MitchB

I re-read the pertinent posts, and several with MAFs said they had better throttle response after the mod. This is (should be, anyway..) a normal reaction to increasing flow through the engine. Didn't mean to say, a MAF mimics the effects of a LWF, although I now see how that could have been read...

Red rooster

Its well known by tuners that a strong 100% motor will give accurate tuning results . A weak motor , will maybe acheive the basic 250 bhp but not a lot more with tuning .
Maybe step one is a compression test on all cylinders , injector flow tests , etc,etc .
If you are going to these lengths, basic mechanical tests are essential .

Very good luck with all this testing .

Geoff
----------------------------------------------------------------
KS400200,the oldest 964 on Rennlist,unless you know differently !

Lorenfb

The promoting and selling of kits, e.g. MAF kit, reminds me of an independent
Porsche shop (now closed) who would promote their "special" air filter kit
as providing about 10 more HP to a '81 911SC. The shop charged $375
for the installed kit. As part of the install (without the customer's knowledge),
the shop would adjust the ignition timing another 3-4 more degrees advance.
The customer always found the engine, after the installed "kit", as having a noticeable
increase in engine responsiveness.

Needless to say, this was a total ripeoff as the shop's customers quickly learned
when another shop did the next tuneup and told the 911SC owner how the
timing was advanced beyond the Porsche spec. The 911SC owner
indicated that the engine had exhibited pinging during the hot weather
after the installation and now understood why.

Some purchasers of engine mods become vunerable to promotions like this
because they don't fully understand the technical aspects or buy into any hype
that's presented. This should be obvious from many of the posts on this thread
and others, as some seem to ignore or fail to accept the technical facts.

Thankfully, the above mentioned shop is no longer around and that most/all
independent shops have much higher standards! Additionally, forums like
Rennlist with the dialogue of its many members provide its members with
the adequate knowledge to make proper product evaluations and in the end,
a rational buy decision.

fast951

Nice.

TR6

Loren, is it a problem to push the timing slightly if higher quality fuel (eg. 91 or 93) is available and the original timing was set for a lower quality fuel? Provided that it isn't pushed to the point of pinging/knocking on 93 octane (if that's what you have available), what is the downside of pushing the timing to that point prior to pinging/knocking to gain some additional power? This is a serious question. I'm not debating whether or not a person can actually "feel" the change in timing in practical terms. That's a different topic and I've stated my opinions previously on it. I'm just asking if there is a downside to pushing timing (provided it isn't to the point of knocking) if higher quality fuel is available to support that timing.

Lorenfb

"is it a problem to push the timing slightly if higher quality fuel (eg. 91 or 93) is available and the original timing was set for a lower quality fuel? Provided that it isn't pushed to the point of pinging/knocking on 93 octane (if that's what you have available), what is the downside of pushing the timing to that point prior to pinging/knocking to gain some additional power?"

1. The quality of fuel today versus the late '80s and early '90s when the 964
was in production is worse. Remember, there was 97 & 98 octane back then.
2. Who says Porsche set the timing on a conservative level other than those who
promote their "performance" chips, i.e. the easiest hype used by most.
3. Porsche designed the 964 and later Porsches with knock sensors so the timing
could be maximized given; various octane levels/qualities, engine temps, and
load conditions.
4. Based on fuels READILY available today, there's little/nothing that can be gained
by "pushing" the timing without having a lower overall torque result when the timing
gets retarded by the knock sensors because of pinging.
5. When the timing is "pushed", the timing margin is reduced, i.e. before the system
begins to retard to the max of 9 degrees. This can result in a lower performing car especially
at the track under hot weather conditions.

Bottom line: The Porsche/Bosch engineers have/had more technical wherewithal even
20 years ago than the so-called tuners of today!

Geoffrey

Loren,

Are you saying that

1) The quality of the mass produced fuels are not as high as they once were, or are you saying that the octane level of fuel available years ago was higher? In the 80/90s the highest octane available generally to me was Sunoco 94. We now have only 93. I would have a hard time believing that the quality of 93 octane fuel today is less than 93 octane fuel of 1990. I have no facts to support this, however, technology in every other area has increased at a rapid rate and I have to assume that the technology of crude oil refinement has made technology advances as well.

2) I have never said that Porsche has used "conservative" timing values, however, they did choose to write the program of the 964 to meet the varying differences between a) production engines, b) climate differences, c) fuel octane availability, and d) warranty and longevity issues. The fact is that the ignition timing of the Porsche produced 964 RS (or 964 CUP) chip has timing values that are increased over the standard street car, AND published a performance figure of +13hp over the standard car. Therefore, it is not a stretch to think that an aftermarket "tuner" can increase timing to that of the standard Cup chip and increase the performance of a stock engine. Further fact is that with MoTeC I have used ignition timing values higher than stock and seen increased performance of the engine with no issues.

