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1992 Town Car Cartier & 2014 Accord LX MTX
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Discussion Starter #1
Hey I was wondering what kind of improvement in gas mileage the 4.1 V8 gave the big body Devilles and Fleetwoods over the V-8-6-4 6.0 V8?
What was the 4.1 rated at? I wanna say 16/25.
What about the V-8-6-4? I wanna say its like 14/22
 

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1989 Fleetwood Brougham d'Elegance|2018 Chevy Colorado Z71
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Well, personally I hear both engines are to be avoided but I would think the V8-6-4 would be the better choice since with that engine you'll be able to actually move the car haha.
 

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Discussion Starter #4
I have driven a 1981 Fleetwood Brougham Coupe with the V-8-6-4 and a 1990 Brougham D'elegance with the 307. They seemed like they had the same amount of power. Both were slow, but I'd imagine the 307 would be a little quicker due to the 4th gear.
 

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1989 Fleetwood Brougham d'Elegance|2018 Chevy Colorado Z71
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That's true. I do love that 4th gear, makes a hell of a difference. Not too many people may agree with me here but the 307 is a good choice for a Fleetwood Brougham engine. The reliability is through the roof....
 

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What I remember of my mom's 85 4.1L was around 21-22 highway. We were all pretty happy when we could make it 500 miles on one tank on a trip (just started to show "L" on the FDC when we got there). None of our cars until then could do that. The car the 85 replaced was a 84 98 307. Which came very very close. Next was our 76 Delta 88 Royale 350. It had a larger tank and only got 400-450 miles per tank highway.

90Brougham350 said:
Around town, I'd bet anything the 8-6-4 whomps the 4.1. On the highway, I bet the 4.1 does pretty well.
And my mom is a lead foot, so we stayed around 75-80 on the highway.
 

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1979 Sedan deVille d'Elegance
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Hello,

Chad, who started this post, drove my 1981 Fleetwood Brougham Coupe with the V8-6-4. The car has 236k miles and just had considerable service work performed. The power is not what it should be since the tune-up was done and I'm guessing the timing is off and once the problem is corrected if anyone is interested I will report back if the performance is better. Mileage is poor at the moment as a result.

The EPA 1985 Gas Mileage Guide lists the HT4100 fuel economy as 16/22 in the full-size rear-drive Fleetwood Brougham.

I can't locate any information on the V8-6-4 although I will try to find some. The 1979 Cadillac with 425 V8 was rated as 14/20 with 425 4-Barrel and 12/18 with 425 EFI.

EPA lists 1989 Brougham with 5.0 V8 as 17/24.

I am always amazed that people are so interested in the V8-6-4. It is a mechanical nightmare that I would not ever consider buying again.

Have fun!

Dave

Dave
 

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'80 Fleetwood Coupe, 1994 and 1995 Mercedes 140 Coupe
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Poor 8/6/4. Always the target.
They get just about 20 MPG on the highway on a steady 60 MPH roll in 80 degree weather with the AC on.

Dunno about around town.

I never owned an HT-4100 RWD car that ran
:histeric:

My 85 Fleetwood 75 limo with HT-4100 got 24-27 MPG on the highway.

Take an 8/6/4 and marry it to the same transmission as the 307 cars and you would have something.
 

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94 Fleetwood Brougham
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That is what I was thinking. A V864 on a THM200 4R with 3.08 gears would be ideal.

The LT1's are rated 17/26 (2.56) 17/25 (2.93) and 17/23 (3.42). Overall they gained power and lost nothing in mpg. We have come somewhere....

I still would like to see a good EFI on a 307. What could it have done in fuel economy if it had a good solid SPFI like the LT1 did. Can anyone adapt a TPI chevy intake to one as a project?
 

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I don't see how OD makes the car faster, it is just used when cruising on the highway..... well, yeah you can then have a shorter gear in the rear end, but still.

