Fuel Grades and CHT's - any impact?

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slow.bus
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Fuel Grades and CHT's - any impact?

Post by slow.bus » Tue Jul 14, 2015 9:33 am

Country gas station I went to this weekend was out of all gas except "regular" ... no mid grade and no premium.
--- 87 regular, 89 mid, 91 premium ... note this is Canadian gas ratings, not USA

I typically put premium in the camper (recommend by mechanic), but suspect that regular should not cause any major issues with my dialed back timing.

Oddly, it seemed as if I ran cooler CHT's since I put in the lower grade (est. 10 degrees) . Yes, many other factors can be at play - but I have made this same trip 3 weekends in a row now and watch the temps (many hills) - and winds were about the same as always - and my overall gear was about the same (but 1 less person in car) - outside temps about the same ... traffic about the same ... speed about the same ...

Any possible scientific truth here ... cheaper gas burns faster if I recall ... does the grade difference act a bit like a timing change? Or was I just imagining it ... or just all sorts of small variations adding up

I am making same trip again this weekend - and will stick with the mid-lower grade gas to see if the trend continues
1981 Westfalia
Dents & Dings, but no Rust

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Amskeptic
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Re: Fuel Grades and CHT's - any impact?

Post by Amskeptic » Thu Jul 16, 2015 10:24 am

slow.bus wrote:Country gas station I went to this weekend was out of all gas except "regular" ... no mid grade and no premium.
--- 87 regular, 89 mid, 91 premium ... note this is Canadian gas ratings, not USA

I typically put premium in the camper (recommend by mechanic), but suspect that regular should not cause any major issues with my dialed back timing.

Oddly, it seemed as if I ran cooler CHT's since I put in the lower grade (est. 10 degrees) . Yes, many other factors can be at play - but I have made this same trip 3 weekends in a row now and watch the temps (many hills) - and winds were about the same as always - and my overall gear was about the same (but 1 less person in car) - outside temps about the same ... traffic about the same ... speed about the same ...

Any possible scientific truth here ... cheaper gas burns faster if I recall ... does the grade difference act a bit like a timing change? Or was I just imagining it ... or just all sorts of small variations adding up

I am making same trip again this weekend - and will stick with the mid-lower grade gas to see if the trend continues
Premium burns slightly slower, maybe more out past the exhaust valves? I use horsepiss/kerosene cheapo in all my VWs since forever.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

slow.bus
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Re: Fuel Grades and CHT's - any impact?

Post by slow.bus » Fri Jul 17, 2015 6:14 am

but what type of hay do you feed your horse ... or do they graze ... and is it male or female? Hormones mess up everything. I NEED the details
1981 Westfalia
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Randy in Maine
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Re: Fuel Grades and CHT's - any impact?

Post by Randy in Maine » Fri Jul 17, 2015 7:17 am

OK I will bite....

Why would you run premium 93 octane in a relatively stock VW bus engine?
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slow.bus
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Re: Fuel Grades and CHT's - any impact?

Post by slow.bus » Fri Jul 17, 2015 10:21 am

the simple answer is that I was told to by my engine builder.

he is a well known supplier and builder (but I am choosing not to share his name - so we do not make this a discussion about him) - and when the new / fully rebuilt motor was installed last year - he indicated I should run premium (91 RON in Canada ... 93/94 is hard to come by locally).

perhaps that was just during break-in ... regardless, since he said that - I have always tried to run 91

I am certainly open to changing - just never though much of it - saving a few $ is a good thing, I just never put much though into it until this week when I could only buy regular and noticed the CHT's

what do people here typically run (other than kerosene and horsepiss) and what are the known / believed pro's and con's as it relates to our engines? I am fairly well aware of the debates for normal FI modern cars, and the "needs" for premium for turbo's and high compression engines etc
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Randy in Maine
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Re: Fuel Grades and CHT's - any impact?

Post by Randy in Maine » Fri Jul 17, 2015 10:38 am

Stock US buses were and are set up to run 87 octane fuel as it is determined today ( want to say that the change in determining octane as well as horsepower in the US happened in about 1974).

