I don't remember seeing back cuts cost 10 or 15 cfm at peak before. Usually they just boost the low numbers, then the gains flatten out at some point and you don't see any more gains.

I can't answer your question but those look like good flowing heads, the 440-1 heads on my 69 Dart only flowed 325, and it went 9.82 at 136 with a 500" pump gas motor at 3200 pounds. I always wanted to have the heads cnc ported up to 370 cfm or whatever the new programs are doing, then get the right cam to match, I think it would have gone 9.40's.

I should have added that the flow chart posted with no backcut was something done a week prior before his 4.50" Chrysler bore plate arrived. I just wanted a quick test to see if they were worth a crap and as advertised all around since I got them thru an Ebay auction. They were tested on a 4.35" Chevy bore plate and possibly centered over the cylinder too much so perhaps that inflated the #'s? That was my initial thought, but we also tested the 30° backcut that day on the same plate and the #'s then were very similar to the ones posted here from the Chrysler plate. Just a few cfm higher in the low and mid-lift #'s on the Chrysler plate with nearly identical #' from .500 on. I'm sure the 10cfm given up on the peak lift #'s is worth less power than all the low and mid lift flow gained with a backcut.

My guess for power would be roughly 775 hp on the high end, given what a lot of 440-1 headed motors make. The converter and gears I think will keep you a ways above 10.00 but you should have a pretty good mph. A lot is going to depend on the true stall of the converter. For decent performance you need something with at least 5200 stall. If the motor makes an honest 775 hp, and the converter and gear ratios are optimized, then the computer says 9.98 at 136 mph under IDEAL conditions.
I built a 499 with bowl ported 440-1 heads, 13/1 compression, alky injection and Methanol, cam was 283/290/108 UltraDyne roller,5500 stall with a Torqueflite, car went 9.34 at 142 mph at 3,000 race weight. My computer says 727 hp for that run. That motor pushing 3900 lbs would go about 10.20 at best.

Normal deal is if back cut on intake valve hurts flow your short turn shape is wrong.

The other normal deal for angle change is 15* so normal 45* seat back cut would be 30*
But I have found the 33* back cut works better on most 45* seat valves.

The other thing to keep in mind seat width and back cut width will change flow curve
Plus shape of valve will dictate back cut.

I have talked to larry and my buddy is good friends with him.

I don't back cut exhaust valve due to the damage it does in respect to reverse flow.

But a good intake port will like a back cut.

The 30* backcut in this case is the configuration I would go with. Look at that flowrate @ .400" its excellent. Don't care much about what happens below .250" lift. J.Rob

Some of this isn't quite so.

I always look for ways to kill low lift (low lift being relative here, as low lift for a .600 lift cam is not the same as low lift for a 1.000 lift cam) in most everything I do. As for the mids,...if I'm testing and the low lift goes away and takes a bit of the mid with it, as long as I gain some back at MAX lift for the cam you are using I ignore it. The confusion come in with what is low lift, what is mid lift etc. Anything under .600 is a street cam so low lift would be .100-.250 or so. If you were using an .800 lift cam I would spend time at .100-.300 trying to lose some flow to gain it elsewhere.

All that said, when talking back cuts, usually I give the number of degrees less than the seat angle as the back cut angle. Since air doesn't bend more than 7-8 degrees, that is about all the back cut they will take. For example, if you are using a 45* seat, a 7 degree back cut would equal a 38* degree cut (45-38). You actually used a 10 and 15 degree back cut.

I can tell you I actually quit using back cuts a while ago. I have learned the hard way that even if a back cut increases flow anywhere in the curve, you can (and probably will) lose horsepower. I have done many heads that had a flow LOSS that picked up HP, for many reasons. Most of the time is was not back cutting the valves. An increase in airflow won't always mean an increase in HP.

I don't remember seeing back cuts cost 10 or 15 cfm at peak before. Usually they just boost the low numbers, then the gains flatten out at some point and you don't see any more gains.

Some of my SB stuff has lost 10 cfm with a wide back cut. Combination specific IMO.