Possible 454 swap?

[77crewcab]

Okay in my burb I am running about 10-12 mpg right now in mixed driving but with a lot of 60-70mph highway, this is on a pretty worn and beaten carb 350. I have really been thinking of rebuilding the 454 I have and putting it in the burb rather than a TBI 350. From what I gather I would be getting around the same mileage as what I have now. Maybe a little more with more power to move the beast. For those of you that have done the same how did you fair on the mileage issue after putting in the bigblock. Mine will probably a 468, with 781 heads with big valves when done.

What part of the 350 TBI stuff could be used if I wanted to do TBI on the 454?
Would this require a regear? I currently have 3.42 gears with 31 inch tires.
Also I would probably rebuild the 700R4 while I am at just to make sure it is up to snuff, but what upgrades should I do while I am at it? Torque convertor stall?

This would be for a daily driver with towing a 5k trailer about twice a month less than 100 miles. Thank for any input!

 

[dremu]

Okay in my burb I am running about 10-12 mpg right now in mixed driving but with a lot of 60-70mph highway, this is on a pretty worn and beaten carb 350. I have really been thinking of rebuilding the 454 I have and putting it in the burb rather than a TBI 350. From what I gather I would be getting around the same mileage as what I have now. Maybe a little more with more power to move the beast. For those of you that have done the same how did you fair on the mileage issue after putting in the bigblock. Mine will probably a 468, with 781 heads with big valves when done.

What part of the 350 TBI stuff could be used if I wanted to do TBI on the 454?
Would this require a regear? I currently have 3.42 gears with 31 inch tires.
Also I would probably rebuild the 700R4 while I am at just to make sure it is up to snuff, but what upgrades should I do while I am at it? Torque convertor stall?

This would be for a daily driver with towing a 5k trailer about twice a month less than 100 miles. Thank for any input!

I don't think that a stock TBI will like a 468 with the big valves... that's a LOT of motor, believe you me -- I know Check Greg's thread about his and what he's looking at for FI... to properly feed that much motor you either gotta be a SERIOUS electronics geek (and coming from me, that says something), or throw lots and LOTS of money at it. Or possibly both.

Also, a 700R4 isn't gonna survive behind ~420hp and ~560ft-lbs, IMHO, no matter how it's built. At the least you'd need it rebuilt like a Vette tranny... but towing, oy.

Otherwise a TH400 is cheap but has no OD, or a 4L80E is really nice, but ex-fricken-spensive.

Gearing, oy. With OD, you could go to 4.10:1. Without it, I'd hafta do the math for RPM for that tire speed ... with such an engine build you'd have enough torque that you could run 2:1 gears and still move ... but towing would make me want 3.73:1 or maybe even 4.10:1. I run 4.10:1 on 235-85-16's (hmm, 31.7" diameter) on the sixpack ... she won't go anywhere real quick, but she can pull a house off the foundation.

All of that said, a TBI 350 might be the best course for budget and mileage. Big blocks are NOT cheap, and while I've not had mine running long enough to judge mileage, I can't imagine it'll be good =))

I used to own a TBI 3/4 Burb, and even with 4.10's and a TH400 she did okay, and would tow ... not quick, but would do it all day, and get passable mileage the rest of the time.

-- A

 

[77crewcab]

Well the 454 is getting rebuilt anyway either for the burb or for my 60 SWB. But my thinking is that if the mileage will be close in the burb then it would be a good deal for all the extra torque. I drive very mild to start with and the tranny shop I go to says they can build it to work behind the BBC as long as no OD towing is used. I would like to look for a 4L80E or even look at a 5 or 6 speed down the line. But for the next year at least would be limited to the 700R4. A TH400 with a gearvendors would even be okay with me.