gradyex

Maybe its just me and this is all in my head but any 997 or 997S owners feel a slight horsepower difference on some days? I mean on some days my car seems to run like a bat out of hell and other days it almost feels that I'm driving around with 4 passengers and a full tank of gas all the time. I know its normal to feel slight variations in perceived horsepower with climate variations, fuel quality issues, and excessive weight on board but anyone else here think that on some days your car feels a lot peppier than others? That's with just you driving alone with the same gas in your tank as the day before when the car felt 5-10 horsepower stronger? Also, what do you guys think about the use of octane boosters? Do any particular brands work better than others or thats not a good idea at all? I personally tried one brand (104+) and didn't notice any horsepower gains. My car runs great and this is something that I can say about most of the vehicles that I have owned in the past, especially the high performance ones. Any thoughts as to your 997 or 997S being more sensative to this or not? Your feedback would be appreciated. Cheers.

Moogle

refer to this thread to discover why putting anything higher than 93 octane won't have positive performance gains.

https://rennlist.com/forums/996-gt2-gt3-forum/192801-93-octane-or-94-octane.html

MMD

Along time ago I "learned" that on a rainy day the car's engine performs better than a dry day. Why? I "learned" that the increased humidity in the air benefitted more even combustion in the cylinders; therefore performance would be improved. Perhaps this is true?

JohnnyBahamas

The difference in performance between 91 and 93 octane in a 11.8:1 compression engine, as in a Carrera S, is noticible. No one asked, but I feel like typing... it runs better because octane makes the fuel less volatile, meaning that the fuel won't pre-ignite for any of a variety reasons, and that means that the engine's sensors won't send pre-ignition data to the engine computer, causing that computer to "de-tune" the engine to protect it from pre-ignition detonation damage... oh, like bending a valve or blowing an exhaust manifold bolt out onto the road. So, using manufacturer recommended octane rated fuel means you'll get full performance through the entire power band.

There are very effective ways to boost 91 to 93 that work very well, but because they are expensive, at about $24 per tank on top of the 91 octane gas cost, and probably illegal in some states, I will admit in writing that I don't know what they are and that I have never used them...ever. Though, I understand that information is on the web for those that won't be stopped.

Factually, the octane boosters that are for sale over the counter (OTC) are functionally useless... unless they contain lead or MTBE, which they can't anymore I heard someone say once. All they can be made of these days is a high octane hydrocarbon rated under the same R+M/2 octane formula (an explanation of which is also on the web).

The proof is in the simple mathematics if you're interested. First, for standardizing units assume that the OTC products are all in quart volume, and you can imagine how being less than a quart, as most of those products are, would make those smaller volume products even less useful. Next, assume a 16.9 gallon gas tank as in a 997. The equation in words - What would the octane rating, we'll call that n, of a quart of booster, .25 gallon, have to be to boost 16.65 gallons of 91, full tank of 16.9 gallons less the quart to be added, to create 16.9 gallons 93 octane?

Run the resulting equation of (.25n) + (16.65 x 91) = (93 x 16.9) works out to n = 226.2 octane per QUART! Who ever asked if algebra was useful?

As a reference, pure toluene is 114 octane (R+M/2). So, unless the OTC octane booster states in writing somewhere that it is 226.2 octane per quart, or contains lead, or contains MTBE, then it can't be raising you to 93.

Point, feel lucky if you live in a state that still sells 93 octane... or research more on the web.

jcnesq

In Cali, there are still a few gas stations around that carry 100 octane fuel, easy way to boost your octane. Not cheap at $5.00+/gal., but not too expensive either.

JohnnyBahamas

Damn! If that's right you could just put 4 gallons of 100 octane in your tank and fill the rest with 91 octane and you'd be running 93.13 octane... assuming a 16.9 gallon tank as in a 997.

I'd do that in a heartbeat.

SrfCity

I seem to notice a difference too. It's my theory that the car's performance is not unlike getting exercise. If you take it easy(slightly get your heart rate up etc.) then you have a tendency to feel a little sluggish. On the other hand if you're pushing it, your performance level increases and you've got more zip.

It seems as if the cars performance level adjusts to driving habits. When I take it easy the car just seems a little slower for whatever reason. I've read that a car that is driven hard will actually kick out more horse power.

rss997

I feel the car is more peppy when I am on a fun run and on the gas ! It seem to be that maybe it really gets hot and everything works better...I dont know just a thought...I am far from an expert.

soltino

With all the Electronics these days it may be that something is going bad but is intermittant at this stage.

If very noticeable, maybe have a diagnostic run on the bad day.

tino

PV

Go to the link provided by Moogle. Very good in depth discussion via mvd and others.

JohnnyBahamas

Anyone interested in finding out if there is a high octane gas station near them under this specific brand, check this website - http://www.rockettbrand.com/dealers/dealers.htm

Noting of course that you'd blend 4 gallons of 100 octane with 12.9 gallons of 91 octane to get 93 octane, in a 997's 16.9 gallon tank, and that anything over 93 is unnecessary.

OCBen

I'm no combustion engineer nor a meteorologist, but I don't think it has anything to do with the increase in humidity. If anything, moisture would be a detriment to combustion. If there is better performance on a rainy day it's probably due to an increase in oxygen density due to an increase in air density due to cooler air masses and higher atmospheric pressure. All I know is I really feel for those drivers in Denver and other high altitude locales.

Help me out here Johnny if you still have your slide rule handy.

1999Porsche911

One of the biggest benefits of h-gher reletive, it lowers the octane requirements of the engine.

JohnnyBahamas

Once again, I'm clueless. I haven't researched that one.

The late and very great John Lingenfelter was using water injection on his major HP creations but I don't know if that was for cooling the chamber or oxidizing the fuel or both. Whatever the reason... water was being sprayed into the mix so there must be something to it.

Somebody knows.

OCBen

Something in the water, eh?..... Fire water is what I'm thinking...