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Hrududu

My car needs premium, I'd rather it didn't.

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Ever since I replaced my head gasket last winter, my car has needed premium gas in order not to knock. With the recent gas prices I tried to put in midgrade (89) and the car did not like it one bit. It would hesitate and accelerate really rough and the knock was still there. Before I did the head gasket I was able to run regular 87 octane without issues, and now I have to run 91 or the car runs like crap. Could this be as simple as adjusting the timing? I did have to reset the timing when did the head gasket because I let the tensioner spring, but I made sure all the marks on the cam, crankshaft, and chain were lined up and used a light to set it. Would fooling around with the distributer help me out any? I'd just really lke to drive this every day again, but I can't do that with gas costing so much.

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Hmmmm, I've always use premium because I thought it matched the octane rating of regular in 1971. I believe that changing timing and/or compression ratio will change your fuel needs.

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With the milage these things get and the high octane fuel that must be an expensive fill up?

Mine runs great on the cheap stuff - that "cheap" is a relative term of course.

I'ld say our cheap price is higher than your good stuff at $1.19 9/10 a litre.

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With the milage these things get and the high octane fuel that must be an expensive fill up?

Mine runs great on the cheap stuff - that "cheap" is a relative term of course.

I'ld say our cheap price is higher than your good stuff at $1.19 9/10 a litre.

~$4.61/gal, not including conversion rates.

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it could be that the head gasket you put on was thinner than the previous one. that would do it.

They also re-surfaced the head, but they took off an absolute minimum. That was my assumtion that the new gasket, plus the shorter head may have raised compression, but who knows. The difference for filling up with premium over regular is only about $3 per fill up, but thats still almost an extra gallon of gas or a meal at Burger King. Every $3 adds up.

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There is a gas station here in town that sells 101, is there any other gas station like that where you guys are at??

Not at a station, but the drag strip sell the purple 100+ octane racing fuel. Thats not the point though. Im trying to LOWER the level of octane the car needs. It does fine on 91, but i would prefer to run 87 and save that $0.20 per gallon difference.

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All the early Z's were designed to run on 87 (MON+RON)/2 gas, but sometimes needed a bit more octane after carbon built up in the combustion chambers.

Do 77 Z engine controls include a knock sensor (retards timing if a mike hears pinging)? If so that circuit would make the engine hesitate and feel rough when it's knocking. If not knocking mild enough to leave the car driveable wouldn't make it hesitate or be rough during accelleration. Those symptoms sound like an engine controls problem, a wiring fault or a sensor or control unit going bad. If that's the trouble it might be causing the knock, too.

You've already checked mechanical alignment during reassembly. Enough about that.

My only other thought is that an edge of the (wrong) head gasket projecting into the combustion chambers would become a hot spot and cause knocking. Did anyone make sure the gasket openings really match the head?

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They also re-surfaced the head, but they took off an absolute minimum. That was my assumtion that the new gasket, plus the shorter head may have raised compression, but who knows. The difference for filling up with premium over regular is only about $3 per fill up, but thats still almost an extra gallon of gas or a meal at Burger King. Every $3 adds up.

if you run a higher compression, you get better fuel economy. at least that's what my dad told me years ago....

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Mine definately pre-fers the premium stuff...! I've thought about going cheaper and getting an octane booster additive, but I figure if she runs good on .20 cents per gallon more ....why add an additive...? Any thoughts...???

Chris...

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All the early Z's were designed to run on 87 (MON+RON)/2 gas...
I beg to differ. That may be the case for 280Zs and 260Zs, but not for 240Zs. The owner's manual for my '71 240Z says to use "a proper grade of gasoline of above 95 octane..."

Granted, that was not the same 95 that we see now as AKI or (MON+RON)/2, but I still believe that the old 95 is probably more than today's 89. I know that my late '71 will ping on today's 92 AKI if the timing is advanced much past stock, and even at stock timing on 89 AKI. Yes, there could be some carbon build up, but that doesn't change the fact that I need premium fuel. The reason doesn't matter. If you need it, you need it.

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my '72 L24 ran well on 87, as did my current flat F54/P79 combo.

of course, with the F54 and N42 (10.5:1) i'm going to be running 91 :D

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The book for my '72 (05/72) calls for a minimum octane rating of 87. It runs fine with the 87 we have today (I usually use Sunoco with an occasional tank of Texaco).

