I purchased a 350 crate engine a couple of years ago.
I picked up a rear end gear set from Mark around the same time. He donated it free of charge.
I intended to install it but finances would not allow it at the time. Forward to this spring. I took the rear end to have it installed in my Impala and was told that the rear end was totally wrong..
I had a 3.37 rear end ratio and was looking to get better gas mileage. With it being already apart I made the choice to have a new set of gears put in. The new ratio is 3.08.
With this new ratio I was expecting to see an improvement. With my 283 I was getting in the range of 10-12 mpg.
This has now dropped to 8-9 mpg, and I had a performance shop that builds drag racing cars change the jets in the 1406 to what they said was the leanest possible from the tuning kit that I bought.
I am running a 3 speed automatic TH 350 with 235/60 X 15 Radial T/A and used the Edelbrock 1406 carb that I had on my 283.
When I purchased the Crate Engine the recommended carb was an Edelbrock 1405
Is changing the carb going to be of any help.
Electronic ignition with headers.
What to do?
-- Edited by oshawacliff on Monday 1st of August 2016 09:52:21 AM
Curious, did you change the speedo gear set in the trans to match the new gear ratio? The other two items I would look at is the crate engine power band and the torque converter. As I don't know the set up I would be guessing at the engine is out of power curve and lugging or that the converter is below flash and is slipping. Just guesses.
Your mileage looks to be quite low, is that just general city driving or highway driving? In my cars, I don't even bother with city mileage, but always keep track of mileage on my long trips. On my recent trip 3300 mile trip from Calgary to Iowa and back for POCI, I made 16 mpg (imperial gallons) with my 454 4 speed Parisienne. That's with a 450 hp LS6, 4 speed and 3.07 gears.
As Eric has suggested, is your speedo (or actually the odometer) calibrated appropriately?
Your mileage shouldn't be anywhere near that bad on the highway.
I love that you're quoting Imperial gallons seventy2plus2! I've been telling any of my friends that were upset about Brexit not to worry, at least we can go back to calling temperature in Fahrenheit.......
oshawacliff
How about you google the mileage for a trip of reasonable length from your favourite gas station back to the same gas station. Top up before and after to get an accurate consumption figure.
64PARCONUK I like that idea. I will be taking a trip to Peterbough Ont in the next few weeks. I can check some of my mileage figures on my Gas Buddy website . 60 percent highway on long hauls.
Just a thought my GPS is within 5km of 100 when the speedo is indicating 100.
Cliff
-- Edited by oshawacliff on Monday 1st of August 2016 12:28:13 PM
Just a thought my GPS is within 5km of 100 when the speedo is indicating 100.
Cliff
-- Edited by oshawacliff on Monday 1st of August 2016 12:28:13 PM
Do you mean 100 mph on your speedometer or 100 miles on your odometer? This might sound odd considering the same cable feeds the speedometer & odometer, but the two can vary. In my Parisienne, the odometer is bang on, but the speedo reads about 10% low. The odometer was checked over a 10 mile stretch of straight highway against the grid roads here in Algerta, and the speedometer against a couple GPS units.
Either way we're getting a bit off topic here, your fuel mileage may be about right for around town driving, but way low for highway driving.
-- Edited by seventy2plus2 on Monday 1st of August 2016 02:44:37 PM
I agree. I had a 283 (2 bbl) with PG and 3.08 gears. I got 24 - 25 mpg highway.
Changed to a 330 HP 350 CID, 700R4 & 3.73:1 and I get >20 mpg highway. Of course, it depends on how I'm driving...
That's in a Beaumont so a little lighter, but still...
I think dceneric might have hit on it. Is your converter slipping?
You can calculate the engine RPM at various speeds for your set up and compare when you're on the road. If actual engine RPM's are high, you may be slipping the converter.
If your speedo was right for 3.37 gears, it would be reading about 10% low with the 3.08 gears. (Speedo would read 60 mph, when actual speed would be 65.6 mph). That's not enough to account for your poor gas mileage.
