Better gas mileage and performance.

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX
my truck has 3.42s and 30" tire. OD is basically useless unless on flat ground or going down hill. I live in mountainous terrain, I would think that takes a big bite out of mileage. I had a 2bbl 305 w/ 2004R in an early 60s impala about 15 years ago. I would get 23-24 mpg, but this was in the prairies where roads are flat. i also knew nothing about carb or ignition tuning.

@L31MaxExpress I should get your help with my timing map sometime. I haven't had time to mess with it but it is a neutered for sure.

I tested the Express van at one point on a long road trip when it was stock with the 4L60E and 3.42s. OD was useless in terms of fuel mileage compared to 3rd gear. It was constantly in and out of lockup and often downshifted to 3rd on its own. It was not until I started adding power that overdrive became a useable gear. Then I swapped to the 4L85E then put the 3.73 rear gear. At 70 mph the 4L85E and 3.73s added ~400 rpm and overdrive became useable and actually netted a small mpg gain. With the 383 there are roads flat enough here that it could use a taller overdrive ratio and other roads that a split between the current OD and 3rd would be nice. That is where the 6L90E will soon be an awesome addition.

The Tahoe was under geared with the 3.42s and 32" tall tires, but that little 305 did not seem to mind pulling along at 1,700 rpm with basically zero manifold vacuum. By that point I had learned how to make a good shift point and TCC lockup schedule and keep the thing in overdrive under moderate power yet still have ample response to downshift to hold speed without continually hunting the gears. When the 305 downshifted to 3rd as it often did, it still managed decent fuel mileage because it was 45 cubic inches smaller than a 350, thus less air and less fuel. The cammed 305 was like a 5.3L, it wanted to rev to make useable power, so I let it. Running 75 mph if I needed more power it would even downshift to 2nd if the go pedal was pinned to the floor.
 
Last edited:

tayto

I'm Awesome
Joined
Nov 11, 2020
Messages
724
Reaction score
762
Location
Canada
i swapped to ECM controlled distributor this spring. Have not had time to mess with it much since I relocated for work and now bought a new place, moving etc. the truck runs and as long as im careful doesn't detonate. I have an EBL kicking around that i've had since 2010 and loaded a stock truck TBI cal. however still running the Qjet with no TPS so my lockup is a bit whack at the moment. better than previous with no ECM control and it would lockup immediately in 4th, yuck. I EFI tanks ready to go, I just need time to swap them and I think I'm just going to put a TBI on it.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX
i swapped to ECM controlled distributor this spring. Have not had time to mess with it much since I relocated for work and now bought a new place, moving etc. the truck runs and as long as im careful doesn't detonate. I have an EBL kicking around that i've had since 2010 and loaded a stock truck TBI cal. however still running the Qjet with no TPS so my lockup is a bit whack at the moment. better than previous with no ECM control and it would lockup immediately in 4th, yuck. I EFI tanks ready to go, I just need time to swap them and I think I'm just going to put a TBI on it.

I ordered a Holley port fuel manifold this weekend. They had the Vortec one for $198 and the standard 1955-1986 pattern version for ~$170. Fuel rail with regulator and crossover lines was ~$110.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX

this one?
1955-1986 version

This is the Vortec one.
 

Martin Evans

I'm Awesome
Joined
Mar 15, 2022
Messages
118
Reaction score
138
Location
Garden City ID
Accelerating slow has never saved any fuel for me. In fact it is just the opposite. Give the pedal a good 1/3-1/2 throttle shove and keep it open until you are up to cruising speed. The engine is most efficient accelerating a vehicle near its peak torque rpm. I am not saying stand on the go pedal, but give it enough throttle to couple the torque converter well, get it through the lower gears and into overdrive quickly and get it into lockup as soon as possible. You will actually burn more fuel starting off slowly by staying in the lower gears longer while the torque converter slips away wasting fuel.
Yeah, that bugs the crap out of me when the person in front of me takes half a mile to get to 30 mph. My car gets about 15-20 mpg while accelerating moderately and then will get about 40 mpg once I get to speed. Most vehicles perform in a similar manner. Therefore, it makes sense to get to cruising speed sooner rather than later.
 

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,595
Reaction score
15,492
Location
Choctaw, OK
So it would take 5 years just to break even on a cheap, $3500 car.
Yeah, but each vehicle is getting half as many miles. Your truck will depreciate slower.

I wonder if I change octane or go to 55 mph will I see improvement.
Please don't go slower than the speed limit. I don't need people running into the back of me when I get stuck behind you.
 

tayto

I'm Awesome
Joined
Nov 11, 2020
Messages
724
Reaction score
762
Location
Canada
1955-1986 version

This is the Vortec one.
looks like a nice manifold and cheap. but i think to much intake for what i'm doing. im tempted to buy one and shelf it. I have a squarebore to tbi adapter plate i bought of dctrumpet about 10 years ago that would work well here.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX
looks like a nice manifold and cheap. but i think to much intake for what i'm doing. im tempted to buy one and shelf it. I have a squarebore to tbi adapter plate i bought of dctrumpet about 10 years ago that would work well here.
I would shelf it. Holley is starting to discontinue small block stuff left and right due to emissions tampering laws. A TBI unit works great as an air valve and flows much better with the injector pod out of it. The old Edelbrock MPFI conversions worked very well considering they were basically a Torquer 2 low rise single plane manifold.
 

tayto

I'm Awesome
Joined
Nov 11, 2020
Messages
724
Reaction score
762
Location
Canada
I would shelf it. Holley is starting to discontinue small block stuff left and right due to emissions tampering laws. A TBI unit works great as an air valve and flows much better with the injector pod out of it. The old Edelbrock MPFI conversions worked very well considering they were basically a Torquer 2 low rise single plane manifold.
would you do regular intake pattern or vortec? i will probably goto aftermarket heads one day and have been avoiding the vortec style pattern because usually the intake costs more. is there any advantage to the vortec style? taller ports?
 
Top