20 mpg or not?

[INSIDIOUS '86]

Originally Posted by mrhino

Thanks to Insidious I revisted the Tuned port Idea and Iv decide to give it a shot. These old tuned port make a sh!t tons of torque ( well in this case a 1/4 sh!t ton) and combined with those old "junk" swirl port heads, which were only designed to make torque. Iv increased my chances of achieving my 20 mpg goal. I have also decided to use a diffident cam to better suite this combo. 196* 206* @.050 and 109 LSA .431 .451 with 1.5 rockers

Looks good. Doing the same thing but with a 283 with tbi heads and a tpi system. Just on a SLIGHTLY smaller k5...lol
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[MrBeast]

I would say you have a snowball's chance in H-E double hockey stick of getting 20mpg out of a 350 unless you have full EFI, custom tune, no emissions equipment and a 4L80E

Considering you are in a CC dually you are going to need 19.5's to bring the rolling resistance down, and lots of other things.

Really you would be better off tossing a Cummins in it.

I have a Vortec 454 in my 2000 CC Dually, it is much more aerodynamic than yours, everything on it has been tip top tuned, cats and emissions gear removed, running 65mph I get 14 mpg empty.

with a 350 you are going to find that with a 350 you are going to be underpowered in that dually which means less MPG's especially when you hook a trailer to it.

[MrBeast]

Originally Posted by mrhino

Thanks to Insidious I revisted the Tuned port Idea and Iv decide to give it a shot. These old tuned port make a sh!t tons of torque ( well in this case a 1/4 sh!t ton) and combined with those old "junk" swirl port heads, which were only designed to make torque. Iv increased my chances of achieving my 20 mpg goal. I have also decided to use a diffident cam to better suite this combo. 196* 206* @.050 and 109 LSA .431 .451 with 1.5 rockers

Running a TPI will help with the MPG's I would suggest looking into running a 411 ECM and sequential MPFI the TPI engines were all bank to bank, the sequential engines were much more economical.

[mrhino]

Originally Posted by MrBeast

I would say you have a snowball's chance in H-E double hockey stick of getting 20mpg out of a 350 unless you have full EFI, custom tune, no emissions equipment and a 4L80E

Considering you are in a CC dually you are going to need 19.5's to bring the rolling resistance down, and lots of other things.

Really you would be better off tossing a Cummins in it.

I have a Vortec 454 in my 2000 CC Dually, it is much more aerodynamic than yours, everything on it has been tip top tuned, cats and emissions gear removed, running 65mph I get 14 mpg empty.

with a 350 you are going to find that with a 350 you are going to be underpowered in that dually which means less MPG's especially when you hook a trailer to it.

I think, I do have have a snowballs chance. I may not hit that 20 mpg mark but its gonna be close. What does a 4l80 have to do with gaining mpg. in fact it has A lower final Gear raito than the 700, thus a higher cruising RPM.

Im not sure what your meaning by 19.5 what is that.

Tossing in a cummins.

I dont know if comparing a 454 to this small block is quite a fair comparison.

You do realize catalytic converters EGR and other emissions help fuel mileage. removing that stuff would surely hurt mileage.

I don't believe this engine is going to be under powered. If it were in anything else it would for sure make 20 and then some. By the way the truck is not a dually and wont be pulling very many trailers.

I am looking in to the sequential over the batch fire. cost, reliabilty, and ease of installation will all play a role in my decisions on that.

[MrBeast]

Originally Posted by mrhino

I think, I do have have a snowballs chance. I may not hit that 20 mpg mark but its gonna be close. What does a 4l80 have to do with gaining mpg. in fact it has A lower final Gear raito than the 700, thus a higher cruising RPM.

Im not sure what your meaning by 19.5 what is that.

Tossing in a cummins.

I dont know if comparing a 454 to this small block is quite a fair comparison.

You do realize catalytic converters EGR and other emissions help fuel mileage. removing that stuff would surely hurt mileage.

I don't believe this engine is going to be under powered. If it were in anything else it would for sure make 20 and then some. By the way the truck is not a dually and wont be pulling very many trailers.

I am looking in to the sequential over the batch fire. cost, reliabilty, and ease of installation will all play a role in my decisions on that.

I misread your thread, for some reason I thought you were running a dually, I actually just got done reading your build.

In your setup I think the 5.7 with the TPI manifold will be great.

I for some reason thought you were building this truck as a tow pig not as a DD for your wife.

19.5's are 19.5" wheels that mount commercial truck tires, they have a much stiffer side wall and thus much less rolling resistance and better MPG's but not applicable to your application.

one thing to consider with the 411 ECM is that you can run individual coil packs if you want to.

