hello im working on a turbo install and i was wondering if a 90mm granatelli will work as a blow through if not is there any things i should do to use it as drawthrough
That's a pretty big MAFS for blowthrough.. I had a 90MM SCT MAFS for my drawthrough setup, but changed to a 3" Pro-Tube setup for my blow through. I've heard great things about the Professional Mass Air Systems meters, but I haven't started my car with my new meter yet.
You can basically use any MAF in either draw through or blow through in a properly designed sytem with no ill effects or decreased range. But the kicker here is a "properly designed system". What this means is you have to maintain the integrity of laminar airflow though the MAF. If you take a 90mm (about 4") and neck it down to 3" tubing, you'll disrupt laminar airflow and never get a clean signal - the result will be horrid driveability that cannot be 'tuned around'.
In the case of a 90mm MAF, you'll need 4" tubing ahead of and behind the MAF for as long as you can fit it - our 95 Turbo car has 4" tubing and it was a bear to fit it all in a nice straight run. My turbo Lightning has the same thing. If you run reducers right off the MAF or near the MAF you risk having issues. I know someone will come on and say they do this with no problems, but in our experience of tuning hundreds of blow through cars, for 99% of them what I said is true.
My Lightning even had an issue with stright 4" connectors off the MAF, so we had a MAF 'saddle' machined to match a 90mm LMAF, then welded it right on a section of 4" pipe and put the electronics right in the pipe. The result is, for both our turbo vehicles, driveability like stock - and the Mustang is a 700 RWHP vehicle, the Lightning is 500+ RWHP.
Why didn't we just go with draw through and avoid all this? With a turbo, usually bigger turbos, the mass of the turbo wheel causes it to keep spinning for a bit when you lift the throttle, this spin-down created a MAF backwash that cannot be tuned around in most cases and causes stalls after you lift. The cure for this is to lengthen the inlet tube before the MAF - this adds more air volume which buffers the backwash - and in our cases, there just was not enough room. We chose option #2: go to a properly designed blow through setup.
We have tuned a few blow through cars with the Professional Mass Air blow through tubes (3") and they work really well - those of you who have read my previous posts know I was never a big fan of 'calibrated' MAFs because usually the calibration is not even close - but I found out the quality of the PMAS units we have used are really good and the numbers from the flowsheets are pretty accurate. I like them so much that we became a dealer for them.