340 Build Advice
I run 3.55 gears and I'm even considering switching to 3.23. There's really no need for me to run anything like 3.91, I'm not drag racing the car. It's a driver and may see occasional autocross. Do you think the car is gonna spin out the tires that much? I run one of the widest tires a non-tubbed/spring relocated dart can, 15x8's.
Like
@goldduster318 says. it depends on your tires.
Now, the following is/are my experiences, and are my opinions.
But 255 streets are a waste of time at even 300hp.
My current car is a 1968 Barracuda 367/A833Commando/3.55s, and she goes 93 in the Eighth at 3467 pounds/me in it. The Wallace makes that to be 433 hp.
It spins 295 BFGs, or Cooper Cobras, or even 325/50-15 BFG-DRs right thru 2 gears, and more. With 3.55s in the back 6800 in Second is 80 mph. On the shift, into Second-over (GVod) the Rs fall to 5300, and guess what, that is just a wee bit over the power peak of my 230*cam, so ....... sometimes it just keeps on spinning........
And that is just what you are looking at with a goal of 400 to 500 hp, on 255s. or on any street tire that fits inside the factory tubs, for that matter.
Someone here on FABO, recently stated that it would cost over $3000 to fix that, by mini-tubbing, moving the springs, narrowing the rear, and installing some sticky fattys on appropriate wheels. I dunno if that's enough. Actually I doubt it.
In fall of 1970, I purchased a nearly new 70 Swinger340/A833/3.55s , and drove it until 1975. I can tell you without reservation, that car, on the factory tires, was the sickest-handling performance car ever brought to market, EVEN WITH the rally suspension. I was only just 17, the car looked awesome in PantherPink, but what a pos it was, as to handling; even just switching lanes a lil too abruptly could send it into a tizzy. That is the car I learned to drive in and after five years and many many sets of tires, I was still learning,lol. And that was with a pure-stock 275hp-advertised 340 that went 14.4 in the qtr spinning a very long way, on the PolyGlass E70-14s. It also easily laid rubber thru two gears with bias-ply G60-14s, or later, on radials. Not a hope in heck would I myself, with over 50 years of bag-driving street-experience, try to autocross that Dart on factory suspension with a stock 340 never mind a mean 340; No matter what tires are in the stock tubs. IMO you will get black-flagged for spending more time off-track than on.
But I can tell you another thing about that Swinger. Given a big open parking lot and a few strategically abandoned shopping carts, late at night, me and my younger brother, would have a chitload of fun, "testing the limits"! lol. Good times! Little Brother is gone now..... all I got are the memories.
Ok so like I said, those are my experiences.
The 340 was totally stock including the exhaust..
The 367 is a high-compression, eddy-headed, pussy-cat with a Hughes 230/237/110 cam in it, plus all the usual bolt-ons.
Dare I say this: if your stock 340car, on stock suspension, on the street, cannot spin street tires, in the stock tubs, to; right thru First gear and at least part way thru Second with 3.55s, then, either;
1) that 340 is sick/way out of tune, or
2) you got a pair of fantastic tires, or
3) IDK, maybe yur running downhill? .....
4) I would not install low-profile tires, on hi-dollar wheels, on any Street Dart that gets
driven because the curbs will eat your expensive wheels. Just one hit in today's world is likely to ruin your summer.
IDK, maybe I'm just a crusty old man, I dearly loved that car. I wish I would have had it 20 years ago, and did it up like I did my Barracuda. Such is life.