390 buildup Qs

edaddi

I have some newbie stuff for you guys if you don‚Äôt mind‚Ä¶well..first off‚Ä¶The 304 in my CJ is on its way out. A friend gave me a 390 to put into my jeep but it has a missing rod, and the reason for that is unknown. I‚Äôve never done a rebuild before, but I am really looking forward to it. I‚Äôve been reading the forums here for about a week or so, and there is obviously allot more I need to understand about the process and just the terminology in general. Before coming here I was planning on getting the Edelbrock performer heads, cam, and EFI mostly because I knew of nothing else available for the AMCs and Edelbrock has a good reputation. Now I see there are other options. But‚Ä¶I‚Äôm sure somebody has built something with the Edelbrock stuff already‚Ä¶.are there any write-ups anywhere to satisfy my curiosity?

I‚Äôm primarily a trails and mud kinda guy. I like the torque on the trails and the HP/RPM for the mudruns. So I‚Äôm really torn as to where, in the RPM range (powerband?), I want the most power. But I do know I want more HP than the rest of the people I run with. :mrgreen:

I‚Äôm not sure I‚Äôm gonna have the technical ability, well anytime soon, to be able to pick out every component. So I‚Äôve kinda been on the look out for kit, but at the same time am worried they won‚Äôt be the best for my application. What are your thoughts on kits like this one? Is there other any other places you‚Äôd recommend getting packages from?

Books‚Ä¶.what AMC books are worth getting? I‚Äôd like to have a good rebuild book next to me when doing this. I also want to know more about things like what a compression ratio will do for me, what the different numbers on the cam specs are‚Ä¶little stuff to most of you‚Ä¶.but I‚Äôm a computer geek and have no idea what it all means and does for me.

I‚Äôm sure I‚Äôll have more questions‚Ä¶.but now I‚Äôm just rambling‚Ä¶

TIA

jeepsr4ever

Before we go any further did you realize that a 390 will not bolt up to a 304 used in a jeep. The tranny belllhousing bolt pattern is different for the Gen2 Gen3 blocks the 390 is a gen2 and the 304 form 71 up is a gen3.

edaddi

jeepsr4ever wrote
Before we go any further did you realize that a 390 will not bolt up to a 304 used in a jeep. The tranny belllhousing bolt pattern is different for the Gen2 Gen3 blocks the 390 is a gen2 and the 304 form 71 up is a gen3.

humm...it was bolted up to a t150. I'll have to ask how.... I know he unbolted it, and bolted in a fresh 360...

tufcj

111!!! I have to disagree. The gen2 and gen3 engines are basically the same. The only thing that changed was the heads and deck height starting in 1970. 67-69 are gen2 and 70 up are gen3. You're probably thinking of the gen1 (287 and 327) rambler engines. What did change (73/74?) was the crankshaft, so the flywheel/flexplate is different. What casting number is on the 390? If it's 3190806, it's a 68-69 390, with 7/16" head bolts and square port heads. If it's 3195529, then it's a 1970 390, and will have 1/2" head bolts with the better "dog leg" heads. The casting # is on the upper left rear of the block, on the bellhousing web. The dog leg heads flow much better, about 20% in stock form. Some reports show up to 50% better, but I've never seen it in flow bench testing. Unless you're all out race, or weight is an issue, save your money on the aluminum heads and put it into port/polish and quality 3 angle valve job in the cast iron heads. AMC engines are externally balanced, so you need the harmonic balancer and felxplate/flywheel for the specific displacement engine you have. You can't use a 304 flywheel on a 390. You'll have to make the cam decision, but you can't have it all. Go for top end HP, and you sacrifice low end torque, go for torque, you lose some HP. That will all depend on how much and what you use the Jeep for. Think about it and be honest with yourself. I put way too much cam in my Jeep on the first rebuild. Ran like mad on the highway and in mud bogs, but couldn't pull itself out of a wet paper bag at idle. I was much happier with a low RPM torque cam. Good luck Bob tufcj

jeepsr4ever

maybe the heat is getting to me Bob

edaddi

tufcj wrote
111!!! I have to disagree. The gen2 and gen3 engines are basically the same. The only thing that changed was the heads and deck height starting in 1970. 67-69 are gen2 and 70 up are gen3. You're probably thinking of the gen1 (287 and 327) rambler engines.

What did change (73/74?) was the crankshaft, so the flywheel/flexplate is different.

What casting number is on the 390? If it's 3190806, it's a 68-69 390, with 7/16" head bolts and square port heads. If it's 3195529, then it's a 1970 390, and will have 1/2" head bolts with the better "dog leg" heads. The casting # is on the upper left rear of the block, on the bellhousing web.

The dog leg heads flow much better, about 20% in stock form. Some reports show up to 50% better, but I've never seen it in flow bench testing. Unless you're all out race, or weight is an issue, save your money on the aluminum heads and put it into port/polish and quality 3 angle valve job in the cast iron heads.

AMC engines are externally balanced, so you need the harmonic balancer and felxplate/flywheel for the specific displacement engine you have. You can't use a 304 flywheel on a 390.

You'll have to make the cam decision, but you can't have it all. Go for top end HP, and you sacrifice low end torque, go for torque, you lose some HP. That will all depend on how much and what you use the Jeep for. Think about it and be honest with yourself. I put way too much cam in my Jeep on the first rebuild. Ran like mad on the highway and in mud bogs, but couldn't pull itself out of a wet paper bag at idle. I was much happier with a low RPM torque cam.

