My 1970 challenger T/A was just restored inclusive of a complete engine overhaul.Carbs were restored and dist. was replaced with a factory electronic with the orange box. The cam that was installed was a comp cam XE-268H-10, stock forged pistons with a true (so i am told) 10.5 compression ratio. My concern is, what should the vaccuum read at idle. My engine is reading 10 pounds. Car has twenty miles on the engine.
Thanks in advance.

"" My engine is reading 10 pounds""

Is this a reading in D or is this in N?

With that CC cam, I would guess that you should have around 14" vacuum at 900-950rpms in N.

What is your initial timing? You might just be too low of initial with the cam swap.

Note: I almost put that same cam in my motor during my last cam swap.

Vaccuum was checked with the car in neutral. Just called my mechanic to find out what the timing is set at and will post shortly. I called Comp cams and asked them what the vaccuum should read and their response was between 8and 12. I wanted another opnion. Based on the specs I have given, what should the timing be set at. I have been told that if it is too far advanced, it will cause too much "ignition" and damage the engine. If so, what is too much adn what is acceptable??

""their response was between 8and 12.""

That seems like an in-D vacuum reading at around 900-950rpms or so.

Don't worry about the "too much advance" theory for now. Members like me will tell you to throw as much initial at it that you can until the starter gives you fits. Once you know how much it will take, then we can help you with the rest of the distributor setup. I would suggest that what ever initial that you currently have, bump it up my 5 and reset your N rpms and take another vacuum reading. Then bump it again and reset your N rpms, then take another vacuum reading. This test will give you some options. As long as the vacuum increases and your starter can spin it at startup, then it will be fine.

Reference: I ran 18 initial on my 340 with the stock starter and 24 with a mini starter.

what is the elevation where you live?

Fix your initial timing. Sounds like your mechanics fell out of the 1970's and set it up timing via total method which is not the best way to do things.

Do as Y07 has suggested. More initial will clean up the idle and get it to run better at idle with more vacuum. You'll need to modify the distributor curve so your total number doesn't go out of range.

This car has the same cam, easily idles at 850 in park and 750 in gear, pulls 14". IIRC, it has 16-18 initial. If your car won't idle that low, the issue is likely in your ignition settings.

Thanks Guys. Just spoke to him and the timing is set at 8 degrees at idle?? runs at 33 degrees with the advanced disconnected reved up to 3000rpm?? Let me know your thoughts on this then I will tell you my tale of woe and my reason for posting this.

Needs AT LEAST twice what you have for initial. Must have looked at a service manual for that 8* reading. Throw all the out because even back then, they didn't run well with the recommended idle timing. Turn it to 16 and reset the idle speed. I'll bet it's snappier!

You then need to recurve the distributor, it has WAY TOO MUCH mechanical advance in it.

33 Total is kind of light for total on an open chambered SB.

Needs more initial, 33 degrees total is in the range, small blocks typically like 34 but experiment some.

I'd run 15-20 initial. You can do it the easy way and hook the vacuum advance to manifold vacuum if you're only concerned with increasing idle quality and not performance, or just as a temporary solution. You may end up with some other undesirable symptoms depending on the rest of the setup though, but probably not. You will just be losing some off idle performance.

what would those undesireable symptoms be??

""what would those undesireable symptoms be??""

I have been running manifold vacuum for about 4 months now. I have 18 initial timing (only during cranking, once the engine fires and the manifold vacuum is reached, then the extra 14 degrees is in) and 32 degrees at in-D-idle.

The only issues that I have found:
- idle circuit needs to be richer to run the extra idle timing.
- With my auto, once I had my in D rpms tuned and then I put the car into P or N, the idle rpms would climb about 200rpms and make the engine deisel during shot off. I added an idle solenoid and the problem solved.
- My vacuum can is designed for 12"hg at idle in D (or in N for a manual). I had to tune my idle to get the 12"hg in D, but once I did, the engine idles great in D. I have ran with 11 3/4"hg and had no ill affects. I also tried 11 1/2"hg and the idle started to wonder. So as long as I have 11 3/4" or more in D, then it idles great with 32 degrees of timing.

