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Motor swap.

Blue85 said:
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?

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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I’ve already been down that rabbit hole with the atomic or sniper. Researched it and it’s 2000 bucks for me to venture on that. I’ve had Quadra jet before and it has a bigger port for vacuum advance. When you take the hose off it’s a very strong vacuum. When you take the hose off, the avenger it’s not strong at all, until you throttle up. Ultimately the 454 definitely has a stopping point for mpg, verses 350, there’s more options to get the most out of it. Especially my 454. It has flat top pistons because originally I was going to put a blower on it. I have a lot of low end torque, and very high compression, that a stock 350 wouldn’t have.
 
What is the math on what a 2-5 MPG increase will actually save you? How many miles do you put on this truck every year?

Assuming a few things here but:
gas is $5/gal - high estimate for premium gas - worst case scenario
you drive 6,000 miles a year, which is a LOT for a toy/play truck,
You actually manage to get 12 MPG with a 350, which I think is unlikely. All other things remaining the same, that's a 71% increase in MPG over your current 7 MPG. Chances are you will need to make other changes to see 12+ mpg. EFI and a 700r4 or 4l60e would get you there but that's a pretty expensive proposition.

You would save about $1785 per year going from 7 to 12 MPG. Not too shabby there IF you can get this project done for zero cost / straight trade / minimal downtime. I'm sure someone out there wants to make this trade happen but your pool of local candidates is likely very slim.

At 1500 miles per year, your savings is about $446 per year and this swap is not worth the effort in my opinion.
A 3MPG increase will net you $1285/yr savings at 6000 miles and $312/yr at 1500 miles.

Not trying to talk you out of it so much as highlight any variables that may have been missed.
 
Polymath said:
What is the math on what a 2-5 MPG increase will actually save you? How many miles do you put on this truck every year?

Assuming a few things here but:
gas is $5/gal - high estimate for premium gas - worst case scenario
you drive 6,000 miles a year, which is a LOT for a toy/play truck,
You actually manage to get 12 MPG with a 350, which I think is unlikely. All other things remaining the same, that's a 71% increase in MPG over your current 7 MPG. Chances are you will need to make other changes to see 12+ mpg. EFI and a 700r4 or 4l60e would get you there but that's a pretty expensive proposition.

You would save about $1785 per year going from 7 to 12 MPG. Not too shabby there IF you can get this project done for zero cost / straight trade / minimal downtime. I'm sure someone out there wants to make this trade happen but your pool of local candidates is likely very slim.

At 1500 miles per year, your savings is about $446 per year and this swap is not worth the effort in my opinion.
A 3MPG increase will net you $1285/yr savings at 6000 miles and $312/yr at 1500 miles.

Not trying to talk you out of it so much as highlight any variables that may have been missed.
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Yikes. Wasn’t expecting the science, but makes sense. Thanks
I guess the real answer is someone else in the White House, that could help with everyones fuel problems. Then I wouldn’t have to change anything? Lol
 
Yeah. A lot of people start thinking about ways to save on gas when they are filling up the tank but few actually do the math. My mom was dying for a hybrid vehicle many years back because it got twice the gas mileage of her car. Turns out it would have taken her 6 years to pay off the difference of cost in the hybrid versus non-hybrid car because she only drives 5k/yr and at that time, the upgrade to a hybrid motor was about $5k over the gas motors. $5k is a lot of dang fuel.

It gets better when you assign dollar values to your time and the overall enjoyment factor of having the bigger motor.
"If I had a dollar for every time in my life I wished I had more power/torque..."
"If I spent less time upgrading the car and more time enjoying what I have..."

Sadly, I don't ever expect fuel to drop in price by a considerable amount over the long haul. It'll see spikes and dips but will always average up. The real magic trick is ensuring that your income averages up as well.

I don't usually love math but I love the logic it brings with it. If you can assign values to all your variables, your choices can become very clear.
 
I’ve read through all of this and based on my experience you are going the wrong way to swap out a BBC for a SBC for fuel economy reasons.

I’ve gone from running a 5.3 with EFI to an 8.1 with EFI. Wanna take a guess at the difference in fuel economy between the two under the same conditions? None. I’m getting the same mileage with the 8.1 that I used to get with the 5.3.

I know it’s backwards in logic but when you consider the 5.3 was getting spun to the moon downshifting on grades or even pushing a headwind the 8.1 is doing it at a much lower rpm with minimal downshifting.

Keep in mind my truck weighs in over 7,000 pounds with either engine/trans combo. It’s pushing the aero equivalent of a barn door with a Four Wheel pop up camper on the back. Same tire size and axle ratio between the two at 4.10’s and 35’s.