[INSIDIOUS '86]

Individual coil packs will help mpg and power overall adding a msd helps too.
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[jitteryguy]

Originally Posted by mrhino

I went back and forth on what gears to run. I had 3.73 available to me if I wanted them. In the end I decided to keep the 4.11. Here is my thinking. The truck will spend a good portion of time driving my wife back and forth to work. Through town with lots of stops and turns. I figured since she is a big girl as a couple of you had pointed out.( the truck, not my wife she reads these posts from time to time) The shorter gear would aid in getting those big tires and girth of the truck moving much much easier and would result in less fuel being burned, at least through town. Yes it sacrifices fuel mileage on long freeway trips. but the taller gears make it much more difficult to turn those tall tires and get her up to speed. Gears are a trade off its one of those things where you cant have your cake and eat it to. For me there were really only 2 logical choices for gears. 3.73 or 4.11 I chose the ones I thought would do the best considering where the truck would spend much of is time. Maybe 3.73 would have been a better choice IDK.

the TH400 had a first gear ratio of 2.48 and the 700R4 has a firts gear of 3.06 ,
this will help with get the big truck roll'n even with a 3.73 or higher gear set.

[Firebirdjones]

Originally Posted by mrhino

Within the week or so, the wife & I will be starting the engine build for the crew cab project we have going on. Over the weekend, It brought up a interesting debate with a few buddies that I trust and respect for their engine performance knowledge. My Goal with this engine is to get 20 MPG. A couple said it could be done and a couple said it wouldn't happen. Everyone made their points and theories. The debate and conversation was educational and interesting so I thought Id ask it here and see what some of the thoughts are.

The truck is a 88 1 ton crew.
4:11 rear
305/70/16 tires
700r4 trans

the engine will be a .30 over 5.7
58cc 187 swirl port heads with a mild port job.
20cc dished pistons
vortec Roller Cam 191º/196º 0.414"/.428" lift on a 111º LSA.
1 5/8 headers

so do you think it will get 20 MPG?

It's really going to depend on alot more than just what you have listed there. Your ability to sharply tune the engine with a wideband as well as driving habits, the elevation you live at etc....are all going to play a role. All you can do is maximize your efforts and see what you get.

Those tires are just about 33" tall. Even with the .70 overdrive I'd like to see the rpm knocked down further for max highway fuel economy, and that would require knocking some of that gear out. With the 3.06 first gear the truck gets moving easily enough and doesn't need those 4.11's. A 3.73 would work nicely and drop the cruise rpm another 3-400, probably worth another mpg.

You going carb or fuel injection? Either will do the job well enough if you can tune the carb properly (again using a wideband). To maximize fuel injection you'll need tuning software with the wideband, and concentrate on lean cruise conditions with light throttle input. Lots of variables here and alot to be gained.

If I can get 14 mpg highway from a 502 in my 79 1 ton with no overdrive then I see no reason why you can't do better with a 350.
I've never maximized my combo as far as squeaking mpg out of it. Still has heavy 16.5 steel wheels, mechanical fan, and few other tweaks that can be addressed for max efficiency. Basically a sharply tuned quadrajet on a performer intake with a tweaked distributor, headers, 3" exhaust, cold air intake setup is all that's been tweaked on. Stock 3.73 gears with a stock 30" tire running a 400 turbo. Seems to work pretty good for what I use it for so it's left alone.
My blazer is probably the closest to your combo. But I've installed a 6.0 LS engine in front. I run the 4L60E (electronic version of your 700) and also use a 33" tire but I installed 3.73 gears for a mix of performance and economy. The 6.0 (364 cubes) is a stock 04 LQ4 down to the stock exhaust manifolds. I removed the mechanical fan and went dual electric to cut down on some drag. Custom 2 1/2" dual exhaust. I tuned it with a wideband, concentrating on lean cruise, aggressive DFCO tables, some throttle and timing table tweaking as well as trans table tweaking etc...This is a 4x4 still using the stock (heavy Hp robbing) 205 transfer case and the truck weighs 4,960 lbs. I get 17 mpg around town, and 22 mpg highway.

So yeah, 20+ is doable in these old boxy trucks with the right parts, but what I've done isn't cheap either.

If it were my truck (and you probably don't want to hear this ) and I were going for a fuel economy effort, I'd probably ditch the 355 idea, and grab a 5.3 LS to swap in. The electronic fuel injection alone allows more tuning options and more tweaking, it'll make more power too, and more likely to give you the fuel economy your after.