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Posted by: Jeffs9146 Sep 2 2003, 06:30 PM

As it says above, does the original 2.0 914/6 use leaded fuel or is unleaded ok? The book says 98 octain but it doesn't say anything about Leaded or Unleaded. My 74 had an Unleaded Only sticker but the 6 doesn't!

Jeff

Posted by: ArtechnikA Sep 2 2003, 06:44 PM

the original 914.6 used leaded fuel because that's all there was in 1970 unless you were in one of the rare areas where Amoco 100 Clear was available. (i wasn't).

it is required in catalytic convertor cars, and possibly it's recommended for thermal reactor cars too; i don't know if your '74 is a cat car or not. (911's were, lots of other cars were too - but some weren't. BMW tried for a long time to get by with thermal reactors and avoid the unleaded requirement - and those last few cars were dogs...)

it was an issue for American muscle cars that were trying to run valve seats directly in their cast-iron heads. aircooled cars have always run very hard valve seat inserts and are unaffected by the absense of lead - usually, they're better off without it.

BTW - that 98 number was a Research number; it's approximately equivalent to the 92-94 "AntiKnock Index" Research-Motor average posted for conventional unleaded premium.

Posted by: Jeffs9146 Sep 2 2003, 06:55 PM

OK so if I am hearing you right; Unleaded is ok and Octane Booster would help get the 92-94 numbers!

Thanks for the info!

Jeff

Posted by: sixerdon Sep 2 2003, 06:56 PM

You got it Rich. Those were the good old days when they used to call it "High Test" and there used to be an oval sticker on the expansion tank. Gas used to smell a lot different then than it does now. A good drag on the fumes would make you smile and would give you the posted times you read in those old articles!
Everyone with 914's be it 4 or 6 cyl. should take care of what information is useful in the owners manuals. A lot of the information is obsolete.
Don

Posted by: URY914 Sep 2 2003, 06:57 PM

Therefore Rich you are old enough to remember leaded gas and others here have never heard of it.

Sorry

Paul

Posted by: ArtechnikA Sep 2 2003, 07:00 PM

except that you can't possibly add enough Octane Booster to get those numbers - just run pump premium - it'll be fine.

you gotta read the fine print on the octane booster label - when they talk about raising the octane rating "4 points" they mean from 92 to 92.4

just run pump premium unleaded.

Posted by: vsg914 Sep 2 2003, 07:03 PM

Jeff, if ya want 93 octane ya gotta move to Oklahoma!

Posted by: ArtechnikA Sep 2 2003, 07:04 PM

no need to be sorry, i neither advertise nor conceal that i am the same age as my '53 356 1500N Coupe; for the arithmetically challenged, that means i'm 50. most days i don't feel it; some days i can feel it creeping up on me...

oh - i MIGHT also have heard of leaded gas in flight school where we learned 100LL is the blue stuff called for in the POH (Pilot's Operating Handbook) ...

Posted by: ArtechnikA Sep 2 2003, 07:07 PM

local Sunoco stations here in PA have 94 ...

interestingly, there's a section on octane in the Bosch MFI book (spent a lot of time with that this weekend getting my idle mixture and 6 airflows balanced...) that mentions that starting with the 2,4 MFI engines 87 Octane is specified, and due to the slower burn rate of higher octane fuels, runnign higher octane fuel can result in excessive CO levels.

just a thought for those 'more is better' discussions - especially for anyone having trouble getting a car though an emissions test ...

Posted by: Andyrew Sep 2 2003, 07:12 PM

Leaded? Whats that?

jk.. actually I learned it when my dad got his car, that was the turning from dork to p-car freek.



Andrew

Posted by: Jeffs9146 Sep 2 2003, 07:14 PM

I think I will stay in California, thanks!



OK, no lead and no boost!! Cheaper is better!! It won't matter when I get the 3.2L!

Jeff

Posted by: mikester Sep 2 2003, 08:13 PM

Just a note, check the method used to calculate the octane rating.

The octane rating is ROZ/RON where as pump octane is calculated as (R+M)/2. The label inside my porsche shows the method used; with a 91 as the number. The factory sticker is for RON only where as pump octane is an average of RON and MON ((R+M)/2). If your engine is not stock and of higher compression or not properly cooled and running warm then more octane may be required but a stock engine (4 cylinder, I don't have a six so I don't know sixes) with proper cooling shouldn't require any a higher than 87 octane rating. If you've got the european domed pistons, your compression ratio is higher, thus it may require higher octane to reduce preignition.

