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Thread: one-third of a tank.... $37!

  1. #1
    Vulture of The Western World Eric's Avatar
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    one-third of a tank.... $37!

    My Trans-Am reeequires premium, which is well over $4 per gallon right now. I just topped off the tank; $37 and change.... used to be able to fill it for that.....

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    Re: one-third of a tank.... $37!

    Quote Originally Posted by Eric
    My Trans-Am reeequires premium, which is well over $4 per gallon right now. I just topped off the tank; $37 and change.... used to be able to fill it for that.....
    In some sense that is OK. There is a great deal of satisfaction in owning that kind of car and it's use is discretionary.

  3. #3
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by jdm
    Quote Originally Posted by Eric
    My Trans-Am reeequires premium, which is well over $4 per gallon right now. I just topped off the tank; $37 and change.... used to be able to fill it for that.....
    In some sense that is OK. There is a great deal of satisfaction in owning that kind of car and it's use is discretionary.
    True!

    I thank the Motor Gods that I have it as a toy - not everyday transpo... I don't think I put more than about 700 miles per year on it these days... if that... so a tank does last awhile...!

  4. #4
    D_E_Davis
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by Eric
    ... I don't think I put more than about 700 miles per year on it these days... if that... so a tank does last awhile...!
    While the really good parts slowly evaporate (s).


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    Re: one-third of a tank.... $37!

    Quote Originally Posted by D_E_Davis
    Quote Originally Posted by Eric
    ... I don't think I put more than about 700 miles per year on it these days... if that... so a tank does last awhile...!
    While the really good parts slowly evaporate (s).

    The secret is to fill it in the summer.

  6. #6
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by D_E_Davis
    Quote Originally Posted by Eric
    ... I don't think I put more than about 700 miles per year on it these days... if that... so a tank does last awhile...!
    While the really good parts slowly evaporate (s).

    I always keep the tank near full (top off every time I drive) so that keeps evaporative loses down, I think - and helsp keep the fuel fresh, too. The octane seems to maintain its value - because (believe me) I'd know right away if the fuel quality was sub-par. These old Pontiacs are very sensitive to octane and remember, no knock sensor electronics. With appx. 9.5:1 CR (high for a Pontiac) detonation is always right around the corner.....

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    Re: one-third of a tank.... $37!

    Quote Originally Posted by Eric

    I always keep the tank near full (top off every time I drive) so that keeps evaporative loses down, I think - and helsp keep the fuel fresh, too. The octane seems to maintain its value - because (believe me) I'd know right away if the fuel quality was sub-par. These old Pontiacs are very sensitive to octane and remember, no knock sensor electronics. With appx. 9.5:1 CR (high for a Pontiac) detonation is always right around the corner.....
    OmiGod Eric Eric Eric!
    Too much of your good wife's pre-menopausal. Go have some children. Or as nurses say to me, "you ought to get out more often"...

    Fuel within margins of volatity is a result of crude. Refined stuff with additives is down to various needs. Gasoline, diesel, fuel-oil.
    It smells. It drives engines. It doesn't go 'off' any more than any volatile compound.

    The big Oilcos have to judge not only how to get stable supply but how to invest in the plant to feed industry and cars.

    (I can just hear Henry fulminating)
    Would you invest? Free-market capitalist that you are?
    Next you will be making a private tank of leaded 96-octane for your beloved... who is in West Virginia reading about movie stars in the hairdressers?
    Women OTOH are practical. Imagine your good wife in summer dress smiling on a bicycle.
    Cars are for fun.
    Real life is cold, ...

    The Chev LS1 Aus-built sedan has a worse wind-whistle at 55mph than ever. Completely incurable. It's a pile of s**t., with only a strong motor, and even that after 6 years and 70K miles all the front pulleys make a noise like God is dying, when cold, no estimate available for repair, even after several trips to very good GM mechanics. "Wait 'till it breaks"...
    So when I fire up a GM LS1., I get 15W40 at freezing a noise like ... first it fires (just like my BMC Minis) and settles to about 1,200rpm, whining, noisy, after 70K miles always serviced, and clunks and whirrs and squeals. Cold sepentine rubber belts. Misalignment? Cannot be repaired with $.

