DAT240Z Posted July 22, 2002 Share Posted July 22, 2002 Yesterday I fill up my tank and went on a 210 mile trip at 105 miles my gas gauge was reading a little less than 1/2 full so I fill up and check my miles it took 6.8 gallons to fill the tank( 76Z). Which amount to 15.4 mpg? I was hoping to do better than that or am I wrong. I was thinking around 25mpg. This is the set up I have 83zxt, 1980 sp. and the stock 240z rear end I'm running about 8-9psi boost. I did notice at 70mph the rpm was around 3500, that seam a bit high. Is three a better tranny, rear end combo that would give me better mpg with good performance? Quote Link to comment Share on other sites More sharing options...
Mike C Posted July 22, 2002 Share Posted July 22, 2002 I think the T5 is the best trans as its first gear is the closest to the 4 speeds and it has the most overdrive. 22% I believe. With 3.36 however (If your 240 rear is stock, I would have thought rpm would have been a little lower. Mine is about 3000 at 70 with an 80 model 5 speed and 3.54 gears. I have 25" tall tires which can make a difference as well. Sounds like you may have 3.90s in your car? Quote Link to comment Share on other sites More sharing options...
DAT240Z Posted July 22, 2002 Author Share Posted July 22, 2002 Hi, my rear end is stock, and i'm running 195/60/14 tires Quote Link to comment Share on other sites More sharing options...
SHANE Posted July 22, 2002 Share Posted July 22, 2002 i would get about 10-11 MPG Quote Link to comment Share on other sites More sharing options...
DAT240Z Posted July 22, 2002 Author Share Posted July 22, 2002 Nat I have new wires, plugs, cap rotor. one thing I have notice is that car only runs when the timing is fully retarded, if I try to advance it just little it runs shitty and have no pull to it. At idle it jumps around from 1k to 500 and dies any ideas? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 22, 2002 Share Posted July 22, 2002 First thing I would get your ignition timing problem solved. Maybe your distributor drive is off a tooth - you should be able to idle well with 20 degrees advance (20BTDC), and it should not waver. Check your idle switch on the throttle body, and make sure it closes when the throttle is closed - this can cause an unstable idle, as the ignition timing will wander with rpm. Past that, you may need a new O2 sensor or a new fuel pressure regulator (both can cause over-richening), but I highly recommend an air/fuel mixture gauge and a fuel pressure check before throwing money into parts you may not need. Once you fix this issue, you can dig deeper. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted July 23, 2002 Share Posted July 23, 2002 The 82-83 ZX trans has the best overdrive, it is a .745, and it is a good match to 3.90's or 3.70's, but its gear spacing is not good for numerically lower gears. You should turn about 3k rpms at 75 mph. The T5 is also good and it has slightly less overdrive, .78. I have this trans in my car right now, and with 3.90's, I run about 70 mph at 3k rpms. I ran more mph when I had 3.56's back there. I get perhaps 20 mpg at best. Probably closer to 15, I can't stay out of the boost. Make sure you don't have a fuel leak too. Datsuns get bad mileage once the rpm's get over 3k, at least that has been my experience. Keep below that, and you should be happier. Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted July 23, 2002 Share Posted July 23, 2002 on a trip last summer i got 24 mpg with the ac on.i have a 77 with 81zxt engine.i run a 3.7lsd with a 82 na trans. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 23, 2002 Share Posted July 23, 2002 Your mileage is extremely low. Even with stock electronics, you should break mid 20's. I am running a factory Z31 ECU and I get 27 mpg (91 octane, 5000' elevation, averaging 80+ mph). Check your ignition timing, plugs, wires, cap, rotor, O2 sensor, and fuel pressure regulator. Quote Link to comment Share on other sites More sharing options...
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