Chevy 454 verses 350 on gas mileage

Discussion in 'The "Other" Bench' started by ronbz455, Aug 4, 2012.

  1. ronbz455

    ronbz455 Big Butz Racing

    I have a 454 in my pull truck and it drinks gas like water. I started out in the old days with a 6.2 diesel and it got 18 MPG but no power. I have just been handed a couple of 350's and a racing cam and he said try that. He will be buying my 454 if it works. Has anyone tried a small block Chevy in a pulling truck with race modifications and seen if the power was ok and if the gas mileage was better than the Big Block?
     
  2. sean Buick 76

    sean Buick 76 Buick Nut

    I would not do it. I find the SBC terrible for TQ unless it has AFR heads and a 383 bottom end.

    I say keep the 454 in place, port the heads optimize the quench of the chambers, and add a water methanol injection kit to cool down the air and fuel. Snow makes a good kit or junkyard your self a kit that is triggered by full throttle. Make sure your timing is in quick in the rpm and use a ported vacuum source for the vacuum advance. Shoot for 32 degrees total timing and limit the vacuum advance to 10 degrees. Use some taller narrow tires and inflate them up to close to the max rating. ensure the brakes are not dragging, remove any extra weight and tune the carb using an air fuel meter like a LM-1. Lastly use a vacuum gauge to help you drive to get better mileage.

    Also make sure you have a cold air intake setup at very least and make sure you have a free flowing exhaust that still has some back pressure to help the mid RPM torque.

    been there done that with "race 350" engines in a 4x4 truck and it was terrible!!!!! stay away from that combo, keep the cubes.
     
  3. DaWildcat

    DaWildcat Platinum Level Contributor

    I think what you meant is that he should shoot for as little "backpressure" as possible, but not go crazy on large diameter tubing so the exhaust gas velocity stays high.

    Backpressure should always be as close to zero as possible, but not always at the expense of slowing down the exhaust gasses. A decent 2.5" dual system should be more than adequate for a mild 454 that needs to operate around peak torque.

    Devon
     
  4. sean Buick 76

    sean Buick 76 Buick Nut

    As usual you are 100% correct!!!!:TU:
     
  5. ronbz455

    ronbz455 Big Butz Racing

    Ok it has the 9to1 pistons from Jegs, rv cam headers from the Zone, the bbc heads called peanut that I match ported, dual exaust 2 1/4 to the axle, torguer intake which is probably hurting the mileage and a 800 Quad. This truck has so much power that I have a red holly pump on it and if I floor it from a stop it will run out of gas before it hits 3rd gear. I was going to try it in the 1/4 but I would have to fix the fuel issue before I did that. I really want to go to the GS nationals in Bowling Green but am worried about the gas mileage. I even thought about putting a newer 6.0 from a avalanch but I would have to add all the wiring to run the engine
     
  6. Jim Weise

    Jim Weise EFI/DIS 482

    All you have to get rid of there is the single plane manifold.. then it's about a good as a BBC will get for mileage.

    The only thing that will really help is an OD trans, with a lockup converter. Best option for towing is a 4L80E, now that the controller boxes have come way down in price. Still a substantial investment, but on that will pay off in the long run, as long as you keep the truck.

    If your truck is like the 3 or 4 mid 70-early 90's 3/4 ton GM trucks I have owned, it has at least 3.73 gears in it, if not 4.10, and even with the tall 16 or 16.5 tires, it still turns around 3000 rpm at 70..

    The new trucks get better mileage because they are geared to run the motor about 1600-1900 rpm. Hook a heavy trailer to one, and tow without the OD, really work it, and you will see them get 8-10 MPG. Back in the day, Tim Hol, a buick guy and member here, worked at a GM dealership, and we towed with a different new truck every week. They were Demo's, or used trucks (typically 6mo to 1 year old) and we tried every combo, towing my 26ft enclosed. From 1/2 ton 2WD to fully loaded 4X4 1 Ton gas engine stuff. Best mileage was with the Duramax obviouisly, but we did have a few 1/2 ton 4x4's, that if you drove nice, with the tow-haul off, you could get 12-14 MPG with.

    But most of them got the same 10mpg that my old 3/4 ton GM stuff did. They didn't have enough power to keep them in OD and lockup.

    If I decide to fix the body on my current 89 3/4 ton Suburban, which already has the 455 Buick, I am going to build a motor like Edouard's, and back it with a 4L80E. And buy an air deflector for the roof of the suburban. If I can get 14 with it, it will double the mileage the the tired 73 455/TH400 gets now. It does turn 2900 rpm at 65mph



    JW
     
  7. sean Buick 76

    sean Buick 76 Buick Nut

    Swap to a dual plane intake and a Q jet off a 455 Buick.
     
  8. ronbz455

    ronbz455 Big Butz Racing

    Wow Fred Catlin said the same thing. I bought the intake cause it was 50 bucks. So you guys are saying with a dual plane intake I would increase my mileage by how much?

    ---------- Post added at 02:49 AM ---------- Previous post was at 02:47 AM ----------

    I have a 800 Qjet on it that works well.

