964AFM to 993MAF
06-27-2009, 10:57 PM
#46
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Maybe my memory is failing me, However I do not forget important things .. Nothing personal, but I do exchange emails with lots of people.
06-27-2009, 10:58 PM
#47
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06-27-2009, 11:02 PM
#48
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Now ,now gentlemen, we are loosing focus, my original question has been answered to my satisfaction, so lets put down the swords and all get along; this is a place for positive and knowledgeable feed back, and like in most things there are more than one answer to a question as well as several opinions.
06-27-2009, 11:08 PM
#49
I'm not choosing sides here, but, really, *any* gain and you win?! Surely there is *some* gain to what you're doing. Why not choose a number and pick a fair fight? Do I hear 10%, 15%? . . .
Sorry, I couldn't resist . . .
Sorry, I couldn't resist . . .
06-27-2009, 11:15 PM
#50
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In my opinion, he made a fair counter-offer. If you see it otherwise, please explain your differences. As usual, Loren asked fair questions that you've not answered.
06-28-2009, 08:52 AM
#52
Nordschleife Master
Does an AFM (barn door wide open) have the same air flow capability of MAF?
06-28-2009, 09:09 AM
#53
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1) barn door with filter (stock)
2) barn door, no filter (not recommended for long engine life)
3) no barn door, no filter (simulating the very best MAF air flow possible)
One and two are the big difference. From curve 2 (AFM) to curve 3 (best MAF possible), the difference is very small.
You can get a big power increase from larger injectors, free-flow exhaust, supercharger, turbocharger, or bigger displacement. In that case you outgrow the standard engine controls and you will need a remap.
The Otto cycle engine was invented well over 100 years ago. The technology is highly developed. Replace a 2-barrel carburetor with a 4 barrel, and you will see power increase on most older engines. The AFM to MAF on the 964 is an upgrade, but to get much benefit, you will need to spend a lot more money.
John Vittesse did not invent the MAF. He buys them and installs them using technology developed by others. The lowly KIA has a MAF sensor. They are no longer exotic or expensive.
06-28-2009, 03:37 PM
#55
The only possible benefit of a MAF over an AFM is imrpoved AFRs and
or increased intake airflow which assumes that the AFM is restrictive
and thus the engine with stock cams and engine volume is less than
optimum, i.e. less than max VE (volumetric efficiency) was achieved
using an AFM by Porsche versus a MAF sensor.
The AFRs for the stock engine are most likely very near ideal
or to the point where minimal tweaking won't produce much
torque increase. So, that leaves air restriction as the key issue.
Thus any comparative test needs to focus on JUST that!
Remember, the key benefit of the MAF utilization in the 993 and
ALL later OEM engine management systems is better emissions
control.
"MAF plus re-map are the only modification."
And the most important aspect of that is that ONLY the fuel maps get
modified for the MAF output versus the AFM output. Allowing an
unknown chip mod doesn't really singularly evaluate the effect of
a MAF mod. If a referee were utilized, he'd have to confirm that
the ignition maps were stock.
Bottom line: And that's the REAL problem with resolving the issues
confronted in this thread, i.e. the chip mod would not be open for
evaluation.
or increased intake airflow which assumes that the AFM is restrictive
and thus the engine with stock cams and engine volume is less than
optimum, i.e. less than max VE (volumetric efficiency) was achieved
using an AFM by Porsche versus a MAF sensor.
The AFRs for the stock engine are most likely very near ideal
or to the point where minimal tweaking won't produce much
torque increase. So, that leaves air restriction as the key issue.
Thus any comparative test needs to focus on JUST that!
Remember, the key benefit of the MAF utilization in the 993 and
ALL later OEM engine management systems is better emissions
control.
"MAF plus re-map are the only modification."
And the most important aspect of that is that ONLY the fuel maps get
modified for the MAF output versus the AFM output. Allowing an
unknown chip mod doesn't really singularly evaluate the effect of
a MAF mod. If a referee were utilized, he'd have to confirm that
the ignition maps were stock.
Bottom line: And that's the REAL problem with resolving the issues
confronted in this thread, i.e. the chip mod would not be open for
evaluation.
Last edited by Lorenfb; 06-28-2009 at 04:01 PM.