3) I would say this another way, Porsche designed the programming for longevity, performance, and warranty given a lowest common denomonator (91 octane fuel) and the knock sensors provide an additional layer of protection. Remember, there is about 3-4 degrees of ignition timing where the engine makes peak torque BEFORE detonation begins to drop the torque - THIS IS A FACT. If the knock sensors are active, something is very wrong.

4) I agree that if the knock sensors are active then the car is making less torque. However, one can simply install the Cup chip timing (remember the 483 brain chips don't work in the street 473 brains) and gain +13hp (Porsche released performance number) as long as you run 93 octane fuel.

5) This is true, but so what? If I reduce the ignition timing from stock, then I increase the timing margin before the knock sensors are active. Is this a good thing?

fast951

When properly tuning a engine, many variables must be accounted for and handled correctly. Some of the variables: Temp changes (hot/cold), altitude changes, fuel octane.. are just a few.
This is nothing new and nothing unique to the 964. All of the variables must be accounted for and handled correctly. This is part of the tuning process!

Ritter v4.0

Loren- you know more about this than I ever will, but one of your criticisms of after market chips boasting increased power was that by using the equivalent of voodoo economics, they would advance the timing to in effect "fake" the increase.

I installed a Steve Wong chip in the Spring and then endured one of the hottest summers on record in Georgia, including several track events where the ambient temps were north (should be south really) of 100F. Using only 93 pump gas I never experienced any engine knock and the car ran great- the power gain, though modest, was apparent- especially once changing back to stock.

Given that experience (and that of others) could it be that you are correct, but at the same time wrong, in that, modest timing "push" not only does no harm but actually provides some marginal benefit?

N51

David,

I thought one of the advantages of the knock sensor was to detect what the ear cannot. If you had access to a hammer, it would be interesting to check codes before and after a hot day at the track.

TR6

An interesting point. How does one know if their 964 is knocking without a tool to read out the data? My guess is that (theoretically) you'll never hear it knocking because the computer will retard the timing before you could hear it knock. I suppose the car might feel a slightly more sluggish as the spark is retarded. But you may not even notice. Anybody have thoughts on this?

Geoffrey

I have several thoughts on this.

1) Yes, at times, under some circumstances you can hear detonation on a 911, even with knock sensors pulling timing.

2) There is inaudable detonation that occurs and can cause damage, so you cannot rely on your ears to hear if the engine is detonating.

3) On an engine without knock sensors, you can make the engine detonate and you can hear it, and you can have the engine detonate and not hear it but see the torque drop on a dyno from detonation .

Ritter v4.0

"Spark is retarded" is no longer politically correct- its been replaced by "spark is regressed".

Nevertheless, interesting point. Maybe the knock was being managed, but I can't say I noticed any drop off in performance.

springer3

I have driven about six different 964s, and never heard one ping audibly. I drove mine with the hammer set to record knock sensor counts. I deliberately floored it from low RPM while climbing a hill (the poor man's dyno). I recall seeing something below 100 counts during the counting period on my hottest uphill run. Most runs resulted in counts in the single digits to teens. Driving the way the car is intended to be driven, I did not see more than an occasional knock sensor count. This was with 93 octane (R+M)/2 pump gas.

Correcting John's recent contention, I have never run avgas except in an airplane. I only speculated that it would be necessary to avoid problems on hot days if timing was even more advanced than the factory settings. If the factory settings are indeed for 91 octane, I don't see the harm in pushing the timing a couple of degrees. I can't believe that is going to add more than a few HP. I can say from my hill climb tests that a 964 is a pig right after the knock sensors activate. There will be an embarassing dyno moment on a hot day if the knock sensors keep activating because the timing is advanced too far.

I don't think you can read knock counts on the hammer after the event - it is a menu setting that must be activated before the car is driven.

The factory has teams of engineers and technicians spending hundreds of hours on high-quality bench dynos with every available control. The factory's worry list includes emissions, fuel effeciency, reliability, longevity, and NVH. I am not saying factory settings cannot be changed to take advantage of better fuel or higher risk tolerance on the part of the owner. I am saying that after reading all the MAF threads I am much better educated and will try to understand the trade-offs before I change any factory engine control settings.

Geoffrey

Running aviation fuel in a car is not appopriate. Aviation fuel is designed for engines that operate at a steady state RPM, at higher altitudes, at cold temperatures, not an engine that is constantly changing RPM and changing RPM at a very fast acceleration rate. You will do more harm running aviation fuel instead of regular automobile fuel or racing fuel.

I know that old time drag racers used aviation fuel, however, it is the wrong fuel for an automobile.