Fuelrags Posted August 14, 2008 Report Share Posted August 14, 2008 Hey Guys, Supposedly the Hitachi Carburator was just replaced when I bought my 620. I'm averaging 18 MPG. does that sound right for a 4-Speed? I have an Aftermarket Air Cleaner and just had a 2 1/4 inch full Exhaust installed....Martin Quote Link to comment
datsunaholic Posted August 14, 2008 Report Share Posted August 14, 2008 Unfortunately, that's about what my Mom's '73 w) L16 gets. Sometimes low 20s, but that's driving a constant speed UNDER 55mph (I believe the best mileage I got was at around 45MPH. The mileage fell off a cliff above 55, mid teens around 60MPH). It's those darn 4.88:1 rear gears coupled with the 4-speed. Yes, it's low, but it's that low compression head used to make it run on 87 octane. The L18s and L20Bs actually get better mileage, but they also had better gear ratios. I can say that that monster exhaust won't help gas mileage. I got around 25 with my '76 KC, until I put a 5-speed and a Weber on. Then it was 32. Quote Link to comment
72 327 Posted August 14, 2008 Report Share Posted August 14, 2008 If it helps or makes you feel any better I get 8 MPG in my 72' 620. Quote Link to comment
DatDoug Posted August 14, 2008 Report Share Posted August 14, 2008 If you want good mileage talk to Datsunfish. He's got a set up inj his 72 620 thats getting him 30+ mpg! Of course he only weighs bout 98 pounds:fu: Quote Link to comment
banzai510(hainz) Posted August 14, 2008 Report Share Posted August 14, 2008 get a electronic ignition adjust the mixture and time the motor again. drive it very conservatively. Dont hammer the pedal down always using the acell pump on the carb and drive a constance 55mph. I got 26 mpg out of my 521 when I drove more on the hiway. But average is 22/23mpg. A 1.75 -2inch exhaust would be more than enough to handle a semi built L motor Quote Link to comment
]2eDeYe Posted August 14, 2008 Report Share Posted August 14, 2008 Yep, get some backpressure and it'll run more efficiently, prolly get a bit more power too. Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 If it helps or makes you feel any better I get 8 MPG in my 72' 620. OK NOW,THAT'S WORTH IT!:cool: So how much of a pain in the ass was it to drop that 'Bad Boy' in there?:blink: Quote Link to comment
72 327 Posted August 14, 2008 Report Share Posted August 14, 2008 Not too big of a pain. I see guys on here do 10 times more work on there trucks to go back to stock or another motor. Its totally worth the fun of getting 80 miles to a tank of gas:). Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 2eDeYe;73876'']Yep, get some backpressure and it'll run more efficiently, prolly get a bit more power too. Actually,once I removed that Stock 'PEE' size exhaust, I got better MPG and more power on the Highway with the 2 1/4 Exhaust...Hmmm:blink: Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 Not too big of a pain. I see guys on here do 10 times more work on there trucks to go back to stock or another motor. Its totally worth the fun of getting 80 miles to a tank of gas:). What did you do for mounts and driveshaft, may I ask? Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 get a electronic ignitionadjust the mixture and time the motor again. drive it very conservatively. Dont hammer the pedal down always using the acell pump on the carb and drive a constance 55mph. I got 26 mpg out of my 521 when I drove more on the hiway. But average is 22/23mpg. A 1.75 -2inch exhaust would be more than enough to handle a semi built L motor Yeah,that's my problem, I always 'mash' down on the Pedal after been driving my 230hp 300ZX Turbo!(pictured above):cool: Quote Link to comment
72 327 Posted August 14, 2008 Report Share Posted August 14, 2008 Mounts are off a 76 Monte Carlo and drive line is cut to fit from a 1/2 ton Chevy pickup. Just parts that where avalible at the junk yard when it was built. Quote Link to comment
