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Thread: The 389?

  1. #1
    Join Date
    Sep 2008
    Location
    Pittsburgh, Pa.
    Posts
    75

    Default The 389?

    delete............
    Last edited by Jeff K; January 22nd, 2015 at 06:28.

  2. #2

    Default

    I think you would be much happier with the 4" stroke. Since you will need new pistons anyway you can specify the relief volume you need to keep your compression ratio down in the 9-9.3:1 range.

  3. #3

    Default

    You confused me between the 389 and the 462. If you already have a 462 why aren't you planning on using it? I was only recommending the 4" stroke over the 3.75" stroke.

  4. #4
    TININDN Guest

    Default

    Jeff:

    FWIW, I've built several 389's, and here's my opinions:

    1. You can get about 350 HP +/- out of these engines with some headwork and an after market cam with similar specs as discussed in Ron Hoffman's earlier post. Mac once told me that they never went above 0.400 lift with Pontiac cams in those days, because the heads just wouldn't breathe any better. So, to "wake it up", just do some bowl and short side radius work, bigger valves (9770716 heads) and increase the lift with a more aggressive modern cam lobe profile. With a 2:56 gear, and a TH400, even with the low gear set, and considering you want street performance, this is a logical plan, IMO.

    2. If you want more HP out of a 389, you will need to take advantage of the "short stroke" and do it with RPM's, which doesn't really fit with your car weight, gear and transmission combo, IMO. If you're talking a '64 goat, with a 4-speed, and rear gears in the 4's, then a 7,500 RPM motor might make sense. Horsepower is torque factored for time, so RPM's = HP.

    3. Jim's recommendation of a 4" stroke certainly should give you more grunt down low.

    I had a racer buddy, back in the day that had a '62 425A Bonnie ragtop hydro, and after I waxed him with my '64 Cat, he went traded the '62 for a '64 Bonnie ragtop tripower 389 with hydro, and he got that car to run close to 14 flat on 7" slicks and open exhaust and pass NHRA E/SA tech for stock.

    I'm puzzled as to your choice of a RA-4 cam in the first place, and don't think you would gain anything with a mechanical roller, unless you want to operate upstairs. A hydraulic roller would be my choice, if any, but I question the gain versus the extra dollars spent, if you stick with choice #1.
    Also, those TH400's are stout, but they can be HP vacuums, IMO.

  5. #5
    TININDN Guest

    Default

    Quote Originally Posted by Jeff K View Post
    Dave do you think I'm making a mistake swapping the 4 speed hydro for the TH-400 with the low gear set? I'm a little apprehensive.. My present combo does pullout hard.. I can obliterate new GTOs at the stop lights with my present combo...
    Yes - with the 2.56 rear gear, I would stick with the original trans - I'm building a '64 Bonnie wagon, and the hydro is rebuilt and ready to go with a 3:08 posi rear gear.

    As far as the 389 goes, and FWIW, here's my theory -

    The 389/400 over square engine with a good rod length to stroke ratio and lower piston speed is the most efficient Pontiac engine design; the square 421/428, next best, the under square 455 on the bottom of the list, IMO. Using similar combos, to achieve the same goal, you should be able to get more HP per cubic inch with the 389/400, followed by the 421/428, and lastly the 455.

    Now, if you are building a street light to street light combo, that has basically slightly warmed-up stock type components, flip the list upside down, especially with an automatic transmission. The longer stroke motors make more torque, and more HP, down low, even if it isn't more HP per cubic inch, both of which give better street light to street light performance in a heavier car.

    I never got beat in my '64 Cat by a '63 or '64 421 HO car. I think the stock heads on the 421 HO engines, which were the same heads on my 389, coupled with the fact they used the same cam, simply didn't allow those bigger motors to breathe well enough to adequately fill the cylinders, and make any more HP than the 389. But, we're talking stock engines, and the 389 had at least 500 more usable RPM's, without kicking the rods out.

  6. #6
    022561 Guest

    Default

    Gee Jeff, If you don't mind me jumping in here I think I agree with Jim on this one. I would fresh up the engine you already have in there, replace the 041 with a 068. You have a great trans to go with the 2.56 gear. Put the old 389 in there for a month while you put the 462 together and no worries. 455's in stock trim are good for 5,200rpm , the 068 makes power from idle to 5,500rpm and the combo somewhere around in super tune around 500ft. lbs of torque. Torque is the name of the game in that big heavy car of yours. Now go to it!! Want to really snap your neck?? Put in a 3.23 posi for fun. I bet with 3.42's and a good set of slicks you could be in the 13.80's. Remember it only takes about 20 minutes to change pumkins.

    Don

  7. #7
    TININDN Guest

    Default

    Quote Originally Posted by Jeff K View Post
    Maybe I should sell the TH-400 and pick up a 2.97 or 3.08 rear end....

    My TH-400 is the one that's in the photos in Cliffs new TH-400 book. So it's kind of a star...
    Just a suggestion - do your RPM calculations based on rear tire diameter first before swapping rear gears - I wouldn't want to spin that long stroke motor much past 2,200 RPM's at 75 MPH for extended cruises - but that's just my preference - I run 3.23's in my '63 Cat with a slim jim and a 255/70R-15 rear tire - it's just about right for me with a 389 at 70 MPH -

  8. #8
    TININDN Guest

    Default

    Jeff -

    I like to stuff a big tire in those rear wheel wells - the 255/70 R15 at 29" is my choice, but requires a 5" - 5.25" backset on the wheel -

    check out Diamondback also, if you want some custom sidewall treatments -

    http://dbtires.com/
    Attached Images Attached Images

  9. #9
    022561 Guest

    Default

    Jeff, don't get rid of the T400 ! Save it for another project. I would urge you to go lower than a 3.08. A 3.23 or deeper to fool around with or to take to the drag strip. Remember 20 min to change and use a flexible braded line on one side so you don't have to disconnect to bleed the brakes. FYI Jeff, the Mac # 10 is the same as a 041 except it's a solid lifter cam and the Mac # 7 is almost like a 744 just a few deg. diff.

    Don

  10. #10

    Default

    Quote Originally Posted by 022561 View Post
    Gee Jeff, If you don't mind me jumping in here I think I agree with Jim on this one. I would fresh up the engine you already have in there, replace the 041 with a 068. You have a great trans to go with the 2.56 gear. Put the old 389 in there for a month while you put the 462 together and no worries. 455's in stock trim are good for 5,200rpm , the 068 makes power from idle to 5,500rpm and the combo somewhere around in super tune around 500ft. lbs of torque. Torque is the name of the game in that big heavy car of yours. Now go to it!! Want to really snap your neck?? Put in a 3.23 posi for fun. I bet with 3.42's and a good set of slicks you could be in the 13.80's. Remember it only takes about 20 minutes to change pumkins.

    Don
    I agree, go to a lower ratio as the first thing you do. A street race is less than an 1/8 mile in most cases and the gearing will make this more fun than anything else.

    I would say to go as high as a 3.73 (not sure if that exact ratio was avail for your axle) as you will not be using this as a daily driver.

    I have a 3.70 on my 427 Vette and she turns about 2500RPM at 55mph -- quite reasonable. granted the Vette is only 3400 pounds but I can actually take off in 4th gear with a little clutch slip.

    Ken

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