What is the difference in cam specs? You have another 120 odd cubes...new diff ratio takes a bit more to get off the line. Is the carb squart pump different and pumping in more fuel on take off. So many variables! A tough one.
-- Edited by koolconvertible on Monday 1st of August 2016 03:38:31 PM
-- Edited by koolconvertible on Monday 1st of August 2016 03:49:02 PM
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cutting a roof off a four door is NOT a convertible.....
65 Parisienne convertible.one of 49 built for RHD export market,402BBC, T400, 2500 stally, posi rear, upgraded brakes with front discs, FUEL FAST efi custom built by me.
Will get it to my shop Exceltec Auto in Markham and have him set up a tach and go for a tour to see what is actually happening.
Will use the gps to get an accurate road speed to verify the speedometer speed.
I think I can set my GPS to read MPH and then I would get a very accurate reading to compare to the speedometer.
Will pull the top off the carb to determine which needles are in the carb now.
Supposed to be the leanest possible.
I've found over the years that the typical mileage in my bone stock 60's V8 cars is in the 12-15MPG US (15-18 CAN MPG) on a typical tank of gas which means a mix of easy in town and open road cruising. Vehicle weight seem to be the main variable with my big cars like my 428 AC equipped Bonnevilles at the low end. Surprisingly engine size doesn't seem to be a large factor and highway gearing while good on a long multi-hour cruise doesn't seem to translate into better mileage on typical mixed use fill-ups. Part of why smaller engines don't seem to help is perhaps most of the cars I've had with 350's had 2bbl's while my 400 and 428 cars have had Qjets. I know from my early driving days in the 80's that a Qjet was always better on gas than a 2bbl, I guess the smaller primaries result in more throttle opening which improves efficiency.
All that being said when I messed around with cars in my younger days things like aftermarket carbs and cams or hi perf torque converters did brutal things to economy and single digit fuel economy were the norm. I had a hopped up 70 TA with a 350LT1 from an early 70's Z-28 with a Holley double pumper, big cam, headers and 4.11 gears. I was in the 6mpg range in normal driving!
Ok Time for an update Grandson and I took a trip to Lindsay and he took his gps set to kph and I took mine with it set to mph Checked the speedo and the mileage. All appeared to be within a couple of mph and miles distance Assume speedo and odo is accurate
Finally bit the bullet and bought a Edelbrock 1405 which was the spec carb for the crate engine that I bought.
I was running an Edelbrock 1406 which I transferred over from my 283 and I was getting reasonable gas mileage with that setup for the 283
The vacuum lines have been switched between ported and ??
MILES PER GALLON Fuel Purchase History - 2016 Purchase
Date Price ) Litres Purchased Total Cost Odometer (km) Station MPG * Notes 9/5/2016 1.159 75.165 $87.12 278,722 Shell Y - [Edit] [ Delete] Fill up in Brampton from Kingsville 9/4/2016 1.149 70.030 $80.46 278,481 Shell Y 9.03 To Leamington 9/3/2016 1.136 65.057 73.90 278,235 Shell Y 9.87
8/27/2016 1.239 78.715 $97.53 278,011 Shell Y 9.68 New Edelbrock 1405 8/11/2016 1.199 30.147 $36.15 277,776 Shell Y 8.41 Markham to Etobicoke to pick up 1405 8/11/2016 1.219 6.465 $7.88 277,674 Shell Y 9.51 Oshawa to Markham 8/11/2016 1.209 26.634 $32.20 277,647 Shell Y 11.76 Trip to Lindsay some 100 mph runs using both gps units ] 8/10/2016 1.199 60.257 $72.25 277,555 Shell Y 9.7 All Highway fast running 7/23/2016 1.209 75.129 $90.83 277,397 Shell Y 7.37 To Niagara and Trenton on cruise 7/17/2016 1.159 80.364 $93.14 277,126 Shell Y 10.15 Trip to Pelham cars show some slow on QEW 7/1/2016 1.269 67.841 $86.09 276,870 Shell Y 8.97
Mileage seldon above 10 mpg usig cruise control whenever possible
Note speedo mileage not accurate as the original speedo quit working and wasnt repaired for about 5 years of driving just started record keeping at 200,000
-- Edited by oshawacliff on Wednesday 28th of September 2016 08:28:34 PM
Wow, that truly is awful mileage. I just can't even begin to suggest what the problem could be but assuming this is mostly highway driving, my thought is your mileage should be at least 50% better than that.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
Wow, that truly is awful mileage. I just can't even begin to suggest what the problem could be but assuming this is mostly highway driving, my thought is your mileage should be at least 50% better than that.
