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Discussion Starter · #1 ·
Dear Guys...I have a '69 Beaumont with a truck 454, and TH 400. The car is well tuned up and has no gasoline leaks anwhere. Calculations ( rpm calculators, and turning wheel with cover plate removed from rear pumpkin ) indicate 3:55 rear. I am getting about 5.5 mpg with this car, driving very conservtively. My mechanic, and some enthusiasts have advised me that this is about right. I have had other muscle cars, 396/325, LS 6 crate motor Chevelle 425 hp, and a '68 Coronet 440 ( can I say that here? ) and this is still by far the worst gas mileage I have ever had. I am wondering if I should be looking at a compression test or experience slippage somewhere in the new torque converter for the answer. Oh, by the way, the car runs well. Is this gas mileage acceptable for conservatiive driving? Opinions please. Thanks in advance. R.B.
 

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I get 8-10 with a light foot cruising around,,,only 5.5 seems awful bad to me...my big truck used to do better than that


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Bob West
1972 Malibu
454+
TH350-3.73's
1.79 60 ft.
12.06 @ 112.89
 

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Discussion Starter · #3 ·
Me again, sorry about that...I have recently come to believe that it might be a 3.73 rear ratio. I have no facilities for taking the rear apart in this weather to search for numbers. If it's a 3.73 I can maybe believe the numbers. However, I am not trying to answer the question. I would still like to hear what other people think. I read some posts of guys regularly racing big blocks at the track and getting 12 miles to the gallon in daily driving. Sumpin's gotta give. Can anyone sort this out for me...thanks R. B.
 

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If it is light throttle conservative driving, something is out of whack. For me, my warmed over 427 with 3.73's gets 13 mpg on the freeway and 8 around town. But if I hot foot it around, that can get that low (and worse). Maybe you should get a second opinion from another mechanic.

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My70ChevelleSS
Craig Sanden
"Together we stand, devided we fall"
 

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rb, Is that a stock light truck motor? I have known many weldors over the years with 454's in 1 tons w/fabricated steel beds with a welding machine on them (heavy). The ones I've talked to about it claimed 7-9 mpg.

I have owned cars with mech. cam, rect. port big blocks with big gears & although at the time I wasn't concerned with gas mileage, I certainly don't remember it being THAT low.

My brother had a stout built oval 454 & he was always griping about his 9 or 10 mpg.

Sorry this isn't much help but it seems it should be a more. Let us know if you find a problem.
Good luck, Pete
 

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Admittedly I have 3.07 gears but I get 10-12 mpg in my big block around town. With the wide ratio 4-speed, I have to give it a bit more to get going than say an automatic, but I would think the 5 mpg is on the low side even for an occasional heavy foot.

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Dale
TC Gold #92/ACES #1709
67 SS & 67 Elky
Dale's Place
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Integrity: If you have it, it doesn't matter - If you don't have it, it doesn't matter.
 

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R.B.,

I have a 396 / ??? with a hydraulic cam that sounds like a 375 hp motor, 355 posi and a 750 CFM Holley. I drive pretty easy most of the time and I’m getting 7.75 mpg. I’d like to do better.

I believe you can check your gear ratio by following this procedure:
Lift both rear wheels off the ground.
Turn the rear wheel one full rotation.
Count the number of times the drive shaft turns.
If the drive shaft turns 3-1/2 times you have a 355 rear.
If the drive shaft turns 3-3/4 times you have a 373 rear.

Some one please correct me if this does not work.

Bubba


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ACES member #04788
Maryland Chevelle Club member #075
Have you ever noticed that those instruments designed to detect intelligent life in the universe are all pointed AWAY from Earth???
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by Bubba396:
R.B.,

I have a 396 / ??? with a hydraulic cam that sounds like a 375 hp motor, 355 posi and a 750 CFM Holley. I drive pretty easy most of the time and I’m getting 7.75 mpg. I’d like to do better.

I believe you can check your gear ratio by following this procedure:
Lift both rear wheels off the ground.
Turn the rear wheel one full rotation.
Count the number of times the drive shaft turns.
If the drive shaft turns 3-1/2 times you have a 355 rear.
If the drive shaft turns 3-3/4 times you have a 373 rear.

Some one please correct me if this does not work.

Bubba


<HR></BLOCKQUOTE>

I have another idea.. Why don't you just check what's the rear axle code.. It's beside the 12 bolt.. Right from it (Passanger side)

Just post the numbers and letters that you have there on Tag Team.. and you'll know for sure what you have.

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Shai

1972 Chevelle Malibu custom 4dr
Restoration started: February 10th 2001
TC member #1278
 

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That is unless someone changed it from the factory ratio before you got it.

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Leo Paugh
Maryland Chevelle Club #017
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progress has little to do with speed, but lots to do with direction.
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My 454 gets about 8-10. Doesn't matter what I do it still falls in that range.

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1969 Caprice 4400LBS!!
454/M-20
12-bolt 4.10 Posi
13.45 @ 105
323HP @ 5200RPM
382lb-ft @ 3300RPM at the wheels!
Andy and Nick's Muscle Car Half-way House
 

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Hehehe, that what my 427 did with an 850, didnt matter how it was driven.

R.B., I wont share what my big port, 7000 rpm rat gets becuase you wouldnt believe it. But some thoughts...

If its a low compression motor I can see it. Rich in FLA has one he cant above 10mpg in. And here I am geting 15-17. Compression has EVERYTHING to do with a motors VE or efficiency. But the same token, my car came with a low compression 396 and I got it to 14 mpg. How.....?

