Hey Clois
those numbers look close to predicted but I think you might be able to find a few more HP like you said. Here are the possible numbers from dyno2000
I believe you stated the rear wheel results were
HP 371 @ 5500
TQ 393 @ unknown
Dyno2000 flywheel results were
http://www.cobralads.com/dyno2000/428_cj1.gif
HP 446 @ 6000
TQ 447 @ 5000
if we take off 15% for parasitic drag and 5% for sidepipes
HP 357 @ 6000
TQ 358 @ 5000
and that is an error of less than 5%.
CARB
I think you might find a few more HP with a new demon carb or high end holley. Here is an example
http://www.bgfuel.com/demoncarbs/demon_charts.htm
One thing to note, if you go with a road demon or a vacuum speed demon, you will not see an increase in peak HP, but you will see an overall power band increase throughout the range, but the peak HP will not change much. I believe that the low-end and medium Demon carbs with vacuum advance, go rich at the top as a safety precaution. Ryo and I saw this at Westech. John Baechtel explained it to us. If you want to achieve maybe 15-25 more peak HP, I would go with a mechnical speed demon or race demon, or higher-end holley. like the two nascar 830 models.
http://www.bgfuel.com/demoncarbs/products.htm
http://www.holley.com/HiOctn/ProdLin...C/0-80785.html
http://www.holley.com/HiOctn/ProdLin...0-80509-1.html
The trouble with these carbs is "price" and you end up paying $1000 for 20HP which may be worth it to some and not to others. You actualy gain more than peak HP though. It's amazing to see on the actual dyno the way the demon carbs can increase the width of the graph 15-20HP from 3000-5500.
TIMING
I personally don't think MSD spring adjustments have anything to do with "peak" HP and TQ on a dyno and here's why. These springs determine "when" the distributor is at FULL advance or "ALL IN". Here is the tech page from the MSD manual
http://www.cobralads.com/msd.gif
Even if an engine has the slowest advance rate (2 large silver springs) and the red bushing, the distributor is still all-in at 5500. If peak HP is at 5800, the springs had finished doing their job 300 rpm ago. In the case of your 428CJ, a medium silver and a blue, I believe this means the distributor was all-in at 3500, from that point onward, the engine is at total advance. I think what you were seeing in each run where springs were adjusted, is just common variations because of temperature, barometer, and engine heat. Someone please correct me if I'm wrong...I believe an engine wants the fastest advance curve possible (without detonation). This is to achieve the strongest overall powerband. TOTAL timing directly effects peak HP, not the timing acceleration curve?
SPARK PLUG
I am skeptical of 99.9% of spark plug tricks, but here is an interesting one from the August FF&MM. This trick is supposedly worth 5lb TQ on a stock mustang. If you look at the electrode on a plug, it is long. Cut it back and camfer it to be cenetered. In testing, this gave 5lbs TQ extra from 2000 an on in a stock mustang. MMFF confirmed the test. The author also wrote that he had seen up to 20HP when switching to Autolite AR133s in a stock 5L.
hope this info was interesting
Andy
http://www.cobralads.com