    ---------- Post added at 03:10 AM ---------- Previous post was at 02:49 AM ----------

    Hey Jim thanks for your help. I have a 700r4 that I rebuilt with a Gil younger shift kit. I pulled it out twice and the valve body twice to get the shift points right and now that works good but I can Idle in the entrance and watch the gas gauge go down. I really want to be a part of this Buick club but I can't afford to be there. The main reason is the price of gas getting to the race. When the race was here at Indy is was like heaven. Right down the street from me. I want to put a Buick in all races cause I did it with no money.
     
  9. DaWildcat

    DaWildcat Platinum Level Contributor

    There is no way to know what your fuel economy gains might be, but the advice is sound. The dual plane intake manifold should be your next step, then you need to figure out ignition timing.

    Devon
     
  10. ronbz455

    ronbz455 Big Butz Racing

    So Jim you actually put a 455 Buick in your tow truck? nice.
     
  11. Jim Weise

    Jim Weise EFI/DIS 482

    Yes, there are a number of guys around who have done the same.. I first did in in the early 90's, in a clapped out small block 3/4 ton 2WD Chev pickup I had at the time. Towed about 15K miles with that one, pulled the motor and junked the truck. As I recall even towing my big trailer, I got abouit 11mpg with that one. Stock 70 SR motor with KB113 cam.

    If you have an OD trans and working lockup converter, then you might want to check for fuel leaks... what the heck are you towing, and what kind of mileage are you getting?

    JW
     
  12. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I had an `88 3/4 ton 2wd Suburban with a TBI 454, TH400 and 3.42 gears and it got 11mpg on it's best day without a trailer behind it. It would tow like an ox but not very thrifty. Unless you use yours to tow everyday it seems like you could buy a lot of gas for what it would cost you to swap engines to get an increase of probably less than 5mpg. My `96 GMC K1500 will tow my open trailer just fine. Towing a trailer it wouldn't pass my Suburban going uphill but it will pass a lot more gas stations. It rides better, too. I'd just except the fact that you get bad mileage with your truck and leave it at that, or buy something that does better.
     
  13. ronbz455

    ronbz455 Big Butz Racing

    Yea I will try to find an intake but I have a 28 foot enclosed trailer with a golfcart, toolbox, 3485 lb Buick and thats about it. But that don't explain why it uses so much fuel idling. I have checked for fuel leaks. I will get the intake and see what happens. Does anyone here have one for sale? I prefer an aluminum but a good stock on will work.
     
  14. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    My dad has a "vortec" 350 in his '99 suburban (2wd, standard gear ratio in back, Std size 16" tires...etc.) and he's managed 19mpg Highway with it. that's with nothing in the SUV, removed the back seat etc. It has no aftermarkets modifications, stock as it came from the factory. I'm sure the fuel injections helps a bit.
     
  15. ronbz455

    ronbz455 Big Butz Racing

    How does it do pulling a loaded trailer?
     
  16. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    My mom pulled an 2-axle maybe 20-ft enclosed trailer full of boyscout stuff and it handled fine, she didn't seem to notice it being a dog or anything but She wasn't keeping track of mileage at the time.

    I know it's a completely different family of engines, but a freind of mine has a '97 Dodge 1500 4wd ext. cab with the magnum 360 when he has that thing loaded up in back, and pulls a car trailer with a 5000+ lbs Dodge WC-52 he gets about 11 or so.:Do No:
     
  17. ronbz455

    ronbz455 Big Butz Racing

    I found a new dual plane intake on ebay for 133.00 free shipping. Check that one out and see if there is any reason I should not buy it to put on the 454, round port 88 heads.
     
  18. DaWildcat

    DaWildcat Platinum Level Contributor

    A link to the specific auction would be a big help...

    Devon
     
  19. mpvance

    mpvance Well-Known Member

    I had a '79 suburban 454 th400 3.08 rear that got about 18 mpg on the highway really cruisin'. Unfortunately around town it was about 5mpg's. I bought a 4 cyl dodge avenger (35-40 real mpgs) for what it was costing me in gas in the truck. Still kept the truck for towing my 26Ft toy hauler about 8000Lbs. This truck could pull that trailer and gain speed o the hills of I-75 from Tennessee back home to Kentucky, mileage towing was better than around town 6-8 never really checked it just figured it was what it was. Loved that old truck. However, so did the rust.

    Fast forward, kept the 454/Th400 from the 79, it's in the garage. Bought an '86 3/4 converted to 1 ton, but 350/Th400/4.11 combo, 3000rpm at 70mph. Put a 700r4, now 2200 rpm at 70 mph but its a dog, nowhere near the power of the 454. Not happy with the lockup, doesn't seem to unlock pulling a hill an bogs down the motor.

    Needs that 454
     
  20. sean Buick 76

    sean Buick 76 Buick Nut

    Not to hijack the thread however.... Cut the wires from the 7004R and use a toggle switch to lockup the torque converter. This will help you BIG TIME when towing! Send me a Pm if you want the details, but it did wonders for my 4x4 3/4 ton with the same trans.
     

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