    Warm, it runs fine, and over 75mph the wind and road roar drowns out the sealing whistle.
    But we cannot drive even near 75mph.

    The car is s**t. But you saved us in WW2 . I'm curious. What does the US export?

  8. #8
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    "OmiGod Eric Eric Eric!
    Too much of your good wife's pre-menopausal. Go have some children. Or as nurses say to me, "you ought to get out more often"...

    Fuel within margins of volatity is a result of crude. Refined stuff with additives is down to various needs. Gasoline, diesel, fuel-oil.
    It smells. It drives engines. It doesn't go 'off' any more than any volatile compound. "


    My understanding is that gasoline can lose octane value over time due to evaporative losses and chemical oxidation - is that not so?

    Bear in mind that my old Pontiac V-8 is nothing like your modern LS1 except in the most basic way. The 455 is cast iron (yours is aluminum) and the design doesn't tolerate CR much above 9.5:1 without the use of super unleaded (at the very least). Anything more than 10.0:1 and you pretty much have to burn Sunoco race gas, etc., or dial back the timing - or risk detonation.

    The LS1 can easily run close to 11.0:1 on pump gas due to its layout and materials as well as the ECU...

    FYI, the factory CR for the 1976 455 was 7.5:1 .... really. The 400 V-8 in Pete's '79 TA runs something like 8.2:1 CR.... which was considered "high compression" for the time/engine.

  9. #9
    D_E_Davis
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by Eric
    FYI, the factory CR for the 1976 455 was 7.5:1 .... really. The 400 V-8 in Pete's '79 TA runs something like 8.2:1 CR.... which was considered "high compression" for the time/engine.
    So, how come we could run 9.75:1 in the Ford flatheads, on the street?


  10. #10
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by D_E_Davis
    Quote Originally Posted by Eric
    FYI, the factory CR for the 1976 455 was 7.5:1 .... really. The 400 V-8 in Pete's '79 TA runs something like 8.2:1 CR.... which was considered "high compression" for the time/engine.
    So, how come we could run 9.75:1 in the Ford flatheads, on the street?

    I dunno!

    But these are very different designs, too. There is something about the layout of the Pontiac V-8's cylinder head that renders the engine very sensitive to octane. Compression ratios after 1971 never rose higher than 8.5:1 from the factory (including the mighty '73-'74 SD-455 engine). Unlike Chevy and many other V-8s, the compression ratio is determined not by piston shape but by combustion chamber volume; use of the early (pre-1971) heads that had smaller cc chambers and CR above 10.0:1 almost always leads to detonation if pump gas is used.

    There are now aftermarket aluminum heads that allow higher CR - but only in the range of 9.5:1 or so. Higher CR in the Pontiac V-8 risks problems unless one uses race gas.... .


  11. #11
    Administrator Ken's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by Eric
    Quote Originally Posted by D_E_Davis
    Quote Originally Posted by Eric
    FYI, the factory CR for the 1976 455 was 7.5:1 .... really. The 400 V-8 in Pete's '79 TA runs something like 8.2:1 CR.... which was considered "high compression" for the time/engine.
    So, how come we could run 9.75:1 in the Ford flatheads, on the street?

    I dunno!

    But these are very different designs, too. There is something about the layout of the Pontiac V-8's cylinder head that renders the engine very sensitive to octane. Compression ratios after 1971 never rose higher than 8.5:1 from the factory (including the mighty '73-'74 SD-455 engine). Unlike Chevy and many other V-8s, the compression ratio is determined not by piston shape but by combustion chamber volume; use of the early (pre-1971) heads that had smaller cc chambers and CR above 10.0:1 almost always leads to detonation if pump gas is used.

    There are now aftermarket aluminum heads that allow higher CR - but only in the range of 9.5:1 or so. Higher CR in the Pontiac V-8 risks problems unless one uses race gas.... .

