Curious on what ya'll think of this.

We all know that if you had 2 sets of 243 LS6 heads (for example), one had a 220cc runner and the other had a 250cc runner, but both flowed (same bench, same setup) the SAME cfm at any given lift - that the head with the 220cc runner would produce MORE torque than the other head, given that the same cam/etc was used (imagine these two different heads were bolted onto the same exact engine). In this case, its then very easy to determine which is the "better" head, which will provide more torque and HP across the entire rpm range, etc.

So...... What if you had 2 sets of 243 heads, one had a 212cc runner (stock), and the other had a 230cc runner (CNC ported). At .300" lift, the 212cc runner flowed 186cfm, the 230cc runner flowed 215cfm. At .400" lift, the 212cc flowed 224cfm, and the 230cc flowed 254cfm. And so on.

Since the flow-rating at each measured lift is different for each of the two different heads, now how would you determine which is the "better" head for low-end torque and high-end HP, again assuming that the SAME camshaft is used. For this example if you need to, pretend that you're using a stock LS1 or LS6 camshaft with relatively small duration and valve-lift.

On one side, the ported head flows much more than the stock head, so one would think that at any RPM the generated torque from the engine with the ported heads would be higher than the engine with the stock heads. BUT, the ported head also has an intake-runner volume of ~20cc more - which would slow velocity and reduce the generated torque. So how do we accurately compare without installing onto a car and dyno'ing? Can we normalize it?

Normalized Value = CFM / Runner Volume
--> The larger the Normalized Value, the "better" the head is for flow/efficiency.

Would "Normalizing the Head Flow" be a fair way of estimating the 'efficiency' of the heads, and thus provide a true comparison between the two? (see EXAMPLE below)

Stock LS6 Head
Intake Runner Volume: 212cc (just say that its this volume for this discussion... I don't really care if its actually 210cc or 215cc...)
Lift -- Flow -- Normalized Value
.200" - 135 cfm ===> .637
.300" - 186 cfm ===> .877
.400" - 224 cfm ===> 1.056
.500" - 250 cfm ===> 1.179

Ported LS6 Head
Intake Runner Volume: 230cc
Lift -- Flow -- Normalized Value
.200" - 154 cfm ===> .670
.300" - 215 cfm ===> .935
.400" - 254 cfm ===> 1.104
.500" - 285 cfm ===> 1.239


Would it be now safe to say that the Ported LS6 head will produce MORE low-end torque, given the fact that despite the larger intake runners the cfm-increase over the stock-head outweighs the volume increase? That is, more cfm per cc is being obtained by the ported heads over the stock heads, as evidenced by the higher "normalized value" versus the stock heads at any compared lift. Thus, the airflow velocity thru the ported heads must be GREATER than thru the stock heads, and in turn produce more torque and power at any given RPM / cam-lift point....?

Likewise, if the ported heads ended up having normalized values less than the stock heads' normalized values, then would it be safe to assume that velocity is decreased & torque will suffer? (Again, remember that you're comparing the two heads while using the SAME mild / stock cam)


Thoughts, please!!!

 

Now do the "math" on an AFR 205 cc port

(6 cc's smaller than a stock untouched LS6 243 casting and 50 CFM of addtional airflow)

At just .400 lift the smaller port AFR ties the LS6 heads peak number of approximately 250 CFM give or take.

Also, while crunching the numbers consider the fact that alot of the "big port" heads that might flow a little more (our 225's included) don't actually fare as well when you stick a manifold in front of that high flowing intake port. Even a ported FAST lops off quite a bit of flow, but is alot better than a stock LS6 or LS1 intake.

Just some more food for thought....The consistant strong results the AFR 205's help achieve is no accident....its all part of a winning formula and approach to making power.

Regards,
Tony

 

Good points Tony... BUT would you agree that this "normalization" approach is a somewhat accurate (?) method to reach an apples-to-apples comparison between heads with different port sizes and flows? (ignore the variable of different flowbenches / setups...)

 

ttt. Where has everyone gone over the last few months? Seems like we've slowed down in the guru/techie responses....! Let's hear some thoughts on the posts above!

 

It sounds like you may be book educated far beyond your own intelligence. Try reposting your thread in the advanced tech section.

 

Im having my car dynod tommorrow morn with the new PRC Ls6 heads. I have a cam only dyno graph from before the heads. Everything else is the same. The heads have a 230+ cc intake runner. Seat of the pants say it gained everywhere, Ill see for sure tommorrow. Same cam.......same Ls6 intake.

The dyno graphs I have seen shown gains across the board.

 

LOL! More like too educated & intelligent for my own good! Hence I ask too many questions on topics that I'm just starting to learn about.

TTT for this one. Still looking for some other thoughts and opinions to my first posting and to Tony's followup. I'll try the Advanced section as well...

 

I was just having fun. I hope you find the answer