[Lynn]

WTH, here's my 2 cents. Take if for what it is worth. I have never owned a BBC. Have worked and tuned them, including a 375hp 70 Nova that was raced on weekends.

1. Those are some pretty strong numbers. Don't know that you can gain 50hp with a cam swap, UNLESS you are willing to give up some drivability. Just a guess at this point, as we don't know the specs on the cam, but really, assuming those dyno numbers are accurate, you are not leaving much on the table for a driver. If you can't nail down the cam specs, I would just leave well enough alone. You can spend a lot of money, and possibly see almost no gains. Won't cost you any extra to keep what you got. If you do decide to change cams, contact Eric (vintagemuslcecar) or Straub technologies.

2. Stay with a copper core AC or Autolite (Motorcraft would work just as well, as they are made by Autolite) spark plug. Platinum, iridium, unobtanium, etc. seem to work great on late model computer controlled cars. I have seen more than one vintage car fall on its face using new plug technology. Your mileage may vary. I am sure other very informed and experienced guys disagree.

3. Might want to diagnose the "runs like a dog when it is hot" issue before pulling the motor. Although, it is most certainly a tune issue, and nothing to do with the cam choice. I have two turbo cars, and they REALLY suffer at 100 degrees, but that is just part of the game with those. I can't tell you if my 69 Z/28 runs like a dog at 100 degrees, cuz I never drive it in that weather. Black car, black interior and no A/C. The older I get, the less I tolerate heat (may just be grumpy old man syndrome).

Are you using ethanol? Sorry if this has already been addressed, but once you start replying, hard to go back and review. Run straight 100% gas. If you can get to a small municipal airport, try putting about 1/4 tanks of 100LL in with the best 100% gas you can get. I think in the DFW area you can get 92 or 93 pretty easily, is that right? Seeing as the exhaust isn't pure stock anyway, I would highly recommend a wide band AFR meter. They are an amazing tool, and you can really dial in a Holley using one. You will always know if you are rich or lean, and under which conditions.

Lastly, I have a 4.10 and M20 in my Z. Granted, it isn't a big block (I have a motor built to 70 LT-1 specs right now) but I love that combo. Yes, 70 mph = 3600 rpm, but I don't drive it on the highway often. I also don't spend long in 1st gear. 3.55 is a pretty big jump. Frankly, you are going to just fry those street tires with either combination. You would need some drag radials to get any traction at all.