Thread: Q45 MAF, good for 700 HP?

Area of 2.75" ID pipe= 5.94 inches squared
Area of 3.5" ID pipe= 9.62 inches squared

Difference is 3.98 square inches

3.98/5.94 = 67% larger area

Say the 2.75" maf was good to 350whp

350 X .67 = 234

So the mafs hp capability is increased 234whp bringing the total to 584whp

always done it that way and have never had a problem...

My calcs are the same used by many others. A big one in this is the GTR guys. The stock mafs max out at around 530awhp, they go to 3" intake pipes and their mafs are now good to roughly 650awhp with the change.

I understand what you're saying and it's probably the way it's supposed to be done, I guess I just always use the fuel map to fix it. I will be doing it right from now on though

This thread should really be put into a how to or into the Manifesto.....Not a lot of people know that changing a mafs housing size can increase the hp read capability of it. Good information in this thread.
@Shawn B

well for me changing from one maf to another = one click. I suspect this is slightly different.

Does the vq curve stay the same? Multiply all values by the change in area? Wont your idle read lower, potentially hitting the low voltage trigger and going into maf unplugged mode?

I doubt it, id imagine the vq curve would change. Again the modification would need tuning. And yeah as for you guys running safc's and stuff like that, It might be able to somewhat correct for the change in pipe size by messing with hotwire settings but your going to have to tune the fuel side of things as well, guaranteed.

Your calculation is off. Here's an easier way.


5.94/3.98 = 1.49%

350hp X 1.49 = 522hp for 3.5" maf



The 2.75" maf is 67% of the 3.5", or 33% smaller than the 3.5".

Its not off, the same calculation is used when determining the difference in injector size and how much fuel you should be taking away for those that use an SAFCII or want to use math to calculate fuel changes in the VQ tables.

say your ecu is tuned for 370cc injectors and you put in 550cc injectors. Thats a difference of 180cc.

You would take 180/370 = .49/ converted to % by multiplying by 100 = 49%. The 550cc injectors is a 49% larger injector than the 370cc. In other words you would have to take out 49% fuel to get the same a/f ratio you had before. Same goes with calculating maf housing size.

Wow, you suck at math, lol.

It's a real simple calculation. You are making it more complicated than it is.

Take 370cc/ 550cc = .67

Now take .67 x current k value = new K value

That's it.