Agreed, I run a 350 block-Holley avenger and when I had a TH350 with 3:36 gears, averaged 19+ mpg hiway. Now with 700R4 and 3:42, average is 21+ mpg hiway. Around town seems low tho....
-- Edited by 1965CS on Thursday 29th of September 2016 07:18:36 AM
Cliff, have you checked to see if your Vac. advance in distributor is working?? or weights stuck?? Man my Catalina got 15 to 16 with 2 x4 quads on it!!! & Torpedo back will get 25 but that's got O/Drive 5 speed. You say it's running "RICH" I assume you've checked the choke to see that's it on full "open" when warmed up???
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Some times I wake up GRUMPY, but today I let her sleep in !!!!!!!!BLACKSTOCK Ont.
1 question, how is your odometer in km's on a 67 Impala? It would be miles.
If you use miles rather than km's, you are in the 16 - 18 mpg range, which would be about right.
I'm getting you at 15.5 mpg if speedo in mph? Fueled up 09/03/2016@278,235 miles ,drove to 278,481=246 miles
70.03 ltr of fuel=15.48 gal. 246@15.48gal=15.89mpg(aprox)
1 question, how is your odometer in km's on a 67 Impala? It would be miles. If you use miles rather than km's, you are in the 16 - 18 mpg range, which would be about right.
Funny I was just looking over the calculations as you have posted and redid a couple using miles as I am thinking the speedo has to be in miles. Couple of the lower calculations came out to 16.4 and 17.7 which I'm thinking is what you'd be expecting.
So the speedo is in miles. Are you entering the miles or converting to km's. Your chart says km's. Just trying to rule out math errors.
My 65 has a 350, aluminium intake Edelbrock carb L79 cam and 3:31 gears and I routinely 2pull 18 mpg. Yours shouldn't be any different.
If it's just as simple as entering miles as km's your numbers would put you right where you should be.
-- Edited by DANO65 on Thursday 29th of September 2016 09:49:33 PM
x2 Maybe fuel up and write down your mileage'drive it and fuel up again. Post the start and end mileage (in miles from speedo) with the amount of liters.
-- Edited by hawkeye5766 on Saturday 1st of October 2016 12:22:37 AM
I am using the Gas Buddy web site to keep track of my gas mileage.
The speedo in the car is in MPH
The gas buddy converts your litres to mpg in their charts or it also shows ltr per km. You have a choice.
I shows a chart for both so you get a conversion after you have entered you numbers.
Gas buddy is making those calcs based on your speedo being in km/h. Do the math yourself and you'll see your true mileage is 14-17 mpg. Miles per imperial gallon.
Example...
on 7/1/2016 your odometer read 276,870 when you filled the tank. At the next fill on 7/17/2016 the odometer read 277,126 and it took 80.364 litres.
Total miles driven is 256 miles
Total fuel in imperial gallons is 17.70 (80.364 / 4.54)
14.46 mpg.
I'd rather spend 5 minutes with a calculator than spent hundreds of dollars on a carb. That could just be me, I'm kinda cheap that way.
How many miles a year do you put on your car Cliff?
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Prince Edward Island
'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.