    And yet 'bikes, which are also four stroke engines, are able to use CRs in the 11.5:1 to 13.5:1 range, still using straight unleaded petrol, without problems. I think that combustion chamber shape, piston crown shape, the amount of swirl in the incoming charge, the location of the spark plug(s) all of which control the shape and speed of the flame front are significant aspects of cylinder head design. Even back in the 60s we were able to use CRs of 10+:1 on modified minis although we did have access to 4 Star leaded gas. Increasing the CR enables improved thermal efficiency and improved cylinder head and intake/exhaust port design improves volumetric efficiency (I think I've got that right - agreed Rob?). I've only seen one or two V8s but they looked very crude and heavy - performance by virtue of large engine capacity rather than effective design. The Rover V8 was a very tunable engine and significant power increases could be gained by good head modification. I remember a Mustang belonging to one of my 'tuning' fraternity (Jock Topen) being transformed from a reasonable muscle car to a fiery beast by the application of a week or so spent 'improving' on the, rather crude, initial build/design.

    Ken.
    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

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    Re: one-third of a tank.... $37!

    GM run 11:1 c/r in their LS series engines (LS2) with a recommendation to use 87.

  13. #13
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by robmcg
    GM run 11:1 c/r in their LS series engines (LS2) with a recommendation to use 87.
    Yes. The LS1 has the advantage of being aluminum - and its combustion chambers/cylinder head design is such that high CRs on lower octane fuels are viable.

    The Pontiac V-8 is a design that dates back to 1955 - when leaded premium was readily available. It was never re-engineered (as the modern small block Chevy has been) so when low-octane unleaded appeared in the early-mid 1970s, the "solution" was to modify the existing head design with huge combustion chambers (some as large 112 cc) to drop CR down under 8.5:1. - and from 1973 through 1981, most Pontiacs V-8s had CRs in the 7.6:1 range; only the SD-455 and the W72 "TA 6.6" 400 had CRs in the 8 range.... .

    Now, had the design been thoroughly modernized - alloy bnlock and heads, new cylinder heads/combustion chamber layout, modern roller-style cam, EFI, etc. I'm sure it, too, could run on high CR like an LS series V-8. But it was not to be. The line died in 1978 - when the last 400s were made...


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    Re: one-third of a tank.... $37!

    Electronic ignition allows up to what you call 87 unleaded, with conservative timing And a knock sensor.

    All engines are a mix of fuel and 'timimg'. It's no great mystery.

    If you want full power you run a bit rich. If you want economy, you don't. Modern cylinder heads are little different from, say, a 1948 XK Jag.

  15. #15
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by robmcg
    Electronic ignition allows up to what you call 87 unleaded, with conservative timing And a knock sensor.

    All engines are a mix of fuel and 'timimg'. It's no great mystery.

    If you want full power you run a bit rich. If you want economy, you don't. Modern cylinder heads are little different from, say, a 1948 XK Jag.
    I can run 16 degrees BTDC on 93 octane "super" with a CR of about 9.0:1 - that's it. Any more timing (or compression) and I'd need Sunoco 260 100 octane race gas.

    Aluminum really helps dissipate heat relatiive to cast iron - and that by itself allows higher CR.




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    Re: one-third of a tank.... $37!

    Quote Originally Posted by Eric
    Aluminum really helps dissipate heat relatiive to cast iron - and that by itself allows higher CR.
    That is like very clear. And we know. What do you take us for?

    Most regulars here know that already.

    I give up.

    Rob (from 1993 CARS)

  17. #17
    Vulture of The Western World Eric's Avatar
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    Re: one-third of a tank.... $37!

    Quote Originally Posted by robmcg
    Quote Originally Posted by Eric
    Aluminum really helps dissipate heat relatiive to cast iron - and that by itself allows higher CR.
    That is like very clear. And we know. What do you take us for?

    Most regulars here know that already.

    I give up.

    Rob (from 1993 CARS)
    No need t get huffy! Not everyone here does know that, for one!

    You asked for an explanation about why my old Pontiac has low CR and is prone to detonation if lower octane fuel is used... I tried to tell you why...

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