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  1. #11

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    I am looking to use the car for straight line application,maybe a little mountain driving. I would have to say the exhaust manifolds are the "Log" style,very plain tubes.Actually my car came with a 390,but currently has a 343 under the hood now.It seems to handle the 670 very well?
    For your 390 are you looking for mainly street use? Occasionally a weekend drag race up to 5500 rpm or so? Are you looking for reliability, improvement in horsepower (40-60 more) and mileage or is high performance your main goal? Sorry for the extra questions but it'll give me a better idea of what you looking for out of the 390.
    Nothing wrong with the 343, I've had two and both ran strong. One stock, one with mild mods. I used the same carb on both, a 625 Carter (same on my 390s). For street use a 670 is plenty. It's real easy to over carb though.





  2. #12

    Default

    Im probably more interested in high performance,with a degree of reliability.

  3. #13

    Default

    Quote Originally Posted by fenceman
    Im probably more interested in high performance,with a degree of reliability.
    I can tell you what I did to mine. It's running 'about' 365-375 hp. 390 auto. Will go anywhere reliably and gets 22+ mpg on the highway, 18+ city. How's that sound?





  4. #14

    Default

    Quote Originally Posted by Big Bad AMX
    I can tell you what I did to mine. It's running 'about' 365-375 hp. 390 auto. Will go anywhere reliably and gets 22+ mpg on the highway, 18+ city. How's that sound?
    That sounds like the best of both worlds.im all ears..........

  5. #15

    Default

    That sounds like the best of both worlds.im all ears..........
    Okay, here we go.........
    AMX Enterprises in Arvada, CO did the rebuild. I wanted an increase in performance, milage and reliability. 1969 390, stock auto trans, 3.15 rear ratio. I rarely run over 5200 rpm, 5500 is absolute max.

    It was bored .030. I went with cast pistons, stock compression of 10.2:1. Balanced it. The heads are late model 58cc off a 1973 401. Rebuilt the heads, new valve guides, springs, stainless steel valves, both sides. Hardening the seats is a waste of money, they're hard enough already. The larger 58cc chamber (stock is 51cc) equates to an approximate .6 drop in compression so it's running a 9.6:1 ratio.

    Put a new timing chain cover on it - this really is a must for good oil pressure and longevity of your rebuild. At the time I bought an NOS one from Chrysler for $650.00. There were quality issues with the aftermarket pieces then. Aftermarket units are still available and I beleive they have all the initial bugs worked out. They run about $280.00 (if I remember right.)

    The cam is an Erson. .478 lift / 292 duration. Highly recommend for street and weekend performance. Very slight lope. Excellent power throughout the power range but really strong from 3000-5000rpm. Very good economy. Very sensitive to timing though.

    Intake is an Edelbrock Performer. The similar (improved?) Air Gap intakes were not out at that time and I've never had one so I can't comment on those.

    The carb is a Carter AFB 625 CFM (not original carb it's a later model) only 'mod' is it's jetted for this altitude (6,500 to 7,500 feet).

    Distributor and coil - New but stock. Yep, good old single points.

    Exhaust manifolds are stock AMC 1971 Free Flow w/o tubes. These run into 2 1/2" exhaust which go through chambered mufflers and exit via Reproduction Trendsetter sidepipes. What a sweet sound. And from 3000-5000 rpm they really open up and wow. I didn't think they were that loud until a Harley rider flipped me off.

    It has the Borg Warner M12 automatic, it was rebuilt stock with a rebuilt convertor (stock stall) and an NOS flex plate.

    The rear-end is original with the stock R&P. 3.15:1 Ratio.

    I say "It's running 'about' 365-375 hp" because its never been dynoed. All I can do is figure the factory rated them at 315 hp and 425 ft lbs torque. Even though the compression dropped by .6 the later heads, carb, cam, intake and exhaust 'should' be worth about a 50-60 hp gain over the original 1969 factory parts. That's my opinion, I don't have solid numbers behind it though.

    I run only premium fuel with Protek lead additive/octane boost in every tank. The last four tanks of fuel were one through the city and into the mountains up to 10,000 ft and it got 18.5 that tank. Next tank was 90% city driving and it managed 19.5 mpg. Next was city, highway, mountains and it was 18.6. The only all-highway run so far was a 225 mile run with the A/C running maxed out for about 60 miles and it managed 22.1 mpg. 60-65 mph. All runs had at least 'a few' romps. On the highway stay below 3,000 rpm or your milage will stink. With a 3.15 rear 3,000 rpm is 70mph.