One trick for low compression motors is to feed it GOBS of timing advance. Again, this is a crutch for an ineffecient motor but it helps.

You might be a candidate for the ol closed chamber head swap to bump compression, that alot of folks are doing around here. It will certainly help.

But for now, time the motor the way we used to do it as kids. Crank it up till it pings. I bet you'll be running 20 intial - 50 total. this is not good for your bearings! So dont rev the thing to the moon!

Also, I'm wondering if your T400 has a problem.

Since the car has such a problem, and I happen to be eyeing Beaumonts.....I'll take it off your hands cheap! Meet ya in Fort Erie!
Kidding friend, but something is amiss here. And I think its your 8:1. IF you tell us you have better than 9:1, I am befuddled.

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Member #62 Gold/ACES 03112
67 SS396(427-3X2)
Be Big, Be a Builder

[This message has been edited by Gene Chas (edited 01-14-2002).]
 

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RB.I notice you are in Ontario so are you talking U.S. or Canadian Gallons? If you are only getting 5.5 canadian, something is wrong.(5 Canadian = 4.5 U.S.) I got better than that with my 396 with 4:10 gears. Much better. Are you pushing black smoke when you put your foot in it? Are your tailpipes black and sooty inside? I think I would be trying to borrow a carb off a friend and trying it. You did not mention what carb you have.
 

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Discussion Starter · #13 ·
Dear Guys, I certainly appreciate all the suggestions so far....here's a couple more tidbits....I am told ( sorry best I can do ) that the engine was from a Chevy pick up truck ( I didn't know they put 'em in pick-ups, I would have thought a Suburban, but I am assured that it is from a pick-up ), also I was referring to Canadian gallons. The count the rotations has been done, by two mechanics and me standing there and a white grease pencil mark on the tire...they figured 3:55...since then I have done several RPM calculations using computer programs, some from ACES and Team Chevelle and depending upon the tire diameter measured or estimated between 26 and 28, I can get numbers as high as 3.74. The numbers for fuel consumption are based on city driving. I have a superior engine that I am going to transplant, and I am thinking of putting in a 3.08 gear....hope this doesn't offend any of the purists, but short of 1/4 mile racing, I have always found these big block cars have lots of tire frying torque and if anything you have to manage it carefully or all you do is produce tire smoke while a cheaper, lighter car ( we will carefully avoid naming any cars beginning with the thirteenth letter of the alphabet ) go tearing out in front. I am wondering about the tranny. Can internal friction, or slippage ruin gas mileage to the extent I have described. I have a mildly built transmission and the shift points are set fairly low. I have torque converter number 8656948, supposed to have been in everything from BB Corvettes to cube vans, six bolt ups, heaviest converter I could get across the GM parts counter although people have been know to fib to me. I appreciate no one having asked if my emergency brake is on...I have thought of it, it would be worn out by now. Thanks R.B.
 

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Discussion Starter · #14 ·
Dear BCICE...there is nothing coming out of the tailpipes that should not be. The carb is a Holley 750 ( I think ) dual feed, vacuum secondaries. It smells rich a lot of the time. My mechanic said it is both normal and good for these cars to run rich. It is the best starting vehicle I have ever owned, so I was reluctant to tinker with the carb, although that is probably one of the most important pieces of the puzzle. Thanks for pointing it out. As obvious as it seems, I wasn't focussing there. Perhaps a rebuild is in order. Any predictions on how that would aid in the mystery of the disappearing gasoline? I was thinking the rear end gear was the culprit...pinned on the fact that the car runs quite well. I just can't hardly afford to drive it. It is my regular daily driver.
 

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Hi RB
Man you are making me feel good about milage, My super heavy (motor home)454 gets 8-10 mpg towing the shadow. Gene has it right about the timing. When i first got on the road it was 5 mpg but with the timing bumped up 5 more degrees and the quad jetted down 76 to 73 the milage dang near doubled and thats with a 3.73 rear end. Your own clue about smelling rich is the tip off. Also it's a little fussy on the initial start up "cold" due to the leaner mixture but i dont mind.

Good luck

Jim
 

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RB. I don't know what to say, but I will tell you what I would do if it were my car. I would try a Q jet and see what kind of difference that makes. As you probably know, they have small primarys and real big secondarys so if you are just driving around town, I don't think you can beat them for economy. I am also running a 750 with vacuum secondarys. 350 hp 396 with a little better than stock cam and headers.I have all my jet sizes and squirter sizes written down at work so will look them up and post them in the morning for you. I figured my mileage was just a tad better than 8 (canadian) with 4:10 gears!! I sure hope someone more in the know stops in here. Good luck! Terry

EDIT! I know double posts are kind of frowned upon RB, but I would think a good place for your post may be in the peformance forum. You could explain why it is a double post as I have seen others do and have got no negative feedback for it. The folks on here are pretty darn forgiving when a fella truly needs help.

[This message has been edited by bcice (edited 01-14-2002).]
 

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Is the choke stuck partly on maybe?

Or is the trunk full of beer?


Maybe we should check for vacuum leaks too?
Just a thought...

[This message has been edited by Bow_Tied (edited 01-14-2002).]
 

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Now if the trunk was full of beer, he is my kind of guy! He says it smells rich at times. Wouldn't a vacuum leak create a lean condition?
 

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Discussion Starter · #20 ·
Dear Guys...right again. I have the same trouble with beer as I do with gas: however, I thought to post questions re disappearing beer in a different forum...perhaps something starting with A. ( Of course this is tongue in cheek, I do not touch my cars or motorcycle if I have had alcohol. ) R.B.
 
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