevent slippage of the clutches and firmer shifts, but at the expense of more wear on the pump, and greater heat production, potentially shortening the life of the pump. Third, he said most transmission manufacturers recognize components, such as MAF sensors, can fail. So default programs are built into the transmission controllers so that if a minor sensor failure occurs, then the vehicle can still operate, albeit less efficiently. He used the failure of O2 sensors to make his point. A failed O2 sensor causes an engine to run rich, which is a default mode. The situation with a failed or absent MAF is similar, with default line pressures being higher than normal to allow for continued shifting, even if more harshly than with a correctly functioning MAF. Fourth, he pointed out that a dirty MAF may put out an unacceptably low reading, causing reduced line pressure and clutch slippage, and potential transmission failure. It was his opinion that an incorrectly low MAF signal was a worse condition to operate in than a “no MAF signal at all” situation because of default programming in that condition.
Key take away messages for me were that if we run the stock Rover MAF we will likely have greater line pressure because of our larger engines, have firmer shifts, and generate more transmission heat. If we don’t run the stock Rover MAF, the Rover trans controller will DEFAULT to higher line pressures resulting in firmer shifts, and generate more heat. So, “damned if you do…damned if you don’t.” His best advice was to make sure our trannies run as cool as possible to extend pump life, and install a temp gauge to monitor it. My overall impression was that he was not particularly concerned about not running the Rover MAF, but did seem concerned about choking the LS engine by having the Rover MAF cause a restriction in the intake. He was very comical about it.
He did conclude his comments by adding that the Compushift transmission controller is top notch if you can get your hands on one, and it doesn’t need a MAF signal at all.
Captain Aaron….good luck with the MAF signal amplifier. Very intriguing idea. What will you call it?