RWD 4 door challenge

[Kckershovel]

Hello all. Long time lurker first time poster here. First let let me start off with I understand the limitations. I don't expect 100 or even 50 mpg but I would like to get as much as possible 30-35 would be great. I despise fwd cars and I need 4 door family ability. I prefer classic cars but understand the weight and aero drawbacks. I will work out the drivetrain but am having a tough time choosing a platform. For awhile I was looking for a 62-65 fairlane as they are midsize relitively light and available in 4 door. It's tough to find frontal area and cd figures for classic cars. I would go newer if it were worth it. Thought about 80 ish Malibu maybe a wagon. I even considered an corvair but have pretty much crossed that one off for multiple reasons. Okay I'm ready for all helpful replies.

[jamesqf]

I think you'll get much better fuel economy out of a more recent engine, at least with EFI (assuming same HP, of course). So newer engine transplant?

[Kckershovel]

I have lots of drivetrain ideas. Everything from Vw tdi to gm 2.8 v6 or roller block 305 with crank out of l99 4.3 v8 making a roller cam 265. I like distributors and carburetor but have built and tuned a mega squirt car as well so I'm not afraid of efi. I will be looking for efficiency on highway out of low end torque and high gearing. Rear axle in the 2.28-2.41 range and t-5 t-56 or 700r4 auto with lock up converter belly pan front air dam drum or small disc brakes probably steel wheels skinny tires. The stock l99 in the mid 90's caprice were good for mid to high 20's in that big heavy car. So I would think a similar engine in a lighter car with belly pan and proper wheel tires and gearing should return low 30's highway. No AC no power steering. Just wanting to start with the best platform to build from.

[oil pan 4]

If its a GM car then it will likely have the 10 bolt 7.5 or 7.62 inch ring and pinion gear.
Then your only options for numerically lower new gears is 2.73 gears or 3.08 gears.
The numerically lowest I am aware of for the 10 bolt was 2.54 gears, but I know of no one that makes them.
The lowest numbered gear I think you would want to have on a car like that is a 2.73:1.

If you go with an older GM car again it will already have some what small brakes up front.

[Kckershovel]

The late 70's Cadillac Seville came stock with 2.28 some say 2.29 rear gears. The gm 7.5 could be had all the way down to a 2.14 that came in some 79 or 80 malibu's there are ford rear that can be had in a 2.41 so tall rear gear won't be to difficult. I will pic rear axle ratios after deciding on engine trans wheel and tire to get the best flat ground cruise rpm at 70-75 in top gear. I'm thinking 1300-1700 rpm range. I am most concerned with highway mileage. That is why I asked about a light but more importantly aero platform to start from. The Malibu are shaped like a brick as are most cars that fit my size and rwd requirements.

[spacemanspif]

For 1 year right at the beginning of gas price increases I bought a 2.29:1 rear out of a Malibu and swapped it in to my Monte Carlo (78-88 g-bodies). I didn't have a way to calculate miles travelled other than the math that I think was correct/close to accurate. I drove for a week at the "math'd out" RPM for 65mph (1600ish) and got terrible mileage; even worse than with the stock 3.73:1 rear. Once I brought the RPM up to 2000, I started getting much better MPG to the tune of ~25mpg around ~80mph.

Cruise RPM is super important and should not be over looked. A t56 with its double overdrive might never see 5th with such a tall rear gear. 6th might be totally useless n

I like the idea of a 4cyl cummin in a Malibu wagon.

[Kckershovel]

I also know sometimes lower rpm can hurt mpg. Especially with a short stroke engine or one with cam that makes peak torque higher in the rpm range. I doubt I will need or want to spring for the cost of a t56. Like I said drivetrain is not what I will have trouble choosing. I was just hoping someone had a platform I had not considered or could give me data on a good choise. Something like believe it or not the 68 caprice despite being a little heavy has a decent aero profile with fast back roof line and at constant highway speed the extra weight won't matter as much as the aerodynamics. So that would be my choice bla bla yadda yadda. Maybe there just isn't a very good platform to start with?

[darcane]

First gen CTS came with an optional 6-spd behind the V6. A competent driver should be able to hit 30mpg without much trouble.

If you are set on an engine swap in an older car, most classics have terrible aero. Look into Land Speed Racing cars for tips on improving them.

[mcrews]

Man, I'm in!
You certainly know some stuff!
Admire the thinking outside of the box!
Oh yeah,.....big time welcome!!!

A little on topic
I want to restore a 66 mustang with a bolt in rack-n-pinion suspension, a 200 straight 6 w/ a modified head to take efi, and a automatic overdrive tranny.

[Kckershovel]

First I appreciate the cts suggestion. Never considered one of those and it does meet the criteria
. Not as much fun as building something but definitely the most affordable way to get what I was asking for. I just looked at a few and I might just have to own one of those.

Now to the person with the mustang. Have you seen classics inline alloy head with removable intake for the ford small six? If not check it out. Also check out fordsix forum. If it were me I would look for a 250 inline six with the Windsor trans bolt pattern and put the alloy head on it with an ford AOD trans out of a late 80'S ford Lincoln mercury behind it and do either megasquirt Chevy tbi or fast efi for injection.