If you want to run 91 or 93 octane, go for it. It is your money, not mine.
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wcfvw69
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Re: Fuel Grades and CHT's - any impact?

Post by wcfvw69 » Fri Jul 17, 2015 11:18 am

I've only ever run 87 octane gas in my VW's in over 35 years of driving them. These stock engines have lower compression and don't require the higher octane gas. I also had a 911 that said it "required" 91 octane fuel. I ran 87 in it w/no issues at all.

There was an article I can't find on the difference between the low octane fuel and the high octane fuel. It clearly stated there wasn't much bang for the buck in buying the higher octane fuel and it wasn't needed.
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Re: Fuel Grades and CHT's - any impact?

Post by asiab3 » Fri Jul 17, 2015 12:54 pm

Make sure we're not comparing apples to oranges, and note which method we're measuring octane by on an international thread. 91 RON is about the same as 87 R+M/2, isn't it?

I've never had issues with the cheapest fuel I can find, as long as the station looks to receive new fuel more than every decade or so. Of course, this is on a low compression 1584. I built mine with low-ish compression to take it down to Baja and not worry about fuel quality.

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145k miles with me.
322k miles on Earth.

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Re: Fuel Grades and CHT's - any impact?

Post by slow.bus » Fri Jul 17, 2015 1:45 pm

That was my concern too - and I am afraid I confused the systems too

I had to double check - my normal gas is / was 91 octane ... what I put in recently was 87 octane. Not RON
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slow.bus
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Re: Fuel Grades and CHT's - any impact?

Post by slow.bus » Sun Jul 19, 2015 4:46 pm

.... wow, this cheap gas is great stuff :)

Drove same / regular weekend route again and put on about 400km - 200 km almost exactly each way.

Again CHT's slightly lower - but also noticed better fuel economy - was 12L / 100km on the way up (more uphills) and 11.5l / 100km on the way back. I have been averaging 12.5-13 on premium on the same / very similar trip all spring / summer with varying loads of gear. Won't make that trip again until fall - but will try premium again to confirm suspicions
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Re: Fuel Grades and CHT's - any impact?

Post by Amskeptic » Tue Jul 21, 2015 10:18 pm

slow.bus wrote:.... wow, this cheap gas is great stuff :)

Drove same / regular weekend route again and put on about 400km - 200 km almost exactly each way.

Again CHT's slightly lower - but also noticed better fuel economy - was 12L / 100km on the way up (more uphills) and 11.5l / 100km on the way back. I have been averaging 12.5-13 on premium on the same / very similar trip all spring / summer with varying loads of gear. Won't make that trip again until fall - but will try premium again to confirm suspicions
I do not have the sophisticated measurement/analysis capability to find cause and effect with gasoline octane versus performance versus CHTs. Then again, I have never put premium in my VWs, so I can't say that I would or would not notice a difference . . .
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: Fuel Grades and CHT's - any impact?

Post by slow.bus » Wed Jul 22, 2015 12:14 pm

Amskeptic wrote: I do not have the sophisticated measurement/analysis capability to find cause and effect with gasoline octane versus performance versus CHTs. Then again, I have never put premium in my VWs, so I can't say that I would or would not notice a difference . . .
Colin
I am very curious to know if anyone else ever 'observed' or 'tested' this ... was not something I planned to do or find out. While by no means scientific, what I have seen so far is what I have seen. Would have likely never noticed anything except for the fact that I drove the same basic trip for many weekends in a row.
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Re: Fuel Grades and CHT's - any impact?

Post by airkooledchris » Wed Jul 22, 2015 5:02 pm

If I had the ability to get pure gasoline without the bullshit 10% ethenol in it like they do in California, I would use it in a heartbeat. But I won't bother paying for higher octane gas/eth blend because our motors don't need it.

Some folks were spreading false rumours around, a while back now, that it would help keep your head temps lower.
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Bleyseng
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Re: Fuel Grades and CHT's - any impact?

Post by Bleyseng » Wed Jul 22, 2015 9:55 pm

In engines with higher combustion ratio's it does help with pre ignition...I always run it in my 914 with 9 to 1 CR or it pings like mad, not good.
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