I'm new to this site, but have owned my 70 340 performance challenger for thirty years. Its an original # matching car. The car right now is running so well and strong I almost don't feel like messing with it but some of you guys really now what you are talking about so I thought I would give you the spec's on my 340 and see what you guys thought.Basically the engine has been bored out 40 over and the cam is Mopar perf 268-284-50 degrees lift .450/.455 . Headers, Edelbrock 600cfm carb with original dual plane manifold. X Heads. Mopar perf Electronic Ignition( orange module) This is connected to A-833 trans, 8 3/4 rear with 3:23 gears. Timing is set to 36 full advance.Like I said the car runs so well and so strong, but I know there's always room for improvement. Anyway looking forward to some great conversations technical advice.  

I think you have a great street package.
To make this a street/strip combination you will have to take the car to the next level.
I would leave the bottom end alone as long as it is not burning oil and you have good comp., and oil pressure.
The X-heads should be ported & polished with a good valve job.
Cam should be increased to help the heads, say at least a 284/484 Hydraulic, or for all out street/strip go solid, Mopar 284/528 this cam will excite you with its acceleration. Be sure to install a new timing & gear set.
You will need 1.5 adjustable roller rockers if you go solid lift cam.
H.D. clutch.
4.10 gear with as big a tire as possible, M&H 275/60/15 tire is a street legal tire made from drag racing technology.
750 Double Pumper, & an air-gap intake.
Get ready to run some solid 12 second passes.  

Thanks for answering, from what I have read on your replies, you really know what you are talking about and certainly more than me. I agree on the great street package,it really runs so incredible. Great low end and great high end. When I hit third gear it just pulls and pulls and pulls like it just won't quit. The bottom end is great, it actually only has about 6000 miles on it and the heads were ported and polished with a good valve job. I seem to recall something about a triple angle valve job, if that is such a thing.It's been ten years since I had it rebuilt, don't drive it too much but try to run it often. That's great data on the cam and rear. Given the existing cam and heads now, what do you think about the carb and manifold? Would I realize any gains from a different manifold and carb set up? Would they be marginal? Also since this has been bored out 40 over what do you think my displacement would be? Any guestiment on the H.P.? I don't really ever see myself going to the track but just really want to optimize what I have.  

Your current combination will be making about 320 horse power.
Definitly a carb and intake will help with overall performance, but this will depend on how far you want to take the car to the next level.
I would install a 750 Holley or Demon Double Pumper since you have a four speed and you will be able to get the car off the line without to much trouble.
A professional products air-gap intake will give you awesome torque from 1500-6500 rpm, truth is the car will level off well before 6000 rpm with the cam you have.
So with a carb and intake up grade you will pick up a solid 25-30 horse power.
If you add a cam you will have to also go up in gear because of the increased duration, the solid cam I mentioned would be worth a strong 30-40 horse power.
Hope this helps.  

Thanks again for the info. What is a professional products air-gap intake? Do you mean like the Edlebrock performer air-gap? You dont think I will lose a little on the low end with a 750? Also what do you mean when you say level well before 6000 rpm?  

The professional products air-gap is a copy of the Edelbrock unit, I believe summit is selling a copy of this intake under the summit brand now. They advertise it as a stage 111 intake.
What I mean by the engine will level off. If you were on a drag strip and were comparing shift numbers the car would likely run faster shifting at 5800 rpm than at 6500 rpm. Especially with the cam you are using. Will you feel this with the seat of your pants, not likely.
Will you have a little less throttle response with a 750 double pumper over a 600 holley, possible, again it will depend on if you up the cam.
A 750 DP is an awesome carb and one of the most responsive and easy to tune carbs on the market, however everyone knows a smaller carb is always a little more friendly at the lower RPMS.
Can you make a 750 DP as reponsive, absoleutly, tuning, 50 cc pumps, bigger squirters, rear gears etc.
This is likely the all around #1 street/strip carb on the planet. So don't hesitate to get one they are awesome.  

Yes, I do agree, I have heard nothing but positive feedback on that carb. OK I got it on the intake, is it cheaper than Edlebrock or just better in some way or pretty much the same. Thanks again for your info and if I ever do switch to the 750 if you dont mind, I will pick your brain to help me dial it in just right. Thanks again  Bob  

Sounds, good, and your right the professional product is cheaper plus if you ever go with a 360 it has a dual bolt pattern for both the LA and Magnum heads.
if you need any help dialing in the carb or any other part for that matter.

Just e-mail Tom
67mopar@sympatico.ca