What are the pro's con's of running the MAF pre-turbo (vs. on the pressurized side)?

 

that would suck..pun intended.
I'm guessing the air density would change between pre/post turbo, in turn possibly causing a lean condition.

 

BOV would have to be plumbed back around to feed between the maf and the turbo.

 

get a three bar. lose the maf.

 

three bar sounds good BUT, can a 98 be tuned for a 3 bar MAP?

I didn't think of the BOV thing.... Will it make a big difference since it really only opens when I'm not on the gas, I mean so what if it goes a little rich when I get off it, what can happen? Do you think it will screw up my AFR during shifts enough to notice it???

 

Upstream MAF does cause some inlet restriction and will to some extent reduce peak boost (supercharger). But it may help with lower RPM response.

Some say tuning can be a little trickier with upstream (draw through) MAF. Using newer 85mm MAF will also help.

 

Stick with the Push through design..

With your Turbo spooling up quickly the MAF will read the air instantly, but that metered air has not made it to the motor as yet, still going through the intercoolers and all the piping.. This will cause a quick Rich condition, unless you tune for it, but whats the point. The Maf needs to be close to the TB, throttle response will be best with the MAF positioned there, plus easier to tune IMO.. Though there are some people running the MAF before the blower/turbo with good results.

CLint

 

Will the BOV "rich" condition be a factor??? Is it even possible to plumb a BOV to work with a suck through system (it doesn't make sense unless you bleed excess pressure that has already gone through the MAF, but that leads to my original question...)

 

I don't think it would hurt the engine, but you'd lose a little power, might cause it to bog a bit hitting the next gear.

 

how much boost are you running? unless your engine is built to handle 15+psi you don't need a 3bar map

vent the bov to the atmo, no need to return it to the intake to mess with the maf.

 

What HP/PSI rating do you need to switch to the 3 Bar? Kind of curious now...

 

If your bov is venting air that has been read by the MAF, you will be smoking like a hopped-up duramax at part throttle, if it will run at all. Your bov would have to be plumbed so that it blows the excess air in between the MAF and the turbo inlet. In this instance you will also need to take care to not have the bov fitting too close to your MAF 'cause it can really mess with MAF signal at idle & low throttle openings.

Some ppl have measured vacuum between the MAF and the compressor inlet when sucking thru the MAF, hence proving it to be a restriction. On the other hand, blowing thru it is much easier than sucking thru it. Besides, like others have said, havin it as close to the throttle body will make for better response, better driveability, & less tuning issues.

 

im running that an more an i will still be a 2 bar

 

what he said

 

a 2 bar map is suppose to go to 14.7psig, and a 3 bar map is from that up to another 14.7, when you get into diesels the maps go pretty high- its not a h/p rating on which one you use

also awake explain to me why a hopped up diesel blows smoke

it deals with turning their pumps up and all that smoke is excess unburnt fuel

rednecks seem to love maken "smoke" shows

 

IMHO, if more LS1 users would use the suck thru MAF, less users would be converting to SD. A blow thru MAF system often reads inaccurately due to a pressureized, turbulent air stream. A MAF, on the same vehicle, will read totally different switching between these two methods, most accurately using the suck thru. In a blow thru you can usually dramatically change its readings just by rotating it. I think that the points expressed about the better response of a MAF used in blow thru are overstated and are offset by having to go to SD, another words, I think that a suck thru MAF is much more responsive and accurate then a SD system. Usually you will not saturate a suck thru MAF as soon preventing many to be forced to SD. Most factory FI systems use suck thru, correct me if I'm wrong. For these reasons I have found blow thru systems more difficult to tune, some not tunable at all if certain turbulant causing curves exist in the plumbing right before the MAF. If the MAF is saturated or is a restriction, move to a larger one, this is how weve done it for years on most other brands of vehicles.

 

Agreed that 1 bigger problem is Turbulence with a Blow through Design.. However it is still the better choice IMO.. This is why it's important to use a Screened MAF for a push through design, to offset any unwanted air being read by the MAF while the air is being cycled through the piping. The ATI setup is probably the only one I can think of that gives the MAF a reading of Turbulence due to the design and placement of the Surge Valve close to the Driver side intercooler.. With this setup the Driver side of a ATI setup will always be the low pressure side, air bleeding off in that area, causing the air to pass through the passenger side, hitting the MAF wires, the MAF reading this air but it's not going into the engine, (TB Closed) then bleeding off on the driver side with the surge valve.. My LTrims used to be everywhere, but I since then switched to a screened MAF and they have straightened out my Weird LTrims and tuning Woes..



Turbo setups use a Blow through Design, ATI came out with their setup with the Push through Design, and it's doing well, like stated above.. Vortech came out with a Pull through design, probably due to lack of space to put the MAF in the 180 Deg piping from the Aftercooler to the TB. They also put the IAT sensor before the blower, which is a no no IMO. Vortech runs well with the MAF positioned before the blower, but the piping is soo small and tight that what the MAF reads going into the blower, right away it's going into the TB. However, on Vortech setups when your at MAX RPMS and boost, then letting off the GAS closing the TB, the BOV Surge valve blows air back into the piping before the blower. The MAF reads this extra air and causes a rich condition causing you to quickly blow black smoke from the exhaust. If the MAF was positioned before the TB this would not be an issue.



More on this later..




Clint

 

Agreed, IAT before boost, a big no no, BOV plumbing critical. When I stated something like, "most manufacturers of FI systems use the suck thru system", I meant the auto manufacturers, not aftermarket FI systems. The most factory turbos that I see here are on factory Porsches and they always use the suck thru method, works well. I think that the aftermarket FI suppliers use whatever system fits better or cheaper as apposed to what works best. I must confess, most of my SC experiance is with Fords, because they're more popular, and turbos with Porsches. But, many in the Ford tuning community, meaning tuners and tuner software suppliers, prefer the suck thru method for reasons stated in my previous post. There it is common knowledge that the blow thru systems presents the biggest tuning challenges and problems because the MAF is often not giving correct air flow signals through out the RPM range. Yes, a screen helps but does not eliminate most air turbulance. I just finished two twin turbo Vettes that are blow thrus and here again, their MAFs were not providing logical info which required the MAF tables to be tuned. But these two cars is an example of not being a good candidate for a suck thru MAF(s). Obviously I represent just one persons opinion but evertime I see a blow thru come in, it's usually going to be a longer day.