Performance Improvements for All Porsches

[SprintStar]

Originally posted by Wayne at Pelican Parts
Although I'm not a gasoline expert, it is my understanding that higher octane fuels have a lower energy density (not sure if that is the right term for gasoline) than lower octane. The higher the octane, the greater the "pre-burned" fuel. The higher octane fuel with lower energy, ignites and burns slower (what you want) for better and more consistent, even combustion pressures in your combustion chamber over the burn cycle.

-Wayne

Err... Slower burn and less energy. Hmm... Won't that make for a slower car? Don't we all want more energy?

I'm just curious if we use less timing and cheaper fuel, how will the cars perform? I for one have gotten better mileage out of lower octane fuel. Is it due to the higher energy levels?

Sprint.

[911ctS]

An interesting thing ive seen done is the placement of a rheostat in place of the O2 sensor, allowing you to tweak the parameters of your A/F ratio (to a limited extent depending on your DME)

Not sure of the exact model # but i know that both MSD and Jacobs Ign. make a spark unit that allows for knock sensor (piezo electric crystal) input to advance/retard timing. You retain your distributor but have to tack weld your advance weights in the non advance position. Pretty much a replacement for the origional CD Ign.

O ya... Im jelous of you mid west or eastern guys and your 93 octane available at every pump. We've got sunshine here in CA but crap for gas!!! I never go to Arco!!! too many bad experiences there.

[jyl]

May I ask for people's experiences with the aftermarket knock control devices like the J&S Safeguard http://www.jandssafeguard.com/ device mentioned earlier in this thread?

I recall one 930 owner saying he had one and it worked well - this was in a thread several months ago. I've also read opinions that external knock sensors don't work well on air-cooled 911 motors, but the factory uses one on the 964 engine. Surely the race engine gurus here must have had some experience with these devices?

What I am especially wondering about is if the J&S device operates independently of whatever engine management system you have, so you could piggy-back it on top of a Motronic.

Edit: Sorry, I did find these reviews on the web:
http://www.hughesengines.com/features/product_of_the_month/sept_03.asp
http://www.mustangworks.com/articles/poweradders/KnockControl.html
And I found this install guide, not for a 911 but it sounds pretty darn simple anyway.
http://www.scoobymods.com/forums/showthread/t-289.html

[Wayne 962]

Originally posted by jyl
What I am especially wondering about is if the J&S device operates independently of whatever engine management system you have, so you could piggy-back it on top of a Motronic.

I can't see how you would be able to make that work, considering that the Motronic computer controls all aspects of ignition timing.

-Wayne

[Wayne 962]

Originally posted by SprintStar
Err... Slower burn and less energy. Hmm... Won't that make for a slower car? Don't we all want more energy?

Smart, common-sense people often come to this conclusion. However the ICE (Internal Combustion Engine) is not that simple. Due to restrictions on the laws of thermodynamics, a perfect ICE can only be 50% efficient (this is way off the top of my head - I can't recall exactly). 50% of the energy is lost in excess heat. So, more energy doesn't necessarily mean more power and acceleration.

Let's do an analogy. Suppose your trying to push a car along a street. You would get right behind the car on the street and start pushing. This would give you maximum leverage and force. But suppose now, you move off to one corner of the car, so you're pushing at an angle. Even if you use someone much stronger, they are still at a disadvantage because they are not in the optimum location for pushing the car.

In your engine, it's somewhat similar. You want maximum pressure in your combustion chamber *just after* the piston has reached Top Dead Center (TDC). Since fuel takes time to burn, you want to ignite the mixture before TDC to give pressures time to build up in the chamber (pressure resulting from the explosion of the gas/air mixture). Having your pressure at a maximum right when the piston is in the right spot is important to maximizing power. If your mixture ignites prematurely, then the pressures may build up on the piston before it reaches TDC, and it may try to push it in the opposite direction. This is bad, and this is what is called pinging.

