993 MAF vs. 964??
Technical Specialist
Rennlist
Lifetime Member
Rennlist
Lifetime Member
Joined: May 2001
Posts: 5,864
Likes: 25
From: TX
You might want to look over the ninemeister web site, where they discuss various performance upgrades they do for 964's. I believe the web site is <a href="http://www.9mracing.co.uk" target="_blank">www.9mracing.co.uk</a> (no affiliation, etc)
Pro
Joined: Oct 2002
Posts: 637
Likes: 0
From: Tulsa, OK
Performance gain with a switch from the flapper to the hot wire for MAF measurement would probably only result if there is a significant pressure drop across that flapper. It would be interesting to measure, but I'll bet it is minute.
Probably the main reasons for the move to hot wire MAF sensors might be slight improvements in throttle response, and more importantly to Porsche an improvement in reliability since the hot wire has no moving parts and is self-cleaning.
Chip
Probably the main reasons for the move to hot wire MAF sensors might be slight improvements in throttle response, and more importantly to Porsche an improvement in reliability since the hot wire has no moving parts and is self-cleaning.
Chip
Burning Brakes
Joined: Mar 2002
Posts: 1,081
Likes: 1
From: WhippetWorld, .........is it really only this many
As some of you are probably fed up of hearing I have an AMD MAF kit fitted to my C2.
The MAF unit itself is NOT a 993 unit but a Bosche unit used on some Audi`s - apparently a 993 unit will not fit.
There is an interface unit that converts the signal from the MAF into a signal the ECU believes originates from an airflap unit.
The airflap unit is a bottleneck for airflow, responds slower than a MAF and is less accurate for fuel/air ratios as it measures volume rather than mass of air - which is why Porsche changed to MAF for the 993.
Any improvements in "breathing" needs the ECU reprogramming to take advantage - a re-chip.
As for performance gains my C2 261ft/lbs, 298bhp and 4.95s 0-60 on the G-tech.
The MAF unit itself is NOT a 993 unit but a Bosche unit used on some Audi`s - apparently a 993 unit will not fit.
There is an interface unit that converts the signal from the MAF into a signal the ECU believes originates from an airflap unit.
The airflap unit is a bottleneck for airflow, responds slower than a MAF and is less accurate for fuel/air ratios as it measures volume rather than mass of air - which is why Porsche changed to MAF for the 993.
Any improvements in "breathing" needs the ECU reprogramming to take advantage - a re-chip.
As for performance gains my C2 261ft/lbs, 298bhp and 4.95s 0-60 on the G-tech.
Pro
Joined: Oct 2002
Posts: 637
Likes: 0
From: Tulsa, OK
Tony -
You say the "airflap unit is a bottleneck for airfow", but of course almost everything between the cylinder and the atmosphere surrounding the car is a bottleneck for airflow. The real question is how much? I would be much more impressed if you could quote a pressure drop across the flapper unit compared to the hot wire. I don't doubt that the pressure drop is less across the hotwire, but how much? I suspect it is very little, and not worth the expense of an aftermarket replacement for the few horsepower to be gained - at least for most of us.
The hotwire does give driveability improvements because of its greater speed and precision in measurement, but the ultimate arbiter of air/fuel ratio is the oxygen sensor, not the mass flow sensor.
You clearly have a hot setup, but it is the result of many interrelated changes to your powerplant, and does not prove the contribution of the hotwire MAF unit.
Chip
You say the "airflap unit is a bottleneck for airfow", but of course almost everything between the cylinder and the atmosphere surrounding the car is a bottleneck for airflow. The real question is how much? I would be much more impressed if you could quote a pressure drop across the flapper unit compared to the hot wire. I don't doubt that the pressure drop is less across the hotwire, but how much? I suspect it is very little, and not worth the expense of an aftermarket replacement for the few horsepower to be gained - at least for most of us.
The hotwire does give driveability improvements because of its greater speed and precision in measurement, but the ultimate arbiter of air/fuel ratio is the oxygen sensor, not the mass flow sensor.
