I was emailed about this thread and would like to add some some stuff too.
The SS heads issue
Unless superstock has changed rules in the past year, ported heads have been allowed since the mid 80's or so. For instance, look at the allowed port volumes on the 289 heads versus the as cast. I will have to get the rule book out and look at how it used to be written, but basically the valves have to be stock diameter, the valve position and angle had to be stock, and the valve job itself was limited to the angles shown in their chart. Other than that it was balls out port work (within the limits of the NHRA/IHRA port volume for the head). Take for example the C5AE-B head. This is a very nice SS casting. It comes factory as the typical 125-128 cc inlet port, but it is allowed a 155 CC volume limit. Other heads do similar. Generally the SS 289/302 motors end up (depending on volume limits) in the mid 140's for inlet port volume. Exhaust port volume is not so generous though. A typical 289/302 inlet port in SS will flow in the 215-230cfm range (28" H2O).
If S/S rules have changed in past year, then there would be lots of builders going thru the roof, because of years of development and the tossing out of huge amounts of money and time involved in the head flow studies, not to mention all the cams, intakes, and headers. I will check the current rules, but in the past 15 years or so porting was allowed. I have never even heard of them allowing a 'port matched' port that could only be blended inward an inch.
I am assuming the Alex being refferred to is denysenko. He is running pretty well. I think he has a record right now in L.
With regards to 'LSA' and being engine and usage specific, I disagree. That sounds like a magazine article or something. LSA is completely relative to the particular engine in question only. Comparisons of wide vs narrow are done, but it is really only an pointless observation. What can be wide for one motor can be narrow for another.
When you break down timing events and look at durations wth respect to time, the look begins to change. look at the timing events with respect to the overall flow capability and velocity potential and then look at the displaced cylinder volumes and the rpms being used. Then think of units of time thru which charge is drawn in or expelled. Remember flow is unit of volume per unit of time
The reason a pro stock(assume a truck motor) and a S/S cam look so different is mainly because of the flow potential of the inlet (and exhaust) with respect to the displaced to volume. Why can a 360CID truck motor have a 116-120 LSa, but a 360CID S/S motor uses a 104-108 LSA? (both are race motors!!) This gets into whether a motor is restricted or not. the argument about race motors needing a narrower LSA is incorrect. It has to do with flow and displaced cylinder volume.
The chart in the magazine is somewhat misleading, because what I don't think they said. That was that the chart was for an equal inlet capability (not a proportional inlet capability)and not just CID related.
So then the picture starts becoming that CID increases, then for a given inlet capability (and exh) that the port velocity will increase. And this even changes depending on the rpm band and how well the exh (as a system) flows. In general as the proportion of inlet capability drops with respect to the displaced volume, then the exhaust events should be retarded, or cylinder pressure will suffer.
But you still get a sense that its about 'LSA'. think of the truth being the timing events required are what they are. Then the LSA just becomes a calculated angle and is good for discussion, but really should not be the driving factor.
It's like torque and hp. peopl view them as different entities. hp is calculated from torque. just like LSA is calculated from valve events.
I put a lot of time into a write-up called 'cam truth'. Though it may not be interesting to
some enthusiasts, some of you may enjoy it. I also did a valve timing chart that demonstrates the valve events and how they change with respect to flow CID and rpm. It's what I have found to work and the end effect is that enables a single formula to be used to calculate valve events for any motor, based on flow capability, displaced volume, rpm, static CR.
take care
Buddy Rawls
http://www.wighat.com/fcr3
check out cam truth and the valve timing chart
<font size=-1>[ This Message was edited by: buddy rawls on 2/26/02 9:31pm ]</font>