Octane does not prevent the fuel from burning per say, it prevents uncontrolled burning. With proper compression, cooling and timing you won't have to waste money on higher octane to get the proper performance from your engine.

Posted by: ArtechnikA Sep 2 2003, 08:47 PM

"ROZ / RON" is not a method, it's just bilingual -- Research Octane Zeitung / Research Octane Number (same thing...). don't know what method the Europeans are using today (Jeroen ?) but the Research number was typically used in the early 70's -- it tends to produce a higher number for the same fuel and therefore the petroleum companiues liked it -- but the auto industry and "consumer groups" claimed the Motor number was closer to what an operating engine actually required. as a compromise, the number you now see posted is the average of the Motor and Research numbers. this change was mandated by Fedral law somewhere in the early 80's IIRC.

1,7's had a slightly higher static compression ratio and can use midgrade. the /6 owner's manual calls for premium. "should" it need it ? maybe not, and i don't recall any pre-ignition issues, but i'm not risking it nowadays with the 911 ...

Posted by: mikester Sep 2 2003, 08:52 PM

Yeah, I went back to my reading and edited my post accordingly. I'd say that more recent engines probably do require a higher octane - I'm simple stating the research I did with my little a$$ 1.8L. With the recent rise in gas prices and the knowledge of what octane was I came to these conclusions via some research on the net...

I didn't agree with all of it of course...

Posted by: drew365 Sep 3 2003, 09:17 AM

My car has 11.5:1 Mahle pistons. When I'm on the track I run 110 race gas, but when I drive on the street I use premium with booster. So I'm not really gaining much by using the booster. Luckily I don't drive on the street very much.

Posted by: ArtechnikA Sep 3 2003, 10:12 AM

yes, that's your static compression - but i bet you also have high-lift, high-overlap cams to take advantage of that compression at higher rpm. so considering all the charge leakage at lower revs, you actual dynamic compression could be pretty reasonable.

if octane booster is the difference between pinging and not, go for it - just one shouldn't be expecting miracles - and the sellers would like you to believe "4 points" means increasing from 92 to 96 but it doesn't. there's also diminishing returns, because higher-octane pump gas is more likely to already contain some of the chemical goodies in the booster stuff - and you don't get a linear percentage gain.

in olden tymes, we used to mix premium leaded and unleaded to take advantage of this effect -- adding just a little bit of tetraethyl lead to already premium unleaded raised its AKI a lot more than the same amount would increase the AKI of leaded gas.

i have also had to clean the orange manganese fouling from plugs after trying to run too much over-the-counter octane booster - wasn't worth it...

Posted by: Dave_Darling Sep 3 2003, 11:23 AM

Are you sure your 74 wasn't really a CA-spec 75? Unleaded is only required by cars with catalytic converters, and 74s did not come with them. I haven't seen a 74 with that sticker so far, just some 75s and 76es.

To reiterate, unleaded fuel is just fine for any and all 914s. None of them ever required lead in the fuel.

Oh, the difference between the RON and MON ratings of a given batch of gasoline is called that fuel's "sensitivity". RON is generally 8-10 full numbers higher than MON for the exact same fuel, so US pump octane ratings (average of RON and MON) will typically be 4-5 numbers lower than the RON (or ROZ, same thing in German) numbers listed in the owner's manual.

--DD

Posted by: Jeffs9146 Sep 3 2003, 03:23 PM

I think the OP had replace the tank when he rebuilt the motor! That must be the reason for the sticker!

Jeff

Posted by: redshift Sep 3 2003, 05:10 PM

Over near Stone Mountain, there is a place you can buy 114, it's a chain too, and it smells like the high test Mr. Carrol used to pump into my grandmaw's '67 Plymouth VIP...

..she used to say, "Fill 'er up!", and he'd say, "Check the oil, Mizzzzz Dixie?".. "Yep."

Self Serve... PATOOOOOOIE!

If I run anything higher than 87 (local?) in a stock 2.0/4, it runs very cold, too cold.



M

Posted by: Nemo914 Sep 3 2003, 09:02 PM

Wow, learned a lot on this thread. Here is an observation--I was having backfire/sputter problems on deceleration with my stock 72 1.7. I tried everything to fix it, including replacing the exhaust system. Then I had a thought that the problem started when I started using high octane gas. I switched back to 87 and the problem seems to have gone away?? Could this really have been my problem all along?

Posted by: redshift Sep 3 2003, 09:16 PM

Yes.

I haven't ever owned an injected 914 that liked anything expensive. It's hot here, and on a wicked summer day, they will barely idle sometimes on 'the good stuff'.

I guess air density is the big factor, in the very cold, they seem to run ok on it.



M