It's getting to the point where it's cheaper, for my 230 flathead anyway, to just buy the tools and do a three angle VJ myself.

Since I don't already have a 5.2 Magnum to start with, I'm shopping for whatever I can get to make the best daily driver 318. I'm leaning toward port fuel injection for the better fuel mileage. So what year 5.2 Magnum should I shop to buy? Seems that anything 5.2 Magnum after 1995 is a good choice, correct? I may use the Mopar factory performance heads or go for a set of aluminum aftermarket heads with the bigger valves. I have a decent budget so I can select the best cam for torquey power, best Edlebrock EFI intake and a good set of headers.

What’s the lowest gear the 8-1/4 came with? I’m thinking now of still keeping the 904 with hat low first gear instead of an overdrive behind the 360. Also keeping the TBI adapting to the SP intake with 318 heads.

The lowest gear I have seen in a factory 8.25 is 3.92 however I think you are actually wanting to know the highest gear and the highest I have seen is a 2.20 with a 2.45 being fairly common.

The higher number of gear makes it a lower gear rear end. A 4:10 is a low gear, but a 2:76 is a high gear. Sounds pretty dumb, but that is how it works. Its easier to picture the speed at a given rpm. With 4:10 gears at 2,000 rpm, the vehicle speed will be pretty low. But with 2:76 gears at the same 2,000 rpm, the vehicle speed is much higher.

I had a 2:76 gear 8 1/4 in a 54 Dodge pickup for a while. The problem with that high of a gear is that you put your foot into the gas pedal more to get it to crawl away from stop signs. That gear with tall 15" tires sure kills off the stop power. I actually gained about 2 mpg when I swapped in a 3:23 geared 8 3/4 into the truck. I didn't have to step into the gas so hard to get the truck to move.

The OD with the lower gear is the best of both worlds, you get it rolling easier with less throttle input the lower gear, than once at a steady cruising speed on the highway, the OD drops the rpm. Those small block Mopars are very efficient at 1800 -2000 rpm at the chosen mph. Gear the rear end to turn those 1800-2000 rpms at the speed you expect to be driving at the most. Much lower rpm and it works too hard pulling hills of any height and will kill the mpg. Its very hard to find a cam that will produce the torque you need to pull the hills at those low rpms.

What’s the lowest gear the 8-1/4 came with? I’m thinking now of still keeping the 904 with hat low first gear instead of an overdrive behind the 360. Also keeping the TBI adapting to the SP intake with 318 heads.

The OD with the lower gear is the best of both worlds, you get it rolling easier with less throttle input the lower gear, than once at a steady cruising speed on the highway, the OD drops the rpm. Those small block Mopars are very efficient at 1800 -2000 rpm at the chosen mph. Gear the rear end to turn those 1800-2000 rpms at the speed you expect to be driving at the most. Much lower rpm and it works too hard pulling hills of any height and will kill the mpg. Its very hard to find a cam that will produce the torque you need to pull the hills at those low rpms.

The higher number of gear makes it a lower gear rear end. A 4:10 is a low gear, but a 2:76 is a high gear. Sounds pretty dumb, but that is how it works. Its easier to picture the speed at a given rpm. With 4:10 gears at 2,000 rpm, the vehicle speed will be pretty low. But with 2:76 gears at the same 2,000 rpm, the vehicle speed is much higher.

I had a 2:76 gear 8 1/4 in a 54 Dodge pickup for a while. The problem with that high of a gear is that you put your foot into the gas pedal more to get it to crawl away from stop signs. That gear with tall 15" tires sure kills off the stop power. I actually gained about 2 mpg when I swapped in a 3:23 geared 8 3/4 into the truck. I didn't have to step into the gas so hard to get the truck to move.

The OD with the lower gear is the best of both worlds, you get it rolling easier with less throttle input the lower gear, than once at a steady cruising speed on the highway, the OD drops the rpm. Those small block Mopars are very efficient at 1800 -2000 rpm at the chosen mph. Gear the rear end to turn those 1800-2000 rpms at the speed you expect to be driving at the most. Much lower rpm and it works too hard pulling hills of any height and will kill the mpg. Its very hard to find a cam that will produce the torque you need to pull the hills at those low rpms.

Confusion abounds in “gear ratio” as regards good fuel economy.

I suggest talking about MPH for each 1000 rpm, which takes everything into consideration, including tire diameter.

As regards getting the “right camshaft grind” for fuel economy, that is especially tough.
Today “variable valve timing” certainly improves late model engine fuel efficiency
but adjusting “ground in camshaft values”
down to what VVT is truly doing to the valves in today’s “real world”
is nearly impossible because even today’s 1800 page FSM
does not have tables about what modern PCM software commands are making happen to lift and duration.

There is another 10% fuel economy improvement if the air to fuel ratio goes from 14.7 to 18 or more.

There is an old Autospeed.com article about the early year Australia spec Honda Insight
and how at steady cruise speed on a level highway its air to fuel ratio would lean out to 25 to 1.

My opening point was, many new to the automotive world, or those that have not been taught better, believe that a rear end gear in the 4:00 something (4:10, 4:88) is a high rear end gear (big numbers) and that a rear end gear in the 2:00 something (2:45 or 2:76) is a low rear end gear (low numbers) when in fact both of these statements are incorrect. A 4:00 something rear end gear is considered a low gear ratio and a 2:00 something rear end gear is considered a high rear end gear. We need to be sure people learn these things correctly, and if they don't hear it from us, who would they hear it from?

If you are cruising along in your ride at 1800 rpm at 70 mph, and you come to a 5% grade increase on the road, to maintain the 70 mph speed, you have to open the throttle. How much, and for how long you open that throttle for will depend on the torque the motor has. As soon as you open that throttle more then it was opened before the 5% grade, you are reducing the fuel mileage the motor is getting. In the over all picture a one time event probably will not make much difference, but should it happen often, the throttle effect will have more impact on the mpg.

The point someone brought up about the mid 80s 318 2bbl wit the OD and the 2:71 rear gear was interesting. If you actually drove any of those vehicles you fully understand what I am talking about. Even the slightest increase in the grade on the highway would drop the trans out of OD. If the vehicle was running on cruise control, after it dropped out of OD, it would also unlock the converter, and if the hill was big or long enough, it would open the throttle wide open, and might even shift the trans into "passing" gear. I worked at Chrysler as a tech from 86-88. Guess what the biggest complaints about those new OD transmissions were? Constantly engaging and disengaging the OD on hilly country roads. If they were driven and used on pretty level roads, they pulled some pretty good mpg, but throw in a few hills, and that mpg dropped. Chrysler actually limited the availability of getting the high rear gear and the OD in some locations across the country