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Old 09-15-2005, 09:12 PM
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Any 454's with decent gas milage?

I know, I know. 454 and gas milage don't even belong in the same sentence.

I figure since my 350 truck only get 13-15 MPG, how close I could get to that with a mild 454. Any advise?

Here's what Im thinking- 9:1 454, large oval=port heads(maybe peanut port) performer RPM Square bore intake with a 800cfm Q-jet that I got. headers, and a small cam around 210-218 @ .050.

This would be in a full size truck (around 4000 - 4400 lbs), 3.42 gears and I got a 350 trans with a 2500 stall or a pretty fresh 700r4 with the "heavy duty" parts, whatever that means. (SO probably just a stock rebuild).

I dont think the 700r4 will like the 454.

So can I do it with a 350 trans? This is 90% country road highway driving.

BTW, Im not wanting to build a 454 to get gas milage. My truck needs a new engine, I want a 454, just curious as to gas milage.

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Last edited by firechicken383; 09-15-2005 at 09:29 PM.
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Old 09-15-2005, 09:35 PM
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We recently swapped the 454 and running gear out of an 86 3/4 ton suburban into our 89 suburban. With 3.73 rear gears, a TH400 tranny and 245/75R16 tires it gets about 8-10 mpg. That's with a stock intake, dual exhaust out of stock manifolds, and a stock Q-Jet with the stock cam. Plenty of low end, semi decent cruising, but good mpg ain't its strong suit.
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Old 09-15-2005, 10:23 PM
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Ditto to the comment before me. Runnin a 454 in my 64 el camino and get 8/9 mpg (maybe)on very moderate acceleration, 8.75:1 cr, holley 850 w/ hyfire(that doesn't help w/ mileage ). I don't have leadfoot syndrome cuz it's my first bbc and I want to baby it but I do get on it sometimes. Obviously gas mileage will be worse when you do this but you get the idea. Oh, I agree w/ you about the 700R4. I'd probly go for a 400 but you should get away w/ using a 350.
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Old 09-17-2005, 08:56 AM
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I got a 94 one ton with duallies, and a TBI 454. It gets about 10 in the city and 14 on the highway. I swear, although I have not calculated the mpg on my chevelle (cause I don't care!) that with the 454 and spreadbore (in my chevelle), if you stay out of the sec.'s, it gets better mileage than the truck. It may be attributed to the size of the primaries on the spreadbore (looks like about 1" or so) to the TBI throttle blades (look like about an 1 1/2" at least, maybe more).
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Old 09-17-2005, 10:23 AM
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I'll be happy to take your old 350!! Best I can get out of my new 350 is 9.7 mpg. Whats your secret?
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Old 09-17-2005, 03:17 PM
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Your only hope is to put it in front of an OD tranny and get the revs/mile down. More cubic inches just suck more gas/rev, simple fact.
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Old 09-17-2005, 04:04 PM
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I'd take a look at the Comp Cams 255DEH cam, an old Edelbrock Streetmaster or Holley single Plane Street Dominator with a plenum divider or an Edelbrock SP2P topped off with a well tuned Q-Jet and a set of 1-3/4" headers. Back that up with a 700R4 trans with the stock lock up converter a recurved HEI and some skinny tires and you could probably get in the mid to upper teen's for mileage. Rebuild the 350 with the same mods and I think you could do the same or better.
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Old 09-17-2005, 04:10 PM
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I did another jet change 4 days ago and checked the milage intown. About the same, 9.16.

Did one this morning before a job trip. Went 59 miles on the highway and got 13.6. Better, but intown still sucks. I have too much cam for milage anyways and am running almost 3 grand at 65mph. Might have to look into the 700 trany.
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Old 09-17-2005, 07:59 PM
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Ratlover, does that chevelle have a TH350, 400, 700r4?

I know a guy that insist all his past and current chevelles, el camino's, etc with 454's and a TH350, with a mild gear (highway gears) all got 18-20MPG.


I've got 2 700r4's. One is pretty fresh. I really dont think a 700r4 will work behind this 454 will it? At least not a stock one. I thought about a 4L80-E with the aftermarket computer, but by the time I buy both I could almost get a gearvendors overdrive. Oh well, I'll think about it.