The book for my '71 (02/71) calls for "a proper grade gasoline of above 95 octane... If knocking occurs with the gasoline you are using, and it cannot be cured by slightly retarding the spark timing or other engine adjustments, it might be caused by the use of lower grade gasoline, then switch to the next higher grade fuel that will eliminate the knocking." I have gotten the '71 running, but not on the road yet so I cannot comment on how different grades of gas will impact it. It revs up like a rocket ship under no load, but I am assuming that I will be filling up with premium when it gets on the road under load.

Now, all that being said, both have E88 heads, but the '72 has a section in the book on the smog control devices that the '71 book does not address. So, I assume that the '72 was modified somehow to accept the lower octane gas as a pollution reduction effort. Can anyone elaborate?

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John, first you have (correctly) pointed out the difference in octane requirements for the differing years. This is because as the emissions laws tightened up, Nissan (and other makes too) lowered compression ratios. So the '72 needs less octane that a '71. It may be that only the '70 and '71 240Zs will NEED the higher octane, assuming they are stock and well-maintained.

As for the E88, I have found references to show that there were at least four major head variations that had the 'E88' casting mark. The very earliest were almost the same as the E31. I've heard these called "early E88s." These would have come on '71 cars right after the E31.

The second variation was for '72 cars and maybe late '71s as well, and had a different chamber size and shape than the E31, and had the lower compression ratio also. These days I've heard these called "small chamber E88s".

The '73s apparently came with an E88 with a larger chamber yet. These are referred to as "large chamber E88s".

Finally, the US 260Zs had an E88 with larger exhaust valves, and are often called, unsurprisingly, "big valve E88s".

Last, I'm a little surprised that your 2/71 car has an E88, as my 4/71 parts car had an E31. But maybe one or the other of these is not original.

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Thanks for the information on the E88 heads, Arne. I had heard of there being different ones, and was aware of the larger-valve variety for 260's, but you have laid this out for us very well. I appreciate that, because I think I now at last understand! I cannot vouch for the E88 on my early '71 as being an original mate to the block..... the engine # is 030185, and I'm pretty sure it is the original block to the car. The engine compartment data plate is missing, but the number falls in line with the range of block numbers for that approximate date of manufacture (according to those of close mfg. date listed in the "registry" ). Have you heard of any way to determine which head is which among the E88's without pulling them off for inspection? Were there any subtle casting mark differences, for instance? Maybe the lettering? I'll include a picture of the one mated up to my '71 in case there is any value to seeing it. (pause) I went out to look at my '72 & '73 E88's ..... the lettering & numbers on the later two years seems larger than the one on the '71. Also, the 'earlier?' one has a sort of a 'flat' cast in it just between the "4 plugs right where it mates with the block. I'll post pix of what I am trying to describe. Maybe those differences mean something ? I have another E88 that I can check out too, but I have no idea of the origin of the head & therefore can't try to date it. It would be great to figure a way to discern among them without having to pull them.... I'm thinking about putting one of them on my driver to eliminate a persistent valve tap that can't be adjusted out (seems to be excessive wear on the lobe where the stethoscope tells me the tap is.) In light of the differences among E88's I'm not sure now that I want to swap the whole head.... maybe just the cam and mated lifters from another head. I'd prefer not to have to start using high octane fuel as a result of getting the valve tap resolved! I guess that's where this thread started, so we've come full circle. (I guess if we start really talking heads a new thread should be created?)

Also, on the '71 block picture, what is the electrical (I guess) unit just to the right of the dipstick? My others don't have that thing. Any clue what it is?

Thanks again for the valuable information, Arne.

(Both of these pictures are of the same head on my '71.)

post-9676-14150800487881_thumb.jpg

post-9676-14150800488412_thumb.jpg

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Hey DeesZ, looks like your block in the first pic, is a bit wet, kinda like mine is nowadays. Mine has been weeping coolant from the gasket to the outside of the block, and I have to top off the radiator every once on a while.Have you been experiencing the same thing? I recall that our old friend Bambkiller mentioned he had this issue for about three years before he replaced the gasket.

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There is a gas station here in town that sells 101, is there any other gas station like that where you guys are at??

In Espanola?? Where abouts? Love to buy some.

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Also, on the '71 block picture, what is the electrical (I guess) unit just to the right of the dipstick? My others don't have that thing. Any clue what it is?

I'm guessing that's te male side of a plug for a block heater used during winter months to keep the water in the block from freezing and cracking the block.

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91 is premium? You Americans really get a raw deal on fuel.

In Kansas we sure do. Its leftover fuel from Oklahoma and the highest it goes is 91. In lots of other states like Indiana they have 93 for premium.

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