Good luck

Bob
tufcj

Thanks Bob,

It is the 3195529. I also checked out the bolt pattern and it looks like it will work fine.

fuzz401

edaddi-- look at this book it couvers the amc motor and explains a lot of things from basic engin building to building a motor for racing it is in plain english so that any one can under stand it

http://www.HOBBYOBSESSION.com/bjsbook.html

edaddi

fuzz401 wrote
edaddi-- look at this book it couvers the amc motor and explains a lot of things from basic engin building to building a motor for racing it is in plain english so that any one can under stand it

http://www.HOBBYOBSESSION.com/bjsbook.html

Thanks, just ordered it :t:

any other good books?

Dusty

Check out a few of the 401 build up threads here and on pirate4x4 on this page http://www.pirate4x4.com/forum/showthread.php?t=245386&highlight=amc401.

We have discussed Cams and other parts for AMCs. my understanding is that the AMC 390 and 401 share alot of parts and build up similarities but they also are different performing animals too.

I have always heard duration on the AMC is your best friend for torque, lift is your best friend for HP a compromise between those two things because of these motor's liking to breath is where you will find your happy spot.

I opted for a long duration moderate lift cam from Howards. I am hoping to capitalize on the benefits of Dynamic compression..... keeping the valves open as long as possible to suck as much air/fuel in as possible, i passed on the highlift since i dont think (i hope) to need the high 5500+ rpm HP. I also opted for my cam because of a 114 lobe seperation which I expect will smooth out the idle some even with the amount of duration that i will be using. 222@.50 292 adv dur .479 lift

This is only how i have understood it and i could be totally wrong but read through some of those lines you will find MC and these guys really do know what they are talking about. You've got an excellent powerplant there, be thurough with your research don't jump to conclusions and also don't listen to the SHEEPLE out there who love to tell you otherwise and apply Chevy technology and mind sets to an AMC motor they will lead you astray.

MC Doesnt sound like heat is getting to you, probably more like gas fumes. :!:

Dusty

Here are some interesting tid bits too: --------------------------------------------------------------------------- AMC v8 block/crank/rod/piston Specs Contributed By: Michael Baxter AMC deck height = 9.218" (SB Chevy 9.025" for S & Gs) 360 stroke = 3.44" 390 stroke = 3.57" 401 stroke = 3.68" 360 rod = 5.875" 390/401 rod = 5.858" 360 bore = 4.08" 390/401 bore = 4.165" 360 piston compression height = 1.601" 390 piston compression height = 1.56" 401 piston compression height = 1.508" Keep in mind rods become a little shorter when they're rebuilt. DH = deck height CH = compression height DC = deck clearance (above or below deck clearance of the top of the piston at TDC) Formula: stroke DH - ------ - rod length +/- DC = CH 2 1st, if you're going to have custom or off-the-shelf flat top pistons fly-cut for valve notches and dish volume, you might as well set-up good quench. Quench is when the flat area of the pistons corresponds to the flat area of the heads. It does all sorts of good things. You would want the quench clearance to be in the .035-.040" range. Most head gaskets have a compressed height of ~.040" We'll assume .040" for this example. So, if we want .035" or piston to head clearance (quench) and the gasket is .040" thick, we better get the pistons out of the block .005". Deck clearance would be + .005": 3.57" 9.218" - ----- - 5.858" + .005" = 1.58" 2 1.58" is the ultimate CH for your pistons plus any loss of rod length from rebuilding and if you mill any material from the block's decks, you need to subtract that as well. In fact, you have to measure the subject block's DH to be on the safe side. The numbers I quote above are nominal figures. Plus, you never know if any milling was previously done (even at the factory during original production). 360's max. recommended over-bore by AMC is .045". 360 piston pin diameter = .931" 390/401 pin diameter = 1.001" SB Chevy pin diameter = .9272" Remember you can not use a 360 rod on a 390 crank. The 390/401's rod journals are 2.247" while the 360's are 2.094". If you're going to put a 390/401 crank in a 360 block, the 390/401 rods have to come along for the ride. There are a lot of options at this point. You could have custom pistons made. You could sleeve the block to a 4.00" bore (lots more piston availability). You could find some off-the-shelf pistons which are close and work from there. The later probably being the cheapest unless you have to get into offset grinding the crank for a little different stroke. If you punch the block out to 4.125" and re-bush the little end of the rods to the Chevy pin, I found a SB Chevy 400 piston with a 1.56" CH. You would need to mill ~.020 from the decks. Unfortunately it is not a flat-top piston. It has a 12cc "D" shaped dish which is probably not shaped correctly. It might be possible to order a set without the dish so the appropriate quench, notches and dish could be cut. It also might be possible to raise the pin height 0.20" as well. The bottom line is I think it can be done with relative ease in the case of the 390 crank. The whole reciprocating assy. would need to be balanced by a machine shop, though. -- Michael Baxter, [email]MBaxter@Compuserve.com[/email]

edaddi

edaddi wrote
fuzz401 wrote
edaddi-- look at this book it couvers the amc motor and explains a lot of things from basic engin building to building a motor for racing it is in plain english so that any one can under stand it

http://www.HOBBYOBSESSION.com/bjsbook.html

Thanks, just ordered it :t:

any other good books?

Holy Cow I got the book already, that was fast. It's book #61. Looks like good stuff, can't wait to get started on it.

tufcj

This is a pretty good book. It was printed in the early 70s, so casting info and such only goes to 1972. All the principals can be applied to any AMC V-8 motor.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=2484697958&category=34202&sspagename=WDVW

Here's a second set of books. I have both of these, and they are helpful.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7910813115&category=6762

fuzz401

the 2 links are the same