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Discussion Starter #1
thinking about swapping the 12 bolt 3:08 pegleg for a 3:55 posi unit.
i still like to drive 70mph = 3000 rpm now. so i guess if i went to the 3:55's i would run somewhere around 3450rpm @ 70 and about 3000 rpm @ 60 mph. see myself taking maybe 2 - 150-200 miles trips a year and the rest is around town. would this long trip be hard on the 396?
how about 3500 vs. 3000 rpm if i leave the 3:08's?
it has been balanced and has a 280h comp cam. not sure what the CR is, but the motor is a '69 396/350 hp and it has a Richmond T10 manual 4 speed.


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pages.prodigy.net/mtbmtb/rf396ss.jpg

[This message has been edited by mike brown (edited 12-21-1999).]
 

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If you really like to cruise at 70mph and plan on doing so often, I would keep the 3.08 and just put in a posi. Or, you could go with 3.36's. Your motor will be able to stand the 3500 rpm without any trouble, but you're going to feel it "buzzing" in the car. I just went from 3.36's to 3.90's in my 68 and am considering an overdrive tranny already. Just my .02

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Bob (Creedmoor,N.C.)
65 Vette B&M Blown, Richmond 5-speed
68 Malibu B&M Blown, Turbo 350 10" converter
 

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On the same topic, I have a 3.55 open diff in a 70 Malibu, and plan on putting a 396/325hp motor into it. I take a 12 hr road trip twice a year. Would the motor be able to handle it? I wouldn't drive past 70mph, but the car would have 200 extra pounds in weight, and I myself clock in at 150lbs after a good meal. Also, I'd probably keep the TH350 tranny, but give it a heavy-duty street/strip shift kit and a good sprag. Am I good, or just downright asking for trouble? The car has almost no highway time aside from the to/from college trip.
 

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i have taken my car on many interstate
trips. the longest was about 500
miles.that's about 8 hours. stopping for
fuel too.
at 70 mph my 396 turns 3300 rpm. i keep
my cruise max at 3500.
i feel as long as your equipment is in
good shape a few trips a year would be
fine. go for the gear change. for mostly
around town you'll like it too.
good luck
 

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MB, man you're spiining at 70 now. You must be running very small tires, because I spin at 3000 at 67-68 mph with 3.55's and 28" tires. Now, honestly, I've never pulled the cover to physically see the 3.55, but I know that with 2 different pace cars 55 mph = 2400 rpm. I simply did the calc to determine they are 3.55's.

I know this may sound funny, but either you have really, really small diameter tires, or you don't have 3.08's. ( Or your speedo is way off) You might want to measure your tire height and use Wes Vann's equations in the Tech Reference section. Always ensure your speedo is right. I did it with two new vehicles as "pace cars" and got the same result.

If you have small tires, and want more gear for your non- highway driving, go for it. And buy a set of very tall tires for those long trips.

But run some numbers, something doesn't look right here. Hope this helps and doesn't just confuse.

[This message has been edited by Gene Chas (edited 12-21-1999).]
 

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Back when 67's were new I drove from NC to MD every weekend with my 396 w/4:10's. Put 58,000 miles on it in less than a year. Most of it was highway miles ( I won't admit to speeding but..) Also turned M&H's on the weekends. One tough engine.

Rick
67ss bb
TC #326
But all it needs is a harmonic balancer.....
 

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The only thing I would suggest if you are going to cruise at 3000 or better is make sure your heads have been updated with hardened exhaust seats. I ran a 69 chevelle with 3:55s and 14" tires and did a lot of 3000 rpm crusing, and when I tore the engine down after a couple of years the exhaust valves were sunken so badly into the heads that they were barely saveable. Im sure your engine can handle the revs if you can handle paying for the gas, but take care of the heads first.

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70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
55 chevy prostreet
 

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I have a .060 over Olds 455 = 468 in front of 3.73's that I turn 3600 - 3800 RPM with all the time - haven't had a bit of problem. I do agree with Bob - you can really feel the RPM/exhaust buzz at that speed.
 

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I routinely drive my malibu on the 265 mile trip to my parent's, with a non-posi rear(not sure what ratio) and powerglide. I usually maintain around 75 mph on the expressway, and she's really humming at that point. I havn't had a problem with it at all, other than having to stop for gas twice on the way.

Your engine should hold up fine as long as it's built well.

One comment on the noise, with standard manifolds and 2.25" in exhaust, my ears are ringing after such a trip. You get this kind of roaring reverb going in the cab.
 

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Try a set of 4.56 gears running 70+ for about 7 hours. I have done it a few times and i'll say it sucks. But you do what ya gotta do. All for the love of my car. I'd do it again if I had to.

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ACES member #3339
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these cars came from the factory turnign hi r's and held up then so why should now be any different??

my dad had a 69 impala 327 powerglide that ran at highway speed all the time...we never worried about turning hi r's cuz we didnt even have a tach...

personally it does bother me to see my 454 truning 3k to cruise when it has the torque to do the job at 1500 if i had a 2:1 OD tranny...and SUCK fuel...ALMOST as bad as my 300hp johnson V8 outboard...actaully the outbaord doesnt burn fuel..it is "gas cooled"

2mpg no matter what speed i runit at...

how are tire diameters measured..245/60R14 measure 24.5" front to rear diameter or 11.5 radius from b floor to midline which would yield 23" diameter....

my 454 runs 3000 on the tach at 60 but i think the tach is off abit...previous calcuations yield 2840 thru my 3.31 gears

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Rich
Cocoa Beach, Fla
Team Chevelle #380
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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Why don't you throw in the 3.55 and get some bigger tires? You're going to have to change the speedo anyway so why not? 275/60s would look great and help you out with traction. Just my .02

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Joe Y.
68 malibu
Bloomington/Normal, IL
 
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