I tend to agree but not with the last bit. I Haven't had anything to do with those particular heads but looking at their published flow data....they are virtually done at .500 lift... gain only 4cfm at .600 and flow drops at .700".You may gain nothing, you may pick up a couple tenths. I know people on each end of the spectrum. You -should- pick up a little power, however don't expect it to be a different engine. A guy I know with a 351C installed a solid roller with apparantly the same specs as his solid, and ran exactly the same as he did before.
If it's a RACE car that sees limited street use, it might be worth it to step up to the roller. If it's a STREET car that sees a lot of miles, you'll probably be better off with a modern designed solid flat tappet... or a hydraulic roller if you don't rev it too high.
Engines that respond to solid rollers the best, are ones that need all the lift they can get. In other words, if the engine has fairly small heads for its displacement, it's going to need the valve lifted as far and quicky as possible, while keeping duration in check. A roller stands a much better chance of making a significant difference on this type of combo.
Your 393W with stock Edelbrock RPM heads would probably be a good candidate, as long as you don't mind keeping a CLOSE eye on the roller lifters, and it doesn't see TOO many street miles. Keep the idle speed up, and run a fairly tight valve lash to minimize pounding on the valvetrain.
The smaller the head is for the combo, the more 'strangled' it is going to be. In this situation, it is very beneficial to get the valve open to where it needs to be as quickly as possible... then hold it there as long as possible before setting it down... all while staying within the required duration. A slow acting valvetrain on a small set of heads will give the engine 'asthma'. LOLI tend to agree but not with the last bit. I Haven't had anything to do with those particular heads but looking at their published flow data....they are virtually done at .500 lift... gain only 4cfm at .600 and flow drops at .700".
I would tend to think that because the heads are "done" early in the
piece flow wise, you are unlikely to gain much going to a roller.
In other words, if the current cam is meeting head (piston) demand , which is quite high with a 393, you will gain nothing by opening the valve sooner or giving it more lift as the heads flow "window" is already "full".
Some of the answer is already there......Nobody said a 0.800" roller was going to be installed in this 393W with RPM heads. A good roller with the proper lift would probably give this engine a nice little pick-me-up... especially if the solid cam that's in it now is on the slow side.
at .200 sft is 159/166 roller is 170/176
lift 560/576 614/621
same 1.6 rocker arms for both
heads are Stock Edelbrock RPM flow 250 @500
That argument can be made for -anybody- considering switching from a solid flat tappet to a solid roller.Not to me.... some slight gain , yes .... but not enough to justify (roller) cam changing expense imo.
No, not really Mike. We have two major influencing factors here, large(ish) displacement and mediocre head flow. If cylinder demand exceeds head flow capacity gain's are small, you may get alittle better filling earlier in the intake stroke but during the "bulk" cylinder filling period (at max piston speed), the head is already at its capacity..... gains are small/none, in other words - the heads are the bottleneck. If the head has some additional (or untaped) capacity, gains will be much larger ofcourse.That argument can be made for -anybody- considering switching from a solid flat tappet to a solid roller.