good info

Thanks for the info everyone. Here is my tale of woe. I recently completed a complete 100% restoration on my 70' Challenger T/A that I purchased new back in 1971. The car had been of the road since 1988 and stored in my garage. No price was spared in the restoration with the exception of the windshield wiper motor! Several service dealers in my city recommended this machine shop to me for the engine rebuild. I met and spoke with the owner/operator about all of my past experiences, and previous problems, with this 340. He seemed to know what he was talking about, plus he was recommended as "knowing his stuff". Talked to several other shops as well and got estimates from two others. Both other shops were substantially cheaper than the person that was recommended to me. I didn't want it cheap, I wanted it right. I gave him the go ahead to do the engine. I wanted him to rebuild the engine, assemble the engine and then put it on a stand and run it, and tune it. Upon complettion of the engine, my body rebuilder picked up the engine and installed it in the car. When the car was finally completed, my car rebuilder dropped the car off to me in an enclosed trailer. We backed the car out of the trailer and I drove it around the block. The car seem to run fine, but I noticed it had a slight tapping sound. I called the engine rebuilder and voiced my concerns and his excuse was that it was "these new HP cams" and that it would quiet down after some miles. Long story short? It never did. I drove the car for 23 miles in total. As the car revved up to shift (automatic, not standard) the tapping/clicking, became much more noticable. I called him again. He advised me to have my garage look at it as the timing may have been set too high. His interpretation of the noise was "pinging" and not tapping or clicking.
made an appointment with my service mechanic (third party now)that i deal with with my fleet service to have this noise checked. Dropped the car off. As soon as i arrived home i had a call from my fleet service mechanic who then told me that the motor was going to have to come out of it because one of the crank berings was gone. Needless to say, i was shocked. My service guy had taken the car out on the paved sideroad, stepped on it and, bang, the tap became a knock.
Called the engine rebuilder and told himn to get over and see this thing. He did, and all agreed the engine had to come out. Problem was serious, especially after an $8,800.00 rebuild with 23 total miles!! I had my service mechanic take the engine out of the car and take it over to the rebuilder. Two days later I get a call from him and he tells me #7 bearing failed and it failed because of these possible reasons:
1) I didn't use high octane fuel and the bering was caused by ignition(of course high Octane pup gas was used!)
2) Engine must have over heated (it didn't. it ran very cool with the gauge showing always to the far left of the middle)
3) My gauge or sending unit must be faulty ( it wasn't. Just put another send ing unit it the engine and it reads the same. Entire cooling system, hoses, rad, water pump, stat were all new.)
4) timing must have been too far advanced and destroyed the engine due to pre-ignition (it was set at 8 degrees!!)and he set it!
Rad and engine must have pugged up because there was black residue in the rad and engine ( the was some, but the new installer said it was from the debris from the engine rebuild. He said he baked the engine to clean it)

Needless to say, he wasnt going to give me any warranty on the engine. After some pressure form myself and my service mechanic he said he would cover it all, including the re and re. When the engine was done, i was away on holidays whn i had a call from my service mechanic who told me that the rebuilder mwouldn't release the engine to him and that he wanted to be paid for the parts and now wasn't going to cover the re and re. To get the engine back i told him to pay him for the crank bearings and that I would cover him for the re and re. My service mechanic has now put the engine back in the car and I got it back yesterday. Appearantly the engine rebulder didnt even thake the crank out of the engine, he just put bearings on the crank and put it back together. Again, long story short? Another $1300.00 and a very bad experience. All of the above brings me to my vaccuum and timing questions. This idiot that rebuilt my engine has blamed pre-ignition for this Bering letting go in my motor. We dont think that is the case at all. When my service mechanic asked for the old berings he regfused to give them to him. I dont want to go through this again. Your thoughts on the above? How should this engine be set? What should the timing be? Do I need to recurve the dist and how does one do that? Is premuim pump fuel fine?
Thanks to all before hand
JIM

If that thing wasn't completely torn down and cleaned out, you'll be doing it again fairly soon is my guess.

what would cause that #7 bearing to go in 23 miles??

dirt, inadequate clearance (oil/side), misassembly, inadequate oiling

would pre-ignition cause that in 23 miles?

preignition hammers bearings but not that quick. Of course he's going to testify that it had to of been pinging/preigniton like crazy & you ignored it & that's an intangible that might not be able to be proven or disproven

No. Those excuses were poor at best... all of them. He should have been more than happy to follow up on his work. I would have wanted to see the fallout from the bearing spinning for sure. Spun bearings can cause some damage. The extent of what occured could have scored the crank. It irks me to think he didn't stand behind his work and tried to shirk it off on you... and then follows up with going back on his word and not being forthcoming with the damaged part. Especially damning is that his inclination to correct the problem was to simply replace the indivdual crank bearing without removing the crank?? I hate hearing about outfits and people like that.

At 8 degrees timing and what sounds to be a stock dist, there would be no problem whatsoever with any pre-ignition. If there were any, which I doubt, it would not have had any impact on your engine. In fact, until I read this thread, I had not heard that theory before. If it was bad enough you would have heard it and shut it down anyway. I doubt the 23 miles you put on it was very harsh.

My sentiment. Those 23 miles were the most "babied" twenty-three miles that one could put on a 50K restoration that was making a very unwanted noise. Question now is, can i advance the timing to 15 to 20 and can it damage my engine?? Everyone on this thread has said to at least "double" my timing and to recurce my dist. Is there a posible straight answer to this?

also, could my timing being set at 8degrees cause preignition to destry my bearings??

I wouldnt be worried about setting the timing. Id be pulling the pan to inspect the bearings. I then be at the courthouse fileing a lawsuit against the so called builder. Once I got my money back Id be taking it to a repuitable shop and have it completely torn down and totally inspected and cleaned. For 88.00 bucks that engine should be gold plated..
there should of not been anything in the cooling system if the engine was ran through a pressure wash after being baked. Those blocks come out of the baking machines just about spotless. Thats a 3 part processed. Bake, shot blased and then air blasted. The pressure wash ensures a very clean block..

An engine dry start without properly priming the oil system could cause the bearing to die.

Detonation likely isn't your culprit.

there was a fair bit of black accumulation in the coolant when we drained the rad.

8 degrees is fine. That being said, I tend to agree with the other poster. For the motors sake and your piece of mind it should be looked at thouroughly before you accept it as is from the previous outfit. Steps that pertain to integrity and quality seem to have been ignored or overlooked. For 8800 that thing should have been perfect in all aspects... from cleaning and mag'ing right on through all other phases. That experience planted a lot of negative mojo. Who knows what is going on with the bearing cap, journal on the one main... much less the other ones. That would haunt you every time you turned the key. You want to drive this car.. flog it from time to time. that is what it is for. You don't want to go through the remainder of the cars life wondering if the motor is going to take a powder on you again.