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Motor swap.

77snowwheeler

77snowwheeler

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Joined
Apr 17, 2022
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Location
Oregon City
Looking to possibly trade my 454, new motor, under 1500 miles on it, for 350 tbi with icm. 454 is in 77 gmc. I’d like to trade good running 350, with low miles for mine, with RNR as balance for my newer motor. In Oregon. IMG_5208.jpeg
 
bradshawtech said:
Hmm, posting to see where this ends up.

pics and details on the 454…
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I’ll get them tomorrow. Just to explain, when I was building this truck, it was for a pavement queen, for cruise inns and local trips, dinner, icecream runs. Wasn’t to concerned about mileage. Then, I started looking into snow wheelin, and now mileage is a ton more important, because I’m traveling all around oregon, and it’s killing me? Lol I could go out and buy a motor, but I’ve been in this project for over six years and I’m done projecting, sort of speak. What’s most important now is, someone that could do the swap, and done deal. It’s a great running motor, 40 over, and tons of bottom end torque, and large oval port heads covered with rpm oval port intake, and Holly avenger 670 cfm, 4x4 carb. Believe it or not, I have over kill power and over kill torque. Perfect for the original build, but opposite of what I’m actually doing now. Trying to find an easy way out of this situation.
 
This thing only gets about 12 MPG, and it is a 350 TBI. It might get 13 MPG on the freeway with the wind at it back going down hill. Granted it is a 7000 Lbs crew cab. I do not know if going to the trouble of installing a small block is going to net you enough fuel milage to be worth the hassle.

full
 
1-ton said:
This thing only gets about 12 MPG, and it is a 350 TBI. It might get 13 MPG on the freeway with the wind at it back going down hill. Granted it is a 7000 Lbs crew cab. I do not know if going to the trouble of installing a small block is going to net you enough fuel milage to be worth the hassle.

full
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I get 7. It would be worth it.
 
Even if you had the same engine and gearing, you wouldn't get the 12MPG because of all the stuff on the roof. Lose the rack and you might gain a couple MPG right there.

EFI and overdrive are your friends (as is driving slow). Probably either one of those would yield more gains than BBC-->SBC swap. Who tuned the carb and under what conditions? How is the distributor timing curve set up? There are people driving around with no vacuum advance complaining of similar issues.
 
Truck avenger? Those things are horrible on gas, they have them set to run super rich.
 
Chickntrk said:
Truck avenger? Those things are horrible on gas, they have them set to run super rich.
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Yes, I had to detune mine a bit to slow that down. It’s built for quick throttle and performance. It’s crazy fun to drive. As blue85 stated, slow down. Can’t do that. lol.
 
Blue85 said:
Even if you had the same engine and gearing, you wouldn't get the 12MPG because of all the stuff on the roof. Lose the rack and you might gain a couple MPG right there.

EFI and overdrive are your friends (as is driving slow). Probably either one of those would yield more gains than BBC-->SBC swap. Who tuned the carb and under what conditions? How is the distributor timing curve set up? There are people driving around with no vacuum advance complaining of similar issues.
Click to expand...
Well the funny thing is, there’s not much vacuum advance, because it gives air, in higher rpm’s, instead of idle, like a quadraflush. I really miss those, by the way. The reality is. The rack stays so we can venture up to the cascades in 4 feet of snow, and camp. I can’t remember the timing curve, but we set it to spec, for best performance. The carb is set for up to 6000 feet, so I know it runs a little quirky in town for that reason. But, at best, I’ll never get more than 10mpg with that motor, if I will ever get that. I’ll bet I can get 15, on a tbi with the ecm? Even with my 373 gears. Hands down.
 
So, you’re wanting someone to do the swap for you? If so, that is something I can’t do all the way from Colorado.

I have the TBI 350 from the “Munepit” build with the ecm that might be available, I need to check with my friend that said he wanted it but is waffling on it.
 
bradshawtech said:
So, you’re wanting someone to do the swap for you? If so, that is something I can’t do all the way from Colorado.

I have the TBI 350 from the “Munepit” build with the ecm that might be available, I need to check with my friend that said he wanted it but is waffling on it.
Click to expand...
 
I am assuming if your older carburated truck has a 454 that is has a Turbo 400 transmission. The TBI/ECM part number you would want ends in 7074, which is the most common TBI/ECM out there. My truck came from the factory with a 4L80E, and has an TBI/ECM/PCM that ends in part number 7060.
 
1-ton said:
I am assuming if your older carburated truck has a 454 that is has a Turbo 400 transmission. The TBI/ECM part number you would want ends in 7074, which is the most common TBI/ECM out there. My truck came from the factory with a 4L80E, and has an TBI/ECM/PCM that ends in part number 7060.
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Yes it has, the turbo 400. Id like to switch that out for the 700r4, then I’d have the extra gear. Not sure I can get that done though?
 
I don't see a TBI 350 getting 15 mpg in a K5 with lots of accessories, I.E. weight and wind drag.
Since I added a 4" lift, 37s and one ton axles to my '90 Jimmy, (with a visor) it doesn't seem to get more than 11 on the way to and from Moab. Yes, higher elevation than you, but still sucks gas.
BTW, I have a 354 with an Edelbrock performer cam, Edelbrock Proflo 4. 700R4 trans with 4:56 gears.
I haven't experienced the conditions where you are, but I just don't see a 350 getting mpg that high in a modified K5.

I do believe that you could find 1 to 1.5 mpg in your current combination with slowing down and a better carburetor. But that isn't close to what you seek.
 
70jimmy said:
The best I have gotten in my Jimmy is 13 mpg on the 350 tbi. Rig weighs 6200 and it has a turbo 400 np205 and 4.10 gears on 37 inch tires.

I wonder if a fuel injection setup with your current engine would be a better investment?
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Too much money, and work.
 
77snowwheeler said:
Well the funny thing is, there’s not much vacuum advance, because it gives air, in higher rpm’s, instead of idle, like a quadraflush.
Click to expand...
I don't understand this statement. It reads like a Quadrajet gives more air at idle (less at high rpm?).

How many degrees does the vacuum can give?
77snowwheeler said:
Too much money, and work.
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You know that you can put TBI on the BBC, right? That's arguably less work than swapping to a 350.
 
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