Quote:
I'll be happy to take your old 350!! Best I can get out of my new 350 is 9.7 mpg. Whats your secret?
Jmark, whats your vacuum advance and when does it come in?
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Old 09-17-2005, 08:30 PM
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Quote:
Originally Posted by firechicken383
I've got 2 700r4's. One is pretty fresh. I really dont think a 700r4 will work behind this 454 will it? At least not a stock one.
Why wouldn't it? As long as you drive it for mileage the 700R4 should last just as long behind the 454 as it would a 305. With the 3.42 gear the .70 OD knocks the FDR down to a 2.40 to 1 and with the 454 tuned for maximum low RPM torque that should work. My buddy had a '63 Bel Air with a 305, 200-4R and 3.08's and although it was down a little on low end torque because of a mild cam it still got over 20 MPG. With a milder cam and a set of 3.36's it would have done better on mileage but it still worked pretty good. The 454 should have more than enough low end to handle a 2.40 FDR especially if you use the Peanut Port heads, a mild cam and intake and small tube headers.

I have a 4200 Lb. Monte Carlo that currently gets 13 with the original 350, TH350 and 2.73's, it has a 600 Holley on an Edelbrock SP2P and dual exhaust. I'm gathering parts for a stump puller 383 built to run on 87 Octane for it and will swap in a built 200-4R and 3.73's which should not only greatly improve performance but should give the fuel economy a real shot in the arm. With the the incresed torque and improved gearing it shouldn't have to work nearly as hard as the old 350 and even though it will have 33 more cubes it should burn a lot less fuel at the same speeds due to increased efficiency and decreased RPM. That's the plan anyway.

I knew of a 1980 Chevy 1/2 ton pickup that gained 3-4 MPG by replacing the stock 350 4 bbl with a 1970 400 with an Engle RV-100H cam. Plus he could pull his camper up one particular hill in Drive at 55 MPH where previously it always downshifted into 2nd and dropped to 35 MPH by the time he got to the top and his towing mileage picked up the same amount.
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Old 09-17-2005, 08:31 PM
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454 with decent mpg

have 2000 28ft motor home with m.p. ingection i inst dual exhaust and opened up the air inlet ,has a 4spd od trans gets consistent 12mpg tho that is imperial gallons 20% larger than us.that is fully loadedand average for a 4000kl trip or 2400 miles in some steep countrythat would be 9 to 10 miles pr us gallon,being a ford fan i was impressed cliff
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Old 09-17-2005, 09:50 PM
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Quote:
Why wouldn't it? As long as you drive it for mileage the 700R4 should last just as long behind the 454 as it would a 305
Lots of torque and I would surely have to put it to the test. Only one way to know though.
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Old 09-18-2005, 06:46 AM
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Quote:
Originally Posted by firechicken383
Lots of torque and I would surely have to put it to the test. Only one way to know though.
It won't have "that" much torque. Unless it's a pre-'88 trans that hasn't been upgraded with the '88 & later components I don't see a problem unless you deliberately abuse it.

Do you have the 454 already? If mileage and parts breakage are of even a slight concern you may want to reconsider and look into building a stump puller small block. With the cams, intakes and heads available today you can turn your 350 into something that can pull down small buildings and still get decent mileage. Just some food for thought......
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Old 09-18-2005, 08:44 AM
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Actually, my chevelle is a 4 speed manual. I just had to rebuild the trans in my truck with a 454/4L80E. after only 125,000 km it was toast. cost $2800 to get a shop to rebuild it if I pulled it. They said that you have to change oil every 25000 kms or the aluminum valve body wears out. I don't know why you could n't run a 700R4. They are a lot cheaper, and if you do manage to wear one out.. oh, well. The 4L80 was also a very heavy trans. I think it's 70 lbs heavier than a TH400. I found that with my sbc in the chevelle, back when it was still an auto as well, it lost a lot of power to the TH400 compared to the TH350. It takes a bit more hp to turn the bigger 400. I am intrugued by these Gear Vendors O/D for old school trannys like the 350,400 and even the manual trans. the adds claim cluthcless shifting on the O/D gear in between the trans gear range (1st,1st over,2nd,2nd over,etc.)
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Old 09-18-2005, 03:28 PM
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Quote:
Do you have the 454 already?
Yeah, I got 2 blocks, cranks, 1 set of rods, 3 sets of heads.

ratlover, I would like a 4l80-E but for the money I would probably try to get a gearvendors. I would have to buy the trans and then get the control for it. $$$
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