Holley jetting

[dscott]

JLW, Here goes, this is just my opinion and experience. The cam you are using should make peak hp around 5300 to 5500 rpm. To take the engine any higher is a waste and a danger unless the bottom end has been beefed up with good rods, balanced, etc. I never run my engines over 6000 with a stock lower end. Ideally when racing (I'm sure DV can confirm) you want to find your peak torque which is probably around 4700 rpm and have your shift point at 500 rpm above that. Many racers have found this difficult because they feel they are short shifting out of the power band but usually the et's increase. If you try and rev above the 6000 rpm you can get into valve float. Also the power drops dramatically at the higher rpm with the cam you have. You need a pretty wild cam to make your hp at the upper end. The problem you have may not be in the carb. If the valve springs are not designed for the pressures at the higher end you may be getting valve float. What rpm are you having the problem? But then again things change at those rpm's so carb jetting may be it. I have used the 750 Edelbrock with great results on your engine combo. But like I said I don't rev any higher than 6000. I would check your cam card, it should give you a good estimate of the power band.

The stock 650 carb probably has a 6.5 power valve. At the higher rpm you may be making that much vacumn and closing the power valve. If this happens it's the same as decreasing your jets by 8 sizes which can cause a lean condition. This is definitely dangerous because you can melt pistons if you are too lean. You could try a larger power valve and see if that helps. I also think a 650 carb with your combo is too small. The 750 would be better.

Don