camshaft rpm vs cubes

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reversion is caused by a too big intake port... the air is going in sooo slow, that when the piston turns at bottom center(and the valve is still open) , there is not enough energy/speed in the air to keep it running into the engine so the air stops up, and starts to flow backwards ,until the valve Closes.:wack:

this is why it is so important to have the correct size/velocity in the intake port. if the size is optimal, you overfill the cylinder when the cam is in the sweet spot (over 100% filling) thats a good thing:)
IF Your exhaust is to big/flow too god, the blowdown is happening too fast, and you do not get that much help from the exhaust "pullstarting" the intake stroke when the valves overlap..
 
Cudafever said:
LOL
I know it sound like a tall tail but it is true. the thing would hardly idle. When i pulled the heads back off there was soot(aka bad reversion)almost up to the top of the manifold.(only had them head on for a couple of months!)

The only common sense i can put to it, is that at the higher rpm the exh started pulling on the intake instead of pollution it.

It acted like a 2 stroke, and when the power would come on, around 4000 rpm, it was alive!

I pulled them head off and had a set of X heads rebuilt and it would only pull to 5800......but it ran a lot quicker and had a nice idle.
Click to expand...

You can get the same conditions, black soot back up the intake ports and into the carb, with a stock headed/cammed 340. Pretty simple to do.
 
I used a MP cam (284 advertised/484 lift). It was in a 360 with 340 heads, dual plane intake (LD 340), 750 holley and headers. I shifted it at 5700 rpm's. I started at 6000 rpm's at the dragstrip, on the same day, only playing with shift points. Anything from 5700 - 6000, the E.T. stayed the same. Over 6 I lost, under 5600 I lost. I went with 5700, closest to the bottom without loosing any E.T.'s.
 
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