e50095,

Welcome to the site!

First off don't pull the rear end....keep it. I run a 8 3/4 Sure Grip and get great mileage. I had it custom built. With your larger tires and the 3.23 ratio you will be just fine....

I get as much spunk out of my 225 SL6 as you can with a stock 318. There are a couple of things you can do to help it out.

1. at least 9 to 1 compression. This makes a huge difference in torque and ease of starting.....the stock engine is much to low.
2. use a Erson 254 or RV10 cam, see my specs below.
3. recurve the distributor, this makes a huge difference....
4. fine tune the 1920 Holley carb or step up to a Super Six.
5. electric fan
6. 0-30W Mobile 1
7. fuel line mode and heat deflector
8. fine tuning the valve lash
9. port the head
10. change to 2.25" exhaust.
11. etc...

You will be surprised how well the SL6 responds. I love mine after doing the upgrades. Clicl on the red link below my name for pictures. Double click on the picture once it comes up for full screen slide show mode.
I really love driving my Dart with the engine and drive train mods.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Second vote for keeping the 8 3/4, I used one with 3.23's and a sure grip and got 21 mpg at 70mph with 235/70R14's. I was using a lock up 999(or998 not sure which it was) out of a Van with shift kit installed.
Don't wast your time with the Feater Duster intake and carb, you would be much happier with a super six and 2 1/4" exhaust for power and mileage.
If you are willing to tear into a rebuilt engine I also agree with milling the head for compression and a installing a new cam.
I was really surprised at the night and day difference with swapping to an electric fan as well as the HEI upgrade.

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First off, don't kill yourself!!!
Having said that, welcome to the site! It sounds like you've got a cool cruiser/project car, and you've stockpiled some good parts too.
I also vote for keeping the 8 & 3/4 diff. For the engine, I say drop in the 225. Ted gave some good suggestions as far as mods you can do to her.
Have fun, and post some pics if you can!

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"Ja, Ich fahre ein altes auto."
'78 Volare 225
'67 Charger 318

That's a common fear/regret. Either size engine will get you where you're going. (Perhaps it's more important how your wife feels, if she'll be the primary driver? Just a thought...)

Given your reservations, I suspect that if you choose the smaller engine, you'll wish you'd gone with the larger.

You may come to accept the shortcomings of a 170... meaning plan ahead (far ahead) if you think you're gonna pass anyone on a 2-lane road. When one considers how much more satisfying a 225 is to drive, the extra fuel it drinks is surprisingly small. All other things being equal, using stock camshafts and carbs in stock mid-60s A-body cars, my experience with various engines (steady state highway mpg) is 20-22 with a 318, 22-23 with a 225, and 26-27 with a 170. This is when all are in good condition. When not in good condition, all bets are off. I got 13 mpg highway in a 170 once.

Changing to the 2.76 gears you're considering, a good 225 in an A-body ought to return 25 mpg easily, probably more. Remember that you can overdo the overdrive concept: if you run at a lower rpm than the peak of the torque curve, the engine won't be quite as efficient. I really don't know whether using such gears with a 170 would give you the same percentage increase that you'd see with a 225... that little engine would have to work awfully hard to power such a tall ratio, especially if you ever drive in hilly country. I definitely wouldn't try it without changing the low gear set in the 904 tranny, or you'll be swearing at the car every time the traffic light turns green. (A stock 170-auto-3.23 in a 65 Valiant is barely sufficient-- I got 0-60 times in the 14-15 second range.) If you get some data points with a 2.76 gear, please let me know.

Personally, I love the 170, but I've learned to live with it, and i don't expect it to impersonate a V8. (More importantly, I have a different V8 car for when I periodically need my fix.) Actually, even when warmed up a bit with a hotter cam, it's still no speed demon even compared to the average little Toyota or Honda of today. Depending on your local congestion and the courtesy of other drivers, it can be challenging to weasel your way into traffic...

It is satisfying to watch people's eyebrows rise in surprise when they hear you're getting 27mpg in a 40+ year old car. But most of them would be equally surprised to hear of 25mpg, I'll bet.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Go with the 225. I vote for keeping the 8 3/4 also. Also keep the 3.23 gears.
Use the 998 lockup trans. Set up the engine like Aggressive Ted's.
I think 24+ mpg could be possible with good tuning and driving with care.
I've tore up a 7 1/4 and its not fun. The 8 3/4 will be indestructible behind a slant.
I don't think the wife is gonna care too much about fuel mileage if she's driving a convertible! I just could never understand why women like the drop tops so much. Makes them happy though, I'll gaurantee you that. I just don't care for them myself.

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1979 W150 Shortbox
225, NP435, 9 1/4, Dana 44

The Good Life.