]2eDeYe Posted August 14, 2008 Report Share Posted August 14, 2008 Actually,once I removed that Stock 'PEE' size exhaust, I got better MPG and more power on the Highway with the 2 1/4 Exhaust...Hmmm:blink: So you were getting worse mileage before that makes no sense unless your driving style changed? Here's an experiment you can try. Pick up a 2.25" to 1.75" reducer and clamp it to the end of your tailpipe. Drive it that way for a while and see if there is a difference. I had to weld one onto my brothers truck after an 'exhaust' guy oversized his exhaust to 2.5" Got all the power back that he had lost (exhaust size was all that changed). 1.5" to 1.75" exhaust is optimal for a 1600cc motor. Especially if you are running a stock carb. Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 2eDeYe;73885']So you were getting worse mileage before that makes no sense unless your driving style changed? Here's an experiment you can try. Pick up a 2.25" to 1.75" reducer and clamp it to the end of your tailpipe. Drive it that way for a while and see if there is a difference. I had to weld one onto my brothers truck after an 'exhaust' guy oversized his exhaust to 2.5" Got all the power back that he had lost (exhaust size was all that changed). 1.5" to 1.75" exhaust is optimal for a 1600cc motor. Especially if you are running a stock carb. DOOOOHHHH!:mad: Quote Link to comment
banzai510(hainz) Posted August 14, 2008 Report Share Posted August 14, 2008 MY guess is the mashing of the pedal using the Full stroke of the accel pump on the carb. I bet if you just gradually ease on the pedal and get up to speed and shift this can save some gas. But I notice Now when I do it all the people give me dirty looks and Now I fit tthe image of a Old Man driving a Slow Old Datsun Truck!!!!!! DRIVING LIKE A GRANDPA L Motors never got too great of gas milage anyways. They only looked good back in the day when everything else got 8-13mpg Like a VW Beetle. Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 MY guess is the mashing of the pedal using the Full stroke of the accel pump on the carb. I bet if you just gradually ease on the pedal and get up to speed and shift this can save some gas.But I notice Now when I do it all the people give me dirty looks and Now I fit tthe image of a Old Man driving a Slow Old Datsun Truck!!!!!! DRIVING LIKE A GRANDPA L Motors never got too great of gas milage anyways. They only looked good back in the day when everything else got 8-13mpg Like a VW Beetle. :lol:I know what you mean,everyone blows past me on the freeway,I have to stay on the number 1 or 2 lane!:lol: Quote Link to comment
OL YELLER Posted August 14, 2008 Report Share Posted August 14, 2008 :lol:I know what you mean,everyone blows past me on the freeway,I have to stay on the number 1 or 2 lane!:lol: Hold it there "Batman"................Ol Yeller runs from Chino to Hawthorne and back 4 days a week (60 fwy, 605 fwy, 105 fwy) and this OLD granpa drives in the FAST lane or next to Fast lane ALWAYS, and I get a very solid 32/33 MPG weekly..(L16, Hitachi, 4 speed, '89 Nissan rear end gears, 2" Exhaust.) and that is DAILY....so it is not only "possible" to get good mileage at 70 MPH, I am tellin you it is real world...AND that is the Darn STOP and GO of those Freeways at 2:00-3:00 p.m.(goin in in the mornin at 5 a.m. is a "breeze" tho....) Right Jason? (Datsun Dreamer can tell ya bout that commute...Huh?) Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 Hold it there "Batman"................Ol Yeller runs from Chino to Hawthorne and back 4 days a week (60 fwy, 605 fwy, 105 fwy) and this OLD granpa drives in the FAST lane or next to Fast lane ALWAYS, and I get a very solid 32/33 MPG weekly..(L16, Hitachi, 4 speed, '89 Nissan rear end gears, 2" Exhaust.) and that is DAILY....so it is not only "possible" to get good mileage at 70 MPH, I am tellin you it is real world...AND that is the Darn STOP and GO of those Freeways at 2:00-3:00 p.m.(goin in in the mornin at 5 a.m. is a "breeze" tho....) Right Jason? (Datsun Dreamer can tell ya bout that commute...Huh?) Hmmm!:confused: My Speedometer must be off because it reads 70mph and everyone is flying past me!:lol: Quote Link to comment
