Gutted vs Ported upper

[irsmart21]

I think this is a good place to post this. If not, can you move this, Stinger?

I have looked across the forum for a discussion of this and could not find anything.

First, I know a gutted upper is not good without the lower being ported in some way. I am getting ready to put a 60mm TB on my car and have to open the flange to match the adapter. I was all but ready to try my hand at gutting my upper myself, but upon researching the best process, I found conflicting reports on other sites with some experience a loss of lower-end power with gutting. All I have ever read is that gutting is the way to go.

It is my understanding that the porting and gutting can be kind of pointless if you do not run a larger than stock TB, being that the air volume is ultimately restricted by the 50mm TB. I did some math and I am hypothesizing that as long as the collective volume of the runners matched the area of the TB, should that not be enough to meet the air supply that is has increased from the TB upgrade.

TB Size (mm)	TB Dia (In)	TB Radius (In)	TB Area (In2)	Req. Indv. Runner Area (In2)	Req. Indv. Runner Dia (In)
50	1.96	0.98	3.02	0.75	0.98
60	2.36	1.18	4.37	1.09	1.18
65	2.55	1.275	5.11	1.277	1.275
70	2.75	1.375	5.94	1.485	1.375

If the diameter of the individual runners match the above measurements based on the TB size on the car, would that not be enough to at least feel the full benefit of the larger TB and there to effectively not be a bottleneck at the intake? (assuming a fully ported head)


If this is the case, other than the ease of just stripping all of the material out to get max flow, what benefit is there to gutting the upper? I know that I cannot effectively port my upper under my shade tree, but i do not want to gut it if it is going to have an adverse effect on the bottom end/around-town performance.

Just trying to understand it all. Thanks for reading and any replies!

Happy Easter y'all!

[Stinger]

Gutting shortens the intake runner length which shifts peak rpm up (just like a tunnel ram has shorter runners than a stock type V8 intake and makes more power up high). Couple this with increased plenum volume and the additional flow from the ported lower and you get more power. I find that porting the lower offsets the power loss at low rpm from gutting and of course allows more power up top. Larger TB also makes it feel more powerful down low because of the increased flow at small throttle plate angles.

I'm not sure I understand your graph.

[irsmart21]

Thanks for the reply.

The graph from left to right gives you:

TB diameter in MM -> TB diameter in inches -> TB radius in inches -> TB opening area in SqIn -> the TB area divided by 4 (4 runners in the upper) to show the area each runner would need to have to match the TB area -> the necessary diameter of each runner to yield that area.

I had already done the math and figured I would post it. The initial reason for the math was to see, out of curiosity, just how much of an percentage increase the area of the opening was going from a 50mm to a 60mm TB (45% is nothing to scoff at). I personally needed to convert it all to inches to be able to visualize it. After calculating that, I figured that I would calculate to see how much larger the runners might need to be to match that increase in area. I have yet to measure the runners on my upper (as I believe someone ported them in the past).

Hope that was clearer. :-)

 

[irsmart21]

So based on the measurements I took this past weekend, the runners on the upper intake are 1.375" in diameter. According to the math I did, this means (volume wise) they will handle up to a 70mm TB before they would be classified as a bottleneck in the intake system.

I know that a 70mm is tech overkill on any setup, but it at least I know that I am not being restricted with my 60mm TB on there without gutting and porting.

[enemy]

IMO I believe one of the main benefits of gutting the upper is giving our little motor some type of "plenum volume" as Stinger has implied. Otherwise, factory intake generally has none or very little. From my research this is critical especially in a boosted application. (plenum volume up to 200% of engine displacement can be desirable in a boosted application) I noticed with my gutted upper and ported lower that power seemed much more linear throughout the throttle range. Before gutting, I was noticing the "throttle angle effect", or air "tb ski ramp"... whatever ya like to call it.. causing a couple cylinders to be "air lean" or "air rich" at certain throttle positions. A large plenum helps to slow the air down when it enters the area, helping to fill each runner equally. I even went further and added a 3" spacer between the TB and upper to create even more volume after the throttle blade. Even more improvement.
One of the best intake design threads a guy could ask for => www.theturboforums.com/threads/intake-manifold-design.361799/
Long read but a wealth of info in there and a few guys with years of experience!