What grade gasoline do you use?

[ballysdad]

The higher the compression ratio the slower the fuel needs to burn so high octaine gas is recommended. Does anyone use reg gas in their 944? or mid grade? what are your experiences..any knocking or pinging?

[Aslet]

All they need, according to the manual, is the regular low grade gas. They were built as a more economic car, not a pure sports car. I used the low grade gas for 2 years with no issues at all. For the past 6 months I have been using the premium though. This is due to the low amount of miles I put on the car and I was doing about half those miles at autocross and drivers ed events. Since then I have kept premium in the car, since I drive maybe 30 miles a week max on the car (I've been at college), so i figured I would spend the few more cents and have the better gas in the car for the cold winter driving (not that it does anything useful for winter driving). Anyways, the car can use any grade gas with no issues.

P.S.- Higher the octane, less likely it is to detonate prematurely (knock), so in higher compression sports cars with lots of pressure in the cylinders, higher octane stops the gas from lighting at the wrong time, its not really the rate that it burns...

[agent213]

Higher octane does not mean it burns "slower". It simply means it is initially harder to ignite. Think of it as the 'stability factor'. If your owner's manual says "91 octane recommended" you can get away with a lower octane rating unless you're really flogging it. If it says "91 octane only" then you're going to suffer from pre-ignition by putting anything less in it.

I've used regular (87) fuel in my motorcycle when the only station in miles was out of anything remotely resembling high-octane. I kept the revs down, and limped it to a station that sold 91 without any ill effects.

[krystar]

on the 944 NA, u don't need 91. the turbo's though definitely.

[Techno Duck]

My '87 n/a ran fine on 87 octane even with the FRWilk chip. FRWilk actually stated start out on 93, then progressively work your way down to 87...obviously keep a keen ear to see if any pinging develops. I never had problems.

Personally i think unless you have an '88 or '89 8v n/a car which had slightly higher compression, using anything but regular unleaded is a waste of money.

[flash968]

each model is different - it depends on the compression ratio - however, the manual says a minimum of 91 RON which is 88 RON+MON/2 (the way it is measured in the states) - less than that will reduce power

also remember that, as long as you have the compression and timing capabilities, it is well known that each point of octane raised results in 1% of power increase - go from 87 to 91 and you get a 4% increase in power - on a stock 163 hp 944, that is worth 6.5 hp - however, remember that manufacturer hp ratings are based on the highest fuel grade specified, not the lowest - that means to get that 163, you need to run 96 RON, which is 92 RON+MON/2

if you are running 87, your maximum power is now down to 154 - subtract from that any reduction in compression due to age and wear, and you could be seriously down on power - a 10% loss, which is common in an engine with 100k on it, means you could be at 140hp - that's a huge drop

higher grade fuel is a cheap way to keep things running as well as they can - there is a limit though, and there is such a thing as too high - higher octane fuels burn hotter - that can result in burnt valves

if you chip a car, all of this becomes even more evident

another thing to think about is fuel economy - given the same type of driving, you will get better mileage on 91 that you will on 87, to the tune of 10-15% - that offsets much of the cost - this increase falls off dramatically though if you are spending much of the time idling, like when you are stuck in traffic

on my 968, i typically run 3/4 tank of 91 and 1/4 tank of 100 - that brings me up to about 93 RON+MON/2 - much more than that and pretty much all i see is hotter temps - any less and there is definitely a power fall off

the type of driving also determines octane need - on my denali, though it is rated at 87 minimum, and that is what i run most of the time, if we are towing, i run 89 on the flats, and 91 on the hills - definitely makes a difference there too

[theykallmekem]

u always use 93 octane in my 944. even the van (2006 Honda Odyssey Touring) uses it lol. its because im so use to saying 20$ 93 octane, i was in the van and i realized AFTERWARDS that i put 93 lol. its been on it since 06' lol

[nynor]

all my vehicles get high test.

[flash968]

i wish we had 93 here in california - it's been a long time since i saw that here - i did see it back east not too long ago though

i had a calculator somewhere to figure out what european octane converted to in US spec, but it seems to be hiding from me right now

[porsche4life]

I run 91 in mine. It has a hesitation under load if it has 87. That and it says to use 91oktane inside the gas door.

[Techno Duck]

Flash, I really dont understand alot of what your saying.

High octane fuel does not burn hotter, that is completley bogus. Octane does not predict / relate to potential power, heat generated or anything like that. Octane simply is the resistance the fuel has to auto-ignition..this is relevant because the pressure increase in the cylinder will cause the fuel to ignite (pressurize any gas or liquid = higher temperatures). This is why high compression engines, IE race engines / sport car engines require high octane. The compression in the cylinder is so much higher, which means higher cylinder temperatures, which means a low octane gas will ignite based on the compression, not the spark (IE, detonation). Diesel engines run off compression based ignition..thats why gasoline engines have spark plugs. Its detonation that is going to put huge stress on your headgasket and rods. Think about it, the piston is moving up and fuel is igniting causing a further pressure increase while the piston / rod is sitll on the upstroke. Talk about a huge pressure increase in the cylinder, beyond what it was designed for.

