Harrop Hurricane MAF vs Speed Density

[RD in SD]

I have an 09 Z06 E38 with a Harrop Hurricane 8 port throttle body manifold with a custom made ram air set up that brings all the air into one ram air scoop at the front of the car. It currently has a Speed Density Tune and 80Lb injectors. It has a big cam, ported heads . It puts over 600 HP to the ground, idles great, good drive ability. The car has unbelievable throttle response and is wicked fast. Perfect for the track which is why I built it.

OK now for the problem. It gets about 3 to 4 MPG (the DIC says I am getting 25 MPG remember is has 80lb injectors) on the freeway. My tuner and I are thinking about turning the MAF back on using EFI Live and trying to do a MAF tune on it to improve the mileage. The MAF is installed in the air stream after the filter before the plenum splits to go to each bank of cylinders. We are getting a good MAF reading but MAF is disabled. We want to try MAF because we believe it will be easier to tune not because we think it will get better mileage than speed density. The problem is that with 8 x 55M of air coming in the Harrop is very hard to tune. We have it dialed in on the dyno for max horsepower but we did not do anything about 1500 to 2500 RPM rage which is where normal driving occurs. So we were thinking if we use MAF up to maybe 3500 RPM or a certain amount of throttle and then go back to speed density.

So have a few questions.

1. What do you think of the idea?
2. What tables (number please or name) is it that turns the MAF back on?
3. Since the MAF airflow will be different than the stock intake what table will we need to play with to try and dial that in? The tube is bigger than the stock tube so I am anticipating it will throw off the MAF.
4. If we stay with Speed Density as I am sure many of you are going to recommend what is the best way to get it dialed in?

Thanks in advance for your help.

[joecar]

Are you sure the DIC is computing MPG correctly... have you performed independent test (fill tank, drive, fill tank again noting how many miles and gallons)...?

Do you run CL or OL...?

CL usually improves MPG.

1. worth trying.
2. C2901,2,3.
3. MAF table corrected using wideband (i.e. AutoMAF).
4. VE/VVE table corrected using wideband (i.e. AutoVE).

Get both VE and MAF tables corrected over rpm range, then compare driveability between the two.

[minytrker]

You need to tune the VVE (fuel) for part throttle if your staying SD. Going from SD to MAF or MAF to SD will not effect fuel economy if both are tuned correctly. I'm guessing your part throttle fueling is way off which is killing your economy. You will make the same HP in SD or MAF as long as your MAF isnt a restriction, but since its on the car already once the MAF is tuned you will still make the same HP.

[ScarabEpic22]

Lorenz is absolutely correct, if you have dialed in idle and WOT but havent touched part throttle/midrange, you're going to get crap mileage. If you havent touched the stock VVE and are now running 80lb injectors (I assume you scaled the tune as well, depends if you have the 128lb/hr IFR or not), then you're probably getting 8-10AFR at part throttle.

The DIC will always be off, I put in a request for EFILive to add the ECM/DIC scaling tables but Im not sure if that will be happening anytime soon. HPT is working on it now, no idea where it is in their queue. This has been bugging the heck out of me in my TBSS with ID850s on long roadtrips, I have to guess how many miles I actually have left.

[RD in SD]

Thank you for all the information let me see if I can clarify a bit.

Yes I checked the actual mileage becasue the DIC is way off it says I am getting 25MPG but I am not.

I am not trying to say that MAF will provide better mileage than SD I am just saying that we thought it might be easier to tune and possibly more accurate in those part throttle cruising situations being that it can correct itself based on actual air flow. After all the factory does a MAF tune for a reason don't they?

Not sure about closed loop vs open loop will have to ask my tuner.

Thanks for all the input will update you as it goes along.

[RD in SD]

I can't find C2901 what is the name? Looks to me like it should be MAF Parameters which is C0301 to 12, and or Electronic Throttle C0801.

I found MAF Frequency Conversion B1097 which is where I believe we would dial in the changes to the airflow due to the MAFs new location and different airflow. When you say MAF table I assume this is what you were referring to correct?

[joecar]

Yes, correct, for E38/E67 see C0301-12.

Yes, correct; there may be multiple MAF tables covering different ranges, B1097-9.

[RD in SD]

Update. Thank you all for the assistance. For our initial adjustments we left the MAF off and worked on Speed Desity. We found the car was pulling fuel on one bank more than 10% in some areas at cruising speeds. We made adjustments to the VE table and got the Long Term Fuel Trims down around zero or the single digits and it seem to have made major improvements in the mileage. Then we substantially increased the spark from around 20 at low RPM to 40 between 400 and 1800 RPM. Then we found the car needed more fuel but the car was still not balanced between the two banks. We tried to adjust that out with the Harrop throttles but were unable to get them to balance by adjusting the airflow, so we are going to test the O2 sensors next.

[RD in SD]

Update. Thank you all for the assistance. For our initial adjustments we left the MAF off and worked on Speed Desity. We found the car was pulling fuel on one bank more than 10% in some areas at cruising speeds. We made adjustments to the VE table and got the Long Term Fuel Trims down around zero or the single digits and it seem to have made major improvements in the mileage. Then we substantially increased the spark from around 20 at low RPM to 40 between 400 and 1800 RPM. Then we found the car needed more fuel but the car was still not balanced between the two banks. We tried to adjust that out with the Harrop throttles but were unable to get them to balance by adjusting the airflow, so we are going to test the O2 sensors next.

New update: The O2 sensors are OK. We took off the plenums that I created, manually adjusted the flow of each cylinder with a flow meter and got long term fuel trims very close bank to bank. When we put the plenum back on it threw the numbers off again. We suspect two things, 1. The MAF is actually impacting the tune even though we think it is turned off or 2. The plenums I created are affecting the airflow. We will test these two theories this week. Any input is appreciated.

[Chevy366]

New update: The O2 sensors are OK. We took off the plenums that I created, manually adjusted the flow of each cylinder with a flow meter and got long term fuel trims very close bank to bank. When we put the plenum back on it threw the numbers off again. We suspect two things, 1. The MAF is actually impacting the tune even though we think it is turned off or 2. The plenums I created are affecting the airflow. We will test these two theories this week. Any input is appreciated.

Can you throw up some pictures of the Plenums?
Sounds like it may be causing a negative pressure wave in the tract.

[RD in SD]

Here is a link to a pic of my car on the Corvette Forum scroll down a bit and you will see them. This was designed with a lot of input directly from Harrop.

http://forums.corvetteforum.com/c6-z06-discussion/3107093-z06-with-zr1-hood-any-pics.html

[etmotorsports]

In my experience speed density tunes always get better mileage than maf tunes that is if they have been dialed in correctly at part throttle. It is strange to see but alot of engines can cruise at 12.0:1 afr and seem to drive ok until you lean it out then you can see the difference.