Yes. It is inline after a walbro 255. I saw a flow sheet somewhere that shows the Bosch holding flow to 90psi.

 

We're going to run the 3.5" Primo MAF tube for tonight's tuning session, so I'm sending 3dman1 a base MAF calibration to install before he picks me up. Apparently the stock MAF tube is around 2.5" diameter, so if I take the ratio of the cross sectional areas as the multiplier for the MAF rescaling, then it looks like its possible to measure 1.8x the airflow. lol. Seems a bit overkill. Might have to see about running a 3" MAF tube. That would allow measuring ~33% more airflow which is more reasonable.

 

I know of some maxing out the 3" MAF housings on the FPred on a 2.0L, so you should probably just go right to the primo imo.

It idles and drives find if you are worried about that, mine works great.

 

Good to know. Do you know the peak MAF voltage you're hitting?

 

Yep. The most I have seen so far is 4.73V at 8700rpms.

So I would say you should just skip to the 3.5" one

 

I run a 3" AEM intake and I hit 4.75v at 7500rpm, 24psi.

BBX Lite

On a 08 GSR with a BBX (non-lite), built motor, 3" AEM intake. 4.99v at 7500rpm, 30psi

 

1)- pi x (1.75^2) = 9.6211275
2)- pi x (1.25^2) = 4.90873852
------
#1/#2=1.96

3" is 1.44

Just an FYI, I think the AMS Pipe is 3" and AP only scales up the MAF scaling 10-11% if I remember correctly (but I could be totally off here)... so don't go too high!

 

Yeah, I am assuming that the stock tube is 65 mm, which is a bit closer to 2.6". I recall razorlab also mentioning 12-13% for the 3" MAF tube, so yeah, I'll likely have to tone it down quite a bit. 12-13% is roughly 1/3 of the 33-44% for the 3" tube, so perhaps 81%/3 = 27% is appropriate for the 3.5" MAF tube.

 

I ended using a correction factor of 1.5x to bring cruise and WOT AFRs into line. Nice looking intake. 550 whp DJ was producing about 4.7 volts.

 

Multiplying the MAF scalings by a value is not the correct way to scale a MAF. A linear increase to a parabolic curve is not the right solution. You have to do lots of logging of your Fuel Trims and MAF Volts. There are spread sheets out there that help with this.

I usually change the spread sheets slightly to make sure that when STFT = 0 it does not affect the caculations, because that means trims are not being used.

 

I agree on using those spreadsheets, but you have to start somewhere. I'm no math wiz, but I believe a multiplicative adjustment would be logarithmic (where additive would be linear).

 

Multiplication seems like a good starting point to me. A hotwire MAF is just a wire running across the MAF tube opening, so for a given voltage required to maintain the wire temperature, then to first degree the air flow rate past the wire is going to be proportional to the cross sectional area of the tube. Take a ratio of the new and old cross sectional area to get a multiplication factor. Its working out pretty good so far. After settling on a 1.5x multiplication factor, WOT AFRs with the Primo exactly matched what we were getting last week with the stock MAF tube. 1.5x is not far from my estimated correction of 1.8x, and I never got a chance to verify the ID of the stock MAF tube or the Primo.

With that said, I fully expect that there are some second order effects due to the position of the hotwire in the tube and due to wall drag. The cruise trim is not quite where it was at with the stock MAF tube. (I don't take any stock in the idle trim with 1680 cc/min injectors and the current limitations of the AP.) I will likely do some more tweaking of the lower voltage part of the curve after we get done making power.

 

Cooling based off wind speed is a logarithmic equation.

 

Actually cooling/heating equations are differential equations....I don't want to relive that class though.

 

Perhaps you're misunderstanding what I did. I didn't change the underlying form of the MAF scaling table. I simply multiplied all the values by 1.5. The exponential form of the scaling remains.