Can someone help me please.  I am new to the mopar restoration world.  I have a 1973 Challenger Ralley.  I am planning on putting a 383 out of a 66 Newport into the car with the 727 trans that came with it.  I have run a compression check and the numbers show good.  It had a 2BBL Carb on it and I have acquired a cast iron 4bbl manifold that I am planning on installing a Holley 780 on.  It will have headers.  I am tring to figure out what size cam to install.  I called Comp Cams help line to get some suggestions and that told me that they need the gear ratio for the rearend which I was able to find to be 323. They also said that they need the compression ratio.  How do I figure out that?  I tried to decypher the engine codes to do it with no luck. B383, 12 7 2 ,R were stamped by the distributor.  The side of the block has 2468130-3, 10/26/65 on it.  Can someone either tell me how to find the compression ratio to the motor that I have or give me a cam suggestion.  I plan on having a 2000 RPM Stall convertor in it.  I plan on driving it for pleasure and maybe taking it down the track a couple of times to see what it will do.  I really appreciate the info.  

What you have is about 8.5 to1 when it was new. Your best bet is do a rebuild before you install it. You will be miles ahead, you can put what ever ratio you want and have a good set of forged slugs to boot. if your going to keep the old heads you will be killing your self with small valves. Find a set of 452s (they have hard ext. seats so you wont have to have them replaced + larger valves) alot of people will tell you to get 906 heads but there hard to find and dont come cheep and dont have hard ext. seats! If you stay with iron heads try to stay down to about 9.0 to 1 ratio. Your cam with the iron manifold I would go with the Mopar magnum repro. and their springs,be sure to get new rockers,shafts and push rods. this combo with a good set of headers should get you around 330 hp. dump the 323s and get at lest 355s but if your not on the high way alot 392s would be better. You will need a posi to go with the gears also, if your car was big block to start with it should have a 8 3/4 rear this is a good rear end. Run 2 1/2"-3" exhaust with some good mufflers and have lots of fun!!  

Thank you for your input.  So for my own sense of curiosity, what benefit would I get by using an aftermarket Alum intake manifold?  Would it be enough gain to offset the expense.  The rear end is an 8 3/4 even tthough the car was original with a 340.  I know very little about rear ends, is it possible that it is already a posi or a limited slip since it is an 8 3/4 ?  

The iron intake wont flow as good as an aluminum and is alot heavier. An aluminum intake will give you more hp. right out of the box even if you go with replacement type like the Mopar #P4529117. This intake will use all the stock mounts for ac.,coil and choke. Weiand makes avery good intake also as does Edelbrock. I run a Edelbrock performer RPM on my 78 D150 it does a very good job. Look under the seats for a build sheet it will tell you if your car came with a posi. If i can be of any more help let me know Im always ready to help! 

hello  i was wondering if you  still have the 340 that came in your car or the 340 parts  

I do have some parts.  The 340 was not in the car at the time when I got the car it had a 318 w/727 which I still have both and all of the pieces that go with it.  what might you be looking for?  

believe it or not many of these aftermarket dual planes for mopar were designed from the originals. I have a 4 barrel intake from a 71 400hp you can have for nothing, just pay shipping.  

BC I have a true 70 340 short block dated 4-16-69, never been apart 700 bux. also a good pro built 727 small block trans with good bands and aluminum drum with ta 3500 converter and a new new b&m pro shifter with cable, it also has a cheeta valve body. lemme know if this can help you. I live in s.fla