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

[Hrududu]

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.

[bpilati]

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.

[e_racer1999]

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

[agemeansnothing]

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

[e_racer1999]

there's a gas station over in el cajon that still sells racing gas i believe...

[Sailor Bob]

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.

[e_racer1999]

i bought gas at $4/gal yesterday

[e_racer1999]

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.

[Hrududu]

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.

[Hrududu]

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.

[DaveN]

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?

[e_racer1999]

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....