    Power wise (keep in mind 7,800 ft and a 3.15 rear) with no wimpy power braking, just off the brake and on the throttle from an idle to wide open it'll smoke the tires off the line through first gear. It gets a good 10-12 feet in second, no chirp in third. I have not had it on the track for 1/4 mile times.

    It is exactly what I wanted when deciding to rebuild it. Much better milage, more power and it's as reliable as the sunrise, I'd drive it anywhere.

    I could upgrade the ignition and get a couple more horses out of it but I grew up with points and have little desire to change it. If I was racing and wanted every .01 sec I would but I don't so I won't.

    I think donsjave has a similar rebuild in his '70 AMX 390, 4-speed. Maybe he can advise if he did anything different and how satisfied he is with its performance.

    Hope that helps.





  6. #16

    Default

    Thanks,ill start the decision process...

  7. #17
    Join Date
    Jan 2005
    Location
    Arkansas
    Posts
    17

    Default Piston specs.

    Quote Originally Posted by Big Bad AMX
    Just an FYI: Ye old AMC Service Spec books show the '70 360 and 390 valves to be:
    Intake = 2.025"
    Exhaust = 1.625"

    The '70 304 valves are:
    Intake = 1.787"
    Exhaust = 1.406"
    What does the book say about piston specs? I'm trying to get pistons and need to know what the compression distance and pin dia are in order to make sure I get the 69 pistons and not 70 up.
    Also, is there any way to get a copy of the book?

    Thanks,
    barron

  8. #18

    Default

    Here's what the spec books show-

    Piston / Cylinder info for 1969 390:
    Compression ratio: 10.2:1
    Cylinder Compression Rating: (cranking speed at sea level): 145 PSI
    Bore and Stroke: 4.166" x 3.574"
    Piston to Bore Clearance: .0010"-.0018"
    Piston Pin to Piston Clearance: All Pieces Room Temperature: .0003"-.0005"
    Piston Ring Width: All Engines Top and Second Compression: 5/64"
    Piston Ring Side Clearance: 290-343-390: 1 and 2 .002"-.004" 3 .000"-.005"
    Piston Ring Gap Clearance:All Engines: 1 and 2 .010"-.020" 3 .015"-.055" (Rail Gaps)
    Cylinder Bore Diameter: 390: 4.165"-4.167"
    Cylinder Bore Out of Round: All Engines....Max .005"
    Cylinder Bore Taper: All Engines....Max .003"


    Piston / Cylinder info for 1970 390:
    Compression ratio: 10.0:1
    Cylinder Compression Rating (cranking speed at sea level): 145 PSI
    Bore and Stroke: 4.165" x 3.574"
    Piston to Bore Clearance: .0010"-.0018"
    Piston Pin to Piston Clearance: All Pieces Room Temperature: .0003"-.0005"
    Piston Ring Width: All Engines Top and Second Compression: 5/64"
    Piston Ring Side Clearance: 290-343-390: 1 and 2 .002"-.004" 3 .000"-.005"
    Piston Ring Gap Clearance:All Engines: 1 and 2 .010"-.020" 3 .015"-.055" (Rail Gaps)
    Cylinder Bore Diameter: 390: 4.165"-4.167"
    Cylinder Bore Out of Round: All Engines....Max .002"
    Cylinder Bore Taper: All Engines....Max .005"

    They don't have pin dia or skirt length to pin. There is a visual difference between the early/late years so it's not easy to mix them up.

    The AMC Service Specifications books are small measuring approx. 4 1/2" x 6 3/4". So they can be carried in a pocket. Your best bet is to contact Tony Zamisch at California Classic AMC since he gets them in from time to time. Or try the AMC Classifieds or ebay.

    Edit: You can now download the AMC Service Specifications books free from this website. See this thread for more information:
    http://www.amx-perience.com/American...read.php?t=911


    .
    Last edited by Big Bad AMX; 04-02-2008 at 11:33 AM. Reason: Added link to free The AMC Service Specifications books





  9. #19
    Join Date
    Jan 2005
    Location
    Arkansas
    Posts
    17

    Default Pistons

    Well, I am having trouble finding pistons for my 69. I did find some 060 over for a 70 model. The only difference I see is the recessed head. Does anyone see any reason I shouldn't use these? From what I can reason, they are the same except for the .135 recess in the top. From the compression ratio spec difference in the 60 vs 70, it looks like I will only be losing .2 compression. That with the 70 heads dropping it to 9.6 will give me 9.4 theoretically. Is this a problem? 9.4 still seems like a decent spec.The only other choice at this time appears to be custom pistons at 2-3 times the cost.

