Im in the process of putting a 3.42 posi rear in the car now. I was just wondering if anyone has done this before and was wondering how it is with a 3.42. Im just a little worried about gas mileage, and highway cruising, and was wondering if its going to scoot pretty well or not. I just got done rebuilding the engine, slightly better than stock, but nothing that should give me a lot more HP over stock. Any info would be greatly appreciated.
In my opinion 3.42 is not a good road gear nor is it a good gear for mileage. The result is somewhat affected by tire height but a 3.08 or a 3.23 is tops for much road use. You would give up very acceleration little by dropping back to those ratios. As for scooting we do not know what engine( guess a 455) and what your expectations are. It is all relative -- one man's scooter is another's slug depending on what he is use to.
I agree 3.42 might be a little too big, the again find the tallest tire you can fit in it if you are set on the 3.42. Ask anybody with a 71-72 Riv GS that's the rear that came in that.
I'm not going to be doing some highway cruising, and gas isnt a big deal, I just dont want it to be too terrible. It's a 455, cam, ported heads, SPX intake, headers and 3" exhaust. Scooting to me would be low 14's, high 13's compared to the stock 2.73 gears.
I think that that gear will give you a better holeshot if you can get the power down, just not the best for highway milage. Here this should help. it's a quote from a diff thread: with 342's at 60 to 65 mph = 3000 RPM. If you like driving 70mph+ suggest looking at 308 or 323's or 273s
Gas mileage with a car of that weight I am guessing 10 mpg on premium. One of the Riv GS guys can tell you what they are getting with a similar rear .
Thanks, Im also putting a 2600 stall in it. Even if I do go highway cruising, I won't have any problem going 55-65 mph, I will be in no hurry going anywhere.
spx intake Hi did you have to cut the hood to make that SPX fix under that massive hood? Chris DeMik:3gears:
With 3.42 rear: RPM MPH 1500 35 2000 40 2400 55 2800 65 3000 70 I don't drive highway much, and the RPMs don't bother me at all around town. The only way I'll drop back to a 3.07 gear from my 3.42's is if I'm paid a million dollars to do it.
Re: spx intake Thats a good question. I'm waiting on the carb before I put it on. I don't think so, but I'm planning on it being very close. If not I'll just have to buy something else.
It would cost $1 mill. to pull the ones I have installed too!! Much better performance. Sounds like you crave power with your upgrades too. :3gears:
Yeah, mine revs kinda high with the 3.42's, but I still travel with the car a lot, I drive 75 or 80 and have never had problems. When you think about it, the difference between them and 3.07 is only about 500 rpm's or so at highway speeds. The difference in mileage is minimal at best and I would only trade mine for 3.91's if I could. :Brow:
Hey Butthair, Are you kin to Butthead? Your doing what my plans are with my 70 Riv. Well, as soon as I work the bugs out of my 71 GS. I planned on using the same intake with worked heads and Mid sized cam. I talked to RamAir about making me a breather and tubes for the high-beam holes. When you get the carb. on, let me know the clearances so I can talk to them again about the base on the breather. Hope it all clears. Give us a first name too. I hate calling you Butthair all the time!!! Have a good one.
I didn't want to get too crazy with the car, I wanted to leave it stock looking at first, then I wanted to go faster. As of now its in the low 15's with the 2.73 gear. I'm a little worried about this SPX intake, the more I look at it the less I think its going to work. I really hope it does work though. I'll let you know. You can call me butthair if you want but my first name is Dave.
My 69 Riviera GS came with a 3.42, it's a good "all around" gear. We need a decent gear to get our heavy rivs movin' quickly. RPMs on the freeway: 70MPH--3000, 90MPH--4000, 105MPH--5000 ( with standard 235/70/15inch tires). If the SPX intake dosen't fit don't sweat it, you'll get "excellent" results with a massaged dual-plane. It's possible to have a 100% stock appearing Riv and still dip into the high 12's; with the right components(and no NOS). It's all in the cylinder heads, cam and compression. Steve
Well this thread doesnt matter anymore because they dont make a 3.42 for a 70 riv. Oh well, I guess Ill be slow all my life.
