Tuning w/MAF vs Speed Density

[REDROCKET02Z06]

Please see my sig. for mods. Does anyone have any experience with tuning using the mass air flow sensor opposed to using speed density for a forced inducted car? What are the pro's and con's of each?

[PerforminNorman]

I was trying to keep my car MAF but I kept blowing them apart so I just went ahead and changed it over to Speed Density. I can't tell you much about the tuning side of it as I just leave that to the experts.

[REDROCKET02Z06]

Originally Posted by PerforminNorman

I was trying to keep my car MAF but I kept blowing them apart so I just went ahead and changed it over to Speed Density. I can't tell you much about the tuning side of it as I just leave that to the experts.

What typr of FI set up are you running and how much boost?

Thanks man.

[PerforminNorman]

Originally Posted by REDROCKET02Z06

What typr of FI set up are you running and how much boost?

Thanks man.

I have a twin turbo setup on a 402 with dual nozzle methanol injection. I don't have a predetermined amount of boost. I can just dial it up with my electronic controller. I don't have it completely finalized as I was dyno tuning and found out the weak link was the clutch. Right now it is tuned with 7 psi boost and 12 degrees of timing and is pushing 720 rwhp and lots of torque. I don't remember the torque number but it is way up there. I'll get my new clutch soon and go back to the tuners.

[REDROCKET02Z06]

Originally Posted by PerforminNorman

I have a twin turbo setup on a 402 with dual nozzle methanol injection. I don't have a predetermined amount of boost. I can just dial it up with my electronic controller. I don't have it completely finalized as I was dyno tuning and found out the weak link was the clutch. Right now it is tuned with 7 psi boost and 12 degrees of timing and is pushing 720 rwhp and lots of torque. I don't remember the torque number but it is way up there. I'll get my new clutch soon and go back to the tuners.

Thanks man that sounds like one mean beast.

[RalphP]

You didn't get any real answers and I just came on the site for the first time in weeks, so here you go.....

I have tuned my car both ways. However, with twin turbos and not an SC, the tuning would be a little different but the same in principal.

If your MAF does not hit its upper limit or "clip" up to your engine's maximum HP (in other words it is able to meter the air coming in up to the maximum amount your SC engine can ever stuff in there) then you are fine to tune with the MAF. You have sort of limited control over AFR under boost because none of the tables in the MAF tune are able to be adjusted when the manifold absolute pressure (MAP) goes above ambient air pressure but it can work OK.

In my case, the MAF hit the upper limit at just over 4K rpm and my tuner give me my car back in a nearly un-drivable condition and said there was an experimental new MAF that would get me to 6K and I said "no thanks" and took over the tuning myself. Problem is once the MAF is done there is pretty much no way to properly control AFR after that point. And no way to manage the transition between where the MAF is working and where it is not working.

So I got the HP Tuners 2 bar SD operating system installed a wideband O2 that logs data in HP Tuners and did my own tuning and could not be happier.

You download the new operating system, install it, pop in a $79 GM 2 bar MAP sensor in place of the old one and then just go to town. The big advantage is that the new system meters fuel based on MAP and you have complete tables to work with that cover the range from full vacume to 15 psi of boost including the VE table and a separate boost-only table that allows you to depermine what AFR to use depending on whether you are on or off boost at any RPM and throttle setting. Plus you get to determine when that boost table is selected.

I have been running my SD tune for a year now and the car runs flawlessly. It is definitely a time-consuming exercise to get the AFR dialed in for all conditions but worth it. HPT even gives you an AFR error table that makes the job a lot easier. Finally, when all done you can still turn on long term fuel trims and closed loop operation via the O2 sensors in order to get that perfect AFR and fuel economy while cruising around.

HTH

[REDROCKET02Z06]

Originally Posted by RalphP

You didn't get any real answers and I just came on the site for the first time in weeks, so here you go.....

I have tuned my car both ways. However, with twin turbos and not an SC, the tuning would be a little different but the same in principal.

If your MAF does not hit its upper limit or "clip" up to your engine's maximum HP (in other words it is able to meter the air coming in up to the maximum amount your SC engine can ever stuff in there) then you are fine to tune with the MAF. You have sort of limited control over AFR under boost because none of the tables in the MAF tune are able to be adjusted when the manifold absolute pressure (MAP) goes above ambient air pressure but it can work OK.

In my case, the MAF hit the upper limit at just over 4K rpm and my tuner give me my car back in a nearly un-drivable condition and said there was an experimental new MAF that would get me to 6K and I said "no thanks" and took over the tuning myself. Problem is once the MAF is done there is pretty much no way to properly control AFR after that point. And no way to manage the transition between where the MAF is working and where it is not working.

So I got the HP Tuners 2 bar SD operating system installed a wideband O2 that logs data in HP Tuners and did my own tuning and could not be happier.

You download the new operating system, install it, pop in a $79 GM 2 bar MAP sensor in place of the old one and then just go to town. The big advantage is that the new system meters fuel based on MAP and you have complete tables to work with that cover the range from full vacume to 15 psi of boost including the VE table and a separate boost-only table that allows you to depermine what AFR to use depending on whether you are on or off boost at any RPM and throttle setting. Plus you get to determine when that boost table is selected.

I have been running my SD tune for a year now and the car runs flawlessly. It is definitely a time-consuming exercise to get the AFR dialed in for all conditions but worth it. HPT even gives you an AFR error table that makes the job a lot easier. Finally, when all done you can still turn on long term fuel trims and closed loop operation via the O2 sensors in order to get that perfect AFR and fuel economy while cruising around.

HTH

It all made sense and did help. My situation is that the person that built the engine and tuned it at 14psi of boost used the MAF and it was a flawless tune from idle to wide open throttle. I upgraded the system to an 8 rib pulley system and the crank pulley was larger in diameter and resulted in upping the boost to 17psi. My local speed shop tuned the car with MAF up to a certain point from what I understand and speed density after that. The problem is the car falls on it's face at about 4,500 rpm's at gradual throttle in first through fourth gear. It does however get much better gas mileage at interstate driving speeds under normal throttle. I'm getting a new 4.50" pulley from ATI Proharger to get the boost back down to 12-14psi and personally feel that from the original tune the MAF tune was much more reliable all around. I think my local speed shop is a better tuner so maybe after we reduce the boost we can get the tune dialed in.

[RalphP]

Your problem may be similar to mine which drove me to a speed density tune. The car stumbled badly every time I tipped into the throttle at mid-rpms and then went like crazy after fighting its way up to around 4500 to 5000 rpm. The cause was an overly rich condition when I got on the throttle but prior to boost building up.

Obviously the engine needs a lot more fuel once it is on boost but in the MAF tune the only way to add the fuel the engine needs on boost is via the PE or Power Enrichment fuel adder table. This table basically throws a multiplier on the fuel requirement calculated by the MAF and the table is divided into RPM bands so you can decide how mucn to add at each rpm. PE mode is triggered by a separate table of throttle position (%) vs rpm. Problem is the ECM has no way to know if you are on or off boost, so you have to load the tables to give you enough fuel when you are on boost but that means while you are trying to build boost it is pouring in way too much fuel. That was my problem and I am not sure that is your problem but it may be. I never had this problem when I was running 6 lbs of boost but it came on bad when I went up to 12 lbs of boost and a lot more fuel was needed. The SD operating system eliminates this issue completely since fuel is added based on MAP vs RPM which is of course directly related to the boost level. So you can tune it to a gnats ass!