06-28-2009, 06:31 PM
#56
This is an overlay comparing a 3.6 964 engine with OEM AFM and a Split Second MAF with PC based air fuel ratios. Engine has chip and SS camshafts.
Last edited by rsscotty; 06-01-2013 at 11:11 PM.
06-29-2009, 08:19 AM
#57
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Nice chart. Credible. The cam mod violates the rules of the bet (start from stock), but I should not have worried. The cams and chip took the car from stock (247 HP) to 285 HP. That is a nice 15% gain, but the AFM is not optimized for such a significant power increase.
Average gain with the MAF and map change alone is about 5 HP (2%), and peak gain is 14 HP (5%). Colin's values for difference in air flow between the MAF and AFM are close: 2% average, 4% peak. Per Colin's data, take out the paper element (or use an oiled cloth filter like the MAF kits use), and most of this difference disappears. I do not recommend oiled cloth filters - too many reports on this forum and others about grit in intake when using cloth filters. My intake was oily but grit free when I cleaned it last winter, so the paper element stays.
Average performance increase from the MAF is the same as a 63 lb weight reduction. Peak difference is the same as getting 157 lb weight reduction (assuming original weight is 3200 lb). 10 HP will get you around the track faster, but unless your butt dyno is quite sensitive, you will not be able to feel a difference. It is about the same performance difference as running with full fuel, and running near empty.
Average gain with the MAF and map change alone is about 5 HP (2%), and peak gain is 14 HP (5%). Colin's values for difference in air flow between the MAF and AFM are close: 2% average, 4% peak. Per Colin's data, take out the paper element (or use an oiled cloth filter like the MAF kits use), and most of this difference disappears. I do not recommend oiled cloth filters - too many reports on this forum and others about grit in intake when using cloth filters. My intake was oily but grit free when I cleaned it last winter, so the paper element stays.
Average performance increase from the MAF is the same as a 63 lb weight reduction. Peak difference is the same as getting 157 lb weight reduction (assuming original weight is 3200 lb). 10 HP will get you around the track faster, but unless your butt dyno is quite sensitive, you will not be able to feel a difference. It is about the same performance difference as running with full fuel, and running near empty.
06-29-2009, 08:30 AM
#58
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Colin:
Very nice, and credible. Air temperature and barometric pressure are documented, and equal for each run.
This tells me I can increase peak power by as much as 10 HP (a 4% increase) simply by running with no air filter. All other factors equal, the MAF and AFM curves actually cross each other several times. Peak power is equal. Of course our track speed depends on the average power across the RPM range. The MAF power averages about 4 HP greater (2%). The same acceleration increase can be achieved by removing 64 lb of weight - about what you get by replacing the stock seats, or by removing the stock passenger seat for a track session. Weight reduction improves acceleration, but also makes you faster in turns, lowers fuel consumption, and improves braking. Power increase improves only acceleration.
Did I miss anything?
Very nice, and credible. Air temperature and barometric pressure are documented, and equal for each run.
This tells me I can increase peak power by as much as 10 HP (a 4% increase) simply by running with no air filter. All other factors equal, the MAF and AFM curves actually cross each other several times. Peak power is equal. Of course our track speed depends on the average power across the RPM range. The MAF power averages about 4 HP greater (2%). The same acceleration increase can be achieved by removing 64 lb of weight - about what you get by replacing the stock seats, or by removing the stock passenger seat for a track session. Weight reduction improves acceleration, but also makes you faster in turns, lowers fuel consumption, and improves braking. Power increase improves only acceleration.
Did I miss anything?
We found similar results from the exhaust comparison, a non-cat set up with either combination of cup pipe/side silencer or rear silencer/g-pipe working similarly well (although the G-pipe version is noisier).
All the best.
06-29-2009, 08:56 AM
#59
Nordschleife Master
The AFRs for the stock engine are most likely very near ideal
or to the point where minimal tweaking won't produce much
torque increase.
or to the point where minimal tweaking won't produce much
torque increase.
07-15-2009, 05:48 PM
#60
Former Vendor
We've installed Johns MAF kit recently on a completely stock (including catalytic converter) 1993 RS America solely because the stock unit had failed. The vehicle never left the dyno during the install, the results speak for themselves.
-Warren
-Warren