datzenmike Posted August 14, 2008 Report Share Posted August 14, 2008 2eDeYe;73885']So you were getting worse mileage before that makes no sense unless your driving style changed? Here's an experiment you can try. Pick up a 2.25" to 1.75" reducer and clamp it to the end of your tailpipe. Drive it that way for a while and see if there is a difference. I had to weld one onto my brothers truck after an 'exhaust' guy oversized his exhaust to 2.5" Got all the power back that he had lost (exhaust size was all that changed). 1.5" to 1.75" exhaust is optimal for a 1600cc motor. Especially if you are running a stock carb. I agree. No one needs a 3" exhaust. Size is everything to a male I guess:D My '78 has a 2" down pipe (Z-24 motor) to just under the cab, reduced to the stock 1 3/4" to behind the cab, a reducer back up to 2" and into a real muffler,(so I can enjoy my music) and a 2" elbow downward. Cross sectional area of an exhaust pipe with a diameter of: 1.5"...... 1.7 sq. in. 1.75".... 2.40 sq.in. 2.0"...... 3.14 sq. in. 2.25".... 3.97 sq. in. 2.5" ...... 4.90 sq.in. 2.75"..... 5.93 sq. in. 3.0"...... 7.065 sq. in. Twice the diameter of the 1.5" As you can see, doubling the diameter increases the cross sectional area not by two times, but by four times!!!! The same as 4, 1.5" pipes... this is an insane overkill! If you want to flow twice as much exhaust as your 1 3/4" pipe you only need to go up to a 2 1/2" pipe. This will flow as much as dual 1 3/4" pipes. If you have a 1 3/4" pipe and only go up to a 2" pipe, this will give you an increase of just over 75%!!!!!! Big pipes are totally over rated. How much do you need????? Quote Link to comment
]2eDeYe Posted August 14, 2008 Report Share Posted August 14, 2008 Just enough to get the job done right :lol: Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 I agree. No one needs a 3" exhaust. Size is everything to a male I guess:D My '78 has a 2" down pipe (Z-24 motor) to just under the cab, reduced to the stock 1 3/4" to behind the cab, a reducer back up to 2" and into a real muffler,(so I can enjoy my music) and a 2" elbow downward. Cross sectional area of an exhaust pipe with a diameter of: 1.5"...... 1.7 sq. in. 1.75".... 2.40 sq.in. 2.0"...... 3.14 sq. in. 2.25".... 3.97 sq. in. 2.5" ...... 4.90 sq.in. 2.75"..... 5.93 sq. in. 3.0"...... 7.065 sq. in. Twice the diameter of the 1.5" As you can see, doubling the diameter increases the cross sectional area not by two times, but by four times!!!! The same as 4, 1.5" pipes... this is an insane overkill! If you want to flow twice as much exhaust as your 1 3/4" pipe you only need to go up to a 2 1/2" pipe. This will flow as much as dual 1 3/4" pipes. If you have a 1 3/4" pipe and only go up to a 2" pipe, this will give you an increase of just over 75%!!!!!! Big pipes are totally over rated. How much do you need????? Yeah, I guess I was compensating for something else!:o Well I was just trying to improve the flow! Ya' know,the Tim"Tool Time"Taylor thing ARR!,ARR!,ARR!:lol: Quote Link to comment
Bleach Posted August 14, 2008 Report Share Posted August 14, 2008 also be sure youre using stock tire sizes. If the tire size is smaller then your speedometer reading is off. 4.375 rear axel, 5-speed, 1.75" exhaust, and the L16 should be a good combo. Quote Link to comment
Fuelrags Posted August 14, 2008 Author Report Share Posted August 14, 2008 also be sure youre using stock tire sizes. If the tire size is smaller then your speedometer reading is off. 4.375 rear axel, 5-speed, 1.75" exhaust, and the L16 should be a good combo. Wheel I guess my Combo is totally off;Aftermarket Aircleaner,2 1/4 inch exhaust,205/50/15 tires=18 mpg average....AHH What the Hell!, at least I'm not driving a Hummer H2:D Quote Link to comment
dat521gatherer Posted August 14, 2008 Report Share Posted August 14, 2008 anything around 20mpg is nothing to complain about. my last two tanks were 19.6 and 19.5mpg. i changed my driving habits somewhat. coasting whenever possible turning off engine when pulling in to a spot. not opening up the secondary (stomping on it) thats hard to not do.:D this is on my 71-521 l16 weber dgv with ei dizzy installed last month. installed the dizzy on the 19.6mpg tank so the ei dizzy doesn't look to help at all. it's all in how you drive. i'm hoping for 20+ on my current tank. i'm also going to retard my timing back from 12 to 10. and try to tweek the air/fuel again. Quote Link to comment
Bleach Posted August 14, 2008 Report Share Posted August 14, 2008 205/50 ?? wow... with a 15" wheel, 205/70/15 is factory tire size. If you calculated 18mpg based on your odometer then you're probably only getting 16mpg. You're way off. Keep your wheels and slap a 4.11 diff in there from a 1979 truck. That'll get you closer to stock gearing. Quote Link to comment
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