Yes if I fog the 8.1 like a manic it gets 8 mpg. But if I drive it sane and maintain 65-70 it can knock back 16 mpg which it has done twice going to Moab. Around town mileage is closer to 12-13 just like the 5.3 was.


You are fighting an uphill battle for mileage with a carburetor on either engine. I can guarantee a carb equipped small block won’t have the torque the big block does down low which you’ll surely miss when snow wheeling. If anything to better help the small block you might have to go deeper on the axle gearing to keep the SBC wound up into the meat if the torque curve to maintain speed better without as much or frequent downshifts. Regearing the axles is a spendy operation too.

I’ve read you don’t want to mess with EFI or it’s too expensive but you won’t meet your goals with a carb on either engine. You could always choke it down with a 2bbl carb to limit the fuel consumption but say goodbye to what power you did have before.

I’ve mentioned this before but on these trucks there is no free lunch when it comes to power and fuel economy. These trucks are HEAVY and need torque to get moving. You can build a small block for low end grunt but it’s still going to suck fuel like a madman. A milder big block is still going to suck fuel but it’s doing so at a much lower rpm which is easier on everything downstream but also on your nerves because you are screaming at 5,000 + rpm on long heavy pulls.

Like polymath mentioned putting a cost to the swap and seeing how long or if the fuel savings pay off is smart.

EFI and OD will net the largest fuel economy gains without question. But if it was me I’d leave the big block in there and have fun. Fuel use is a cost of doing business with these trucks. I watch my numbers like a hawk on every tank but I don’t let the cost keep me from doing what I want. You just have to budget for the fuel on trips and plan on the cost.

I’ve looked at it from a point of view on the long trips I like exploring on. If I traveled by air to a location I’d have that cost, plus transportation when I get there, food, lodging, etc. Throw a figure on each of those items and then looked at what I typically spend on a off road 7 day trip. Fuel, food from the grocery store I cook, drinks bought before leaving, no lodging with the camper, etc. in my case comparing to an average flight somewhere and renting a car or ride shares it’s cheaper going on my week long camping trips even if fuel is closer to $5.00 a gallon. At least that’s how I justify it to myself. But not listening to a small block getting beat to death on the grades and hills is totally worth it. It’s just more enjoyable not worrying about the engine getting hammered on just trying to maintain speed up a grade.
 
77snowwheeler said:
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?
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you won't like the 700r4 with 3.73. I had a 700r4 with 4.1 and 33's need to regear to 4.88, which works out to 3.42 in over drive. SBC power plant and I would murder for 10mpg in that heavy ass, 4" lift, no roof rack pig.
 
77snowwheeler said:
I’ve already been down that rabbit hole with the atomic or sniper. Researched it and it’s 2000 bucks for me to venture on that. I’ve had Quadra jet before and it has a bigger port for vacuum advance.
Click to expand...
What I'm talking about is the TBI Injection that came factory on 454s. It's pretty much the SBC version, but with a bigger throttle body and injectors. It does limit the top end power, but gives reasonable MPG.

As for vacuum advance, why not just hook it to a manifold port?
 
Polymath said:
Yeah. A lot of people start thinking about ways to save on gas when they are filling up the tank but few actually do the math. My mom was dying for a hybrid vehicle many years back because it got twice the gas mileage of her car. Turns out it would have taken her 6 years to pay off the difference of cost in the hybrid versus non-hybrid car because she only drives 5k/yr and at that time, the upgrade to a hybrid motor was about $5k over the gas motors. $5k is a lot of dang fuel.

It gets better when you assign dollar values to your time and the overall enjoyment factor of having the bigger motor.
"If I had a dollar for every time in my life I wished I had more power/torque..."
"If I spent less time upgrading the car and more time enjoying what I have..."

Sadly, I don't ever expect fuel to drop in price by a considerable amount over the long haul. It'll see spikes and dips but will always average up. The real magic trick is ensuring that your income averages up as well.

I don't usually love math but I love the logic it brings with it. If you can assign values to all your variables, your choices can become very clear.
Click to expand...
Inflation is 17%, I got a 4% raise. Yep, that didn’t work. Lol
 
Blue85 said:
What I'm talking about is the TBI Injection that came factory on 454s. It's pretty much the SBC version, but with a bigger throttle body and injectors. It does limit the top end power, but gives reasonable MPG.

As for vacuum advance, why not just hook it to a manifold port?
Blue85 said:
What I'm talking about is the TBI Injection that came factory on 454s. It's pretty much the SBC version, but with a bigger throttle body and injectors. It does limit the top end power, but gives reasonable MPG.