Now, back to octane (and again, this is off the top of my head). The slower burning fuels allow pressure to build up slower and combust slower. So instead of having a big POP at near TDC, you have combustion that takes place over a longer period of time, while the piston is traveling back to the center of the engine. This gives more power because the pressure is uniform along a larger portion of the stroke. Diesel engines have very slow burns like these, so that is why they have a lot more torque (they have more uniform pressures along the length of the stroke.

On a side note, maximum leverage for the piston is when the rod is at a 90 degree angle with the crank. You would think that this is when you want maximum pressure in the combustion chamber, but I don't think it works out quite that way all the time.

-Wayne

[TimT]

I dont have hands on experience with the J&S unit but am familiar with someone that has it on a highly modifed 930. The car has Haltech E6K engine management and waste spark ignition.

The J&S intercepts the signal from the ecu to the coils, if no knock is present, no adjustment is made. If knock is detected, the timing is adjusted.

I thinks that saying air cooled engines are noisier than water cooled engine is an old wives tale. Both air cooled and water cooled engines share the same components, i.e. cams, chains, rockers, pushrods, pistons, valves, crankshafts, etc. The water jacket really prevents us from hearing all the noises that exist in an operating engine, but internally the noise still exists. In an air cooled engine no water jacket, and hence a seemingly "noisier" engine.

Ever listen to an engine with a stethoscope or end of a screwdriver while trying to diagnose something? You hear a nice rythmic cadence whether its a air or water colled engine.

FWIW Im using Bosch donut type knock sensors on one of my engines. The EFI that I chose has 2 channel knock control. However I wont be able to get any dyno time until this permafrost recedes.

[jyl]

I called J&S Safeguard and spoke to the guy briefly. He said their "Universal" units works on a '80s Porsche w/ stock Motronic.

The universal unit is pictured at:
http://www.jandssafeguard.com/images/UniversalApp.jpg

And installation instructions are here:
http://www.jandssafeguard.com/UniInstall.html

He said one location for the knock sensor is under the fuel rail. The Universal unit comes with a GM knock sensor for $495, a Bosch knock sensor costs an additional $50.

I don't have any personal experience with this device - all I'm doing is searching and reading on the web - but it looks really interesting.

[Lorenfb]

Wayne is correct about cylinder pressure and when the optimum ignition
should occur. Check out the Graphs page at this URL (www.systemsc.com).
I've plotted some graphs at the bottom which provide further insights into
what Wayne has discussed.

[brcorp]

I have a couple of questions for LorenfB and Wayne at pelican Parts. Before I ask I'm not trying to turn this into the usual LorenfB Vs Steve Wong pissing match, I'm just looking for some insight.

Here goes.

Loren,

Do you some specific issues with Steve, Steve's product, the way Steve does business or chips in general. The underlying theme of the majority of your threads gives me this impression.


Wayne,

"That said, SteveW's chips seem to get high marks from satisfied customers - we will be carrying them in the catalog in the very near future. For the price, a chip replacement is still one of the best ways to increase off of the line performance. BUT, you're running your engine closer to the edge, which will cause increased wear and possible damage"

Wayne, are SW's chips being carried in the catalog based solely on customer demand or on the merits of the product. It seems an unlikely association given all the controversy associated with this particular performance chip.

I think everybody or almost everybody on the board understands that increasing the output of the engine may result in a potential decrease in service life. That said, every after market component (sport muffler, cat-bypass, free flow air filter, etc) should be considered suspect as it alters the operating parameters established by the manufacturer.

[Wayne 962]

Originally posted by brcorp
Wayne, are SW's chips being carried in the catalog based solely on customer demand or on the merits of the product. It seems an unlikely association given all the controversy associated with this particular performance chip.

Does it matter? Tortelli alfredo is incredibly bad for you, yet restaurants still serve it because people love to eat it. In this case, the product is being carried based on the merits told to me by the customers. I don't have the ability to personally try or endorse every product that we sell in the catalog. Obviously, if something is sub-par, I don't carry it. The product in this case gets high marks from it's users, so I would be silly not to carry it.

As for LorenB's comments and concerns with Steve's chips, I think this was discussed to death in a previous thread - please search the archives.

-Wayne