You clearly have a hot setup, but it is the result of many interrelated changes to your powerplant, and does not prove the contribution of the hotwire MAF unit.
Chip
Burning Brakes
Joined: Mar 2002
Posts: 1,081
Likes: 1
From: WhippetWorld, .........is it really only this many
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Ninemeister
The best 964RS engine that we have tested fitted with the ubiquitous chip, large throttle body, K&N, cup pipe & cat bypass ran on the rollers at 290bhp. The last one we did (last week) came in with 287bhp @ flywheel and 254bhp @ wheels. This is pretty much in line with most RS engines, we have tested over 10 in the last year and all have posted between 280 and 290bhp.
I have tested two cars with a mass flow conversion, Tony Taylor's 964 and a 964RS. Both had 298bhp, Tony's with the AMD conversion with early cast alloy manifolds and the RS with a.n.other conversion and plastic manifolds with a larger throttle body.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">From this it would appear the MAF unit is worth about 10bhp
As I understand it the air/fuel ratios on part throttle is controlled by the signal from the airflow meter. I am sure I have read that the O2 sensor can be disconnected.
From the ninemeisters work with Motec it would seem that the 964 engine will support upto 325bhp without internal mods or forced induction. 300bhp is thought to be the limit that the standard injectors can produce ( Motec has no airflow meter and Ninemeister uses larger injectors with the conversion)
At a cost of 2500 UKP it is relatively cheap HP but it would appear that 300hp is the ceiling for gains without using larger injectors and hence a change in engine management. Motec allows upgrades past this "ceiling"
The best 964RS engine that we have tested fitted with the ubiquitous chip, large throttle body, K&N, cup pipe & cat bypass ran on the rollers at 290bhp. The last one we did (last week) came in with 287bhp @ flywheel and 254bhp @ wheels. This is pretty much in line with most RS engines, we have tested over 10 in the last year and all have posted between 280 and 290bhp.
I have tested two cars with a mass flow conversion, Tony Taylor's 964 and a 964RS. Both had 298bhp, Tony's with the AMD conversion with early cast alloy manifolds and the RS with a.n.other conversion and plastic manifolds with a larger throttle body.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">From this it would appear the MAF unit is worth about 10bhp
As I understand it the air/fuel ratios on part throttle is controlled by the signal from the airflow meter. I am sure I have read that the O2 sensor can be disconnected.
From the ninemeisters work with Motec it would seem that the 964 engine will support upto 325bhp without internal mods or forced induction. 300bhp is thought to be the limit that the standard injectors can produce ( Motec has no airflow meter and Ninemeister uses larger injectors with the conversion)
At a cost of 2500 UKP it is relatively cheap HP but it would appear that 300hp is the ceiling for gains without using larger injectors and hence a change in engine management. Motec allows upgrades past this "ceiling"
Pro
Joined: Oct 2002
Posts: 637
Likes: 0
From: Tulsa, OK
The air fuel ratio at part throttle or wide open is always controlled by the O2 sensors at steady state. With changes in throttle, the DME will use the information from the airflow meter to make initial adjustments to the amount of fuel needed (which is why the MAF, being faster and more precise helps throttle response), but then O2 sensor feedback takes over.
If you disconnect the O2 sensors, the engine runs on a fixed air/fuel map, and will lose fuel efficiency - but from a performance point of view with the right map it doesn't have to lose power and might gain some.
You might be right that the MAF is worth 10 hp, but 10 hp out of 250 is hardly palpable, and this 10 comes dearly from the pocketbook. Its just a matter of how much you want those extra few horsepower.
Chip
If you disconnect the O2 sensors, the engine runs on a fixed air/fuel map, and will lose fuel efficiency - but from a performance point of view with the right map it doesn't have to lose power and might gain some.
You might be right that the MAF is worth 10 hp, but 10 hp out of 250 is hardly palpable, and this 10 comes dearly from the pocketbook. Its just a matter of how much you want those extra few horsepower.
Chip