My '79 dosn't have OD, and has 2.28 gears, at 70mph it is right at 2,000RPM..... overdrive on this car, with the 425 is not needed.
 

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Discussion Starter #11
Oh yes, thanks to dave for letting me drive that monster :D
It was world apart from my '92!
 

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Discussion Starter #12
Bro-Ham said:
The power is not what it should be since the tune-up was done and I'm guessing the timing is off and once the problem is corrected if anyone is interested I will report back if the performance is better. Mileage is poor at the moment as a result.
Oh yeah, what does that average for mileage? The FDC said like 11-12 mpg average when I was driving it. Is that true?

Very cool car :cool2:
 

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Faster, well not really. Quicker? Yes by all means. 2.74 first gear ratio and 3.08's is a heck of a lot more gear and starting torque than 2.28's and 2.48's. With 425's torque it should be on par with an LT1 car off the line. Overall drivability much improved by the no so lazy gear. 2.74*3.08=8.4392 2.28*2.48=5.6544. My LT1 FWB is 5.5746 if I start off in SECOND gear (which does ok mind you, but having 1st is a lot more fun when you punch it). Mine is 10.652 in first. That is a lot of extra oooommpppphhh to get the car moving. And allows you to do it with less gas pedal to accomplish the same acceleration performance that you would with the 2.28's and THM400's 2.48 first.

2000 rpm is still a gas waster. If you can get it down to 1500 rpm you will save on gas due less friction and 25% less combustion events per minute. That alone is a gas saver. You can likely go lower (Like GM did with 2.56's and OD), but you really need a small cam and high velocity heads to make that work well.

Not needed? Well, yes, but OD and shorter gears is much welcomed.

Night Wolf said:
I don't see how OD makes the car faster, it is just used when cruising on the highway..... well, yeah you can then have a shorter gear in the rear end, but still.

My '79 dosn't have OD, and has 2.28 gears, at 70mph it is right at 2,000RPM..... overdrive on this car, with the 425 is not needed.
 

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Discussion Starter #14
Rick, in your 79, where does 1st gear end?
 

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It should somewhere around 20-30 MPH if my memory serves me correctly from driving a 79 Coupe. I've thought of the idea of installing the TBI from a 1990 307 onto my 89 but I dunno how well it would work. The carb can sometimes be troublesome and you can't compare to the convenience of FI.
 

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Discussion Starter #16
Yeah thats one thing that '81 had. I could start the car with out pumping the gas 3 times like on that '90 Brougham with the 307.
 

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I'm guessing 75 mph is around redline.... And that is a conservative Cadillac redline....

A friend of mine ran 2.29's and a THM350 with a 400 Pontiac to the tune of 106 down the quarter, and that was second gear..... Top speed? 165-170 is what the tach was calculating to...

I~LUV~Caddys8792 said:
Rick, in your 79, where does 1st gear end?
 

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Hi Chad,

The Fuel Data Center reading changes constantly. I played with the average fuel economy button and it didn't change from the instant so I don't know. I have to admit I've never checked the mileage.

I got just about 16 MPG on my trip from Wisconsin to Florida and back to Wisconsin in the '79 Sedan deVille. I am leaving back for Florida again on Tuesday if all goes well. The carb is being adjusted and hopefully the fuel economy will increase.

I would love to remove the 8-6-4 stuff from my 1981 since the car runs great in 8 cylinders. I also sometimes wish my '79 425 was fuel injected. Not a perfect world.

Dave
 

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DopeStar 156 said:
It should somewhere around 20-30 MPH if my memory serves me correctly from driving a 79 Coupe. I've thought of the idea of installing the TBI from a 1990 307 onto my 89 but I dunno how well it would work. The carb can sometimes be troublesome and you can't compare to the convenience of FI.
No can do, my friend. The 307 was still carbureted in 1990. When they switched to the 305 in '91 it became TBI, and 175 horse.
 

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Discussion Starter #20
Look at the Oldsmobile Custom Cruiser's 307. In 1991, it got TBI.
 
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