No, it wasn't Jim. Ill PM you so you know who I called.
It's not just reversion that's a *****. It's does the head flow as well backwards as it does in forward direction. If the head flows just as good backwards, any reversion you have at overlap is magnified. Thats why I don't like back cuts, except with SOME 50* seats and all the 55* seats I have used can use a back cut. You use a lot of 50/55 degree seats do you? But a 45* seat almost never a back cut. Why? Because it increases low lift flow and makes the low lift flow better backwards. Now, as the exhaust valve is closing and there is a low pressure in the exhaust port and the header and you open the intake, all that initial flow (which at low lift is MUCH higher than what the flow bench says at 28 inches) doesn't go into the chamber, but right across the seat and out the exhaust port.
If you are closing the intake too late, the piston goes around BDC and pushes the intake charge back out the intake port. This is what causes standoff and you can see it with stack injectors as fuel will come back out the stacks at idle. If you have a carb, every time air goes through the booster it picks up fuel. So, the air stream picks up fuel on the way in, the piston pushes the column of air goes back out the carb and picks up fuel again (now twice what you need) and then the air turns around to go back into the engine and it gets air a third time (now that is 3 times the fuel you need. You can see exhaust on the bottom of the carb and sometime in the carb when this happens. Usually with a long, slow lobe do you see this. Not so much any more. The cam is seldom the culprit for the above paragraph--it was the old, poor flowing, shitty combustion chamber, turbulent, valve limited heads that were responsible for exhaust up the carb. LOL
There is a good article and graph by Jim McFarland on the HotRod site but damn if I can post the link to it. The graph shows how reversion is much more significant at overlap the intake valve closing. But you keep recommending a tighter LSA which increases the overlap triangle you just contradicted yourself--STOP. Just stop.
I think there is more going on with your stuff that just the porting. I've seen many many valve jobs that were power killers. I already talked about back cuts, but the numbers guys love the fact that a back cut almost always looks good on the flow bench.Back-cuts do always look good on the bench--I almost never do them. Seat width is a big deal,Correct and wider is better in this case -not sayin why but th angle and width of the top cut is HUGHECorrect and the chamber machining removes any and all chance of an optimum top cut being achieved, specifically when it comes to pressure recovery. Your heads could be a valve job away from being what they are advertised.If the heads are like mine short of welding up the chamber ain't no valve job away from being any better.[/QUOTE]
J.Rob