A typical engine, like the 944 series..especially the US market 8v n/a (not including the '88, '89 and ROW cars) will not benefit at all from higher octane gas. They are not high compression engines by a long shot and i dont think your analogy of a 163hp stock 944 holds true. There is nothing on the 944 (not counting the 951 or 968) to adjust the timing automatically. You can switch the fuel quality switch on the DME to advance the timing or put on a adjustable timing gear, but it dosent make any sense to me why anyone would advance the timing like that just so they can run higher octane fuel and get an extra 10hp out of the car..at the risk of destroying the engine.

It is true that most engines nowdays designed for a midgrade or premium fuel will not respond well to low octane fuels with the obvious felt decrease in power, higher fuel consumption and increase in emissions. Thats because these engines have adjustable timing based on knock sensors (timing retarded if knock is sensed). The 8v n/a (again, excluding the '88 and '89 model) dosent have this. Basically if your relatively new engine with engine management that has knock control is designed to run on 89 octane, you will get no more power from that engine if you run 91 or 93, but you will notice a difference running 87. The engine management will let the car run on low octane preventing damage to your engine, but it will not make any adjustments for the engine to run better on higher octane fuel that what is the minimum required. Of course you need a chip / tune to take advantage of this as you stated.

Basically what im trying to get at, if your engine is not designed to run on a high octane fuel, your wasting your money. The US market, 8v 944 (in stock form) for example is one such car.

[flash968]

if you notice every early on, i said "if you have the compression and timing"

it is also still true that the engine is rated at the highest fuel specified - octane levels below that result in lower output - take it to a dyno - i did - you'll be depressed - i was

timing curves are controlled by the DME - this adjusts advance based on load, rpm, temp, etc - lower octane fuels result in less advance, and therefore less power

advancing timing, within limits, does not necessarily mean doing any harm to the engine - it does require that everything be up to snuff, but i've advanced timing on countless engines without damage - 4 degrees is usually pretty darned safe - i wouldn't go much past that though without modifications

what i meant by "higher octane fuel burns hotter" was perhaps a misstatement jumping to the result - they burn longer, therefore causing the engine to run hotter - come on over and i'll take you for a spin and you can watch the gauges and see just how much of an effect it has - i tried some straight 100 - not good - got really hot really quick

the 944 at 10.6:1 is definitely "high compression" - even the 9.5:1 US version is high compression - high compression has typically been defined as anything over 9:1

by the way, i was quoting the 163 of the ROW version, which is more affected by octane, as the higher the compression, the more affected

[Dave L]

I go by the manual. 87 for the 944 8v when I had it and Premium of the 944s 16v. If you chip cars or perform other mods then yes perhaps higher grade is required but other wise I will go with what the mfgr says.

[flash968]

the workshop manual specs 88 minimum to 92 maximum - no idea what the owner's manual specs

i never understood the desire to have less power and fuel economy though than available though, so i run the highest it is specced for

in a car that gets 20 mpg on 87, it is actually cheaper to run 91 - follow the math:

87 is $1.69/gal
91 is $1.84/gal

20 gallon tank - 87 tank is $33.80 - 91 tank is $36.80

range on 87 at 20mpg 400 miles
range on 91 is 440 miles at even the conservative increase of 10% (i've gotten better)

differential is .9090909

the same 400 miles that costs $33.80 on 87 only costs $33.46 on 91

food for thought - again, this really only applies to moderate throttle highway - around town it falls down

[VINMAN]

Been running 87 in mine forever, never a problem.

[fbgh2o]

94 Octane only.

[flash968]

lol - i never had a problem with vanilla..................until i tasted chocolate

[agent213]

wtf , how does 91 increase your mileage? i'd love to see this control test....

[flash968]

it works if and only if your car is designed to run on high octane fuel (like the 944) - it's not that your car will get better mileage than what is specced with 91 if you go higher - it is that your car will get WORSE mileage than specced with the lower grade fuel

just like power ratings, fuel economy ratings are based on the highest fuel specced for the car - if the car was rated at 26mpg, it is nearly impossible to get than on less than the higher of the specified fuels (in the case of the 944, that would be 92) - in the event of running 87 on a car that got 26 on 92, you would then get about 23.4 or less

try it out - do the math - see if it then makes sense for you

[krystar]

so even the 8v na's are specced for 91/93 ?