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Old 03-04-2008, 01:45 PM   #1
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lower octane fuel=performance drop

in belgium we have a choise of 95 and 98 RON octane fuel

wich according to wikipedia would be the equivalent of 90-91 and 94 in the us
there's a 10 cent difference/liter in price

98 is recomended for my engine, wich is carburated so it isn't going to adjust for anything like modern engines do. but since i recently read in the manual it could also run 95 (with the notice "if nocking occurs see your dealer for engine adjustments..." talk about engine management) i decided i'd give it a try, to see if i haden't been wasteing my money on perhaps a small performance gain. 98 is the most expensive fuel you can get here (around 8$/gallon )

I filled up yesterday with 95 and i suppose theres quite some fuel in the lines as it wasn't untill i came back from work i noticed something changeing... the gaspedal seemd to become spongy... and suddenly it was all the way to the floor with the car barely accelerating like it would otherwise do with less than half the travle. it didn't run exacly bad... it seemed to run smoother but the power and response just wasn't there.

i think i'll refill early this tank with 98 to straighten things out and see what the FE hit is, but it seems from an economic and performance point of view high octane fuel is the best choise for my car.

well...now i know what i'm paying those extra 10 cents for... maybe a 50/50 mixture might work out better... i could find out by filling up with 98 halfway trough the tank.
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Old 03-04-2008, 05:39 PM   #2
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I don't think what you described is something due to the gas. The gas might cause the car to ping a little bit, in which case you could probably back the timing off a couple of degrees, but it shouldn't have the performance impact your describing.

I will be interested to see if your performance does come back.
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Old 03-04-2008, 07:53 PM   #3
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My parent's old Kadett (Actually a Vauxhall Astra) with the 1.3 motor ran fine on 96 RON unleaded. Also confused as to why you're using a 1.6 carb, generally makes motors a bit "difficult" and usually thirstier when you upsize the carb without having it rejetted for that application.
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Old 03-04-2008, 08:09 PM   #4
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Quote:
Originally Posted by Gary Palmer View Post
I don't think what you described is something due to the gas. The gas might cause the car to ping a little bit, in which case you could probably back the timing off a couple of degrees, but it shouldn't have the performance impact your describing.

I will be interested to see if your performance does come back.

I agree. It shouldn't make that big of a difference in power. um, I don't see your car even needing 90-91. hell, I run 87 on a 9.1 compression, maybe a little more cause I have the japan engine. you need a higher octane when you increase compression, which increses heat. what the hells the compression ratio of your car anyway.

all an octane rating is it ability to resist detonation. your car's not going to run better or worse. running premium in a car that doesn't need it isn't going to do ****.
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Old 03-04-2008, 10:16 PM   #5
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same odd thing with my chevette, says it can run E10 as long as its 87 octane or higher. which ours is. if i fill up with 90 octane(midgrade) it instantly gets 5-10 more mpg!!! it drives the same, might be a bit peppier but barely noticeable.
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Old 03-04-2008, 11:47 PM   #6
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well it was only my first impression, i'll drive it again today, but there definately was something going on there... i can't think of anything that would have otherwise caused such a behavior, but A-B-A testing should be

the 1.6 carb was just a replacement....the old one had a tiny gasket on one of the regulator screws that was leaky, and the thing just wouldn't tune, this one is the same, exept for the jets maybe, but since it ran much better and got better FE with the new carb i left it as it was.... maybe swapping the jets in from the original carb would do some good
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Old 03-05-2008, 05:01 AM   #7
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Originally Posted by lunarhighway View Post
in belgium we have a choise of 95 and 98 RON octane fuel

wich according to wikipedia would be the equivalent of 90-91 and 94 in the us
there's a 10 cent difference/liter in price

98 is recomended for my engine, wich is carburated so it isn't going to adjust for anything like modern engines do. but since i recently read in the manual it could also run 95 (with the notice "if nocking occurs see your dealer for engine adjustments..." talk about engine management) i decided i'd give it a try, to see if i haden't been wasteing my money on perhaps a small performance gain. 98 is the most expensive fuel you can get here (around 8$/gallon )

I filled up yesterday with 95 and i suppose theres quite some fuel in the lines as it wasn't untill i came back from work i noticed something changeing... the gaspedal seemd to become spongy... and suddenly it was all the way to the floor with the car barely accelerating like it would otherwise do with less than half the travle. it didn't run exacly bad... it seemed to run smoother but the power and response just wasn't there.

i think i'll refill early this tank with 98 to straighten things out and see what the FE hit is, but it seems from an economic and performance point of view high octane fuel is the best choise for my car.

well...now i know what i'm paying those extra 10 cents for... maybe a 50/50 mixture might work out better... i could find out by filling up with 98 halfway trough the tank.
I'll shoot in the dark as I don't have anything really to see.

But, perhaps, you've got a carbon build up in the combustion chamber. Maybe it's related to the carb, maybe it's related to something else, I don't know.

But as carbon builds up, and builds up in unique places within the combustion chamber, it can change the flame pattern. That increases the "need" for the engine to have a higher octane fuel.

Maybe it just needs to be decarbonized to return the combustion chamber to normal.
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Old 03-05-2008, 05:46 AM   #8
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though, detonation from carbon build up has to be rare, cause I've never heard it or seen it. the question is what extreme conditions (mechanicly, a/f mixture, pcv, etc) have to occur to build significant carbon build up. or is it gas related. the 10% ethenal in some fuels
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Old 03-05-2008, 05:51 AM   #9
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maybe.... i've driven the car to work today... it's drivable, but it still needs more throttle to get going like it used to. this morning with a cold engine it was really bad tempered (but my automatic choke is having issues sometimes so that might not be related... unless the 98 would cause the temperature to rise faster wich would in turn make the choke come off sooner)

might running some acetone in the fuel work for the carbon if it would be there.

i've been looking for info on my engine but i can't find anything detailed. all i know is that it's an S version the S versions of opel engines had about +15HP over the normal version with the same displacement, and they where more optimised for high octane, but i don't know what exactly is different... maybe the timeing or something. or maybe the carb wich is a twin barrel. (i think ... pierburg 2E3)
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Old 03-05-2008, 06:52 AM   #10
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though, detonation from carbon build up has to be rare, cause I've never heard it or seen it. the question is what extreme conditions (mechanicly, a/f mixture, pcv, etc) have to occur to build significant carbon build up. or is it gas related. the 10% ethenal in some fuels
When I was in the lawn and garden industry, we saw it a lot.

Similarly, we see it in racing engines with fuels that leave a lot of carbon.

Really has something to do with combustion chamber shapes, fuel additives, lots of variables.
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