    Barron

  10. #20

    Talking reply for whats it worth

    Quote Originally Posted by Big Bad AMX
    Okay, here we go.........
    AMX Enterprises in Arvada, CO did the rebuild. I wanted an increase in performance, milage and reliability. 1969 390, stock auto trans, 3.15 rear ratio. I rarely run over 5200 rpm, 5500 is absolute max.

    It was bored .030. I went with cast pistons, stock compression of 10.2:1. Balanced it. The heads are late model 58cc off a 1973 401. Rebuilt the heads, new valve guides, springs, stainless steel valves, both sides. Hardening the seats is a waste of money, they're hard enough already. The larger 58cc chamber (stock is 51cc) equates to an approximate .6 drop in compression so it's running a 9.6:1 ratio.

    Put a new timing chain cover on it - this really is a must for good oil pressure and longevity of your rebuild. At the time I bought an NOS one from Chrysler for $650.00. There were quality issues with the aftermarket pieces then. Aftermarket units are still available and I beleive they have all the initial bugs worked out. They run about $280.00 (if I remember right.)

    The cam is an Erson. .478 lift / 292 duration. Highly recommend for street and weekend performance. Very slight lope. Excellent power throughout the power range but really strong from 3000-5000rpm. Very good economy. Very sensitive to timing though.

    Intake is an Edelbrock Performer. The similar (improved?) Air Gap intakes were not out at that time and I've never had one so I can't comment on those.

    The carb is a Carter AFB 625 CFM (not original carb it's a later model) only 'mod' is it's jetted for this altitude (6,500 to 7,500 feet).

    Distributor and coil - New but stock. Yep, good old single points.

    Exhaust manifolds are stock AMC 1971 Free Flow w/o tubes. These run into 2 1/2" exhaust which go through chambered mufflers and exit via Reproduction Trendsetter sidepipes. What a sweet sound. And from 3000-5000 rpm they really open up and wow. I didn't think they were that loud until a Harley rider flipped me off.

    It has the Borg Warner M12 automatic, it was rebuilt stock with a rebuilt convertor (stock stall) and an NOS flex plate.

    The rear-end is original with the stock R&P. 3.15:1 Ratio.

    I say "It's running 'about' 365-375 hp" because its never been dynoed. All I can do is figure the factory rated them at 315 hp and 425 ft lbs torque. Even though the compression dropped by .6 the later heads, carb, cam, intake and exhaust 'should' be worth about a 50-60 hp gain over the original 1969 factory parts. That's my opinion, I don't have solid numbers behind it though.

    I run only premium fuel with Protek lead additive/octane boost in every tank. The last four tanks of fuel were one through the city and into the mountains up to 10,000 ft and it got 18.5 that tank. Next tank was 90% city driving and it managed 19.5 mpg. Next was city, highway, mountains and it was 18.6. The only all-highway run so far was a 225 mile run with the A/C running maxed out for about 60 miles and it managed 22.1 mpg. 60-65 mph. All runs had at least 'a few' romps. On the highway stay below 3,000 rpm or your milage will stink. With a 3.15 rear 3,000 rpm is 70mph.

    Power wise (keep in mind 7,800 ft and a 3.15 rear) with no wimpy power braking, just off the brake and on the throttle from an idle to wide open it'll smoke the tires off the line through first gear. It gets a good 10-12 feet in second, no chirp in third. I have not had it on the track for 1/4 mile times.

    It is exactly what I wanted when deciding to rebuild it. Much better milage, more power and it's as reliable as the sunrise, I'd drive it anywhere.

    I could upgrade the ignition and get a couple more horses out of it but I grew up with points and have little desire to change it. If I was racing and wanted every .01 sec I would but I don't so I won't.

    I think donsjave has a similar rebuild in his '70 AMX 390, 4-speed. Maybe he can advise if he did anything different and how satisfied he is with its performance.

    Hope that helps.
    I did basically the same thing as Bad did to his car and can attest to the power gains and the such. I did install electronic ignition on the car since I was suffering somewhat from a high idle miss (lean miss ?) and it meaning the miss was detectable at high way speeds. AMX Enterprises did the basic engine rebuild and did a great job on it. Managed to find a stock 70 forged crank for it (guess they are a little different from year to year) and had it installed replacing the crank that was somewhat beaten up due to abused. Gas mileage depends again on the rpm's that engine is running, below 3000 rpm it runing at about 17-18 mpg and above 3000, it runs at about 15. Car has the 4 speed manual with 315 gearing. Runs like you what what. Guessing that engine is cranking out about 350 horses although I have never dynoed the car itself or the engine. Just taking basic numbers from AMC and adding in for the intake and the 51 cc heads on the car.

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