As for vacuum advance, why not just hook it to a manifold port?
Click to expand...
I called Holly about the vacuum and suggested I go straight to full manifold, and he said the carb wouldn’t like it. I did it anyway, and it didn’t change anything.
Click to expand...
 
IMHO if you want mileage you should be looking into a newer generation engine,(loads more work in the swap though) something like the GEN V lineup. I'm running a L83 (5.3) with a th400 and 4:10 gears. When I had 35" tires I got an honest 17 mpg and dropped to 14 mpg with 37s. No roof rack or winch and it sits around 4-5 inches of lift.

EDIT: just say the reply about the EFI being too much work. Good luck with your rig!
 
Blue85 said:
What I'm talking about is the TBI Injection that came factory on 454s. It's pretty much the SBC version, but with a bigger throttle body and injectors. It does limit the top end power, but gives reasonable MPG.

As for vacuum advance, why not just hook it to a manifold port?
Click to expand...
I ran Performance fuel injection systems GM Tbi kit on my old stockish 350. It ran great. No tuning and just set base timing. It came with the distributor and all new parts and reman throttle body.

I see they sell a kit for a 454, as long as his cam isn’t too rowdy for tbi they can adjust the prom with his kit if he gives the guy his engine specs. Probably only gain 2mpg or so. But may be worth the time at 1150$ for the 454 kit currently.

But if efi isn’t his thing then I’d say finish a complete tune on the Holley carb with the whole Holley tune kit (secondary cams and jet down).And drive slower? Save more money for gas each time out. I’m another vote for a small block won’t help this situation.
 
Desert_K5 said:
IMHO if you want mileage you should be looking into a newer generation engine,(loads more work in the swap though) something like the GEN V lineup. I'm running a L83 (5.3) with a th400 and 4:10 gears. When I had 35" tires I got an honest 17 mpg and dropped to 14 mpg with 37s. No roof rack or winch and it sits around 4-5 inches of lift.

EDIT: just say the reply about the EFI being too much work. Good luck with your rig!
Click to expand...
I also considered selling my 77, and getting a 96 gmc 3/4 ton short box, because it’s only a foot longer with the extra cab, and my rack will fit right on it. But no one wants to give me 17,000 for my truck. It’s worth every cent and more. I have every bit of that much cash in it. Not including labor. It wouldn’t be as cool, but it would definitely be more practical, for me.
 
77snowwheeler said:
I’ve already been down that rabbit hole with the atomic or sniper. Researched it and it’s 2000 bucks for me to venture on that. I’ve had Quadra jet before and it has a bigger port for vacuum advance. When you take the hose off it’s a very strong vacuum. When you take the hose off, the avenger it’s not strong at all, until you throttle up. Ultimately the 454 definitely has a stopping point for mpg, verses 350, there’s more options to get the most out of it. Especially my 454. It has flat top pistons because originally I was going to put a blower on it. I have a lot of low end torque, and very high compression, that a stock 350 wouldn’t have.
Click to expand...
You can put tbi from a stock gm engine for a couple of hundreds.
The problem is the built 454 will probably not agree with the ecm.
If you have the specifications of your build, post up here and let the experts chime in.
If a TBI can be tuned for those specifications I have a complete setup on my 454 that I would sell you cheaper than the sniper.

And no way in hell you will come close to 25 mpg with a 350, not even the vortec, I know I have all of the above.
350 carb
350 tbi
350 vortec.
The only gain with tbi was reliability.
The virtec was smoothness an quiet.
11mpg was my number for all.
I am getting 12mpg with my 454 vortec
 
imiceman44 said:
You can put tbi from a stock gm engine for a couple of hundreds.
The problem is the built 454 will probably not agree with the ecm.
If you have the specifications of your build, post up here and let the experts chime in.
If a TBI can be tuned for those specifications I have a complete setup on my 454 that I would sell you cheaper than the sniper.

And no way in hell you will come close to 25 mpg with a 350, not even the vortec, I know I have all of the above.
350 carb
350 tbi
350 vortec.
The only gain with tbi was reliability.
The virtec was smoothness an quiet.
11mpg was my number for all.
I am getting 12mpg with my 454 vortec
Click to expand...
Sounds great, except I built the motor so long ago, and moved about four times, I don’t have the cam specs. It’s bored 40 over with flat top pistons, large ovel port heads, and hydraulic rockers. I’d be very interested in the 454 set up?
 
My 79 blazer got a bit over 12 mpg on flat land on my recent trip, using my GPS speedo.
Sbc400, th350, 3.73 gears
Dropped considerably in the mountains..
 
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