Large capacity MAF

[Mike Litherous]

Hey chaps.

Warning : not commodore related.

Was just chasing a large hp capacity Bosch style maf.

I currently have a Porsche 803 maf rated at 1000 kg/h which I’m maxing out at 5v at around 5000 rpm at approx 75% throttle. I can get a Porsche turbo 809 maf but it will also max out before or close to the 7000rpm cutout. It will give me no headroom. It’s used in a blow through application and is in a 3.5” (approx 90mm) housing which I can’t enlarge easily.

I heard around the traps that there is a large capacity maf that can handle up to 1700bhp but I can’t find any info on it.

Application:
Bmw e34 540i (4.0ltr v8) with vortech supercharger running currently about 500bhp, with Siemens deka 60 lb/hr injectors, turbosmart adjistable fuel pressure reg and the OEM computer with boost friendly chip and a trusty old jaycar DFA fuel adjuster where I can adjust or correct the fuel signal at 128 load/voltage points along the maf. I’m running approx 8psi boost at redline.

Basically i tune the twilight zone aftern effective maf reading by fuel pressure so I have a nice 11.5:1 a/f ratio at 7000, and have full tuning ablity to around 5000 or below. After 5000 it goes pretty rich around the 10:1 mark then tapers down to the cutout at 11.5:1. It’s prob ok to live with like this but I’m leaving hp on the table and it will make the cat converters work harder than they need to.

Also in this setup i have plenty of headroom in the boost and fuel department but if i go more the tuning issue will be worse.

Can i simply add a resistor to the maf wire that feeds the computer giving me more range, but this way the maf will see voltages of maybe as high as 7v.


Sorry for long post but u need all the info to digest it I guess.

 

[Deuce]

I thought catalytic converters were for filtering by-products of lean ignition?
Or do you mean the carbon will block them up?
Sorry i can't help maf question.

 

[monstar]

Check this

See my MAF in this clip is similar to the Bosch 803. It is cartridge style used by GM (called LS7 MAF) outside AU:
View media item 440
I fabricated the housing (amongst other things) and scaled the frequency conversion. Pretty common in LS NA.

Yours is 5v so is not frequency conversion but voltage transfer function still same same in order to scale air flow.

I’d do the calcs and source or fabricate a housing with a larger cross section, swap the 803 cartridge MAF in and scale the 0-5v transfer function using the sensor calibration table in the tune.
Much safer, cheaper and easy.

 

[Mike Litherous]

Cheers for reply. Xsect of 89mm maf is housing is 0.00622m2

If went 100mm Xsect is 0.00785m2 or approx 26% larger.

Space is pretty tight which may cause direct radiator contact which is no good. Also then I would need a transition reducer in the pipe prior to the maf.

On the jaycar DFA u can run a voltage offset so the computer sees less voltage than it makes.

On a side note finally had a boost gauge installed today and we have 10psi at 7000rpm. Thought with the pulley change it would make 7-8psi. No wonder it’s starting to go very hard